International Concrete Abstracts Portal

To determine the characteristics of deterioration of concrete under freezing and thawing, acoustic emissions of mortar were measured and analyzed. Acoustic emissions of the ice formation were examined to establish test conditions. In addition, propagation properties of acoustic emissions, such as wave velocity and amplitude, were examined with an acoustic emission (AE) pulser. The test results for water showed that acoustic emissions due to ice formation took place during both thawing and freezing. The test results with mortar showed that most acoustic emissions occur during the freezing and that the number of acoustic emissions does not increase with the number of freezing and thawing cycles. The test also showed that the propagation of acoustic emissions is effected by air content and curing period. Therefore, the propagation properties must be considered to evaluate the frost damage of mortar with acoustic emission events. Further, wave velocity and amplitude measured with an AE pulser decrease as the number of freezing and thawing cycles increase. It is concluded that the wave velocity and amplitude of AE pulse propagation can be used as indicators to evaluate the degree of frost damage of mortar.

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.

Discusses the utilization of silica fume concrete admixture to prevent reinforcing steel corrosion. The mechanism of steel corrosion in salt-impregnated concrete is described, along with laboratory test date showing how ordinary concrete's corrosion-prone characteristics are altered by the use of silica fume. The mineral admixture significantly lowers the concrete permeability to prevent chloride ingress to the reinforcing steel level, while simultaneously increasing the concrete's electrical resistance to corrosion currents. Test data from the FHWA 90 day Chloride Ponding Test indicates a 98 percent reduction in chloride penetration. The AASHTO T277 rapid chloride permeability test shows a 10-times impermeability and 25-times resistivity improvement with the use of 12 percent silica fume. T he Time-to-Corrosion FHWA/NCHRP 244 slab test is scaled-down steel-reinforced deck, from which macrocell corrosion current, AC resistance, half-cell potential, and chloride absorption are measured. Zero corrosion current was measured after NaCl was ponded in alternate soak/dry cycles for 48 weeks. The second phase test program evaluated the corrosion performance of full-sized concrete bridge sections, including beams, columns, piles, and bridge deck panels. The test members were subjected to environments simulating salt water and deicing agents for 370 days. Test results show that silica fume admixture prevents salt-induced corrosion of steel a reinforcing bar and tensioning strands.

The durability in seawater of high-strength concretes produced with the addition of silica fume replacing a part of the cement was investigated. The influence of the wet-curing time on the behavior in seawater of high-strength mortars (strength in excess of 60 MPa) in which a part of the cement was replaced by densified silica fume, was determined. The various curing times applied to the specimens, after mold removal, were 48 hr, 7 days, and 28 days at 100 percent relative humidity, followed by storage for 28 days at 20 C and 50 percent relative humidity before the start of tests for resistance to seawater for 1 year. Investigation of the porosity of these mortars shows that, just after curing, the silica fume, as expected, reduces the total porosity of the reference mortar (25 to 45 percent) and substantially alters the pore-size distribution--the shorter the curing time, the more marked this effect. However, as hydration continues at 50 percent RH, the porosity of the reference mortar decreases and the differences in total porosity with respect to the mortars containing silica fume become smaller--the longer the initial curing time and the higher the C3 A content of the cement, the greater this effect. This explains the results of resistance to seawater, where it is found that silica fume contents of less than 10 percent do not lead to any significant improvement in behavior in seawater. This shows that the type of curing and the ambient conditions under which strength increases may limit the beneficial effects of silica fume on durability, when the addition of the silica fume is accompanied by a corresponding reduction of the cement content. It is also found that the best curing method is the specimens in fresh water for the first 7 days, while a curing time of only 48 hr is highly detrimental in terms of the subsequent behavior of the mortars in seawater.

The biological effects and chloride penetration studies were carried out on a 10-year-old concrete structure of the arch bridge on the island Krk in the North Adriatic. Concrete cores of 100 mm diameter were drilled from three main locations of the structure and tested for chloride content at depths 0 to 10, 10 to 20, and 20 to 40 mm. The influence of aggressive organisms on the elements below sea level was determined. The biological life of the concrete below sea level was massive, the value being 1300 units per mý at a depth of about 18 m. The shell Recellaria Dubia can make depressions of 5 to 10 mm diameter.