SA Affordable Housing March - April 2019 // Issue: 75 | Page 13

FEATURES
Concrete’s green challenge
Concrete has cemented its role in the affordable housing space
but is criticised for not being ‘green’ enough.
By Warren Robertson
In 2016 alone, world cement production generated about 2.2 billion tonnes of CO 2 .
M
uch emphasis is put on the affordable housing sector
to build homes in a sustainable way; everything
from insulation to heating, bricks, plumbing and
electricity are carefully planned to ensure that homes
benefit residents and the environment.
However, one aspect that is often taken for granted in
the affordable sector is concrete, which has been around
for millennia.
The type of concrete that is most commonly used in our
modern built environment was patented in the early 1800s
by a bricklayer in England. Known as Portland cement this
technique involves cooking limestone and clay in an oven
and then grinding it to a powder to make ‘artificial stone’.
This cement has helped build tens of thousands of buildings
around the world from the Sydney Opera House in Australia
to the Burj Khalifa in Dubai.
However, despite its ubiquitous presence, concrete's
environmental credentials are coming under increased
scrutiny and the results are less than flattering.
www.saaffordablehousing.co.za
It turns out that the production of Portland cement is one of
the single most environmentally destructive activities that
humanity involves itself in. The first step in the process is
the quarrying of raw materials mainly limestone and clay,
which are then crushed. This process creates airborne
pollution in the form of dust and these ground materials are
mixed with others such as iron ore or ash and are fed into
huge, cylindrical kilns and heated to about 1 450C (2 640F).
Usually this heat is provided by burning fossil fuels, most
commonly coal. This process of ‘calcination’ splits the
material into calcium oxide and CO 2 and a new substance
called clinker emerges as marble-sized grey balls. The
clinker is cooled, ground and mixed with gypsum and
limestone and this new cement is transported to ready-mix
concrete companies. Each of these final steps requires more
machinery and therefore more power.
According to the Cement Sustainability Initiative (CSI) it
takes 200kg of coal to make one metric ton of cement and
about 300 to 400kg of cement is needed to produce one
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