Construction

Concrete without cement? You must be joking

Unibeton technical director Christopher Stanley explains the science behind the manufacturer’s Portland-free concrete

What would you think if someone told you that they could build you a concrete building or structure without using Portland Cement?

Probably say stop wasting my time and rapidly show them the way out.

In the 18th and 19th centuries many important civic buildings were built using a medium strength limestone from Portland in Dorset which was fairly easy to quarry and carve, but was it was very expensive and could only be used for the most prestigious buildings.

The inventor Aspdin tried to re-create this stone artificially with a totally new type of cement, which he called Portland Cement. Although his invention was at the cutting edge of technology, it took almost another 40 years to gain acceptance in England’s very traditional construction industry. Now it is time for a game changer again.

In recent years it has become important to reduce the carbon footprint of concrete in order to enhance the environment for future generations.This can be accomplished by partially replacing some of the cement in the mix with waste materials, such as powdered slag from steel making; ash from electrical power generation and rice husks from agriculture.

These materials are not cementitious in their own right, but when mixed with cement, have similar properties of strength development together with enhanced durability.

In order to enhance the environment, there is a need, where possible, to reduce the amount of cement used in the construction process, without compromising either the strength or long term durability of the concrete. To a certain extent we are restricted by minimum cement contents, set out originally in BS Code of Practice CP110 for structural concrete, which have never been revised in the light of modern advances in concrete technology.

The available options are therefore to include a variety of cement replacement materials in the mix, which do not compromise the engineering properties of the concrete.

UNIBETON is leading the new revolution is sweeping through the construction industry, making durable, strong concrete, without using any Portland cement. These concretes use naturally occurring waste products and newly developed polymer compounds.

UNIBETON are now manufacturing environmentally friendly concrete without Portland cement that has compressive strengths up to about 75MPa together with improved durability and greatly enhanced fire resistance.

These concretes can also have a carbon footprint of only 7% compared to traditional concrete where Portland cement is used, and are very suitable for use in precast concrete and some in-situ concretes which require a higher initial strength for the early demoulding of formwork.

Another interesting advance is in the manufacture of concrete wood. It is now possible to make concrete that can be sawn, drilled and screwed in the same way as traditional timber but which saves cutting down valuable forests which have the ability to absorb large amounts of carbon dioxide and convert to back into oxygen.

The other advantage of concrete wood is that it does not rot or get eaten by beetles; and all these products can now be produced for the same price as traditional concrete.

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