The project comes against the background of the DWA’s response to the needs of the communities in Botswana’s north-eastern and central districts. The DWA embarked on the R74-million project in October 2004. “The remoteness of Ntimbale dam and specified strength require-ments for the various concrete structures that made up the entire project varied and that was the reason why PPC Cement’s OPC 42,5N was specified for this pro-ject, as it is a cement ideally suited to a variety of construction applica-tions and is known to consistently achieve the strengths required forprojects of this nature,” says Muir-head.
He adds that the contractors required a 20 Mpa strength for the mass concrete, skin concrete and the ogee spillway. The dental concrete, valve chamber, retaining walls, outlet works and parapet walls required a 30 Mpa strength. “The roller-compacted concrete dam wall required a 20 Mpa strength and the nonrunoff sectionsof the dam wall had to achieve a 15 Mpa strength,” explains Muir-head. The contractor established an on-site batching plant and made use of 53-mm crushed aggregate for the concrete mix design. PPC Cement has been supplying its cement products to the Botswana market for almost a century, predominantly from its slurry and Zimbabwe factories. In 1996, however, the company decided to establish its blending and packing plant in Gaborone and, in so doing, has continued to support infrastructure development in Botswana. Muirhead says water supplies in north-eastern Botswana have been erratic for many years and, consequently, these areas have not been spared the ravages of the dry spells experienced in the region.