Effects of porous shale waste brick lightweight aggregate on mechanical properties and autogenous deformation of early-age concrete

摘要

High-strength and high-performance concrete (HSHPC) easily generates early-age cracking owing to the large autogenous shrinkage (AS), which severely affects the durability of concrete. Internal curing (IC) by lightweight aggregate is one of the effective methods to mitigate early-age AS of HSHPC. To reduce carbon emissions and increase waste resource re-utilization efficiency, crushed porous shale waste brick (PSWB) is introduced as IC agent. However, a comprehensive understanding on the effects of PSWB addition on the performances of concrete is still lacking. Therefore, the influence of PSWB on the setting time, mechanical properties and autogenous deformation of concrete was investigated experimentally in this study. The test results showed that the setting time and mechanical properties were strongly affected by PSWB. PSWB addition retarded the initial and final setting times. The compressive and splitting tensile strengths first increased and subsequently decreased with PSWB content, but the 28-day decrease rate of compressive strength was no more than 5.0% compared with the reference group. In addition, the dynamic elastic modulus decreased with PSWB content. The internal relative humidity in concrete was significantly improved with PSWB incorporation. For PSWB content = 15%, the autogenous deformation showed rapid expansion first and then shrinkage, but the development rate of retraction was remarkably inhibited by PSWB. The interesting feature of the concrete with PSWB content 15% was that the concrete first expanded followed by a slight retraction, and then expanded continually until the age of 28 days, which was of great benefit in AS-induced cracking control. The mechanism of the initial expansion of PSWB concrete was mainly due to the C-S-H gel swell with the IC water ingress. (C) 2020 Elsevier Ltd. All rights reserved.