Examining soaking duration of coarse clay and shale lightweight aggregates for internal curing in conventional concrete

摘要

Cracking of concrete structures due to shrinkage of concrete is well documented throughout the literature. One method utilized to reduce shrinkage in concrete is internal curing (IC). Though IC is typically used to control autogenous shrinkage, in this investigation, two coarse (clay and shale) lightweight aggregates (LWA) were investigated to determine the impact of using these materials to mitigate drying shrinkage in conventional concrete (i.e. w/cm 0.36). Further, the effects of the LWA additions on the mechanical properties of concrete targeted for use in conventional bridge decks were also investigated. LWA replacement rates of 59, 119, and 178 kg/m(3) were utilized in this investigation along with soaking durations of 1, 3, and 7-days. The addition of the LWA reduced the unit weight by 6.7% for the clay material and 6.0% for the shale material. The compressive strength was reduced by more than 16% for each LWA and the modulus of elasticity was reduced by more than 11%. However, modulus of rupture data indicated a strength gain for the clay material (4.3%) and a slight reduction (8.5%) when using the shale LWA. A replacement rate of 178 kg/m3 decreased shrinkage for both clay (7.7%) and shale (8.3%) LWA when compared to the control concrete mixture. The research further determined that a 1-day soaking duration reduces shrinkage when compared to the control mixture for this investigation; however, a 3-day soaking duration was required to fully leverage shrinkage protection in conventional concrete specimens using coarse and medium LWA for internal curing. (C) 2020 Elsevier Ltd. All rights reserved.