Light Weight Concrete - Types and Applications

MC-Bauchemie India Private Limited

The greatest advantage of lightweight concrete is that it maintains most properties of conventional concrete. Mr. Sunny Surlarker, Head of Admixture Division with MC-Bauchemie India Private Limited shares with Built Expressions that it can be used for internal as well as external applications. 

The functional principle of the MC-Foam Generator III

BE: Is lightweight concrete chemically compatible with common additives? What are the additives generally added?

SS: Yes. Lightweight Concrete / foam Concrete is chemically compatible with common additives. There are different types of Lightweight Concrete. Lightweight Concrete is a combination of cement slurry or cement, Lightweight Aggregates and / or sand along with many supplementary cementitious materials like Pulverized Flyash, GGBSF, Metakaolin and/or silica fume to impart mechanical properties and a foaming / aerating additive. Therefore, fillers, plasticizers, accelerators are generally compatible with the LWC to an extent, but efficiency of these materials in the mix design is to be verified prior to use.

BE: What is the difference between Foam Concrete, Cellular Concrete, Light weight Aggregate concrete and Autoclaved Light weight concrete?

SS: Cellular Concrete and Autoclaved Lightweight Concrete are similar technologies involving use of aluminium as an additive to cement sand mortar. The aluminium powder reacts with the free lime and water in the cement sand mortar to generate hydrogen gas, which aerates the mix. The resultant cast mix is then autoclaved / steam cured at high temperature to create a stable Lightweight Concrete. This technology is used primarily in production of masonry units, selected precast building elements like walls, and selected concrete products.

Lightweight Aggregate concrete on the other hand is produced like normal concrete, but use lightweight aggregate and fillers such as pumice, selected slates, shales, coarse GGBSF and or / flyash, silica fume, metakaolin, etc. Concretes using certain stronger lightweight aggregates can be used for structural applications.

The name foam concrete is appropriate, as opposite to foamed concrete, as concrete is not foamed but only preformed foam (using a chemical foaming agent and a foam generator) is added to normal concrete or to a premixed cement slurry or cement and sand mortar or cement with many supplementary cementitious materials to get a lightweight material. This material is primarily used as fill material and does not need steam curing or autoclaving.

BE: What are the advantages and disadvantages of LWC as compared to conventional concrete?

SS: The greatest advantage of lightweight concrete is that it maintains most properties of conventional concrete. It can be used for internal as well as external applications. The production of foam concrete, for example, is relatively simple and does not need special machineries except to produce preformed foam with different foaming agents available.

Few other advantages are enlisted as under:

1. Easy to place and finish
2. Reduction of dead weight of structure
3. Can be precast or cast in situ
4. Excellent insulation – Thermal & Acoustic
5. Lightweight filling material
6. Excellent as underlays in flooring
7. Can be impregnated or coated easily
8. Resistant to fire
9. Nails/fittings can be driven into elements easily
10. Easy to produce cut, saw and carry

Disadvantages of Lightweight Concrete include:

1. Lower Compressive Strengths due to lower density
2. Higher shrinkage Values
3. Higher Porosity
4. High Moisture Transport
5. Slower Drying and Curing Times

BE: Can you briefly describe the role of LWC in Precast industry?

SS: Applications of LWC in the Precast Industry Include Blocks, and Lightweight Elements such as panel walls, lintels, etc. Although applications are limited certain structural Lightweight Concretes may find applications to expand use in precast elements for the building construction industry.

BE: What are the areas in which LWC can be used? Can LWC be used as structural concrete?

SS: Conventionally Lightweight concretes can be used for several non-structural applications as under:

• Backfills
• Light weight blocks, bricks etc.
• Light weight in situ walls
• Filling of cavities in building utilities
• Insulation concrete for roofs before waterproofing.
• Trench reinstatements
• Flooring underlays
• Walls & floors of low cost housing with insulation properties.
• Roofing for low cost housing
• Concretes where thermal insulations are required
• Filling of cavity walls
• Lightweight precast elements for internal & external purposes.

A lot of research is going on for developing structural light weight concretes and development of such high strength, high flexure foam concretes can be of tremendous use to civil engineering industry to enable to reduce weights of structural components. It is reported that foam concretes of nearly 50 MPa are already designed at laboratory levels and it would be a matter of time when the success can be translated to construction sites. This is made possible by use of very low w/c ratio of around 0.3 and supplementary cementations materials like microsilica in slurry form, aluminosilicates, finely ground GGBFS with higher reactivity levels to impart desired mechanical properties.

BE: How do you rate the growth of LWC in India?

SS:  Lightweight Concrete is already being used in decent volumes across India. It finds tremendous application in lightweight masonry units and as fill materials in hollow partition walls, leveling course on terraces and exposed areas, filling sunk portions in bathrooms and the like. It is often used as a substitute to brick-bat coba as a fill material. As a technology, awareness of this field is gradually increasing and will soon find wider applications.