International Concrete Abstracts Portal

Copper, nickel and lead slags of Canadian origin have been studied to evaluate the feasibility of their use as partial portland cement replacement in concrete and mine backfill. Pozzolanic activity of the slags was tested in mortars and the corresponding Ca(OH)2 and non-evaporable water contents at the same age were obtained by thermogravimetric analysis. The relationship between pozzolanic activity and glass content, measured by SEM and image analyzer, was assessed as well. It is concluded that non-ferrous slags could be used as partial Portland cement replacement in concrete and mine backfill if Portland cement and transportation costs justify it.

SP91 This contains 78 symposium papers, bringing together the expertise of representatives from industry, government and universities. These volumes present the latest advances in the use of fly ash, silica fume, slag and natural pozzolans in concrete. New technologies are explored to provide ways in which these valuable mineral by-products can best be used to conserve both resources and energy. Case studies include: the effect of fly ash on physical properties of concrete; evaluation of kiln dust in concrete; effect of condensed silica fume on the strength development of concrete, and the influence of slag cement on the water sorptivity of concrete.

This study investigated the accelerated test results of pozzolanic cement concretes. The accelerated test method used is the ASTM C 684-74 Boiling Water Method. The Portland-Pozzolan cement used contains 30% natural pozzolan. The laboratory work involved the production of concrete mixes with cement contents of 300 to 450 kg/m3, water-cement ratios varying between 0.3 and 0.63. Maximum agregate size was chosen to vary between 15 and 40 mm and both gravel and crushed aggregates were used. 28 day compressive strengths ranged from 14.2 to 35.5 MPa. From each concrete mix five 150x300 mm cylinder specimens were cast. Accelerated cure was applied to two specimens cast in covered molds. The other three specimens were cured under standard conditions for 28 days. The production, curing, capping and testing of specimens were in accordance with the relevant standards. Analysis of the results reveal a power type relationship between the accelerated and the standard strength results and the coefficient of correlation was found as 0.967. The linear relationship also gives a high coefficient of correlation (0.963). Using the linear relationship 28-day strengths can be estimated with 2.4 MPa accuracy within 90% confidence limits. The relationship is compared to and found to be in agreement with those proposed by other investigators. However accelerated strengths given by the pozzolanic cement seems to be a little higher than the others.

This paper reports the results of an investigation to develop heat-curing cycles for portland cement/fly ash concrete for use in the precast industry. The fly ash was incorporated into concrete not as a replacement for cement but as a partial replacement for fine aggregate. The variables considered were temperature of curing, preset time and duration of heating. The results of the investigation indicate that portland cement concrete (W/C = 0.40) in which 18% of the fine aggregate has been replaced by fly ash can be heat-cured to accelerate strength development at ages ranging from 12 to 24 h, and compressive strengths of the order of 30 to 45 MPa can be achieved at these ages. Two of the most promising heat-curing cycles for the materials under investigation consist of a 12-h cycle at 90°C with a preset time of 2 h or a 24-h cycle at 55° to 70°C with a preset time of 4 h. However, it is emphasized that each precast concrete producer will have to perform investigations to optimize the heat-curing cycle that best suits his materials and production needs.

As a pozzolan, fly ash has been used to replace some of the portland cement in concrete. Because of its many advan-tages, the use of fly ash in concrete will undoubtedly increase. Although many studies have been conducted on the physical properties of concrete containing fly ash, very little research has been reported on the fatigue properties of fly ash concrete. Since most concrete pavement design procedures currently in use are based on the consideration of concrete fatigue, the importance of fatigue properties of concrete pavement containing fly ash is evident. The purpose of this study was to evaluate the fatigue properties of concretes containing fly ash and compare these properties to those of concrete without fly ash. More than 350 concrete specimens at four levels of cement replacements (0, 25, 50 and 75%) and two types of fly ash (high-calcium and low-calcium) were cured 28 days and subjected to compressive fatigue loading in which the stress varied from essentially zero to a predetermined maximum stress as percentages of the compressive strength. The fatigue strength of concrete containing fly ash was found to vary with both type of fly ash and cement replacement ratio. Concretes with equivalent or higher compressive and fatigue strengths could be obtained with cement replacement of 25% by weight of low-calcium fly ash or 50% by weight of high-calcium fly ash.