GREEN MASONRY – A MEANINGFUL CONTRIBUTION TO SUSTAINABLE DEVELOPMENT:
Article Date: 14 January 2008
 Genuinely environmentally friendly bricks are hard to come by. However, Concrete Manufacturers Association (CMA) member, Cape Brick, a concrete brick manufacturer based in Cape Town, delivers just that, eco-friendly bricks with the lowest embodied energy content of all the bricks manufactured in this country.
Embodied energy is defined as the energy consumed in the manufacture and transportation of construction materials. To manufacture a masonry product with a low embodied energy, raw materials need to be sourced as close to manufacturing plants as possible and contain a high percentage of recycled material. Energy consumption during the manufacturing process should also be low.
Often selected as the product of choice for green building by the leading experts on sustainable energy, Cape Brick’s recycled bricks are engineering grade, load-bearing and structural concrete masonry units and are approved by the CMA.
Cape Brick was one of the first masonry manufacturers to use recycled aggregates which it obtains from construction and demolition waste material. Waste material is recycled into crushed aggregate which is used as the main ingredient in all the company’s products at a rate of 60 000 tons per year. For instance, its 14 MPa concrete plaster brick consists of 96% recycled materials and only 4% virgin cement.
In addition to recycled crushed aggregate, Cape Brick’s concrete bricks consist of a mixture of sand, stone, cement, and granulated correx slag, a waste by-product of the steel manufacturing industry. The use of slag in the concrete mix further reduces the amount of cement required and results in an additional and considerable lowering of embodied energy.
Recycled aggregate is produced in a crushing and sieving process, using reinforced concrete from demolished structures. After an initial crushing, materials such as reinforcing steel and other contaminants are removed. The remaining material is then sieved, filtered and re-crushed, yielding the original sand and stone that was used in the composition of the concrete.
The direct environmental benefits of green masonry are:
• Fewer virgin aggregates have to be quarried, reducing the impact on the environment.
• Most quarries are located far from their markets, and not using freshly-quarried materials results in reduced transport requirements.
• Construction and demolition rubble is normally dumped, so using it as a raw material source eases the pressure on landfill sites.
• Most landfill sites are located far from the demolition site, so using these materials results in reduced transport requirements.
• Cape Brick’s own waste material is reprocessed and therefore does not have to be dumped, easing pressure on landfill sites and reducing transport requirements.
Besides being modest in its energy needs, recycled material-based concrete masonry is generous in its payback. No change in construction technique and it is also cost-effective.
It is actually superior to that of quarried materials, available at a similar price, offering higher compressive strengths. The end product is a truly green building material, a recycled brick with a low embodied energy which is itself fully recyclable.
Concrete masonry has other sustainable development attributes. It is naturally thermally efficient and it assists in moderating ambient temperatures so that buildings retain warmth in winter and keep the heat at bay during summer, thereby lessening the need for artificial climate control and its concomitant energy requirements.
The secret of concrete masonry’s energy efficiency lies in its mass. The thermal mass of concrete acts as a buffer, absorbing the excesses of external temperatures as they move through a wall, making the insides of buildings more comfortable.
Two other CMA members, Western Cape-based False Bay Bricks and Columbia DBL, recently gained NHBRC approval for a range of thermally efficient single-leaf hollow-core concrete blocks which can be used without plastering. Other CMA manufacturers are currently in the process of analysing the physical characteristics of concrete blocks in order to ensure consistent thermal resistance values and comply with the NHBRC’s monitoring requirements.
“The Green Building” in Westlake Business Park, Cape Town, a sustainable development built using Cape Brick’s Maxi bricks. With a recycled materials component of 70% and minimal carbon dioxide emissions produced in the manufacturing process, these bricks are truly environmentally friendly.
This house in Tokai, Cape Town, was built with Cape Brick’s imperial brick, a 14MPa plaster brick comprising 96.5% recycled materials. The brick has the lowest embodied energy of any masonry unit on the market today. It is also an engineering-grade, load bearing structural concrete masonry unit approved by the CMA.
Again, Cape Brick’s environmentally-friendly imperial brick was used to build this house in Camps Bay, Cape Town.
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