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。本研究的目的是开发控制收缩裂缝由于惰性粉末和化学外加剂的组合。主要研究结果如下：（1）将缓冷高炉矿渣粉、石灰石粉等惰性无机外加剂与聚羧酸系聚合物和醇系聚合物组成的有机外加剂一起掺入砂浆中，砂浆的自收缩明显减小。然而，效果取决于所添加的有机外加剂的种类。另一方面，粉煤灰的掺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。相反的作用有时会导致较小的拉应力/抗拉强度比，从而导致低的抗裂性。因此，很明显，为了防止由于自生和干燥收缩而产生的裂缝，需要进一步开发复杂的收缩减少外加剂。（2）聚乙烯亚胺类减缩剂对水泥有很强的吸附作用，不会降低水泥浆体中孔溶液的表面张力。但是，它具有减少自收缩和干燥收缩的效果，并且在强度方面显示出良好的发展。此外，硫酸钙的组合使用增强了减少收缩和增加强度。（3）根据Rietveld分析、选择性溶解和压汞实验数据，可以计算出二元共混体系中C-S-H的密度。结果表明，随着粉煤灰置换率的增加，C-S-H的密度逐渐降低。这表明粉煤灰水化形成的C-S-H凝胶体积大于OPC水化形成的C-S-H凝胶体积，具有自愈合作用。因此，开发新的方法来防止裂纹的这种自我愈合效应将在未来的预期。

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.