International Concrete Abstracts Portal

The studies reported were concerned with the application of high-strength concrete to structural members as related to some aspects of their design, construction and behavior. With regard to construction, tests were performed on the consistencies and strengths of concretes of low water-cement ratios using superplasticizers. The superplasticizers used were the 5 brands being marketed in Japan. The influence on consistency of fineness of cement was also studied. In examinations made by design calculations, monorail piers were used as case studies. The relation between concrete strength and cross-sectional dimensions, and quality of reinforcing bars required when applying high-strength concrete to structural members were investigated. In structural tests, the stresses, bending strengths and ductilities of model piers using high-strength concrete were studied.

This paper reviews the application of a sulphonated melamine formaldehyde condensate superplasticizer (Melment L10) as a water-reducer-under laboratory conditions and in practice. Emphasis is on basic data on the compressive strength and stabi of green concrete, especially as it affects the production of concrete blocks, pipes and extruded concrete products. The results indicate that whenever high performance concrete is required, the use of the superplasticizer permits placing and proper compaction at almost any water-cement ratio, thus ensuring high quality concrete.

Strength, elasticity, shrinkage, swelling and creep of water-cured and steam-cured concretes (made with a rapid-hardening Portland cement) with and without the superplasticising admixture, Irgament ‘Mighty’ 150, have been compared over a period of one year. The mixes have the same workability but the one with the admixture clearly has a lower water-cement ratio. Compared with the admixture-free concrete, the superplasticiser concrete has a higher strength and a higher modulus of elasticity when continuously stored in water from the age of one day. However, when exposed to drying at the age of two days, the superplasticiser concrete has higher shrinkage and creep at a constant stress-strength ratio, and, at later ages, lower compressive strength and modulus of elasticity. For the tests in which the same two concretes were subjected to a six-hour cycle of steam curing and then stored in water, the compressive strength and static modulus of elasticity are initially higher but, at later ages, this is reversed for the superplasticiser concrete; in addition, the creep is higher for this concrete. When the same steam-cured concretes are exposed to drying at the age of one day, none of the properties investigated is affected by the presence of the superplasticiser.

This paper describes the results of an investigation to improve the drying shrinkage, thermal diffusivity and coefficient of thermal expansion of comparatively rich-mix concrete by the use of admixtures. Three types of superplasticizers were examined. Shrinkage tests were performed on 100x100x400 mm prismatic speci-mens in a controlled room where the temperature and the humidity were kept at 20°C and at 50 % R.H.. Two series of tests were made, one to make clear the character of shrinkage of concretes of low water-cement ratio and another to examine the effect of dosage of superplasticizer on shrinkage. Thermal diffusivity tests and the tests for the coefficient of thermal expansion were carried out using 10x20 cm cylindrical specimens of gravel concretes having a maximum cement content of 700 kg/m3, and attempts were made to improve these thermal properties by reducing the unit water content by the addition of a certain superplasticizer. It was found that the addition of superplasticizer to reduce the unit water content by about 20 percent, while maintainingthe constant consistency of concrete, gave a maximum increase of thermal diffusivity of more than 14 percent, a maximum decrease of coefficient of thermal ex-pansion of about 7 percent and a maximum decrease of drying shrinkage of almost 12 percent at 350 days drying. It is concluded that a suitable choice and use of superplasticizers should be used more specifically to improve drying shrinkage and thermal properties.

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.