Concreting roads is expected to cut costs and enhance durability
The ministry of works and human settlement (MoWHS) is working on adopting a cementitious-based pavement technology to construct roads in the country instead of conventional bitumen method.
To test and demonstrate the technology, the ministry is paving a 10 km stretch from Yadi to Ngatshang in Mongar with concrete. The work is contracted and about five km has been competed. The Department of Roads (DoR) will pave another 10.5 km from Ngatshang to Korila with concrete.
MoWHS secretary Phuntsho Wangdi said DoR gulps more than 80 percent of the ministry’s budget and it is timely to look at how DoR could optimise the use of scare resources without compromising on quality.
“We would like to adopt this technology because of the benefit in terms of cost, low maintenance, less input of resources and maximum usage of locally produced materials, cement being the main ingredient,” said Phuntsho Wangdi.
This is because for every kilometer of road constructed, the cementitious technology becomes cheaper by Nu 700,000 compared to the conventional bitumen technology.
In the bitumen method, six layers are laid starting with the preparation of sub grade, which also applies for the concrete technology. The second layer is the granular sub base, about 250mm thick made of graded gravel and sand designed to seep water. The base is topped with three layer of water bound macadam, dense bitumen macadam and asphalt concrete. Given the technical specification of the North East-West highway, roads are supposed to be 600mm thick.
However, in the cementitious technology, the third layer is made from soil existing at the site. The soil is mixed with a chemical mixture, pulverized (crushed) with stones, compacted and then compressed. The chemical mixture is designed to suite the soil conditions and its ingredients vary. “It is not something that can be purchased of the shelves,” the secretary said. “The thickness of the road would be same as the bitumen built roads.”
While the chemical mixture is available in India, he said that an equipment called pulveriser is required. The pulveriser would ensure that the chemical reaction and the process completes within 25 minutes after the mixture is poured.
Even with the requirement of the equipment and the need to import the mixture, the secretary said that it is still beneficial and cost saving.
“This technology is meant for marshy areas and sub-zero temperature zones, which is most suitable to our condition. The ride is also more comfortable,” he said.
He claimed that the durability of concrete road is 50 percent higher than the bitumen surfaced road. For instance, the Doebum Lam in Thimphu has already reached its life of eight to 10 years. Should a road of similar thickness be constructed with concrete technology, its life span would be extended to 13-15 years.
Besides the initial capital requirements, cost saving, Phuntsho Wangdi said would also come from the maintenance and repair. Over a period of 30 years, he said the bitumen built roads would require at least four periodic maintenances, each costing Nu 16.9M a KM. However the concrete method was found to require at the most two treatments, and the cost being cheaper by Nu 700,000 a km, saving the national coffer Nu 1.4B a year.
These figures are based on the average cost the DoR incurs in repairing existing roads throughout the country. The figures are also derived from the Bhutan Schedule of Rates (BSR) 2017 instead of the contractors’ estimates because it was found that contractors usually quoted 20-30 percent lower than the actual cost.
While all resources used in the concrete method are available at home, the country will have to import the chemical mixture. The secretary said that it would be more beneficial to have a factory set up in the country and that plans are underway. But the country must have at least 50 km of road constructions a year for the factory to breakeven. “This will take some time,” he said.
The stretch between Yadi and Korila was chosen to test the new technology as it caters to three different soil conditions. “Yadi is hot, Ngatshang is moist and Korila is cold,” Phuntsho Wangdi said. “But the main reason is that all components of the East-West road are already tendered.”