The Development of Beneficial Utilization of Coal Combustion Products - Part 2

Mechanical Properties

A test cylinder of 3 inch diameter by 6 inch length was cast with the concrete mixture following air curing in the laboratory at 70º F ± 5ºF until the time of testing. Table 4-58 shows the test results for the mixture. Electrical resistance of the concrete was measured using copper plates (3-in. diameter on each end) across the 6 inch length of the concrete sample.

The test indicated a resistance of 69.6 ohms at the age of 39 days. The electrical resistivity was calculated to be 208 ohms-cm from the measured resistance, using the following equation below:

R =  ρL / A

where: ρ = resistivity; L = length; A = cross section area

Using the standard method, concrete per ASTM C-39 and ASTM per ASTM D-4832, the compressive strength for the concrete cylinder sample resulted in a compressive strength of 3070 psi at the age of 50 days. These results show another way to increase the electrical conductivity of concrete by using spent activated carbon sorbent and carbon fibers.

Long Term Field Performance Testing of Conductive Concrete Resistivity at Three We Energies Sites

We Energies has performed ground resistance testing at three of its sites in different soil environments. Factors such as the soil type, moisture content and temperature influence soil resistivity. Table 4-59 shows the typical resistivity versus the soil type. The locations of the sites selected included, Caledonia Landfill with a clay environment, Pewaukee SCC Landfill with a sand and gravel environment, and Germantown Power Plant with a near surface limestone bedrock environment. An ongoing project is being conducted in these three different environmental conditions where conductive concrete foundation blocks were installed for impedance measurement.

Table 4-59: Soil Resistivity Based on Soil Type*

Ground Resistivity Testing (43)

This test is performed by using the four-pole testing method in which two voltage and two current poles are used. The actual resistivity is the average of the resistivity calculated for each measurement point.

1. Caledonia Landfill

This site is located near the landfill’s leachate collection load out station in the Town of Caledonia near Oak Creek Power Plant. The texture of soil at this location is primarily clay. During the testing, the soil was moist due to rain. The average soil resistivity calculated at this site was 37.1 ohm-meter. Figure 4-31 shows the variation of the resistivity versus probe spacing.

Figure 4–31: The ground resistivity profile at Caledonia Landfill site in clay soil

2. Pewaukee System Control Center Landfill

This site is located at System Control Center landfill in Pewaukee. The soil texture is sand and gravel with thin layers of silt and clay overburden. Due to the sand and gravel texture, the measured resistance is higher than that at the Caledonia Landfill site. The average soil resistivity calculated at this site is 126.8 ohm-meter. Figure 4-32 shows the resistivity profile.

Figure 4–32: The ground resistivity profile at Pewaukee System Control Center site in sand-gravel soil.

3. Germantown Power Plant

This site is located at N96 WI9298 County Line Road, Germantown near Germantown power plant. The site has bedrock near the ground surface. The measured resistance did not show consistency, which is normal in grounds with high resistivity. The average resistivity calculated at this site is 538.5 ohm-meter. Figure 4-33 shows the resistivity profile.

Figure 4–33: The ground resistivity profile at Germantown Power Plant site in soil near surface bedrock

Test Results

The electrical resistivity results for each test site are consistent with the texture of the soil. Typically, grounding systems are designed to have a resistance of below 5 ohms. Hence, it is important to understand the soil environment when designing a grounding system. In sites with higher resistivity, like Germantown power plant, larger grounding grids are typically required to lower the total resistance.

The next phase of this testing was the installation of a conductive concrete block at each of the three sites and measuring the seasonal resistance, inductance and capacitance for a period of time to obtain the grounding characteristics for this material.

Conductive Concrete Resistivity Field Testing (44)

The purpose of this test is to characterize the impedance profile of conductive concrete for electrical grounding. It is performed by installing conductive concrete foundation blocks at the three sites with different soil environments. The conductive concrete is designed to have a compressive strength of 3,000 psi and has the following components in the mixture: cement (Class C fly ash and Portland cement), aggregate (3/8 inch aggregate and torpedo sand), water, and additives include Class F – high carbon fly ash with LOI of about 20%, carbon fibers, paper manufacturing wastewater residual fiber, and superplasticizer. The paper manufacturing wastewater microfibers residual reinforces and substitutes for an air/void system for freeze/thaw protection in the concrete.

Seasonal ground resistance measurements were conducted to properly characterize the grounding resistance profile of the conductive concrete. The first test was performed in fall on December 8, 2010, a second test in winter on March 3, 2011, a third test in summer on August 26, 2011 and finally a follow up study will be conducted in spring 2013. A rebar cage was built in a 5’ long x 2’ wide x 5’ deep foundation with a copper test lead welded to the cage and cast into the conductive concrete foundation. The copper test lead provides the electrical connection to the conductive concrete foundation. Figure 4-34 shows the conductive concrete foundation at the Caledonia Landfill site. The testing was performed by measuring the resistance between the test lead connecting to the conductive concrete and a test lead connecting to the utility network ground (neutral). A variable frequency power supply was used to apply a voltage between conductive concrete and the utility ground. The impedance of the conductive concrete block has been measured at a frequency range of DC through 800 kHz. During this test, the conductive concrete slab has shown higher impedance for DC current than AC current. The impedance values beyond 100 kHz were not trusted due to signal attenuation, noise, and interference. A Fluke meter and an oscilloscope were used for voltage and current measurements.

Figure 4–34: The placement of conductive concrete slab during construction at the Caledonia Landfill site

1. Caledonia Landfill

This site is located near the landfills leachate collection load out station in the Town of Caledonia near Oak Creek Power Plant. The texture of soil at this location is primarily clay. For the Fall measurement, it had snowed several days before the testing and snow was on the ground but the soil was not frozen. For the Winter measurement, there was snow on the ground and the ground was frozen. For the Summer measurement, it was sunny but it had rained for several days before that and the soil was moist. Figure 4-35 shows the impedance profile for fall, winter and summer seasons.

2. Pewaukee SCC Landfill

This site is located at the SCC landfill in Pewaukee. The soil texture is sand and gravel with thin layers of silt and clay overburden. Figure 4-36 shows the impedance profile for fall, winter and summer season.

3. Germantown Power Plant

This site is located at N96 W19298 County Line Road, Germantown near Germantown power plant. It has bedrock near the surface ground. As shown in Figure 4-37, the impedance is higher than the other two sites, due to rocky soil. For comparison to the conductive concrete, a ground rod was also installed near the concrete slab. Figure 4-37 shows the impedance profile for fall, winter and summer seasons, and Figure 4-38 shows the impedance profile for the ground rod for comparison.

Figure 4–35: The impedance profile of the conductive concrete vs. applied frequency for fall, winter and summer at Caledonia Landfill

Figure 4–36: The impedance profile of the conductive concrete vs. applied frequency for fall, winter and summer at Pewaukee System Control Center Landfill

Figure 4–37: The impedance profile of the conductive concrete vs. applied frequency for fall, winter and summer at Gemantown Power Plant site

Figure 4–38: The impedance profile of a ground rod installed during fall, winter and summer season at Gemantown Power Plant site

Impedance Test Results on Conductive Concrete

After applying voltage with variable frequencies, the results have shown that there is ohmic resistance at higher frequencies during both fall and winter seasons. There is greater impedance in winter than fall due to frozen ground. As seen in the Figures 4-34 to 4- 36, the impedance value is stable at low and mid frequencies (100 Hz – 50 kHz). At the Pewaukee site, the summer impedance is slightly less than winter and fall impedances for lower frequencies; and the summer impedance is less than winter and fall for higher frequencies. At the Germantown site, the impedance for summer is calculated less than the impedance in winter and fall seasons. Also, the impedance of the ground rod is 60% higher when compared with the conductive concrete block.

Electrically Conductive High-Carbon Fly Ash (HCFA) Concrete Used at a Telecommunication Tower

A telecommunication tower in Rudolph, Wisconsin was frequently struck by lightning causing damage and communication outages. Copper grounding wires had been installed underground from each guy wire anchor to the base of the tower. The guy wiring was configured radially in trios, with equal spacing from the tower (as a tripod structure). “The grounding system must comprise a conductor with sufficient conductivity and cross section to handle the energy of a lightning strike, and the interface between the conductor and earth must have sufficient surface area to transfer the energy into the ground. Since, the earth is not a good conductor, the interface must be large” (45). Therefore, for two of the grounding legs a trench (1ft wide x 6 in. deep) was dug where the copper wire and the high-carbon fly ash concrete is placed. Figure 4-39 shows the placement of the HCFA conductive concrete in the grounding trench for the Rudolph Tower.

Table 4-60 shows the conductive concrete mixture used for this site. It was estimated that within 28 days, the compressive strength would reach 3000 psi.

Table 4-60: Conductive Concrete Mix Design

Figure 4–39: Construction with electrically conductive high-carbon fly ash concrete as a grounding enhancement for a telecommunication tower in Rudolph, WI.

• Carbon Fiber is added to the concrete mix on site
• Placement of copper wire in the trench
• Filling the trench with the high-carbon fly ash conductive concrete
• Normal shrinkage cracking due to carbon fiber mix
• Completion of concrete placement
• Cover installation above the grounding

Conductive Concrete Tests: Compressive Strength and Ground Resistance

The compressive strength for the HCFA conductive concrete at the Rudolph tower was measured at ages of 3, 7, 14, 28, 56, and 91 days for two batches. Figure 4-40 shows the average compressive strengths over the time period. As shown, the compressive strength surpassed the estimated strength at 28 days and attained 4155 psi. An overall ground resistance measurement was taken over two time periods and is shown on Figure 4-41. On the second test day (9/5/2006), the overall resistance had decreased, providing an effective grounding resistance for the tower.

Figure 4–40: Average compressive strength of the HCFA conductive concrete versus the age at Rudolph Tower

Figure 4–41: The overall ground resistance of the HCFA conductive concrete over two test dates at the Rudolph Tower.

Use of Conductive Concrete for Energy Storage – Electric Cell (46)

Electrically conductive concrete is a relatively new material when compared to the long history and development of conventional concrete materials. In fact, in the past emphasis was placed on preventing conductivity and providing concrete with a focus on resistance. More recently, conductive concrete has been developed with the goal of providing pavements with snow and ice melting capabilities. Design efforts have also been focused on development of enhanced electrical grounding systems for the power industry. Researchers have also been considering the potential for monitoring structural members for stress, strain, and cracking by monitoring a change in resistance of the concrete member.

The conductive concrete applications described above are all in introductory research, development, and demonstration stages. The potential for new applications is bright for this revolutionary new material. Imagine bridges that never get icy, buildings that are never harmed by lightning, and electric vehicles that recharge while driving. Such scenarios are possible with electrically conductive concrete and backfill materials using high-carbon fly ash. This innovative new material can also serve for potential energy storage purposes (47).

The main objective of this research was to evaluate the potential of a conductive concrete-zinc electric cell (in a saturated brine electrolyte) for storing electric power. The capability of the battery was evaluated by measuring the cell electrode potential as it is charging and discharging.

Materials and Methods

The mix design on a cubic yard basis for the 3 in. (76.2 mm) by 6 in. (152.4 mm) conductive concrete cylinder that was used as a cathode was composed of 300 lb Class C fly ash, 500 lb Portland cement, 1375 lb 3/8 in. Aggregates, 1075 lb Torpedo sand, 300 lb Class F fly ash (High Carbon fly ash), 400 lb of the City of Milwaukee water and 36 lb Carbon Fibers with a water to cementitious materials ratio of 0.36. These ingredients were homogeneously mixed dry before adding the measured amount of water.

