FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: LOW-COST, HIGH-PERFORMANCE MATERIALS USING ILLINOIS COAL COMBUSTION BY-PRODUCTS

ICCI Project Number: 96-1/3.1A-6

Principal Investigator: Tarun R. Naik

Center for By-Products Utilization

University of Wisconsin-Milwaukee

Other Investigators: Shiw S. Singh, Rudolph N. Kraus

Project Manager: Daniel D. Banerjee, ICCI

This project was carried out to establish high-volume use technologies for manufacture of cement-based products using Illinois coal ashes. The entire project work was completed in two phases (Phase I, year 1; and Phase II, year 2). Phase I work was primarily directed toward optimizing mixture proportions and production technologies for concretes and masonry products containing Illinois coal ash through lab investigation during the year 1994-1995. In Phase I, a number of candidate mixtures for concretes, bricks, blocks, and paving stones were established based on strength and durability performance data. In Phase II (September 1, 1996 thru August 31, 1997), mixtures selected from Phase I were field tested and evaluated to establish optimum mixture proportions and production technologies for commercial applications.

A total of 15 concrete mixtures consisting of five non-air entrained, five non-air entrained with a high range water reducing admixture (HRWRA), and five air entrained concrete mixtures were manufactured at the facilities of United Ready Mix, Inc., Peoria, IL. Two of each type of concrete mixtures were control mixtures without fly ash and the remaining contained fly ash up to a maximum of 60% of total cementitious materials. Concrete mixtures were tested for strength and durability related properties such as compressive strength, splitting tensile strength, flexural strength, drying shrinkage, abrasion resistance, deicer-salt scaling resistance, freezing and thawing resistance, and chloride-ion penetration as a function of age. A total of 15 cast-concrete product mixtures consisting of five brick mixtures, six hollow-core block mixtures, and four paving stone mixtures were manufactured at the facilities of Best Block Co. in Racine, WI, near the Illinois state border. Brick and block mixtures contained up to a maximum of 56% fly ash while paving stone mixtures contained up to a maximum of 30% fly ash of total cementitious materials. The brick and block mixtures were tested and evaluated for compressive strength, absorption, density, and shrinkage as a function of age. Block mixtures were also tested for freezing and thawing durability. Paving stone mixtures were tested and evaluated for compressive strength, absorption, density, abrasion resistance, and freezing and thawing resistance. Based on strength and durability performance data, as well as economic considerations, optimum mixtures for concrete and masonry products were established for commercial production in Illinois.

EXECUTIVE SUMMARY

Coal combustion by-products generated from combustion of Illinois coals are primarily low-lime, ASTM Class F, variety. Although a substantial amount of research has been conducted on utilization of conventional Class F fly ash in concrete and concrete products, its utilization rate is much lower compared to ASTM Class C fly ash in the USA. This is because of its lower cementing values and greater plant-to-plant variability in properties such as fineness and loss on ignition (LOI). Therefore, there is a lack of commercial products containing high volumes of Class F fly ash compared to Class C fly ash. Utilization options available for clean coal ashes generated by burning Illinois coals is more limited. Fineness and LOI properties of coal ash can be improved by processing and beneficiation. In light of the above, a need exists for developing technology for high-volume uses of Illinois coal combustion by-products. Therefore, this investigation was focused toward developing high-volume Illinois coal ash (Class F) use technologies for commercial production of low-cost concrete and masonry products.

The activities of the project were divided into two phases (Phase I, Year 1: Lab Testing; and Phase II, Year 2: Field Testing). Phase I of this project was successfully completed in the year 1994-1995. Phase I work was primarily concerned with establishing optimum mixture proportions and production technologies through extensive laboratory testing and evaluation. In Phase I, a number of candidate mixtures for concretes, bricks, blocks, and paving stones, were established based on strength and durability performance data. In Phase II of the project, these candidate mixtures were field tested and evaluated in order to establish mixture proportions and production technology for large-scale commercial manufacture of concrete and masonry products. This final report deals with the activities related to Phase II.

