International Concrete Abstracts Portal

Discusses the findings from the study of bond that forms a part of a major laboratory evaluation of the characteristics of repair materials carried out in the Building Research Centre. The important properties of repair patching materials that can affect the bond of a repair, such as shrinkage, thermal movement, compressive, shear, and tensile strength, are evaluated. The importance of surface preparation is also discussed.

The durability of concrete is generally regarded as its ability to resist the effects and influences of the environment while performing its desired function. In an offshore or marine environment, the concrete can be subjected to the influences of wetting and drying, freezing and thawing, abrasion by ice and other debris, chemical attack or mineral depletion by water it is in, salt accumulations, and attack by marine organisms. The paper reviews these dteriorating mechanisms and also reviews the recent trends in strength development for concretes made with modern materials. Chloride ion penetration into concrete information from 33-year old Gulf of Mexico offshore concrete platforms is presented. The advantages of supplementary cementing materials in offshore and marine concretes are discussed along with recommendations for producing durable marine concretes.

Low-calcium fly ash (ASTM Class F) is being increasingly incorporated into portland cement concrete as a partial replacement for cement. The replacements commonly used are 15 to 25 percent by weight of cement. CANMET has recently developed concrete in which high volumes of low-calcium fly ash are incorporated with slumps in excess of 150 mm being obtained by the use of large dosages of superplasticizers. Typically, in high-volume fly ash concrete, cement content is kept at about 150 kg/m3 and the water-to-cementitious materiaes ratio is about 0.32. The fly ash content is about 56 per cent by weight of the total cementitious material. This paper presents data on several aspects of durability of this new type of concrete. The aspects discussed include freezing and thawing cycling, resistance to chloride ion diffusion, deicing salt scaling resistance, carbonation, and volume stability. Data on the role of high volumes of fly ash to control alkali-silica reaction in concrete are also presented. It is concluded that, in general, high-volume fly ash concrete has excellent durability characteristics. The only exception is the deicing salt scaling tests, in which the above concrete performs poorly.

The long-term durability of glass fiber reinforced (GFR) mortars and concretes manufactured by the premixing method was investigated. Microhardness measurements and the quantitative back-scattered electron image (BSE) analysis were made in the regions around glass fiber strands embedded in the cement paste. Changes of flexural strength and toughness in the GFR mortars with age were found to be related to the features of microstructure in the interfacial regions. The toughness of the GFR mortars decreased with age in response to the increase in microhardness at the immediate vicinity of strands and around 70 to 100 æm from the interface. The solidification in the regions around 70 to 100 æm from interface, as well as the formation of the hydration products in the spaces among the glass filaments, appear to relate to reduction in toughness in GFRC composites.

Cellulose fiber reinforced cement can provide the highest performance-to-cost ratio among fibrous cement composites considered for the replacement of asbestos cement. Such composites can find applications in the production of thin flat and corrugated cement sheets, nonpressure pipes, and many other thin-sheet cement products. There are, however, concerns regarding the moisture-resistance of cellulose fiber-cement composites. Considerable differences in flexural strength and fracture toughness values are observed when the specimens are tested at different moisture contents. This paper presents the results of a comprehensive experimental study concerned with the effects of moisture content on flexural performance characteristics of cellulose fiber reinforced cement. The cement composites considered in this investigation incorporated 0 percent, 1 percent, and 2 percent mass fractions of kraft pulp. The moisture conditions investigated included oven-dried, air-dried, and saturated. Comprehensive sets of replicated flexural test data were generated and analyzed statistically. Analysis of variance techniques were employed to derive reliable conclusions regarding the moisture-sensitivity of the flexural strength and toughness characteristics of cellulose fiber reinforced cement composites. The results generated in this study indicate signficant effects of moisture content on flexural performance of cellulose fiber reinforced cement. There is a tendency for flexural strength to decrease and flexural toughness to increase with increasing moisture content of the composite material. Microstructural studies indicate that high moisture contents tend to damage the fiber-to-matrix bond strength, leading to changes in failure mechanism that can describe the trends observed in moisture effects on flexural performance of cellulose-cement composites.