Forty percent by weight of iodized NaCl was dissolved in de-ionized water in a plastic container to make a saturated NaCl brine electrolyte. The conductive concrete was placed into the electrolyte and centered in the middle of the plastic container. A cylindrical galvanized zinc plate was inserted into the electrolyte and clipped at the wall of the electrolyte container. A voltmeter was then connected in the circuit (Figure 4-42). The cell was then charged for 45 minutes using a12.8V battery, and the rate of charging was recorded initially after 5 minutes, then every 10 minutes for 45 minutes. After the charging process, the battery was disconnected, and the conductive concrete-zinc cell was allowed to discharge for 36 minutes, and the rate of discharge recorded.

Figure 4-42: The experimental set-up showing the charging and discharging process.

A: A plan view sketch B: The charging set-up, and C: The discharging set-up. The spacing between the galvanized zinc plate and the conductive concrete cylinder was approximately 35 mm. The copper plate atop the conductive concrete cylinder is used only as wire attachment aid.

Results and Discussion

Figure 4-43 shows the charging process graph. The voltage increased steadily from 11.17V to 11.72V in 45 minutes when charged using a 12.8V battery. When power was disconnected, the cell discharged monotonically from 1.069V to 1.044V in 36 minutes (Figure 4-44). No drop in voltage was observed in the 12.8V battery after charging the Conductive Concrete-Zinc cell. These results indicate that the conductive concrete- zinc cell has the potential of storing electrical power. However, a longer charging time is required to provide more charge to the cell. Alternatively, an AC-DC transformer may be used to charge the cell for a longer period of time before it is allowed to discharge.

Figure 4-43: Change in voltage with time as the Conductive Concrete-Zinc cell is charged with a 12.8V battery

Figure 4-44: Change in voltage with time as the Conductive Concrete-Zinc cell is discharging after removal of the 12.8V battery

Conductive Concrete Containing We Energies High-Carbon Fly Ash and Pulp Mill Residuals In Place of Air Entraining Agent for High Durability Concrete (48)

This research work was performed by the Center for By-Products Utilization at the University of Wisconsin -Milwaukee and involved the testing and usage of high-carbon fly ash (HCFA) in non-air entrained concrete with microfibers from residual wastewater treatment solids from pulp and paper mills to produce high-durability concrete as a substitute for specialty chemical air-entraining admixtures. An air-entraining agent is a manufactured chemical admixture (AEA) added to the concrete mixture to resist the freezing and thawing environment. But AEA limits the effectiveness in the presence of HCFA in a concrete mixture. An air-entrained concrete has to meet specified criteria such as bubble size and spacing within the mortar fraction of the concrete to provide the necessary durability. Thus the incorporation of the pulp and paper mill residual solids in the presence of the high-carbon fly ash can produce a “green” concrete that provides freezing and thawing resistance to the concrete.

Materials

Materials utilized consisted of one source of Portland cement, clean concrete sand, HCFA, fibrous residual, and a high-range water-reducing admixture (HRWRA). ASTM Type I Portland cement was used that met the requirements of ASTM C-150. Natural sand was used from a source in southeastern Wisconsin meeting ASTM C -33 requirements as the fine aggregate ingredient. For the coarse aggregates, a crushed quartzite with a maximum nominal size of 19 mm was obtained from a source in south-central Wisconsin, again meeting the ASTM C-33 requirements. One source of HCFA was used in the concrete mixture for this project from We Energies Valley Power Plant. The HCFA was collected from burning bituminous coal at the plant. The chemical composition and physical properties of the HCFA are presented in Table 4-61 and Table 4-62, respectively, along with the requirements of ASTM C-618 for coal fly ash. The HCFA did not meet the LOI, fineness, and the strength activity index requirements. The source of fibrous residual was from a fiber reclaim process and was obtained from Biron, Wisconsin. The as-received moisture content of the residual solid is 253% of the oven-dry mass. Since cellulose fibers can decompose readily in a warm and humid environment, the residual solid was stored at 4ºC until its use in the concrete mixtures. Before adding the residual solids to the concrete, the fibers are first deflocculated by mixing in water. A water-reducing and set-retarding admixture was used in three of the concrete mixtures made with Valley Power plant HCFA. The admixture is a modified sodium gluconate, and meets the requirements of ASTM C-494 for Type B (retarding admixtures) and Type D (water-reducing and retarding admixtures). The manufactures recommended dosage rate of the water-reducing admixture is 125-375 mL/100kg of cement (2-6 fluid oz/100lb).

Table 4-61: Chemical Composition of High-Carbon Fly Ash

Table 4-62: Physical Properties of High-Carbon Fly Ash

There were three non-air-entrained concrete mixtures containing approximately 550 kg/m3 of Valley HCFA and one reference mixture, Ref-2, which did not contain fly ash or residual solids. The concrete mixtures containing the HCFA are V-8, V-9 and V-10; and contain increasing amounts of fibrous residuals from 7 to 21 kg/m3 (0.30% to 0.88% of residuals by mass % of concrete). All concrete mixtures contain HRWRA and the dosage was approximately the same, regardless of the residual content. However, the dosage of HRWRA in V-8 to V-10 is much higher than Ref-2. The density of the fresh concrete decreased as the amount of residuals increased in the mixture. Table 4-63 shows the mixture proportions.

Table 4-63: Mixture Proportions and Fresh Properties of Concrete Made with Valley HCFA

Discussion of Test Results

Compressive strength of the concrete mixture was evaluated at the ages of 7, 28, 91 days as shown in Table 4-64 and Figure 4-45. As shown, the compressive strength of all three mixtures containing HCFA was lower than the reference mixture, which contained none of the HCFA and fibrous residuals. As the amount of fibers was increased in the concrete mixtures, the compressive strength decreased. However, at the age of 91 days, the strength ranged from 29.8 to 34.7 MPa, which was 60 to 70% of the strength of the reference mixture. Therefore, new mixture proportioning is necessary to achieve a compressive strength higher than 30 MPa.

Table 4-64: Compressive Strength of Concrete Made with Valley HCFA

Figure 4-45: Compressive Strength of concrete containing Valley HCFA and fiber residue

The test mixtures were evaluated for resistance to freezing and thawing cycles in accordance with ASTM C-666, Procedure A. Results are shown in Table 4-65. All concrete mixtures containing HCFA and the fibrous residuals had a higher resistance to freezing and thawing than the reference material. Mixture V-8 containing 7 kg/m3 of fibrous residuals (0.30 mass % of concrete), had the highest resistance to freezing and thawing and had the lowest compressive strength compared to the reference material. The resistance to freezing and thawing can potentially be increased if the compressive strength is increased to a level comparable to the reference mixture, greater than 35 MPa.

Table 4-65: Freezing and Thawing of Concrete Made with

The concrete mixtures were also tested for the resistance to surface scaling when subjected to de- icing chemicals. Table 4-66 shows the results from the tests for the resistance to salt-scaling. Through 50 cycles of freezing and thawing, the two mixtures that achieved the highest resistance to scaling were the mixtures with the lowest amount of fibrous residuals, mixture V-8 and V-9. Mixture V-8 contained 7kg/m3 (0.30 mass % of concrete) and mixture V -9 contained 14kg/m3 (0.60 mass % of concrete). The lowest amount of residuals contained in mixture V-8 has the best performance, with a visual rating still at zero (no visible scaling) at 50 cycles. Overall, all concrete mixtures containing fiber residuals and HCFA performed better than the reference concrete mixture.

Table 4-66: Salt-Scaling Resistance of Concrete Made with Valley HCFA

Development of Self-Consolidating Concrete Containing We Energies Class C Fly Ash (49)

Self-Consolidating Concrete (SCC) is a relatively recent innovation in concrete technology and was originally developed in the late 1980s at the University of Tokyo, Japan. Self-consolidating concrete is defined as a “concrete which can be placed and compacted into every corner of a form work, purely by means of its self-weight thus eliminating the need of vibration or other types of compacting effort”(49). It is also referred to as self- compacting concrete, self-leveling concrete, super-workable concrete, highly flowable concrete, non-vibrating concrete. The reason for developing this concrete was the concern of maintaining homogeneity and encapsulating into highly reinforced structural elements with complete compaction through the action of gravity thus improving the overall durability of the concrete.

Adjustments to the traditional mix design with the right water-to-cementitious ratio and use of superplasticizer creates flowable cement paste as well as susceptibility to segregation. Superplasticizers contain sulfonic acid groups that neutralize the surface charge on the cement particles and cause dispersion, thus releasing the water tied up in the cement particle agglomeration and reduction of viscosity. On the other hand, amendment to the aggregate proportion with a decrease in coarse aggregate and use of mineral admixtures such as fly ash, blast furnace slag, limestone powder and other similar fine powder additives, increases the fine materials in the concrete mixture thus generating high flowabilty. The spherical characteristic of fly ash particles helps in reducing friction during the flow of the mortar fraction in the concrete to increase fluidity in the SCC with segregation avoidance. Nonetheless, the slump-flow has to be maintained similar to the concrete using Portland cement when utilizing fly ash in SCC resulting in a decreased dosage of superplasticizer. Usually, the benefit of using fly ash in concrete is for “improved rheological properties and reduced cracking of concrete due to the reduced heat of hydration of concrete” (49). Therefore, the incorporation of one or more mineral additives “having different morphology and grain-size distribution can improve particle-packing density and reduce inter-particle friction and viscosity” (49). The use of such mineral additives also reduces the cost of cement due to the abundance of coal fly ash in the USA and other countries.

SCC can incorporate several minerals and chemical admixtures such as high range water reducing admixture (HRWRA) and viscosity modifying admixture (VMA). The HRWRA ensures high-fluidity and reduces the water-to-cementitious material ratio. The VMA enhances the yield value by reducing bleeding and segregation and increases the viscosity of the fluid mixture. The high-fluidity and segregation- resisting power are the key characteristics in maintaining the homogeneity and the uniformity of the self-consolidating concrete.

Figure 4-46:U-flow test apparatus.

Fibers are sometimes used in SCC to “enhance its tensile strength and delay the onset of tension cracks due to heat of hydration resulting from high cement content in SCC” (49). Also for the development of economical and environmentally friendly SCC, high-volumes of fly ash can be utilized.

Self-Compactability Test of Self-Consolidating Concrete

To evaluate the rheological properties of SCC, a number of test methods can be employed such as the slump- flow, U-flow, V-flow time, L-box and J-ring test. These test methods measure the self-compactability by evaluating the filling ability, passing ability (resistance to blocking) and stability (segregation resistance).

Slump-flow test is a common test method used for evaluating the flowability of SCC using ASTM C-1611. It measures “the capability of concrete to deform under its own weight against the friction on the surface of the base plate with no other external resistance present” (49). This way the consistency and cohesiveness of the concrete can be determined. The concrete is filled in an ordinary Abram’s slump cone without tamping. Then the cone is lifted and the diameter of the concrete after the flow has stopped is measured. SCC is characterized by a slump-flow of 650-700 mm (26-28 in.). A slump-flow ranging from 500 to 700 mm (20-28 in.) is considered as a proper slump required for a concrete to qualify for use in SCC. At more than 700 mm (28 in.), the concrete might segregate and at less than 500 mm (20 in.) the concrete is considered to have insufficient flow to pass through congested reinforcement. However, this test cannot distinguish between SCC mixtures and superplasticized concrete.

