International Concrete Abstracts Portal

The paper investigates the shear strength and the failure modes of high strength concrete beams with and without steel fibers ( fC = 110 MPa). Sixteen reinforced high strength concrete beams (3600x350~200 mm) were tested under different combinations of shear force and bending moment. The beams were singly reinforced and without shear (web) reinforcement. The test results indicated that the addition of steel fibers to high strength concrete increases the ultimate shear strength, improves the brittle characteristic and transforms the failure mode into a more ductile one. The average gain of the ultimate shear strength due to the addition of steel fibers varied from about 14% to 14 1% depending on the shear span to depth ratio and the longitudinal steel ratio. Four modes of failure of reinforced high strength concrete are clearly distinguished as; diagonal tension, shear compression, shear flexure, and flexural failure. In general, cracks in fiber reinforced concrete beams are closer, narrower, and more than those in beams without fibers. This reflects the effect of steel fibers in redistributing the stresses beyond cracking.

A laboratory test and a case history of deteriorated reinforced concrete slab repair are presented. Since several structural problems have been reported for reinforced concrete slabs, it is necessary to establish repair techniques for such slabs. Many structural problems of reinforced concrete slabs derive from a decline in rigidity with age. Although several techniques have been developed, their effectiveness has not been ascertained, especially over the long term. A laboratory test was conducted to ascertain the effectiveness of repair techniques. Based on the test results, the overlay repair technique was applied to actual slabs. In the case history, short and long-term performances of the repaired slabs were measured for more than 2000 days. Changes in the rigidity and natural frequency of the slabs were examined. The material properties and adhesive strength of old and new concrete were also examined. Although the static and dynamic performances of the repaired slabs improved remarkably, their performances gradually decreased with age. It is important to allow a reasonable margin of error for repairing deteriorated slabs.

Three repair mortars were compared in terms of chloride attack preventive capability to propose an appropriate repair method applicable to the damaged concrete structure by chloride-induced corrosion. The repair methods were the cover replacement method and the surface coating method. The ability of these two methods to prevent corrosion were compared in terms of corrosion area and mass loss after 10 years’ outdoor exposure. It was proven that the cover replacement method extending over the backside of reinforcing steel using SBR polymer cement mortar with a corrosion inhibitor was effective while the surface coating method was applicable when the amount of chloride in concrete structures was excessive.

The effects of slag content and polymer-binder ratio on the properties of autoclaved and combined wet/dry-cured polymer-modified mortars using ground granulated blast-furnace slag (slag) and polymer dispersions such as a styrene-butadiene rubber (SBR) latex, and poly (ethylene-vinyl acetate) (EVA) and polyacrylic ester (PAE) emulsions are examined. As a result, the strength of the autoclaved polymer-modified mortars reaches a maximum at a slag content of 30% except for the autoclaved EVA- and PAE-modified mortars, and tends to increase or decrease with increasing polymer-binder ratio. The strength of the combined wet/dry-cured polymer-modified mortars reaches a maximum at a slag content of 40%, and is inclined to increase with increasing polymer-binder ratio. Irrespective of the curing conditions, their water absorption and chloride ion penetration depth tend to decrease with increasing slag content and polymer-binder ratio except for the autoclaved PAE-modified mortars. Their carbonation depth increases or decreases with increasing polymer-binder ratio.

The damage in concrete structures generally starts with rnicrocracking and thus it is important to find and explore these microcracks in concrete in order to ensure appropriate safety and serviceability. The purpose of the present study is to identify the damage characteristics of concrete structures due to cracking by employing the acoustic emission techniques. A comprehensive experimental study has been done. The cracking damages under tensile and flexural loadings have been identified and the bond damage between steel and concrete have been also characterized. It is seen that the amplitudes and energy level of Acoustic Emission (AE) events are found to be relatively small for bond cracking damages and large for tensile cracking damages. The present study provides useful data which can be used to identify the various types of cracking damages in concrete structures. This will allow efficient safety management of concrete structures through monitoring of internal cracking based on acoustic emission.