NaOH Activation of Raw Soils: Effect of NaOH Content on the Drying Kinetic and Its Modelling

NaOH activation of soils is an affordable and promising way to improve mechanical properties of earthen bricks. If for well-activated geopolymers, the hard polymeric network limits the influence of water on mechanical properties, for the weakly activated one, as non-calcined raw clayey soils, the influence of water on these properties would be more critical. This work aims to determine the effect of sodium hydroxide concentration on the drying kinetics of bricks made with raw clayey soils, and to model this kinetics. The results show that the drying kinetics is governed by the diffusion of water due to the absence of free water. The drying duration increases linearly with the increasing of NaOH content, while the volumetric shrinkage decreases, probably thanks to the reduction of the material porosity during the formation of the zeolitic structures. Besides, the drying duration is strongly and negatively correlated with the initial drying rate (−0.97) and bricks did not show visible cracks. Among the five parametric models tested, the Khazaei’s model is the best in terms of all statistical criteria considered. For all models used, the coefficient of determination is ranged from 0.993 to 0.999, and the evolution of the models’ parameters is in accordance with that of the drying kinetics observed.