Center for By-Products Utilization

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1 Center for By-Products Utilization PROPERTIES OF CAST-CONCRETE PRODUCTS MADE WITH FBC ASH AND BLENDS OF FBC ASH AND WET- COLLECTED COARSE CLASS F FLY ASH By Tarun R. Naik, Rudolph N. Kraus, Yoon-moon Chun, and Francois D. Botha Report No. CBU REP-493 January 2004 Accepted for Presentation and Publication at the Eighth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, Las Vegas, May 23-29, Department of Civil Engineering and Mechanics College of Engineering and Applied Science THE UNIVERSITY OF WISCONSIN MILWAUKEE

2 Properties of Cast-Concrete Products Made With FBC Ash and Blends by T. R. Naik, R. N. Kraus, Y. Chun, and F. D. Botha Synopsis: Cast-concrete hollow-core blocks, solid blocks, and paving stones were produced at a commercial manufacturing plant by replacing up to 45% (by mass) of cement with fluidized bed combustion (FBC) coal-ash and by replacing up to 9% of aggregates with wet-collected, low-lime, coarse coal-ash. Castconcrete product specimens of all three types exceeded the compressive-strength requirements of ASTM from early ages, with the exception of the paving-stone mixture with the highest ash content. The cast-concrete products made with up to 40% replacement of cement with FBC ash were equivalent in compressive strength (89% to 113% of control) to the products without ash. Partial replacement of aggregates with wet-collected coarse ash decreased compressive strength of cast-concrete products. The resistance of hollow blocks and paving stones to freezing and thawing decreased sharply with increasing ash contents. Abrasion resistance of paving stones also decreased with increasing ash contents. Since almost all of the cast-concrete products met the strength requirements of ASTM, they could be used indoors in regions where freezing and thawing is a concern. They could also be used outdoors in a moderate climate. Keywords: abrasion resistance, blocks, cast-concrete products, compressive strength, flue-gas desulfurization (FGD) material, fluidized bed combustion (FBC) ash, freezing and thawing, masonry units, paving stones, wet-collected ash. 1 (MS #LV60) (Revised 29 JAN 2004)

3 Tarun R. Naik, FACI, is a Professor of Structural Engineering and Director of the UWM Center for By-Products Utilization (UWM-CBU) at the University of Wisconsin-Milwaukee. He is a member of ACI Committees 123, Research; 214, Evaluation of Results of Tests Used to Determine the Strength of Concrete; 229, Controlled Low-Strength Materials (CLSM); 232, Fly Ash and Natural Pozzolans in Concrete; and 555, Concrete with Recycled Materials. He was also Chairman of the ASCE Technical Committee on Emerging Materials ( ). Rudolph N. Kraus is Assistant Director of the UWM-CBU. He has been involved with numerous projects on the use of by-product materials including utilization of foundry sand and fly ash in CLSM, evaluation and development of CLSM, evaluation of lightweight aggregates, and use of by-product materials in the production of cast-concrete products. Yoon-moon Chun is a Postdoctoral Fellow at the UWM-CBU. His research interests include the use of coal fly ash, coal bottom ash, and used foundry sand in concrete and cast-concrete products, and the use of fibrous residuals from pulp and paper mills in concrete. Francois D. Botha received his Ph. D. degree in Materials Science from the University of Bath in England. Presently he is working as a Project Manager at the Illinois Clean Coal Institute (ICCI). He is involved in implementing and monitoring projects in the area of coal-combustion by-products. Earlier he was with Sasol Oil and Gas company in South Africa. INTRODUCTION The overall utilization rate for coal fly ash, bottom ash, and flue gas desulfurization (FGD) materials in the USA was approximately 32% in 2001 (35 million tonnes out of 107 million tonnes) 1. Most of the fly ash was used for cement-based products manufacturing, while most of the FGD material was used for gypsum-based wallboard manufacturing. Compared with conventional coal fly ash and bottom ash, the utilization rate of FGD material (generated from low- SO x technologies) in cement-based products is much lower. There is a significant lack of commercial cement-based products that utilize FGD material. Due to the Clean Air Act Amendments of 1990, the quantity of FGD material will increase significantly 1. Finding practical solutions to this ash problem is essential because of shrinking landfill space, environmental concerns, and increased public awareness. Compared to conventional coal ash, relatively very little work has been conducted to-date in developing cement-based products containing FGD material. Recent research studies 2-13 have shown various potential applications for FGD material. The UWM Center for By-Products Utilization (UWM-CBU) has conducted a number of research projects on high-volume uses of both ASTM 2 (MS #LV60) (Revised 29 JAN 2004)

