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Send  Share  RSS  Twitter  11 Dec 2008

BULDING: Concrete Masoners Put Their Case

 



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THE claims regarding environmental issues relating to products and services are often misleading because the subject is a complex matter that is fraught with misinformation and half truths. The claims often only select snippets of information, and the attributes often have no real impact on the environmental issues at large, says Bob Low of Inca, talking on behalf of concrete masoners.

It is therefore key to any discussion relating to environmental issues, to ask the right questions, namely:-

•           What environmental issues are being addressed? (e.g. global warming, energy, biodiversity, water scarcity etc)

•           Are the claims material to environmental issues at large?

•           Is the entire ‘cradle to grave’ life cycle (i.e. manufacturing, operational life and end of life) taken into account?

The main concern with environmental issues today relate to global warming, which is directly proportional to the amount of carbon dioxide emitted into the atmosphere. Over 90% of CO2emissions in South Africa are produced in the burning of fossil fuels to produce energy. It is therefore safe to assume that the energy employed during the entire life cycle of the product has a direct impact on global warming issues.

It is estimated that South Africa produces 3.5 billion bricks per annum which equates to 1.6 million tons of CO2 per annum. To put this into context, brick production has the equivalent global warming contribution as the annual emissions from 360 000 average sized sedan cars.

Bricks also constitute approximately 30-60% of a buildings total embodied energy. The global warming effect from masonry products is therefore substantial and material to the environmental issues at large.

One has to analyse the carbon footprint of masonry holistically. The energy employed in the manufacturing of the product  (i.e. embodied energy), the energy efficiency of a building built with different masonry materials (i.e. operational energy), and the energy savings resulting from recycling all have be taken into account, before a fair judgment can be made about a products complete environmental impact, Low says. 

Embodied energy refers to the amount of energy required to produce the product. Clay and concrete bricks (also called cement bricks in the industry) both employ energy intensive processes. The main contributor of the carbon footprint in clay bricks is in the firing process. Clay is fired in kilns at 1000°C for 2 - 3 days.

The main contributor of embodied energy in concrete is cement. Cement only comprises  10% of a concrete brick. Cement is produced by heating limestone and other materials at 1450°C for 30 minutes. It therefore stands to reason that concrete bricks employ substantially less energy to produce than clay bricks. International and local research concur that the embodied energy of clay products are 2.5MJ / kg whilst concrete bricks are 0.95MJ / kg, according to Low.

The operational life refers to the energy utilized in the life time of the building to heat and cool the ambient temperatures. Clay and concrete have marginally different thermal properties. Concrete generally has a higher thermal capacity (i.e. ability to store heat), which enables the product to store heat at night and release this stored heat during the day. Clay has however better thermal resistance properties making it a better insulating material. Clay and concrete therefore effect the energy utilization of a building differently in different climatic conditions.

“This is however a nebulous comparison as studies show that the choice of masonry has a marginal effect of a buildings energy utilization as more than 80% of heat is transferred via windows, doors and ceilings,” says Low.

He points out that all concrete is 100% recyclable and makes an excellent aggregate to produce other concrete bricks. Clay bricks can be recycled to form sub-base materials in the construction industry. The recycling process ultimately reduces the total embodied energy by only 0.08 MJ / kg (i.e. 8%) which has a marginal effect on the cradle to grave total carbon footprint of clay and concrete masonry.

Low says the correct choice of masonry products will have a massive impact on green house emissions and energy consumption. Embodied energy, the only differential between masonry products, is the most critical and important factor in the entire life cycle of masonry in a building and can account for up to 60% of a buildings embodied energy. Masonry has little impact on the energy utilization during the life of a building and all masonry materials can be recycled effectively.

Concrete has a carbon footprint 2.5 times less than an equivalent clay brick, and the choice of concrete can therefore reduce the carbon emissions of a mid size residential dwelling by 30 tons, which is equivalent to a cars emissions for 7 years. The choice of masonry material is the easiest and most cost effective manner to substantially reduce a buildings carbon footprint, says Low.


 
 
 
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