U-flow test characterizes SCC by examining the behavior of the concrete in a simulated field condition. In this test, the degree of compactability can be indicated by the height that the concrete reaches after flowing through an obstacle as shown in Figure 4-46. First, the concrete is filled in the left chamber with the sliding door completely closed. Then the door is opened and the concrete flows past the reinforcing bars into the right chamber. For highly congested reinforcing areas, SCC should flow to about the same height in the two chambers. According to the dimensions in Figure 4-46, the concrete with a final height of more than 200 mm is considered SCC. At the end, this test measures the filling, passing, and segregation properties of SCC.

V-flow test measures the flow time of the SCC. The apparatus is a v-shaped funnel with a rectangular cross-section. The concrete is poured into the funnel completely with a gate blocking the bottom opening. Then once filled, the gate is opened and the time for the concrete to flow out of the funnel is recorded, which is known as the V-flow time. “A flow time of less than 6 seconds is recommended for a concrete to qualify as a SCC” (49).

L-box test is another test method that indicates the filling, passing and segregation-resisting ability of the concrete. Concrete is placed inside the vertical portion of the testing apparatus as shown in Figure 4-47. The gate placed at the horizontal portion simulates reinforcement. Once the concrete has flowed to a resting position, the heights of concrete H1 and H2 are measured. The ratio of H2/H1 is used as a measurement of passing ability. Ratio values of 0.75 and higher are considered to qualify as SCC.

Figure 4-47: L-Box apparatus.

J-ring test assesses the blocking behavior/passing ability of SCC. The apparatus of this test consists of a reinforcing bar ring that is placed around the base of standard slump cone. The slump flow with and without the J-ring is measured and the difference is calculated which measures the passing ability of SCC.

Advantages and Disadvantages of Using Self-Consolidated Concrete

The mechanical properties of SCC are similar to a regular concrete with similar water-to -cementitious ratios. Studies related to “durability aspects such as chloride permeability, deflection, rupture behavior, freezing-and-thawing resistance and chloride diffusivity and other properties of SCC reported either comparable or better results compared with conventional concrete, mainly due to improved homogeneity of the self-consolidated concrete”.

The advantages of using self-consolidating concrete over traditionally placed and compacted concrete are as follows:

• Cost savings on machinery, energy, and labor related to consolidation of concrete by eliminating this step during concrete placement operations.
• High-level of quality control due to more sensitivity of moisture content of ingredients and compatibility of chemical admixtures.
• High-quality finish, which is critical in architectural concrete, precast construction, as well as for cast-in-place concrete construction.
• Reduces the need for surface defect patching. Increased service life of the mold/formwork.
• Promotes the development of a more rational concrete production Industrialized production of concrete.
• Covers reinforcement effectively, thereby ensuring better quality of cover for reinforcing bars.
• Reduction in the construction time.
• Improves the quality, durability, and reliability of concrete structures due to better compaction and homogeneity of concrete
• Easily placed in thin-walled elements or elements with limited access.
• Ease of placement results in cost savings through reduced equipment and labor requirement.
• Improves working environment at construction sites by reducing noise.
• Eliminate noise due to vibration; effective especially at precast concrete products plants, hence reducing the need for hearing protection.
• Improves working conditions and productivity in construction industry.
• It can enable the concrete supplier to provide better consistency in delivering concrete, thus reducing the need for intervention at the plants or at the job sites.
• Provides opportunity for using high-volumes of by-product materials such as fly ash, quarry fines, blast furnace slag, limestone dust and other similar fine mineral ingredient materials.
• Reduces workers compensation insurance premiums due to the reduction in chances of accidents.

The disadvantages of using self-consolidating concrete are as follows:

• More stringent requirements on the selection of materials compared with normal concrete.
• More precise measurement and monitoring of the constituent materials. An uncontrolled variation of even 1% moisture content in the fine aggregate could have a much larger impact on the rheology of SCC.
• Requires more trial batches at laboratory as well as at the ready-mixed concrete plant.
• Costlier than conventional concrete based on concrete ingredient and testing costs.

Development of Economical High-Strength Self-Consolidating Concrete

Materials and Mixture Proportions

Type I Portland cement was used in this investigation that met the requirements of ASTM C-150. ASTM Class C fly ash (from OCPP) was used in this study as a partial replacement for Portland cement. Cement was replaced by fly ash at a ratio of 1:1.25 by mass. Table 4-67 shows the physical properties of the fly ash. Natural sand (fine aggregate) and pea gravel (coarse aggregate) were used as aggregates where physical properties conformed to ASTM C-33 requirements. Two chemical admixtures, Glenium 3200 HES and Rheomac VMA 362, were used as a HRWRA and a VMA, respectively. The dosage of admixtures varies based on the desired properties for the SCC mixtures. Table 4-68 shows the mixture proportions and fresh properties of self-consolidating concrete. Each mixture (SC 1 – 4) was batched and mixed in the laboratory in accordance with ASTM C-192.

Table 4-67: Physical Properties of Class C Fly Ash

Table 4-68: Self-Consolidating Concrete Mixture Proportions and Fresh Properties

Mechanical Properties

As shown in Table 4-68 and Figure 4-48, each mixture was tested for both fresh and hardened concrete properties, respectively. For the fresh concrete properties, slump-flow and U-flow tests were performed to determine the flow and the self-compactability behavior. Additionally, the air content and the fresh density of SCC were determined by the applicable ASTM test method. The hardened SCC was tested for compressive strength using 4” diameter x 8” long cylindrical specimens meeting the requirements of ASTM C-39. The concrete strength was obtained at the ages of 3, 7, and 28 days.

Higher densities were observed as the replacement of cement by the Class C fly ash in the concrete mixture was increased with densities of 2339, 2369, and 2377 kg/m3. The use of high-volume Class C fly ash in SCC significantly reduces the requirements of superplasticizer as well as viscosity-modifying agent. This indicates that it is possible to manufacture economical self-consolidating concrete by using high-volumes of Class C fly ash. It is further obvious that the use of high-volumes of Class C fly ash not only reduces the amount of cement but also reduces the superplasticizer and viscosity-modifying agents significantly while maintaining the desired 28-day strength of about 7000 psi (48MPa) or higher.

As expected, the compressive strength increased with age as shown in Figure 4-78. In general, the SCC strength decreased with increasing fly ash amounts at the very early ages (ie: 3 and 7 days). The SCC made by replacing 35% of cement with fly ash (SC 2) showed a strength of 4200 psi (29MPa) at the age of 3 days. However, this mixture resulted in higher strength than the control mixture (SC1) at 28 days with a compressive strength of 9000 psi (62MPa). SCC mixtures containing 50% fly ash (SC3) of the total mass of cement plus fly ash also performed well compared to the control SCC mixture at the age of 28 days. The SCC mixture containing 60% fly ash also showed a comparative strength at the age of 28 days with the control SCC mixture. Without any doubt, as the age progresses the SCC with fly ash will outperform the control mixture. In general, all the SCC mixtures containing high-volumes of Class C fly ash developed high-strength in the range of 7000 – 9000 psi (48-62 MPa). This type of high-strength, economical, self-consolidating concrete has many applications in the construction industry, including the precast concrete industry.

Figure 4-48: Compressive strength (MPa) of self-consolidated concrete mixture

Summary

Based on the experimental study for development of high-strength, economical, self-consolidating concrete incorporating high-volumes of Class C fly ash, the following general conclusions can be made:

• Use of high-volumes of Class C fly ash in the manufacturing of SCC reduces the cost of the SCC production by significantly reducing the amount of superplasticizer and viscosity-modifying agents compared with the normal dosage for such admixtures in SCC, because of decreased friction between paste and large aggregate particles resulting from the ball bearing effects of spherical fly ash particles.
• High-strength, economical SCC for strengths of about 9000 psi (62 MPa) at 28 days can be manufactured by replacing at least 35% of cement by Class C fly ash.
• High-strength, economical SCC in the range of 7000 - 9000 psi (48-62 MPa) at a 28-day age can be manufactured by replacing up to 55% of cement by Class C fly ash. High amounts of fly ash in concrete leads to lower early age strength.
• High-strength, economical SCC can be beneficial for many applications in construction, including the precast industry, as it can be manufactured by replacing high-volumes of Portland cement with Class C fly ash.

Sample Specifications are included in Appendix 12.6 for an SCC mixture.

Chapter 5 - Controlled Low-Strength Material (CLSM) Containing We Energies Fly Ash

Introduction

During the past two decades fly ash has been increasingly used in the manufacture of controlled low-strength material (CLSM). CLSM is defined by ACI Committee 229 as a “self -compacted cementitious material used primarily as a backfill material in lieu of compacted fill with a compressive strength of 1200 psi or less.” However, where future excavation is anticipated, the ultimate compressive strength of CLSM should be less than 300 psi. This level of strength is very low, compared to concrete, but very strong when compared to soils. The composition of CLSM can vary depending on the materials used in the mixture. CLSM has the unique advantage of flowing and self-leveling. Hence, in applications like filling abandoned underground tanks or voids under pavements, CLSM may be the only viable method of completely filling the void. Additionally, there is no cost associated with vibrating or compacting the material in place.

CLSM may be known by such names as: unshrinkable fill, controlled density fill, flowable mortar, plastic soil-cement, soil-cement slurry and K-Krete (50). We Energies has used the registered trademark, Flo-Pac® for its CLSM. The range of strength required varies with the type of application. However, CLSM is normally designed to develop a minimum of at least 20 psi strength in 3 days and 30 psi at 28 days (ASTM C-403 penetration resistance numbers of 500 to 1500).

A compressive strength of 100 psi is equivalent to the load bearing capacity of a well compacted soil with a capacity of 14,400 psf which is comparable to a densely compacted gravel or hard pan type soil. Where CLSM is used as a support layer for foundations, a compressive strength of 300 psi to 1200 psi is sometimes used. However, applications involving CLSM with strength in this range are very limited and often not necessary.

The CLSM mixture selected should be based on technical and economic considerations for a specific project. The desired strength level and flowability are two significant considerations for CLSM. Permeability, and shrinkage or expansion of the final product (hardened CLSM) are additional considerations.

We Energies CLSM Developments

The development of CLSM containing We Energies fly ash has been a long process involving manufacturing several trial mixes and studying their properties. Various parameters were considered; however, compressive strength and excavatability are primary considerations. In the early trials, a wide variety of sample strengths were developed, some of which were higher than normally recommended for CLSM.

Several CLSM mix designs were developed and tested using We Energies fly ash at the Center for By-Products Utilization (CBU) at the University of Wisconsin-Milwaukee (UWM). The scope of these tests was to evaluate fly ash, the properties of the mixes and to study potential field applications. The mixes were prepared using various percentages of Class C and Class F fly ash with various proportions of other ingredients. It is important to note that Class F fly ash can be used in much higher proportions (sometimes replacing aggregate) than cementitious Class C fly ash which is introduced primarily as a binder.

