Abstract
Cathode ray tube (CRT) glass, when disposed, is considered a hazardous material due to its lead toxicity. Currently available disposal methods for this material are being phased out due to their adverse environmental impacts. A study of the durability, material mechanical properties, and the potential for adverse environmental impact of the use of hazardous waste materials as a component in portland cement concrete is presented. This dissertation uses CRT glass as a test bed material to promote sustainable construction materials and hazardous waste recycling. An important goal of this dissertation is to fill an existing knowledge gap between the research methodology applied to assessing concrete durability and methods of evaluating environmentally detrimental leachates such as lead that is found in CRT waste materials. CRT glass was used to substitute up to 30% of the fine-aggregate component of a typical South Florida non-structural concrete mixture. An organic biopolymer admixture solution of guar gum and boric acid was used in the concrete mixture to bind and encapsulate the lead ions to the cementitious matrix. Additionally, modifications to accelerated aging, diffusion, and durability tests were developed and combined to innovatively simulate the service life of CRT-concrete and to evaluate the effects that concrete deterioration (i.e. micro-crack formation from alkali-silica reaction expansions, micro-structure changes due to accelerated aging, and surface spalling from freeze-thaw testing) have on contaminant leaching. The biopolymer solution was shown to be effective by encapsulating lead leachate to concentrations that are below US government-regulated drinking water limits. Additionally, the compressive strength of CRT-concrete was comparable to the control mixture. The results of the modified deterioration and leaching tests show that microcracks, surface spalling, and loss of modulus of elasticity had an adverse impact on the durability and strength of the composite material. A relationship between alkali-silica reaction expansions and the gradient in contaminant leaching could not be observed due to the rapid rate of saturation of the leachate solution with the constituent of concern. The results from combined accelerated aging and diffusion tests revealed that lead leaching behavior for specimens that were exposed to an elevated temperature and a neutral pH environment deviate slightly from the behavior typically found in purely diffusion controlled specimens. However, Crank’s numerical solution to Fick’s 2nd Law of Diffusion was still able to conservatively predict the contaminant release. Finally, the combined freeze-thaw/diffusion tests showed that surface deterioration of CRT-concrete results in a statistically significant increase in lead leaching. Overall, the use of CRT glass as a component of concrete was shown not to be detrimental to the structural and durability performance when compared to control mixtures. Furthermore, a framework was developed to guide researchers, regulatory agencies and environmental engineers through a number of structural, environmental, and management-related issues that need to be addressed during each phase of the life cycle of a concrete material that contains recycled waste aggregates. A maximum use of 10% CRT glass is recommended to meet the durability (alkali-silica reactions) and environmental requirements. Lastly, the observed relationship between the combined durability and leaching tests demonstrates the importance of encouraging researchers and regulatory agencies to consider durability as a contributing factor in the assessment of a material containing hazardous wastes for possible adverse environmental impact.