Microstructural effects of environmental salinity on unbound granular road pavement material upon drying

Abstract

Areas of high environmental salinity are predicted to increase over the next 40 years in Australia, due to land use and climatic changes. This presents a risk to road assets as accumulation of salts within roads has been found to cause damage to thin bituminous surfacings. It is in this context that the present study explores the microstructural changes caused by environmental salt crystals accumulating within unbound granular road pavements. Fine-grained specimens were prepared by static compaction, immersed in different solutions, and finally either freeze-dried or oven-dried at 40°C. The effects of different drying procedures and salinity on soil's microstructure were explored via mercury intrusion porosimetry and scanning electron microscope observation. Results suggest that a freeze-drying process can significantly modify the microstructure, which should be taken into account when conducting any microstructural analysis on high-salinity soil specimens.

Drying effect on the microstructure of compacted salted silt

“…However, the intruded void ratios were slightly different from the corresponding initial void ratios. Two phenomena could be considered to explain such slight difference: (i) the heterogeneity of compacted specimens (Delage et al, 1996); (ii) the precipitation of salt crystals during drying which might fill the pores and reduce the pore volume (Liu et al, 2016b;Zhang et al, 2017).…”

“…MIP and ESEM have been widely applied to investigate the soil microstructure. These techniques allow identifying and quantifying the changes in micro-fabrics under the effect of suction (Simms & Yanful, 2001, 2002Boso et al, 2005;Romero et al, 2011;Burton et al, 2015;Liu et al, 2016aLiu et al, , 2016bMenaceur et al, 2016;Sun & Cui, 2018). Liu et al (2016a) pointed out that three modes of pore size evolution existed during drying for reconstituted clayey soil.…”

“…Zhang et al (2017) investigated the microstructure of silt slurries upon drying and reported that the sodium chloride (NaCl) solution led to a noticeable reduction of total porosity, and an increase in predominant pore entrance diameter. Liu et al (2016b) performed MIP and SEM tests on oven-dried and freeze-dried compacted specimens which were initially immersed in distilled water or salt solutions. They observed that the total void ratio and the volume of macro-pores decreased as salt concentration increased due to the crystallization of salts: the higher the salt concentration, the more the precipitated salts and the more the pores filled by salt crystals.…”