Kaolin samples of the same mass were treated at 700°C for the same duration of 30min by varying the rate of calcination (1, 2.5, 5, 10, 15 and 20°C/min) in order to obtain metakaolins which were used to produce geopolymers. Depending on the nature of each type of material, kaolin, metakaolins and geopolymers were characterized using thermal analysis, chemical analysis, XRD, FTIR, particle size distribution, specific surface area, bulk density, setting time and compressive strength. FTIR and XRD analyses showed that metakaolins except at 1°C/min contained residual kaolinite whose quantity increased with the rate of calcination of kaolin and which influenced the characteristics of geopolymers. Thus as the rate of calcination of kaolin increased, the setting time increased (226min (rate of 1°C/min)–773min (rate of 20°C/min)) while the compressive strength reduced (49.4MPa (rate of 1°C/min)–20.8MPa (rate of 20°C/min)). From the obtained results the production of geopolymers having high compressive strength along with low setting time requires that the calcination of kaolin be carried out at a low rate

The aim of this work is to valorize volcanic scoria by using them as starting material for geopolymers production. Nevertheless, volcanic scoria possesses low reactivity. Various amounts of metakaolin (5%, 10%, 15%, 20% and 25%) were added into two volcanic scoria (ZD and ZG) in order to improve their reactivity. Two alkaline solutions were used to activate the aluminosilicate materials. The starting materials were characterized by particle size distribution, specific surface area, chemical and mineralogical composition. The geopolymers were characterized by the setting time, XRD, FTIR, SEM and compressive strength. The results indicated that volcanic scoria have low specific surface area (2.3m2/g for ZD, 15.7m2/g for ZG), high average particle size (d50=13.08μm and 10.68μm for ZD and for ZG respectively) and low glass phase contents. Metakaolin have a smaller average particle size (d50=9.95μm) and high specific surface (20.5m2/g). The compressive strength of geopolymers increased in the ranges of 23–68MPa and 39–64MPa for geopolymers from ZD–MK and ZG–MK respectively. This study shows that despite the low reactivity of volcanic scoria it can still be used to synthesize geopolymers with good physical and mechanical properties