Pre-compression and capillarity effect of treated expansive subgrade subjected to compressive and tensile loadings

Pavement structures often are under tension and compression mobilised by the coupled effects of traffic loads and swelling stress. Seasonal moisture variations cause capillarity rise and volumetric movement within the subgrade. The objective of this investigation is to evaluate the pre-compression and capillarity effect of expansive subgrades stabilised with activated fly ash (α-FA), and sisal fibre, analysed for tensile (qt) and compressive qu strengths. Moulding moisture content corresponding to the optimum water content was used to prepare the subgrade soils by random inclusion of 0.25 %, 0.5 %, 0.75 %, and 1.0 % of sisal fibre by dry mass of the subgrade soils treated with 20 % and 30 % of α-FA. Confined pre-compression stresses equivalent to 10 kPa and 20 kPa after 12 h of preparation were applied followed by 14 days of air-curing condition. Subsequently, the prepared subgrades samples were subjected to capillary rise through soaking. The test results revealed that both tensile and compressive strengths of 10 kPa and 20 kPa precompressed specimens decreased from 1.48MPa to 0.98MPa on average due to the capillarity effect, compared to non-capillary specimens. Without capillarity effects, an equivalent strength increases of 12.21 % and 63 %.11 were recorded for 10 kPa and 20 kPa of pre-compressed specimens compared to un-precompressed specimens tested under tension. The results further revealed that the subgrade soils treated with the combination of fibre and α-FA exhibited significant strength resistance under tension. The strength indices (qt/qu) of 0.13 to 0.31 as the proportionality of tensile and compressive strengths is closely correlated for all the pre-compressed composites due to fibre deformability.