CLSM production is an excellent use for fly ash that does not meet all of the ASTM C-618 requirements for use in concrete. The strength level required for CLSM is low when compared to concrete and can be easily obtained with off-spec fly ash. High carbon content can be a reason for concern in air-entrained concrete where air entraining admixtures are absorbed yielding inadequate or variable concrete air content. In CLSM, air content is often not a requirement and hence the presence of carbon particles does not affect its properties.

CLSM Produced with We Energies High-Lime (ASTM C-618 Class C) Fly Ash

The mixtures shown in Table 5-1 were developed using ASTM C-618 Class C fly ash produced at We Energies Pleasant Prairie Power Plant from burning western United States sub-bituminous coal. The chemical and physical properties of the PPPP fly ash are listed in Chapter 3, Tables 3-1 and 3-2. The mixtures were produced at a commercial batch plant using standard procedures that were monitored to assure homogeneity of the products.

Table 5-1: Mixture Proportions and Field Test Data for CLSM (and Low-Strength Concrete) Produced With Class C Fly Ash

The first three mixtures were produced with low cement content and relatively low water content.

Mixtures C-1 to C-3 showed very low slump and did not flow as desired in a flowable slurry. Hence, new mixtures were developed, taking into consideration the drawbacks of previous mixes. (51)

The new mixes C-4 to C-7 showed good to very good flowability. A detailed discussion of the research can be obtained from reference 51.

Figure 5-1 is a graph showing compressive strength vs. age for these mixtures. Figure 5-2 shows 28-day compressive strength vs. total cementitious material, and Figure 5-3 shows 28-day compressive strength vs. water to cementitious materials ratio for these mixtures. Table 5-2 shows the CLSM compressive strength test results.

Figure 5-1: CLSM Compressive Strength vs. Age Comparison (Class C Fly Ash)

Figure 5-2: CLSM 28-Day Compressive Strength vs. Total Cementitious Material (Class C Fly Ash)

Figure 5-3: CLSM 28-Day Compressive Strength vs. Water to Cementitious Material Ratio

Table 5-2: High Fly Ash CLSM Test Data 500-1200 psi Specified Strength Range at 28-Day Age

It can be concluded from these test results that:

• As the water to cementitious materials ratio increases, the compressive strength decreases for the low slump mixtures.
• The compressive strength did not change significantly for the higher slump mixtures as the water to cementitious materials ratio increased between 1.0 and 2.0.
• All mixtures behaved well and can be used as a basis for selection of mixtures for CLSMs or low-strength high fly ash content concrete for non-structural applications.
• The compressive strength results for all these trial mixtures are at a level where easy excavation will not be possible.

CLSM Containing We Energies Valley Power Plant Off-Spec (ASTM C-618 Class F) Fly Ash

The mixture proportions used in this project were designed to have a compressive strength of 500 psi to 1500 psi. This strength level is similar to the strength levels of many natural rock formations and can be used as foundation support, capable of distributing the load uniformly.

The CLSM mixtures were produced at a commercial batch plant in New Berlin, Wisconsin. The mixtures contained ⅜” (maximum size) pea gravel, in addition to fly ash, cement, sand and water. The final mixtures were designed with high slump (7” to 9”.).

From each concrete mixture, 6” diameter by 12” high cylinders were prepared for compressive strength and other tests. Cylinders were tested from each mixture at the ages of 3, 5, 7 and 28 days. Shrinkage was noted to be very low, ranging from 0 to 1/32” for the 12” high cylinders. A detailed discussion of this research can be obtained from reference 52.

Table 5-3 gives the chemical and physical test data for mixtures produced with off-spec ASTM C-618 Class F fly ash from Valley Power Plant. Tables 5-4 and 5-5 show mixture proportions, field test data, and compressive strength data for the various mixtures.

Figure 5-4 is a graph showing compressive strength vs. age for these mixtures. Figure 5-5 shows compressive strength vs. total cementitious material for the same mixtures, and Figure 5-6 shows compressive strength vs. water to cementitious material ratio for the above mixtures.

Table 5-3: Chemical and Fineness Test Data for Class F Fly Ash from Valley Power Plant

Table 5-4: Mixture Proportions and Field Test Data for Class F Fly Ash CLSM

Table 5-5: Class F Fly Ash CLSM Test Data

Figure 5-4: CLSM Compressive Strength vs. Age Comparison (Class F Fly Ash)

Figure 5-5: CLSM 28-Day Compressive Strength vs. Total Cementitious Material

Figure 5-6: CLSM 28-Day Compressive Strength vs. Water to Cementitious Material Ratio

The following conclusions were made from this research (52).

• The compressive strength decreased as water to cementitious material ratio increased.
• All mixtures showed good flowability and workability.
• Shrinkage was minimal.
• The mixture designs developed performed well and can be used as a basis for selecting mixture proportions for CLSMs or low-strength concrete with high slump for non-structural applications, using the same materials.
• All of these mixtures will not be easily excavatable.

CLSM Made with We Energies Port Washington Power Plant Off-Spec (ASTM C-618 Class F) Fly Ash

This study was conducted by We Energies with a local ready mix firm to determine various properties of CLSM material containing off-spec ASTM C-618 Class F fly ash from Port Washington Power Plant (PWPP). CLSM fly ash slurry was initially used for limited applications in filling abandoned underground facilities and voids such as tunnels, manholes, vaults, underground storage tanks, sewers and pipelines. Another obvious application is the backfilling of trenches for underground utility lines. For this application it is important that the backfill material be compatible with the underground utility line material. Also, the material should be easily excavatable and also provide for special needs such as high thermal conductivity for underground high-voltage transmission lines.

ASTM C-618 chemistry tests were not performed on PWPP fly ash at the time of this research because this fly ash was not used for the production of concrete. However, fly ash from Valley Power Plant that used the same coal was tested. The chemical composition is shown in Table 5-3 for reference purposes. The physical properties of PWPP fly ash are shown in Table 5-6.

Table 5-6: Physical Properties of Port Washington Power Plant Class F Fly Ash

CLSM laboratory trial mixtures using PWPP fly ash were also developed at the Center for By-Products Utilization (CBU) at the University of Wisconsin-Milwaukee (UWM) laboratory in November of 1991. The mixture proportions and corresponding compressive strength test results are shown in Table 5-7 (laboratory tests) and Table 5-8 (ready-mix plant production tests). Figure 5-7 is a graph showing compressive strength vs. age for these mixtures.

Table 5-7: Laboratory CLSM Mixture Proportions for PWPP Class F Fly Ash and Compressive Strength Data

Table 5-8: Ready Mix CLSM Mixture Proportions for PWPP Class F Fly Ash and Compressive Strength Data

Figure 5-7: Compressive Strength vs. Age Comparison (Class F Fly Ash with One Bag)

The compressive strength test results for mixtures 1 – 3 at a 28-day age ranged from 39 – 62 psi and are comparable to many undisturbed or re-compacted soils, which makes it suitable as a backfill material. Mixture 4, with a 28-day compressive strength of 276 psi, may be suitable in applications below foundations where future excavation concerns are not important. It is important to note that all four mixtures contained only one bag of Portland cement and that mixture 4 contained both coarse and fine aggregates.

Electric Resistivity, Thermal Conductivity and Plastics Compatibility Properties of CLSM Produced with We Energies Fly Ash

Figure 5-8: CLSM flows into place and completely filled this underground equipment vault.

Electric resistivity, thermal conductivity and plastics compatibility evaluations were performed on solidified CLS M fly as h slurry produced from a mixture of 1,275 lbs. of Valley Power Plant fly ash, 150 lbs. of Type 1 Portland cement and 1,050 lbs. of water per cubic yard (53).

Compressive strength tests were also performed per ASTM C-39 for comparison of these special properties. Electrical resistivity tests were performed in accordance with California Test 643-1978. Moisture content in the selected samples varied from 20% to 100%. Thermal conductivity tests were conducted using the thermal needle test method (Mitchell and Kao, 1978). Electrical resistivity test values are used to predict corrosiveness of soils. The electrical resistivity values obtained from the tests indicate that CLSM fly ash slurry is not considered corrosive. Table 5-9 shows commonly used soil corrosivity vs. resistivity values.

Table 5-9: Electrical Resistivity vs. Soil Corrosivity*

Thermal conductivity results exhibited a near linear relationship with moisture content. Thermal conductivity increases with an increase in moisture content and dry density. In applications like backfill for underground power cables where high thermal conductivity is desired, high-density, low porosity mixtures are preferable. Thermal conductivity values of high-volume flowable fly ash slurry are typically lower than sand, silt and clays but higher than peat.

A study conducted by Dr. Henry E. Haxo, Jr. of Matrecon, Inc., Alameda, California, concluded that high-density polyethylene-coated steel gas pipe, medium-density polyethylene gas pipe and low-density polyethylene jacketed cable would not be adversely affected by CLSM fly ash slurry (53).

Figure 5-9: Excavating hardened CLSM with a backhoe at We Energies Valley Power Plant in downtown Milwaukee, Wisconsin.

Tables 5-10 and 5-11 show the electrical resistivity test results and thermal conductivity test results respectively.

Table 5-10: Resistivity Test Results CLSM Fly Ash Slurry (ohm-cm)

Table 5-11: Thermal Conductivity Test Results CLSM Fly Ash Slurry (BTU/hr-ft-°F)

It can be concluded from this research that:

• Good quality CLSM fly ash slurry for utility trench backfill can be produced with off-spec Class F fly ash produced at PWPP and VAPP.
• CLSM fly ash slurry using PWPP or VAPP fly ash has less corrosion potential than typical soil used for trench backfill.
• High-density, very low porosity CLSM should be used where high thermal conductivity is desired, such as backfill around underground power cables.
• CLSM fly ash slurry has no adverse effect on polyethylene plastics used for underground gas lines and power cables.

Conductive CLSM Containing We Energies High Carbon Fly Ash (US Patent 6,461,424 B1) (40)

Materials

Materials used in this project consisted of one source of fly ash, cement, clean concrete sand, crushed quartzite limestone aggregates, and taconite pellets. Materials were characterized for chemical and physical properties in accordance with the appropriate ASTM standards. Table 5-12 shows the mixture proportions.

Type I cement (Lafarge Cement Co.) was used throughout this investigation. One source of fly ash was used for this project (We Energies, Port Washington Power Plant, Units 2 and 3).

The CLSM mixtures were proportioned to maintain a practical value of flow that would not have excessive segregation and bleeding. The flow was reduced for mixtures containing sand and gravel to maintain the cohesiveness and the workability of the mixture.

Fresh CLSM properties such as air content (ASTM D-6023), flow (ASTM D-6103), unit weight (ASTM D-6023), and setting and hardening (ASTM D-6024) were measured and recorded. All test specimens were cast in accordance with ASTM D-4832. These specimens were typically cured for one day in their molds at about 70 ± 5°F. The specimens were then demolded and placed in a standard moist-curing room maintained at 100% relative humidity and 73 ± 3°F temperatures until the time of test (ASTM D-4832).

Table 5-12: CLSM Mixtures with We Energies High Carbon Fly Ash

Mechanical Properties of CLSM with We Energies High Carbon Fly Ash

The CLSM strength increased with increasing age. In general, the rate of strength increase was the highest for the mixtures containing aggregates (sand and/or stone) content. Compressive strength for Mixture 100 (fly ash and cement) was 50 psi at the 28-day age. Compressive strength of Mixture 100S and 100SG were higher, 140 psi and 130 psi, respectively, even with reduced cement content, as shown in Table 5-13.

