Reducing the cracking potential of ultra-high-performance concrete (UHPC) with the prewet expansive agent

Abstract

With superior mechanical strength and durability, ultra-high-performance concrete (UHPC) is becoming an emerging material for resilient infrastructures. However, due to its high shrinkage, the high early-age cracking potential hinders its promotion. The expansive agent (EA) is therefore intensively used to reduce the shrinkage. However, the insufficient free water and dense microstructure of UHPC limit its expansion effect, thus affecting EA’s capacity on shrinkage reduction and cracking control. To achieve the minimum cracking potential of UHPC, the CaO-type EA was prewet with mixing water before concrete batching. Results indicated that, after 45-min premix treatment, the 4% prewet EA compare to the 4% EA without prewet, shown: (1) increase in 3-day and 28-day splitting tensile strengths of UHPC by up to 10% and 5%; (2) reduction in 3-day and 28-day autogenous shrinkage of UHPC by around 20% and up to 30%; (3) reduction in the peak and cumulative cracking potential of UHPC by up to 30% and 25%. The prewet process of CaO-type EA was proven to efficiently increase the content of expansive products in UHPC, which contributes to reducing the autogenous shrinkage and increasing tensile strengths, therefore significantly enhancing the cracking resistance, especially at early ages.