Effects of redispersible polymer powders on the structural build-up of 3D printing cement paste with and without hydroxypropyl methylcellulose

摘要

This paper studies the effects of polyvinyl acetate-ethylene (VAE) based redispersible polymer powder (RPP) and polyvinyl acetate-vinyl versatate-ethylene (VVE) based RPP on the structural build-up of 3D printing cement paste within several hours of hydration. At the same time, two cases of the presence or absence of hydroxypropyl methylcellulose (HPMC) were considered. The build-up performance of cement paste was assessed by the hysteresis area, dynamic yield stress ratio, static yield stress, shear modulus and ultrasonic plus velocity from the dynamic shear test, static shear test and ultrasonic wave transmission test. In addition, the limit layer thickness and printing velocity were calculated by dynamic and static yield stresses to quantitatively characterize shape stability and printing efficiency of cement paste. Results indicate that both VAE with higher ethylene content (VAE1) and WE decrease the structural build-up rate of cement paste, independent of shear test modes. However, VAE with lower ethylene content (VAE2) increases the structural build-up rate of cement paste under dynamic shear test whereas decreases the growth rate of static yield stress. The dynamic yield stress ratio of cement paste containing 2% VAE2 is 0.57, which is 83.9% higher than that of pure cement paste. In addition, HPMC alters the effects of VAE2 on the structural build-up of cement paste. VAE1 and WE decrease the shape stability of cement pastes with and without HPMC, while VAE2 is beneficial to the shape stability of cement paste. Limit layer thicknesses of cement pastes with 4% VAE2 are 7.3 mm and 14 mm in the absence and presence of HPMC, which are about 3.0 and 5.8 times that of pure cement paste. In the absence of HPMC, WE decreases the limit printing velocity of cement paste in the first tens of minutes. VAE1 and VAE2 can improve the printing efficiency due to the increase of limit printing velocity in the first tens of minutes. In the presence of HPMC, only VAE2 significantly improves the limit printing velocity of cement paste. (C) 2020 Elsevier Ltd. All rights reserved.