研究了减缩剂、膨胀剂等裂缝控制材料对混凝土抗压强度和收缩性能的影响,并结合低场核磁共振、扫描电镜试验分析了裂缝控制材料对水泥的水化特性以及混凝土孔隙结构影响规律.研究结果表明:在混凝土中掺入减缩剂和膨胀剂后,试样的干燥收缩率明显降低,膨胀剂的改善作用效果优于减缩剂.与基准组相比,减缩剂和膨胀剂试样 90 d的干燥收缩分别降低了4.1%~10.3%和14%~21.7%.同时,减缩剂试样应变发展速率系数从 80.48降低至54.59,而膨胀剂试样降低至 41.69.微观测试结果表明:膨胀剂的加入加速了水泥早期水化进程,但后期的水化程度低于基准组.减缩剂和膨胀剂的掺入一定程度上削弱了混凝土基体的微观结构,增加了基体中有害孔的含量,但降低了混凝土中孔径<50 nm的孔隙含量.
The influence of crack control materials such as shrinkage and expanding admixture on compressive strength and shrinkage properties of concrete were studied.The hydration characteristics of cement and the evolution law of pore structure were evaluated by low field nuclear magnetic resonance and scanning electron microscope tests.The results show that the drying shrinkage of the sample decreased significantly.Concerning drying shrinkage performance,the effect of expanding admixture is better than that of shrinkage admixture.Compared with the control sample,the drying shrinkage of the shrinkage and expanding admixture samples at 90 days decreased by from 4.1%to 10.3%and from 14%to 21.7%,respectively.Meanwhile,the strain development rate coefficient of the shrinkage admixture sample decreased from 80.48 to 54.59,and that of the expanding admixture sample decreased to 41.69.The microscopic test results show that the expanding admixture can improve the early hydration of cement.The hydration degree of the later stage is lower than that of the control sample.The addition of shrinkage and expanding admixture weakened the concrete matrix's microstructure,increased the content of harmful pores in the matrix,and reduced the content of pores volume with pore size<50 nm.