International Concrete Abstracts Portal

SP-144 Eighteen review papers and twelve research papers are included in the Proceedings of the Mohan Malhotra Symposium on Concrete Technology: Past, Present, and Future. The purpose of the Symposium was to serve as a forum for discussion on the current state of the concrete industry and technology, and to identify important issues that need to be addressed in the future. The proceedings of the Mohan Malhotra Symposium, which excel for the variety and richness of information contained in the 30 papers, reflect the respect and admiration of the authors for the honoree. As a researcher, scholar, and technology-transfer crusader, Mohan has undoubtedly made unique contributions to the concrete technology. It would indeed be a fitting tribute to him if the deliberations of the Mohan Malhotra Symposium are able to make a significant impact in preparing the concrete industry for the 21st century.

Physicochemical processes, such as thermal effects, fluid transfer, and alkali-aggregate reaction, can induce expansion, damage, and cracking of concrete structures. Maintenance and repair are costly on the one hand, and the prediction of service life is still difficult on the other. A mechanical model (for characterizing the degradation of concrete) using the thermodynamics of irreversible processes is presented. The state of concrete as a material is described by different variables for damage, mass transfer, alkali, and temperature. The choice of variable depends on the physicochemical process and volume of the concrete structure considered. To justify the modeling, major hypotheses must be discussed. This model has already been applied to a gravity dam, and a good relationship between predicted and actual damage induced by thermal effects has been obtained.

Presents the results of an experimental investigation conducted to determine the flexural fatigue strength of high-strength lightweight concrete under water. This concrete was produced using expanded shale aggregate and high-performance concrete admixtures such as silica fume and superplasticizer. Properties of fresh concrete and elastic and mechanical properties of hardened concretes are presented. The fresh concrete was tested for slump, air content, unit weight, and temperature. The hardened concrete was tested for moist-cured dry weight, compressive strength, modulus of elasticity, and flexural fatigue strength. The investigation indicates that a highly workable high-strength lightweight concrete can be produced successfully. The high-strength lightweight concrete had a higher endurance limit (10 to 16 percent) than normal weight concrete of equal compressive strength. In general, there was no reduction in the flexural fatigue strength for the lightweight concretes when tested under water. The static flexural strength determined from specimens that had successfully resisted 2 million cycles was always greater than that of specimens which had not undergone fatigue loading.

This research was conducted to present state-of-the-art information on fatigue behavior of plain concrete with and without mineral admixtures and to evaluate fatigue characteristics of Class C fly ash concrete under flexural stress. A number of studies have shown that concrete fatigue strength is significantly influenced by a large number of variables, including stress range, loading rate, load history, stress reversal, rest period, stress gradient, material properties, etc. Effects of these parameters on fatigue characteristics of concrete are addressed. In general, endurance of fatigue flexural limit of plain concrete was found to vary between approximately 50 and 70 percent of its static flexural strength. But it can be lower than 50 percent when concrete is tested in water. Experimental investigations conducted in this research revealed that a fly ash concrete mixture with 15 percent cement replacement showed superior performance relative to high-volume fly ash mixtures with 50 percent cement replacement with respect to compressive strength and flexural fatigue strength. However, fly ash concrete mixtures showed essentially the same results when the flexural fatigue strength was expressed as a percentage of the flexural static strength.

With increasing knowledge of the importance of mineral admixtures, many kinds of by-product mineral admixtures have become widespread as an important constituent of cement concrete. By-product mineral admixtures such as fly ash, rice husk ash, and ground granulated blast furnace slag are attracting much attention as materials that not only contribute to the improvement of concrete performance (for example, high strength, high durability, and reduction of heat of hydration) but are also indispensable to the reduction of energy and carbon dioxide generated in the production of cement. Describes the current status of by-product mineral admixtures for concrete and their future outlook.