Erosion by abrasion, cavitation and/or chemical attack in concrete hydraulic structures deteriorates spillways, stilling basins, chutes, slabs and transverse joints, concrete blocks under water gates, and any irregular surface subjected to high water flow rate. Countless overlays are commercially available for repairing deteriorated surfaces. However, the essential data provided by manufacturers is very limited and, even if it is available, it is normally limited to room temperature values. This persuaded the Canadian Electrical Association to support a comprehensive study on commercial overlays, especially from the viewpoint of resistance against erosion and the severe climatic conditions observed in northern parts of Canada. This paper presents laboratory test data on the erosion resistance and durability properties of various types of commercial overlays such as cementitious grouts, polymer-modified cement-based mortars, and epoxy mortars.

Most studies dealing with the problem of reinforcement corrosion have been carried out using exposure tests in which entire specimens (with their continuous reinforcement) were exposed under uniform conditions. The present paper describes the results of some of the experiments carried out to clarify the characteristics of corrosion occurring under a combination of different conditions. Experiments were carried out by subjecting reinforced concrete specimens to different exposure conditions in the laboratory and a marine exposure site. From the laboratory studies using continuous reinforcing bars in specimens subjected to diverse and simultaneous exposure conditions, it was found that corrosion occurs in those parts of the bars that are exposed to cyclic wetting and drying and at the interface of the submerged and aerially exposed parts. Some aspects of the corrosion monitoring using natural potential measurements under these conditions and the importance of water movement in determining the chloride concentration in concrete are also discussed. From the study of cracked and uncracked reinforced concrete marine environment, it was found that the presence of flexural cracks does marginally accelerate the initiation of corrosion at crack sites. Further, the presence of stirrups in the shear span of these beams was also found to have a significant restraining effect on the initiation and propagation of corrosion-induced longitudinal cracks along the main reinforcing bars. Once the width of these cracks exceeds a certain value, the corrosion of the bars and the widening of such cracks apparently becomes a vicious cycle.

The strength and toughness durability of carbon fiber reinforced cements (CFRC) in inorganic acidic environments was investigated by subjected prismatic flexural specimens (15 x 15 x 150 mm) to two acidic environments (H2 and HNO4) at the age of 28 days for up to 90 days. The pH of the two acids was maintained at 4.0. Eight CFRC mixes and three volume fractions of pitch-based carbon fibers were investigated. It was concluded that while plain unreinforced cements had considerable retrogression in their mechanical properties, carbon fiber reinforced cements had no appreciable effect on either the strength or the toughness, at least for the duration of exposure investigated.

The purpose of this research is to examine the resistance to repeated freezing and thawing cycles of non-air-entrained and air-entrained concretes containing high dosages of condensed silica fume. Testing was carried out on a total of 76 air-entrained and non air-entrained cylindrical specimens. The compressive strength and the complete stress-strain curves of the specimens under uniaxial compression were determined from different freezing and thawing cycles. The influence of the treatment on the shape of the stress-strain curves was investigated. In addition, the dynamic modulus under the same cyclic conditions was determined. To investigate both the spacing factor and the specific surface, the air void and pore structure characteristics of hardened specimens were studied.

This paper gives the results of an investigation undertaken to determine the scaling resistance of concrete incorporating fly ash, and discusses factors affecting that resistance. A total of 21 air-entrained concrete mixtures were made. Water/(cement + fly ash) ratios of 0.35, 0.45, and 0.55 were used, and reference concrete (without fly ash) and concrete incorporating 20 and 30 percent fly ash as replacement by mass for cement were made. Two aggregate types were used in the investigation. The test results show that concrete incorporating up to 30 percent fly ash performed satisfactorily under the scaling test with minor exceptions. Extended moist-curing or drying periods did not affect significantly the performance of the reference and fly ash concretes in the scaling test, at least within the periods investigated. Membrane curing appears to improve somewhat the durability of concrete under the combined action freezing and thawing and deicing salts; this is especially true for fly ash concrete.