Physico-Chemical Substantiation of Obtaining an Effective Cement Composite with Ultrafine GGBS Admixture

To solve a number of problems in construction materials science, composites with nano and ultrafine admixtures were analyzed. Their properties were studied, taking into account the variants of homogenization and stabilization of the system. To characterize the processes of the structure formation of a new material, mathematical methods were also applied. According to the literature review, the aim of the work was formulated. The subject of this research is to conduct physico-chemical studies that characterize the processes occurring during the homogenization and stabilization of the cement system with GGBS components and to establish the effect of the admixture on the properties of the composite. To achieve this goal, an ultrafine admixture based on GGBS was obtained, and the possibility of its introduction into the cement system in the form of a stabilized suspension instead of mixing water was considered. To provide increased characteristics of cement stone modified with the ultrafine admixture, a number of tests were carried out to study homogenization and stabilization of fine slag particles in suspension. The ultrasonic processing parameters were defined to provide uniform distribution of fine slag additive in the suspension: the processing time is 15–20 min, the frequency of ultrasonic vibrations is 44 kHz, the temperature of the dispersed medium is 25 ± 2 °C. To define physical and chemical processes appearing during the introduction of fine slag into water and water-polymer dispersed medium, the mechanism of interaction between fine slag and water was studied. In addition, the mechanism of chemisorption on the surface of fine slag particles and the stabilization mechanism of ultrafine slag particles with a plasticizer was studied to form the concept of aggregate and sedimentation stability of slag particles in suspension. It was found that the stabilization of fine slag particles by a plasticizer is significantly influenced by the hardness of water. The higher the water hardness, the more plasticizer required to stabilize the fine slag particles. At the same time, it was established that the concentration of the plasticizer should not exceed the critical micelle concentration value. If it is exceeded, the plasticizer solution transforms into the micellar colloidal system, and the stabilization of fine slag suspension will not occur. The studies of homogenization and stabilization of the slag suspension allowed the authors to substantiate the possibility of uniform distribution of fine particles in the cement matrix, followed by the formation of a denser and stronger cement stone structure. Cement-sand samples based on Portland cement (OPC) and slag-Portland cement (SPC) with GGBFS admixture showed higher compressive and flexural strength characteristics in the initial hardening periods and at 28 days. It was found that modified samples are more stable in an aggressive medium. On the 90th day of exposure, the resistance coefficient was 0.9 for a modified sample based on OPC and 0.98 for a modified sample based on SPC. The increased sulfate attack resistance of the samples is due to the formation of a dense stone with reduced porosity. It is noted that the porosity of modified OPC samples decreases by 14% and by 18% for SPC-based modified samples compared to the control sample at 28 days. Due to the fact that pores in the cement stone are blocked with hydration products, which make the structure of the cement stone denser, the filtration of aggressive solutions deep into its structure is difficult. Thus, the obtained concrete based on a cement composite with ultrafine slag can be applied as a protective layer of steel reinforcement in a reinforced concrete structure.