RCC Roller Compacted Concrete in history

RCC roller compacted concreteThe first Roller Compacted Concrete (RCC) dam of the world was Alpe Gera at Sondrio in North Italy. It was executed from 1961 to 1964. The technology in that period is not what it is today. This dam had a total quantity of concrete of 1,800,000 cubic meters of concrete. Concrete feeding to the dumpers moving on dam was done by use of 6 cubic meters skips  moving on an inclined haulage track. This method of construction was found to be expedient then.

With the advent of opening the economy, speedy and economic construction of dams for hydro power and/ or irrigation has become necessity of the day. Though the technology of RCC dams is more than two decades old in India, the first RCC dams for Ghatghar Pumped Storage Hydro Project in Maharashtra has been undertaken in 2001-2002. It was conceived to complete the lower dam of 81 metre height and 390 metre length at the crest in two seasons. However, the learning  curve took more than estimated time and the dam is expected to becompleted in 2006 to 2007 working season.

The concept of RCC involves placement of concrete in  the dam on a continuous basis in layers of 300 mm compacted thickness. The placement rates can be as high as 600 m3 per hour. Since there is no block joint shuttering, the placement of concrete becomes a continuous operation except for breakdown of plant or inclement weather. Some time is taken in provision of galleries and shafts. These however could be minimized by proper overall planning for provision of galleries and shafts.

Prior to the advent of placing conventional concrete by belt conveyors in dams, the methods for placement adopted were use of cableways (radial, luffing and parallel); revolver cranes; hammer-head cranes and tower cranes. When construction of RCC dams was started, placement was done by conveyor belts supported by dumpers, scrappers and dozers. Alternatively, a complete belt conveyor system to have a geometrical coverage of the dam area was designed. This has been evolved by Rotec Industries of Elmhurst, Chicago, USA. This has been used in India in Omkareshwar and Baglihar hydro-electric projects and is going to be deployed for construction of Subansari dam of 2,000,000 cubic meters in the State of Arunachal Pradesh being executed by NHPC. The highlights of the equipment in this layout are use of Tower Belts with geometrical control of 100 m radius and a crane hook load of 25 tons.