Rheological and viscoelastic characterizations of fly ash/slag/silica fume-based geopolymer

Abstract

A greener, cleaner cement called geopolymer has recently been developed instead of Portland cement as a grouting material, with improved grout properties and reduced carbon dioxide emissions. Nevertheless, the investigation of geopolymer's rheological and viscoelastic characteristics is still inadequate for grouting materials. Therefore, in this paper, the rheological and viscoelastic properties of geopolymer grouting material (GGM) with different content of fly ash (FA), slag (SL), and silica fume (SF) are studied. It is concluded that for the shear stress with a fixed shear rate (100 s−1), using 20 %–30% SL to replace FA significantly partially increases the shear stress of FA-based GGM. Further use of 20 %–30% SF to partially replace SL reduces the shear stress of FA/SL-based GGM. The yield stress and plastic viscosity of GGM present similar trends with the shear stress. In contrast, the slump spread shows a change rule contrary to the above parameters. The static rheological behavior of all GGMs fits a Bingham model regardless of the time and mixture. An approximate linear decline of storage modulus (G′) was detected in the frequency sweep test, indicating the pseudoplastic dynamic rheological behavior of GGMs under the oscillatory shearing. The yield stresses of GGM with FA, SL, and SF are decreased over time under shearing load. These results signify that GGM with FA, SL, and SF can quickly recover good workability after retempering. SL and SF increase the G′ of GGM due to higher chemical adhesion and specific surface area, respectively, as evident from the amplitude sweep test. Using 20 %–30% SF to replace SL partially rose the peak G′ significantly and lowered the decline slopes of the G′ curve in the frequency sweep test. The fluctuation of G′ cure is also remitted considerably by the inclusion of SF. Calorimetric and Fourier Transform Infrared Spectroscopy (FTIR) tests revealed the quick generation of C-(A)-S-H, leading to the poor flowability of GGM with FA and SL. The rapid dissolution of SF increases the modulus of the activator and reduces the basicity of the activator, leading to the results of using SF to improve the flowability of GGM with FA and SL. The study indicates that geopolymer is suitable for using grouting material instead of Portland cement paste. Different combinations of FA, SL, and SF can be used to modify the flowability of GGM.