Concrete

1. It is difficult to imagine modern structure without concrete. Concrete is the very building material which led to great structural innovations. The most important quality of concrete is its property to be formed into large and strong monolithic units. The basic materials for making concrete are cement, aggregate and water. Cement is the most essential and important material for making concrete of high quality. Cement is made of limestone and clay. It is burnt at high temperature and ground up into powder. Depending on the kind and composition of the raw materials different types of cement are obtained. Portland cement, blast furnace cement are suitable for putting up marine structures.

2. Concrete is made by mixing cement, water, sand and gravel in the right amount. As soon as it is thoroughly mixed it is poured into forms that hold it in place until it hardens. Cement starts hardening one hour after the water has been added and the process of hardening lasts for about twenty-eight days. The process is called concrete curing.

3. The characteristics of concrete depend upon the quality of the materials used, grading of the aggregates, proportioning and amount of water. The most important requirements for concrete are: it should be strong, hard, durable, fire-resistant and economical. Concrete may be divided into two classes: mass or plain concrete and reinforced concrete where it is necessary to introduce steel. Plain concrete can be used for almost all kinds of buildings. Reinforced concrete is used for building bridges and arches, dams and dock-walls, for under-water structures, for foundations, columns, beams and so on.

4. At present two types of new building materials are successfully used by our builders: alkali-slag concrete and silica concrete. Silica concrete is light, acid-proof and contains no cement. It is widely used in aviation and in under water constructions.