Repairing Hinkley B

Work involved completing more than 300 significant repairs over a six-month period in 2018. The project used AkzoNobel’s range of Intercrete concrete repair materials. It followed a programme work undertake by CSC Services a year earlier.

Hinkley Point B, located in Bridgewater, Somerset, started construction in 1967. It was the first UK advanced-gas-cooled reactor to start generating electricity. The 965MW unit is expected to continue operating until 2023 when it is expected to enter the decommissioing phase.

With widespread areas of spalled reinforced concrete across the power station, planning aimed to mitigate potential health and safety issues and minimise impact on plant reliability. The concrete had spalled due to the age of the buildings and their environmental exposure. There were also some areas where water ingress had accelerated degradation.

CSC Services explained that the defective concrete was broken out to allow for exposed reinforcement to be prepared and treated. First, Intercrete 4871, formerly known as Steel Reinforcement Protector 841, was used to protect the steel rebars. Then, Intercrete concrete repair mortars were applied. "Intercrete 4871 forms a highly alkaline coating which not only protects the steel from aggressive acid gases, moisture and chlorides, but passivates the steel surface chemically to prevent further rust formation," CSC said.

Intercrete 4801 (formerly Monomix HD) was the material used for the concrete repair work. It is a high-strength, waterproof, class R4 structural repair mortar that can be used for repair, rendering and profiling of vertical, overhead and horizontal surfaces. The high bond strength of the material exceeds the tensile strength of concrete and its dense matrix offers low permeability to water, even at pressures of 10 bar. It also has high diffusion resistance to acid gases and chloride ions.

For the structural waterproofing, Intercrete 4841 was specified. This a high performance, two component, waterborne cementitious modified polymer coating that provides reinstatement of effective cover on precast and in-situ reinforced concrete. This enhances durability to achieve specified design life. CSC Services says a 2mm application of Intercrete 4841 is equivalent to 100mm of good quality concrete. It forms a hard, highly alkaline coating which protects concrete from the effects of aggressive acid gases, moisture and chlorides, and also enhances chemical resistance. Independent testing carried out at the VINCI Construction Technology Centre in Bedfordshire has confirmed that Intercrete 4841 can provide an effective barrier to chlorides for at least 30 years.

The repair works completed by CSC at Hinkley Point B come was carried out in accordance with BS EN 1504, the pan European standard for concrete repair.