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In this study, 2 x 2 x 2-m reinforced concrete slabs with an overlay containing initial chloride contents of 0.2, 0.7, and 0.2 percent Cl were electrochemically treated. An electrical field at current densities of 0.7, 1.0, and 1.3 A/m 2 was applied across the overlay at biweekly intervals for a total duration of 8 weeks. During each intermission, the cores were taken from the slabs to determine chloride distribution profiles. Chloride diffusivities in concrete before and after electrochemical treatment were also determined by using a rapid method. The effects of an electrical field on chloride distribution profiles and chloride diffusivity in concrete are discussed. Results show that the electrochemical treatment has no apparent influence on chloride diffusivity, and that this treatment has a limit beyond which the further removal of chloride ions becomes difficult. It is difficult to remove chloride ions homogeneously from concrete using the reinforcement as a cathode.

Hydro=Quebec has undertaken a major study of shotcrete as a repair material for concrete dams. Six dry-mix shotcretes and one wet-mix shotcrete were shot on an old concrete slab and into sampling boxes using Types 10 and 30 portland cement, silica fume, superplasticizer, and polypropylene and steel fibers. An air-entraining agent (AEA) was added to all mixes except one to verify the effect of air entrainment on shotcrete. After wet-curing for 3 days at approximately 20 C and exposure to field conditions for 25 days, prisms and cylindrical specimens were taken from each of 600 x 600 x 150-mm shotcrete slabs. These specimens were then subjected to 500 freezing and thawing cycles, and tested for air-void parameters, compressive strength, and bond to old concrete. Freezing and thawing results showed that five of the six air-entrained mixtures yielded a durability factor (DF) over 100 after 500 freezing and thawing cycles, whereas one showed a DF of 84, although its spacing factor L was only 159 m. The one mixture with no AEA gave a DF of 64 with L of 272 m, although its corresponding air-entrained mix gave a DF of 102 and L of 234 m. The overall results showed that: 1) freeze- and thaw-resistant wet- and dry-mix shotcretes incorporating silica fume can be produced using proper proportioning and AEA; 2) silica fume shotcrete can be shot on a 70-deg inclined wall in thicknesses of up to 150 mm without sagging and can produce a good bond; 3) the wet-mix process produces better homogeneity than the dry-mix process.

An organic shrinkage-reducing agent consists mainly of lower alcohol alkaline oxide adducts. This is a very effective agent for reducing drying shrinkage of concrete, but some research has reported suspicion that concrete using this agent has poor frost resistance. The purpose of this study was to investigate the frost resistance of concrete. Research focused on the viscosity of capillary water, a solution containing the agent, and it was found that the viscosity was somewhat higher than normal capillary water; therefore, the pressure of the solution during freezing would be very high, which causes accelerated concrete deterioration. However, this agent is intended for use for concrete exposed to frequent drying conditions. Freeze-thaw testing was carried out on concretes with the agent with saturations under 100 percent. The continuous monitoring of concrete exposed to cold environment conditions outdoors for 8 years has not shown any problems.

Three Canadian aggregates were evaluated for potential alkali-aggregate reactivity (AAR) in concrete mixes made with CSA Type 10 high-alkali cement and two silica fume blended cements. The aggregate types investigated included a quarried carbonate rock (limestone) and two gravels from glacial deposits mainly composed of granitic and sedimentary rock fragments. The concretes were proportioned to meet the requirements normally applied to offshore concrete structures, and therefore had high strengths and cement contents greater than 400 kg/m 3. The mechanical properties of these concretes, including compressive, flexural, and splitting tensile strengths, as well as Young's modulus of elasticity, were evaluated at various ages. The susceptibility to AAR of these "job-type" concrete mixes was evaluated by casting concrete prisms from the preceding mixes and subjecting them to the various accelerated curing conditions in the laboratory. For comparison purposes, mortar bars were also made and tested according to the ASTM P 214 (1990) accelerated mortar bar test procedure. Testing of the materials was replicated in two independent laboratories. The AAR concrete prism and accelerated mortar bar test results performed in this study showed that all three aggregates investigated may be considered potentially reactive. None of the concrete prisms made with these aggregates and the silica fume blended cements, however, showed significant expansion after 12 or 18 months of testing either in 1N NaOH or relative humidity > 95 percent at 38 C. More long-term concrete prism tests and/or field testing is needed to evaluate the effectiveness of blended cements in reducing the expansion due to AAR, especially for highly reactive aggregates.

The long-term durability of a number of special types of concretes has been tested by exposing various large-scale concrete specimens to different outdoor conditions. The concretes tested include concretes made with different types of cement and incorporating various quantities of fly ash and silica fume (microsilica) as well as mixtures thereof. In one test series, full-scale precast concrete units were installed as functional members of a fish-ladder. The units, comprising concrete with up to 50 percent of silica fume (related to the cement content), are subject to the action of lake water and freezing and thawing. They have been in service for nearly 15 years, and the results demonstrate the excellent durability of concrete with silica fume. In another test series, concrete panels and slabs are exposed to Danish outdoor climates (freezing and thawing during winters) in connection with frequent use of deicing salts. The test series also comprises large-size panels, installed in a harbor at the west coast of Denmark. For this test series, 10-year results are now available.