Properties of cement-based bolt-grouting materials modified with alunite and gypsum

This paper discusses the development of a grouting material with a short setting time, early strength, high strength and appreciable volume expansion. The main properties of the grouting material were studied with respect to different ratios of added alunite and gypsum. The results showed that when the appropriate amounts of alunite and gypsum were added to the mortar the setting time was controlled between 0·5 h and 1·5 h, compressive strength on the first day and the third day reached 20 MPa and 40 MPa, respectively and the pull-out force of a 1 m long sample on day 14 was 90 kN. Microanalysis of the material using mercury intrusion porosimetry, scanning electron microscopy and x-ray diffraction revealed the presence of numerous expansive crystals structures that existed steadily for a long period.