Inhomogeneous Distribution of Compressive Strength from Surface Layer to Interior of Concrete in Structures

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Title: Inhomogeneous Distribution of Compressive Strength from Surface Layer to Interior of Concrete in Structures

Author(s): N. Yuasa, Y. Kasai, and I. Matsui

Publication: Special Publication

Volume: 192

Issue:

Appears on pages(s): 269-282

Keywords: compressive strength; curing; drying; porosity

Date: 4/1/2000

Abstract:
Changes in the quality of concrete due to ambient conditions start from its surface immediately after the demolding, whereby the quality of cover concrete, particularly strength and durability, is likely to be lower than that of the interior parts. This study deals with effects of drying on the compressive strength of cement paste and concrete. Cement paste specimens with a very small cross section were prepared using normal portland cement and the relationship between the pore structure and the compressive strength was investigated. Next, the inhomogeneity of porosity of concrete was measured. Finally, the distribution of compressive strength from the surface layer to interior of concrete was estimated, using two equations relating pore volume to compressive strength. The results can be summarized as follows. (1) The relation between the total pore volume and the natural logarithm of compressive strength obtained from the hardened comment paste a liner compressive strength obtained from the hardened cement paste a liner correlation for each water-cement ratio. (2) The smaller was the distance from concrete surface, the larger was the total pore volume. This tendency was greater for the concrete of larger water-cement ratio and for the concrete of earlier drying initiation. (3) Compressive strength of concrete near the surface was lower in accordance with the increase of total pore volume. The difference of the strength between the surface layer and interior of concrete was approximately 20 MPa. (4) It was at most to the depth of 5cm from concrete surface that the compressive strength decreased due to drying in the case of concrete with water-cement ratios of .4 and .6, and it was at most to the depth of 10 cm in the case of concrete with a water-cement ratio of .8.