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This study focuses on the effect of consolidation time and water immersion on the thermal behavior of geopolymers based on mixture of kaolin and argillite calcined at 750 °C. In order to assess the fire resistance water and thermal treatment at 1000 °C were performed. Compressive strength and structural changes of the samples before and after treatment were investigated. It was demonstrated that the age of geopolymer (7, 14 and 28 days of consolidation) does not have a significant effect on strength neither before (22 MPa) nor after (30 MPa) thermal treatment. The results also show that all samples present higher compressive strength ratio (σafter/σbefore ~ 1.4). The geopolymer samples do not exhibit structural variation over the time in agreement with the compressive strength values. The good performance of compressive strength after 1000 °C was due to the formation of the same crystalline phases after heat treatment such as zeolite (4%) and leucite type phases (62%) and wollastonite (18%) which were also evidenced by SEM observations. The decrease of compressive strength after water immersion (16 MPa) and after thermal treatment (19 MPa) was explained by the decrease of arcanite by 70% as well as the amorphous phase content. Nevertheless, leucite (46%) and wollastonite (24%) were formed. In conclusion, the use of mixture of kaolin and argillite calcined at 750 °C leads to water and thermal resistant geopolymers.

International audience; The purpose of this work is to identify the effect of the cation nature on mechanisms of the sand consolidation with alkaline silicate solution at low temperature (70 °C). Three diluted lithium, sodium and potassium silicate solutions with [Si] = 2.8 mol/l were used to agglomerate sand composed of grains which mean diameter is 340 μm. According to the cation, different behaviors were observed in terms of the drying time and the material cohesion. Essentially, the drying time increases with decreasing cation size. In contrast, the compressive strength raises when the cation size increases inducing intra-granular rupture highlighted by SEM observations. This could find an explanation in the cation hydration sphere of cations. The strength of the cation-water electrostatic interaction becomes less important as the size of the cations increase leading to more ionic bonds. Despite their strong consolidation, potassium-based materials have a high solubility in water. This result is consistent with the ionic nature of bonds