Structure and properties of fine concretes based on composite binders

Introduction. Wide introduction of fine concretes in the practice of monolithic building construction is limited by their low crack resistance due to considerable shrinkage. To reduce the shrinkage adverse effect on structure and properties of the fine concretes, it is suggested to use for their preparation composite binders, including expanding sulphoaluminate-based cements. Using the fine concrete with enhanced physical and technical properties improves produceability of construction, reduces labor input of concrete casting and allows building installations of complicated architectural forms. Material and methods. To study processes of fine concrete structure formation and properties, concrete mixes were prepared on the base of medium silica sand, dispersed ash entrainment and expanding additive. Activity of the ash entrainment increased at the expense of mechanical and chemical activation. Dispersity of the particles was monitored by means of laser granulometry. The composite binder was prepared by means of thorough homogenization of the basic CEM 42.5 Portland cement and different sorts of mineral aggregates, including an expanding additive based on calcium sulphoaluminate. Maturing conditions at a certain moisture content were simulated for every composition with subsequent evaluation of concrete performance. Results. Results of the study include effect of different mineral additives distinguishing in mineral composition, dispersivity and degree of hydraulic activity on shrinkage amount and kinetics, fine concrete porous structure parameters and strength. It is understood that amount of expansion has an effect on porous structure characteristics of the fine concrete and its strength performance. The study assessed an influence of maturing conditions on the various-composition fine concrete. A considerable influence of maintaining optimal moisture content during hydration on fine concrete technical properties is committed. Conclusions. It is understood that introduction of up to 10 % of expanding sulphoaluminate-based component in basic Portland cement allows to obtain fine concrete with enhanced crack resistance, impenetrability and longevity.