International Concrete Abstracts Portal

The Canadian association of large public real estate companies has initiated a 5-year research project aimed at determining the most cost-effective way to rehabilitate deteriorated parking structures. A sample of 49 garages includes office, retail, and residential buildings. The repair history of each building has been documented and, in some cases, a formal condition survey of the garages is undertaken yearly. The collected data serve as a basis for the evaluation of the effectiveness of the various repair techniques and strategies. The project is now in its third year. The investigation was carried out concerning the excessive cracking noted in some garages constructed with epoxy-coated reinforcing steel. The benefits of intensive maintenance and good housekeeping have been shown by the analysis of the case history of a garage. Various types of concrete sealers have been evaluated by testing in the laboratory 57 products applied to 8 types of concrete substrate. Preliminary results indicate waterproofing membranes are an effective means to reduce the moisture content in the slab.

Long-term exposure test results of reinforced concrete beams are reported. One hundred forty-nine pairs of beams with open cracks were exposed to sea air for 2 to 20 years. The main variables were thickness of concrete cover, type of cement, cement content (water/cement), and crack width. The type of cement has a great influence on the depth of chloride ion penetration. The thickness of concrete cover is the most important factor in the prevention of corrosion of the reinforcing steel. With a thin cover, the crack width has no influence on corrosion of reinforcing steel. Epoxy coating is effective in improving corrosion protection. Measurements of electrical potential on the surface of concrete give valuable information on corrosion activity of reinforcing steel.

Exposure tests of silica fume concrete with embedded steel bars were carried out in marine environments such as the Inland Sea of Japan, the Pacific Ocean, and the Sea of Japan, in the Kansai district. The effects of water-to-cementitious material ratio, silica fume content, chloride ion content in mixing water, and concrete cover on the chloride corrosion of reinforcing steel were studied by measuring half-cell potential, electric resistance, pH value, depth of carbonation, pore volume, and chloride ion content. When tap water was used as the mixing water and concrete cover was 10 mm, the longitudinal crack due to chloride corrosion was observed in silica fume concrete specimens in about 3 years. Chloride ion penetration into silica fume concrete was much lower in comparison with concrete without silica fume, however, chloride at the region 2 cm from the concrete surface was high enough for embedded steel to corrode. When concrete cover was 25 mm, no longitudinal crack was observed in silica fume concrete specimens until about 3 years. It is necessary to keep sufficient concrete cover, even in silica fume concrete. Chloride corrosion in concrete was accelerated by using silica fume when saline solution was used as the mixing water.

A comprehensive research program was carried out to evaluate the quality of the outer layer of concrete (the covercrete), in terms of its durability and protective value to the underlying reinforcing bars. Part of the results of that investigation are presented in this paper, namely those dealing with the influence of the concrete grade and cement type on the permeability to oxygen and water absorption properties of the 'covercrete' of concrete specimens subjected to 7 days moist + 21 days dry curing. The results obtained show that the permeability to oxygen is reduced 40 times when the concrete strength is raised from 25 to 85 MPa, whilst the rate of water absorption is reduced by a factor of 4. In addition, the cement type (including Portland and blended cements) seems to play only a secondary role in the quality of the 'covercrete' of concretes of the same grade, especially above 25 MPa.

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.