Soil cross breeding: Mechanical strength analysis of intermixed soils used as unfired earth brick

Mechanical strength of brick is significantly influenced by soil properties, deeming some soils unusable. This paper investigates the effect of mixing soils from different sources, Hyogo (a chlorite soil) and Tokyo (an albite soil) from Japan, on the flexural and compressive strength of unfired earth brick. Before conducting strength tests on moulded bricks made from original soil mixes and intermixed soils, both soil samples were individually separated into two portions, sand and fines. To better understand the strength behaviour of the resulting brick specimen, the physical and chemical properties of used raw materials were characterised using various techniques including X-ray computed tomography (X-ray CT) X-ray diffraction (XRD), water and nitrogen sorption, X-ray fluorescence (XRF) and ionic conductivity. The results revealed that the replacement of the fines portions in unadulterated soil mixes induced an increase in flexural and compressive strength for brick specimen made with albite soil, while significant reduction in strength was recorded with brick specimen made with fines portion replaced in chlorite soil. Furthermore, the former intermixed soil exhibited higher strengths than specimen made from unadulterated soils. Chlorite clay minerals comprised of desired properties to enhance performance of albite soil sand particles in a brick composite. This justified the dependence of selected soil parameters that play critical roles in the performance behaviour of the produced bricks. The obtained findings could serve as guidelines to production and performance enhancement of unburnt brick by amalgamating various soils. • Amalgamating of soils clearly impacted brick strength behaviour. • Soil physical properties alone were insufficient to justify performance. • Water influence coincided with soil mineralogy and chemical composition. • Clay pore structure and surface behaviour aligned with brick performance. • Mechanical strength can be tailored and/or predicted based on soil properties.