The suitability of replacing Portland cement by an as received dealuminated calcined kaolin waste obtained from an alum production factory through the extraction of aluminum, also by dealuminated samples treated with lime solution, is investigated. The chemical and mineralogical compositions of the samples are measured. Their pozzolanic reactivity and their surface areas were determined. The effect of replacement on the setting time, the flowability, rate of flowability loss and strength of mortars was tested and compared to control OPC samples and others containing silica fumes. It was found that the as received dealuminated kaolin and that treated with lime possess higher pozzolanic reactivity and show larger surface areas than silica fumes. The incorporation of the as received dealuminated kaolin in OPC paste accelerates the setting time; while the lime-treated samples lead to retardation. The flowability of the OPC mortar is little affected by the as received DK samples and is strongly reduced by the lime-treated one and silica fumes. The three admixtures cause strong flowability loss with time. The 56d-compressive and tensile strengths of the mortars improve with 5 and 10% OPC replacement by DK.