International Concrete Abstracts Portal

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.

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.

This report documents a survey conducted for the purpose of evaluating the concrete protection effects of chloride attackmeasures applied to a newprestressed concrete bridge locatedin a chloride attack environment. The chloride attack measures which consisted of (1) applying a concrete protection lining, and (2) installing waterproofing panels, were performed on different girders of the same bridge, respectively. Then, roughly twelve years after the time of construction, the protection effects of each method were evaluated based on appearance, chloride content and chipping surveys. Both methods were found to have sufficient barrier effects against the ingress of corrosive factors into the concretefromthe outside.

Many reinforced buildings were damaged by the Hyogoken-Nanbu Earthquake of 1995. In order to clarity the actual state of carbonation of the concrete and the chloride ion content in concrete of buildings in Hanshin area, the depths of carbonation and the amount of chloride ion were measured in 117 concrete samples that were obtained from 97 damaged buildings. The effects of carbonation depth and chloride ion content with regard to the corrosion of steel were also investigated. The measured carbonation depths were wildly scattered, and some of the concrete being heavily carbonated. The amounts of chloride ions in old river sand concrete were small. Large amounts of chloride ion were found mixed with sand, not only from the ocean but also from rivers in the buildings that were built between 1960 and 1978. These chloride ion were thought to be induced through sea sand and an admixture. The concentration of chloride ions in concrete were small for buildings that had been constructed after the regulation of the amount of chloride in concrete that was instituted in 1986. A great deal of the steel embedded in the carbonated concrete was severely corroded. The degree of steel corrosion tended to increase with an increase in the amount of chloride ion as well as carbonation depth.