FORMATION OF CEMENT STONE MICROSTRUCTURE IN THE PRESENCE OF COMPLEX CHEMICAL ADMIXTURES

This article experimentally investigates the possibilities of technological regulation of cement stone and concrete microstructure parameters through the introduction of chemical admixtures of various natures. Based on studies concerning the influence of chemical admixtures on cement hydration processes and cement stone microstructure, a comparative evaluation of the hardening and pore formation of cement stone with accelerating, plasticizing, and complex admixtures was performed. Specifically, the study focused on the impact of complex chemical admixtures, including a superplasticizer like С-3 (likely a naphthalene sulfonate-based type) and LST (lignosulfonate) combined with accelerators such as NaCl or KCl, Na2CO3, K2CO3, Na2SO4, K2SO4 on the pore formation characteristics during the hardening of two types of cement: Portland cement PC CEM I 42.5R and slag Portland cement SPC CEM II B-S 32.5 R. These cements differ in their mineral composition, slag content, and consequently, their hydration rate and structure formation. It was established that cement stone, whose porosity is characterized by a minimal pore radius and an optimal ratio between the volumes of gel pores and capillary pores, can be achieved through the complex application of an accelerator and a plasticizer. The synergistic effect of the superplasticizer reducing the water-cement ratio and improving particle dispersion, alongside the chloride accelerator speeding up early hydration, contributes to this refined pore structure. Furthermore, a novel approach for evaluating the effectiveness of modifying the cement stone structure is proposed using the coefficient Kef, defined as the ratio between the volumes of gel pores and capillary pores (ratio of dynamic microstructural indices). This quantitative information regarding the cement stone's microstructure and the limits of its regulation under the influence of internal and external factors allowed for the formulation of a concept regarding the possibilities of achieving specified concrete properties by modifying the corresponding parameters of the cement stone's microporosity.