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% 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% over the same period.
Recycling In 2008, the sector replaced 26.5% 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% 
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%, dust emissions by 68 per cent and NOx by 51%
Health and safety The sector has reduced accident rates of its employees by 80% in the last ten years. The target is to achieve a further 50% reduction in accident rates by 2015.
 
Additional cementitious materials
 
CO2 The use of 50% GGBS can reduce embodied CO2 by over 40%, compared with a traditional 100 per cent Portland cement concrete mix. 30% fly ash can reduce embodied CO2 by over 20% Limestone fines can reduce embodied CO2 by 15%
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 GGBS 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% is additional cementitious materials.
Source: Concrete Credentials: Sustainability, MPA - The Concrete Centre, 2010

New to the site

Factsheet 18 - Embodied CO2e of UK cement, additions and cementitious material

 

Embodied CO2e of concrete

Spinnaker Tower, Portsmouth. 50% GGBS was used in its construction.

Publications and tables

Specifying Sustainable Concrete

Concrete Credentials: Sustainability

Material efficiency

Related links 

For more information on cementitioius materials and concrete follow the links below: