Mechanisms for efficient clay dispersing effect with tannins and sodium hydroxide

Substituting the industrial additives in building materials with natural ones can reduce the embodied carbon in the construction sector. In this paper, the dispersing effect of oak tannin as natural dispersant on clay materials is studied in combination with sodium hydroxide. Through rheological measurements, adsorption tests, and zeta potential measurements, the deflocculation mechanism of tannin under varied NaOH environments has been highlighted. The results show that the dispersing ability of tannin can be increased greatly with the incorporation of NaOH. By adding NaOH in the system, the kaolinite deflocculation mechanism of tannin is changed from steric hindrance to combined steric hindrance and electrostatic repulsion forces. This shift stems from two aspects: the transformation of the tannin chemical structure and the modification of kaolinite by NaOH. The results indicate that tannin coupled with NaOH can be a promising superplasticizer for earthen materials, with the potential of producing poured earth based on this combination.