04354nam a2200337 4500 MY-KuUP 20260306122222.0 t||||fr|||| 000 0 ta 260306t20252025my a|||fr|||| 000 0 eng d THE0010424 (Local) Hardback UMPSA eng UMPSA rda FTKA .M37 2025 r Thesis Maryam Moh’d Subhi Fadil Al Jaber, author. Peat soil stabilization using gypsum and concrete waste to activate microbially induced calcium precipitation (MICP) / Maryam Moh’d Subhi Fadil Al Jaber Kuantan, Pahang : UMPSA, 2025 © 2025 xv, 250 pages : illustrations ; 30 cm. + 1 CD-ROM. rdacontent text rdamedia unmediated rdacarrier volume rda text file PDF Faculty of Civil Engineering Technology Thesis (Master of Science) -- Universiti Malaysia Pahang - 2025 Includes bibliographical references Tropical peat soils present significant geotechnical challenges due to their high organic content, excessive compressibility, and low strength. This study investigates Microbially Induced Calcite Precipitation (MICP) as a sustainable stabilization technique, utilizing Magnesium-Rich Synthetic Gypsum (MRSG) and concrete waste as biocatalysts to stimulate indigenous microbial activity. Control soil samples (C1, C2, C3, and C4) were collected from Gebeng, Kuantan, Pahang, Malaysia, at depths of 0.5 m for C1 and C3, and 1 m for C2 and C4. Stabilized samples were prepared by mixing 10% MRSG and 10% concrete waste by dry weight and cured for 7 and 28 days. The stabilization process induced a substantial pH increase, shifting from strongly acidic (3.47–4.0) to near-neutral conditions (6.44–7.35), while simultaneously supplying critical elements required for MICP activity, including calcium ions that facilitate calcite precipitation. This pH modification, combined with the chemical inputs from the additives, altered the microbial community structure, leading to a decrease in overall bacterial diversity but a targeted enrichment of MICP-related bacteria. Deoxyribonucleic Acid (DNA) sequencing of the untreated soils revealed low populations of MICP-related bacteria, with Pseudomonas at 0–0.03% and Bacillus at 0.07–0.09%, while Stenotrophomonas and Brevibacillus were nearly absent. After stabilization, substantial microbial enrichment occurred; Pseudomonas and Bacillus reached 19.23% and 30.63% in S1; Pseudomonas (31.98%), Brevibacillus (21.22%), and Stenotrophomonas (1.28%) in S2; Bacillus (42.80%) and Stenotrophomonas (8.32%) in S3; and Pseudomonas (61.48%) and Brevibacillus (21.55%) in S4. These microbial shifts directly enhanced calcium carbonate precipitation, reflected in substantial improvements in Unconfined Compressive Strength (UCS), with increases of 542.18% in S1, 393.15% in S2, 405.41% in S3, and 207.29% in S4. Dense calcite networks bridging soil particles were identified through Scanning Electron Microscopy (SEM) and elemental mapping. Energy-Dispersive X-ray Spectroscopy (EDX) analysis confirmed significant enrichment of calcium and carbon within the stabilized samples, reflecting the substantial precipitation of calcium carbonate. X-ray Diffraction (XRD) analysis further verified the dominance of calcite as the primary mineral phase, accompanied by minor amounts of vaterite and dolomite, indicating successful mineral transformation through MICP. The presence of strong carbonate and sulphate functional groups detected by Fourier-Transform Infrared Spectroscopy (FTIR) spectra, together with the improved thermal stability observed in Thermogravimetric Analysis (TGA), provided further evidence of extensive microbial mineralization and the formation of stable calcite networks. This study demonstrates that indigenous bacteria can be effectively stimulated to achieve in-situ MICP stabilization of tropical peat soil, offering a cost-effective and environmentally friendly alternative without the need for external inoculation or chemical treatments. Faculty of Civil Engineering Technology Dissertations Universities and colleges Dissertations Theses Dissertations lcc THESIS 0 0 lcc 0 0 10000 10000 2026-03-06 0 FTKA .M37 2025 r Thesis T000004794 2026-03-06 12:22:50 2026-03-06 THESIS 0 0 lcc 0 0 10000 10000 2026-03-06 0 CD13998 T000004795 2026-03-06 12:23:31 2026-03-06 THESIS 104276 104282