硅灰和减缩剂对混凝土自收缩和孔隙的影响

Effects of Silica Fume and Shrinkage Reducing Admixture on Autogenous Shrinkage and Porosity of Concrete

硅灰和低水胶比会降低混凝土总孔隙率,但增加了混凝土自收缩,使其产生微裂纹。本文研究了掺入硅灰和减缩剂(SRA)对不同水胶比的混凝土自收缩和微观、宏观尺度孔径分布的影响。结果表明:掺入10%(体积分数)的硅灰会使混凝土自收缩增加27.3%~28.8%;而加入减缩剂使混凝土自收缩降低68.0%~85.1%,且对含有硅灰的混凝土样品降幅更大。此外,掺入硅灰和减缩剂可以使混凝土总孔隙率分别降低5.1%~6.0%和35.9%~39.7%,但硅灰会增大混凝土100 nm以下孔隙和100μm以上孔隙的体积占比,而减缩剂对这两类孔隙的体积则会起相反作用。同时,自收缩与100μm以上孔隙体积分数呈明显正相关关系。

Silica fume and low water-binder ratio will reduce the total porosity of concrete,but increase the autogenous shrinkage of concrete and lead to microcracks.In this paper,the effects of silica fume and shrinkage reducing admixture(SRA)on autogenous shrinkage and pore size distribution in micro and macro scale of concrete with different water-binder ratios were studied.The results show that the autogenous shrinkage of concrete increases by 27.3%~28.8%with the addition of 10%(volume fraction)of silica fume,while the autogenous shrinkage of concrete decreases by 68.0%~85.1%with the addition of SRA,and even more to the concrete samples containing silica fume.In addition,the addition of silica fume and SRA reduces the total porosity of concrete by 5.1%~6.0%and 35.9%~39.7%,respectively,but silica fume increases the proportion of pore volume below 100 nm and above 100μm,while SRA has the opposite effect on the volume of these two types of pores.At the same time,there is a significant positive correlation between autogenous shrinkage and pore volume fraction above 100μm.