A tiny project in central London marks a major step forward for the use of a high-performance concrete in the UK.
The Building Centre in central London will host the construction of a new ultra-thin concrete staircase using the material. While it may not be of the same scale as its use in major international projects such as the Seoul footbridge (below) and the Shawnessy Light Rail train station in Calgary, Canada, the Building Centre project marks a turning point for the material.
It will be the first time Lafarge Cement’s Ductal high-performance concrete has been used in the UK and the move has been welcomed by industry heads.
“It just takes the whole concrete industry a step further forward,” says Martin Clarke, chief executive of British Precast. “It will allow designers and architects to specify stronger, thinner sections. It brings an elegance to the design where it has been used, one that is difficult to achieve with conventional concrete,” he adds.
Developed by Lafarge Cement alongside project partners, contractor Bouygues and chemical producer Rhodia, the material is a high-strength, durable and flexible concrete composite.
It features an extremely high cement and granular particle content and metallic or organic fibre reinforcement.
There is no large aggregate in the mix at all, ensuring the finish on the cast face of the material is extremely fine.
The high cement to water ratio in the mix ensures that even when the concrete has hardened or gone off, there is still an amount of cement in the material’s matrix that has not reacted with the water.
Should the material crack under stress these particles of cement hydrate with water in the air and seal the cracks, making it a self-healing concrete.
Strength under pressure
The material is incredibly strong under compression loads. According to Lafarge, Ductal concrete can be as much as eight times stronger in compression than traditional concrete.
Its mechanical strength is supported by its fibre reinforcement content. In traditional fibre-reinforced concretes just one per cent of the volume is taken up by reinforcement, in Ductal this figure rockets to as much as four per cent.
The reinforcement takes the shape of chopped steel or organic fibre strands rather than traditional bar reinforcement, enabling it to be formed into almost any shape.
Thanks to the absence of passive reinforcement it can be used to cast extremely thin structural members and can also be cut and sanded into shape.
Lafarge Cement’s precast products vice president claims the installation, due to be completed in July, will encourage more designers to use the material. “Its characteristics are unique in the world of mineral building materials,” he says.