Segregation Characteristics of Concrete Containing a High-Range Water-Reducing Admixture


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Title: Segregation Characteristics of Concrete Containing a High-Range Water-Reducing Admixture

Author(s): T. Soshiroda

Publication: Special Publication

Volume: 68


Appears on pages(s): 121-138

Keywords: aggregates; placi admixtures; aniso tropy; bl ; fresh concretes; hardened ng; plasticizers; remolding eeding ( concret tests; concrete); c es; mix prop oarse ortion-split-

Date: 1/1/1981

The segregation tendency of concrete containing a high-range water-reducing admixture and its effects on the homogeneity of the concrete after hardening have been studied. Segregation during placing was investigated by means of a modified remolding test. The clearance of the inner ring in Powers' testing apparatus had been reduced to restrict the movement of concrete more severely for measuring workability of the concrete with high slump. After jigging was complete, the degree of segregation of coarse aggregate was examined by comparing the mass of coarse aggregate inside of the ring with that outside. Segregation during and after placing, including bleeding, was investigated by examining the variation of internal structure of hardened concrete caused by segregation and bleeding. The anisotropy in the direction of casting and the heterogeneity relative to the depth were examined as the variation on 150-mm cube specimens and 150- by 150- by 450-mm columns, respectively. For the former, the tensile anisotropies were determined by the splitting test changing the loading direction. For the latter, splitting tensile strengths, unit weights, coefficients of water absorption and coarse aggregate contents of both the top and the bottom portions were determined and compared relative to the depth. There is no great difference in the resistance to segrega-tion during placing and the effects of segregation on the homogeneity after hardening between the concrete containing the admixture and the conventional air entrained concrete without the admixture when slump, water-cement ratio and fine aggregate percentage are held constant. Excessive dosage of the high-range water-reducing admixture tends to promote segregation of fresh concrete and subsequently tends to increase the heterogeneity of hardened concrete with the depth.