SGR sand made from rocks

Ongoing construction of SGR Phase Two (PHOTO Jenipher Wachie)
Are you hoping to sell sand to the Chinese contractor behind the second phase of the Standard Gauge Railway? We have bad news for you.

The contractor has figured out a way of making sand out of the volcanic rocks strewn all over the Rift Valley floor, thus ditching ordinary construction sand.

They call it m-sand and it is produced by crushing rocks, quarry stones or larger aggregates into sand-sized particles.

In making the big shift from river sand to manufactured sand, the contractor hopes to stem the tide of wasting riverine ecosystems across the country. But there are other factors that have made the Chinese contractor ditch river sand.

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With river sand, developers and builders are often at the mercy of unreliable suppliers, price fluctuations, erratic supplies and inconsistent quality.

Wastage is also high for river sand as it has to be sieved on site before use. Sporadic lifting and imposition of bans on sand mining by county governments has further compounded the problem.

According to construction experts, sand accounts for about 35 per cent of the volume of concrete used in the industry. Its demand has recently ballooned as the country rides a real estate boom, leading to plunder of river beds.

Officials from China Communication Construction Company say m-sand will now be used in all the civil works on the 120-kilometre line between Nairobi and Naivasha as well as the intermediate stations in Ongata Rongai, Ngong, Mai Mahiu and Suswa.

“We have almost eliminated river sand in our projects by switching to manufactured-sand. The shift will not only address ecological issues but significantly improve project efficiency,” says Steve Zhao, CCCC Kenya spokesman.

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The officials say using m-sand will not only lower the cost of big projects but also deliver them faster. For example, the 20 pillars erected over Nairobi National Park took only four months to construct.

Reduction in costs emanate from the fact that manufactured sand can be produced in rocks mined closer to construction sites, thus reducing the costs of transportation.

In addition, manufactured sand guarantees a consistent and clean supply since it is free of silt and clay elements, and has denser particle packing than river sand.

Reclaimed quarries

“Land used for quarrying rock can be reclaimed for commercial or residential purposes or used for wetland restoration. Already, we have mined and reclaimed a few quarries around here as per our agreements with the locals,” says Zhao

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Li Guang Ming, the man charged with ensuring that the sand – and the ensuing concrete mix – meets the highest possible standards says the decision to create m-sand was based on the fact that the railway traverses a region endowed with volcanic rocks with the chemical qualities needed to create sand.

As the company’s dean of material testing centre, Ming says the switch is a boon not just to railway construction but can be harnessed to support the government’s mass housing programme under the Big 4 agenda.

When we visited the camp located at Ole Kasasi near Ongata Rongai in Kajiado County, Ming and his colleagues were busy monitoring the computer system that controls the mixing plant.

The plant produces concrete mix as per the demands by the different sections of the railway construction. All the systems here are linked to the company’s head office in Lavington, Nairobi, and can also be monitored from CCCC global offices in China.

“We have tested the rocks and found that they produce high standard sand that bonds well with the other materials. The concrete mix is much better than what you get from river sand,” Ming says.

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Might the new “discovery” replace sand as we know it?

Volcanic rocks, said Ming, are in ample supply in the Rift Valley and are typically considered waste material since people do not use them for any widespread purpose.  

However, he said when mixed with a reduced amount of cement, some volcanic ashes have inherent properties that naturally bind with water and other materials to form cement-like pastes.

When used in concrete mixes, the volcanic ash is known as a supplementary cementing material and can supplement cement on its own. Concrete with volcanic ash can be used for all types of construction projects, he said.

The SGR contractor routinely uses 20 to 35 per cent volcanic ash in concrete mixes. “Cement production takes a lot of energy because high temperatures are involved. Volcanic ash forms under high heat and high pressure. However, nature is kind and does all those chemical reactions for us,” says Zhao.

The firm produces an average of 350 metric tonnes of manufactured sand daily from its plants located in the seven section camps along the Phase 2A corridor. Already, 600,000 metric tonnes of manufactured sand have been utilised on the second phase of the project.

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Standard Gauge RailwayChina Communication Construction Company