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.

The chemical composition of mineral trioxide aggregate

Abstract: Mineral trioxide aggregate (MTA) is composed of Portland cement, with 4:1 addition of bismuth oxide added so that the material can be detected on a radiograph. The cement is made up of calcium, silicon and aluminium. The main constituent phases are tricalcium and dicalcium silicate and tricalcium aluminate. There are two commercial forms of MTA, namely the grey and the white. The difference between the grey and the white materials is the presence of iron in the grey material, which makes up the phase tetracalcium alumino-ferrite. This phase is absent in white MTA. Hydration of MTA occurs in two stages. The initial reaction between tricalcium aluminate and water in the presence of calcium sulphate results in the production of ettringite. Tricalcium and dicalcium silicate react with water to produce calcium silicate hydrate and calcium hydroxide, which is leached out of the cement with time.

Thaumasite formation and deterioration in historic buildings

Abstract: Thaumasite and ettringite can be found among the deterioration products of cementitious materials exposed to sulphate attack. This can occur in concrete structures, as well as in masonry walls of historic buildings erected before the advent of Portland cement. Masonry walls of historic buildings may contain gypsum or other sulphate salts for different reasons. When they need to be repaired, CSH and CAH, formed by the hydration of hydraulic binders used for restoration, can react with water and gypsum or sulphate salts and produce thaumasite and ettringite. Due to these reactions, degradations of the repaired historic buildings can occur causing expansion, cracking, spalling and strength loss. In order to assess preliminarily the chemical compatibility of a repairing cementitious material with the presence of gypsum or sulphate salts inside historic buildings, the Anstett test can be adopted. Alternatively, protection measurements, based on the hindrance of water to penetrate the walls, should be adopted since in the absence of water both thaumasite and ettringite cannot be produced, even in the presence of gypsum, or other sulphate salts inside the historic buildings.

Theoretical analysis of the effect of weak sodium sulfate solutions on the durability of concrete

Abstract: A theoretical analysis of the detrimental influence of weak sodium sulfate solutions (Na2SO4) on the durability of concrete is presented. It was conducted using a numerical model that takes into account the coupled transport of ions and liquid and the chemical equilibrium of solid phases within the (partially) saturated system. Numerous simulations were performed to investigate the influence of various parameters such as water/cement (w/c) ratio (0.45, 0.65 and 0.75), type of cement (CSA Type 10 and Type 50), sulfate concentration (0–30 mmol/l of SO4) and the gradient in relative humidity across the material. All input data related to the properties of concrete were obtained by testing well-cured laboratory mixtures. Numerical results indicate that exposure to weak sulfate solutions can result in a significant reorganization of the microstructure of concrete. The penetration of sulfate ions into the material is not only at the origin of the precipitation of sulfate-bearing phases (such as ettringite and eventually gypsum) but also results in calcium hydroxide dissolution and C–S–H decalcification. Data also clearly emphasize the fact that w/c ratio remains the key parameter that controls the durability of concrete to sulfate attack.