Table 5-13: Compressive Strength of CLSM Mixtures with

The compressive strength of Mixture 100S and 100SG at the age of 28-days indicates that a backhoe may be required to excavate these mixtures in the future. However, standard excavation practices typically do utilize a backhoe for excavations for efficiency. Therefore, the 28-day strength levels of the 100S and 100SG mixtures should not be expected to pose a problem for future excavations with mechanical equipment.

Electrical Properties of CLSM with We Energies High Carbon Fly Ash

The electrical properties of the CLSM mixtures are shown in Table 5-14. The electrical resistivity of the air dried CLSM prepared is in the range of 3 - 6 x 103 ohm-cm. The resistivity values of the saturated specimens were lower than that obtained for air dried specimens. The permeability of most CLSM specimens prepared with high carbon fly ash exceeds that of air, indicating a greater capability to carry an electrical current. The use of fly ash having greater levels of carbon would further decrease the resistivity of the resulting CLSM. In addition, the increased concentration of high carbon fly ash in the composition will result in increased conductivity. The most significant decrease in resistivity occurs when increasing the high carbon fly ash content in the controlled low-strength materials from 22%–32%. This is evident in the high carbon fly ash controlled low-strength material mixtures for both the saturated and air dry specimens.

Table 5-14: Electrical Properties of CLSM Mixtures

Conductive CLSM Containing We Energies High Carbon Fly Ash and Carbon Fibers (US Patent 6,821,336) (41)

Electrically conductive CLSM is advantageous where lower electrical resistance is sought, such as for use in structures where it is necessary to protect electrical equipment from lightning strikes. Ideally, electrically conductive CLSM has the following features:

• Provides low inductance, low resistance and subsequently low impedance values for all frequencies up to 1 MHz,
• Conducts energy efficiently across and through its surface without damage while providing true equalized ground potential rise values,
• Conducts energy efficiently into the earth quickly and seamlessly by providing the lowest impedance-coupling path,
• Compatible with copper, aluminum and galvanized steel products, and
• Fully excavatable, without heavy equipment

Conductive CLSM is made by using electrically conductive materials in close contact with each other throughout the CLSM. Electrically conductive additives include carbon fibers, steel fibers, steel shavings, carbon black, coke breeze, and other similar types of materials.

Since high carbon content fly ash is readily available as a coal combustion product, and carbon is known to be highly conductive, its use as an additive to CLSM to lower electrical resistance has been investigated. The goal of this testing work was to determine the feasibility of incorporating carbon fibers in the CLSM to lower electrical resistance of these construction materials. The lower electrical resistance of these construction materials can potentially reduce the required length, or entirely replace, the grounding electrodes currently in use for protection of electrical equipment from lightning strikes.

Materials

Materials utilized in this project consisted of one source of fly ash, cement, and carbon fibers. One source of fly ash was used for this project (We Energies, Presque Isle Power Plant). This selection was made to represent a typical high-carbon fly ash available from We Energies. Type I cement (Lafarge Cement Co.) was used throughout this investigation. Carbon fibers were used in one CLSM mixture (Mixture CLSM-B) to attempt to enhance the electrical resistance characteristics.

All CLSM ingredients were manually weighed and loaded in a rotating-drum concrete mixer. The CLSM was mixed using a rotating-drum mixer. Fresh CLSM properties such as air content (ASTM D-6023), flow (ASTM D-6103), and unit weight (ASTM D-6023) were measured and recorded. Air and CLSM temperature were also measured and recorded. CLSM test specimens were prepared from each mixture for compressive strength (ASTM D-4832) and density. Compressive strengths of the CLSM mixtures were evaluated at the designated ages of 3, 7, 14, and 28 days. All test specimens were cast in accordance with ASTM D-4832. Three CLSM test specimens were tested at each test age. These specimens were typically cured for one day in their molds in the University of Wisconsin at Milwaukee – Center for By-Products Utilization laboratory at about 70° ± 5°F. After setting, the test specimens were then demolded and placed in a standard moist-curing room maintained at 100% relative humidity and 73° ± 3°F temperature until the time of test.

Mixture Proportions

Two different types of electrically conductive CLSM mixtures were tested. CLSM mixture proportions and fresh CLSM test results are shown in Table 5-15. The CLSM mixtures were proportioned to maintain a “practical” value of flow that would not lead to excessive segregation and bleeding.

Table 5-15: Electrically Conductive CLSM Mixtures

Mechanical Properties

The compressive strength data for the CLSM mixtures are presented in Table 5-16. Compressive strength of the high-volume fly ash CLSM mixture (Mixture CLSM-A, fly ash and cement) increased slightly between the ages of 3 and 28 days. Compressive strength for Mixture CLSM-A was 70 psi at the 3-day age, and increased to 85 psi at the 28-day age. When carbon fibers were introduced into the CLSM mixture, compressive strength was significantly reduced, to approximately 10 psi. The 28-day strength levels achieved for the CLSM-A and CLSM-B mixtures should not be expected to pose a problem in case of future excavation.

Due to the addition of carbon fibers, the flowability of the CLSM was significantly reduced for Mixture CLSM-B. In order to obtain flow characteristics for a typical CLSM, water for Mixture CLSM-B needed to be increased by approximately 30% over the amount used for Mixture CLSM-A (CLSM without fibers). Reduced flowability is to be expected since the fibers would tend to interlock and restrict the flow of the mixture.

Table 5-16: Compressive Strength of CLSM Mixtures

Electrical Properties of CLSM Mixtures

The electrical resistivity values of the CLSM mixtures shown in Table 5-17 and Figure 5-10 are for air-dried specimens and Table 5-18 and Figure 5-11 are for saturated specimens. Electrical resistivity of high-carbon fly ash mixture CLSM -A, increased from 162.8 ohm- cm at the age of three days to over 55000 ohm-cm at the age of 28 days. Saturated specimens increased from 162.2 ohm-cm to only 535.7 ohm-cm at the age of 28 days. A significant improvement in the electrical resistance of CLSM occurred when carbon fibers were incorporated in Mixture CLSM-B. Both air-dried and saturated specimens exhibited very low resistivity of approximately 13.2 ohm-cm or less when tested at ages between 3 and 28 days. These results illustrate that using carbon fibers in CLSM has a greater positive effect on lowering the resistivity above that normally achieved through the use of high-carbon fly ash alone. Electrical permeability decreased slightly when carbon fibers were used (Mixture CLSM-B).

Table 5-17: Electrical Resistivity of CLSM Mixtures – Air-Dried Specimens

Table 5-18: Electrical Resistivity of CLSM Mixtures - Saturated Specimens

Figure 5-10: Electrical permeability of High Carbon Fly Ash CLSM Mixture CLSM-A

Figure 5-11: Electrical Permeability of High Carbon Fly Ash CLSM Mixture Containing Carbon Fiber CLSM

Dried vs. Saturated Specimens

Measurements taken for saturated CLSM specimens produced significantly smaller resistivity values compared to the air-dried specimens when tested without carbon fibers (Mixture CLSM-A). For the dried specimens, the aging process affected the resistivity significantly; the older the specimens, the higher the resistivity. The aging process affected the dried specimens more than the saturated ones. This indicates adding moisture to the material in place improves its conductivity. For the mixture containing carbon fibers, Mixture CLSM-B, air-dried specimens also had a higher electrical resistivity, but the difference between saturated and air-dried specimens was much less. Typically the difference between air-dried and saturated specimens was one ohm-cm or less. This can be attributed to the conductivity of the carbon fibers used in the mixtures.

Conductive CLSM Containing We Energies Fly Ash and Spent Carbon Sorbent (US Patent 7,578,881) (42)

This patent involves the testing of CLSM for increased electrical conductivity with the presence of both We Energies HCFA and spent carbon sorbent. The goal of this work was to determine the carbon and mercury in the spent carbon sorbent incorporated in CLSM to provide an electrical pathway throughout the CLSM for conducting electricity, without a severe deleterious effect upon mechanical properties (such as compressive strength), thus permitting the use of the electrically conductive CLSM in construction materials and applications.

Materials

Materials utilized consisted of one source of fly ash, cement, clean concrete sand, gravel aggregates, and a particulate material including fly ash and a spent activated carbon sorbent having adsorbed mercury. One source of clean concrete sand was utilized in this investigation as fine aggregate, meeting the ASTM C-33 requirements. The coarse aggregate used was natural river gravel with a maximum nominal size of ⅜ inch. Type I Portland cement was used throughout this investigation. One source of cementitious fly ash was used for this work from We Energies Pleasant Prairie Power Plant that met the requirements of ASTM C-618, Class C fly ash.

The spent activated carbon sorbent particulate material including fly ash that passed the electrostatic precipitator and was captured in the downstream baghouse was obtained from a coal fired electric generation facility that uses activated carbon sorbent to capture mercury. All CLSM ingredients were manually weighed and mixed by hand in a mixing bowl. For fresh CLSM, an estimate was made of the unit weight for determination of approximate mixture proportions and a general visual observation of the workability was made. Table 5-19 shows the mixture components.

Table 5-19: Concrete Mixture Proportions

Table 5-20: Concrete Mixture Test Results

Mechanical Properties

A 3 inch by 6 inch test cylinder was cast with the CLSM mixture where it was air-cured in the laboratory at 70º F ± 5ºF until the time of testing. Table 5-20 shows the test results for the mixture. Electrical resistance of the CLSM was measured using copper plates (3-in. diameter on each end) across the 6 inch length of the concrete sample. The tests resulted in a resistance of 95.9 ohms at the age of 39 days. The electrical resistivity was calculated to be 286 ohms-cm from the measured resistance, using the following equation:

R = ρL / A

where: ρ = resistivity; L = length; A = cross section area

Using the methods of ASTM C-39 and ASTM D-4832, the compressive strength for the concrete cylinder sample resulted in a compressive strength of 50 psi at the age of 50 days.

Commonly-Used CLSM Mixtures

We Energies has been testing and utilizing controlled low-strength materials containing fly ash for construction for over 25 years. Though several mixture proportions have been tried, a few mixtures are commonly used that are excavatable by ordinary methods. These mixtures usually are required to be self-leveling and essentially free from shrinkage after hardening. The mixtures that are most commonly used are designed to reach a state of hardening such that they can support the weight of a person in less than 24 hours.

We Energies has developed and marketed three different CLSM mixtures under the commercial name Flo-Pac. Flo-Pac is self-leveling and self-compacting and is placed to lines and grades shown on the construction plans. Table 5-21 shows the mix designs for Flo-Pac 1, Flo-Pac 2 and Flo-Pac 5.

Table 5-21: Commonly Used High Carbon* Class F Fly Ash

Pilot Projects Using We Energies CLSM

We Energies has utilized CLSM fly ash slurry on the following projects, where low strength and flowability were essential.

Abandoned Steam Service Tunnels

This was the first documented We Energies pilot project utilizing CLSM fly ash slurry. The project involved filling two obsolete brick lined steam service tunnels in downtown Milwaukee in December 1983. One tunnel was 6 ft. in diameter by 290 ft. long and the other had a 5 ft. by 4 ft. wide ellipsoid cross section.

