STUDY OF THE STRENGTH OF CONCRETE ON QUARTZ-GLAUCONITE SAND WITH A COMPLEX ADDITIVE

The article presents the results of a study examining the effect of a complex additive of microsilica, MasterGlenium ACE 430 superplasticizer based on a polycarboxylate ester, and a hardening accelerator (calcium nitrate) on the strength of fine-grained concrete with quartz-glauconite sand – a waste product from phosphate ore processing at the Polpinskoye deposit in the Bryansk region. An analysis was performed of the chemical and mineral composition, structure, true and bulk density, void content, fineness modulus, and water requirement of quartz-glauconite sand as a concrete aggregate. It was found that the main minerals contained in quartz-glauconite sand are quartz, glauconite, fluorapatite (fluorite), and potassium feldspar. The presence of fine glauconite particles of varying degrees of destruction in sand leads to an increase in the specific surface area of quartz-glauconite sand and an increase in water demand by 57-71%. Using a three-factor experimental design, equations and response surfaces were obtained for the strength of fine-grained concrete with quartz-glauconite sand after 28 days of curing as a function of the amount of components in the complex admixture. It was found that the combined addition of 15% microsilica, 1.5% MasterGlenium ACE 430 superplasticizer, and 2.5% calcium nitrate accelerated the strength gain of fine-grained concrete with quartz-glauconite sand, increasing its compressive strength from 9.6 to 30.9 MPa and flexural strength from 2.2 to 6.7 MPa.