Development of Shrinkage Crack Control Method due to Combined use of Inert Powder and Chemical Admixture

防止混凝土开裂实际上是混凝土设计的关键问题之一。本研究的目的是研究惰性粉末与化学外加剂联合使用对收缩裂纹的控制。主要研究结果如下：(1)在砂浆中加入慢冷高炉渣粉和石灰石粉等惰性无机添加剂，并与聚羧酸盐基和聚氧烷基醇基聚合物组成的有机外加剂后，砂浆的自缩水率明显降低。然而，效果取决于所添加的有机混合物的种类。另一方面，粉煤灰的加入也显著降低了水泥混合料的自收缩，但促进了其抗拉强度的降低。相反，有时会产生较小的拉应力/抗拉强度比，导致抗裂性低。因此，很明显，为了防止自收缩和干燥收缩引起的裂缝，需要进一步开发复杂的减少收缩外加剂。(2)聚乙烯亚胺基减缩外加剂对水泥吸附较强，对水泥浆体孔隙溶液的表面张力没有降低作用。但对自收缩和干燥收缩有一定的抑制作用，强度有较好的发展。此外，硫酸钙的联合使用增强了减少收缩和提高强度。(3)二元共混体系中C-S-H的密度可通过Rietveld分析、选择性溶解和汞侵入等数据计算。结果表明，随着粉煤灰替代比的增加，C-S-H的密度逐渐降低。这说明粉煤灰水化后的C-S-H凝胶体积大于OPC水化后的C-S-H凝胶体积，具有自愈作用。因此，利用这种自愈效应来防止裂缝的新方法将在未来得到发展。

Prevent concrete from cracking is actually one of the key issues for the design of concrete. The purpose of this study is to develop control of shrinkage crack due to combination of inert powder and chemical admixture. Most important results are summarized as follows:(1)When the inert inorganic additives such as slowly cooled blast furnace slag powder and limestone powder were added to the mortar with the organic admixtures which consist of polycarboxylate-based and polyoxyalkylene alcohol based polymer, autogenous shrinkage of mortar decreased markedly. However, the effect varied depending on the kind of organic admixture added. On the other hand, addition of fly ash also reduced significantly the autogenous shrinkage of cement mixes, but promoted to decrease their tensile strength. The opposite effects sometimes brought out a little tensile stress / tensile strength ratio, resulting in a low resistance of cracking. Hence, it was clear that to prevent crack due to autogenous and drying shrinkage, further development of sophisticated shrinkage reducing admixtures were required.(2)The polyethyleneimine based shrinkage reducing admixture absorbed strongly on to cement, providing no reduction of surface tension of pore solution in cement paste. However, it had an effect to reduce autogenous shrinkage and drying shrinkage, and showed good development in strength. Further, the combined use of calcium sulfate enhanced to reduce shrinkage and increase in strength.(3)The density of C-S-H in binary blends system could be calculated from data of Rietveld analysis, selective dissolution and mercury intrusion. As a result, the density of C-S-H became lower as increasing replacement ratio of fly ash. This implied that the volume of C-S-H gel due to fly ash hydration was larger than that of OPC hydration, providing elf-healing effect. Therefore, development of new method to prevent crack by this self-healing effect will be expected in future.