Mix proportioning of mortars in tension,with particular reference to developing countries

Production of cement based rainwater harvesting tanks in developing countries differs from the situation in industrialised nations, with low aggregate quality, negligible labour costs relative to material cost and use of unreinforced mortar in tension. The present paper details an experimental programme undertaken on mortars made with representative materials to determine their tensile performance. It appears that in lean mortars a synthesised sand, containing 20 wt-% kaolin clay (representative of local sands, often used in construction in Africa) gives higher strengths than clay free (standard) sand, while the same level of montmorillonite lowers the strength for rich or lean mortars. Economic modelling indicates that, for bending loading (maximum stress inversely proportional to thickness squared), using kaolin contaminated sand is preferable to using standard sand. However, the montmorillonite contaminated sand must cost around 2/3 less than the imported sand to become competitive. For membrane loading (maximum stress inversely proportional to thickness), kaolin contaminated sand is preferable only when it is considerably cheaper than standard sand, and montmorillonite contaminated sand is never preferable in practical situations.