Lightweight Concrete

The bulk density of ordinary concrete is about 23 kN/m3 is known as the lightweight concrete and it is prepared form the following materials:

(1) Binding material: The ordinary Portland cement and it varieties can be used as binding material. If local binding material such as lime-slag, lime-cinder, etc. is available, the same can also be adopted as the binding material.

(2) Aggregates: For lightweight concrete, the loose porous materials are used as the aggregates. The natural porous aggregates can be obtained by crushing lightweight rocks. The artificial porous aggregates can be obtained from industrial wastes.

(3) Steel: The lightweight concrete is highly porous and hence it leads to the corrosion of reinforcement, if not properly protected. Hence the light weight concrete should be made adequately dense when used for R.C.C. work. Sometimes the reinforcement is coated with anti-corrosive compounds, when lightweight concrete is adopted.

(4) Water: It is necessary to use pure drinking water to prepare lightweight concrete. The strength of lightweight concrete mainly depends on the amount of water in the mix. The water-cement ratio for achieving optimum strength of lightweight concrete should be carefully worked out. As water content reaches to its optimum value, there is corresponding increase in the strength of lightweight concrete.

Following are the advantages of lightweight concrete:


(1) The local industrial waste, if found suitable for lightweight concrete, can be economically utilized.

(2) The reduction in weight of concrete helps easy removal, transport and erection of pre-cast products.

(3) The use of lightweight concrete results in the reduction of cost to the extent of about 30 to 40% or

The only drawback of lightweight concrete is that the depth of carbonation i.e. the depth within which corrosion can occur under suitable conditions is nearly twice than that of normal concrete. Hence special are will have to be taken to provide sufficient cover to the reinforcement of the lightweight structures to grant protection against corrosion.