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 paper, corrosion-inhibiting admixture systems are classified as active, passive, or passive-active, depending on the mechanism(s) by which corrosion inhibition is achieved. Also, a simple analytical equation that relates chloride ion contents in treated concretes to that in companion untreated concrete is presented. Using this equation, chloride ion content versus screening efficiency curves have been for passive and passive-active inhibitor systems. If chloride ion threshold and chloride screening efficiency data are available, these curves can be used to determine and "equivalent chloride ion threshold" for passive and passive-active inhibitor systems and to compare directly the effectiveness of passive and passive-active inhibitor systems on time-to-corrosion relative to active inhibitor systems. Corrosion test data have been used to show the validity of this analytical procedure. The data show that the procedure can be used to rank the effectiveness of corrosion-inhibiting admixtures in delaying the time-to- corrosion of steel in concrete and that passive and passive-active inhibitor systems can delay the onset of corrosion longer than active inhibitor systems. In combination with corrosion rate data, the relative overall effectiveness of corrosion-inhibiting admixtures can be determined.

Presents the results of laboratory and field tests conducted by the authors over a twelve year period on the long-term durability performance of silica fume based concretes, shotcretes, grouts, and concrete slab overlays. The silica fume mixture proportions varied, from 2 to 22 percent of silica fume by weight of cement, and included normal portland cement, shrinkage compensating cement, normal weight and lightweight aggregates. Laboratory and field specimens were tested for compressive strength, bonding strength, chloride permeability, electrical resistivity, and freezing and thawing durability. The exhibited long-term performance characteristics indicate that silica fume based concretes, shotcretes, and grouts provide excellent protection to embedded reinforcing steel in chloride environments. As the materials age, they become stronger, lower in permeability, and higher in resistivity. Silica fume modified materials produce one of the best cementitious products available for adverse concrete environments.

Silica fume has been available commercially in the United States for over 10 years. Until recently, there has not been a well-accepted consensus specification for it. This paper deals with the question of a specification for silica fume for use in concrete by reviewing the following areas. 1. ASTM and AASHTO efforts to develop a specification for silica fume are described. The author's comments on these documents are presented. 2. The status of international efforts to develop silica fume specifications is reviewed. Work from Australia, Canada, Norway, RILEM, South Africa, and other European countries is reviewed to indicate the direction that is being taken outside the United States. 3. Recommendations, based upon the author's experience with silica fume since its introduction to the United States, for what a specification for silica fume for use in concrete should include are presented. The use of silica fume is increasing every year. Some engineers, particularly those in public agencies, have been hesitant to use the material because of the lack of a standard specification. Most engineers wanting to use silica fume have developed their own specification for silica fume with provisions that may have little or no relationship to the performance of the material in concrete. A consensus needs to be established to increase the confidence of specifiers wanting to use silica fume.