Key Engineering Materials Vols. 302-303

Abstract: The ASTM C1202 method is observed that the total electric charge passed is not an ideal indicator for classification of concrete quality when different binders are considered. Considering the drawback of the ASTM 1202 method, a simple modification to the ASTM C1202 method is recommended. The modification involves an additional test using curing water as electrolyze solution. The difference in the total charge passed obtained between standard test and test performed in curing water is suggested as an indicator for concrete quality. The test results show that there exists a good correlation between the ACSIRO and the ASTM C1202 methods. The relationship can be formulated as a linear function.

Abstract: This paper presents the results of an experimental investigation to determine the flexural fatigue strength and fatigue life of concrete beams reinforced with monofilament polyacrylonitrile fibers (PAN fiber for short). The performance of fresh concrete and the elastic and mechanical properties of hardened concrete are compared by samples with and without fibers. The toughness calculated according to both ASTM and JCI methods increased with the addition of fibers. The toughness indexes I5 was 3.8-4.2 times，I10 was 5.8—6.8 times that of the plain concrete. The equivalent strength was 0.63-0.87 MPa for PAN fiber reinforced concrete. When compared to plain concrete, the endurance limit of concrete beams only reinforced with PAN fiber is increased by 12 percent.

Abstract: Exposure test on chloride ion penetration behavior into Concrete in coastal area was implemented. The distances between concrete specimens and coast were changed in the range from 50 to 150 meters, and water-cement ratios (W/C) were 45, 55, 60 and 65 %. The total chloride ion content at each different depth from surface of concrete specimen was measured at the age of 1, 2, 3, 5, 7, 8 and 10 years. In this paper, apparent diffusion coefficient (D) and chloride ion content on surface of concrete (C0) were calculated by inverse analyses from the measured total chloride ion content, and the chloride ion penetration behavior was simulated using the calculated D and C0. As a result, the chloride ion penetrated in concrete with a W/C of 60 % at a point 50 m from the sea for 10 years was estimated approximately 0.2 kg/m3.

Abstract: Two Reinforcement Concrete (RC) roof slabs, with a size of 1.5 m×6 m, suddenly dropped from the roof after 32 years service in a steel rolling workshop of a steel mill. By in-situ inspection and lab investigation, it was found that the failure of the roof slabs were due to the severe corrosion of the prestressed steel bar, which was induced by concrete degradation connected closely with the service environments of the slabs.

Abstract: Crack prevention is still a main consideration in dam concrete technology. This paper summarizes the author's understanding about the factors affecting cracking-resistance of dam concrete, such as cold shrinkage, drying shrinkage, autogenous volume deformation and tensile strain capacity, etc. The tensile strain capacity is an important parameter in evaluating crack resistance of dam concrete. Reducing volume shrinkages and decreasing adiabatic rise of temperature are the effective measures for enhancing crack resistance of dam concrete, rather than raising the tensile strain capacity impractically especially by increasing cement content of concrete excessively.

Abstract: Crack width is a significant parameter for assessing service life of reinforced concrete structures in chloride-laden environments. Corrosion-induced concrete cracking is a predominant causal factor influencing premature degradation of reinforced concrete structures, incurring considerable costs for repairs and inconvenience to the public due to interruptions. This gives rise to the need for accurate prediction of crack width in order to achieve cost-effectiveness in maintaining serviceability of concrete structures. It is in this regard that the present paper attempts to develop a quasi-brittle mechanical model to predict crack width of chloride contaminated concrete structures. Assuming that cracks be smeared uniformly in all directions and concrete be a quasi-brittle material, the displacement and stress in a concrete cover, before and after surface cracking, were derived respectively in an analytical manner. Crack width, as a function of the cover depth, steel bar diameter, corrosion rate and time, was then determined. Finally, the analysis results were verified by comparing the solution with the experimental results. The effects of the cover depth, steel bar diameter and corrosion rate on the service life were discussed in detail.

Abstract: The influence of early-age crack on concrete cover was studied in this paper. Cracks in concrete increase the permeability of concrete, the section where cracking occurs should be treated as getting thinner. The formation and propagation mechanism of the early-age cover crack, and cover crack depth were two main topics, which were discussed mainly based on the dual boundary element method. At last, the ultimate analytical method was used to determine the minimum thickness of concrete cover.