4 Class F and Class C fly ashes in cementitious products for the last two decades. The UWM-CBU has also worked on concrete using FGD material since the late 1980 s 6. This research project was conducted to develop manufacturing technology for the use of FGD material and wet-collected, low-lime, coarse coalash in dry-cast concrete masonry products. Hollow-core blocks, solid blocks, and paving stones incorporating the ashes were manufactured at a commercial manufacturing plant in Rockford, Illinois, USA. Materials EXPERIMENTAL PROCEDURES Type I portland cement (ASTM C 150) was used in this research. Fine crushed limestone and natural sand were used as fine aggregates. Crushed limestone with a 9.5 mm nominal maximum size was used as coarse aggregate. One source of wet-collected, low-lime, coarse coal-ash (WA) with 29% moisture content and one source of fluidized bed combustion (FBC) ash obtained from Illinois, USA, were used. FBC ash is an FGD material. The FBC ash was used as a partial replacement for cement, and the wet-collected, coarse ash was used as a partial replacement for aggregates. The wet-collected coal-ash was a mixture of fly ash and bottom ash. A water-reducing admixture (ASTM C 494, Type A) was used in producing the solid blocks. Mixture Proportions Five mixtures of hollow-core concrete blocks (Table 1), five mixtures of solid concrete blocks (Table 2), and five mixtures of paving stones (Table 3) were manufactured. For each type of concrete masonry product, a control mixture was proportioned without coal ash. The rest of the four concrete mixtures were proportioned with FBC ash as a replacement of up to about 45% of cement by mass. Two of the four mixtures with the FBC ash also contained wet-collected coarse coal-ash (WA) as a replacement of up to 9% of aggregates by mass. In general, as the amount of coal ash in cast-concrete products increased, water-cementitious materials ratio (W/Cm) increased and the density of the castconcrete products decreased. Manufacturing of Cast-Concrete Products All ingredients for each type of cast-concrete masonry product were automatically batched at the commercial manufacturing plant, with the exception of coal ashes. The required quantities of coal ashes were manually loaded into the plant s mixer. Before the wet-collected ash was added to the dry-cast concrete mixtures, particles of the wet-collected ash larger than 9.5 mm were removed by sieving. After the FBC ash and wet-collect ash were added to the mixture, the quantity of the mixing water was modified to obtain the required 3 (MS #LV60) (Revised 29 JAN 2004)

5 consistency of the mixture for loading it into the casting machine for dry-cast concrete products (hollow-core blocks, solid blocks, and paving stones). All mixing, casting, and steam curing of all dry-cast masonry units were performed by the manufacturing plant following their standard commercial production procedure. Steam curing was done for 6 hours at 64 C and at atmospheric pressure. The test specimens for each type of masonry product were brought to the laboratory for strength and durability testing. The specimens were stored indoors at 23 ± 2 C and at relative humidity of 50 ± 10% until the time of testing. Nominal dimensions (width height length) of the cast-concrete units were mm for hollow-core blocks, mm for solid blocks, and mm for paving stones. Nominal face-shell thickness and web thickness of the hollow-core blocks were both 30 mm. Testing Hollow blocks, solid blocks, and paving stones were tested for compressive strength and water absorption (ASTM C 140). Resistance of saturated surfacedry hollow blocks and paving stones to 50 cycles of freezing and thawing (ASTM C 1262) was determined. Resistance of saturated surface-dry paving stones to abrasion by sandblasting (ASTM C 418) was also determined. Hollow Blocks RESULTS AND DISCUSSION All hollow-block specimens exceeded the strength requirement of ASTM C 90 (13.1 MPa minimum) from an early age (Fig. 1) (by an average of 42% at 15 days). After initial steam-curing, following normal practice, only air curing was provided. Therefore, the compressive strength of the hollow blocks remained relatively constant from 15 to 91 days. The compressive strength of hollow blocks generally decreased slightly with increasing FBC ash content (Table 4, Fig. 1). Overall, hollow blocks cast with Mixtures HB2 (29% FBC, 0% WA) and HB3 (39% FBC, 0% WA) showed about 4% and 6% lower average compressive strength compared with Control hollow blocks (Mixture HB1) (Table 4). Partial replacement of aggregates with wet-collected coarse coal-ash appreciably decreased the compressive strength of hollow blocks. This is probably because coarse fly ash and bottom ash are not as dense and strong as the natural limestone. Overall, hollow blocks cast with Mixtures HB4 (34% FBC, 8% WA) and HB5 (45% FBC, 9% WA) showed about 20% and 23% lower average compressive strength than Control hollow blocks (Mixture HB1) (Table 4). However, because the all the hollow-block mixtures exceeded the minimum strength requirement of ASTM, the amount of cement in Control Mixture HB1 could be reduced. 4 (MS #LV60) (Revised 29 JAN 2004)

