Effective binder based on the artificial anhydrite for manufacturing of filling mixtures

The article exposes the results of research on the development of filling mixtures based on artificial anhydrite obtained after the interaction of concentrated sulfuric acid and limestone flour. The anhydrite derivation method has a significant impact on its properties and brings more options for the application. The key features of artificial anhydrite are high compressive strength which is more than 50 MPa and extended setting time which is more than 10 hours. In order to use it as a binder in the filling mixtures, it is necessary to modify properties of the anhydrite by integrating the hardening activators. In the relation to the study it was found that the optimal activator providing desirable setting start time (at least 2 hours) and a sufficient set of strength in the first 7 days of hardening is a mixture of 5% portland cement CEM I 42,5 and 1% of potassium sulfate, where 100% is the mass of binder. The additional inclusion of Melment F10 plasticizer in the amount of 0.4 to 1% of the binder ensures the achievement of the such parameters as the 0.3 water-binder ratio, setting start from 120 to 225 min, final setting time from 180 to 355 min, compressive strength after 24 hours from 6.9 to 13.3 MPa, after 7 days from 24.0 to 33.5 MPa. The microstructure of the binder has been analyzed and the modification options of the artificial anhydrite have been revealed in order to regulate its technical and technological properties., Two compounds of the filling mixture have been developed on the basis of the obtained binder, technical properties of compounds satisfy the maximum requirements for filling materials for depleted underground spaces. Research results have shown an opportunity and a prospectively of integrating the modified artificial anhydrite in structures of filling mixtures