Properties of Bolt-Grouting Mortar Modified with Mineral Bauxite by Chemical Activation

In this paper, the authors study the properties of cement-based bolt-grouting mortar that has been modified by adding mineral bauxite and gypsum. The results showed that when the bolt-grouting mortar consisted of approximately 12.5% bauxite and gypsum with a 1.0% addition of Portland Cement Association (PCA) type 4 (polycarboxylate superplasticizers), with a water-binder ratio equal to 0.3, it had the ideal properties, including a setting time between 0.5 and 1.5 h. The expansion rate on the 3rd day was larger than 0.09%, and the long-term expansion rate after 28 days stabilized at around 0.18%; the values of compressive strength at the 3rd and 28th days reached 34 MPa and 68 MPa, respectively. The maximum pullout load measured on a 1-m-long specimen on the 14th day was 71 and 87 kN. The hardened mortar was dense, as expected. The microanalysis using mercury intrusion porosimetry (MIP) and X-ray diffraction (XRD) showed that the total porosity of hardened mortar was less than 2.5%. There were plenty of ettringite crystals in the hardened paste, which was found to be able to endure steadily for a long period of time. The properties of cement-based, bolt-grouting mortar can be significantly improved by adding mineral bauxite and gypsum.