DMRB Flexible Road Pavement Design Using Re-Engineered Expansive Road Subgrade Materials with Varying Plasticity Index

Abstract

Pavement thickness is a very vital component during the design stage of a road construction project. Pavement design helps to determine the costs of the project over a certain period to ascertain how the cost of road pavement construction affect the life cycle cost of the road. Road pavements are designed based on the type of subgrade material and the expected traffic load to help clients and decision-makers make decisions on the project. In this study, expansive road subgrade materials were improved using lime and cement and their California Bearing Ratio (CBR) was used in road pavement design. The study used the Design and Manual for Roads and Bridges (DMRB) as a guide to investigating the effect of stabilised expansive road subgrade with varying CBR values on road pavement design. The mineral structure, characteristics, Atterberg limit, compaction CBR, swell and microstructural analysis (scanning electron microscopy (SEM) and Energy Dispersive X-ray (EDX)) of stabilised subgrade materials were investigated. The results show an increase in California Bearing Ratio (CBR) values and a reduction in swell values while curing age increased for stabilised subgrade materials. Treated samples show high Calcium Silicate Hydrate (C-S-H) gel formation after 7 and 28 days of curing. The thickness of road pavement was observed with an increase in CBR values. The study established that the thickness of road pavement and overall construction cost can be reduced using cement and lime as additives in subgrade stabilisation.