Search

Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [ABSTRACT FROM AUTHOR]

The present study demonstrates the effect of using natural kenaf fibres on the strength behaviour of weak subgrade soils. The two types of soils classified as silt of high compressibility (MH) and clay of intermediate compressibility (CI) are used in this study. Laboratory compaction, soaked California bearing ratio (CBR) and unconfined compressive strength (UCS) tests are conducted on soil samples reinforced with kenaf fibres at four different percentages (i.e., 0.0625%, 0.125%, 0.25% and 0.50%) by weight of soil. Maximum improvements of 150% in CBR and 84% in UCS are reported when silty soil is reinforced with kenaf fibres, whereas these increases are only 18% and 40%, respectively, in case of clayey soil. Smaller post peak strength loss and greater failure strain are observed for soil samples reinforced with various percentages of kenaf fibres with more pronounced effect in case of silty soil. The scanning electron microscope images indicate significant bonding between soil particles and fibres in case of silty soil, thus causing stress transfer from soil to reinforcing material, which leads to strength enhancement, whereas this is lacking in clayey soil. Multiple linear regression analysis is used to develop predictive models for soaked CBR and UCS in terms of compaction characteristics and fibre content. [ABSTRACT FROM AUTHOR]