Abstract. Biomass aggregate (BA) is a by-product of biomass industries which is less dense and more porous than natural aggregate. In this two-part study, BA was mixed with fly ash and alkaline liquid, and heated in an oven at 80 °C for 24 h to produce coated biomass aggregate (CBA). The first part of this study was focused on the density, specific gravity, Los Angeles test, water absorption, aggregate impact value, and aggregate crushing value of BA, CBA, and normal aggregates (NA). The second part was focused on compressive strength and water permeability of pervious geopolymer concrete (PGC) that was produced with BA and CBA. Pervious concrete is a non-slip porous pavement concrete that allows water to slip through. In this study PGC was prepared from alkaline solution: fly ash ratio of 0:5, fly ash/coarse aggregate ratio of 1:7, Na2SiO3/NaOH ratio of 2:5, and NaOH concentration of 10 molarity. PGC was cured at 80°C for 24 h. PGC made with CBA had higher compressive strength without much effect on water permeability. It has been found that PGC made with BA and CBA had lower density than PGC made with NA. Results indicated that both BA and CBA are viable alternative aggregates for producing PGC.

Cement stabilisation is a common chemical ground improvement technique. However, the energy-intensive production of Portland cement and its associated high carbon dioxide emissions give soil–cement mixtures a low sustainability rating. Cement treatment of fine-grained soils is particularly problematic due to the relatively high cement contents used in practice (i.e. >12% by mass). Decreasing the amount of cement necessary to ensure appropriate mechanical performance in roadway subgrades, particularly fine-grained subgrades, could rapidly enhance the sustainability rating of cement stabilisation. This work explored the behaviour of low- and high-plasticity clays treated with low cement contents (3–6% by mass). In this experimental study, the small- and large-strain mechanical responses of the materials were evaluated using P-wave velocity and unconfined compression tests, respectively. The results indicate that the small-strain stiffness and strength of soil–cement mixtures is very sensitive to changes in compaction water content and compactive effort. The authors conclude that while the practical application of low-cement–soil mixtures is possible, it requires strict construction control and adherence to very tight tolerances, which makes it impractical for most highway construction projects.

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