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.

In this study, the use of a new permeable sheet was evaluated in making the surface layer of concrete denser, thus improving the performance and durability of the concrete. The application of permeable sheet was confirmed effective in the lowering of water-cement ratio corresponding to the decrease of pore volume; this resulted in the increase of pull-off of tensile strength, rebound number, pulse velocity, and pin penetration resistance in the surface layer. It was also observed that the air bubbles were likely to move from the internal portion to the surface with the expelled flow of water, remarkably reducing bugholes on the concrete surface. The use of new type of permeable sheet improved resistance to freezing and thawing cycling and reduced the depth of carbonation and the ingress of chloride ions. Furthermore, the water tightness was also improved.

In recent years, there has been an increasing demand for high- performance concrete with better workability, higher strength, and greater durability to meet current structural design needs. In Japan, studies of highly flowable concrete with self-compacting properties have been undertaken with the goal of improving reliability of concrete compaction in forms having complicated shapes or densely arranged reinforcement. To produce highly flowable concrete, it is necessary to create high-fluidity concrete by adding a superplasticizer and to eliminate segregation by adding a viscosity-controlling admixture or a large volume of powdered material. It is also necessary to provide the concrete with the ability to pass between the steel reinforcing bars to make it self compacting; this is achieved by controlling the rheological properties of mortar and volume of coarse aggregate. In this paper, the properties of self-compacting concrete are described.

Describes improvements in the performance characteristics of cement- based matrices when reinforced with pitch-based carbon fibers. Under tension and flexure, increases both in strength and strain capacity were reported as a result of fiber reinforcement. Carbon fiber reinforced cement composites were also much more impact resistant that the parent matrix. Under compression, however, no increases either in the compressive strength or in the elastic modulus were noticed. Crack propagation in these composites was characterized using crack growth resistance curves (R-Curves) in which it was demonstrated that carbon fibers lead to a higher resistance to both nucleation and growth of cracks. This paper emphasizes the desired durability characteristics of these composites and discusses their current and future applications.