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.

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.

A detailed investigation was made to study the shear transfer between precast prestressed beams and in situ concrete in a relatively new method of construction of continuous bridge decks where the ends of precast beams are connected to an integral in situ crosshead away from the supports. The main advantages of this method are: Increasing the span length, standardization of the beams, elimination of the deep support girder, obtaining full continuity for the dead and live loads, and possibility for using straight beams in skew and curved bridges. The prestressed beam used in the investigation was an inverted T-section, and it was concluded that: 1) The shear force is transferred from a small length at the end of the beam. 2) The in situ concrete nibs can take this shear force without stirrups. 3) There is no need either to project all the bars into the in situ concrete or to prestress the connection transversely. 4) The shape of top flanges of the prestressed beam had a significant effect on the shear transfer capacity of the connection. 5) For the beams without top flanges, the shear strength of the connection can be modified by using transverse prestressing, web shear connectors, or projection of the bars.

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.

Concrete structures, old or new, often experience formation of cracks, even though these are accounted for by the designer at the time of construction. To repair these cracks, a large number of injectable inorganic materials (cements and cementitious grouts), organic materials (epoxies, polyurethanes, polyester, etc.) and mixtures of both have been used successfully and unsuccessfully. Cementitious materials seem to arouse great controversy among engineers, especially with regard to the acceptance levels of the consistency (water-cement ratio) to be used for injection. A hydraulic facility in Quebec is therefore evaluating a number of cementitious materials as well as various epoxies and polyurethanes for repairing its concrete structures. The paper describes the results of a study performed in the laboratory using normal portland cement (Type 10) and high early-strength cement (Type 30) both with and without superplasticizers, and two ultrafine cements, and recommends an arbitrary lower and higher limit of the water-cement ratio, which could be suitable for crack injection. It also presents some physical and mechanical data on these cements. 110-691