May 2016 – Specialist (TSA) Thaumasite Sulphate Attack investigation

May 2016 – Specialist (TSA) Thaumasite Sulphate Attack investigation

Screenshot 2016-07-07 17.09.39Nicholls Colton Group’s specialist work at the Stroudwater Motorway Interchange in Gloucester featured in New Civil Engineer.

Nicholls Colton Group have recently carried out a special investigation to establish the prevalence and extent of thaumasite sulphate attack (TSA) on twelve reinforced concrete bridge piers and their foundations at Stroudwater Interchange, Gloucestershire.

Working from inside specially constructed cofferdams placed around the pier bases, the Nicholls Colton team collected incremental concrete dust samples which were then returned to our UKAS-accredited laboratory for testing. The samples were analysed to determine their sulphate, chloride and cement contents. The sulphate content of the concrete was used to determine the risk TSA posed to the concrete by the ground surrounding the piers. The chloride content was used to evaluate the risk of reinforcement corrosion and the cement content was used to assess the ability of the concrete to resist these aggressive ions.

TSA affects bridges whose buried portions are exposed to earth or backfill which contains large amounts of sulphate ions. These ions attack the calcium aluminate hydrates (C 3 A) in the concrete,
creating expansive sulphoaluminates which soften the concrete and can lead to exposure and corrosion of the reinforcement. TSA is a rare form of sulphate attack and only affects concrete in very wet ground, predominantly in the south west of the UK.

Nicholls Colton Group’s works, which were fitted around the client’s work programme, took place over the course of four weeks. The results were issued within days of the works being carried out to allow decisions to be made in order to progress the project.

The May 2016 edition of New Civil Engineer contains a featured article about this important and specialist project.

You can read the article here http://www.newcivilengineer.com/technical-excellence/how-to- identify-thaumasite- sulphate-attack/10004806.article