6 The average water-absorption values of hollow blocks were in the range of 80 to 127 kg/m 3. All hollow block specimens met the requirement of ASTM C 90 for water absorption (208 kg/m 3 maximum). Test results for mass loss of hollow blocks due to 50 cycles of freezing and thawing are given in Table 4. The results were evaluated as a comparison of the performance between the various hollow-block mixtures. The mass loss increased sharply as the amount of the FBC ash and wet-collected coarse coalash increased. The hollow blocks would be suitable for indoors use or outdoors use in a moderate climate (e.g., southern Illinois, USA). Typically masonry blocks are not saturated and then exposed to a freezing and thawing environment, but if the blocks are expected to be subjected to this type of environment, use of higher percentages (above 30%) of ash materials might have to be avoided. Solid Blocks All solid concrete-masonry block specimens exceeded the strength requirement of ASTM C 90 (13.1 MPa minimum) from an early age (Fig. 2) (by an average of 29% at 14 days). After initial steam-curing, following normal practice, only air curing was provided. In spite of this, however, the strength of the solid blocks increased considerably with age (an average of 42% increase between the ages of 14 days and 150 days). This may be due to the thickness (100 mm) of the solid blocks, which probably made the initial steam-curing less effective than in the cases of hollow blocks with 30 mm thick face-shells and webs, and 40 mm thick paving stones. Solid blocks made with FBC ash showed higher compressive strength than those made without FBC ash (Table 4, Fig. 2). Overall, solid blocks cast with Mixtures SB2 (29% FBC, 0% WA) and SB3 (40% FBC, 0% WA) showed about 12% and 13% higher average strength than those cast with Control Mixture SB1 (Table 4). Partial replacement of aggregates with wet-collected coarse coal-ash appreciably decreased compressive strength of hollow blocks. This is because wet-collected coarse fly ash and bottom ash are not as strong as the natural aggregates. Overall, solid blocks cast with Mixtures SB4 (34% FBC, 7% WA) and SB5 (45% FBC, 8% WA) showed about 17% and 14% lower average compressive strength than Control solid blocks (Mixture SB1) (Table 4). Since solid-blocks Mixtures SB1, SB2, and SB3 exceeded the minimum strength requirement of ASTM considerably, the quantities of cement in these mixtures could be reduced. The average water-absorption values for solid blocks ranged from 159 to 184 kg/m 3. All solid block specimens met the absorption requirement of ASTM C 90 (208 kg/m 3 maximum). Paving Stones All paving stone specimens, except those made with the highest ash contents (Mixture P5 [44% FBC, 7% WA]), exceeded the compressive strength requirement of ASTM C 936 (55 MPa) from early age (Fig. 3) (by an average of 5 (MS #LV60) (Revised 29 JAN 2004)

