The synthesis and characterization of an expansive additive for M-type cements

The expansive admixtures for M-type expansive cements were prepared by mixing of aluminate cement and gypsum. Hydrated samples were investigated by thermal analysis, infrared spectroscopy, and scanning electron microscopy. The main attention was focused on the formation of ettringite and the influence of water-to-cement and water-to-gypsum ratio on the process. The results of thermal analysis and infrared spectroscopy indicate high water-to-cement ratio and high water-to-gypsum ratio as the most proper condition for the formation of ettringite. It was observed that the value of water-to-gypsum ratio close to 1.76 supported the formation of monosulfate phase in the expansive mixture. The SEM indicates an oriented crystal growth of ettringite crystals that produces the expansive stresses.