On the effects of density on water retention properties of expanded perlite

Compacted and, in some cases, natural soils exhibit a double porosity network due to an aggregated-type fabric. Its evolution (swelling and shrinkage), when subjected to stress or hydraulic path, may be very significant, strongly affecting the hydro-mechanical overall response. A similar structure is recognized also in compacted expanded perlite. Having in addition a micro porosity intrinsic to the grain and being basically not affected by swelling-shrinkage effects, the expanded perlite can be suggested as model material in getting insights into the hydro-mechanical behaviour of aggregated soils. Under this assumption, an experimental programme was carried out on compacted expanded perlite samples, to investigate water retention properties and pore network structure and how these are influenced by the sample density. The results showed that, provided that no grain crushing occurs, a change in void ratio only affects the macro pores level, leading to smaller characteristic pore size and poorer pore size grading. The water retention curves appear to be in agreement with this observation.