Technical investigations revealed that the concrete supplied by Lafarge Tarmac to Costain contained inclusion of calcined dolomite – that is burnt or partially burnt dolomite. When exposed to water, calcined dolomite is subject to an expansive reaction that causes spalling.
Costain used the contaminated concrete for barriers on its £225m contract to upgrade the M1 to managed motorway between junctions 28 and 31 for Highway England.
In response to a freedom of information request, Highway England disclosed: “Last year a small amount of burnt lime from an on-site kiln cross-contaminated the material used to make the concrete. The lime eventually became wet, and when wet lime causes parts of the concrete’s surface to expand and break off. The contractor is working with the original concrete supplier to carry out remedial work at no direct cost to Highways England. We are not party to financial arrangements between the contractor and their supplier and in consequence do not hold information on the cost incurred by these works, which in any case is not being imposed on the taxpayer.
“Although we have had to resequence works taking place in the area affected, the overall duration of the works is unchanged and we remain on course to complete the works between Junctions 28 and 31 towards the end of the year.
“The suppliers concerned have put rigorous testing procedures in place, and we’re checking our processes to prevent a recurrence. The problem of cross contamination in the material has been identified, and we have established new processes to ensure that this will not happen again.”
Lafarge Tarmac’s own investigation found that the source of the problem was its Whitwell Quarry concrete plant. The primary crusher at Whitwell Quarry had been out of action at the time due to a motor failure so some reclaimed aggregate was mixed in to stockpiled aggregate, resulting in “deleterious material in the form of calcined dolomite entering the concrete aggregate manufacturing process”.
One other construction project, not related to Highways England, was also affected by the contaminated material and investigated, but details of this were redacted from documents released by Highways England.