“…2 (a and b, respectively). Reflections characteristic of mullite 3Al 2 O 3 × 2SiO 2 , anorthite CaO × Al 2 O 3 × 2SiO 2 and quartz SiO 2 predominate in the x-ray diffraction pattern; hematite Fe 2 O 3 , grossite CaO × 2Al 2 O 3 , tridimite SiO 2 and gehlenite 2CaO × Al 2 O 3 × SiO 2 , which, according to [17], upon firing is formed as a result of the interaction in concrete of calcium aluminate with free silica.…”