Takeshi Yamato

MECHANICAL PROPERTIES, DRYING SHRINKAGE AND RESISTANCE TO FREEZING AND THAWING OF CONCRETE USING RECYCLED AGGREGATE

This paper presents the results of an investigation to determine the performance characteristics of concrete made with recycled coarse aggregate from a plant. Slump and air content of fresh recycled aggregate concrete are studied. The compressive strength, drying shrinkage and resistance to freezing and thawing were investigated experimentally when the types and combinations of coarse aggregate, admixture, air content and so on were varied. It was found that the recycled aggregate concrete decreased the compressive strength at 7 to 28 days as compared with those properties of the control concrete. The decrease in strength can be suppressed low by partial use of recycled coarse aggregate. Drying shrinkage of recycled aggregate concrete showed larger value than conventional crushed aggregate concrete. The use of shrinkage reducing agent can reduce the drying shrinkage of recycled aggregate concrete. The resistance to freezing and thawing of recycled aggregate concrete was lower than that of control concrete of similar composition. The decrease in resistance to freezing and thawing can be suppressed low by partial use of recycled aggregate, reducing the water cement ratio and increasing entraining air.

Chemical Resistance of Concrete Containing Condensed Silica Fume

This paper studied chemical resistance of concrete containing condensed silica fume (CSF), 5 percent H2SO4, 5 percent HCl, and 10 percent Ha2SO4. The deterioration of concrete was investigated by measuring the changes in weight and modulus of elasticity. The penetration depth of chloride ion by 3 percent NaCl solution spray and the carbonation depth by 5 percent CO2 gas were also measured. Chloride was measured by colorimetry. Mortar and concrete containing CSF show higher compressive strengths at 28 and 91 days than the control mix. The penetration depth of chloride into CSF concrete was reduced and at 10 percent CSF, the penetration depth was reduced by 65 percent. At 30 percent CSF, carbonation depth is increased with respect to the control concrete.

FROST DURABILITY OF HIGH-PERFORMANCE CONCRETE INCORPORATING SLAG OR SILICA FUME

This paper presents the results of laboratory studies conducted to determine freezing and thawing and scaling resistance of high-performance concrete. High-performance concretes were made using a combination of different cementitious materials (blast-furnace slag and silica fume). The water-to-cementitious materials ratio was 0.27, and the bulk volume of coarse aggregate and fine aggregate per unit volume of concrete were fixed at 0.50 and 0.60, respectively. All mixtures used a superplasticizer and were non-air-entrained. Test cylinders were cast for testing in compression at 1 and 28 days, and test prisms were cast for determining resistance to freezing and thawing cycles in accordance with ASTM C 666, Procedure A, and for resistance to scaling from deicing chemicals according to ASTM C 672. The curing methods were water curing and steam curing. The air-void parameters of the hardened concrete were determined on the sawn sections. The test results indicate that non-air-entrained, high-performance concrete with steam curing showed low durability factors. High-performance concrete with water curing performed satisfactorily when subjected to up to 1500 cycles of freezing and thawing. Water-cured, high-performance concrete showed no appreciable scaling after 100 freezing and thawing cycles, showing high resistance to scaling.