Comparison of the CAC-containing and CAC-free hydraulic binders in term of the hydrated matrix formation within refractory castables designed for the fast drying procedure

In this work, two types of cement-free and CAC-containing binders were designed, prepared, and studied. The main purpose of this work was to demonstrate an alternative route to elaborate CAC-free hydraulic binder systems designed for monolithic refractories, e.g., castables. The fundamental research presented in this paper was focused on comparing CAC-containing and CAC-free (mixtures of simple oxides such as MgO and Al2O3) hydraulic binders in terms of hydrated matrix formation within refractory castables designed for fast-drying. Complete structural (XRD, FTIR) and thermal (D(TA-TG-EGA(MS)) characterizations of the hydration products of the mixtures allowed us to determine their reactivity. The effects sample composition and temperature on the hydration behavior of binders were explored by using the TAM Air isothermal calorimetry system at two temperatures (20 degrees C and 50 degrees C). It has been proven that the main hydrate in the cement-free system was hydrotalcite Mg6Al2CO3(OH)(16)center dot 4H(2)O, which was confirmed by the presence of a characteristic diffraction line at 2 theta = 11.498 degrees. Mg-Al hydrotalcite was not synthesized in samples with CAC. Additionally, CAC-containing binders that contain free MgO introduced with spinel raw material were characterized by greater reactivity than the second CAC-containing sample because they contained larger amounts of hydrated phases. The findings obtained for the CAC-based binder showed that elevated temperature induced alterations in the calorimetric curve that were the same as those observed for the MgO-Al2O3-type cement-free sample. The induction period was shortened, and only one exothermic peak was detected.