Phase II activities of the second year (September 1, 1996 to August 31, 1997) were organized into five tasks: Task I: Manufacturing and Testing; Task II: Optimization of Manufacturing Specifications; Task III: Economic Analysis; Task IV: Demonstration/Technology Transfer; and, Task V: Reports. Task I involved manufacturing of ready-mixed concrete mixtures at the facilities of United Ready-Mix, Inc., Peoria, Illinois; and, production of bricks, blocks, and paving stones at the manufacturing facilities of Best Block Company. These products were tested for strength and durability related properties as required by ACI, ASTM, and/or AASHTO. Test data were used in modifying optimum mixture proportions and material specifications for commercial manufacture of products under Task II. Task III involved a cost-benefit analysis of the manufacture of these new products and economic impact of jobs creation or maintenance in Illinois coal mines. Task IV activities were directed toward transferring the new technologies to potential users and to promote their marketability. Task V involved preparation of quarterly and final reports in accordance with ICCI requirements. These reports include details of products manufacturing, field work, test data collected; and, recommendations for optimum mixtures for each product, based on strength and durability performance, for future commercial manufacturing applications.

A total of 15 ready-mixed concrete mixtures, consisting of five non-air entrained, five non-air entrained with HRWRA, and five air entrained, were manufactured in Peoria, IL. Each mixture was batched and mixed at a ready-mixed concrete plant of the United Ready-Mix, Inc. (URMI), Peoria, Illinois. Mixtures were transported by a conventional ready-mixed concrete trucks to a nearby storage facility of the URMI. Fresh concrete tests were performed and test specimens were cast. A total of 15 cast-concrete products mixtures were manufactured at the facilities of the Best Block Company. These cast-concrete mixtures were five brick mixtures, six hollow-core block mixtures, and four paving stone mixtures.

The five non-air entrained concrete mixtures, consisted of two no-fly ash mixtures and three fly ash mixtures. The reference mixtures were proportioned without fly ash to have strengths of 4,000 and 5,000 psi at the age of 28 days (structural-grade, office building, concrete). The fly ash mixtures were proportioned to have fly ash concentrations of 18%, 35%, and 45% of total cementitious materials.

The five non-air entrained concrete mixtures with HRWRA were composed of two no-fly ash mixtures and three fly ash mixtures. The reference mixtures without fly ash were proportioned to have strengths of 4,000 and 5,000 psi at the age of 28 days (structural-grade, industrial building, concrete). The fly ash mixtures had fly ash concentrations of 19%, 37%, and 60% of total cementitious materials.

The five air entrained concrete mixtures consisted of two no-fly ash mixtures and three fly ash mixtures. The reference mixtures were proportioned without fly ash to attain strengths of 3,500 and 4,000 psi at the age 28 days (for driveways and roadways, and IDOT specified mixtures, respectively). The fly ash mixtures were proportioned to have fly ash concentrations of 20%, 30%, and 40% of total cementitious materials.

Four reference mixtures: two for bricks, one for blocks and one for paving stones, were manufactured without fly ash. Additional brick mixtures were proportioned to have fly ash concentrations of 20%, 30%, and 50% of total cementitious materials. Additional block mixtures were proportioned to contain fly ash at five levels of cementitious materials (12%, 25%, 35%, 45% and 56%). Additional paving stone mixtures were proportioned to have fly ash concentration of 15%, 25%, and 30% of total cementitious materials.

For all five non-air entrained and five HRWRA concrete mixtures, test specimens were evaluated for compressive strength, splitting tensile strength, flexural strength, abrasion resistance, and drying shrinkage as a function of age. For the five air entrained concrete mixtures, test specimens were evaluated for compressive strength, splitting tensile strength, flexural strength, shrinkage, abrasion resistance, freezing and thawing resistance, salt scaling resistance, and chloride ion penetration resistance as a function of age. The bricks and block mixtures were tested for compressive strength, absorption, density, and shrinkage as a function of age. The block mixtures were also tested for freezing and thawing resistance. The paving stone mixtures were tested for compressive strength, absorption, density, abrasion, and freezing and thawing resistance.

