Final Report: Value-Added Use of Milled Mixed-Color Waste Glass as a Supplementary Cementitious Material in Environmentally Friendly and Energy-Efficient Concrete Building ConstructionEPA Contract Number: EPD10044
Title: Value-Added Use of Milled Mixed-Color Waste Glass as a Supplementary Cementitious Material in Environmentally Friendly and Energy-Efficient Concrete Building Construction
Investigators: Balachandra, Anagi
Small Business: Technova Corporation
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2010 through August 31, 2010
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2010) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Green Buildings
Description:An integrated experimental/theoretical investigation was undertaken to determine the value of milled mixed-color waste glass (a market-limited and abundantly available waste) as partial replacement for cement in concrete productions. The effects of partially replacing cement with milled waste glass on the engineering properties of concrete as well as the environmental, energy, and cost implications of concrete production and use were investigated.
Summary/Accomplishments (Outputs/Outcomes):Mixed-color waste glass, when milled to about the particle size of cement and used in concrete as replacement for about 20% of cement, improves the moisture barrier qualities, durability, and mechanical performance of concrete. These improvements result from the beneficial chemical reactions of milled waste glass with cement hydrates, which yield chemically stable products capable of refining the pore system in concrete. Major environmental, energy, and cost savings can be realized by partial replacement of cement with milled mixed-color waste glass.
Partial replacement of cement with milled waste glass benefits the microstructure and stability of cementitious materials. A denser (less porous) and more homogeneous structure is produced when milled waste glass is used as partial replacement for cement, which benefits the resistance to moisture sorption and thus the long-term durability of cementitious materials. Partial replacement of cement with milled waste glass also benefits the stability of cementitious materials when potentially deleterious reactions between cement hydrates and the reactive aggregates is a concern.
Waste (mixed-color) glass, milled to average particle size of 15 μm, when used as replacement for about 20% of cement, makes important contributions to the engineering properties of concrete. The early-age compressive and flexural strengths of recycled glass concrete (within a few days after mixing) tend to be somewhat lower than those of normal concrete. The later-age strengths of recycled aggregate concrete, however, tend to exceed those of normal concrete. Milled waste glass also benefits the dimensional stability (by reducing drying shrinkage movements), abrasion resistance, and the moisture sorption rate of concrete. The benefits of milled waste glass tend to be more pronounced in recycled aggregate concrete than in normal concrete. These beneficial effects can be attributed to the pozzolanic reactions of milled waste glass with cement hydrates, which refine the capillary pore system of concrete, reduce its connectivity, and also enhance the chemical stability and binding qualities of the cementitious matrix.
The field concrete materials were subjected to comprehensive experimental evaluation. Recycled glass concrete produced by partially replacing cement with milled waste glass of micro-scale particle size was found to be compatible with conventional concrete production and construction techniques. Use of milled waste glass as partial replacement for cement in concrete enhanced the resistance of field concrete to moisture sorption and transport of deleterious ions, resulting in improved durability characteristics. The abrasion resistance and long-term strength of field concrete also benefited from partial replacement of cement with milled waste glass.
A key contribution of milled waste glass is towards enhancement of the barrier qualities against moisture sorption of normal and especially recycled aggregate concrete. Given the important effects of moisture sorption on durability of concrete-based infrastructure systems, numerical analyses were undertaken to assess the corresponding benefits of milled waste glass to the service life of typical concrete pavement and bridge deck systems under freeze-thaw attack. Analyses were conducted in different climatic conditions. The benefits of milled waste glass to service life of concrete infrastructure systems under freeze-thaw attack were, as expected, more pronounced in climatic conditions with a larger number of freeze-thaw cycles. These improvements were as high as about 40% and 30% in the case of recycled aggregate and normal concrete systems. The more pronounced benefits of milled waste glass to physical properties of recycled aggregate concrete were reflected in the corresponding gains in service life of concrete-based infrastructure systems. Freeze-thaw attack was used here as an example of deterioration mechanisms. Depending on climatic and exposure conditions, other degradation mechanisms (sulfate attack, corrosion, etc.) may dominate service life of concrete-based infrastructure systems. Similar benefits of milled waste glass are expected in such climatic conditions.
The macro-level moisture transport characteristics involving sorption and diffusion in concrete are dependent upon the microstructure, especially the capillary pre system characteristics of concrete. Significant improvements in the moisture barrier qualities (and thus durability) of concrete can be realized through improvement of the microstructure of concrete (especially its interfacial transition zone [ITZ] region in the vicinity of aggregates). Refinement of size distribution and partial blocking of capillary pores are the most important microstructural improvements brought about by the pozzolanic reactions of milled waste glass in concrete, bringing about important gains in the moisture barrier qualities, durability, and dimensional stability of concrete. Such pozzolanic reactions are more pronounced in the ITZ, which offers desired chemistry and high porosity for such reactions. Recycled aggregate concrete has two ITZs, one between old paste (in old mortar clinging to recycled aggregate) and the original aggregate, and the other between the old (clinging) mortar and new cement hydrates. The strong presence of ITZs in recycled aggregate concrete implies that the pozzolanic reactions of milled waste glass would have more pronounced effects in recycled aggregate concrete when compared with normal concrete. Experimental results have confirmed these predictions, which point at the enabling role of milled waste glass towards value-added use of recycled aggregate (demolished concrete) in new concrete construction. The pozzolanic reactions of milled waste glass overcome the key drawbacks of recycled aggregate concrete (high moisture sorpotion that results in increased drying shrinkage and reduced durability).
The partial replacement of cement with milled (mixed-color) waste glass developed in this project offer the following environmental, energy, and cost benefits: (1) reduction of anthropogenic CO2 emissions by 1-1.6% (equivalent to removing about 15% of the world's automobiles) by reducing cement consumption in concrete; (2) saving about 0.4% of primary energy consumption (about 1% of industrial energy consumption) by partially replacing energy-intensive cement with milled waste glass; (3) value-added use of currently landfilled (mixed-color) waste glass, which is available at quantities needed to support large-scale market transition of the technology; (4) value-added use of demolished concrete as coarse aggregate in concrete construction, which lowers the energy consumption and the CO2 emissions in the United States by 4.2x1010 MJ/yr and 7.2 million tons, respectively, corresponding to 0.06% saving of total energy consumption in the United States, and reduction of total CO2 emissions in the United States by 0.12%; (5) savings of about $1 billion/year in the United States ($12 billion/year worldwide) in production cost of the concrete-based infrastructure by partially replacing Portland cement with milled waste glass; (6) close to 25% life-cycle cost saving of the concrete-based infrastructure due to gains in the moisture resistance and durability of concrete resulting from partial replacement of cement with milled waste glass in concrete; and (7) cost savings approaching $1.2 billion in the United States resulting from replacement of coarse aggregate in concrete with demolished (recycled) concrete.
A coalition of waste management and waste glass processing firms, the concrete industry, and transportation agencies managing concrete-based infrastructure systems has been formed towards commercial implementation of the technology. This coalition already has implemented a field demonstration project, and is preparing for industrial-scale milling of milled waste glass, and large-scale implementation of the technology in concrete construction projects.