Advancements in concrete material sustainability : supplementary cementitious material development and pollutant interaction
Taylor Lange, Sarah Clare
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Calcined clay and fly ash supplementary cementitious materials (SCMs) used in cement based materials were examined for their chemical and mechanical performance, as well as their pollutant interaction. This dissertation addresses three primary research questions, namely: (i) can zincite additions facilitate the use of calcined clay as SCMs by compensating for reductions in early-age mechanical performance or by compensating for their reduced pozzolanic reactivity, (ii) can cement renders, containing metakaolin calcined clays, be engineered for passive carbon dioxide and ozone removal, and (iii) how do the specific activity and emanation fractions of concrete constituents, including fly ash and metakaolin, as well as assembled concretes impact concrete radon emanation and indoor radon concentrations? The first question relates directly to the development of new, sustainable material options, which can replace a portion of cement in a concrete mixture. Results from the experiments with zincite showed that the treatment method removed the dilution effect that occurs when using less reactive materials to substitute a portion of portland cement, but did not considerably influence mechanical properties. Therefore, zincite additions are not a good means of enhancing the utilization of non-kaolinite clays in concrete. As an integrated system, the latter two questions of this dissertation investigate the interaction between airborne pollutants and the cement based materials containing SCMs. The use of SCMs in render and concrete systems resulted in different pollutant uptake and exhalation behavior, relative to non-SCM control systems. For pollutant uptake, render systems containing metakaolin increased the carbon dioxide ingress while decreasing the ozone uptake. For radon exhalation rates, modeling results demonstrated that concretes without fly ash have a higher probability of containing less total radium and lower radon exhalation rates, when compared to samples with fly ash, assuming an emanation fraction of 5%, as suggested in the literature. Experimental results demonstrated that metakaolin, fly ash and control concretes had emanation fractions of 7%, 9% and 13%, respectively, confirming that (i) an assumed fraction of 5% would underpredict indoor radon concentrations and potential health consequences, and (ii) SCMs can reduce the total concrete emanation fraction. This dissertation demonstrates how the use of sustainable material selections, such as calcined clays and fly ashes, not only influences the microstructure and mechanical performance of the cement based materials, but also alters the interaction of the material with its surrounding environment.