Evaluation of the structural characteristics of cement and fly ash stabilized desert sand

Soil improvement or stabilization is a process of altering the physical characteristics of soils to improve their rheology, namely their shear strength characteristics. This process is beneficial when the readily available soils for road construction, is unable to withstand the projected traffic loads. Whether the improvement or stabilization focuses on the base layer or the subbase layer, or both, the bearing capacity of the whole pavement is increased, which results in meaningful technical due to added strength, economic due to reduced costs and environmental consequences because of lesser transport associated pollution. It is well documented that Natural Desert Sand (NDS) referred to as dune sand is unfit for road construction. NDS is made up of fine and rounded particles, and therefore, it lacks the coarseness and angularity found in mechanically controlled and Crushed Fine Aggregate (CFA) that inherently creates an interlocking mesh, resulting in a stronger aggregate skeleton. As a result, bases or subbases made of NDS do not provide adequate support for even lowvolume roads, compared to bases or subbases made of CFA. Therefore, adequate road construction material needs to be hauled, imported and even shipped over long distances in African countries like Senegal, Mali, Benin, Chad, Cote d’Ivoire, Algeria and Libya. Ordinary Portland Cement (OPC) has however been used for many decades in small quantities to improve soils performance in compression, or in larger quantities to stabilize and increase flexural strength by increasing the rigidity of the soils. In addition to the recourse to OPC, recourse in reasonable quantities to cheaper and readily available NDS, adjacent to the projected road alignment, saves on extracting, crushing, importing and hauling or shipping over long distances, good quality materials. This ultimately saves valuable and scarce aggregate resources which would have otherwise provided the needed coarseness and angularity. This thesis investigates the improvement (flexible behaviour of the pavement in compression) and even the stabilization (rigid behaviour of the pavement in flexure) of NDS with OPC and with a combination of OPC-fly ash (FA), for bases and subbases of low-volume roads crossing desert land and subject to overloaded trucks. By increasing the base and subbase strength with these cementitious binders, the thickness of the asphalt concrete (AC), base and subbase layers can be substantially reduced. This is due to the s