Experimental evaluation of mechanical characteristics and durability of concrete specimens under combination of chloride-sulfate environment conditions and sulfate aggregate

In this paper, In addition to considering the different environmental conditions (sulfate, chloride and normal environment) and long-term effects on the concrete, effect of unhealthy sulfate aggregate due to high sulfate levels were assessed. For this purpose, 48 compressive cubic concrete specimens and 30 rectangular beam were made with specific mix design and cured for 6 months at simulated environments, then compressive and flexural strength tests were conducted. Results indicated that the compressive strengths of all specimens at the healthy environment were increased but the strengths of specimens with sulfate aggregates were decreased. Effect of unhealthy aggregate on reducing compressive strength of concrete specimens was more negative in comparison with unsuitable environment and also the strengths were reduced more than 10 percent under combined effects until 6 months while the strength of concrete with healthy aggregate and environment indicated an increase more than 20 percent. The compressive strengths both aggregates at chloride and sulfate environment were increased up to 3 months but the strengths of concrete specimens with sulfate aggregate and sulfate environment were rapidly decreased up to 24%. Negative effect of unhealthy aggregate and environment on reducing flexural strength was more than that of compressive strength. The flexural strengths of specimens at chloride and sulfate environment were not decreased up to 28 days but the strengths were respectively decreased more than 6 and 13% at chloride and sulfate environment while this strength was increased up to 15% at concrete specimens with healthy aggregate and environment.