Development of stabilization additive for peat soil using mg-rich gypsum and concrete waste / Ayah Abdel Rahman Almsedeen

Faculty of Civil Engineering Technology

Thesis (Doctor of Philosophy in Civil Engineering) -- Universiti Malaysia Pahang Al Sultan Abdullah - 2025

Includes bibliographical references

Peat soil poses significant challenges for civil engineering applications due to its high compressibility, low shear strength, and high organic content. These poor properties have limited infrastructure development in peat-rich regions worldwide, highlighting the importance of effective stabilization methods. This study aims to develop a sustainable additive from Mg-rich gypsum and concrete waste to improve the weak properties and behaviour of peat soil. Traditional additives such as cement and lime are widely used but have disadvantages, including high cost, carbon emissions, and reduced efficiency in highly organic soils, establishing a need for alternative sustainable solutions. Proctor and unconfined compressive strength tests were used to evaluate the mechanical properties of the stabilized peat soil. The investigations into the mechanism of strength enhancement were conducted on the optimal design mixture, utilizing microstructural analysis through X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The mechanical test results revealed that a combination of 10% gypsum and 10% concrete waste was the optimal additive content, enhancing the strength of peat soil from 36 kPa to 850 kPa after 90 days of curing, an enhancement of approximately 2261%. The microstructural testing revealed the production of cementitious products, such as calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), in the stabilized sample. Statistical analysis using response surface (RSM) methodology was used to design a model by using four variables for the maximum strength of stabilized peat soil. The RSM indicates that the curing time is the most significant factor, and the developed model showed high reliability (R² = 0.963). The consolidated undrained test demonstrated an alteration from ductile to brittle behaviour, and the effective cohesion increased from 27 to 55, while the internal friction angle increased from 12.5 to 20. Additionally, the slope stability analysis using SLOPE/W software confirmed that stabilisation significantly improved the factor of safety for the critical 2:1 slope, increasing it from 1.722 to 3.385, an increase of approximately 96.5%. This analysis is particularly significant as slope performance in peat deposits is directly governed by shear strength, making stability evaluation essential for safe infrastructure development. This study concludes that the G-CW additive is an effective and sustainable solution for peat stabilisation. It not only addresses the engineering challenges of peat but also contributes to environmental sustainability by valuing industrial by-products, consequently reducing waste and reliance on conventional high-carbon stabilizers. The findings provide valuable insights for future applications in geotechnical engineering and infrastructure development over problematic soils.