Properties of grouting mortar modified with alunite/bauxite/gypsum ternary system as expansion component

The ettringite results from alunite/bauxite and gypsum which has the characteristic of fast setting and volume expansion, so the main properties and microscopic structure of grouting material modified with alunite/bauxite and gypsum at different proportion were investigated. The results have shown that the grouting mortar modified with 7-20% content of bauxite/alunite/gypsum had the properties such as the setting time could be controlled below 1 hour, long-term expansion rate stabilized basically as 0.2%, compressive strength of 1, 3 and 14 days were more than 17 MPa, 31 MPa and 50 MPa, respectively; the pullout force of 1 meter sample at 14 days reached 87 kN. The micro-analyzing by using MIP, SEM and XRD showed that there were plenty of expansive crystals and tiny pore structures in harded paste which can exist steadily for a long term. The achievements will provide an important basis to application of cement-based grouting material as first-aid repairing.