减缩剂的作用及其机理

Mechanism and effect of shrinkage-reducing agent used in cement mortar

通过对减缩剂作用和机理的研究表明,减缩剂能较大幅度的降低干燥收缩和相对较小的提高塑性收缩抗裂能力,但在一定程度上降低了砂浆的力学性能。从塑性抗拉强度、表面水份蒸发率和孔结构三个角度对减缩剂的作用机理进行了试验分析,结果表明:减缩剂的加入能较显著的降低水溶液的表面张力,同时也降低了砂浆表面的塑性抗拉强度,增大了表面水份蒸发率,它对塑性收缩抗裂的效果取决于对塑性抗拉强度和毛细管收缩应力影响的权重;表面张力试验表明,减缩剂减小干缩的机理主要在于降低了孔溶液的表面张力;从对孔结构的分析表明,减缩剂掺入后增大了孔隙率,并增加了孔径>0.1μm的孔的含量,从而降低了掺减缩剂的砂浆力学性能。

It investigated a preliminary preparation of SRA （shrinkage-reducing agent） considering to improve the water-retaining property and reducing the surface tension of pore solution in the cement-based materials, which was developed mainly through three steps：（1）The effects of various SRA components on performance of mortar were studied and some valid components are selected; （2）Those valid components were investigated by orthogonal design; （3）The results of drying shrinkage property of mortar with different dosages were compared. Combining with two professional SRAs （JKA,MSA）, the experiments of anti-plastic shrinkage cracking and mechanical property of mortars were made. The results show that SRA can reduce the drying shrinkage with a large extent and strength with a certain extent. Moreover,SRA can slightly improve the property of anti-plastic shrinkage cracking. Besides,some experiments are made to analyze their mechanism from the plastic tensile strength, the speed of water evaporation and the pore size distribution,which shows that SRA can reduce the plastic tensile strength with a certain extent and increase the rate of water evaporation and porosity,especially the content of pores with diameter of more than 0.1μm.