Effects of hydroxypropyl methylcellulose on anti-dispersion and rheology of alkali-activated materials in underwater engineering

Abstract

To explore the feasibility of applying alkali-activated materials (AAM) to underwater engineering. The effects of hydroxypropyl methylcellulose (HPMC) on the anti-dispersion and rheological properties of AAM were investigated. NaOH was selected as the activator, and granulated blast furnace slag (GBFS) and fly ash (FA) were used as precursors. The characteristics of anti-dispersion, rheology, and hydration heat change of alkali-activated slurry with 6 kinds of HPMC content (0, 0.2%, 0.4%, 0.6%, 0.8%, and 1%) and 4 kinds of alkali content (Na2O: 3%, 5%, 7%, and 9%) were discussed. The anti-dispersion was characterized by turbidity. The fluidity, gel time, yield stress and plastic viscosity were obtained from rheological tests. The hydration heat was measured by isothermal calorimetry. The results show that HPMC can improve the anti-dispersion of alkali-activated slurry with alkali content (Na2O: 3%, 5%), and the effect was good when the content exceeded 0.6%. Compared with that without HPMC, the turbidity was reduced by 98.4% at 1% HPMC content. With the increase of HPMC, the fluidity and gel time decreased, and the yield stress and plastic viscosity increased at the initial stage. The fluidity of alkali-activated slurry decreased by 23% and the plastic viscosity increased by 916%. It is due to the thickening effect of HPMC, which can change the anti-dispersion and rheology of slurry. The mechanism of HPMC can increase the attraction between raw material particles, and the molecular chains overlap to form a network structure that can wrap the alkali-activated slurry. The evolution of shear stress and hydration heat show that HPMC can delay the hydration reaction of AAM. When the alkali content is high (Na2O: 7%, 9%), HPMC has no obvious improvement in the anti-dispersion of alkali-activated slurry. The increase of HPMC content has no effect on the yield shear stress and plastic viscosity at the initial stage. It shows that HPMC fails at high Na2O content, which leads to loss of thickening effect. The paper is expected to guide for using HPMC in underwater engineering to improve the anti-dispersion and workability of AAM.