Effect of different superplasticizers on the mechanism, workability, and microstructure of biomass-activated grouts

Abstract

To promote the application of alkali-activated grouts in engineering, this study investigated the compatibility of different superplasticizers with biomass-activated grouts (BAGs) for the first time. The effects of naphthalene sulfonate (NSS), polycarboxylate (PCS), and melamine-sulfonated superplasticizer (SMS) and mechanisms by which they affect the workability of BAGs were revealed. The adsorption, dispersion, and microstructural characteristics of the BAGs were evaluated by total organic carbon (TOC), zeta potential, nuclear magnetic resonance, X-ray diffraction, Fourier-transform infrared, and scanning electron microscopy analyses. The fluidity of the BAGs treated with NSS, SMS, and PCS increased by 24.4, 20.4, and 41.0%, respectively; the NSS samples showed the lowest rate of fluidity loss (8.9%). Owing to the instability in alkaline environment, the rate of fluidity loss obtained with PCS and SMS was 15.9 and 15.3%, respectively. These values were significantly higher than that of the control (11.5%). Grout containing different superplasticizers is a shear-thinning fluid that conforms to the power law model. NSS and PCS shortened the initial setting time by 12.9 and 6.2%, and increased the 28 d compressive strength of the BAGs by 18.2 and 10.4%, respectively. Microstructural analysis showed that the superplasticizer can promote hydration of silicon and aluminum in the raw materials, thus optimizing the pore distribution and compactness of the hardened grout. The addition of NSS and PCS reduced the porosity by 4.17% and 2.84%, respectively. Considering the above properties, NSS has the best applicability to BAGs. The results can promote the engineering applications of geopolymer grouts with superplasticizers.