FINAL TECHNICAL REPORT

September 1, 1997, through August 31, 1998

Project Title: CCBS-BASED LIGHTWEIGHT MATERIALS USING FIBERS

AND AIR ENTRAINMENT CHEMICALS

ICCI Project Number: 97-1/3.1B-1

Principal Investigator: Deepak Dutta, Southern Illinois University at Carbondale

Other Investigators: Y. P. Chugh, M. Prichard, and H. Wilcox

Southern Illinois University at Carbondale

Project Manager: Dr. Dan Banerjee, ICCI

ABSTRACT

Using financial supports of Illinois Clean Coal Institute, Dr. Chugh and his research team at the Mining Engineering department of Southern Illinois University at Carbondale have developed lightweight artificial supports, for underground mines, using coal combustion by-products. These supports contain 70% fly ash from Gibson power plant and 30% binders and admixtures. Mine demonstrations of these supports have indicated their comparable performance to or better accomplishments than wooden supports currently being used in underground mines. However, polyester fibers constitute 15-20% of the material cost of these supports. Another issue is the use of preformed foam for density reduction. Laboratory scale productions have indicated 10% density variations from batch to batch. To reduce the costs of fibers and control the quality of finished products, this project investigates the use of waste carpet fibers and air entraining chemicals.

Studies conducted in this project using fly ash from Lake of Egypt and Grand Tower power plants indicate that it is possible to use air entraining chemicals to reduce product densities to 85 pcf and 65 pcf without sacrificing the strength. In fact, for the lower density (65 pcf) products, air entraining chemicals give 20% increased strength due to the low water content of the mix. For higher density (85 pcf) products, air entraining chemicals and preformed foam are indistinguishable with respect to strength of samples containing Lake of Egypt fly ash. However, most of the air entraining chemicals are not cost competitive with the preformed foam. The cheaper varieties lack sufficient air entraining capabilities.

Large size (5 in. x 5in. 24 in.) crib-tie elements with waste carpet fibers exhibit comparable post-failure characteristics to that of the crib-tie elements containing commercial fibers. Economic analyses indicate the cost of production of a 5 in. x 5 in. x 72 in. post using commercial fibers and disposable molds is $5.16. The cost of production drops to $4.83 and the rate of return improves by 45% if waste carpet fibers are utilized. Considering the cost-competitiveness, use of waste carpet fibers is a better choice over the commercial fibers.

EXCUTIVE SUMMARY

Using air-entraining chemicals and waste carpet fiber, this project seeks to improve lightweight coal combustion by-products (CCBs) based artificial underground supports. Dr. Y. P. Chugh of Mining Engineering Department at Southern Illinois University (SIUC) has developed these artificial supports using 70% F-type fly ash from Gibson Power plant. The lightweight materials developed using CCBs have strengths ranging from 2,500 to 2,800 psi at 95 pcf density. With the financial supports from the Illinois Clean Coal Institute and the cooperation of SIPC's Lake of Egypt, AMEREN/CIPS's Grand Tower, and SIUC power plants, Dr. Chugh is designing a pilot scale commercial facility to manufacture these supports using fly ash from Lake of Egypt (F-type), Grand Tower (F-type), and SIUC (FBC) power plants.

In the earlier projects, the CCBs-based artificial supports were developed using commercially available polyester fibers (to simulate the post-failure characteristics of wooden supports) and preformed foam was used to entrain air into the material for density reduction. Commercially available fibers were effective but they added approximately $0.80 to the cost of a post of size 6 in. x 6 in. x 96 in. Laboratory studies indicated that the density reduction using preformed foam could result in 10% density variations of final finished products. To improve the quality control and reduce the cost of the finished product, air entraining chemicals and waste carpet fibers were suggested in this project. However, the fly ash source for the development of this lightweight products changed from Gibson to Lake of Egypt and Grand Tower power plants. Hence, we needed to ascertain that the same types of products could be developed using Lake of Egypt and Grand Tower fly ash.

