Cementitious materials
Cementitious products comprise the glue that holds concrete
together. These materials include traditional Portland cement and
other cementitious materials, such as fly ash, ground granulated
blastfurnace slag (ggbs), limestone fines and silica fume. These
materials are either combined at the cement works (to produce a
composite cement) or at the concrete mixer when the concrete is
being produced (the cementitious product is called a combination in
this case).
Fly ash and ggbs are the most commonly used of these materials
in the UK. These secondary materials are useful by-products of
other industrial processes, which would potentially otherwise be
sent to landfill.
Ggbs is a useful by-product recovered from the blast-furnaces
used in the production of iron. It can be used un-ground as a
coarse aggregate or as a supplementary cementitious material (where
it can replace up to 70% of cement in a concrete mix). Fly ash is a
useful by-product of coal-fired power stations and is
environmentally beneficial. If it were not used in composite
cements or as an addition at the concrete mixer then the material
would be wasted and sent to landfill.
Using ggbs or fly ash in concrete, either as a mixer addition
or through a factory made cement, significantly reduces the overall
greenhouse gas emissions associated with the production of
concrete.
Concrete credentials: sustainability
Cement
| CO2 |
Direct annual CO2 emissons have reduced by nearly 40
per cent since 1990 in absolute terms. The cement industry met the
UK's 2010 Climate Change Agreement target four years in advance and
is continuing its commitment to improvement. This compares
favourably with the UK construction industry, which overall
recorded an increase in CO2 of more than 30 per cent
over the same period. |
| Recycling |
In 2008, the sector replaced 26.5 per cent of its fuel from
waste-derived material including scrap tyres, pelletised sewage
sludge and meat and bone meal. |
| Biodiversity |
All cement plants and quarries have, or are linked to,
biodiversity action plans. |
| Resource depletion |
The consumption of natural raw materials needed to make
cement has reduced significantly in the last ten years. Between
1998 and 2008, the sector has increased the use of waste-derived
raw materials by over 50 per cent. |
| Waste |
The cement sector is a net user of waste. Waste-derived
materials are actively sought as replacements for natural raw
materials and fossil fuels. The sector uses over 1.4 million tonnes
of waste in this way and produces 45,000 tonnes of waste per
year. |
| Emissions |
The cement industry has worked hard to reduce its emissions to
air by investing in new technologies. From 1998 to 2008,
significant reductions have been achieved. SOx emissions
have reduced by 75 per cent, dust emissions by 68 per cent and
NOx by 51 per cent. |
| Health and safety |
The sector has reduced accident rates of its employees by 80
per cent in the last ten years. The target is to achieve a further
50 per cent reduction in accident rates by 2015. |
Additional cementitious materials
| CO2 |
The use of 50 per cent ggbs can reduce embodied CO2
by over 40 per cent, compared with a traditional 100 per cent
Portland cement concrete mix. 30 per cent fly ash can reduce
embodied CO2 by over 20 per cent. Limestone fines can
reduce embodied CO2 by 15 per cent. |
| Recycling |
The concrete industry recycles by-products from other
industrial processes. Ggbs, a by-product of iron production, and
fly ash from electric generating plants can both be used as
additional cementitious material in concrete mixes. |
| Resource depletion |
Every tonne of additional cementitious material used in
concrete mixes saves about 1.4 tonnes of raw materials. |
| Waste |
Ground granulated blast furnace slag and fly ash are
by-products of other industries. These products can be diverted
from landfill by being used as additional cementitious material in
concrete mixes. As a proportion of total cementitious materials
used in ready-mixed and precast concrete, 31.8 per cent is
additional cementitious materials. |
Source: Concrete Credentials: Sustainability, MPA - The
Concrete Centre, 2010