International Concrete Abstracts Portal

The alkali-silica reaction (ASR) was recognized by Stanton in 1940 and is still today a world-wide problem. The basic reaction mechanisms are reasonably well understood and in many cases a prevention of the ASR is possible. However, there are still severe damages on concrete structures caused by alkali-silica reaction, especially related to slow/late aggregates. This paper presents the experiences with the German Alkali-Guideline during the past decades in Germany and introduces latest approaches in developing forward-looking test methods to assess the durability of concrete regarding ASR due to alkali-reactive slow/late aggregates. The emphasis is particularly placed on assessing the influence of an external alkali supply, i.e. the impact of de-icing solutions, on pavement concretes. For this purpose the cyclic climate storage was used and proved as appropriate method.

The expansion of laboratory heat-cured mortar and concrete specimens caused by delayed ettringite formation (DEF) is often the object of scientific investigation. However, cases of this expansion in normally-cured concrete are rarely reported in the literature. The results presented in this paper show that concretes made with a relatively moderate cement content of 300 kg/m3 can develop a temperature as high as 72 °C at the centre of massive elements, and that in such a case, it can be vulnerable to DEF and subsequent expansion. Four concrete mixtures made with different commercial cements having a W/C of 0.55, were used for casting cubic concrete samples measuring 0.2 m3. The temperature of fresh concrete was 30 °C. The maximum temperature developed at the centre of the samples varied between 64 and 72 °C. After 400 days of storage in lime-saturated water, two samples showed a significant expansion. One sample was severely cracked. This experiment shows that DEF-related expansion is not possible only in steam-cured precast concrete members, but that cast in-place massive concrete structures in hot climatic conditions can also be sensitive to DEF.

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.