Rheological Characterization of Different Clay Minerals for Sustainable Pourable Clay Concrete

Abstract

Cement production contributes around 6% to 10 % of global CO2 emissions, fuelling the exploration of alternatives with lower environmental footprints. This study focuses on revitalizing an age-old building material, clay, due to its minimal environmental impact and positive attributes such as practically infinite recyclability and favourable hygro-thermal behaviour. However, different challenges are faced when working with clay, particularly the physically demanding, labour-intensive nature of raw earth construction, predominantly seen in regions with low-cost labour, notably developing countries. To make clay as versatile as traditional cement based concrete, it must be pourable. Additionally, the diverse behaviour of clay, influenced by its origin and mineral composition, significantly impacts pourability, water absorption, and consequently, the drying behaviour. This complex relationship highlights the importance of fully understanding its rheological properties, especially with the method of small amplitude oscillatory shear (SAOS), to investigate the nature of interactions (short range or long range colloidal) of each clay mineral or clay mix. To address these challenges, this study investigates locally sourced clays with varying chemical and mineralogical compositions, focusing on tailoring the fresh properties of pourable clay concrete. Firstly, mini-cone spread tests have been conducted to define the water demand of the different clay minerals for a range of water-to-solid ratios (w/s) for which a workable and stable paste is obtained. Then, the results were correlated with their chemical composition as well as their particle size distribution. Secondly, the same clay minerals at different w/s were investigated with small oscillatory rheological tests. This approach enables rapid assessment of clay paste performances within the initial hours, supporting the selection of promising compositions for subsequent mechanical evaluations in the solid state. The results gained in this study hold the potential to create clay-based concrete with tailored properties, contributing to the advancement of sustainable construction practices.