LIGHT WEIGHT CONCRETE

One of the disadvantages of conventional concrete

is the high self weight of concrete. Density of the

normal concrete is in the order of 2200 to 2600 kg/m3.

This heavy self weight will make it to some extent an

uneconomical structural material. Attempts have been

made in the past to reduce the self weight of concrete

to increase the efficiency of concrete as a structural

material. The light-weight concrete as we call is a

concrete whose density varies from 300 to 1850 kg/m3.

There are many advantages of having low density.

It helps in reduction of dead load, increases the

progress of building, and lowers haulage and handling

costs. The weight of a building on the foundation is an

important factor in design, particularly in the case of

weak soil and tall structures. In framed structures, the

beams and columns have to carry load of floors and

walls. If floors and walls are made up of light-weight

concrete it will result in considerable economy. Another

most important characteristic of light-weight concrete is most important characteristic of light-weight concrete is the relatively low thermal conductivity, a property which improves with decreasing density. In

extreme climatic conditions and also in case of buildings where air-conditioning is to be

installed, the use of light-weight concrete with low thermal conductivity will be of considerable

advantage from the point of view of thermal comforts and lower power consumption. The

adoption of light-weight concrete gives an outlet for industrial wastes such as clinker, fly ash,

slag etc. which otherwise create problem for disposal.

Basically there is only one method for making concrete light i.e., by the inclusion of air

in concrete. This is achieved in actual practice by three different ways.

(a) By replacing the usual mineral aggregate by cellular porous or light-weight aggregate.

(b) By introducing gas or air bubbles in mortar. This is known as aerated concrete.

(c) By omitting sand fraction from the aggregate. This is called ‘no-fines’ concrete.

Light-weight concrete has become more popular in recent years owing to the

tremendous advantages it offers over the conventional concrete. Modern technology and a

better understanding of the concrete has also helped much in the promotion and use of light weight concrete. A particular type of light-weight concrete called structural light-weight

concrete is the one which is comparatively lighter than conventional concrete but at the same

time strong enough to be used for structural purposes. It, therefore, combines the advantages

of normal normal weight concrete and discards the disadvantages of normal weight concrete.

Perhaps this type of concrete will have great future in the years to-come. Out of the three main

groups of light-weight concrete, the light-weight aggregate concrete and aerated concrete

are more often used than the ‘no-fines’ concrete. Light-weight concrete can also be classified

on the purpose for which it is used, such as structural light weight concrete, non-load bearing

concrete and insulating concrete. The aerated concrete which was mainly used for insulating

purposes is now being used for structural purposes sometimes in conjunction with steel

reinforcement. The aerated concrete is more widely manufactured and used in the

Scandinavian countries; whereas in U.K., France, Germany and U.S.A. owing to the

production of large scale artificial industrial light-weight aggregate, light-weight aggregates

concrete is widely used. In some countries the natural dense graded aggregate are either in

short supply or they are available at a considerable distance from the industrial cities. In such

cases the use of locally produced light-weight aggregates in the city area offers more

economical solutions. These factors have led to the development and widespread use of

considerable varieties of industrial light-weight aggregates of varying quality by trade names

such as Leca (expanded clay), Aglite (expanded shale), Lytag (sintered pulverised fuel ash),

Haydite (expanded shale).