International Concrete Abstracts Portal

Alkali-aggregate reaction (AAR) affects some civil engineering structures and is responsible for unrecoverable swelling and cracking that can affect their functional capability. Modelling the behavior of concrete subjected to AAR is complex. The difficulty is linked to the number of parameters that govern such chemical processes. In order to control the safety level and the maintenance costs of degraded structures, a realistic prediction of the mechanical impact of AAR is compulsory. The aim of this work is to present a new strain visco-elasto-plastic orthotropic damage model including chemical pressure induced by AAR. Experimental results were used to verify the capability of the model to describe the mechanical behavior of degraded structures under different external loading conditions.

The penetration of chloride through cement-based materials is of great importance because chlorides are one of the main agents contributing to the corrosion of reinforcing bars in concrete. The concrete must act as a barrier that protects the reinforcing steel. Thus, the durability of the structure depends on the transport properties of concrete.This work documents the issue of chloride penetration through CEM-I concrete structures. Immersion tests have been carried out with a sodium chloride solution. Several times of exposure are tested along with the influence of the material age on the chloride ingress. Additionally it is shown through a numerical model how a multi-species description of the ionic transport contributes to the prediction of chloride penetration.

This paper reports results of a study conducted to assess the effect of chloride concentration on initiation and propagation of reinforcement corrosion. Since it is expected that the tolerable chloride concentration will vary with the type of cement, the combined effect of cement type and the chloride concentration on reinforcement corrosion was evaluated. Concrete specimens were prepared with Type I, Type V, and silica fume blended cements and they were exposed to sodium chloride solutions with varying chloride concentration. Reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. After two years of exposure, the reinforcing steel bars were removed from the concrete specimens and they were examined for the extent of corrosion and the gravimetric weight loss was determined. The electrochemical and gravimetric weight loss measurements indicated a good correlation between the chloride concentration in the exposure solution and the corrosion activity. The time to initiation of reinforcement corrosion and its rate were influenced by the type of cement and the chloride concentration in the exposure solution. Least reinforcement corrosion was noted in the silica fume blended cement concrete specimens followed by Type I and Type V cement concrete specimens.

Water is generally accepted to be one of the main factors affecting Alkali-Silica Reactions (ASR) in concrete. The water content in ASR affected structures is normally expressed as relative humidity (RH). However, the measurement of RH is notoriously very difficult and uncertain, particularly in the field. The degree of capillary saturation (DCS) may be a more suitable parameter to characterize the water content and the progress of damage on structures due to ASR. The relation between the RH in concrete and the DCS varies depending on several factors, where the water/binder-ratio is the most important one. For more than 100 Norwegian concrete structures the DCS has been determined on specimens cut from drilled concrete cores, according to a special procedure. The water content has been determined at depths in the range from about 100 to 400 mm from the surface, depth ranges where it is considered to be rather stable and uninfluenced by seasonal changes in the weather. The results show a good correlation between the presence of ASR in a concrete structure and the DCS. With only a few exceptions the degree of capillary saturation of the concretes with pronounced ASR is higher than 90 %. The extent of damages generally increases with increasing water content above this level.

Self compacting concrete (SCC) can be placed without any compaction, avoiding some health risks as well as environmental problems. The two essential properties of SCC are a high flowability and a high segregation resistance, obtained by the use of either a large amount of fine particles (P) or a viscosity modifying admixture and a superplasticizer. Already there is a lot of knowledge about composition and workability of SCC, however there are questions regarding long-term durability due to significant difference in the mix proportions of SCC in comparison to traditional concrete. The degradation mechanisms of cementitious materials are greatly influenced by the penetration ability of aggressive fluids, and there is an important relation between the ‘pore structure’ of solids, fluid transport properties and degradation. If the pore structure of SCC turns out to be different from traditional concrete, some changes in durability behaviour might be expected. An experimental program was set up to study the pore structure of self-compacting concrete. Mercury intrusion porosimetry (MIP) was used as a testing method. As MIP can use only small-size specimens, it is customary to study hardened cement paste specimens with similar W/C ratios and curing ages as in actual concrete. In this study tests were performed on samples of hardened cement paste of several ages in order to evaluate the relative influence of various parameters on both traditional and self compacting concrete mixtures.