Figure 5-12: ASTM D-6103, Standard Test for CLSM Flow Consistency

Over 420 cubic yards of CLSM slurry material were produced from a mixture of 2,152 lbs. of dry Class F fly ash, 859 lbs. of water, and 88 lbs. of Type I Portland cement. The fly ash was loaded directly into the ready-mix truck. The cement and water were also added directly and the drum was rotated at least 60 times during transit.

The CLSM flowable fly ash slurry was pumped into the tunnel. The maximum distance of CLSM flow was approximately 130 ft. Cylinders measuring 6” x 12” were prepared, and unconfined compression tests were run on the cylinders after 7 and 28 days, showing strengths between 50 and 100 psi, and greater than 100 psi, respectively. The project was completed over 25 years ago and no problems have been detected. Figure 5-13: CLSM flowing through a funnel to fill an underground tunnel in downtown Milwaukee, Wisconsin.

Figure 5-13: CLSM flowing through a funnel to fill an underground tunnel in downtown Milwaukee, Wisconsin.

Figure 5-14: We Energies' Flo-Pac CLSM being placed in a direct buried steam pipe trench in downtown Milwaukee, Wisconsin.

Sidewalk Cavity

This project was undertaken in 1984 and involved filling a hollow sidewalk cavity containing former locker room facilities in downtown Milwaukee. The CLSM flowable fly ash fill covered a length of about 80 ft., width of 14 ft. and a depth of 7 ft. The final top leveling layer was filled with sand (54).

About three hundred cubic yards of CLSM slurry were prepared using 1,950 lb. of dry Class F fly ash, 1,000 lb. of water and 128 lb. of Type 1 Portland cement. This mixture was placed directly into the cavity from ready mix trucks. Though minor shrink-age cracks were observed the following  day,  no voids  or settlement was noticed.

Figure 5-15: CLSM being placed in lifts to manage the load on basement walls.

The site was excavated, using a tractor mounted backhoe, after several months to install a water supply lateral. The hardened slurry was easily rippable and the excavation had straight walls on each side. CLSM slurry with a compressive strength of less than 300 psi at 28 days worked well for this type of an application.

WisDOT Low Permeability CLSM with We Energies Fly Ash (55)

To ensure containment of contaminated soils and groundwater, WisDOT developed a CLSM with low permeability for use as a migration/con-tamination barrier during normal construction and construction emergencies. Strict physical requirements were specified for the WisDOT low permeability CLSM. The material needed to be flowable, with a maximum compressive strength of 100 psi, a maximum permeability of 1 x 10-6 cm/s and less than a 24-hour time of set.

Class C fly ash from We Energies’ Pleasant Prairie Power Plant (PPPP) was used extensively during WisDOT low permeability CLSM mixture design study. The mixture using We Energies’ PPPP Class C fly ash was one of two mixture designs which meet the above engineering properties requirement, as shown in Table 5-22.

Table 5-22: WisDOT Low Permeability CLSM Mixture Design with We Energies Class C Fly Ash

Precautions to be Taken When Using CLSM Flowable Fly Ash Slurry

When properly mixed and placed, CLSM can provide construction savings by eliminating the need for labor intensive compaction efforts with standard granular materials. However, the following important construction considerations must be followed for success.

Figure 5-16: CLSM compression test cylinders. Note the color difference between those CLSMs based on Class F (dark) and Class C (light).

CLSM is placed as a liquid. Hence it exerts fluid pressure. If CLSM is placed against basement walls or other structures, verify that the structure is capable of taking this lateral pressure. If the structure is not capable of handling this pressure, it can be braced externally until the CLSM slurry solidifies, or the CLSM slurry may be placed in multiple lifts so that one lift hardens before the next is placed.

• Secure tanks, pipes and cables so they don’t float in the excavation.
• Fresh CLSM flowable fly ash slurry that is placed in deep excavations behaves like “quick-sand” so it must be protected from accidental entry until it hardens.
• Low-strength CLSM material where future excavation may be required at a later age should be specified with a maximum strength (or a range of strength) that will allow for easy excavation with normal equipment. The addition of coarse aggregate to the mixture generally makes excavation more difficult.
• When transporting CLSM flowable slurry in a ready-mix truck, the driver should be aware of the liquid nature of the material being transported. CLSM may spill out of the back of a ready mix truck with quick stops or while travelling up hills. It is better to transport CLSM stiff and add water at the job site for high flow requirements.

Advantages of Using CLSM Fly Ash Slurry

CLSM fly ash slurry has several advantages when compared to conventional compacted backfill. The slurry mixture can be designed to meet the requirements of particular applications. The following are the major advantages:

Figure 5-17: Filling a tunnel with twin 30" diameter steam mains in Milwaukee, Wisconsin

• CLSM fly ash slurry is flowable. The flowability can be increased or decreased by varying the water content. Hence, it can be used to fill inaccessible areas like retired sewer mains and tunnels where con-ventional ways of backfilling are difficult or economically not feasible. The flowable slurry fills voids completely, thus avoiding future settlement.
• The level of strength can be increased or decreased depending on the application. Where future excavation is required, the strength may be limited to the range of 50 to 300 psi maximum. Where higher strength is specified, such as base material for foundations, changing the cementitious and aggregate proportions may increase the strength.
• Unlike conventional backfilling methods, no tamping or vibration is required to place CLSM.
• Long-term settlement is virtually nonexistent. Except for the initial shrinkage settlement of less than 1/8 inch per foot, there is no additional settlement after hardening. Hence, on pavement repairs and similar applications, a smoother ride can be expected.
• There are substantial cost savings in using CLSM slurry, when compared to labor intensive conventional methods of backfilling. Fly ash slurry does not need compaction or vibration.
• Utilizing fly ash for this application is making beneficial use of a coal combustion product, which is helpful to the environment. It preserves sand and gravel pits, crushed stone quarries, valuable landfill space; saves land that would otherwise be dedicated for these uses; and contributes to sustainable development by completely utilizing this resource and preserving virgin materials for future generations.

Figure 5-18: Volumetric mixer used for production of fast setting and excavatable CLSM in the Chicago area.

Sample Specifications are included in Appendix 12.4 for the current CLSM mixtures.

Chapter 6 - Commercial Applications of We Energies Bottom Ash

Introduction

We Energies bottom ash can be beneficially utilized in a variety of manufacturing and construction applications. These applications include both confined and unconfined geotechnical uses, as an ingredient for the production of soil products and as an aggregate for concrete products. When using bottom ash, it is important to compare the applications and material properties to local and state regulations and specifications. In order to evaluate potential applications, We Energies has studied the properties and performance of its materials with the assistance of several consulting firms and research institutions. We Energies bottom ash is predominantly used for the following applications:

• Road base and sub-base
• Structural fill
• Pipe Bedding/Backfill
• Drainage media
• Aggregate for concrete, asphalt and masonry
• Abrasives/traction
• Manufactured soil products

Road Base and Sub-Base

STS Consultants, Ltd. conducted a study for We Energies to evaluate the potential use of Pleasant Prairie Power Plant bottom ash as a base course in road construction (56) . The study evaluated potential applications, and initiated durability and structural testing of bottom ash from We Energies Pleasant Prairie Power Plant.

The following tests were performed:

• Particle size analysis (ASTM D-422)
• Moisture-density relationship test - to establish maximum dry density (ASTM D-698-78, Method A).
• California Bearing Ratio (CBR) test - to develop a basis for comparison of bottom ash material with conventional base course aggregates (ASTM D-1883).
• Laboratory permeability test (ASTM D-2434)
• Direct shear test - to determine the angle of internal friction (ASTM D-3080)

The scope of this study included establishing an equivalent thickness of bottom ash compared to conventional aggregates in road construction. To address frost susceptibility in a meaningful manner, a sample of bottom ash was compacted into a 6” mold at its optimum moisture content. The mold with its perforated base was placed in a container of water for three days to allow the sample to absorb water. The sample was then frozen and subsequently thawed. Volume change measurements were made after both freezing and thawing.

The gradation of bottom ash tested was comparable to a silty fine to coarse sand with little gravel. However, bottom ash was considerably finer grained than the conventional gradation for fine aggregate.

The PPPP bottom ash exhibited a maximum dry density of 88.5 lbs/cu ft. and optimum water content of 28%. Conventional aggregates have maximum densities in the range of 105 to 120 lbs/cu ft. at optimum moisture contents typically in the range of 8% to 16%.

The CBR test results showed PPPP bottom ash had a CBR value on the order of 30% of that of conventional aggregate. In general, more coarsely graded and more angular materials tend to exhibit greater stiffness and tend to distribute load more evenly. The results showed that when used in a comparable thickness, bottom ash exhibits less favorable load distribution characteristics and would be more flexible, i.e., greater surface deformation under a load, than for conventional aggregates.

However, based on accepted pavement design principles, it was estimated that this source of bottom ash can be used at approximately 1.5 times the thickness of conventional aggregates achieves a comparable stress level in the underlying clay subgrade. For equivalent deformation, it was estimated that the thickness of bottom ash should be two times the thickness of conventional aggregates to maintain similar deflection at the surface of the base course layer (56). Figure 6-1 shows the stress penetration CBR curve for PPPP bottom ash.

The report also evaluated frost susceptibility, since bottom ash contains more fine-grained particles than conventional aggregates. The permeability study of compacted bottom ash was in the same range as conventional base course aggregates, i.e., 8 x 10 -4 to 5 x 10 -5 cm/sec. However, due to the presence of slightly higher fines when compared to conventional materials, it is recommended that bottom ash be used at locations with reasonably good drainage.

The direct shear test indicated an angle of internal friction of 40 degrees and cohesion of 750 psf, for the ash tested. The friction angle is consistent with this type of material. Figure 6-2 is a graph showing the normal stress vs. shearing stress relationship. However zero cohesion was expected due to its similarity to silty sand. Freeze- thaw test results showed a volumetric expansion of the compacted ash of 0.4% upon freezing. But after thawing, the net volumetric expansion was 0.1%.

Table 6-1 shows the gradation for PPPP bottom ash and crushed aggregate base course (crushed gravel) per the 1996 Wisconsin DOT Standard Specification for Highway and Structure Construction at the time of testing. A comparison of We Energies’ bottom ash to crushed aggregate base course in 2012 Wisconsin DOT Standard Specifications can be found in Chapter 3.

Table 6-1: Grain Size Distribution (ASTM D-422) PPPP Bottom Ash and Comparison with WDOT Crushed Gravel Specification for Crushed Aggregate Base Course

Figure 6–1: Loading Stress vs. Penetration (California Bearing Ratio) Curve for PPPP Bottom Ash

* Limited to a maximum of 8% in the base course placed between old and new pavement

Figure 6-2: Normal Stress vs. Shearing Stress PPPP Bottom Ash

Field Study

Following the initial study conducted on the suitability of bottom ash from PPPP as a base course, another study was commenced with field observation and testing on the performance of bottom ash during construction of another roadway in the Lakeview Corporate Park (57). The purpose of the testing was:

• To further evaluate the equivalency ratio using field plate load bearing tests.
• To evaluate frost susceptibility during a winter season by level survey techniques.
• To observe the general performance of the road subgrade for various thicknesses of base course.

Plate Load Test

As part of the road subgrade preparation, crushed limestone was placed in thicknesses varying from 0” to 6”. Bottom ash was placed above the proof rolled subgrade and leveled with a Caterpillar 14G grader. Bottom ash was then compacted close to its Modified Proctor maximum dry density, in the range of 83 to 95 lbs/cu ft. Crushed stone and gravel were placed in a parallel stretch of roadway and compacted to approximately 100% of its Modified Proctor maximum dry density. Plate load tests were performed in accordance with Military Standard 621A (Method 104).

