International Concrete Abstracts Portal

Concrete is a characteristically porous material, and whatever improvements are made in its formulation and fabrication, micropores and microvoids would always exist on their surfaces. These defects encourage the transport of aggressive agents into the body of concrete, bearing in mind that cracking, depth, and quality of cover concrete and the overall quality of concrete are the three factors that influence the penetration of these agents. Surface coatings on concrete have an important role in preserving the durability of concrete and the steel embedded in it. This paper presents test data on an acrylic-based highly elastic surface coating. The strength and elasticity of the coating, its ability to bridge cracks under static and dynamic loadings, its resistance to natural weathering, heat, oxidation, sunshine, and rain are discussed. Data are also presented on the adhesion strength of the coating to concrete substrate and its resistance to carbonation and chloride penetration. Both short- and long-term test data are presented. It is shown that a highly elastic rubber coating can provide long-term durability and stability to concrete structures, and that it can maintain its integrity, continuity, and adhesion to concrete under very aggressive environmental conditions.

A detailed investigation was made to study the shear transfer between precast prestressed beams and in situ concrete in a relatively new method of construction of continuous bridge decks where the ends of precast beams are connected to an integral in situ crosshead away from the supports. The main advantages of this method are: Increasing the span length, standardization of the beams, elimination of the deep support girder, obtaining full continuity for the dead and live loads, and possibility for using straight beams in skew and curved bridges. The prestressed beam used in the investigation was an inverted T-section, and it was concluded that: 1) The shear force is transferred from a small length at the end of the beam. 2) The in situ concrete nibs can take this shear force without stirrups. 3) There is no need either to project all the bars into the in situ concrete or to prestress the connection transversely. 4) The shape of top flanges of the prestressed beam had a significant effect on the shear transfer capacity of the connection. 5) For the beams without top flanges, the shear strength of the connection can be modified by using transverse prestressing, web shear connectors, or projection of the bars.

The wind tunnel tests were carried out on rigid models of tall buildings with square plan shape to study the effects of interference on wind loads on tall buildings. This paper presents the results of the same. Effects of various geometric and flow parameters on total force and moments are reported, which are deduced from the wind pressure values obtained on isolated instrumented buildings in the vicinity.

In this paper, the effect of high-strength bars in web reinforcement is evaluated based on the test results in Japan. Discussions have centered on the effect on members' shear strength and reinforcement performance for splitting bond failure along longitudinal reinforcements. High-strength bars with a yield strength of 80,000 to 130,000 N/cm3 proved to be very effective in increasing the shear strength of members, especially for high-strength concrete. However, high-strength bars were no more effective than normal strength bars in preventing splitting bond failure. Formulas were derived for normal and high-strength bars to predict the ultimate shear force at shear failure as well as splitting bond failure in members.

Presents a study on the flexural behavior of reinforced concrete beams containing steel fibers. Several series of reinforced concrete beams have been tested. The present test program includes two series of singly reinforced concrete beams and one series of doubly reinforced concrete beams. The fiber contents for each series were varied from 0 to 2 percent by volume. The load was applied in flexure at the third-points. The deflections at the center- and quarter-points of the beam were measured, and the strains of concrete and steel at various points were also measured and automatically stored in the computer. The crack widths and crack spacings at each loading step were observed during the incremental loading process. The load-deflection curves were generated from the measured data. The present tests show that the crack widths increase almost linearly with the increase of steel stress and that the crack widths at the same loading steps are remarkably reduced as the fiber amounts increase. Fiber addition was found to improve considerably the ductility and load-carrying capacity of reinforced concrete members.