两种混凝土减缩剂的性能及其作用机理

Properties of Shrinkage Reducing Admixtures(SRA)in Concrete and Its Mechanism

测试了2种混凝土减缩剂(SRA1和SRA2)对砂浆、混凝土的收缩性能,混凝土新拌性能、硬化性能的影响,并从表面张力、离子浓度、水化放热速率和水化程度等方面探索了SRA1和SRA2对水泥基材料的作用机理.结果表明:减缩剂对水泥基材料干燥收缩的抑制作用主要表现在7d前,对自收缩的抑制作用在后期依然显著;SRA1的减缩机理主要是降低浆体孔溶液的表面张力与K^+,Na^+质量浓度,SRA2减缩效果优于SRA1,但未明显降低浆体孔溶液的表面张力及K^+,Na^+质量浓度,而是通过早期影响水泥水化进程,改变水化产物形态从而减少了水泥的宏观体积收缩.

Effects of two types of shrinkage reducing admixtures（SRA1and SRA2）on shrinkage performance of mortar and concrete as well as properties of both fresh and hardened concrete were investigated.The mechanism of shrinkage reducing was analyzed from the surface tension and ion concentration of pore solution as well as the hydration heat release rate and hydration degree of cement paste.Experimental results indicate that the inhibiting effect of SRA on drying shrinkage is significant before 7d,while it plays a longterm inhibiting effect on autogenous shrinkage.The shrinkage-reducing mechanism of SRA1 is mainly the synergistic effect of reducing surface tension and K＋,Na＋concentration of pore solution of cement-based materials.It is interesting that the shrinkage-reducing effect of SRA2 is better than that of SRA1,though the reduction of surface tension and K＋,Na＋concentration is not as bigger as for SRA1.However,the reduction of bulk shrinkage induced by changing the morphology of the hydration products at early age due to retardation of hydration may be the main reason for the shrinkage-reducing of SRA2.