Influence of additives on poured earth strength development

The aim of this paper is to study the influence of the deflocculation/flocculation process on the cohesion of clay-based materials by investigating the changes in their internal structure. Indeed, as the cohesion of earth materials finds its origin in the capillary forces between clay particles, strongly linked to the porosity of the material, the relationship between the additives, porosity and compressive strength must be understood. The fresh state properties and hardened state properties of the clay mortars, mix designed with different types of mineral additives (phosphate-based as a dispersant and calcium and magnesium based as a coagulant), were determined and compared to those of their micro- and macrostructure based on thermal gravimetric analysis. The results show that the dispersant has a strong impact on the compression strength of clay-based materials due to the optimized organization of the clay particles during the deflocculation step, leading to an increase in the capillary force intensity. Experiments confirm that coagulants decrease the global porosity and compression strength according to their solubility and reaction time. When the reaction between the dispersant and the coagulant is slow, the benefit of the dispersant on clay platelet organization, which influences the mortar stiffness and global porosity, is maintained, and the final strength is high. The TGA confirms that the coagulant has no impact on the microporosity and that the earth material returns to its initial state. Finally, guidelines for mixing and pouring can be highlighted to maximize the strength of poured earth without the addition of hydraulic binder.