Comparative research: Early-age deformation of alkali-activated/cement-based ultra-high performance concrete

Alkali activated slag ultra-high performance concrete (AAS-UHPC) is a promising low-carbon cementitious material that can effectively utilize industrial solid waste and reduce pollutant emissions during the production of cementitious materials compared with ultra-high performance concrete (UHPC), and it also exhibits excellent mechanical properties. The objective of this study is to conduct a comparative experimental analysis of the workability, mechanical properties and deformation behavior of UHPC and AAS-UHPC. In this study, AAS-UHPC prepared with lower water/cement ratio (w/b) has good flowability, faster setting time and higher strength. Although the early hydration rate of AAS-UHPC was similar to that of UHPC, its cumulative heat of hydration was higher. In chemical shrinkage experiments, the shrinkage value of AAS-UHPC increased with increasing water bath temperature and remained at about twice the strain value of UHPC. The age-early drying shrinkage of AAS-UHPC can be divided into four phases: transient deformation, dormant, accelerated, and slow development. stage, accelerated stage and slow development stage. Self-shrinkage is divided into three stages: dormant stage, accelerated stage and slowly developing stage. Compared with ultra-high performance concrete, AAS-UHPC has a longer dormant phase of early age shrinkage, and the deformation in this phase is mainly plastic shrinkage. Starting from the accelerated stage, the relative humidity decreases rapidly due to the strong occurrence of hydration reaction and shrinkage of pore structure. This leads to a rapid increase in the modulus of elasticity of AAS-UHPC, which results in greater deformation. In the later stages, the rate of shrinkage development slows down due to the basic formation of the concrete skeleton.