The bulk density of ordinary concrete is about 23 kN/m3. The concrete having bulk density between 5 to 18 kN/m3 is known as lightweight concrete and it is prepared from the following materials:
- Binding material: The ordinary Portland cement and its 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.
- 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.
- Steel: The lightweight concrete is highly porous and hence it leads to the corrosion of reinforcement, if not properly protected. Hence, the lightweight 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.
- 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 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.