The Effect of a Complex Mineral Additive on the Structure Formation of Cement Stone

Introduction. The cement industry is rapidly improving, introducing multicomponent cements and using industrial waste as additives to increase efficiency and reduce costs. Studying the effect of finely dispersed active additives on the composition of cement paste is an important task for improving the quality of concrete. Materials and methods. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were used to conduct the study. Using CEM I 52.5 N Portland cement, metakaolin (MK), mechanically activated fly ash (FA) and date kernel ash (DKA), cement stone samples were prepared for testing. These samples included a control composition consisting of 100% Portland cement and three other compositions with varying combinations of the aforementioned finely dispersed active additives, partially replacing Portland cement. Results. TGA showed that partial replacement of Portland cement with finely dispersed additives possessing pozzolanic activity (10% by weight of MK or a mixture of 6% MK, 1% FA, and 3% DKA by weight) leads to a decrease in the content of free Ca(OH)₂ (portlandite) in the cement stone by 7–16% by weight after 28 days of hardening compared to the control sample. The X-ray diffraction results confirmed a de-crease in the intensity of the Ca(OH)₂ peaks and an increase in the peaks of low-basic calcium hydrosilicates (C-S-H) in the compositions with the used finely dispersed active additives, which confirms their pozzolanic activity. Conclusions. The use of these active mineral additives allows for the optimization of the phase composition of cement paste by binding excess calcium hydroxide into additional low-basicity hydrosilicates, which will contribute to an increase in the density and strength of the cement paste in multicomponent binder concrete, as well as its corrosion resistance. Furthermore, the highest pozzolanic activity was demonstrated by a multicomponent binder composition in which Portland cement was partially replaced with a mixture of metakaolin, fly ash, and date kernel ash in the specified quantities.