An investigation into the effectiveness of shrinkage reducing admixture in mitigating creep in one-part alkali activated slag and fly ash binder concrete

Abstract The creep behaviour of alkali-activated concrete with a high slag content is a potential concern for designers. Studies have shown that, in such materials, creep at later loading stages can significantly exceed that observed in ordinary Portland cement (OPC) concrete, particularly when a high volume of blast furnace slag is used. Thus, developing effective mitigation methods to address this concern is crucial for promoting its large-scale application. This study investigates the effectiveness of shrinkage-reducing admixture in mitigating the creep of alkali-activated slag-fly ash (AASF) concrete. Admixture to binder weight ratios of 0, 3, and 5% were considered. The results show that after 365 days of loading, incorporating 5% admixture reduces the total creep of AASF concrete by up to 30%, compared to the case without shrinkage reducing admixture. In addition to reducing the magnitude of creep, the admixture also reduced the rate of creep development in the AASF concrete mixtures tested, resulting in a trajectory closely resembling that of OPC concrete. While AASF concrete without shrinkage reducing admixture exhibited degradation in long-term mechanical performance (degradation of elastic modulus), attributed to severe shrinkage cracking developing in the matrix with time, the introduction of either 3% or 5% admixture maintained a relatively constant elastic modulus with time and markedly enhanced the compressive strength at all ages. It is shown that a strong correlation exists between changes of pore sizes ranging 0.1-10μm and the reduction in creep for AASF concrete. The findings of this investigation contribute to an improved understanding of the creep mechanism of AASF concrete and offer options for customising the mix design to enhance its long-term performance.