Evaluation Studies on Marine Clay Stabilized with Foundry Sand and Geopolymer as Subgrade for Flexible Pavement

Abstract

Marine clay deposits prevalent along coastal corridors present significant geotechnical challenges due to their low shear strength, high compressibility, and volumetric instability under fluctuating moisture conditions. This research proposes an advanced stabilization strategy for marine clay subgrades through the synergistic use of foundry sand (FS) and alkali-activated geopolymer (AAG) binders formulated from sodium hydroxide (NaOH) and sodium silicate (Na?SiO?). The objective of present investigation is to develop a sustainable and high-performance subgrade material suitable for flexible pavement applications in coastal environments. A comprehensive experimental program was carried out to investigate the effects of foundry sand content and activator molarity on the mechanical and durability performance of the stabilized marine clay. Laboratory tests including Atterberg limits, compaction characteristics, unconfined compressive strength (UCS), and California Bearing Ratio (CBR) tests were conducted. The inclusion of 10% FS and 1.5% AAG reduced plasticity index by 71%, increased maximum dry density from 1.58 to 1.72 g/cc, and improved soaked CBR from 1.34% to 8.07%. These findings confirm the potential of FS–AAG blends as sustainable, high-performance stabilizers for marine clay subgrades in flexible pavement applications. The optimized formulation exhibited substantial gains in Compaction and CBR values with improved moisture resistance, confirming its suitability for sustainable pavement foundation systems. This study contributes to the advancement of eco-efficient soil stabilization techniques by utilizing industrial by-products and minimizing dependence on conventional cementitious materials in coastal infrastructure development.

Introduction

The study focuses on marine clay soils along India’s east coast, particularly within the Visakhapatnam–Chennai Industrial Corridor (VCIC). These soils, formed over thousands of years through geological, sedimentary, and geochemical processes, are soft, highly compressible, and weak due to high moisture content, low shear strength, and clayey texture. The deposition of fine sediments during Holocene sea-level fluctuations, combined with saline and organic matter influences, created extensive marine clay deposits near Kakinada, Machilipatnam, and Chennai. These soils pose engineering challenges for infrastructure due to high compressibility, low bearing capacity, and poor drainage.

The study investigates soil stabilization using Foundry Sand (FS) and Alkaline Activator-Based Geopolymers (AAG):

• Marine clay was collected from Kakinada (soft, highly plastic).

• Foundry sand is a high-purity industrial by-product used in casting, which can be recycled for geotechnical applications.

• Geopolymers (NaOH + Na?SiO?) act as sustainable binders to enhance strength, durability, and load-bearing capacity of soils.

Objectives: Characterize marine clay properties, evaluate FS and AAG as stabilizers, optimize mix proportions, and test performance through CBR and cyclic plate load tests.

Key Findings:

• Differential free swell (DFS) reduced from 95% to 40% with optimal FS + AAG treatment.

• Atterberg limits (Liquid Limit, Plastic Limit, Plasticity Index) decreased significantly, improving soil workability and reducing plasticity.

• Optimum Moisture Content (OMC) decreased and Maximum Dry Density (MDD) increased with FS + AAG, indicating improved compaction and strength.

• The optimum AAG percentage for treatment was 1.5%, combined with 10% FS, for best geotechnical improvement.

Conclusion

1) It is noticed from the laboratory test results that the Differential Free Swell Index of Marine Clay has been reduced by 42.11% on the addition of 10% Foundry Sand (FS) and it has been further reduced by 27.27% with an addition of 1.5% Alkali-activated geopolymer (AAG) when compared with untreated Marine Clay. 2) It is observed from the laboratory test results that the Liquid limit of Marine Clay has been decreased by 8.81 % on the addition 10% FS of and it has been further decreased by 25.22 % with an addition of 1.5% AAG. 3) It is observed from the laboratory test results that the Plastic limit has been increased by 25.30% on addition of 10% FS and it has been further increased by 3.97% with an addition of 1.5% AAG. 4) It is noticed that the Plasticity Index has been decreased by 33.41% on addition of 10% FS and it has been further decreased by 64.78% with addition of 1.5% AAG. 5) It is observed from the laboratory tests that the OMC of the Marine Clay has been decreased by 48.27% on the addition of 10% FS and it has been further decreased by 7.92 % with addition of 1.5% AAG. 6) It is observed from the laboratory tests that the MDD of the Marine Clay has been increased by 6.96% on the addition of 10% FS and it has been further increased by 2.38% with addition of 1.5% AAG. 7) It is observed that the CBR of the Marine Clay has been increased by 334.33% on the addition of 10% FS and it has been further increased by 38.66% with addition of 1.5% AAG. The optimized mix of 10% foundry sand and 1.5% alkali-activated geopolymer significantly enhances marine clay subgrade strength and can be adopted for coastal pavement foundation systems.

References

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Copyright

Copyright © 2025 Dr. D. Koteswara Rao, Sangepu Sairam. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.