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

Marine clay soils along India’s coastline, particularly in the VCIC, have formed over thousands of years through geological, sedimentary, and geochemical processes. These soft, highly compressible clays originated during the Holocene epoch due to alternating sea-level fluctuations, river sediment deposition, and marine transgressions. The soils are fine-grained, highly plastic, and contain high moisture content, often exceeding 100%, resulting in low shear strength and poor drainage, which pose challenges for infrastructure development.

Materials and Methods:

• Marine Clay: Collected from Kakinada at 1.5 m depth, representative of deltaic soft clay soils.

• Foundry Sand (FS): Industrial by-product from metal casting, high in silica, used for soil stabilization.

• Alkaline Activator Geopolymers (AAG): Made from NaOH and Na?SiO?, used as eco-friendly binders to enhance soil strength and durability.

Objectives:

1. Characterize physical, chemical, and engineering properties of Kakinada marine clay.

2. Investigate the effectiveness of FS and AAG in improving soil geotechnical performance.

3. Optimize FS–AAG mix proportions for maximum strength and durability.

4. Evaluate improvements via California Bearing Ratio (CBR) and cyclic plate load tests.

Key Findings:

• Untreated marine clay is extremely soft, highly plastic, with low bearing capacity (CBR 1.52%) and high swell potential (DFS 82–95%).

• Addition of 10% FS with varying AAG (0.5–1.5%) significantly reduced differential free swell from 95% to 40%, improving soil stability.

• FS and AAG effectively enhance strength, reduce plasticity, and provide a sustainable alternative to conventional cement stabilization.

Significance:
The study demonstrates that combining industrial by-products (FS) with geopolymers (AAG) offers an eco-friendly and efficient solution for stabilizing weak coastal marine clays, supporting resilient infrastructure development in VCIC.

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.