Rheological properties of self-compacting lightweight concrete mixtures on hollow microspheres

Introduction. Self-compacting concrete (SCC) technologies are actively used in modern construction, which are developing in the direction of lightweight self-compacting concrete (LWSCC) technology. The main advantage of LWSCC is to reduce the weight of concrete and reinforced concrete structures while maintaining structural integrity, load-bearing capacity and high mobility. The purpose of the study is to evaluate the rheology of the flow of the studied mixtures depending on the varying factors of W/C and the concentration of plasticizer Cpl and the ratio of filler (fractionated sand and quartz flour).Materials and methods. The object of the study is concrete mixtures on hollow microspheres. The design average concrete density is 1,400 kg/m3. The following composition is presented: Portland cement, ceramic microspheres, complex silica additive, fractional sand, quartz flour, hyperplasticizer and water. The results of studies of the rheological characteristics of LWSCC were obtained. The key rheological parameters are shear stress and viscosity.Results. Reducing the W/C increases the viscosity and shear stress of the concrete mix, regardless of the Cpl. A similar dependence is observed in compositions with variable Cpl. An increase in Cpl reduces the density of the mixture, reducing viscosity and shear stress. The limiting value of Cpl is noted, when this value is overcome by rheological parameters of mixtures tend to zero as the volume of the additive increases. The evaluation of the rheology of mixtures using the Ostwald de Waele equation shows the greatest importance of the W/C ratio for density and the possibility of changing the flow pattern of mixtures from pseudoplastic to dilatant with varying studied factors. Replacing the fraction of fractionated sand with flour from 100 to 0 % increases the density of the mixture by almost three times.Conclusions. The results determining the possibility of changing the rheological nature of the LWSCC flow on hollow microspheres with varying studied factors are presented. A comparative analysis of the obtained rheological curves is performed using the Ostwald de Waele equation for heavy and light mixtures with hollow microspheres. The role of filler dispersion in controlling the rheological properties of the studied LWSCC is considered.

self-compacting lightweight concretes, rheology, hollow microspheres, Ostwald de Waele equation, shear stresses, water-cement ratio, plasticizer concentration