Analysis of sandpits and suitable cement choice for optimum performance in Bamenda, Cameroon

Abstract

Sand properties and cement selection play a critical role in determining the performance and durability of concrete, particularly when aggregate mineralogy and chemistry are insufficiently characterised. This study investigates the mineralogical and physico-chemical properties of sands sourced from five sandpits (Wum, Mbengwi, Ndop, Chomba, and Mbatu) in the Northwest region of Cameroon and evaluates their compatibility with three commercial 42.5R-class cements (CIMAF, Dangote 3X, and MIRA-CO). Mineralogical characterisation was performed using X-ray diffraction, and mortar mixtures were prepared at a fixed sand-to-cement ratio (2.5) to assess water demand and mechanical performance. Mortar cubes with a size of 70 mm were prepared to evaluate the mechanical properties. Results show that Ndop sand exhibited the highest water absorption, at 15.17%, while Mbengwi recorded the lowest water absorption, at 8.07%. Chomba was found to be the densest sand, with a specific gravity (SG) of 2.537 g/cm3, whereas Ndop sand had the the lowest SG (2.427 g/cm3). The fineness moduli were within the normal range. Mbatu sand required the highest water-to-cement ratio (80%) when used with CIMAF and MIRA-CO cements, whereas Chomba required the lowest value (65%) when used with Dangote cement. In terms of mechanical properties, the highest 7-day and 28-day compressive strengths were recorded for CIMAF and Dangote cements, respectively, whereas MIRA-CO cement yielded the lowest strength values. The Dangote-Mbengwi pair achieved the highest 28-day compressive strength of 27.54 MPa, whereas the Mbengwi-MIRA-CO pair exhibited the lowest of 12.36 MPa. A similar trend was observed in tensile strength. The Dangote-Mbengwi pair was the best combination. Blended cements with pozzolanic additives exhibited superior long-term strength when combined with sands of low chemical reactivity and a high CaO/SiO₂ ratio, whereas fly ash-based blends performed better with more acidic sands. It is recommended that each sand be used with the cement with which it performs best in order to achieve improved properties.