Chris Lloyd from Flexcrete Technologies gives detail of the concrete protection system provided at London Bridge to enhance durability of the station. London Bridge station, built in the 1830’s, is one of the oldest railway stations in the world. Located South East of London Bridge on the River Thames, it is the fourth busiest station in UK, bringing some 50 million passengers into the capital each year.
London Bridge Station
In November 2011, Costain was awarded a design build contract worth £400m for the redevelopment of the station, involving the provision of a new concourse at street level and improving the entrance and exit points to ease access. The aim is to help enhance the capital’s infrastructure, improve the journeys of thousands of passengers who pass through the station every day and to increase passenger capacity to 75 million passengers annually.
The work being carried out at London Bridge station is said by Network Rail to be the most ambitious redevelopment of any London station in a generation and one of the most technically demanding projects ever undertaken on the UK railway. Once complete in 2018, the new concourse will be bigger than the pitch at Wembley Station with new retail and station facilities, and will unify the station for the first time so that passengers can access all platforms from one place.
The redevelopment of London Bridge station forms a key part of the Government’s £6bn Thameslink Programme, which aims to increase the frequency of trains through the heart of the capital. London Bridge station is vital to unlocking the capacity needed to run up to 24 trains an hour through London, which will in turn help relieve pressure on the London Underground.
With a project of this scale and complexity, the amount of fresh concrete being cast is of high volume and structural mortars and fairing coats have been used to enhance the concrete finish and increase the durability of the construction. Flexcrete Monomix, an advanced, waterproof, low density, class R3 structural mortar, was specified and has helped contribute to rapid construction – a factor which is critical for this project as the station is remaining open and fully operational throughout the complete duration of the redevelopment works to minimise disruption to passengers.
High Strength Concrete Protection
Incorporating the latest proven cement chemistry, microsilica, fibre and styrene acrylic copolymer technology, Monomix is a pre-packaged, single component product, only requiring the addition of clean water on-site, to give an easily trowellable mortar with application thicknesses up to 80mm. Suitable for application to vertical, horizontal and overhead surfaces, it develops exceptional bond strength, excellent tensile and abrasion resistance, high diffusion resistance to acid gases and chloride ions and low permeability to water, even at 10 bar pressure. Its high compressive strength reaches 23.5MPa within just 24 hours, further increasing to 42MPa within 28 days. Monomix is CE marked in accordance with BS EN 1504 Part 3, the pan European concrete standard and it is also approved by the British Board of Agrément (BBA).
The ability to apply Flexcrete products to ‘green’ or freshly laid concrete also led to the selection of Monolevel FC for application to the concrete where a fair faced finish was required. Monolevel FC is an engineering quality fairing coat which can be used in thin screed applications to level both vertical and horizontal concrete surfaces and to reinstate cover, whilst providing a fair faced, anti-carbonation finish.
The high bond strength of Monolevel FC exceeds the tensile strength of concrete and its dense matrix provides excellent protection from the ingress of acid gases, moisture and chlorides. Importantly, it is also non-toxic when cured and releases no hazardous solvents or heavy odours during application – a critical consideration for a high profile project such as this in the public arena. Monolevel FC is suitable as an exposed finish without needing further protection or coating. For this project, it was important that the fairing coat matched the existing colour of the freshly cast concrete so it was specified in white.
These high performance products have helped enhance the finish as well as the durability by providing additional protection against water, carbon dioxide and chloride penetration to ensure that the design life of the structure will not only be achieved but extended.