Based on the test performed, a subgrade reaction modulus of 380 pounds per cubic inch (pci) was calculated. A similar test performed at the surface of the native subgrade gave a reaction modulus of approximately 212 pci. This gives a modular ratio of bottom ash to subgrade of approximately 1.9. Originally, a modular ratio of approximately 3 had been calculated. Conservatively, a modular ratio of 2 is appropriate.

Level Survey

The road surface was initially surveyed to establish a baseline for the determination of freeze-thaw effects. The level survey conducted on February 9, 1989, recorded a maximum surface heave of 0.6”, but after the spring thaw, the surface elevations were within ± 0.24”. These heaves were observed on both surfaces with and without bottom ash base course. The survey did not find any distinct pattern of response with the bottom ash experiencing neither greater nor lesser net heave during freeze-thaw cycles.

General Road Performance

The surface of the concrete road was inspected initially and found to be in competent condition, free of substantial ruts, cracking and other signs of pavement distress. The pavement was observed again after spring thaw and found to be in good condition. This indicated that the subgrade performed satisfactorily through the first winter.

It was concluded that the PPPP bottom ash materials are well suited for use as general structural fill in road subgrade preparations or below structural elements. Based on field observations, it was recommended to use bottom ash in a 2 to 1 thickness ratio compared to conventional base course material, to enhance the performance of the pavements. The reason for this recommendation is the lesser degree of stiffness of the bottom ash. It was concluded that in well-drained pavement sections, bottom ash base course (in the recommended thickness) should perform well.

Bottom Ash as Base Course Aggregate for Flexible Pavement Sections

The earlier study evaluated the performance of bottom ash as a base course material for a rigid pavement section. Though the pavement section performed well, a rigid pavement was used in that study and the performance of that section cannot be assumed to represent the behavior of less rigid pavement sections. Hence, a second pilot study was undertaken to evaluate the use of bottom ash for conventional base course aggregate in a flexible pavement section, such as parking lots and bituminous-paved roads (58).

A.W. Oakes & Son had observed that the actual performance of bottom ash in constructed haul roads was excellent. From this experience, they suggested that the ash might be effective at lesser thicknesses than recommended in the original study performed by STS Consultants, Ltd. A.W. Oakes & Son suggested that a pavement section consisting of 4” – 6” of bottom ash over 4” – 6” of open-graded crushed stone would serve as an excellent base for a heavy duty asphalt pavement.

Pavement Construction

A failed section of pavement 24 ft. wide by 55 ft. long located at the entrance drive of A.W. Oakes & Son Land Reclamation Landfill Facility in Racine, Wisconsin, was replaced with 4¾” of bituminous concrete pavement placed over 4½” – 6½” of bottom ash which was over 8” of an open-graded crushed stone base layer. The test section was constructed in November and December of 1993. Field density tests were performed by STS Consultants on the in-place bottom ash and on the in-place bituminous pavement using a nuclear density meter (58).

Figure 6-3: Bottom ash base course for concrete building slab in Racine,

Pavement Performance

The test pavement was evaluated by STS Consultants, Ltd. on March 21, 1994; November 22, 1994; April 20, 1995 and April 22, 1997. The field observations revealed that the pavement section performed well with only minor rutting in wheel traffic areas. The depth of rutting increased slightly over the years, but was not considered abnormal. The asphalt surface showed no signs of alligator cracking.

No direct correlation can be made with the adjoining pavement, since the age and construction of this pavement is unknown. However, from field observations, it was concluded that the pavement section appeared to be comparable to or better than the adjacent pavement throughout its existence until 2010.

We Energies Bottom Ash Backfill

We Energies bottom ash has been successfully used as a backfill material on numerous projects. PPPP bottom ash is a clean, durable, torpedo sand-like material. Other We Energies bottom ashes are finer or include gravel size gradation particles as well.

The suitability of bottom ash as a backfill material can be understood from its close resemblance to commonly used natural granular backfill materials. In most cases, the most critical factor is the gradation of backfill material.

Sieve analyses indicated that bottom ash from PPPP meets the gradation requirements for a granular backfill material by the WDOT. PIPP bottom ash did not meet all of the requirements, but PIPP bottom ash can be blended, washed or screened to meet the MDOT requirements. Other analyses have shown that bottom ash from OCPP also meets the WDOT gradation requirement for granular backfill. Permeability of the backfill is a common concern, especially in applications where the backfill material is subjected to a moist environment. Permeability is also one of the major reasons that sand is a preferred backfill material when compared to clay.

Figure 6-4: Bottom ash structural backfill being used for building construction in Racine, Wisconsin

Since the gradation of bottom ash and sand are similar, they tend to exhibit similar permeability. Clean fine sand has a coefficient of permeability (K) in the range of 0.004 to 0.02 cm/sec (59). The drainage characteristics associated with the above K values are considered good. Most We Energies bottom ashes have a coefficient of permeability in this range and can be considered to provide good drainage when used as a backfill material.

Table 6-2 gives the coefficient of permeability for We Energies bottom ash and conventional backfill materials.

Table 6-2: Permeability and Drainage Characteristics

Bottom ash has a lower density than conventional backfill materials. Conventional backfill materials (like sand) typically have a maximum dry density of 105 to 120 lbs/cu ft. We Energies bottom ash has a maximum dry density in the range of 49 to 89 1bs/cu ft. VAPP bottom ash showed the lowest dry density of 49 lbs/cu ft., and PPPP bottom ash had the highest density of 89 lbs/cu ft.

Bottom ashes from VAPP and MCPP have a higher percentage of fines and are more sensitive to moisture changes. However, bottom ash from other power plants performed well when compacted at the optimum moisture content. Soil generally exhibits lateral earth pressure. Structures such as retaining walls have to be designed, considering the lateral pressure exerted by soil retained by the structure. The angle of internal friction for various backfill materials is shown in Table 6-3.

Table 6-3: Approximate Friction Angle

The friction angle of bottom ash is very similar to that of well-graded sand and gravel. The lateral earth pressure on the structure can be reduced because of the lower material density. Assume that the dry unit weight of a specific bottom ash in such a situation is only 2/3 of the dry unit weight of conventional backfill material. Because the friction angle value remains more or less the same, the lateral earth pressure will also be reduced to 2/3 of regular fill. Due to the reduced lateral pressure on the wall, it can be designed as a thinner section, with less reinforcement, or with a higher safety factor.

Bottom Ash as an Anti-Skid Material

Bottom ash performs as an excellent anti-skid material when spread on ice or snow covered roads. Bottom ash does not have the corrosivity of salt, as only a very small fraction of it is soluble. The performance of bottom ash as an anti-skid material is not temperature dependent. For this reason, bottom ash can be considered a better anti-skid material than road salt. The WisDOT recommends the following rate of application (60):

• A rate of 500 pounds per mile on average snowy and icy roads.
• A rate of 800 pounds per mile at intersections, hills, curves and extremely icy areas.

Used tires are sometimes burned with coal in some power plants. Bottom ash produced from plants that burn tires may contain steel wires that are left from the steel belted radial tires. Bottom ash containing steel wires is not suitable for use on roads as steel can puncture tires of vehicles traveling on these roads.

We Energies power plants do not burn used tires with coal. Hence, the bottom ash will not contain such steel wires and is acceptable for use as an anti-skid material on roads. Bottom ash will usually require screening to meet anti-skid material gradation requirements.

Bottom Ash as an Aggregate in Asphaltic Concrete

A.W. Oakes & Son replaced fine aggregates with bottom ash in asphaltic concrete mixtures for paving projects. Since bottom ash particles are porous, the consumption or absorption of asphalt binder is higher than when the conventional fine aggregate is used. Hence, from a purely economical point of view, We Energies bottom ash is not best suited as an aggregate for asphaltic concrete. However, other bottom ash sources have been extensively used by West Virginia Department of Transportation for asphalt roads, particularly for secondary roads (61).

Bottom Ash as a Bike Trail Base and Surface Material

Bottom ash has been successfully used as a base and surface material for bike trails and as a surface course material in parks and for running tracks.

In several states in the United States, bottom ash has been used as a finish grade surfacing material. The New River Trail in Virginia surfaced a portion of its 57-mile route with bottom ash. This project demonstrated significant savings in cost compared to a similar crushed stone surface (61).

We Energies Bottom Ash as a Manufactured Soil Ingredient

We Energies studied the properties of bottom ash and its use as a soil-amending agent to heavy clay soils to increase its workability and porosity. Studies conducted at the University of Wisconsin-Madison (62) revealed that land application of bottom ash had no negative effect on the crops or soil during the five-year period of study.

Bottom ash from the OCPP and PPPP were used on farms in Kenosha County, Wisconsin, at a rate ranging from 100 to 200 tons per acre. Bottom ash was tilled into the soil to a depth of approximately 10”.

Corn was grown on this field for two years and soybeans were grown for one year. Chemical analysis conducted on the soil throughout the three-year study revealed that there was no appreciable movement of nutrients or heavy metals below the 10” plow layer. Chemical analysis of corn and soybean seed and edible tissue for heavy metals and nutrient uptake indicated no adverse effect. Crop yield at the bottom ash treated soils was generally higher than from the non-treated soils.

The Scott’s Company of Maryville, Ohio, studied the properties of We Energies bottom ash and determined that it is suitable as an ingredient in manufactured soil products. The bottom ash from Milwaukee County Power Plant, Port Washington Power Plant and Valley Power Plant were used in their studies.

Figure 6–5: “Before” grass growing on We Energies’ landscaping with Scott’s 10% bottom ash topsoil blend at We Energies’ Milwaukee County Power Plant.

The investigation determined that the addition of 10–15% (weight basis) of bottom ash provides desired soil porosities. In addition, the ash blended soils exhibit excellent micronutrient composition.

The mixture also meets all of the state and federal limits for trace elements in composted soils. Bottom ash has been blended with peat, compost and manure to manufacture about 300 cubic yards of manufactured topsoil for We Energies landscaping projects with excellent results.

Figure 6–6: “After” grass is growing on landscaping with Scott’s Hyponex 10% bottom ash topsoil blend at We Energies’ Milwaukee County Power Plant.

Table 6- 4 shows the summary of total ele-mental analysis results for fly ash and bottom ash with a comparison to Wisconsin DNR, NR 538 standards, together with various naturally occurring materials.

Table 6-5 shows ASTM water leach test data, in a similar fashion.

Additional information on environmental considerations is provided in Chapter 9.

Table 6-4: Total Elemental Analysis Comparison of Sample We Energies Fly Ash, Bottom Ash and Natural Materials

Table 6-5: ASTM D3987 Water Leach Test Data Comparison of Sample We Energies Fly Ash, Bottom Ash and Natural Materials

We Energies Bottom Ash as a Soil Ingredient for Green Roofs

We Energies bottom ash was also used experimentally as a portion of a soil ingredient in green roofs. Green roofs involve growing plants on rooftops, thus replacing the vegetated footprint that was lost when the building was constructed. Establishing plant material on rooftops provides numerous ecological and economic benefits including storm water management, energy conservation, mitigation of the urban heat island effect, increased longevity of roofing membranes, as well as providing a more aesthetically pleasing environment to work and live. Examples of green roofs are shown in Figures 6-7 and 6-8.

