A2/A282 and the M25 1B-3 Widening Project

A2/A282 and the M25 1B-3 Widening Project

Contractors: Costain Limited
Concrete Supplier: J. Clubb Limited
Volume: 20,000 m3
Admixtures Used: Rheobuild 716, Glenium 123 and Pozzolith 324N
Concrete Description 35.0 N/mm2, 40.0 N/mm2 and 50.0 N/mm2

The A2/A282 Dartford Improvement and M25 Junction 1B-3 Widening scheme was instigated to upgrade these routes and tackle congestion, whilst improving safety and journey time reliability and supporting economic growth. By combining the two elements within one project, abortive work at the interface of the two schemes would be avoided and disruption to road users limited, allowing complete construction within the minimum possible overall period of time and minimizing the overall cost.

Contractor Costain Ltd received an award for Responsible Construction and Site Management from the Environment Awards for Kent Businesses 2006 in recognition of its endeavours to protect wildlife and biodiversity and prevent contamination of water courses. Costain also recycled waste where possible and set up a stakeholder forum to discuss issues.

Concrete containing BASF admixtures was used in the construction of abutments and composite deck and for piling. The concrete contained cement replacements (ground granulated blastfurnace slag) at percentages ranging from 50-70%.

30,000 litres of Glenium 123, a versatile “one-stop” water reducing/superplasticizing admixture, was used at a dosage of 0.50% by weight of total cement. It was specified to provide high compressive strengths (C50+), low water contents and very low water/cement ratios < 0.40 at S3 consistencies as well as pumping ability.

Its compatibility with the CEM 1 and GGBS is an important feature as is the fact that it produces low permeability, chloride resistance concrete. It demonstrated economic/technical benefits compared with previously used admixtures such as Rheobuild 716.

7000 litres of Pozzolith 324N ‘water reducing/plasticizing admixture’ was used at a dosage of 0.40% by weight of cement. Used for medium compressive strengths (C35 & C40), reduced water contents and water/cement ratios of 0,50 at S3 consistence pumped, Pozzolith 324N has provided consistent water reduction and mix stability for mid-range structural concrete.

1000 litres of Rheobuild 716 ‘high range water reducing/superplasticizing admixture’ was used at 1% dosage rate, with benefits similar to Glenium 123, which replaced 716 in the early stages of the contract.

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