高吸水性树脂对高强混凝土自收缩的减缩机理

Shrinkage-reducing Mechanism of Super-absorbent Polymer in High-strength Concrete

测试了高吸水性树脂(SAP)作为内养护剂对高强混凝土自收缩的减缩效应。通过自身-干燥收缩一体化计算模型,对预吸水SAP的减缩机理进行了定量分析。自收缩测试结果表明:掺入预吸水SAP对高强混凝土早期自收缩的减缩率达90%以上。各配比混凝土的收缩实验曲线与模型计算结果吻合良好。模型计算结果表明,预吸水SAP对高强混凝土早期自收缩的减缩机理主要有两点:一是在混凝土内部相对湿度维持在100%的阶段,掺入预吸水SAP会在混凝土中引入一种自膨胀变形,从而大幅抵消化学减缩,有时甚至出现自膨胀现象;二是在混凝土内部相对湿度下降阶段,加入SAP可以显著延缓混凝土内部相对湿度的降低,从而减缓了临界孔径的下降趋势,大大减小了同龄期混凝土内部毛细孔负压及收缩应力值,从源头上减小了自收缩产生的驱动力。

Shrinkage-reducing effect of super-absorbent polymer （SAP） as an internal curing agent on the high-strength concrete （HSC） was experimentally investigated. The quantitative analysis of its mechanism was conducted based on the capillary stress based model. The experimental results show that the pre-soaked SAP decreases the autogenous shrinkage and the reduction ratio can reach 90%, compared to the reference samples. The experimental shrinkage curves of HSCs at different mix proportions fit the simulated data obtained by the model. The simulated results show that there are mainly two factors contributing to the shrinkage-reducing effect of pre-soaked SAP. At the moisture saturated stage （the relative humidity, RH=100%）, the pre-soaked SAP causes an expansive deformation that compensates the ordinary chemical shrinkage to some extent. When the internal RH reduces 〈 100%, the addition of pre-soaked SAP mitigates the RH reduction process, delays the decline of the critical pore radius and reduces the capillary pressure of concrete. The driving force of autogenous shrinkage is thus reduced.