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Coarse marble was mixed with a high-kaolinite and a high-illite clay, pressed and fired. Contact zones occur around the CaO-grain after firing; these were studied by line-scanning electron probe micro-analysis. Solid state reactions during firing are diffusion-controlled. The contact zones are composed of several layers. The tricalcium silicate layer is formed through dicalcium silicate from kaolinite at temperatures higher than 1100°C; from illite it is formed directly at only 1000°C. Rhythmic diffusion occurs at higher temperatures. The diffusion constants and activation energies are calculated for the different layers.

The change in reactivity of the silicate anion complex of tricalcium silicate, β-dicalcium silicate and portland cement during hydration was studied by measuring the rate constant ( k ) of the silicomolybdic acid formation. The three anhydrous starting materials have identical k values indicating their identical monosilicate anion structure. During hydration the value of k decreases continuously; the rate of decrease of k is highest in case of cement and lowest in case of β-dicalcium silicate. The decrease of k can be attributed to the formation of bridging oxygen ions in the silicate complex. k tends to reach a final, limiting value; beyond this k can still be decreased by special techniques as e.g. by regrinding and rehydrating the hardened samples.

The hydration of the iron-bearing phase of portland cement or brownmillerite, can be easily studied by Mossbauer-spectrometry, because a very significant difference exists between the spectra of anhydrous and hydrated brownmillerite. The Mossbauer spectrum of anhydrous brownmillerite shows a magnetic hyperfine structure and iron is present in a complex environment. During hydration the magnetic hyperfine structure disappears and only one sharp line remains showing that all iron atoms are surrounded by the same, very symmetric environment. The hydration is almost complete after 14 days. The hydration product is a solid solution of tricalcium aluminate hexahydrate and tricalcium ferrite hexahydrate (hydrogarnet). The full quantity of iron is bound in this hydrate and is present in an octahedral environment. Excess aluminum is present in the form of amorphous hydroxide.