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The authors have proposed a partially pre-cooling system for massive structures, such as gravity concrete dams. It is discussed in this paper how the effectiveness of the proposed method is discussed using the finite element analysis. In the ordinary pre-cooling system, pre-cooled concrete is placed in the entire region (width and depth) of a massive structure. In the proposed system , pre-cooled concrete is placed only in the surface layer. In order to evaluate the effectiveness of this system, a thermal stress analysis was conducted by the finite element method. The key parameters were the dimensions of the cooling system and cooling temperatures. The results show that the proposed system is rather effective than the conventional cooling system in terms of the thermal stress condition of massive concrete structures. In addition, the cost benefit is adequately expected.

The use of high strength normal weight and lightweight aggregate concrete (i.e. with water/binder ratios below 0.40) have shown that the concrete may be more sensitive to cracking the first hours and days after casting (due to autogenous shrinkage and thermal strains), than normal strength concretes. Two test rigs have been built in order to investigate the problem. The Shrinkage-Rig determines the free deformations (e.g. autogenous and thermal deformations), and the special Stress-Rig determines the stresses when the concrete is restrained against the deformations. The paper presents the results from testing of one high strength normal weight concrete and one high strength lightweight aggregate concrete, both with water/binder ratio 0.38, in the test rigs. Both concretes were exposed to two different temperature histories generated from heat of hydration. The normal weight concrete developed relatively high tensile strains during the cooling phase. The corresponding stresses in the Stress-Rig became very high, and in one case the concrete failed. The lightweight aggregate concrete, however, did not develop any tensile strain, due to a lack of autogenous shrinkage caused by the water supply from the LWA grains. Consequently, no severe tensile stresses were built up in the Stress-Rig.

High-strength and high-fluidity lightweight concretes have been developed using silica fume blended cement and belite-rich cement with a designed compressive strength from 40 to 60 MPa. Test conditions and parameters were water-cement ratio of 0.22,0.33 and 0.40, curing temperature of 5, 20 and 35 C, curing method of standard and sealed curing and 3 types of high-range AE water-reducing agent. Influences of above factors upon flow, flow time, compressive strength, permeability, pore size distribution and total pore volume were studied. The major findings of this study are as follows, (1) Compressive strength of silica fume blended cement concrete was higher than that of belite-rich cement concrete and the effect of water-cement ratio was small. Compressive strength at 7-day were 80 to 90% of the 28-day strength at any curing temperature. (2) Compressive strength of belite-rich cement concrete significantly increased at water-cement ratio of 0.3 to 0.4, and its evolution from 28 to 91 days became larger at lower curing temperatures. (3) Total pore volume of silica fume blended cement concrete at the age of 28 days was smaller than that of belite-rich cement concrete at all curing temperatures of 5, 20 and 35 “C, and compressive strength became larger with a decrease of total pore volume.

This paper describes rapid testing methods for determining blocking behaviour, deformability and segregation resistance of self-compacting concrete. Laboratory test results have shown that the proposed methods can reduce the required extent of laboratory testing and enable the tests to be carried out in less time. A simple apparatus for segregation resistance testing is also proposed. This apparatus and modified L-box apparatus are considered useful for rapid testing of segregation resistance, deformability and blocking behaviour of fresh self-compacting concrete.

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 W/C and increasing entraining air.