Early-age shrinkage behavior of cement-fly ash paste under wind speeds: A study using BSE-IA and MIP techniques

While laboratory studies have shown that fly ash (FA) can reduce shrinkage in cement-based materials in the absence of wind, its impact on cement-based materials under wind speed conditions has not been extensively studied. This research investigates the influence of FA on the early-age shrinkage of cement paste under various wind speeds. The corresponding changes in pore structure were tested using mercury intrusion porosimetry (MIP) and backscattered electron image analysis (BSE-IA). The results show that under wind speed conditions, FA is not effective in reducing early-age shrinkage of cement paste. In fact, high levels of FA content can increase shrinkage values under wind speed conditions. Both wind speed and FA increase water evaporation, but they have different impact times. Although both wind speed and FA decrease mesopore content below 50 nm and increase water evaporation, they have opposite effects on early-age shrinkage. This suggests that mesopore content and water evaporation alone cannot fully characterize the change trend of early drying shrinkage. The two-factor parameter rs, which combines water evaporation and MIP-based pore size distribution, can effectively characterize drying shrinkage trends under the combined effects of wind speed and FA. BSE-IA can intuitively characterize pore size distribution above 200 nm, while the results of MIP underestimate the distribution of large capillary pores. Therefore, the current rs obtained based on MIP may be smaller than the actual value. With the advancement of testing technology in the future, rs can be further optimized.