Crushed Stone Aggregate (Kokoto), by the Truckload

What it is

Kitovu sells crushed stone, known in Tanzania as kokoto, by the full truck in Zanzibar: a big tipper truck, loaded loose, for TZS 1,600,000. Crushed stone is the coarse aggregate of concrete, angular stone broken in a quarry crusher, which carries the load once the cement paste has set around it. It is also laid and compacted as a base under floor slabs, paths and yards.

Price per cubic metre

The price is for the truck. Many sellers quote stone per cubic metre instead, so the card also gives an estimate of about TZS 88,900 per m³: the truck price spread over an assumed 18 m³, the load a big three-axle tipper commonly carries (our calculation). Kitovu has not yet confirmed how many cubic metres its truck holds. Ask for the load in m³ with your order; if it is 15 m³, a cubic metre comes to about TZS 106,700 (our calculation).

The stone size in stock is not in Kitovu’s records yet either. Quarries grade their stone into size bands. In its bulletin on concrete aggregates, E1-16, the American Concrete Institute lists bands like 4.75–19 mm and 19–37.5 mm, and treats anything that stays on a sieve with 4.75 mm openings as coarse aggregate. Ask which size is in the truck. The aggregates page explains the bands and how they are chosen.

How it is used

How large the stone may be is set by the slab and the steel. ACI E1-16 caps the nominal maximum stone size in three ways: a fifth of the narrowest width between the form faces, a third of the slab thickness, and three-quarters of the clear gap between neighbouring bars. Whichever cap is smallest wins. Take a slab 120 mm thick with 30 mm between bars: a third of the thickness allows 40 mm, three-quarters of the gap allows 22.5 mm, so stone of 20 mm or less suits it (our calculation).

Before you order a truck, check the stone size against those limits and against your drawing. A base course under a floor or a yard can take larger stone than a thin reinforced slab.

Volume for a job

A truck of about 18 m³ covers, for example, a hardcore base 15 cm thick over 120 m² (our calculation: 18 ÷ 0.15). Loose stone settles when it is compacted, so a compacted layer takes more stone than its finished volume; the reply on WhatsApp can confirm whether one truck is enough.

With the other materials

Concrete needs cement and sand as well as stone. Kitovu sells Cement for Concrete and Mortar by the bag and Building Sand, by the Truckload in Zanzibar; for a base laid on soft ground, Kitovu’s non-woven geotextile, laid first, keeps the stone from sinking into the soil.