There is a need to reduce the amount of greenhouse gas emissions coming from the construction industry, specifically, those embodied in concrete. With various government initiatives being created to encourage environmentally sustainable practice it is necessary to quantify the embodied emissions in concrete. Especially those associated with recycled materials being substituted into mix designs.
Scope & Aim
The aim of this study is to carry out a life cycle assessment (LCA) for the production of concrete to determine its embodied GGE. In particular it will aim to look at what effect the use of BFS has on embodied GGE and water consumption. Furthermore, a maximum transportable distance for BFS will be determined. This study will specifically look at GGE and will not include any other types of emissions, such as carcinogenic emissions from transport. All concrete mixes used in this study are designed to be 32 MPa mixes.
There are various materials that are now being utilised as substitutes in concrete mix designs. The main three are fly ash, blast furnace slag and recycled aggregate. It has been previously found that the use of fly ash reduces the amount of embodied emissions in concrete, but not the water consumed. It was also found to be environmentally viable to transport fly ash over vast distances. Neither blast furnace slag nor recycled aggregates have been studied in this manner.
A life cycle assessment was undertaken to investigate the effect of blast furnace slag on embodied greenhouse gas emissions and embodied water in concrete. Various emission factors and water consumption rates were used to calculate the embodied greenhouse gas emissions, water consumption and maximum transportable distances for blast furnace slag.
It was found that blast furnace slag reduces the embodied greenhouse gas emissions in concrete, however, fly ash reduces them slightly more. The type of supplementary cementitious material used was found to be negligible as the variances between the two types of materials were minimal. The water consumed in the production of concrete was not found to be significantly changed when blast furnace slag is used. Blast furnace slag was found to be capable of being transported vast distances before reductions in emissions became negligible.
Concrete manufacturers can be confident that if they use any amount of supplementary cemeintitious material they will be producing a ‘green concrete’. Also they can be assured that if
there is no local supply of supplementary cementitious materials it is environmentally viable to source them from elsewhere.
The methods used in this study could be applied to recycled aggregates in future work to quantify their effect on the embodied greenhouse gas emissions in concrete.