7 25% when all ages are considered, excluding Mixture P5). The strength of paving-stone specimens cast with Mixture P5 was 10% or less lower than the ASTM requirement. This slight shortfall in strength can be readily overcome by increasing the amount of cement and/or by improving the curing regime. After initial steam-curing, following normal practice, only air curing was provided. Therefore, in general, the compressive strength of paving stones remained relatively constant between the test ages of 15 and 56 days. Paving stones made with partial replacement of cement with FBC ash showed lower compressive strength than the control paving stones (Table 4, Fig. 3). Overall, the average strength values of paving stones cast with Mixtures P2 (23% FBC, 0% WA) and P3 (34% FBC, 0% WA) were about 11% and 6% lower compared with those cast with Control Mixture P1 (Table 4). Partial replacement of aggregates with wetcollected coarse coal-ash appreciably decreased the compressive strength of paving stones. This is probably because the particles of the wet-collected coarse fly ash and bottom ash are not as strong as the natural limestone. Overall, the average strength values of paving stones cast with Mixtures P4 (34% FBC, 7% WA) and P5 (44% FBC, 7% WA) were about 17% and 32% lower compared with those cast with Control Mixture P1 (Table 4). However, because most of the paving-stone mixtures met the minimum strength requirement of ASTM, the amount of cement in Control Mixture P1 could be reduced. The average water-absorption values of paving stone specimens ranged from 1.5% to 2.8%, with the exception of those cast with Mixture P5, whose absorption was 4.8%. All paving stones met the absorption requirements of ASTM C 936 (5%, max.). Test results for mass loss of paving stones due to 50 cycles of freezing and thawing are given in Table 4. The relative performance of the various pavingstone mixtures was evaluated. The mass loss increased sharply as the amount of the FBC ash and wet-collected coarse coal-ash increased. However, the paving stones would be suitable for indoors use or outdoors use in a moderate climate (e.g., southern Illinois, USA). If paving stones are expected to be saturated and then exposed to a freezing and thawing environment, use of higher percentages (above 30%) of ash materials might have to be avoided. Test results for abrasion resistance of paving stones are included in Table 4. The results are given in volume-loss per unit sand-blasted-area, which is equivalent to average depth of sandblasted cavities on the surface of paving stones. The results were evaluated by comparing the performance of the various paving-stone mixtures. The average depth of the cavities increased gradually as the ash contents in paving stones increased. The average depth of the cavities of paving stones made with up to 34% replacement of cement with FBC ash (Mixtures P2 and P3) was only slightly higher than the control paving stones (Mixture P1). Paving stones cast with Mixtures P2, P3, P4, and P5 exhibited 17%, 23%, 55%, and 85% more damage due to abrasion than those cast with Control Mixture P1. 6 (MS #LV60) (Revised 29 JAN 2004)

8 SUMMARY AND CONCLUSIONS Cast-concrete hollow-core blocks, solid blocks, and paving stones were produced at a commercial manufacturing plant by replacing up to 45% (by mass) of cement with FBC ash and up to 9% of natural aggregates with wet-collected, low-lime, coarse coal-ash. Based on the strength and durability test results obtained for the cast-concrete products manufactured in this research, the following conclusions may be drawn: (1) Cast-concrete product specimens of all three types exceeded the minimum compressive strength requirements of ASTM from early ages, with the exception of paving stones with the highest quantities of ashes (Mixture P5 [44% FBC ash, 7% wet-collected coal-ash]), which fell short of the strength requirement by less than 10%. (2) The cast-concrete products made with up to 40% replacement of cement with FBC ash were equivalent in compressive strength (89% to 113% of control) to the products without ash. (3) Partial replacement of aggregates with wet-collected coarse coal-ash decreased compressive strength of cast-concrete products. Curing should be improved, or cement content should be increased. Additional tests are needed. (4) Resistance of paving stones and hollow blocks to freezing and thawing decreased with increasing ash contents. These products would be suitable for indoors use or outdoors use in a moderate climate (e.g., southern Illinois, USA). (5) Abrasion resistance of paving stones decreased with increasing quantities of ash. It might be possible to improve the abrasion resistance of the paving stones incorporating the ashes by improving the curing regime, or by increasing the amount of cement. Additional tests are needed to verify this. ACKNOWLEDGMENT The authors express their deep sense of gratitude for the grants made possible by the Illinois Department of Commerce and Community Affairs through the Office of Coal Development and Marketing and the Illinois Clean Coal Institute. The UWM Center for By-Products Utilization was established in 1988 with a generous grant from Dairyland Power Cooperative, Lacrosse, Wisconsin; Madison Gas and Electric Company, Madison, Wisconsin; National Minerals Corporation, St. Paul, Minnesota; Northern States Power Company, Eau Claire, Wisconsin; We Energies, Milwaukee, Wisconsin; Wisconsin Power and Light Company, Madison, Wisconsin; and Wisconsin Public Service Corporation, 7 (MS #LV60) (Revised 29 JAN 2004)

