International Concrete Abstracts Portal

Compressive fatigue strength of concrete in a submerged condition deteriorates drastically compared with concrete in an air-dried condition. One of the reasons for the lowering of fatigue strength in submerged or wet concrete appears to be the influence of the reduction of the bond at the interface between the aggregate and the cement paste. However, this reduction may be mitigated by reducing the calcium hydroxide content and filling the voids at the interface. In this study, compressive fatigue tests were performed in submerged conditions using concrete composed of blast furnace slag or silica fume. The 2-million-cycle fatigue strength of this submerged concrete improved up to 44 percent of its static strength in water compared to 31 percent for ordinary concrete in water. However, this was found to be smaller than 56 percent for ordinary concrete in air. During these tests, the pH of the water in the test tank and the strain of the specimens were measured, and the amounts of calcium hydroxide that oozed out from the specimen and the strain behavior were investigated. The increase in fatigue strength is due to an improvement in the aggregate interface bond and watertightness. However, the expansion of cracks just before failure, which is a distinct characteristic of fatigue in water, was not checked.

The resistance to freezing-and-thawing and chloride diffusion of antiwashout underwater concrete was investigated to evaluate the applicability for tidal zone in cold districts or reinforced concrete structures in marine environments. Comparisons were made with ordinary portland cement concrete of similar mix design. Two types of cement (ordinary portland cement and portland blast furnace slag cement) were used. Two types of blast furnace slag (Blaine fineness 500 and 700 m²/kg) were used as a cement replacement (slag content 30 and 50 percent by weight). The results show that antiwashout underwater concrete without blast furnace slag shows poor resistance to freezing-and-thawing compared with normal concrete. But the freezing-and-thawing resistance can be improved with blast furnace slag. This is due to the fact that concrete containing blast furnace slag has dense pore structures. Pore volume in the range of 10 to 10 3 nm in radius decreases significantly with blast furnace slag. Similarly, chloride diffusion depth becomes smaller with blast furnace slag.

Gypsumless Portland cements (GPC) are inorganic binders, which may be described aas system of: ground Portland clinker (specific surface of 400-500 m2/kg - Blaine), a surface-active agent with hydroxyl groups and a hydrolyzable alkali metal salt (carbonate, bicarbonate, silicate). New cements, developed in recent years, are able to reach both higher strengths and fracture toughness than ordinary Portland cement (1,2,3). New developments in the making of very strong cements have resulted from modifying cement compositions and manipulating the microstructures (4).

In High-Strength Concrete in general high-quality aggregate is used. This aggregate has a high compressive strength and often a high modulus of elasticity. This high modulus of elasticity of the aggregate strongly influences the deformation behaviour of high-strength concrete. Results show that there is a direct and linear relationship between the shrinkage value and the modulus of elasticity of the concrete. The highest modulus of elasticity of concrete was 85 GPa. The compressive strength at the age of 28 days was in the range from 102 to 182 MPa. A design aid is given to show the interrelation between modulus of elasticity and shrinkage strain of the concrete on one side and modulus of elasticity of the aggregate, modulus of elasticity of the matrix and matrix content on the other side.

This paper describes the characteristics of a super low-heat cement mixing the ternary components of cement, blast-furnace slag, and nace slag cement modifying portland blast-furnace slag cement into a low-heat type. The results of mass concrete model experiments conducted using these cement are also reported. The super low-heat cement used in furnace slag: fly ash at ratios of 23:50:27. The low-heat blast-furnace slag cement was a 60% mixture of blast-furnace slag in normal portland cement. In the experiments concerning characteristics of concrete, concretes using super low-heat cement or low-heat blast-furnace portland cement or portland blast-furnace slag cement Class B. Mass concrete model experiments were compared for the cases of using super low-heat cement, and portland blast-furnace slag cement Class B. According to the test results, in case of unit cement content of 300 kg/m2, the adiabatic temperature rise of concrete using super low-heat cement is approximately 15°C lower than the moderate heat portland cement. That of concrete using low-heat blast-furnace slag cement is approximately 5°C lower than portland blast-furnace slag cement Class B. Mass concrete model experiments show that the strength gain of super low-heat cement concrete is higher than that of conventional low-heat cement concrete, and this cement is effective in control of thermal cracking because of exceedingly low temperature rise.