The Hindu 20.01.2010
New concrete promises to increase durability
Staff Reporter
| It is developed by INSWAREB researchers |
VISAKHAPATNAM: A new concrete developed by the Institute of Solid Waste Research and Ecological Balance and Ecological Balance (INSWAREB) here promises to increase the durability of concrete apart from addressing sustainability issues.
Christened ‘No-Aggregate Concrete (NAC)’, the mixture doesn’t contain stone (coarse aggregate) as in the case of conventional concrete. N. Bhanumathidas and Kalidas of INSWAREB claim that preliminary studies have proved that the durability of concrete could be increased by 10 to 20 times with the use of NAC.
The transition zone i.e., the ‘zone of bond’ between the cement matrix and stone (coarse aggregate) results in accumulation of free lime and formation of low density crystals of lime that develop weak links and micro cracks due to tensile shrinkage. Dr. Bhanumathidas and Kalidas feel that avoiding coarse aggregate in concrete, without sacrificing the performance requirements, gives a new definition to concrete that is devoid of transition zone. Fine and coarse aggregate are added to cement to render workability and application.
The researchers claim that the mixture developed at INSWAREB labs doesn’t contain coarse aggregate but uses fly ash as pozzolanic binder and micro aggregate nullifying the role of coarse aggregate. They say the strength of NAC ranges between 40 MPa and 80 MPa, which is two to four times the strength of conventional concrete thus saving money and material.
“Though density of this concrete is around 1,800 kg/cu. m as against 2,400 kg/cu. m. for conventional concrete, the increased strength is achieved to due to microstructure properties and better bonding. The mixture contains cement, fly ash, additives and chemical admixtures,” Mr. Kalidas said.
The differential density would open up new vistas in designing structures resistant to earthquakes. Avoiding the use of coarse aggregate conserves natural stones and saves hillocks and hills. “A 10-foot diameter dome would be constructed by INSWAREB at Sheelanagar for demonstration of NAC. The product developed would be sent to the Ramco Research and Development Centre in Chennai for micro structure studies,” Mr. Kalidas added.
