ESTABLISHING THE CORRELATION BETWEEN COMPRESSIVE STRENGTH OF SMALL SIZED WET SCREENED CONCRETE CUBES AND FULL SIZE LARGE CONCRETE CUBES FOR MASS CONCRETE OF DAM

Abstract

The concrete used in dams and other structures may vary in character depending on the use of ingredients and site conditions. All concretes generate heat as the cementitious materials hydrate. Most of this heat generation occurs in the first days after placement. For thin concrete sections such as pavements, heat dissipates almost as quickly as it is generated. For thicker concrete sections (mass concrete), heat dissipates more slowly than it is generated. The net result is that mass concrete can get hot. Management of these temperatures is necessary to prevent damage, minimize delays, and meet project specifications. The most effective way to diminish the temperature rise of mass concrete is to reduce the heat generation. This can be achieved by using cement of low heat generation and/or by reducing the cement content. In this regard, the one cost effective method is the choice of the largest possible size of coarse aggregate. For a given weight, higher the maximum size of aggregate, lower is the surface area of coarse aggregates and vice versa. As the surface area decreases, the water demand also decreases to coat the particles and generate workability. Larger maximum size of coarse aggregate requires lesser fine aggregate content to maintain cohesiveness of concrete mix. Because of its lower water demand, advantage of higher maximum size of coarse aggregate can be taken to lower the cement consumption. For quality control during construction, preparation of check specimens for determining compressive strength is necessary. This requirement in case of mass concrete using large size coarse aggregates is difficult to meet because of the lack of laboratory and testing equipment to handle large specimens. Therefore special measures had to be considered from which the “wet-screening” method is the most commonly used one. To determine the relation of compressive strength between the large size cubes and small size cubes, 45cm cubes were cast using actual concrete mix which includes large size aggregates and 15 cm small size cubes were prepared from wet screened concrete mix.