They may have been the necessary solution to post–war housing shortages, but concrete multi-storey buildings’ structural integrity has come back to haunt planners and maintenance teams. Nic Collins of Sika explains how they can be made fit for the future.
The high and medium-rise blocks of the mid to late 20th century were made primarily from concrete as the material enabled contractors to meet requirements for speed and longevity, while also offering flexibility to building designers.
While it is a relatively durable and robust building material, concrete can be severely weakened by poor manufacturing or a very aggressive environment. As a result, the durability of these reinforced ‘streets in the sky’ has become a serious issue over the years.
Premature deterioration, chemical degradation, unexpected and uncontrolled cracking caused by corrosion of the reinforced steel, and poor appearance and finish became commonplace, with these high rise towers losing their once-futuristic looks. With growing demand for additional social housing set against shrinking budgets, the need to repair, maintain and extend the life of these high rise concrete buildings in the most cost effective and reliable way has never been greater.
Structural decay
If its structural integrity or load-bearing abilities are compromised, it is vital that a building is refurbished, restored and strengthened if it is to remain a viable asset for the 21st century. During the refurbishment process, it is crucial to get the specification right first time to ensure buildings are not just returned to their former aesthetic standard, but also meet building standards and regulations.
These include European Standard EN 1504, which helps owners and construction professionals to fully understand the requirements of the different stages of the repair and protection process. So, how can we ensure refurbished building stock is fit for the long term?
An approach that can completely seal a building envelope, stop water ingress, control air leakage, and repair and strengthen structures in refurbishment and restoration projects, is one way in which this can and is being achieved. Building owners wanting to repair and protect their buildings for the long term need to take into consideration the whole life costs of repairs.
A total approach to tackling corrosion
Developed by concrete repair specialists Sika, the Total Corrosion Management (TCM) approach encompasses concrete repair and protection, corrosion control and structural strengthening systems. Helping to prolong and extend the life of buildings and structures as well as provide a viable and cost effective alternative to demolition and rebuilding, it is appropriate for a wide range of applications including commercial and industrial buildings, residential properties, and bridges and tunnels. A focus on products, technologies and processes combine to make the firm well equipped to make the UK’s ageing buildings and infrastructure facilities fit for the future, thereby reducing the costs and disruption of unplanned repairs and maintenance.
As well as improving the aesthetics of buildings, companies expert in maintaining concrete structures can also deliver efficient and reliable structural strengthening systems. For example, using fibre-reinforced polymer (FRP) plates, fabrics and post-tensioned systems, solutions have the ability to increase the load capacities of beams, columns, walls and slabs in concrete substrates.
Tower block makeover for the future
One project that demonstrates the potential of the post-war modernist block to be renovated for the future is the Four Squares Estate in Bermondsey, south London. Built between 1971 and 1975, the estate comprises 691 homes across four near-identical seven-storey blocks – New Place Square, Lockwood Square, Marden Square and Layard Square. Following a structural inspection by consulting engineers Arup, all housing blocks were deemed to be structurally sound, but large areas of previously uncoated concrete were exhibiting reinforcement corrosion.
Working closely with clients Keepmoat and Southwark Council, specialist contractor Barwin and Sika carried out on-site trials to demonstrate the potential to penetrate the concrete to reach the steel and restore it to a state of ‘passivity’.
With the tests showing the system successfully encapsulated and protected the reinforcement, the corrosion inhibitor was specified as part of the Total Corrosion Management solution – that also comprised repair mortars and protective coatings.
“Due to its age and on-going exposure to the elements, all four buildings’ concrete exteriors were suffering from corrosion, as well as stalactites, excessive sediment and efflorescence caused by leaking balconies,” said John Connell, contracts manager at Barwin.
“A two-stage jet wash was required to clean and prepare the previously uncoated substrate before the application of a mixed corrosion inhibitor across all external elements.”
Designed to extend the service life of aesthetically valuable concrete surfaces, more than 60,000 m2 of Sika Ferrogard 903+ was spray-applied by Barwin’s team of operatives. The product penetrates the concrete to provide a protective layer around steel reinforcement whilst maintaining the aesthetics of the structure.
Appointed to complete a series of refurbishment projects on behalf of Southwark Council, Barwin then applied Sika MonoTop to repair the damaged concrete frame. The system’s first layer inhibited corrosion and improved the lifespan of the steel reinforcement, whilst also acting as a bonding bridge for the second layer – a repair and re-profiling mortar.
Weatherproofing
To provide a final layer of weather protection, a further specialised solution was specified. For the soffits and remaining concrete surfaces except ringbeams, SikaGard 675W anti-carbonation coating was applied to seal against the ingress of water, chlorides and carbonation. With the external concrete structures fully repaired and protected, these ageing tower blocks have been given a new lease of life.
Sika’s solutions have given the clients and residents peace of mind that their new-look properties will provide hundreds of residents with a high quality, attractive and sustainable home for years to come. If we are to robustly refurbish the UK’s existing building stock rather than tear it down, careful consideration of solutions is required – as well as technological innovation and fresh architectural ideas. Meeting the ever changing needs of the built environment, expert approaches can future proof structures using maintenance and renewal solutions that make economic as well as ecological sense.
Nic Collins is area sales manager, property, at Sika UK
This feature was published in the September 2016 issue of Housing Management & Maintenance.
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