International Concrete Abstracts Portal

SP-145 In 1994, The Canada Centre for Mineral and Energy Technology (CANMET) in association with the America Concrete Institute, sponsored a third international conference on the Durability of Concrete This Special ACI publication presents the 65 conference papers accepter for publication. For Your Convenience, Durability of Concrete has been divided into two parts. Part 1, which contains 34 papers, covers the areas of: 1. Deicer Salt Scaling of Concrete 2. Freezing and Thawing Phenomenon 3. Performance of Concrete in Marine Environments 4. Corrosion of Steel to Fluoride-Ion Attach 5. And other Topics Part 2, containing 31 papers, covers the areas of: 1. Alkali-Aggregate Reactivity 2. Coatings for Concrete 3. Carbonation 4. High-Volume Fly Ash Concrete 5. Durability of Concrete

This paper describes the results of a ten-year marine exposure test of reinforced concrete. Sixteen pre-cracked test specimens were examined. The target crack width was 0.2mm. The dimensions of the specimens were 15x15x100cm. Ordinary deformed bars and epoxy-coated deformed bars, as well as normal portland cement and portland blast-furnace slag cement were used. The water-cement ratio in the mixture proportions ranged from 0.320I to 0.483%. The effect of nitrite-based corrosion inhibitor was also examined. From the exposure test results, the following conclusions were drawn: When the water-cement ratio was low, the penetration of chloride ions into the concrete was low; the chloride-ion content on the surface of blast-furnace slag cement concrete was greater than on the surface of concrete made with ordinary cement, but was smaller inside; there was a tendency for the chloride-ion content around the reinforcing bars in concrete portions with small cracks to be greater than in portions with large cracks; ten years of exposure caused an increase in crack width due to the corrosion of the reinforcing bars; although the effectiveness of epoxy-coated reinforcing bars in preventing corrosion was obvious, severe corrosion was found in one coated bar. The epoxy-coated bars used were produced for the first time in Japan, and test results indicate that there were problems with the early production technology; there was no beneficial effect from corrosion inhibitor after ten years.

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.

Corrosion of reinforcing steel is a major cause of concrete deterioration and, consequently, of loss of serviceability of concrete structures. Presents the results of a laboratory investigation to assess the effects of fly ash on the resistivity and rate of corrosion of reinforcing steel in concrete. Environmental exposure conditions were simulated in the laboratory, and corrosion tests were carried out on specimens corroded naturally or under accelerated conditions. Results show that fly ash is a very effective addition to improve the resistivity of concrete and to reduce the rate of corrosion of reinforcing steel. The resistivity of fly ash concrete is approximately double that of the resistivity of an equivalent normal portland cement concrete. Results are used to propose a model relating resistivity, porosity, and permeability of concrete with the rate of corrosion of reinforcing steel.

In Australia, the Cement and Concrete Association has sponsored a number of research projects addressing aspects relating to deterioration of concrete structures caused by corrosion of the reinforcement. The overall objectives of these projects were to identify the factors influencing steel corrosion and to quantify their effect on initiating corrosion and on the rate of corrosion. The ultimate objective was to provide practicing engineers with the relevant parameters that can be used in the design and specification of concrete structures to minimize the risk of corrosion of reinforcing steel. Reviews the major corrosion research carried out in Australia. Article attempts to correlate research findings to the conditions in practice and to quantitatively predict design life of reinforced concrete structures in an environment simulating severe exposure conditions in Australia. The design life predictions presented should be considered within the context of the assumptions and approximations made. Data presented in this paper showed that the influence of binder type is more in the medium-strength concretes in terms of time to potential jump (initiation) and corrosion rate (propagation). Therefore, it is recommended to optimize concrete mixture proportioning with respect to binder type in this range of concrete strengths to utilize the benefits possible from different binders.