Lifecycle assessment of alkali activated cement concrete

Climate change is one of the most important environmental problems that our planet Earth is facing. This is due to the increased emission of greenhouse gases such as carbon dioxide. Concrete, the most consumed material in the construction industry is reported to be responsible for about 8% of worldwide carbon dioxide emissions. The manufacturing of ordinary Portland cement is both resource and energy-intensive and is accountable for 1.35 billion tons of carbon dioxide emitted annually. Hence potential alternative to Portland cement widely recognized is the adoption of alkali-activated cement. Alkali-activated cement commonly utilizes industrial by-products such as fly ash, GGBS, etc. along with alkali activators such as sodium silicate and sodium hydroxide. The literature review indicates that the environmental impact due to the usage of Portland cement can be reduced by the adoption of alkali-activated cement. However, the manufacture of alkali activators is likely to contribute to the emission to the environment. In addition, the heat curing commonly adopted during the production of concrete to activate the alkalis might also have a bearing. Hence a comparative study using the lifecycle assessment (LCA) method is carried out to assess the impact due to the production of alkali-activated cement concrete using supplementary cementitious materials (SCM) fly ash and GGBS with varying proportions of alkali activators (sodium silicate and sodium hydroxide). Data is extracted from the published literature corresponding to two different compressive strength ranges of OPC concrete and alkali-activated cement concretes that have utilized four varying proportions of alkali activator ratios. It is then analyzed by the ‘cradle to gate’ approach using LCA software SimaPro. The impact assessment is done using the ReCiPe 2016 method. A comparison of results and their interpretation is done based on its compressive strength ranges, the alkali activator ratios, and the effect due to change in the SCMs utilized.