Tuesday, July 11, 2017

concrete cancer

Concrete cancer can be avoided during the preparation stages of concrete reinforcement work but a lot of the time corners are cut in favour of profit and the job is not done to standard.

concrete cancer

Let's look at the characteristics of reinforced concrete as a first step to understanding how and why the cancer happens.

concrete cancer eating away at a balcony causing a structural issue
The strength is concrete all depends on the steel reinforcement running through it and if the steel work is not done properly the concrete will eventually fail.

typical slab pour with re-mesh

The minimum depth of any steel work needs to be at least 40mm below the surface of the finished concrete to avoid moisture from penetrating and subsequently rusting the steel.

diagram showing correct placement of steel reinforcing for concrete

If the steel is less than 40mm (to outside) from the surface then spalling occurs.
Spalling is when the steel inside the concrete rusts and expands causing the concrete to flake or chip away, causing more moisture to penetrate and more cancer to form.

As a building product the manufacture of cement is possibly the most impacting on Nature but if done properly it can outlast many other building materials and therefore be better for the environment in that instead of re-building every 30 to 50 years, the concrete structure will last hundreds or even thousands of years.

Having fixed many remedial concrete cancer issues in a variety of buildings I can say that the 40mm rule is not being adhered to one hundred percent, making concrete and the cement used to make it the worst material for building from an environmental standpoint, ( And what other standpoint is there?)

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