Effect of internal curing on early-age properties of concrete under simulative natural environment in arid regions

Abstract

The potential for the use of internal curing in concrete under a natural environment remains unclear. Therefore, this research concerns understanding the effects of three internal curing agents (superabsorbent polymers (SAP), lightweight aggregate (LWA), and perforated cenospheres (PCs)) on the early-age properties of concrete under simulative natural environment in arid regions. Concrete specimens selected underwent a daily temperature cycle from −5 °C to 40 °C and a constant relative humidity of 35 % in an environment chamber prior to various macro-/micro-structural tests. Compressive strength, splitting tensile strength, autogenous shrinkage, crack resistance characteristic as well as morphology, phase composition and pore-structure were measured. Results show that only internal curing via SAP can increase 28-d compressive strength because large pores in concrete are transformed into small ones by promoting cement hydration. Furtherly, internal curing can reduce both temperature sensitivity and autogenous shrinkage of concrete and improve crack resistance. The analysis reveals that the compressive strength and early-age autogenous shrinkage of internally cured concrete are greatly affected by extra water to cement ratio ((w/c)IC), both decrease as (w/c)IC increases. Moreover, the rate of water release from internal curing agents also affects autogenous shrinkage of concrete and LWA had a higher early-age water release rate than PCs. After comparison, SAP is more suitable for the arid regions with large temperature variation and the best content of it is 0.2–0.3 % of cementitious materials.