International Concrete Abstracts Portal

The manifestation of cracking in concrete has been considered. Using thin-section techniques, it is possible to analyze crack patterns in concrete. Based on classical mechanics theories, the crack patterns can be categorized according to the stress situation at the point of incipient cracking. Various deteriorating mechanisms in concrete cause different stress conditions in the hardened cement paste, in the aggregate, and at their interface. Combining the features of crack patterns in a given concrete with other data secured from petrographic analysis of thin sections and knowledge of the mechanisms of various deteriorating (or harmless) processes, it is possible to diagnose with increased accuracy the field performance of the concrete.

The last few years have seen the cost of repairs and rehabilitation of major constructions become an urgent concern. In particular, the ever increasing use of reinforced concrete in corrosive and marine environment for the construction of bridges, tunnels, causeways, canals, dams, docks, retaining walls, multistory parking facilities, etc., has resulted in severe premature deteriorations. It has been established that these deteriorations are due mainly to the corrosion of the steel reinforcement in the concrete. This obviously has led many building codes to adopt a more stringent view on the durability of reinforced concrete against corrosion in specific constructions. Many procedures and techniques such as dense and latex concrete covers, epoxy-coated reinforcing steels, synthetic membranes, etc., have been used more or less successfully to meet these requirements. All these techniques, however, are expensive and their long-term efficiency is questionable. Therefore, the need for a more positive alternative to replace conventional steel reinforcing bars, at least for some applications, becomes conspicuous. This has led to the development of a new composite fiber glass rod. This new product has been evaluated in terms of mechanical properties and structural behavior as a reinforcing element and the results are presented in this paper. Immediate as well as long-term applications are discussed in terms of experimental as well as theoretical and economical considerations.

During a comprehensive research program on in situ determination of concrete strength, the influence of core dimensions on mean compressive strength results and their dispersion was studied. Tests were conducted on 14, 11, 9, and 5 cm diameter cores, usually with a length/diameter ratio l/d = 1; cores with l/d less than 1 were also tested. Cores were drilled from 20 cm cast concrete cubes, stored in a moist room. When using 5 cm diameter cores, the curing conditions of the cubes were varied. The 28-day strength results showed that dispersion increases with increases in concrete strength, maximum aggregate size, and reduction of core diameter. A good correlation was found between the mean compressive strengths of cubes and cores, both for the results of cores with l/d = 1 and l/d = 0.6. The mean compressive strengths of cores were the same as those for cubes and were not influenced by the core diameter. Thus, the use of small diameter cores may be possible. In this case, however, the concrete from the surface must be removed when preparing the cores, if the concrete was not moist-cured.

Presents a discussion of the objectives, scope, and progress of a 4-year research project on the mechanical properties of high-performance concretes with particular reference to highway applications. High-performance concrete is defined by certain requirements of strength and durability.

Repair and strengthening practice is based mainly on intuition, and reliable experimental data available on the repaired/strengthened reinforced concrete structural member behavior are very limited. However, the subject has recently started to receive researchers' attention, and a few experimental studies are being carried out in various European and North American countries. Current research activities in this field at the Middle East Technical University and Gazi University, Ankara, Turkey, are briefly introduced. The projects reviewed are: 1) jacketed column behavior under uniaxial load or combined axial load and reversed cyclic bending; 2) behavior of beams strengthened for flexure under monotonic, repeated, and reversed cyclic loading as well as beam strengthening by epoxy glued steel plates; 3) slab repair and strengthening; 4) system behavior improvement by introducing either cast-in-place reinforced concrete infills or masonry infills; 5) epoxy anchorage of new steel into the existing concrete. Results obtained from the test series already completed are briefly reported, and the other series in progress are briefly introduced.