AfriSam ready-mix concrete used in the construction of the new Brakpan reservoir
The City of Ekurhuleni, as part of a commitment to address water capacity constraints within its region, has embarked on building 29 reservoirs during the period 2018 to 2021. This will see a combined storage capacity of 550 Mℓ being added to the infrastructure.
The construction of a new reservoir at Sallies Village in Brakpan, adjacent to the existing reservoir, has commenced. When completed, the 18- Mℓ reservoir will be 8.2 m in height with a diameter of 60 m and a slightly sloped concrete roof, according to the project specifications issued by implementing agent the Development Bank of Southern Africa. Ancillary works include a perimeter fence, new access road, chambers and guardhouse. Elements where concrete is specifically required include the strip footings, walls, column bases, columns, column heads and roof.
Superway Construction won the contract for the construction of the new reservoir and AfriSam secured the contract to supply 2 500 m3 of ready-mix concrete. All concrete will be supplied according to the consulting engineers’ material specifications for an impermeable water retaining structure.
The reservoir will be constructed in three lifts for the full circumference, ensuring stability for the reservoir walls. Initial planning has commenced for the roof to be poured in a single pour of 630 m3.
The SANS 2001-CC1-2012 specification for the structural concrete used for the project requires fly ash as a supplementary cementitious material (SCM). As the standard operational mix supplied by AfriSam’s Sub-Nigel plant contains slagment, a customised concrete mix changing from slagment to fly ash has been developed.
The slump was initially set at very low levels of between 10 mm and 60 mm but due to concerns related to the specified high minimum binder content, ambient temperatures and the need to pump the concrete, a slump of 125 mm was agreed upon, in accordance with SANS 878 specifications.
The water:cement ratio is calculated to not exceed 0.5, to ensure that the shrinkage specifications of 0.3 mm to 0.45 mm are met. A crystalline water proofer is incorporated into the mix to further enhance permeability properties while a CHRYSO curing compound allows for adequate cementing reactions to aid strength gain, impermeability, abrasion resistance and durability. A well-graded aggregate is used for the special application.
AfriSam's fit-for-purpose custom mix aims to provide a workable mix which accommodates placing techniques and meets project specifications.