Challenges in Life Cycle Assessment (LCA) of stabilised clay-based construction materials

The preference of clay-based materials for sustainable construction is well-established. The establishment of sustainability credentials of emergent construction materials is very subjective, and most available tools such as LEED, BREEAM, CEQUAL, ARUP SpeAR , ATHENA among others are not fully equipped or equipped at all to deal with individual material systems, such as composite cement- or lime-based cementitious systems, including clay-based blocks and bricks. The main problem emanates from the challenges of the audit of each aspect of the material processing, and especially the quantification of the relevant transport, energy, environmental and other inputs into the composite product. The variability in material ingredients, and lack of data (emission, energy, transport etc.) for each aspect of the manufacturing processes involved creates major challenges. Incorporation of materials with long and complex recycling processes as plastics, tyres, glass, among other recyclables further exacerbate the challenge. These incorporations create unsurmountable problems in terms of accurate material trails and data for input in a robust Life Cycle Assessment (LCA) of individual products. This paper reports on a simplified approach towards full LCA of seven clay-based brick products developed in UK (4) and Spain (3), based on known material data and estimated energy inputs in the manufacturing processes. The UK-based bricks comprise of Lower Oxford Clay (LOC), stabilised using combinations of hydrated lime, Ground Granulated Blast-furnace Slag (GGBS) and Portland cement (PC). In order to test the robustness of the proposed approach, results on UK-based bricks are compared with a parallel LCA on clay-based product developed in Spain. Finally, the clay-based products are compared with a typical Portland cement-based concrete block and fired clay brick. In the LCA, boundary conditions include fixed transport, thus attempting to factor only the i) material ingredients, ii) their known atmospheric emissions, and iii) estimated energy inputs during processing. Results suggest that the most challenging aspect in the undertaking of LCA is the availability of reliable input data. Results also show that there are numerous parameters that can reliably and corroboratively facilitate the comparison of performance, besides carbon dioxide emissions.