Abstract
Due to ever increasing anthropogenic induced environmental pollution, various methods of mitigation are being explored, especially in the cement and concrete industries, where the production of cement accounts for approximately 7% of global CO2 emissions. Moreover, a means to consolidate recyclable plastic waste is urgently needed to redirect plastic waste that could otherwise be recycled. One possible solution is the use of portland limestone cement (PLC), a greener alternative to ordinary portland cement (OPC), in combination with high-density polyethylene (HDPE) resin as a fine aggregate substitute. The production of PLC requires less energy than typical OPC, and the use of HDPE in concrete would incentivize a new market for recyclable plastic, and thus, the combination may result in substantial environmental benefits. To explore the feasibility of such mixtures, a study plan was devised to explore effects of PLC and HDPE fine aggregate resin on the fresh and hardened concrete properties. To maximize the environmental benefits, various commonly used supplementary cementitious materials (SCMs) and water-reducing admixtures were used in the investigation. Ultimately, ten total concrete mixtures were devised that included straight OPC and PLC mixtures, PLC and Class F fly ash with varying degrees of resin fine aggregate, PLC with Grade 120 slag cement with varying degrees of resin fine aggregate and select SCM mixtures with the addition of a water-reducing admixture. In general, the addition of plastic resin for all mixtures increased the bulk electrical resistivity. Concrete unit weight decreased by 2% and 6% when the HDPE resin replaced 5% and 10% of the fine aggregate, respectively. No apparent effect in slump was observed, although it was noted that the plastic resin mixtures were qualitatively easier to work with. A decrease in compressive strength is noted for most mixtures with plastic resin, with fly ash mixtures resulting in the highest reduction of compressive strength, and slag cement resulting in the least amount of reduction of strength. A similar trend is noted for elastic modulus of respective mixtures. Overall, 40% slag replacement of PLC and 5% replacement of fine aggregate by HDPE resin resulted in equivalent compressive strength to OPC mixtures, with an increase in the modulus of toughness.