9 Green Bay, Wisconsin. Their financial support and additional grants and support from Manitowoc Public Utilities, Manitowoc, Wisconsin are gratefully acknowledged. Notice to Journalists and Publishers: If you borrow information from any part of this report, you must include a statement about the State of Illinois support of the project. REFERENCES 1. Kalyoncu, R.S., Coal Combustion Products < (March 2003), 11 pp. 2. Clarke, L.B., Utilization Options for Coal Use Residues: An International Overview. Proceedings of the Tenth International Ash Use Symposium, ACAA, Orlando, Florida, EPRI Report No. TR , Vol. 2, pp to 66-14, January Clarke, L.B., Smith, I.M., Management of Residues from FBC and IGCC Power Generation: An International Overview. Proceedings of the Ninth International Ash Use Symposium, ACAA, EPRI Report No. GS-7162, Vol. 3, pp to 70-15, January ICF Northwest, Advanced SO 2 Control By-Products Utilization: Laboratory Evaluation. EPRI Report No. CS-6044, September ICF Technology Incorporated, Laboratory Characterization of Advanced SO 2 Control By-Products: Spray Dryer Wastes. EPRI Report No. CS-5782, May Naik, T.R., Patel, V.M., and Peiper, L.A., Clean Coal By-Products Utilization in Roadway, Embankments, and Backfills. Report No. 116, UWM Center for By-Products Utilization, University of Wisconsin-Milwaukee, September Rick, R.D., Hilton, R.G., and Smith, C.L., Utilization of Flue Gas Desulfurization Sludge. Proceedings of the EPRI-EPA 1990 SO 2 Control Symposium, Session 3B: By-Products Utilization, Vol. 1, May Henzel, D.S., Commercial Utilization of SO 2 Removal Wastes in the Application of New Advanced Control Technology. Proceedings of the EPRI-EPA 1990 SO 2 Control Symposium, Session 3B: By-Products Utilization, Vol. 1, May Forsythe, R.C., and Bolli, R.E., Ohio Edison Company s Clean Coal Technology and Waste Utilization Program. Proceedings of the EPRI-EPA 8 (MS #LV60) (Revised 29 JAN 2004)

10 1990 SO 2 Control Symposium, Session 3B: By-Products Utilization, Vol. 1, May Naik, T.R., Kolbeck, H.J., Singh, S.S., and Wendorf, R.B., Low-Cost High- Performance Materials Using Illinois Coal Combustion By-Products - Phase I. A Final Report to Illinois Clean Coal Institute, Carterville, IL, October Naik, T.R., Kolbeck, H.J., Singh, S.S., and Kraus, R.N., Low-Cost High- Performance Materials Using Illinois Coal Combustion By-Products - Phase II. A Final Report to Illinois Clean Coal Institute, Carterville, IL, October Naik, T.R., Banerjee, D.D., Kraus, R.N., Singh, S.S., Characterization and Application of Class F Fly Ash and Clean Coal Ash for Cement-Based Materials. Proceedings of the Twelfth ACAA International Symposium, Orlando, Florida, January Naik, T.R., Banerjee, D.D., Kraus, R.K., Singh, S.S., Use of Class F Fly Ash and Clean Coal Ash Blends for Cast-Concrete Products. Proceedings of the Twelfth ACAA International Symposium, Orlando, Florida, January Table 1 - Mixture Proportions of Dry-Cast Hollow Blocks Mixture Name HB1 HB2 HB3 HB4 HB5 FBC Ash Content (% of cement plus FBC ash) Wet-Collected Coal-Ash Content (% of aggregates plus wet-collected coal-ash) Cement (kg/m 3 ) FBC Ash (kg/m 3 ) Water (kg/m 3 ) W/Cm* Wet-Collected Coal-Ash, SSD (kg/m 3 ) Fine Crushed Limestone, SSD (kg/m 3 ) Sand, SSD (kg/m 3 ) Stone Chips, 9.5 mm max., SSD (kg/m 3 ) Density (kg/m 3 ) * W/Cm = Water/(Cement + FBC Ash) 9 (MS #LV60) (Revised 29 JAN 2004)

