Mineralogy, Particle-Size Distribution and Cement Dosage as Joint Controls of the Physico-Mechanical, Microstructural and Water-Transport Response of Some Cement-Stabilised Lateritic Soils from Western Cameroon in Road Construction

Lateritic soils are widely used in tropical road infrastructure, yet their response to cement treatment depends strongly on the properties of the untreated material. This study examines three lateritic soils collected at Ndandut, Kafeng and Bantoum III, in western Cameroon, under a common experimental programme combining particle-size distribution, consistency limits, Proctor compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric/differential thermal/derivative thermogravimetric analysis (TGA/DTA/DTG), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), water absorption, open porosity and capillary absorption. Cement contents of 0, 3, 5, 6 and 8 wt.% were investigated. At 8 wt.% cement, CBR rose from 46 to 145% for Ndandut, from 18 to 105% for Kafeng and from 32 to 115% for Bantoum III, while the corresponding 28-day UCS increased from 1.10 to 5.10 MPa, 0.83 to 4.10 MPa and 1.25 to 5.50 MPa, respectively. The highest final CBR and UCS values were reached by the soils with lower fine fractions, whereas Kafeng, with 89.82% passing the 0.075 mm sieve, remained the lowest-performing material across the tested series. Thermal analysis confirmed dehydration and clay mineral dehydroxylation, while the event recorded between 800 and 900 °C is interpreted cautiously, since no carbonate phase could be independently established from the available mineralogical evidence. SEM–EDS revealed treatment-related changes in particle arrangement and Ca-bearing regions but did not provide sufficient evidence to uniquely identify individual hydration phases. Water absorption, open porosity and capillary absorption all decreased with increasing cement content. The proposed Stabilisation Suitability Index (SSI) is presented solely as an empirical screening descriptor, since its weighting scheme and min–max normalisation were derived from the three soils studied and have not yet been independently validated. Collectively, these results indicate that cement dosage cannot be specified independently of mineralogical composition and fine fraction, and that these factors must be considered jointly when assessing the stabilisation of lateritic soils.