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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.

This Symposium Publication contains the proceedings of the Fourth CANMET/ACI/JCI International Conference held in Tokushima, Japan, in June 1998. Sixty-two refereed papers were accepted for presentation at this conference and for this publication. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP179

This paper deals with various types of silanes (alcohol or water sol-vent, polymerization degree) and silane systems, which are typical hydrophobic agent as repair materials. From the viewpoint of the deterioration mechanism, water control in concrete structures is one of the most important repair strategies. Therefore, various types of surface treatments which can control water content in concrete structures are applied for repair work. Silanes and silane systems were one of the most important for hydrophobic treatment. In this study, the effect of various types of silanes and silane treatment systems on the hydrophobicity of treated concrete is investigated. Furthermore, water control property in concrete treated with silane system is discussed.`

Portland cement contains sulfur compounds from the clinker phase and from added calcium sulfate (e.g. gypsum) which acts as a set regulator. The purpose of this investigation was to study the influence of the sulfate content in the clinker phase on the performance of superplasticized concrete mixtures in terms of initial slump level at a given water-cement ratio (0.49, slump-loss rate, and compressive strength at early and later ages. Two batches (A and B) of clinker from the same kiln source were studied, the main difference being the content of sulfate (SOs) in the clinker (0.72% and 1.40% respectively). Different percentages of natural gypsum, as set regulator, were interground in a laboratory mill to manufacture portland cements: A1 , A2 , A3 from clinker A, and B1 , B2 , B3 from clinker B. Three levels of total sulfate content in terms of SOs were set: 3.0% in portland cements A1 and B1 , 3.5% in portland cements A2 and B2 ; 4.0% in portland cements A3 and B3. At a given sulfate content in portland cement, the lower the clinker sulfate content, the more effective is the slump increase of the concrete caused by the superplasticizer addition. Moreover, the lower is the clinker sulfate content, the lower is the slump-loss rate of the superplasticized concrete mixture. Finally, at a given water-cement ratio, there is a reduction in the compressive strength at early ages (< 3 days) when the low sulfate clinker is used to manufacture portland cements. These results are related to the effect of the clinker sulfate content on the degree of cement hydration: the lower the clinker sulfate content, the lower the early cement hydration in terms of gypsum consumption, ettringite formation, and tricalcium silicate (alite) hydration.

Desalination is the electrochemical method aiming to remove chlorides from reinforced concrete structures. Until now, it has been applied only to reinforced concrete structures and not to prestressed concrete structures. In this study, desalination was applied to chloride contaminated concrete specimens with pretensioned prestressing steel bars. As a result of the slow strain rate tensile test of prestressing bars after applying desalination, significant influence of treatment on the elastic behavior and plastic behavior until the tensile strength point was not shown but the influence of hydrogen embrittlement due to treatment was impacted on the fracture strength and the contraction rate of fractured sections. As a result of absorbed hydrogen measurement of prestressing steel bars from treated specimens, the release peak of diffusible hydrogen was found. Furthermore, as a result of keeping treated specimens for 1 month, the first peak of diffusible hydrogen (around 470 K) and the change of the fracture behavior due to hydrogen embrittlement disappeared.