LWC- Imparting Economic Advantage over Regular Concrete

Mr. Raj Pillai, Executive Director, Concrete Products Division, Sobha Developers Ltd.,

Mr. Raj Pillai, Executive Director, Concrete Products Division, Sobha Developers Ltd. shares exclusively with Built Expressions that the flowable characteristic of Controlled Low Strength Material (CLSM) can be readily placed into tight restricted accesses of areas where placing and compacting is difficult and the general aspects of LWC.

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

RP: The density of LWC is approximately 80% of that of normal weight concrete i.e., LWC density typically ranges between 1440-1840 kg/m3 against 2240-2400 kg/m3 of normal concrete. Therefore the most important advantage of using LWC is the possible decrease in the construction cost due to the reduction in weight of the structure. A good example is the Oakland weigh bridge in San Francisco where an estimated 3 million dollars cost saving was achieved by using LWC in the construction of the upper deck of the bridge.

The LWC also provide good thermal insulation when compared to ordinary concrete and in case of precast concrete structure LWC facilitate easy transport of concrete elements. Some of the advantages and disadvantages of using LWC are as follows:-

Advantages

• Thermal insulation:-LWC has lower thermal conductivity when compared to ordinary concrete.
• Fire resistance:-LWC may protect other structures from the effects of fire due to its low thermal conductivity.
• Sound insulation: - It’s better in LWC.
• Speed of construction: - The construction speed could be faster by using LWC in precast construction.
• Economy: - Saving in reinforcement steel and cement could be obtained that result in reduction of costs.
• Quality Control: - Prefabrication of LWC units can lead to better quality control in construction.

Disadvantages

• One of the major disadvantage of LWC has been the inability to provide consistent compressive strength and density throughout entire area
• Relative Higher cost of production
• Could be fragile in some application
• Production of LWC needs special equipments and are captive in nature
• In lower density ranges LWC does not develop compressive strength of plain concrete

BE: What different types of LWC are being used in India?

RP: Light weight concrete can either be No fines concrete, light weight aggregate concrete, and foam autoclave or aerated concrete.

No fine concrete can be defined as LWC composed of cement and fine aggregate with uniformly disturbed voids throughout its mass. No fine concrete is usually for both load bearing and non load bearing walls for external and partitioned walls.

Light weight aggregate concrete can be produced using a variety of aggregates.

Light weight aggregates originates from either,

• Natural material like vermiculite, pumice etc
• The natural treatment of natural raw material like clay, slate or shale
• Processing of industrial byproducts like slag or fly ash

 Foam Concrete is a highly workable low density material which can incorporate up to 50% entrained air.

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

RP: Aerated concrete is used in precast factories in order to produce concrete with reasonable high strength and low dry shrinkage. LWC have better nailing and sawing properties than heavier and stronger conventional concrete and this property is an advantage in precast industry. Precast LWC sandwich panel offers a lighter system which is critical for construction industry. It provides a quick and efficient system when construction costs are critical or the job site is subjected to harsh construction environments. Precast LWC sandwich panel can be cast in a controlled environment ensuring structural quality and then placed in the field with less labour than in situ wall. These panels not only provide structural and thermal benefits but also provide architectural benefits.

Transportation and placement of elements is a major issue in precast industry and usage of LWC reduces this bottle neck to a larger extent.

BE: How is Light Weight Concrete different from Controlled Low Strength Material (CLSM)?

RP: Controlled Low Strength Material is a self compacted cementitious material used primarily in backfill in Lieu of compacted backfill soil. Many Terms which are currently used in describing this material are flowable fill, controlled density fill, flowable mortar, plastic mortar cement, soil cement slurry, K-crete and other names.

CLSM is defined as a material that results in a compressive strength of 1200 pounds per sq inch (psi) or less. CLSM is composed of water, Portland cement, aggregate and fly ash. It is a fluid material with typical slumps of 10 inches or more. The primary application of CLSM is as a structural fill and backfill in place of compacted soil. The flowable characteristic of CLSM means it can be readily placed in a trench and into tight restricted accesses of areas where placing and compacting is difficult. CLSM also makes an excellent bedding material as well as an ideal pavement base. However applications that require removal of CLSM at a later date usually limit the maximum compressive strength to less than 200 psi. CLSM materials are also not designed to resist freezing and thawing, abrasive or erosive actions or aggressive chemicals. CLSM hardening time can be as short as one hour but can take upto 8 hours depending on mix design and trench conditions.

BE: When used as structural concrete, what are the advantages and disadvantages of LWC?

In building construction longer spans could be designed and additional floors can be added to existing structures when LWC is used. Smaller footings, fewer piles, smaller pile caps and less reinforcing are required by decrease in foundation loads. Thus compared to ordinary concrete many economic advantage can be achieved by use of LWC. In case of bridges, LWC can be used to create longer bridges spans.

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

RP: Construction industry revolves around 5 M i.e., Money, Machine, Manpower, Methodology and Material. In Indian context , the last three M are more critical and especially in case of Materials , where concrete plays an important role, a lot of improvement is necessary and this can be only achieved by using the latest technology in the field of concrete application. LWC can play an important role here and thereby has immense potential for growth.