Effect of Premature Compressive Loading on the Mechanical and Transport Properties of Concrete

n this study, the effect of premature compressive loading on the mechanical and water transport properties of concrete was investigated. For this purpose, concrete mixtures having 16 mm and 22.4 mm maximum aggregate particle sizes (Dmax) were prepared. 1-day concrete specimens were subjected to an axial compressive stress corresponding to 90% of their compressive strength. The compressive strength, ultrasound pulse velocity, dynamic and static modulus of elasticity, water absorption, and sorptivity of either laboratory air-dried or moist-cured concrete specimens were determined. Test results revealed that, except for the air-dried specimens having Dmax of 22.4 mm, the premature loading did not have any adverse effect on the 2-, 7-, 28- and 56-day compressive strength of concrete. Even, the preloaded specimens showed up to 4% higher compressive strength than the control specimens. Besides, the dynamic and static modulus of elasticity of the concrete mixtures did not change significantly upon premature loading. The water absorption of the preloaded 7-day concrete specimens was 6-7% lower than that of the control specimens. However, this difference was diminished in 28-day specimens. Moreover, the preloaded air-dried specimens showed higher sorptivity than the control specimens. Ultrasound pulse velocity (UPV) measurements were taken on 1-day age specimens immediately before and after application of preloading. The reduction in UPV values upon preloading indicated the presence of some microcracks (damage) in concrete specimens. At later ages, the difference between the UPV values of the control and test specimens reduced. This was attributed to the self-healing provided by the prolonged hydration of cement