Admixtures and sustainable concrete

Admixtures can reduce the embodied carbon content of concrete (ECO 2), despite having a relatively high ECO2 themselves when compared on a ton-for-ton basis. Admixtures are used in very small dosages compared to most other ingredients, and as such they typically contribute less than 1% to the total ECO2 of concrete, while allowing the overall cement content to be reduced. Under BS EN ISO 14044 constituents contributing less than 1% of the impacts can be ignored, and this would apply to most cases of admixture usage. Although admixtures are composed of a wide range of raw materials, they are not generally toxic and indeed most of them have been individually assessed for use in concrete in contact with drinking water by the UK's national water regulators. The assessment covers toxicology of the individual substances in the admixture and leaching tests from concrete.