United States Department of Transportation
i
Utilizing Coal Fly Ash and Recycled Glass in Developing Green Concrete Materials
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2012-06-01
[PDF-1.40 MB]
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TRIS Online Accession Number:01475854
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Edition:Final report; 6/1/2010-8/31/2011.
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Construction and Maintenance;NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;
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Abstract:The environmental impact of Portland cement concrete production has motivated researchers and the construction industry to evaluate alternative technologies for incorporating recycled cementing materials and recycled aggregates in concrete. One such technology is based on using pulverized glass as sand or pozzolan. Currently in the United States more than 600,000 tons/year of recycled glass bottles are stockpiled due to prohibitive shipping costs from recycling locations to glass melting factories. This project demonstrates the potential use of this waste material along with fly ash (another industrial byproduct with landfill rate of 42.4 million tons/year) in developing durable and environmentally positive concretes that can be used for various transportation applications. Toward this objective, the project included two main tasks. In the first task, the deleterious alkali-silica reaction (ASR) induced by the use of silicate glass aggregates was mitigated via the use of fly ash. Mixtures were prepared using one of six different fly ashes. The main objective of this task was to better understand the mechanisms by which fly ash mitigates ASR and to identify factors that most significantly determine fly ash effectiveness against ASR. Through a combination of advanced analytical measurements and numerical simulations, it can be concluded that fly ash is effective against ASR by (a) reducing the alkalinity of pore solution by alkali binding, (b) reducing the mass transport in concrete, (c) improving the tensile strength of concrete, and (d) reducing the aggregate dissolution rate by reducing the concentration of OH- ions per unit surface area of siliceous aggregates. In addition, fly ashes with low Cao and alkali content and high SiO2 and Al2O3 contents were found to be most effective against ASR. The goal of the second task was to provide recommendations and design tools for engineers and materials suppliers to allow proper proportioning and production of “Glasscrete” mixtures (i.e., concrete containing recycled glass fine aggregates as 100% replacement of natural sand. Several Glasscrete mixtures with target slump, air content, and compressive strength were prepared and their fresh and hardened properties compared against concretes with natural sand. All mixtures contained 20% class F fly ash as mass replacement of Portland cement to mitigate ASR. It was found that the use of glass sand results in a reduction in the compressive strength of concrete, potentially due to weakening of the aggregate-paste bonding. In comparison with natural sand concrete, Glasscrete was found to have better workability, lower water sorptivity, lower chloride permeability, and lower coefficient of thermal expansion. On the other hand, Glasscrete showed lower resistance against abrasion.
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