矿物掺合料对高强机制砂混凝土早期收缩开裂性能的影响

Effect of Mineral Admixtures on Early Shrinkage and Cracking Properties of High Strength Machine-made Sand Concrete

针对低水胶比高强机制砂泵送混凝土早期收缩开裂严重易造成建筑物耐久性急剧衰退的问题,通过试验研究粉煤灰、矿粉、硅灰在单掺、双掺和三掺时对混凝土工作性能、力学性能、早期收缩和开裂性能的影响规律,以低场核磁共振仪(NMR)通过孔结构对早期收缩开裂性能的规律进行分析。结果表明:粉煤灰和矿粉的掺入提高了混凝土的工作性能,但硅灰的掺入降低了混凝土的工作性能;矿物掺合料的掺入对混凝土早期强度影响较大,随着养护龄期的延长,后期强度随着水化程度的增加有所升高;粉煤灰、矿粉、硅灰三掺时,高强机制砂混凝土具有最小的早期收缩率和开裂面积;掺入矿物掺合料使混凝土内部孔隙率减小,混凝土内部致密度提高,减小了早期收缩开裂。

Aiming at the problem of severe early shrinkage and cracking of concrete pumped with low water-binder ratio and high strength sand,which is easy to cause a sharp decline in the durability of buildings,the effects of fly ash,mineral powder and silica fume on the working performance,mechanical properties,early shrinkage and cracking properties of concrete under single,double and triple mixing were studied through experiments.The behavior of early shrinkage cracking was analyzed by low field nuclear magnetic resonance(NMR)through pore structure.The results show that the addition of fly ash and mineral powder can improve the working performance of concrete,but the addition of silica fume can reduce the working performance of concrete.The addition of mineral admixture has a great influence on the early strength of concrete,and with the extension of curing age,the late strength increases with the increase of hydration degree.When fly ash,mineral powder and silica fume are mixed,the high strength machine-made sand concrete has the smallest early shrinkage rate and cracking area.The addition of mineral admixtures can reduce the internal porosity of concrete,increase the internal density of concrete,and reduce the early shrinkage cracking.