Stabilisation of peat with colloidal nano and micro silica

Abstract

Peat occurs abundantly in wetlands across Iran, particularly around the disappearing Urmia Lake. Conventional chemical stabilisation has been widely used to tackle the high compressibility and shrinkage potential of peat. Whilst effective, this generally reduces the carbon storage capacity of peat. Exotic stabilisers such as nano-silica (NS) have been shown to be relatively less harmful and without any direct environmental risk. NS has proved effective in improving the mechanical properties (to some extent) and pH-dependent natural structure of peat, but is commercially nonviable. This article presents findings from an experimental study of Urmia Lake peat stabilised with composites of NS and cheaper micro-silica (MS). Unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests were conducted on untreated and treated compacted natural peat soil samples after 7, 14 and 28 days of curing. Nano-silica was varied from 3 % to 9 % (by dry mass) in 3 % increments and micro-silica was varied from 6 % to 24 % (by dry mass) in 6 % increments. The observations are explained in terms of micro-scale events using XRF spectroscopy and SEM imaging. The findings suggest that the UCS of peat can be increased by administration of NS-MS composites, and the effectiveness is dependent on the relative content and particle size of NS and MS. The UCS and elasticity modulus increase with curing time. As manifested in the CBR results, administration of the composites improves the bearing capacity of peat and transforms it into a sub-base with suitable engineering functions whilst safeguarding its ecosystem service provisions