Influence of Low-Pressure Treatment on the Morphological and Compositional Stability of Microscopic Ettringite

Abstract

The impact of low-pressure treatment on the crystal structure, morphology, and chemical composition of ettringite, due to their major importance with respect to processability (i.a., drying conditions) and to the analysis of ettringite-containing samples, is examined utilizing X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and environmental scanning electron microscopy. Synthetic ettringite was treated for various durations (5 min up to 72 h) and at two different levels of low-pressure (4.0 mbar and 60 µbar). Evaluation showed a correlation between the procedural parameters (time and pressure), the chemical composition, and the morphology of ettringite. The experiments reveal that, when exposed to 4 mbar pressure, nearly no changes occur in the ettringite’s morphology, whereas the crystals undergo swelling and slight deformations at very low pressures (60 µbar and 35.3 nbar), which is attributed to the loss of bound water and the partial transformation from ettringite to quicklime, anhydrite, and calcium aluminate. Furthermore, the strongly dehydrated ettringite shows the same morphology.

Effects of Biochar as a Green Additive on the Self-Healing and Properties of Sustainable Cementitious Materials

“…The presence of ettringite in small amounts was also found in the FTIR results discussed earlier. It should be noted that the vacuum drying used for the preparation of the sample for chemical characterization could affect the ettringite structure and reduce its content . Platelike crystals are observed, which are attributed to Ca­(OH) 2 .…”

“…It should be noted that the vacuum drying used for the preparation of the sample for chemical characterization could affect the ettringite structure and reduce its content. 100 Platelike crystals are observed, which are attributed to Ca(OH) 2 . Calcite with a rhombohedral morphology is also evident in the microstructure.…”