Dr. Ranga Rao, Structural Consultant

• LWC vs Conventional Concrete - LWC has density around ¼ of that of normal concrete. Reduction in weight is obtained from either from entrained air (foam concrete) or by the use light weight aggregate (in place of stone aggregate) or both. Besides weight reduction, thermal insulation and acoustics are better over conventional concrete.
• Variants of LWC being used in India - Majority of LWC produced is using foaming agents using either autoclaving or normal means with or without fines but without coarse aggregate. Autoclaving has become more popular due to possibility of production of various precast building components.
• Role of LWC in Precast industry - LWC with low density can be used for wall blocks and medium density with strengths around 15-20 MPa for structural panels in precast industry.
• LWC and CLSM - Applications of CLSM are different from LWC as CLSM is more to do for binding less cohesive or cohesionless material. CLSM is often used for stable backfills (stabilized soils etc.) and in some cases as insulation fills where fly ash – cement mixture is used. In some applications of LWC, fly ash – cement mixture with foaming agents are used.
• LWC as Structural Concrete - Use as structural concrete demands strength as per use. Walls require strength of 2.5 to 3.5 MPa while panels require compressive strength in addition to bending strength.

Advantages:

• Appreciable weight reduction
• Easy to transport, cut, shape, profile, etc.
• Better thermal and acoustic insulation
• Range of structural applications
• Improved fire resistance

Disadvantages:

• Breakages are more during transportation
• Adhesion of LWC surface is poor and calls for special adhesives for overlay
• Surface preparation to form key to overlay (such as plastering) is required
• Present form of roof panels requires separate framing to support roof loads while these panels become dead shuttering.

Difference between Foam Concrete, Cellular Concrete, Light Weight Aggregate Concrete and Autoclaved Light Weight Concrete - Cellular Concrete is a cementitious paste of neat cement or cement and fine sand with a multitude of discrete air cells distributed throughout the mixture to create a lightweight consists of mixing a pre-formed foam  or mix-foaming agents mixture into the cement and water slurry. As the concrete hardens, the bubbles disintegrate leaving air voids of similar sizes concrete.

Autoclaving is a special process by which cellular concrete is produced which has higher strength and ideal for precast.

Light weight aggregate concrete is produced using aggregate which is a by-product from slag, etc. in order to reduce weight. It is possible to achieve desired strength with medium densities to suit particular structural applications

Growth of LWC in India - It has promising future, if technical parameters are improved. Medium density concrete may be better over LWC and offers ideal solution to precast components and composite constructions.