International Concrete Abstracts Portal

Corrosion of steel reinforcements in concrete structures is the most important cause of premature failure. To improve service life of concrete structures, corrosion inhibitors are often proposed and used to prevent chloride induced corrosion and carbonation corrosion. This paper deals with a laboratory investigation both in concrete and in a synthetic pore solution on the effectiveness of mixed-in commercial corrosion inhibitors to hinder corrosion initiation and propagation of reinforcements in concrete structures. The results of a laboratory research aimed at studying the effect of inhibitors added to the concrete mixture are discussed. Three organic commercial corrosion inhibitors and, by comparison, nitrite based inhibitors were added to fresh concrete in concentration suggested by the manufacturers. Experimental tests were carried out on reinforced concrete specimens with carbon steel reinforcement in chloride contaminated concrete (both adding chlorides directly in the mixture and penetrating the hardened concrete by means of ponding cycles). In order to study the inhibitors effect, the results, in terms of two electrochemical parameters, i.e. free corrosion potential and polarisation resistance, are compared with those obtained considering concrete specimens without inhibitors. For comparison purposes, results on some pure organic substances are reported, confirming data obtained on the commercial products. Some positive effects are achieved when both commercial products and pure substances were used at dosage rates higher than that recommended.

Moisture conditions of concrete are critical factors in the Corrosion of reinforce- ment. In this study, various electrochemical measurements were conducted using reinforcement in concretes with the moisture content adjusted to various values to evaluate the corrosion tendencies of reinforcement, thereby investigating the effect of the moisture conditions of concrete on reinforcement corrosion. The anodic dissolution current was found to increase as the moisture content of concrete increased, increasing the corrosion tendencies of reinforcement. With a relative moisture content of 60% or less, reinforcement corrosion is significantly suppressed even when chloride ions are present at a rate of 5.0 kg/m3. In the range of this study, the critical relative moisture content, above which reinforcement corrosion is significantly accelerated, fell in the range of 50 to 60%.

Since 1988, RILEM has been seeking to establish universally applicable test methods for assessing the alkali-reactivity potential of aggregates. Technical committee TC 106 (1988-2000) published two expansion tests (AAR-2 & AAR-3), following international trials, and started to develop two further procedures (AAR-1 & AAR-4), together with an integrated assessment scheme (AAR-0). Successor committee TC 191-ARP (formed in 2000). comprising members from all parts of the world, is now working to finalise procedures AAR-1 & AAR-4 and additionally has a widened scope, to include carbonate aggregates (AAR-5) and also to seek international consistency in approaches to diagnosis and specification. This paper will review the latest progress of TC 191-ARP and, in particular, will outline the principles behind the petrographical examination procedure (AAR-I), report the findings of the international trial of AAR-4 and describe draft recommendations for assessing carbonate materials. The importance of systematic and reliable diagnosis of deterioration in existing structures will be stressed and the initial guidance of TC 191-ARP explained. Finally, the desirability of a global system for preventing damage to concrete from alkali-reactivity will be advocated and the proposals of TC 191-ARP reviewed. The authors are respectively Secretary and Chairman of TC 191-ARP and previously of TC 106.

Most previous investigations of the influence of curing on the durability-related properties of concrete are confused by the influence of factors associated with the assessment procedure or type of test specimen. This paper presents an experimental investigation in which every attempt was made to eliminate factors that would otherwise mask the real influence of curing. The transport based testing regime developed allowed cover thickness specimens to he tested sequentially for sorptivity, vapour diffusion and gas permeability. Mercury intrusion porosimetry and scanning electron microscopy were used to investigate the effects of curing on microstructure. In spite of the inherent variability associated with transport tests, the testing regime was effective in discriminating between the short-term effects of the different curing regimes on concrete transport properties. Generally, the effect of w/c was more important than the effect of curing.

The behavior of ordinary concrete and high strength concrete under chemical attack was studied over a period of more than 5 years. The concrete specimens were immersed in a variety of chemical solutions including 10%, 5%, 1% and 0.1% ammonium nitrate solutions and simultaneously subjected to different flexural loads with load levels of 0%, 30%, 40% and 50% of their initial flexural strengths. The strength and mass changes of the concrete specimens, and the penetration depths of the attacking ammonium nitrate ions into the specimens were measured. The influence of concentration level of the solution on the bending strengths of the concretes was studied and is dis- cussed on the basis of experimental observations