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.

During the mid-1970s, there was a boom in the construction industry in Saudi Arabia. To meet the housing requirements, and to furnish the infrastructure needed for a growing industry, construction had to be carried out at a pace unprecedented in the country's history. In the absence of guidelines, concrete specifications from other industrialized countries were used. However, when the structures started to show signs of deterioration within a short fraction of their design life, it was realized that specifications developed for temperate conditions cannot be used in this region. Field and laboratory studies carried out at King Fahd University of Petroleum and Minerals at Dhahran, Saudi Arabia, showed that concrete in this region should not only be designed for strength, but also for durability. Since permeability is one of the most important properties that control the durability of concrete, much emphasis should be given to the production of dense and impermeable concrete. This paper reports the results of an investigation carried out on a number of reinforced concrete structures exposed to underground and seawater conditions that showed serious signs of deterioration within less than 10 years after construction. The paper recommends repair procedures for the damaged structures and future practices to extend their service life.

It has been reported recently that there exists early-stage deterioration in many concrete structures due to salt injury, alkali-silica reaction, freezing-thawing action, and their combined actions. Thus, it will be important to assess the change in quality of the surface layer of concrete because the deterioration often appears on the surface of the concrete by way of cracking or scaling. In this paper, the authors describe the results of field investigations on the state and the cases of deterioration in three seaside concrete bridges located in Aomori prefecture, in the most northern districts of the mainland. Various tests were performed on surface layers of concrete incorporating conventional nondestructive methods. A large amount of chloride ion, in excess of 1 kg/m3 in soluble chloride, had accumulated at the depth of cover, and severe corrosion of reinforcing bars was observed in all bridges. In the case of a reinforced concrete bridge that had been in service for more than 50 years, not only the depth of carbonation and penetration of chloride, but also sulfate intrusion, were deeper than the cover depth. The severe damage caused by alkali-silica reaction was also observed in the pier of a prestressed concrete bridge and newel post of a reinforced concrete bridge. It was possible that the penetration of chloride greatly affected the degree of deterioration due to alkali-silica reaction. The change in quality of the surface layers of concrete brought about by deterioration was assessed successfully by in situ tests based on the pulloff tensile strength, rapid air permeability, and depth of carbonation.

The work described in this paper is part of a research program aimed at quantifying and, if possible, modelizing, the contribution of metallic glass fibers to the durability of thin concrete repairs (about 5 cm) cast on horizontal surfaces. The tests that have been carried out up to now on fresh concrete overlays (0 to 24 hr) indicate that metallic glass fibers can decrease the magnitude of swelling during the first hours after casting. The tests carried out on hardened concrete overlays (on composite specimens kept under Toulouse natural climatic conditions) indicate significant differences between fiber reinforced concrete overlays and plain concrete overlays. Replicas examined with a scanning electron microscope show that microcracks near the interface between the overlay and the base concrete are less numerous when fiber reinforced concrete is used as a repair material instead of plain concrete. Ultrasonic pulse velocity test results are in agreement with these microscopic examinations. A field experiment was also carried out in Quebec, Canada. This experiment proved that normal mixing procedures are sufficient to disperse these fibers if a proper mixing sequence is used (no balling problems occurred). In spite of correct curing conditions, cracks developed after only 2 weeks in the plain concrete overlays, but the fiber concrete overlays are still uncracked after more than 6 months of exposure.

This paper presents the characteristics of the surface-layer strength of concrete produced using a special curing sheet to improve the surface layer. The curing sheet is attached to the interior of the forms and has the ability to absorb water from the concrete surface and to retain the absorbed water for curing. The surface layer strength was measured by a pullout test that was carried out by modifying the Michaelis test machine and using truncated conical steel cones embedded in the concrete. The 14-day surface layer strength obtained by using the special curing sheet increased by 1.2 to 1.5 times of that obtained without using the sheet. The improved strength is attributed to the lowering of the water cement ratio in the surface layers produced by using the sheet. After freeze-thaw tests, the surface layer strength of air-entrained concrete showed less decrease independent of the use of special curing sheet. The surface layer strength might be a useful index for the evaluation of the quality of the surface layer of concrete.