Effect of recycled aggregates and treated wastewater on concrete subjected to different exposure conditions

Abstract

Conservation and reuse of natural resources in the construction industry are becoming crucial to maintain sustainable and environmentally friendly construction. Thus, this study aims to investigate the feasibility of using 20% recycled aggregate (RA) as partial replacement of and treated wastewater (TWW) in concrete mixes by investigating their individual and couplings effects on concrete subjected to different exposure conditions. The study also analyzes the viability of using TWW as an alternative to TW in concrete curing. Three groups of mixes were developed (Groups I, II & III) with each group consisting of four mixes, making a total of 12 mixes. The four mixes of each group included concrete cast with 1) normal aggregates (NA) mixed with tap water (TW), 2) NA mixed with TWW, 3) RA mixed with TW, and 4) RA mixed with TWW. Concrete mixes of Group I were exposed to TW, while Groups II and III mixes were exposed to TWW and 6% NaCl salt water (SW), respectively. The test results were reported and discussed in terms of mechanical properties and durability aspects. The mechanical properties were assessed by conducting compressive and split-tensile strength tests after 28 and 150 days. The durability evaluation was conducted using indirect and direct tests such as rapid chloride permeability test (RCPT), resistivity tests, and Volhard test method to determine the chloride content, after 90 and 150 days. Statistical analysis was conducted to determine the effect of aggregate type, mixing water, and exposure conditions on the cube compressive strength samples. The statistical analysis results showed that the effect on concrete compressive strength was only significant when 20% RA was used in concrete exposed to TWW. Furthermore, the RCPT and resistivity results showed that all mixes were considered durable in terms of chloride ion penetration. However, the chloride test showed that the RATWW-SW mix exhibited a relatively high chloride content of 0.21% which may indicate a possibility of steel corrosion. This highlights the importance of exploring different durability tests for the durability evaluation of concrete.