粉煤灰超高性能混凝土收缩与抗压强度相关性研究

Research on the correlation between shrinkage and compressive strength of fly ash ultra-high performance concrete

开展粉煤灰(FA)超高性能混凝土(UHPC)自由收缩、基本力学性能和圆环约束试验,探讨其抗压强度与自收缩相关性,测试时间为0～90 d.结果表明:UHPC收缩呈早期增长快, 28 d基本稳定;以自收缩为主, 90 d时约占总收缩的86.6%～95.7%. FA对早期自收缩影响明显,随龄期增大影响减弱, 1～7 d降低51.0%～40.5%, 28～90 d降低28.2%～22.0%;略降低抗压强度与弹性模量, 28 d最大降幅分别为9.3%、 5.0%,提高劈裂强度, 28 d提高近19.2%. UHPC自收缩与抗压强度相关性显著,可根据抗压强度发展预测自收缩;圆环约束下,密闭条件的UHPC开裂风险大于环向干燥;掺入FA能降低UHPC开裂风险.

The test on shrinkage and basic mechanical properties and ring constraint of ultra-high performance concrete (UHPC) mixed with fly ash(FA)was carried out and the correlation between compressive strength and autogenous shrinkage was discussed. The initial time of test was after casting into the mold, and the end time was at 90 d. The results show that the development of FAUHPC was rapid at early age, and be stable after 28 d. Autogenous shrinkage was the substantial part of the total shrinkage, which accounts for 86.6%-95.7% at 90 d. FA mainly reduces the autogenous shrinkage, especially in the early stage, and the trend decreases gradually with age, which decreased from 51.0% to 40.5% at early age (0-7 d), and from 28.2% to 22.0% at stable age(28-90 d). FA had an unfavorable influence on the compressive strength and elastic modulus, and the maximum reductions were 9.3 % and 5.0% at 28 d respectively, while improved nearly 19.2% at 28 d on the splitting strength. The correlation between compressive strength and autogenous shrinkage was significant, and the autogenous shrinkage development can be predicted based on the compressive strength. The evaluation of the cracking performance of UHPC under ring constraint indicates that the cracking risk is greater than that of circumferential drying, and FA can effectively reduce the risk of cracking.