Understanding the acting mechanism of NaOH adjusting the transformation of viscoelastic properties of alkali activated phosphorus slag

Abstract

The transformation of the viscoelastic properties of alkali activated phosphorus slag fresh pastes (AAPS) from the viewpoints of both dispersion effect and hydration was investigated by the in-situ measurement of a microrheology analyzer basing on the measurement of the mean square displacement of particles (MSD). Measurements on microrheological properties, zeta potential, X-ray diffraction, calorimetric response, infrared spectroscopy, SEM and thermogravimetric analysis of AAPS, were carried out. Corresponding parameters (that is Elasticity index (EI), Macroscopic viscosity index (MVI), storage modulus (G′), loss modulus (G″)) were extracted from the MSD curves to quantitatively analyze the changes of viscoelastic properties of AAPS with different NaOH content. Results shown that different NaOH content can lead to notable changes on the viscoelastic properties of AAPS on the base of the various dispersion degree and hydration process of pastes. With the increasing of NaOH content (S1–S5), the transformation of the viscoelastic properties on the AAPS was delayed in terms of the evolution of microrheological parameters with escape time, which owed to the low hydration rate of AAPS merely generating the small quantity of hydration products. In addition to this, electrostatic repulsive force between particles was enhanced promoting the dispersion effect. On the contrary, when the concentration of NaOH reached a threshold (S6–S8), the transformation rate of the viscoelastic properties on the AAPS pastes significantly accelerated. The result was attributed to that higher hydration rate led to more hydration products and stronger cross-linking for inter-particles, together with the decreasing electrostatic repulsive force.