This paper reports results from ASTM C 1012 (sulfate resistance) tests on combinations of fly ash and silica fume with portland cements of varying C3A content. Tests on different types of fly ashes confirm previous findings regarding the effects of fly ash composition. Low-calcium ashes invariably improve the sulfate resistance of mortars made with high-C3A portland cement and generally meet the criteria for high-sulfate resistance provided a sufficient level of replacement is used (e.g. 2 20 to 25% fly ash by mass of cementitious material). Moderate-calcium ashes were generally less effective, but could still be used to produce blended cements of moderate to high sulfate resistance when combined with a high-C3A cement at replacement levels of 20%. High-calcium (i.e. CaO > 20%) fly ashes showed highly variable performance and in many cases replacement levels of 20% to 40% actually lead to increased expansion when compared with high-C3A cement used on its own. Results for a classified ultra fine fly ash indicate improved performance with relatively low levels of ash (e.g. 8 to 16%) producing a high level of resistance when combined with high-C3A cement. It was found that mortars containing moderate to high levels of high-calcium fly ash could be produced to meet the criteria of high-sulfate resistance by using either portland cements of lower C3A content or ternary cement blends containing relatively low levels of silica fume (e.g. 3 to 6% by mass of total cementitious material). However, in view of the highly variable performance observed for mortars containing high-calcium fly ash, the need to test individual combinations of materials is stressed.

Metakaolin is a supplementary cementitious material with pozzolanic properties. Its precursor, kaolin, does not occur in natural conditions as a pure phase but is often mixed in various proportions with many secondary minerals. Two natural clays from the same deposit, mainly composed of kaolinite and quartz have been burnt at a suitable temperature and the resulting calcined products have been blended with laboratory normal portland cement for which the nature of added calcium sulfates as well as free lime content have been varied. Subsequent properties of cement pastes and mortars such as rheology, setting time and compressive strength have been compared. Concurrently, early hydration products have been characterized by means of DSC and combined water content has been evaluated by C02-H20 analyser. The difference of behavior that has been observed as a function of the artificial pozzolan mineralogy and cement chemical parameters is discussed in the frame of the mechanism of early hydration of metakaolin blended cement.

The objective of the study was to evaluate the influence of silica fume on the rate of heat liberation and the accumulated heat in high-performance concretes. Portland cement was replaced by silica fume in amounts from 10 % to 30 % in concretes with water-binder ratios varying between 0.25 to 0.45. A superplasticizer was used to maintain a fluid consistency. The heat of hydration was followed continuously by a semi-adiabatic calorimetric method for 10 days at 20°C. The calorimetric study indicates that the hydration is modified by the presence of silica fume. In the early stages, the silica fume shows a high activity and accelerates the hydration rate compared with the control concrete. The fine silica fume particles provide nucleation sites for hydrate growth. Then the pozzolanic activity takes over and increases the heat of hydration. A substitution of portland cement by 10 % silica fume produces greater cumulative heat of hydration compared with the control concrete.

Autogenous shrinkage and drying shrinkage tests were carried out to determine the shrinkage characteristics of high-strength concrete. Three levels of water-cementitious materials ratios [W/(C+SF) : 20, 30 and 50%], and three levels of silica fume replacement ratios [SF/(C+SF) : 0, 7.5 and 15%] were chosen. The drying shrinkage test with specimens of 1 OxlOx4Ocm under the condition of 20+ 1°C and 6O+ 5%RH started at the age of 7 days or 28 days after the measurement of autogenous shrinkage. The autogenous shrinkage strain was also measured in other specimens until the age of about two years. The autogenous shrinkage strain increased both in its amount and its percentage in the total shrinkage strain with the decrease of W/(C+SF). Almost the same total shrinkage strain was observed after about one year in the specimens under the drying condition independent of the mixture proportions of concrete, the curing method or its period.

Corrosion of reinforcement embedded in concrete is the most common cause of failure in concrete structures. The work is being carried out to investigate the rate and amount of corrosion of steel in concrete where cement is replaced by slag in different proportions. This paper reports a detailed corrosion study, carried out on concrete containing blast furnace slag. The study encompasses slag collected from several premier steel plants in India. Corrosion of steel was examined electrochemically through potentiodynamic study and also by accelerated corrosion study. Micrographic study was also carried out to examine the alteration of pore structure of slag concrete. These studies reveal that increase in slag proportion decreases the rate and amount of corrosion of reinforcement embedded in slag concrete.