Evaluation of Microstructural Characteristics and Mechanical Behavior of Selected Soils for Highway Engineering

Lateritic soils (LS) and lateritic gravels (LG) are widely used in road construction across tropical regions, yet their performance is influenced by variable geotechnical, mineralogical, and mechanical properties. This study presents a comparative evaluation of LS and LG obtained from two borrow pits in Ogun State, Nigeria. Laboratory investigations included index properties, compaction characteristics, unconfined compressive strength (UCS), and microstructural assessments using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Results revealed that LG contained a higher proportion of gravel (34.6%) and fewer fines (18.4%) compared to LS (7.6% gravel, 50.2% fines). LG exhibited superior compaction behavior with a maximum dry density (1.800 Mg/m³) and lower optimum moisture content (13.90%) relative to LS. UCS values after 28 days of curing were 831.74 kN/m² for LG and 600.57 kN/m² for LS, indicating better mechanical performance in LG. Mineralogical and microstructural analyses confirmed predominant quartz peaks in both materials, with LG displaying additional goethite phases and a more porous morphology. The study concludes that LG is a viable alternative to LS for pavement subgrade and sub-base applications, offering improved strength and durability.