International Concrete Abstracts Portal

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.

A design method for avoiding damage due to carbonation-induced corrosion of steel reinforcement in concrete is described. It accounts for the initiation period, during which a carbonation front penetrates the cover concrete, and a propagation period, during which the reinforcement corrodes and produces visible cracking of the concrete. The initiation period is controlled by diffusion of carbon dioxide through the carbonated concrete and is dependent upon the depth of cover, the gas permeability of the carbonated cover concrete, and the quantity of cement hydrate available to buffer the carbonation reaction. The rates of carbonation and reinforcement corrosion are dependent upon the relative humidity within the cover concrete. Estimates of carbonation depth give a reasonable upper bound to a wide range of field measurements. Corrosion rates are estimated on the basis of an upper bound to a range of published laboratory and field data. A sensitivity analysis showed that the main factors influencing the choice of concrete quality were the exposure conditions, depth of cover, and the notional service life: the effects of curing period and cement type were less significant. Estimates of concrete quality for selected combinations of exposure, cover, and service life were compatible with those being considered for European codes and standards. The design method can be used to examine alternative combinations of cover, concrete quality, cement type, and curing period for providing a given notional service life under selected exposure conditions.

The corrosion of steel in reinforced concrete due to the ingress of chlorides is a major cause for the decreased durability of structures built in marine and deicing salt environments. A multitude of research has been conducted to evaluate the corrosion of steel in concrete and to develop protection systems to arrest this process. This paper critically discusses some of the more popular techniques and presents new data illustrating the importance of selecting the right corrosion tests.