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Construction : Feature | December 2018 | Source : CW-India

OPC cement, fly-ash and GGBS adding to strength and quality of concrete in world's leading projects

A concrete breakwater in the Mediterranean Sea constructed by the Romans 2,000 years ago, preserved till date, has been found to have been made of volcanic rock or ash and lime, observes Anil Kumar Pillai, Senior Deputy General Manager, Technical Services, The Ramco Cements.

More recently, in the construction of the Petronas Twin Towers, a combination of silica fume and fly-ash helped achieve 100 MPa concrete strengths, says N Kalidas, Director, Institute for Solid Waste Research & Ecological Balance (INSWAREB).

HCC has made effective use of fly-ash for several projects such as the Delhi-Faridabad elevated highway, the Parama Island flyover in Kolkata and the Bandra-Worli Sea Link in Mumbai.

"We are currently using fly-ash for our Rajasthan Atomic Power Station project, the Tarapur Nuclear Power project and the Mumbai Metro Line-3 project, where we have managed to replace OPC with fly-ash by up to 35 per cent, with the same end result," shares Sanjay Dave, Vice President and Sector Head, Engineering Management (CEMG), HCC.

Dave cites reduced permeability to water and aggressive chemicals as the most important benefit of fly-ash. "Concrete made with fly-ash when properly cured has smaller pores, and hence, creates a denser, less permeable and stronger product. Also, since it produces less heat of hydration compared to OPC, it results in a more controlled mix for construction. At just one-third cost of regular OPC, fly-ash has also helped achieve considerable cost saving."

Concrete manufacturers use both pozzolanic as well as non-pozzolans such as ground-granulated blast-furnace slag (GGBS).

"We use OPC cement, fly-ash and GGBS to manufacture concrete in various formulations, all aimed at ensuring the longevity of the structure," says Anil Banchhor, Managing Director & CEO, RDC Concrete (India).

"We use OPC cement and GGBS in an equal ratio to make ready-mix concrete," says Kiran D'Souza, Sales Manager, RMX Concrete India. While he acknowledges that fly-ash is a popular, readily available additive that helps offer concrete at more competitive prices, he cautions "the utility of fly-ash depends on the availability of high quality material with minimal carbon content.

In the absence of quality fly-ash, we prefer to use GGBS to control the quality of concrete."

According to Ashwani Pahuja, Chief Sustainability Officer, Dalmia Cement (Bharat), making concrete of blended cement costs 7-8 per cent less than relying on OPC alone. For customers, the cost of concrete is generally comparable to regular cement, however, there are added advantages of improved durability.

- CHARU BAHRI

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