Effects of pretreated fine lightweight aggregate on shrinkage and pore structure of ultra-high strength concrete

In this paper, effects of fine lightweight aggregate (LWA) contents and their pretreatment methods on mechanical performance, shrinkage and pore structure of ultra-high strength concrete (UHSC) were investigated. Two pretreatment methods, namely, normal soaking and vacuum saturation were applied to study their effect on internal curing performance of LWAs as compared with un-treated LWAs. In general, the pretreated fine LWA effectively enhanced the flexural strength of UHSC specimens especially at later ages, while no significant improvement was observed for the compressive strength. Pretreated fine LWA using normal soaking and vacuum saturation provided internal curing water for progressive hydration, and enhanced the microstructure at the interface of LWA and the bulk paste. The pretreated fine LWA reduced the autogenous and drying shrinkage. The maximum efficiency was obtained when 10 to 15% fine LWA was used. Pretreated fine LWA under the vacuum condition was the most effective method. This method helped to maintain the internal RH of UHSC for a longer period and decreased the mass loss by reducing the total porosity of the UHSC. (C) 2019 Elsevier Ltd. All rights reserved.