Ettringite

About: Ettringite is a research topic. Over the lifetime, 2702 publications have been published within this topic receiving 67056 citations. The topic is also known as: woodfordite.

Effect of Remineralization on Heavy-Metal Leaching from Cement-Stabilized/Solidified Waste

Abstract: Crushed samples of stabilized/solidified (s/s) waste were leached at constant leachate pH in the pH range 4-7 with nitric acid solutions to evaluate the influence of remineralization on metal release. The s/s waste consisted of synthetic heavy-metal sludge containing 0.1 mol L(-1) copper nitrate, 0.1 mol L(-1) zinc nitrate, and 0.1 mol L(-1) lead nitrate mixed with ordinary Portland cement. Unleached and leached particles were characterized by scanning electron microscopy and energy-dispersive X-ray spectrometry. Two consecutive leaching fronts advancing from the surface of the particles toward the center were identified: the first front was associated with the dissolution of portlandite and partial reaction of the calcium silicate hydrate gel, while the second front was associated with the dissolution of calcium-aluminum hydroxy sulfates such as ettringite and monosulfate. At pH 4 and 5, a remineralization zone rich in heavy metals formed immediately behind the second leaching front. The shell extending from the remineralization zone to the surface of the particles was depleted in calcium, sulfate, and heavy metals. As a result of remineralization, heavy-metal releases to the leachate were reduced by factors ranging between 3.2 and 6.2 at pH 4 and between 74 and 193 at pH 5. At pH 6 and 7, remineralization of Pb and Zn occurred further behind the second leaching front and closer to the surface of the particles. The amount of heavy-metal release depended on both the leachate pH and the remineralization factor.

Hydration and Compressive Strength of Blended Cement Containing Fly Ash and Limestone as Cement Replacement

Abstract: This study examines the effect of high-calcium fly ash in combination with finely ground limestone as cement replacement on cement’s hydration characteristics. Heat released by a hydration reaction was investigated using isothermal calorimetry. X-ray diffraction and thermogravimetric analysis were used to identify hydration products. In this work, fly ash and limestone were used to replace part of Portland cement at 30% by weight in terms of ternary blended cement. All pastes and mortars were cured in water at 23±2 °C. The compressive strength of mortars were examined for a period of 28 days. The results show that the hydration reaction of cement containing fly ash accelerated when limestone powder was incorporated. Thermogravimetric analysis of the samples hydrated at 28 days show similar hydration products such as ettringite, calcium silicate hydrate, portlandite, and calcite. However, the dehydration of monocarboaluminate was observed in ternary blended cements of Portland, fly ash, and limesto...

Identification of thaumasite in concrete by Raman chemical imaging

Abstract: Identification of thaumasite (CaSiO3·CaO3·CaSO4·15H2O) in concrete undergoing external sulfate attack by X-ray powder diffraction or by microscopic techniques is difficult due to its crystallographic and morphological similarity with ettringite. Widefield Raman chemical imaging via liquid crystal tunable filter (LCTF) technology has been used in a preliminary study to determine the presence of thaumasite in association with ettringite (3CaO·Al2O3·3CaSO4·32H2O) and gypsum (CaSO4·2H2O). Raman chemical imaging combines Raman spectroscopy with optical microscopy and digital imaging to provide images with molecular-based contrast. Thaumasite has three major peaks at 658, 990, 1076 cm−1 and three minor peaks at 417, 453, 479 cm−1. Ettringite has major peaks at 990, 1088 cm−1. Gypsum has a major peak at 1009 cm−1 and minor peaks at 417, 496, 621, 673, 1137 cm−1. When these minerals are presented together, Raman chemical imaging provides an excellent way to determine their molecular composition and spatial distribution within the sample.