Solving shrinkage problem of ultra-high-performance concrete by a combined use of expansive agent, super absorbent polymer, and shrinkage-reducing agent

To solve the cracking and interface debonding problems of ultra-high-performance concrete (UHPC) induced by high shrinkage in confined spaces or under strongly restrained conditions, a series of laboratory experiments was performed to evaluate the use of a CaO-based expansive agent (EA) in combination with a super absorbent polymer (SAP) and/or a shrinkage-reducing agent (SRA) to obtain expansive UHPC. The mechanisms underlying these techniques were also investigated. The test results showed that sufficient expansion was obtained by using a high dosage of CaO-based EA in UHPC, but the samples exhibited cracks owing to excessive and delayed expansion. The addition of SAP significantly enhanced the expansion effect of EA in UHPC. Autogenous shrinkage after 3 d and drying shrinkage within 180 d were effectively reduced by using SRA. Moreover, expansive UHPC was achieved by the combined use of EA, SAP, and SRA, in which excessive and delayed expansion was avoided. This was mainly attributed to i) increased initial expansion by using SAP for the reaction of CaO-based EA and ii) reduced later-age autogenous and drying shrinkage by adding SRA.