Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring

•Assessment of geopolymer mechanical properties and porous network over time.•Dependence of mechanical properties with the porous network characteristics.•Linear relation between young modulus and compressive strength.•Evaluation of the elastic properties by ultrasound. The effects of two formulation parameters, by changing the Si/Al molar ratio and the initial water content, were studied to understand their impacts on the aging of the metakaolin-based geopolymer. Five formulations were designed and resulting samples were conditioned under 100% relative humidity. Long-term mechanical characterizations (up to 360days) were conducted to measure the Young modulus and the compressive strength by ultrasound and compression tests, respectively. As well, porosimetry was performed using gravimetric technique (at 28-day term) and nitrogen sorption technique (up to 360days). At fixed Si/Al ratio when increasing the initial water content, results showed a decrease of mechanical parameters and the formation of larger porous network with an increasing effective pore diameter (from 5.3 to 11.1nm). Conversely, at fixed water content when Si/Al ratio increased, porous network characteristics were fairly identical with employed formulations, and mechanical parameters slightly increased. Also, during the seven first days, the mechanical parameter growth became slower when increasing Si/Al ratio.