Strength and durability studies on silica fume concrete

Abstract

Concrete is the most widely used construction material utilized since time immortal. However, the environmental concerns necessitate a reduction in clinker usage in the construction industry that is possible only by the use of supplementary cementitious materials, called mineral admixtures in the making of concrete. These mineral admixtures, when introduced in the cement system, react with calcium hydroxide to form calcium-silicate-hydrate gel. Some of the examples of mineral admixtures are silica fume, fly ash, slag etc. Each of these mineral admixtures posses different properties. The objective of the present study is to investigate the synergistic effect of using a combination of silica fume and Indian fly ash. This study is necessary because silica fume is expansive in nature, and fly ash is cheap and abundantly available in India. Therefore, use of small proportion of silica fume along with large proportion of Indian fly ash, is expected to provide overall economy without compensating in the desirable properties of concrete. The investigation is divided into two parts. In the first part, the concentration is on the strength aspects of the resultant concrete. The major objective of the first phase of the work is to choose the most suitable combination of silica fume and fly ash to improve strength characteristics of concrete. The investigation is carried out for a wide range of water-to-binder ratios and under variable curing regimes. Three different water-to-binder ratios ranging from high (0.45) to medium (0.35) and then to low (0.25) are used to ensure wide variation in strength. Under each water-to-binder ratio, eight mixes are prepared using various combinations of silica fume and fly ash. Out of the eight mixes, one mix is a control mix with no mineral admixture, three mixes are binary mixes having only one mineral admixture, that is, either silica fume or fly ash; and four mixes are the ternary mixes with different combinations of silica fume and fly ash.