Effects of Chemical Stabilisation of Eggshells-Lime and Fly-Ash-Cement on the Structural Strength of Subgrade Soil in Rural Roads

Khan, Mohammad Shanawar; Amin, Shohel · 2022 · Crossref

DOI: 10.21926/rpm.2203013

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Summary

This study investigates the chemical stabilization of subgrade soil for rural roads, specifically comparing the efficacy of eggshell powder (ESP) combined with lime against fly-ash combined with cement. The research is motivated by the poor condition of unpaved rural roads in developing countries like India, where seasonal moisture variations degrade soil bearing capacity. While lime, cement, and fly-ash are common stabilizers, they can be expensive or environmentally taxing. The authors propose ESP, a low-cost, eco-friendly waste product rich in calcium carbonate, as a viable alternative to enhance soil structural integrity and reduce construction budgets. The methodology involved collecting soil samples from three unpaved roads in the Ganderbal district of Jammu & Kashmir, India. The untreated soil was characterized as clay with low plasticity, having a liquid limit of 37 and a plasticity index of 10. Laboratory experiments followed Indian Standard IS: 2720 1985. The study tested two stabilization mixtures: ESP mixed with a fixed 6% lime, and fly-ash mixed with a fixed 4% cement. Both ESP and fly-ash were varied at proportions of 2%, 4%, 6%, and 8% of the total soil mass. Samples were compacted using standard Proctor tests to determine optimum moisture content and maximum dry density. California Bearing Ratio (CBR) tests were conducted on soaked specimens (soaked for four days) to simulate worst-case moisture conditions, measuring load-penetration curves at 2.5 mm and 5 mm penetration. The results indicated that chemical stabilization significantly improved the bearing capacity of the subgrade soil compared to the untreated sample, which had a CBR value of 6.73%. For both stabilization methods, the CBR values increased with the addition of additives up to 4%, after which further increases in ESP or fly-ash content did not yield significant improvements and sometimes led to decreased performance. The optimal mixture of 4% ESP and 6% lime achieved the highest CBR value of 19.06%. The comparative mixture of 4% fly-ash and 4% cement achieved a CBR value of 18.73%. These values fall within the standard range (15–19%) required for subgrade materials in flexible pavement design according to IRC 37-2012 codes. The study concludes that ESP-lime stabilization is an effective, economical, and environmentally friendly alternative to fly-ash-cement stabilization for improving rural road subgrades. The comparable CBR values suggest that ESP can replace more expensive or resource-intensive stabilizers without compromising structural strength. This approach not only enhances road durability but also addresses waste management issues by utilizing kitchen waste. The authors note that increased bearing capacity allows for thinner pavement structures, reducing overall construction and maintenance costs. Future research is recommended to explore seasonal temperature variations, other soil types, and additional stabilizers like geosynthetics.

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