Insight

Thinner and stronger: concrete’s structural versatility

5 March 2019 | By Richard Kershaw

Steel fibre was used to reinforce the main inner lining of the Lee Tunnel in east London, as part of Thames Water’s sewer upgrade (Chris North)

The range of structural applications for concrete is growing significantly, as R&D gathers pace. Cemex national technical manager Richard Kershaw explains.

It’s one of the oldest construction products in the known world, so surely the boundaries for concrete have been pushed as far as they can?

When the Romans invented concrete, they could not have dreamt just how ubiquitous this material would become, how it would shape the development of the built environment across the world and help improve the lives of its citizens – but they must have had some idea that they were on to a good thing.

At a time when Britons were building huts using wattle and daub, Emperor Hadrian – he of wall fame – had commissioned and built the Pantheon in Rome, complete with 42m diameter concrete dome. It still stands today. Since then concrete has become the go-to construction material. There are no parts of the world that remain untouched by it. Today it’s the most consumed man-made material in the world.

But its ubiquity has not stopped its continuing development. Across the world scientists, chemists, engineers, mix-designers and concrete specialists keep pushing the material’s boundaries. Research and development (R&D) has always been an integral part of the concrete sector – and its structural possibilities have grown significantly.

This is partly down to growing use of fibre-reinforced concrete. Increased understanding of the efficiency benefits it offers project managers has seen its popularity increase.

The Concrete House in East Sussex used fibre-reinforced self-compacting concrete

The use of steel fibres to reinforce concrete can reduce or eliminate the requirement for heavy, cumbersome steel reinforcement bars – improving durability and reducing permeability and plastic cracking, while offering a reduction in labour and material costs. It has been proven in both civil engineering and building applications recently.

Contractors used 500 tonnes of steel fibre to reinforce the slip formed main inner lining of the Lee Tunnel in east London as part of Thames Water’s sewer upgrade scheme which will help reduce the number of stormflow discharges in the River Thames.

And Cemex researchers in Switzerland, based at the company’s global R&D centre, have helped deliver an innovative, efficient home in the UK using its Resilia HP fibre-reinforced self-compacting concrete for the structural walls and horizontal elements.

The Concrete House in East Sussex was featured on Channel 4’s Grand Designs and the use of Resilia HP enabled the design team to reduce the amount of steel reinforcement to less than 60% of the original total.

There is a perception that fibre-reinforced concrete is costlier than steel-reinforced concrete, but that isn’t always the case. Developers perhaps don’t factor in the overall construction cost savings. Advances in fibre dosage designs have led to higher tensile and flexural strengths, which can be helpful when value-engineering a scheme.

Those efficiencies will continue to grow, as researchers and academics across the globe are looking at ways to improve the material’s elasticity and ductility. Innovations in development include self-healing concrete, super-thin concrete – even floating concrete. Modern methods of construction will demand thinner, stronger concrete that can provide significant cost savings.

Over the last 30 years we have seen the average strength of concrete we supply soar. In the 1990s, a 40N concrete was considered specialist. Now it is not uncommon – particularly on central London sites – for us to supply 100N mixes.

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