Effect of ettringite morphology on the properties of expanding cement systems

Abstract

The effect of the pH of the reaction solution on the crystallization process and the ettringite morphology is theoretically substantiated and experimentally proved. Using physical and chemical research methods, the dependence of the morphology of crystallizing ettringite on the pH value of the reaction solution was established. It has been established that by introducing mineral micro fillers into the composition of expanding cement, it is possible to actively influence the pH value, the morphology of the resulting ettringite, the expansion kinetics, and the strength of cement stone and concrete based on it. The studies of the technical properties of concrete on the basis of expanding cements of various types have shown that with the introduction of micro fillers into the concrete composition, which intensify volume expansion during hydration of cement stone at the building site or factories for the production of ready-mixed concrete, it is possible to control the kinetics and extent of expansion, expansion pressure, deformative and strength characteristics of concrete and reinforced concrete structures.

Effect of Na versus Ca Sulfate Salts on the Hydration of Calcium Sulfoaluminate Clinker

“…When the calcium sulfate concentration is increased from 5% to 20%, the ettringite takes the form of more voluminous needles (Figure 9). This behavior was also observed by Kharchenko et al [26]. These authors studied the variation in ettringite morphology at a constant pH of 11 while changing the CaSO 4 concentration.…”

“…At longer hydration times and a 20% concentration, the ettringite needles appear to be longer and slenderer. Kharchenko et al [26] observed that at a pH of around 10, small ettringite needles form, while at pH 12 the needles become intermediate in size.…”

Sustainable performance of alkali-activated blast furnace cement concrete with high freeze-thaw resistance

“…Formation of secondary ettringite can cause destruction of concrete due to crystallization pressure on porous sides while volume increases. Advanced freeze-thaw resistance of AABFC concrete in solution of NaCl is caused by the absence of portlandite in hydration products [43] as well as by the absence of ettringite or due to changes in its morphology in highlyalkaline hydration medium from filamentous, needle to prismatic as well as plate shape [44].…”