Govt backs switch to manufactured sand in construction
Isaac Pinielo | Thursday October 27, 2016 18:00
A workshop held by the Department of Mines in collaboration with Botswana Geoscience in Gaborone this week revealed that the characteristics of mortars and concrete using manufactured sand as fine aggregate are superior when compared to the natural sand as fine aggregate.
According to a principal economic geologist for Botswana Geoscience, Nggie Wantlo compared to the natural sand, manufactured sand is cheaper and stronger.
“Manufactured sand costs around P2,500 per 10 cubic metres while river sand costs P4,000 per 10 cubic metres,” he told delegates at the manufactured sand pitso.
Wantlo also explained that in the past the natural river sand was the cheapest resource of sand, but due to the excessive mining of riverbeds to meet the increasing demand for sand in the construction industry, it has been depleted.
“The studies made in rivers around greater Gaborone have indicated that there is virtually no river sand. This is due to the construction boom in rural and urban areas,” he said. Also, Wantlo noted that the depletion is due to the high extraction rate and low production in the river streams. The consequence of this, according to the geologist, is loss of aquifers, land degradation and the natural beauty of land. As a result, he noted that the government suspended issuing of licences for river sand harvest in hot spots.
“Now the sand available in the riverbeds is very coarse and contains very high percentage of silt and clay. The silt and the clay presence in the sand reduce the strength of the concrete and holds dampness,” Wantlo said.
In order to arrest the situation, he said the Ministry of Mineral Resources, Green Technology and Energy Security has embarked on a project to promote the alternative to natural river sand.
He said this is a natural crisis and urged people to use manufactured sand, which he explained is a purpose-made, fine crushed aggregate produced under controlled conditions from a suitable sound source rock.
The manufactured sand is made from crushed rocks. He stated that most people tend to use crusher dust, which he said is a fine-grained by-product of crushed stones but has a lot of dust, which makes it difficult to trowel.
“Crusher dust dries quickly and hence requires blending with river or pit sands to improve its workability,” he said.
He further noted that unlike manufactured sand crusher dust has a rough texture when used for plastering and uses a lot of water and cement.