In this project, we studied the water/powder ratio-density relationship to select the water/powder ratio for mix preparation, tested seven commercially available air entraining agents for their effectiveness to entrain air, developed and tested for strength a large number of 2-inch cubical samples of densities ranging from 52 pcf to 128 pcf. These samples used foam as well as air entraining chemicals. We also developed and tested crib-tie elements of 5-inch x 5-inch x 24-inch size using air entraining chemicals and waste carpet fibers. Nylon based waste carpets were collected from local carpet dealers and shredded to a size of 1.0 to 1.5 inches.

The costs of the most air entraining chemicals were approximately $2.50 per pound and at least 0.5% of these chemicals were required to effectively entrain air for the desired density reduction (65 pcf and 85 pcf). For a full size post weighing approximately 140 lbs. (that had 110 lbs. of solid powder), approximately 0.5 lbs. or $1.25 worth of air entraining chemicals were required. This was not cost competitive with preformed foam. A cheaper air entraining chemical costing $0.50 per pound was also investigated but its air entraining capability was not promising.

While using preformed foam, a minimum of 24% (if Lake of Egypt fly ash was used) or 33% (if Grand Tower fly ash was used) water was required to prepare a mix (70% F-type fly ash and 30% binders and admixtures) before introducing foam into the mix matrix. However, the residence time (or mixing time) before the foam introduction was approximately 4 to 5 minutes. Three percent (3%) foam was required to bring down the density to 85 pcf. Considering 50% of the foam as water, the total water in the final mix was 25.5% (or 34.5%). To reduce the residence time to one/two minutes, 26% (or 34%) water must be mixed with the powder before introducing the foam. It was also found that after mixing the powder with 26% (or 34%) water for about one minute, 0.5% air entraining chemicals and 1% water (no additional water was required for Grand Tower fly ash) could be introduced into the mix and mixed for two to three minutes to bring down the density to 85 pcf (95 pcf for Grand Tower fly ash). To bring down the density to 65 pcf, additional water and/or mixing time were required after introducing the air entrainment chemicals into the mix matrix. However, for a lower density product (65 pcf) the air entraining chemicals had an advantage over the preformed foam. To bring down the density to 65 pcf, large amounts of foam were required. The water content in the finished mix due to the introduction of large quantities of foam was as high as 30-31% when Lake of Egypt fly ash was used. This resulted in agglomeration of high carbon F-type fly ash (from Lake of Egypt) particles and reduced strength. In case of air entraining chemicals, introduction of an additional 1% water coupled with an increase of mixing time by one minute gave a product of 65 pcf. Products containing Grand Tower fly ash required drying for further reduction in density (or gain in strength).

To match the strength obtained earlier by Dr. Chugh using Gibson fly ash, we changed the water/powder ratio, increased the binders and admixtures content to 40%, replaced the F-type fly ash with the FBC fly ash and supplemented the mix with lime. In all cases, limited success was achieved. Using 35% binders and admixtures, we could produce a product of 1000 psi strength at 65 pcf. With 40% binders and admixtures, a strength approximating 2,000 psi could be achieved at 80-85 pcf density. A strength approximating 1800 psi was achieved when samples, containing Grand Tower fly ash, were dried to 85 pcf from 95 pcf.

Large size crib-ties using carpet fibers and commercial nylon fibers were cast in disposable and non disposable molds and tested for their post-failure characteristics. It was observed that the product containing waste carpet fibers exhibited comparable post-failure characteristics as that of the products containing commercial fibers. Drying of products, containing Grand Tower fly ash and cast in non-disposable mold, at a room temperature and using an industrial blower was not very successful and the average density reduction was only 6%. Samples prepared using a mortar mixer and a hand held foam gun showed inconsistent product qualities. To improve the product quality, mixing, foaming, and curing procedures must be improved by initiating a quality assurance/quality control program during the commercial production of lightweight materials.

Economic analyses indicated the cost of production of a 5 in. x 5in. x 72 in. post using commercial fibers and disposable molds was $5.16. The cost of production dropped to $4.83 and the rate of return improved by 45% when waste carpet fibers were utilized. Considering the cost-competitiveness, use of waste carpet fibers was a better choice over the commercial fibers.