Moisture ingress in rammed earth: Part 2 – The effect of soil particle-size distribution on the absorption of static pressure-driven water

A novel adaptation of the initial surface absorption (ISA) test has been presented that is suitable for use with both unstabilised rammed earth (URE) and cement-stabilised rammed earth (SRE). It provides axial symmetry of the imbibed water and has identical test specimen geometry to the proposed initial rate of suction (IRS) ‘wick’ test, which has previously been discussed in this series of papers. The ISA rate for rammed earth is typically lower than that of conventional masonry such as fired clay bricks and in situ cast concrete. Both particle-size distribution and the ratio between total specific surface area to relative clay content (SSAt/CC), appear to be a significant factor in determining the non-saturated permeability of the rammed earth. The addition of ordinary Portland cement to selected rammed earth mix recipes can either significantly increase or decrease the non-saturated permeability of the material depending upon the amount of cement added. There appears to be an optimum level of cement dosage for impeding moisture ingress in SRE, and this level varies with contrasting mix recipes.