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

Abstract

Abstract. 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 waterbinder 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.

Low energy synthesis of anhydrite cement from waste lime mud

“…Thus, it was confirmed that for materials with different structures, it is necessary to select their own additives‐activators. The obtained results were close to those of the anhydrite binder derived from pure sulfuric acid and limestone flour 26 . The authors obtained an anhydrite binder as a mixture of 5% Portland cement CEM I 42.5 and 1% of potassium sulfate, where 100% is the mass of binder.…”

“…7). The experimental results showed higher values compared both to natural and thermal anhydrite 26,27 …”

“…The experimental results showed higher values compared both to natural and thermal anhydrite. 26,27 The presented strength indicators showed that the selected types of additives contributed to the activation of the material synthesized at 45 °C (with a lamellar form of crystals) but did not activate the anhydrite obtained at 25 °C. This can lead to the conclusion that, depending on the structure, shape, and size of the crystals, the same additives-activators act differently on the material.…”

“…The obtained results were close to those of the anhydrite binder derived from pure sulfuric acid and limestone flour. 26 The authors obtained an anhydrite binder as a mixture of 5% Portland cement CEM I 42.5 and 1% of potassium sulfate, where 100% is the mass of binder. The reported compressive strength after 24 h was 13.3 MPa.…”