11 Table 2 - Mixture Proportions of Dry-Cast Solid Blocks Mixture Name SB1 SB2 SB3 SB4 SB5 FBC Ash Content (% of cement plus FBC ash) Wet-Collected Coal-Ash Content (% of aggregates plus wet-collected coal-ash) Cement (kg/m 3 ) FBC Ash (kg/m 3 ) Water (kg/m 3 ) W/Cm* Wet-Collected Coal-Ash, SSD (kg/m 3 ) Fine Crushed Limestone, SSD (kg/m 3 ) Sand, SSD (kg/m 3 ) Stone Chips, 9.5 mm max., SSD (kg/m 3 ) Water Reducing Admixture (L/m 3 ) Density (kg/m 3 ) * W/Cm = Water/(Cement + FBC Ash) Table 3 - Mixture Proportions of Dry-Cast Paving Stones Mixture Name P1 P2 P3 P4 P5 FBC Ash Content (% of cement plus FBC ash) Wet-Collected Coal-Ash Content (% of aggregates plus wet-collected coal-ash) Cement (kg/m 3 ) FBC Ash (kg/m 3 ) Water (kg/m 3 ) W/Cm* Wet-Collected Coal-Ash, SSD (kg/m 3 ) Fine Crushed Limestone, SSD (kg/m 3 ) Sand, SSD (kg/m 3 ) Stone Chips, 9.5 mm max., SSD (kg/m 3 ) Density (kg/m 3 ) * W/Cm = Water/(Cement + FBC Ash) 10 (MS #LV60) (Revised 29 JAN 2004)

12 Table 4 - Average Compressive Strength, Mass Loss Due to Freezing and Thawing (F&T), and Volume-Loss Due to Abrasion of Cast-Concrete Units Type Mixture Name FBC Ash Content* (%) Wet- Collected Coal-Ash Content (%) Average Compressive Strength (MPa) (%) Residue (spall) Due to 50 Cycles of F&T (% by mass) Volume Loss Per Unit Area Due to Abrasion (cm 3 /cm 2 ) Hollow HB Block HB HB HB HB Solid SB Block SB SB SB SB Paving P Stone P P P P * % of cement plus FBC ash % of aggregates plus wet-collected coal-ash Average of results from all test ages (3 test specimens for each mixture per test age) 11 (MS #LV60) (Revised 29 JAN 2004)

13 Compressive Strength, MPa Age, days (FBC, WA) HB1 ( 0 %, 0 %) HB2 (29 %, 0 %) HB3 (39 %, 0 %) HB4 (34 %, 8 %) HB5 (45 %, 9 %) ASTM Minimum Fig. 1. Compressive strength of hollow blocks. FBC: FBC ash content (% of cement plus FBC ash) WA: Wet-collected coal-ash content (% of aggregates plus wet-collected ash) Compressive Strength, MPa Age, days (FBC, WA) SB1 ( 0 %, 0 %) SB2 (29 %, 0 %) SB3 (40 %, 0 %) SB4 (34 %, 7 %) SB5 (45 %, 8 %) ASTM Minimum Fig. 2. Compressive strength of solid blocks. FBC: FBC ash content (% of cement plus FBC ash) WA: Wet-collected coal-ash content (% of aggregates plus wet-collected ash) 12 (MS #LV60) (Revised 29 JAN 2004)

14 Compressive Strength, MPa Age, days (FBC, WA) P1 ( 0 %, 0 %) P2 (23 %, 0 %) P3 (34 %, 0 %) P4 (34 %, 7 %) P5 (44 %, 7 %) ASTM Minimum Fig. 3. Compressive strength of paving stones. FBC: FBC ash content (% of cement plus FBC ash) WA: Wet-collected coal-ash content (% of aggregates plus wet-collected ash) 13 (MS #LV60) (Revised 29 JAN 2004)