Additional loading is one of the main factors in determining both the viability and the cost of a green roof installation, especially when a green roof is not part of the initial design of the building. Bottom ash is a lightweight material.

Figure 6–7: Green Roof at ABC Supply Company,

Blending bottom ash with the soil provides a lightweight growing media for the plants of the green roofs. We Energies bottom ash was used for a small portion of the green roof (as a blended soil ingredient) by ABC Supply Company, Inc. in Beloit, Wisconsin. Additional information can be found on website at: http://www.greengridroofs.com/Pages/system.htm

Figure 6–8: Green Roof at ABC Supply Company, Inc.

We Energies Recovered Ash and Reburning

Coal Ash Recovery (U.S. Patent # 6,637,354) (63)

As part of We Energies’ continued effort to find innovative applications for its coal combustion products, and to preserve valuable licensed landfill capacity, We Energies has patented a process for recovery of coal combustion products from ash landfills. The PPPP ash landfill has been the primary site for ash recovery and occupies an area of approximately 163 acres. It is located north of Bain Station road and south of Highway 50.

The landfill was placed in operation in 1980 and consists of 25 cells with a total licensed capacity of 3,012,155 cubic yards of coal combustion products. Cell 1 was constructed with a natural 5 ft. thick clay liner and cells 2–4 were constructed with a 5 ft. thick recompacted clay groundwater separation liner. Currently only cells 1–3 are filled and cell 4 is partially filled. Since demand for bottom ash and fly ash has continued to increase since the 1980’s, the quantity of material that goes into these landfills is limited. Since 1998, more material has been recovered from the landfill than placed in it. All the material placed originally in cells 1-2 has been recovered and the area has been restored.

The coal combustion materials landfilled in cells 1–4 consist primarily of bottom ash, solidified fly ash and wastewater treatment system solids. We Energies ash reclamation plan is to excavate the landfilled material, crush and screen if necessary, test and store for reuse in compliance with the criteria defined in NR 538, plus boron as an additional leachable parameter in accordance with a cooperative agreement signed with the Wisconsin DNR (64). Any material that is found to be unsuitable for beneficial application such as miscellaneous debris or soil is separated and properly placed in designated areas within the current active cell.

Figure 6-9: Coal ash recovery from the Pleasant Prairie Power Plant ash landfill for use as granular base course material

Figure 6-10: Recovered coal ash from the Pleasant Prairie Power Plant ash landfill

The first pilot projects to reprocess landfilled combustion products were carried out in July 1998 and the second in October 1998. An earthwork contractor who was very experienced in landfill and ash management performed the work. A state certified material testing laboratory was also hired to monitor and sample the processed material. The contractor’s engineer collected samples during the second operation. Samples were collected every 30 minutes from the transfer point where the ash fell onto the stacker conveyor during the entire operation per ASTM sampling procedure D-2234. A composite sample was prepared for every 5000 tons processed and tested. Both ash recovery operations worked very smoothly, and were dust free due to the residual moisture and low fines content of the material processed.

Figure 6-11: Gradation Distribution Range of Recovered Ash

Figure 6-11 shows the grain size distribution range of the recovered ash. It is important to mention that the samples tested had excellent grain size distribution and a small amount of material passing the #200 sieve. Tests run to evaluate the environmental effects of this material also gave encouraging results. The ash met all of the NR538 category 2 criteria with the exception of dissolved aluminum. However the concentration of aluminum was only slightly above the limits (18 to 22 mg/l vs. 15 mg/l criteria).

The only other compounds detected that were within one order of magnitude of the category 2 criteria were antimony, barium, chromium and sulfate. The remaining elements were either non-detectable or were several orders of magnitude below the category 2 criteria.

The first 10,000 tons of recovered ash was used as a sub-base material under pavements. This practice has continued due to the excellent sub-base and base performance of the interlocking angular shaped recovered ash particles for this application. This is an application meeting NR538.10 (5) category 4 standards. However the recovered ash test results meet most of the NR 538 category 2 requirements.

In February 2001, Wisconsin DNR and We Energies entered into an agreement in which an ash sampling and testing procedure was specified. In order to determine the chemical consistency of the coal combustion materials recovered from the landfill, the ash was excavated, processed, and stored in a designated area in the landfill in no larger than 50,000 cubic yard piles. A representative sample was obtained per each 10,000 tons of reclaimed material for testing using guidelines presented in ASTM D-2234. A minimum of five discrete samples of at least 25 pounds each were collected from different locations on the storage pile. These discrete samples were composited, mixed, and volume reduced by manual riffling to develop the analysis sample. Testing was performed to measure category 2 parameters (described in ch. NR 538, Wis. Adm. Code), as well as boron as an additional leachable parameter, for use as sand/gravel/and crushed stone replacement materials. These recovered materials were used in category 4 or 5 applications (described in ch. NR 538, Wis. Adm. Code).

Reburning of Coal Ash (U.S. Patent # 5,992,336) (65)

If coal ash has a significant amount of unburned carbon, it cannot be utilized directly in applications such as concrete and concrete products. According to ASTM C-618, an ash must have a LOI value no higher than 6% for use in concrete. An upper limit of 3% is more realistic. Higher LOI ash cannot be used because of color problems and concerns with the use of admixtures especially for durability under freezing and thawing conditions.

We Energies is utilizing an innovative technique, reburning of coal ash, to treat high carbon coal ash using existing capital installations, and particularly the existing pulverized coal boilers. Coal ash, either fly ash or bottom ash or a mixture of both, is added in a fine particle condition to the furnace of a pulverized coal boiler in a small proportion to the pulverized coal fed to the furnace. The ash is burned with the pulverized coal. The proportion of coal ash is preferably in the range of 1% – 3.5%, by weight of the pulverized coal.

The high carbon coal ash generally results from burning bituminous coal while sub-bituminous coal will typically result in a low carbon ash with an LOI of less than 1%. The high LOI fly ash and bottom ash formed from a pulverized coal furnace burning bituminous coal can be rendered into a usable fly ash and bottom ash having very low LOI such as produced in a pulverized coal furnace using subbituminous coals. This can be achieved by adding the high LOI coal ashes to the coal stream which normally produces low LOI coal ashes.

The bottom ash and fly ash may be handled separately. The bottom ash typically has a larger particle size and may require grinding to reduce it to the size of the pulverized coal stream. The preferred approach for handling of the bottom ash is to add it to the store of coal prior to the coal being ground.

For instance in original tests conducted in 1996, bottom ash having an LOI of 37.9% and a moisture content of 60.0% was added to loaded coal cars using a front end loader. The bottom ash was added at a ratio of 5% of the coal prior to unloading in a rotary car unloader. The coal cars were then unloaded in a normal manner and the coal was transported by a conveyor system to one of five coal silos. The bottom ash and coal mixture was then milled and injected into the boiler with the fuel stream during normal operation in the furnace along with coal from the other four silos and mills that did not contain bottom ash. Thus, the actual ratio of bottom ash to coal transported for combustion was 1% of the overall fuel being burned. The addition of the 1% of bottom ash was not significant from an operational viewpoint. There was no discernable difference in emissions, and the bottom ash coal fuel blend had adequate fineness for combustion. The fly ash from the reburning of the bottom ash exhibited a LOI of between 0.2% and 0.4% and has a slightly reduced calcium oxide content. Bottom ash typically represents less than 20% of the coal ash.

High LOI fly ash can be introduced using four approaches: (1) introduced with the pulverized coal stream entering the pulverizer classifiers. This has the advantage of thorough mixing upstream of the burners and would require only a slight additional volume of air to transport the fly ash; (2) introduced with the pulverized coal stream at each burner location; (3) introduced with the secondary air flow stream as it enters the furnace. The secondary air flow with the fly ash provides sufficient mixing; (4) introduced through heat-resistant or stainless pipes into the furnace either above or adjacent to the existing burner level. Injection points through a waterwall could be used, although this may require modifications of the waterwalls in the boilers.

In the original tests conducted in 1996, a fly ash having an LOI of 26.5% and a moisture content of 0.3% was introduced into a coal pulverized furnace through injection pipes. The fly ash was stored in a horizontal silo from which it was pumped through stainless steel pipes extending through the furnace wall immediately above two coal burners. The hose was connected to a reducer splitter where the 5” diameter hose was reduced to two 2” diameter hoses. The fly ash was pumped at a rate of approximately 1% –2% of the coal flow into the furnace. The addition of the fly ash did not affect combustion. The resulting fly ash from the reburning had an LOI of between 0.2% and 0.5% based upon samples taken at intervals over four days. Reburning of high carbon bituminous coal ash in both sub-bituminous and bituminous pulverized fuel furnaces has now been performed at We Energies Pleasant Prairie and Elm Road Power Plants in Wisconsin and Presque Isle Power Plant in upper Michigan with excellent results.

We Energies Bottom Ash as Fine Aggregate in Concrete Masonry Products

Natural volcanic combustion products have been used in the manufacture of masonry products since ancient times. Several decades ago cinders, a combustion product of lump coal combustion, were used as a lightweight aggregate in the manufacture of masonry blocks. However, not much technical data was available on these products. Today, fly ash and bottom ash have been extensively investigated to determine performance.

We Energies has investigated the suitability of its bottom ash and fly ash in the manufacture of concrete bricks, blocks and paving stones. The following data is from research conducted at the Center for By-Products Utilization (CBU) of the University of Wisconsin-Milwaukee for We Energies at two local manufacturing plants (66).

Concrete masonry products can be manufactured either by the wet-cast process or the dry-cast process. Several mixes were designed at the CBU for the manufacture of concrete bricks, blocks and paving stones using the dry-cast method. Actual manufacture of the dry-cast test products was performed at Best Block Company in Racine, Wisconsin, using standard manufacturing equipment.

Tables 6-6 – 6-8 show the mixture design data for bricks, blocks and paving stones using the dry-cast method. Tables 6-9 – 6-11 show the compressive strength data for the above-mentioned products. The three mixtures for each product have varying amounts of fly ash and bottom ash. Each of the three products also has a control mixture with no fly ash and no bottom ash.

Table 6-6: Dry-Cast Concrete Brick Mixtures

The dry-cast concrete brick mixture BR-1 (control mix) had a 56-day strength that was lower than that of BR-2, a similar mix containing fly ash. Twenty-five percent cement was replaced with fly ash at a 1 – 1.3 replacement ratio. The exact proportions can be seen in Table 6-6.

Brick mixtures BR-3 and BR-4 containing bottom ash and fly ash showed lower compressive strengths at the 56-day age. The compressive strengths obtained were all above 3,000 psi. This level of strength is good for most applications. Similar strength patterns are also seen for blocks and paving stones.

Long-term behaviors of these masonry products were also studied at CBU, and this data showed that concrete bricks, blocks and paving stones with reasonable strength and good durability can be made using fly ash and bottom ash.

Table 6-7: Dry-Cast Concrete Block Mixtures

Table 6-8: Dry-Cast Concrete Paving Stone Mixtures

Table 6-9: Compressive Strength of Dry-Cast

Table 6-10 Compressive Strength of Dry-Cast Concrete Blocks

Table 6-11: Compressive Strength of Dry-Cast Concrete Paving Stones

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Source: We Energies

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