In general, the early-age strength properties such as compressive strength, splitting tensile strength, and flexural strength decreased with increasing fly ash concentration. However, the difference between the reference mixtures and the fly ash mixtures decreased substantiality with increasing age. This was due to the fact that at the early ages, Class F fly ash cementing ability is lower, causing decrease in the strength properties. Whereas at later ages, fly ash helped increase the rate of strength development due to its pozzolanic contributions resulting in improved microstructure of the mortar matrix and improved strength of the concrete.

The non-air entrained concrete mixtures attained compressive strengths in the range of 4,100 - 6,200 psi at 28 days for the concrete mixtures incorporating up to 45%Class F fly ash from Illinois. Therefore, these non-air entrained concrete mixtures with fly ash content up to 45% can be used in manufacture of good-quality structural-grade concretes. The splitting tensile and flexural strength values were also high enough for structural applications. All non-air entrained concrete mixture exhibited excellent performance with respect to abrasion.

The non-air entrained concrete mixtures with HRWRA showed the most encouraging performance. These mixtures attained compressive strengths in the range of 4,400-6,700 psi at the 28-day age. Therefore, it is possible to make high-quality structural-grade concretes with Class F fly ash from Illinois up to a concentration of 60% of total cementitious materials. All mixtures with and without fly ash showed excellent performance with respect to tensile strength, flexural strength, abrasion resistance, and shrinkage.

The air entrained reference concrete mixture attained a strength of 3,550 psi at the 28-day age. All fly ash mixtures showed compressive strength results comparable to the reference mixture up to 40% Illinois Class F fly ash content at the age of 28 days and beyond. The air entrained mixtures with and without fly ash were appropriate for applications in normal construction projects related to driveways, roadways, highways, etc. All air entrained concrete mixtures with and without fly ash showed excellent abrasion resistance and adequate performance with respect to shrinkage. Inclusion of Class F fly ash from Illinois for up to 30% cement replacement improved performance of air entrained concrete with respect to salt scaling resistance, freezing and thawing resistance, and resistance to chloride-ion penetration.

In general, compressive strength of all cast-concrete masonry mixtures increased with age. The rate of increase was generally higher for Illinois Class F fly ash mixtures, due to the pozzolanic reaction of the fly ash.

All brick mixtures containing Illinois Class F fly ash up to 30% cement replacement met the ASTM C 55 Grade S-I and S-II requirements for compressive strength (2,500 psi or higher) and absorption (less than 13 lb/ft³). The 50% fly ash mixture showed a strength of 3,100 psi. However, it did not meet the ASTM requirement for absorption. Therefore, bricks containing up to 30% fly ash are appropriate for use in general construction work where moderate strength and resistance to frost action and moisture penetration are required. The density of brick mixtures varied between 127 and 132 lb/ft³.

Except for the 45% Illinois Class F fly ash mixture, all hollow-core block mixtures met the ASTM C 90 requirement for compressive strength. All mixtures with and without fly ash met the ASTM requirement for absorption (less than 13 lb/ft³). All mixtures containing up to 35% fly ash passed the freezing and thawing durability requirement in accordance with NCMA TEK 2-4A. The 56% fly ash block mixture failed this durability requirement. Thus, block mixtures at least up to 35% fly ash can be manufactured to meet the strength and durability related requirement per ASTM. The density of block mixtures ranged from 132-137 lb/ft³.

All paving stone mixtures with and without Illinois Class F fly ash did not meet the ASTM C 936 requirement for compressive strength (8,000 psi). A higher cement content base mixture and higher compaction would be necessary for the future. They also failed to meet the ASTM requirement for absorption (5%). However, all paving stone mixtures exhibited sufficient strength, in excess of 5,000 psi and 5,800 at the ages of 7 days and 28 days, respectively. Therefore, paving stones without fly ash, or those containing up to 30% fly ash, can be used in normal construction work if ASTM C 936 requirements are accepted to be too rigid.

Economic analysis revealed that use of Illinois Class F fly ash in cement-based materials will result in large savings on material cost as well as disposal cost. If in general a minimum of 30% cement is replaced with Illinois coal fly ash, then total cost savings of 90 million dollars (1997) per year can be realized.