International Concrete Abstracts Portal

An ongoing study investigating the response of a reinforced concrete building rehabifitated after the 1985 Me&% City earthquake is presented. As part of this program, the behavior under cyclic loads of reinforced concrete columns rehabilitated with steel jackets made of angles and straps is king experimentally assessed. First results on the response of the budding and on the behavior of rehabilitated columns are shown. So far, Building BL has responded elastically, with no damage under recent events. It is apparent that BL response follows the soil fundamental frequency. A first look at the behavior of steel jackets made of angles and straps Wugh two column units, indicates that strength and energy dissipation capacities can be improved, especially in undamaged columns.

An exploratory study of the effect of foundation rocking on the shake table response of a quarter-scale two-column bridge bent was conducted. Several innovative details and designs were used in the columns and the cap beam but the footing represented typical substandard and retrofitted spread footings. The structure was tested in three modes: rocking with as-built footings, rocking with retrofitted footings, and fixed base. The foundation flexibility was modeled in the tests using elastomeric bearing pads that were designed to represent the stiffness of spread footings supported on medium soil. The rocking tests were conducted in the elastic range, but the fixed-base model was tested to failure. The Sylmar record of the 1994 Northridge earthquake was simulated on the shake table. The data showed that for the same input earthquake intensity the maximum steel bar strain near the base of the columns in an unretrofitted rocking footing was only 7 percent of the strain in the fixed kame. When the footing was retrofitted but was still allowed to rock, the maximum steel strain increased but was still only 16 percent of the strain in the fixed kame. The retrofit design implications of the results are discussed.

This study presents the experimental results on properties of concrete with replacement of natural aggregate by recycled concrete aggregate (RCA). Experimental data on the creep behavior of concrete mixtures (basic and drying creep) was obtained. The replacement factor of natural aggregate by RCA were 0%, 15%,30%,60% and 10096, and the test conditions were 50% RH and 20°C. The results of these trials were used to provide a comparison with results of tests on the reference concrete, for ages up to 270 days. The creep coefficient data (instantaneous, basic and drying) presented, along with the maximum strain and the specific creep data. The results reveal considerable increase in creep when is increase replacement of natural aggregate with recycled concrete aggregate. The drying creep, especially shower more significant increase when compared to the reference concrete.

In this paper we present theexperimental analysis of samples of concrete where portion of the natural aggregate were replaced with recycled aggregate originating from concrete (RCA). Experimental analysis to obtain the shrinkage properties (basic and dried) of the concrete containing recycled concrete aggregate (CRCA) was performed. The percentages of replacement of natural aggregate with RCA were 0%, 15%,30%, 60% and 100% with test conditions of 50% RH and 20°C. The results of these trials are compared with reference concrete tests, at an age of 270 days. The results demonstrated an increase in the shrinkage of the CRCA that is proportional to the am- of RCA used as a replacement for the natural aggregate. When compared to the derence concrete, the drying shrinkage showing significant changes; however, their evolution over time is similar to standard concrete.

The performance of conventional, polymer-modified, steel-fiber, epoxy, and silica-fume mortars subjected to a high velocity water flow is described. Besides the mechanical requirements and wearing resistance of concrete hydraulic structures, especially spillway surfaces, the high solar radiation and the environmental temperature contribute significantly to decreasing in the lifespan of repairs. Such contributions are particularly evident on surfaces repaired with polymer-modified concrete and epoxy mortar, mainly at the interfaces between the substrate and the environment. This paper presents the results of a comparative study to determine mechanical properties, adherence, and accelerated aging of four repair systems. Two systems exhibited higher performance: the epoxy and silica-fume mortar. Steel-fibers, due to good adherence to the substrate and good mechanical performance, are appropriate for use as an intermediate layer for underwater repair. This system exhibited an apparent corrosion at the steel-fibers on the surface after aging and underwater abrasion tests, which should be considered prior to being used on exposed spillway slab surfaces.