Experimental study on sulfate resistance of concrete with recycled aggregate modified with polyvinyl alcohol (PVA)

Abstract

Using the wastes as a recycled concrete aggregate (RCA) is a promising technology to reduce the impact of construction and demolition wastes on the environment and the shortage of natural resources. However, higher permeability of RCA leads to greater absorption, affecting the RCA concrete's long-term performance. In general, the soil in Iraq contains a high sulfate level, accelerating concrete deterioration reducing concrete strength, and increasing concrete spalling and cracking. The aim of this study is to investigate the impact of sulfate environment on the mechanical properties of pretreated RCA concrete using a PVA agent. The normal aggregate was replaced in four portions of 8 %, 16 %, 24 %, and 32 % RCA, with the same grading and max size as normal aggregate. Two w/c ratios of 0.50 and 0.3 were used with two curing systems, namely sealed and unsealed conditions. The RCAs were socked in 0.5 % PVA of the water volume. The durability of RCA concrete was also experienced by sulfate attack immersing the concrete cubes in magnesium sulfate heptahydrate (MgSo4.nH2O) solution for 150 days after 28 days from casting with the wetting and drying cycle. The compressive strength results showed that the mixes with RCA pre-soaked in PVA have higher strength than the reference mix. For durability, the concrete mix with 32 % RCA exhibited the best durability. When the increased amount of RCA pre-soaked in PVA, the hydration increased, and internal voids decreased. Using 24 % RCA replacement with the sealed curing condition gives a 1.2 % increase in absorption, which is less than the unsealed curing condition of a 1.8 % increase in absorption.