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SP192 In 2000, CANMET, in association with ACI, the Japan Concrete Institute, and several other organizations in Spain and Canada, sponsored a fifth international conference held on June 4-9, 2000, in Barcelona, Spain. More than 120 papers from 35 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 73 were accepted for publication. The accepted papers deal with all aspects of concrete durability. In addition, several sessions dealing with sulfate attack, superplasticizers and supplementary cementing materials, and near surface testing for the durability of concrete were organized. In addition to the papers that have been published in the refereed proceedings, more than 30 papers were presented at the conference.

This work estimated experimentally the critical amount of steel corrosion (Xcrit) needed for concrete cover cracking of a reinforced concrete element where only a fraction of the steel bar length is corroding. The amount of corrosion needed to crack the concrete cover (Xcrit) was ~49 um to ~137 um in specimens with localized corrosion, in comparison to ~15 um to 75 um for uniform corrosion reported for other investigations in comparable systems. An empirical equation is proposed for Xcrit as a function of specimen dimensions (concrete clear cover, C; rebar diameter, ; and anodic length, L). In this equation Xcrit is proportional to the first power of C/ and to the higher power of [C/L+1]. Quantitative determinations of the development and magnitude of stresses produced by corroding steel in concrete have been obtained. Estimated pressures at the steel/concrete interface for C/ > 3 reached values comparable to the concrete compressive strength. The potential use of a fracture-energy-based model to predict Xcrit was supported by indications of approximate agreement between estimates of the work of corrosion expansion and the energy required to crack the concrete.

The corrosion resistance of cracked concrete specimens reinforced with bare, stainless, or galvanized steel plates are compared with the corrosion behavior of bare steel reinforcement embedded in concrete specimens coated with a flexible polymer--cement based mortar both before and after specimen cracking. The results in terms of corrosion electrochemical potential and short-circuit electric current measured on the different steel reinforcements are also compared with those related to galvanized reinforcement embedded in hydrophobic concrete specimens. Reinforced concrete specimens were manufactured for each protection method considered and cured before exposure to the test environments. Some specimens were previously cracked by applying flexural stress. The specimens were exposed to increasingly aggressive environments; forty days of full immersion in a 3.5% NaCl solution, simulating a marine environment, were followed by five months of wet-dry cycles using a 10% NaCl solution, simulating a bridge deck treated with deicing salts. The results for the full immersion condition show that negligible corrosion rates were detected in all the cracked specimens, except those treated with the flexible polymer-cement mortar before specimen cracking and the hydrophobic concrete specimens. On the other hand, for the cracked specimens exposed to wet-dry cycles, high corrosion rates were measured for both bare and galvanized steel reinforcement. This was in contrast to the constantly good behavior of stainless steel reinforcement and also of the galvanized steel reinforcement embedded in the hydrophobic concrete.

To evaluate the degree of corrosion, reinforcements of a fourteen-year-old concrete member were completely bared. The 3-meter long beams were stored in 3-point flexion in an aggressive environment made by sequences of drying and wetting by a salt fog (35g/l). The total chloride content was also measured at the level of all reinforcements. Because of the small concrete cover (10 mm for the stirrups and 16 mm for the longitudinal reinforcement), the chloride content appears to be significantly greater than the threshold usually used to evaluate the initiation of corrosion. Carbonation front was also measured and was only about 4 mm. Nevertheless, the degree of corrosion (mass loss calculation) shows no correlation with chloride content, as some large parts of reinforcement are not affected by corrosion. As a result, corrosion damage seems to be linked to a degradation of the steel-concrete interface. For tensile reinforcement, it corresponds to a mechanical degradation whereas for compression reinforcement it corresponds to the bleeding. This observation leads us to question ourselves about the relevance of a single value for the corrosion threshold. The nature of the interface between the steel and the concrete must be considered.

Over the past decades, numerous laboratory studies have clearly indicated that the use of supplementary cementing materials, and particularly fly ash, can significantly reduce the scaling durability of properly air-entrained concrete. Despite the great deal of research done on the topic, the reasons behind the detrimental influence of fly ash remain unclear. In order to bring more information on the subject, an investigation of the influence of fly ahs on the deicer salt scaling resistance of concrete has been recently carried out. Test variables include water/binder ratio (.40, .50 and .66), class of fly ash (two class C and a class CF), and the percentage of replacement of the cement by the fly ash (, 20 and 40%). An additional series of mixtures was prepared with 25% slag as cement replacement. All deicer salt scaling tests were performed according to a modified version of ASTM C 672 on both troweled and sawed surfaces. The air-void characteristics of all mixtures were determined according to ASTM C 457, and the microstructure of selected mixtures was studied by mans of SEM observations. All test results confirmed that the use of fly ash and slag can reduce the salt scaling durability of concrete as determined in the laboratory. The influence of fly ash and slag does not appear to be linked to their effect on the material pore structure. An explanation linked to its influence on the characteristics of the air-void network is suggested.