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

(1)透水薄板混凝土表面密实度的试验方法。各种表层混凝土试验可用于估算透水薄板混凝土的表面密度。水灰比分析、拉脱抗拉强度分析和空隙率参数分析是评价透水片材对自由水排放和脱气效果的较好方法。(2)稠密面层的制作及其估算。研究了以无纺布为主的三种透水片材，使其表层结构致密。使用时，由于自由水的排出和较大的空隙，使混凝土表面凹坑减少，表面美观度大大提高。水灰比越低，近表面强度越高。在一些情况下，由于混凝土浇筑时固结程度的影响，出现了不完全通风和混凝土质量的变化。(3)透水片材对提高混凝土耐久性的作用。采用透水片材后，其抗冻融性能、碳化性能和氯化物渗透速度均有较大提高。根据透水板的类型和水灰比的不同，不完全脱气可能对混凝土的性能造成不利影响，应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.