SAP类型对水泥砂浆早期抗裂和干缩性能的影响

Influence of SAP Type on Early-crack Resistance and Drying Shrinkage Performance of Cement Mortar

研究了两种不同类型高吸水树脂(Super absorbent polymer,SAP)(聚丙烯酸盐类SAP和复合型SAP)的吸-保水特性,提出以稳定失水率作为SAP在水泥浆体中吸液动力学行为的评价指标,对其改性水泥砂浆的工作性能和不同环境(标准养护环境和自然环境)下的干缩性能、早期抗裂性能和力学性能进行了评价,并采用SEM和XRD对其微观改性机理进行了探究。结果表明:SAP在饱和Ca(OH)_(2)溶液中的吸液倍率呈先增加后减小最终趋于稳定的变化规律;SAP会降低水泥砂浆的初始流动度,同时也可显著缓解随时间延长所带来的水泥砂浆流动度损失;SAP的掺入可明显降低水泥砂浆的干缩率,抑制水泥砂浆面板早期裂缝的生成与萌发;两种类型的SAP均可提高水泥砂浆的早期(7 d之前)力学性能,但聚丙烯酸盐类SAP对水泥砂浆28 d力学性能有不利影响。微观测试表明,标准养护环境下SAP的掺入均有利于AFt、C-S-H和CH的生成,且掺入SAP后水泥水化程度更高。聚丙烯酸盐类SAP在水泥砂浆塑性阶段的释水过程不利于水泥砂浆微结构的发展,而复合型SAP释水之后在孔隙壁上形成了一层无机/有机薄膜,有利于降低孔隙对水泥砂浆的负面影响。

The absorbent properties of two different types of super absorbent polymer(SAP)(sodium acrylate and composite type of polymer)were studied,and the stable water loss rate was proposed as the evaluation index of SAP s water absorption dynamic behavior in cement pastes.The working performance of the modified cement mortar and its early anti-cracking and mechanical properties under different environments(standard curing environment and natural environment)were evaluated.SEM and XRD were adopted to explore the its micro modification mechanism.The results indicate that the absorption of SAP in saturated Ca(OH)_(2) solution exhibits a law of rapid increase,gradual decrease,and final stability.SAP can reduce the initial fluidity of cement mortar.At the same time,it can significantly alleviate the loss of fluidity of cement mortar with time.The addition of SAP can reduce the dry shrinkage of cement mortar and inhibit the formation and germination of early cracks in cement mortar panels.Both types of SAP can improve the early mechanical properties of cement mortar(before 7 d).Still,sodium acrylate type of polymer harms the mechanical properties of cement mortar at 28 d.The standard curing environment and the addition of SAP are conducive to the formation of AFt,C-S-H and CH.The hydration degree of cement is higher after SAP incorporation.The water release process of sodium acrylate type of polymer in the plastic stage of cement mortar is not conducive to the development of the microstructure of cement mortar.At the same time,a layer of inorganic-organic film is formed on the pore wall of the composite type of polymer after water release,which is conducive to reducing the negative effect of pores on cement mortar.