Study of water consumption of dolomite aggregates for concrete under conditions of dry hot climate

Introduction. The basic properties of carbonate aggregates, which are widely used in the manufacture of concrete mixtures working in conditions of elevated temperatures and reduced relative humidity, are considered. Concretes with carbonate aggregates have increased water demand, which is associated with their high water absorption, porous surface and different specific surface area. The methodology for determining the water demand of aggregate by ultrasonic and accelerated methods, which are performed on the same workability mixtures, is given. The obtained results are important indicators and in the future will be taken into account in the calculation of concrete mixture.Materials and methods. Portland cement CEM I 52.5H “HeidelbergCement” in accordance with GOST 31108–2020; dolomite crushed gravel (5–10 mm); and standard monofractional sand in accordance with GOST 6139–2020 were used in the study. The chemical analysis of Portland cement and dolomite aggregate was investigated on the Bruker S4 Pioneer and Bruker S8 Tiger X-ray analyzers. The mineralogical composition of Portland cement was determined on a Bruker D2 laser diffractometer. The water demand of dolomite coarse aggregate was determined by an ultrasonic method developed at the National Research University of Moscow State University of Civil Engineering. Also, the determination of water demand of fine aggregate was carried out by the accelerated method on the same workability mixtures with a diameter of cement paste mixing equal to 170 mm. Determining the average density in a lump in the cement paste of carbonate crushed stone (5–10 mm) was determined in accordance with GOST 9758–2012.Results. Carbonate aggregates are characterized by increased water absorption compared to other aggregates. It was found that the water demand of dolomite aggregate is 5.4 %, and the water absorption and content of dust and clay particles are within 2.6 and 2.95 %, respectively. It was found that the average density of dolomite crushed gravel grains determined in the cement paste was 2.5 g/cm3.Conclusions. In conditions of high temperatures and low relative humidity, the use of dolomite aggregates is especially relevant. However, concrete mixtures with carbonate aggregates have increased water demand due to high water absorption, porous surfaces, and different specific surface areas of the aggregates.

dolomite aggregate, water demand, concrete, Portland cement, dolomite crushing screenings, ultrasonic, cement paste, the period of structure formation