Effects of blast furnace slag diatomite and calcined kaoline on portland cement hydration

Increasing environmental awareness from past to present has to led concentrate of studies to reduce CO2 emissions in the cement industry. Pozzolans attract attention as increasingly have been preferred additive materials due to their positive effects on the environment and their contribution to the strength and durability properties of cement and concrete. In the studies, it is known that the physical properties of pozzolans are mostly dependent on their molecular structures and they are glassy, amorphous or crystalline according to their atomic, structure and vary depending on their chemical composition. For this purpose in the study, CEM I 42.5 R type Portland cement was preferred as binder and blast furnace slag, calcined kaolin and diatomite as mineral additives. In the first stage of the study, raw materials were examined physical, chemical, mineralogical, molecular and micro structures. In the second stage, four types of cement were obtained by substituting 10% to Portland cement these materials, one of which was a reference. The hydration developments of these cement pastes were examined by water requirement, setting time, expansion experiments and for the 28th day of hydration by X-ray diffraction (XRD), fourier transforms infrared spectroscopy (FT-IR), thermal (DSC/TGA) and microstructure analysis (SEM/EDS). In the third stage, the flexural and compressive strengths of cement pastes were determined on the 2nd, 7th, 28th and 90th hydration days. According to the findings, in terms of expansion values was not observed difference while the water requirement and setting time of cement pastes with mineral additives increased. The data obtained from XRD, FT-IR, DSC/TGA and SEM/EDS analyzes performed on cement pastes on day 28 show that especially the amount of portlandite (CH) formed during the advanced hydration process decreases in all mineral-added cement pastes and it was determined that it provides more compact microstructure in cement pastes with increased amount of C-S-H addition. The results show that the flexural and compressive strength values of cement mortars substituted with these mineral additives were obtained at values very close to the reference cement on the 90th day of hydration. In addition, on the 28th day, it was determined that the compressive strength values of all mineral additive-replaced cement mortars were above the minimum value of 42.5 MPa, which is the minimum value specified for PÇ 42.5 R type cement.