Early strength concrete at Scottish water treatment works

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When Scottish Water began a challenging project to build a water treatment works to supply the whole of Edinburgh, the water company’s design and build partner Black & Veatch turned to Tarmac Limited to provide a steady supply of high-quality ready-mix concrete to carry out the work.

Bryan Mackie, construction manager for the project at Black & Veatch said: “The initial difficulty we faced in construction of the treatment building and storage tanks was that they involved regular concrete pouring in high volumes. We required a concrete supplier who could provide a high-quality product and guarantee the security of supply.”

Black & Veatch needed 55,000 m³ of concrete to Scottish Water’s specification to be supplied over 18 months and called upon Tarmac to produce and deliver the material.  

Meeting quality and performance standards

To comply with the latest drinking water quality standards and to ensure that the concrete met the performance demands of Scottish Water, Tarmac is largely supplying two types of ready mix concrete for the works; 34,000m³ of compressive strength class C28/35 and 9,000 m³ of compressive strength class C40/50.

The C28/35 is a CIIIA blended cement and is typically specified for water retaining structures, with a minimum cement content of 325kg per cubic metre and a water/cement ratio of 0.50.

The 9,000m³ of C40/50 CEM I concrete has been specified for the roof of the underground water treatment works, as its properties as a virgin concrete mean that it gains strength more quickly than the C28/35 and will ultimately speed up construction. C40/50 concrete has a minimum cement content of 440kg per cubic metre and a water/cement ratio of 0.45.

Tarmac was also required to supply specialist Toproc Early Strength (ES) concrete and light-density concrete as solutions to some of the projects challenges. Toproc ES was specified as Black & Veatch required an extremely high early-strength concrete to allow them access to areas that they would otherwise not have been able to reach with a slow-drying concrete. Toproc ES typically offers a 24 hour strength in the range of 30 to 40N/mm² and a typical 28 day strength of 70 to 90 N/mm.

The light-density concrete was required to reduce the overall weight of the roof structure with no loss of strength. It is a CIIIA blended cement with a compressive strength class of LC20/22 (22N/mm² strength), a minimum cement content of 400kg per cubic metre and a target workability of S4.

See more on Toproc ES

1 April 2010

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