Study on Early-Age Capillary Pressure and Plastic Shrinkage Properties of High-Volume Fly Ash Concrete

There is a lack of research on the early plastic deformation and capillary pressure of high-volume fly ash concrete (HVFAC) under varying ambient temperatures. This study aims to investigate the effects of water-binder ratio, fly ash admixture, and ambient temperature on the air entry time <i>T</i>, capillary pressure, and plastic shrinkage of HVFAC. Nine different fly ash concrete materials were designed and analyzed to determine the early plastic deformation and capillary pressure of HVFAC under different ambient temperatures. The dosage of different superplasticizers was adjusted to ensure a slump of 180 mm for all the HVFAC mixtures. The results showed that at 20 °C, <i>T</i> increases with the increase in the water-binder ratio and fly ash admixture, while the effect of <i>T</i> is negligible at 35 °C. The plastic shrinkage of HVFAC increases significantly with the increase in curing temperature, and there is a linear correlation between the air entry time <i>T</i> and the plastic shrinkage value at this time. At low water-binder ratios, the capillary pressure threshold <i>P_a</i> increases with increasing curing temperature, while at high water-binder ratios, there is no significant trend observed for <i>P_a</i>. The findings of the study can provide a theoretical basis for preventing plastic cracking of concrete and optimizing early curing methods.