Studies on Improvement of Durability by Making Dense Surface Layer of Concrete Using Permeable Sheets

(1)用透水片材估算混凝土表面密度的试验方法。对表层混凝土的各种试验可以用来估计透水片材混凝土的表面密度。新鲜状态下的水灰比分析、抗拉强度分析和气孔参数分析是估算透水膜对自由水排出和脱气效果的较好方法。(2)制作致密的表层及其估算。为了在表层形成致密的结构，我们检查了以无纺布为主的三种透气片。使用这些片材后，混凝土表面的凹坑减少，表面外观大大改善，因为自由水的排放和大的气孔。随着水灰比的降低，近地表强度也随之增加。一些实例表明，混凝土浇筑过程中由于固结程度的不同，混凝土质量会出现不完全通风和质量变化。(3)透水片材对提高混凝土耐久性的作用。采用渗透膜后，混凝土的抗冻融性能、碳化性能和氯离子渗透速度都有了很大提高。根据透水板的类型和水灰比的不同，不完全脱气可能会对混凝土的性能造成不利影响，应该在不久的将来进行详细的研究。

(1) Test methods estimating the surface denseness of concrete with permeable sheet. Various tests on surface layer concrete are available to estimate the surface denseness of concrete with permeable sheets. The analysis of water cement ratio in fresh state, the pull-off tensile strength and the air void parameters, which are easily measured in every distance from the surface, were superior methods estimating the effects of permeable sheet on discharge of free water and de-airing.(2) Making dense surface layer and its estimation. A total of three permeable sheets, mainly composed of unwoven fabric were examined to making the dense structure in the surface layer. When using these sheets, the pits on concrete surface decreased and the surface appearance was greatly improved because of the discharge of free water and large air void. Then, the near surface strength also increased by the lowering the water cement rtio. Some cases showed the incomplete de-airing and the variation of the concrete quality mainly due to the degree of consolidation in concrete placement.(3) Effect of permeable sheet to improve durability of concrete. Using permeable sheets, the freeze-thaw resistance, carbonation and the chloride penetration speed were greatly improved. Depending on the type of permeable sheet and the water cement ratio, the incomplete de-airing might give the possible disadvantage for the concrete performance, and it should be investigated in detail in near future.