Environmental Impacts of Leachate from Portland Cement Concrete (PCC) with and Without Plasticizer in Highway Construction

Abstract

Portland cement concrete (PCC) is widely used in transportation networks. In addition to its use in pavements, PCC is the primary construction material in bridges, tunnels, over passes, under passes, and similar vital structures in our highway systems. Other related applications include grouting, pipe bedding, and soil stabilization. Use of PCC is also associated with the use of a large number of admixtures. The leaching of chemical constituents from PCC and the effect of removal, reduction, and retardation (RRR) processes on these constituents were assessed by a series of laboratory tests and analyses. PCC leachate was subjected to chemical and toxicity testing to identify specific constituents that are responsible for the observed aquatic impacts. PCC leachate without the plasticizer admixture exhibited a low aquatic toxicity for the test organisms Selenastrum capricornutum and Daphnia magna. PCC-with-plasticizer leachate indicated high growth inhibition (toxicity) for S. capricornutum. It is likely that the small amount of plasticizing admixture and significant levels of aluminum in the leachate contributed to the toxicity observed in the PCC leachate. Complete detoxification of PCC leachates by three representative test soils, Woodburn soil (Mollisol), Olyic soil (Ultisol), and Sagehill soil (Aridisol), was observed during soil sorption tests. No significant changes in the algal EC₅₀ values by photolysis, but a three fold decrease in toxicity due to biodegradation, were observed for S. capricornutum when compared with the control leachate. Results suggest that the observed toxicity in PCC with-plasticizing-admixture leachates is readily reduced or removed only by the environmental processes of soil sorption and biodegradation.