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

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(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.