Roller compacted concrete, a radical change of technology, would make up for lost time

Hydropower: The hydropower sector is mulling over adopting the methodology of roller compacted concrete (RCC) for the dam construction of Punatsangchhu-I hydroelectric project.

Prime Minister Tshering Tobgay, while discussing hydropower during his recent visit to India, brought up the issue when he met with the Indian minister of power, Piyush Goyal, in Delhi.

The decision comes at a time when the project is running about two years behind schedule.  Economic affairs minister, Norbu Wangchuk, said the adoption of RCC is a big shift of technology.

“We need to get experts’ views on this, which is why we’ve proposed to the government of India (GoI) to examine whether the new methodology of RCC could go ahead,” he said.

Lyonpo said that cyclone Aila (in 2009) had already delayed the project by one year, and the right bank landslide of Punatsangchhu further added another year to the delay.

“We’re working on correcting the right bank slide of the river and works are almost complete. So, the project is now running two years behind schedule,” he said.

Therefore, because of the strengthening measure that has to be put in place, lyonpo said the nature of excavation work compelled them to look into a different method of constructing the dam.

Generally, there are two methods of constructing a dam.  One is the conventional way through conventional vibrated concrete (CVC), while the other option would be to adopt the RCC method.

Under CVC methodology, blocks are placed and concreted with cement, aggregate, earth, sand and other common additives.  However, CVC is time consuming, because the heat that the cement generates need to be dissipated.  This means, the cement takes more time to dry up.

“The blocks have to be placed and we have to wait for it to dry up. Then, another level of blocks would be placed and we need to wait again; the process continues,” said lyonpo.

Quite similar to CVC, RCC is a special blend of concrete with similar ingredients but uses fly ash and much lesser water.  Hence, RCC is much drier.

“With RCC, our estimate is that it would save us 13 months. This is a huge potential advantage that we could have,” lyonpo said. “We’ve asked GoI to carry out the examination as soon as possible and come up with a decision so that the project could move ahead.”

Works on the 1200MW Punatsangchhu-I hydroelectric project commenced in November 2008 and was initially expected to commission by November 2016.

In July 2013, it was found that the right bank of the project site had sunk, with the loose rock-face gradually moving down to the base of the dam site being excavated.  The incident extended the commission date by another one year.

While the revised estimated budget stands at Nu 94B, remedial measures for the right bank landslide would cost the project an additional amount of Nu 3.5B.

Tshering Wangdi