Durability of internally cured concrete with silicon-aluminum based fine lightweight aggregate exposed to combined sulfate and wetting-drying attack

The durability of internally cured concrete (ICC) with silicon-aluminum based fine lightweight aggregate (FLWA) exposed to combined sulfate and wetting-drying attack were conducted through evaluating concrete mass, relative dynamic elastic moduli (RDEM), flexural strength, microstructure and erosion products, with the consideration of various FLWA contents, w/b ratios, volcanic minerals and wetting-drying protocols. Results showed that ICC containing 30% FLWA presented better sulfate resistance with less reduction in mass, RDEM and flexural strength since the internal curing and pozzolanic effect of the silicon-aluminum based FLWA contributed to a denser microstructure. Unfortunately, concrete durability decreased when the FLWA content increased to 60%. A higher w/b ratio of 0.55 weakened the sulfate resistance of ICC given a decrease of up to 0.37%, 4.07% and 24.49% in mass, RDEM and flexural strength, respectively, after 210-day attack. More erosion products as well as a higher strength loss were observed as fly ash content increased to 20%. Adding 10% blast furnace slag improved ICC's durability with an enhancement of 2.55% in flexural strength under 210 days of attack. An 80 degrees C-drying temperature speeded up ICC's deterioration with a strength loss of 83.41% at 168 days, and it also changed the damage mechanism by decomposing erosion products. An accelerated degradation process can be expected in the long-term given a drying temperature of 40 degrees C, which can be adopted as an erosion accelerator, despite it benefited the concrete durability at the early attack age.