Admixtures are now an essential component of modern concrete, facilitating environmentally optimised mix design, innovative building design, improved job site placing and enhanced long term durability of the concrete.
Admixtures are chemicals added in very small amounts to the concrete to modify the properties while the concrete is still fluid and also after it has hardened and is in service. Despite the relatively small dosage, the modifications to concrete properties achievable by admixtures can reduce the ECO2 of concrete, mainly through the more effective use of the cementitious component, while maintaining and even enhancing the properties of the concrete.
The effect of admixtures on concrete properties include:
- Reducing the embodied carbon of concrete - because admixtures are used to both increase workability and reduce the water/cement ratio, and hence increase strength and reduce permeability of hardened concrete, without increasing cement content.
- Increased fluidity: reduces noise and energy requirements during placing.
- Optimised mix design: reducing embodied carbon dioxide and energy by enhancing the effectiveness of the cement component.
- Reduced permeability: increases the durable life of the concrete.
- Reduced damage from harsh environments: including marine, freeze-thaw and sub zero situations.
- Improved quality: better finish and reduced service life repair.
All admixtures from UK manufacturers are produced under third party certified ISO 14001 compliant Environmental Management Systems.
The admixture industry has for many years provided detailed information relating to environmental aspects of the production and use of admixtures. More recently, the UK Cement Admixture Association (CAA) has worked in conjunction with the European Federation of Concrete Admixtures (EFCA) to produce generic model Environmental Product Declarations (EPD) independently verified to EN 15804 for a range of admixtures:
- Plasticisers and superplasticisers
- Hardening accelerators
- Set accelerators
- Air entrainers
- Water resisting
These EPDs can be downloaded from the CAA website and in the UK are only applicable to members of the CAA. Further guidance and information on admixtures is available from the Cement Admixtures Association (CAA), www.admixtures.org.uk