Designing Subgrade for Flexible Pavement in Bottom Ash, Lime and Sodium Hexametaphosphate Stabilized Expansive Soil

Abstract

The current study examines the effective use of wastes, bottom ash which is mixed with lime and sodium hexametaphosphate (NAPO3)6, to stabilize the expansive soil in order to make a composite subgrade material for flexible pavement design. The study involves performing laboratory tests on expansive soil samples containing bottom ash and lime alone and along with (NAPO3)6, such as differential free swell, consistency limits, compaction characteristics, unconfined compressive strength tests and California bearing ratio. The results showed that adding an optimal amount of bottom ash (15%), lime (6%), and (NAPO3)6 (4.5%), both alone and in combination, reduces the differential free swell and consistency limits of expansive soil and increased the CBR values, accomplishing it into an effective subgrade material. The thickness of flexible pavement was designed using IITPAVE software by utilising the obtained CBR values, it met the required parameters based on the IRC: 37-2018 recommendations. The software analysis revealed a reduction in pavement thickness for different commercial vehicle traffic volumes (1000, 2000, and 5000), with the highest reduction in layer thickness and construction costs observed when expansive soil was combined with bottom ash (15%), lime (6%), and (NAPO3)6 (4.5%). This technology not only improves the geotechnical characteristics of subgrade soil, but it is also cost-effective and tackles the bottom ash disposal issue. Overall, this research proposes a novel method for developing a composite soil subgrade material for flexible pavement.