International Concrete Abstracts Portal

Cement-based composites are used in the construction of a wide range of structures. During their service life, many of these structures are exposed to various types of aggression; their durability is generally controlled by their diffusivity and permeability of the cement-based composite. Since the assessment of these two properties by laboratory or in situ tests is often difficult and generally time-consuming, a great deal of effort has been made towards developing microstructure-based models to predict them. A critical review of the most recent developments in this field is presented in this paper. The report begins with a survey of the various mathematical concepts developed to characterize the structure of porous media. Empirical and physical models are reviewed in separate sections. Special emphasis is placed on recent innovations in the field of numerical and digital image analysis based modeling. Each model is evaluated on the basis of its ability to predict the mass transport properties of a wide range of cement-based composites and its potential application to the study of other micro- and macro-structural properties.

Presents basic information on a newly developed electrically conductive concrete. The concrete differs from previous inventions in that both high conductivity and mechanical strength are simultaneously achieved. The electrical and mechanical properties of the conductive concrete developed at Institute for Research in Construction, National Research Council of Canada are given. The material has superior electrical conductivity values and excellent mechanical strength. Experimental results of a laboratory-scale study on the application of conductive concrete to deicing and/or snow melting are presented in this paper. The results indicate that heat can be uniformly produced by the conductive concrete heating element when the element is activated by an external electric power supply. The new method is effective for deicing purposes. Power output of the conductive concrete heating element is stable over a wide range of temperature. The minimum heater power output required for deicing at various air temperatures was determined. This value is linearly dependent on the air temperature, ranging from 150 to 855 W/m 2 as air temperature varies from -5 C to -30 C.

SP-154 In 1995, The Canadian Centre for Mineral and Energy Technology (CANMET), in association with the American Concrete Institute and other organizations sponsored a second conference on Advances in Concrete Technology. The objectives of this conference was to bring together representatives from industry, universities, and government agencies to present the latest information and explore new areas of needed research and development. Thirty two papers from 20 countries were reviewed and accepted for inclusion in this new publication based on the symposium subject, advances in concrete technology. The range of subjects is varied due to the wide range of experts involved in this project.

The resistance of rice hull ash (RHA) concrete to freezing and thawing in saline environment was studied in the laboratory, for non-air- entrained high performance and normal concrete. The Swedish standard test for concrete resistance to freezing and thawing in saline environment was used. Although the number of tests was limited, the results were very promising for the use of RHA in non-air-entrained normal or high performance concrete. The laboratory salt scaling for concrete with 15 to 30 percent replacement of portland cement with RHA indicated that RHA concrete without air entrainment would be fairly resistant to freezing and thawing in most applications except for in very severe climates. No indications on an accelerated scaling rate over time was observed for RHA concrete, as opposed to the accelerated scaling rate found for a non-air-entrained high performance silica fume concrete tested.

Electrochemical chloride removal was applied to a concrete test area of about 36 m 2 in a reinforced concrete hall which had been used for more than 10 years as a depot for deicing salt, in an attempt to extract the chloride that had penetrated into it. Since the salt had been stored loosely and the interior of the hall was frequently exposed to outside air, the concrete was heavily contaminated by chloride (up to about 15 percent Cl - in cement). Chloride removal was performed with an average current density of 1 A/m 2 for a period of 132 days. The studies were aimed at determining the changes in total chloride content and the Cl - and OH - concentrations of the pore solution at varying concrete depths. It was shown that the efficiency of chloride removal decreased in the concrete cover with increasing depth and that it was least efficient near the reinforcement. The factor that was identified as being responsible for this was the change in OH - concentration of the pore solution that had been caused by reactions at the electrodes. The OH - concentration of the pore solution decreased in the area close to the surface during treatment, while it rose dramatically around the reinforcement (up to approximately 2.5 mol OH -/L). This resulted in an increase of the Chloride Transference Number and, thus, the efficiency of chloride removal close to the concrete surface, as well as a drastic decrease close to the reinforcement. Hence, a reduction of the Cl - to "harmless" levels was not possible in this particular case. However, practice has shown that in many cases such a reduction can be achieved as chloride contamination is normally much less severe; thus, most of the chloride can be extracted from the reinforcement area before the rising Cl -concentration of the pore solution has diminished the efficiency of chloride removal. If, however, chloride has penetrated beyond the reinforcement, it can be removed to a limited extent only.