Quaternary ammonium compounds as modifiers of the rheological properties of metakaolin geopolymer

Abstract

Geopolymers typically exhibit low yield stress, which is beneficial in most conventional applications but poses limitations for emerging technologies such as 3D printing. This study investigates the use of quaternary ammonium compounds, each differing in the length and number of aliphatic chains, as admixtures to modify the rheological properties of metakaolin-based geopolymers. These admixtures caused a slight increase in the plastic viscosity, but a substantial increase in the yield stress up to 20 times. Time-dependent rheological measurements showed rapid structural recovery of the modified fresh geopolymer paste, which is particularly favourable for 3D printing applications. The dosage and number of long aliphatic chains played a critical role, with double-chained molecules proving more effective than their single-chained counterparts. The interactions of the admixtures with the particles in the fresh geopolymer paste were studied by surface tension and zeta potential measurements, as well as molecular dynamics simulations, which supported the observed rheological behaviour.Geopolymers typically exhibit low yield stress, which is beneficial in most conventional applications but poses limitations for emerging technologies such as 3D printing. This study investigates the use of quaternary ammonium compounds, each differing in the length and number of aliphatic chains, as admixtures to modify the rheological properties of metakaolin-based geopolymers. These admixtures caused a slight increase in the plastic viscosity, but a substantial increase in the yield stress up to 20 times. Time-dependent rheological measurements showed rapid structural recovery of the modified fresh geopolymer paste, which is particularly favourable for 3D printing applications. The dosage and number of long aliphatic chains played a critical role, with double-chained molecules proving more effective than their single-chained counterparts. The interactions of the admixtures with the particles in the fresh geopolymer paste were studied by surface tension and zeta potential measurements, as well as molecular dynamics simulations, which supported the observed rheological behaviour.