Preparation, characterization and rheological analysis of eco-friendly road geopolymer grouting materials based on volcanic ash and metakaolin

Geopolymer has been applied in road engineering as an environmentally friendly material. This study prepared geopolymer road grouting pastes in different mixture ratios of volcanic ash (VA) and metakaolin (MK). The mechanical properties, setting time, bleeding and expansion ratio, fluidity and expansion ratio, time-dependent rheological analysis were systematically evaluated. Finally, the microscopic experiments, including X-Ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy with Energy Dispersive Spectrometer (SEM-EDS), were conducted to investigate the mechanism of geopolymerization based on VA and MK. The results showed that the mechanical strength increased with the content of MK. The flow curve of all pastes fitted the Bingham model. With the increase of MK content, the yield stress and plastic viscosity coefficient increased, which is because the stacked multilayer gullies microstructure aggravated the internal friction of paste particles, which led to decreased expansibility and pumpability. When the mass ratio of VA/MK was 1:0.33, the paste achieved the balance of mechanical strength and rheological properties with superior water retention and deformation resistance. The microscopic experiments showed that MK's mechanism enhanced the mechanical strength of geopolymer due to its high content of amorphous phases, smaller average particle size, and rich content of Al element. The SEM-EDS indicated that the MK improved the mechanical strength also by the improvement of nucleation effect. VA and MK complement each other in mechanical strength development under room temperature and fluidity, which are expected to be an alternative for cement as an eco-friendly road grouting material.