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.

Sulfate attack and the role of internal carbonate on the formation of thaumasite

Abstract: The sulfate attack is known to influence the durability of concrete. In general, significant damage due to sulfate interaction results in the structural breakdown of the concrete structure. However, the precipitation of thaumasite due to sulfate concentration, leaching and the role of internal carbonate in case of limestone filler in cement is still not understood in detail. This work has adopted a combination of experimental and modeled data to investigate the formation of thaumasite under different exposure conditions. Experiments were carried out by using the progressive equilibrium approach (PEA). Further microstructural properties such as porosity, sulfate uptake, phase composition and phase transformation reactions during sulfate attack were investigated. The results show that thaumasite formation is favoured at lower temperatures (8 °C) independently of the type of cement clinker (high and low C3A content) used. Thaumasite was found to form only in cement systems which contained a source of carbonate and at high sulfate contents in the cement paste, i.e. the molar SO3/Al2O3 ratio exceeded 3. Leaching, the reduction of alkalies and portlandite, had no significant influence on the stability of thaumasite. It slightly reduced the amounts of thaumasite formed. Thaumasite formation was found not to be a form of the initial sulfate attack. The phenomenon occurs at the late (last) stage of sulfate attack. The initial sulfate induced deterioration is caused by ettringite formation. The thermodynamic approach used to investigate the chemical aspects of sulfate attack turned out to be a good tool for simulating external sulfate attack. However, in the experiments, the predicted equilibrium conditions have not been reached after 9 months. Limestone addition of a few percent in Portland cement increased the compressive strength and reduced the porosity, especially the capillary porosity. Thereby, also the resistance of Portland cement systems against sulfate attack was increased. Furthermore, the hydration of Portland cement was influenced by limestone addition and monocarbonate was formed instead of monosulfate as stable AFm phase.

Hydration Process and Compressive Strength of Slag-CFBC Fly Ash Materials without Portland Cement

Abstract: This study mixed ground granulated blast-furnace slag (S) and circulating fluidized bed combustion (CFBC) fly ash (CA) without any portland cement or alkaline activator to produce an eco-binder, abbreviated as SCA binder. The hydration process, microstructure, and compressive strength of hydrated SCA materials were investigated. Although both the slag and CA had poor hydration with water, the SCA binder produced satisfactory hydration products with sufficient cementitious properties. These hydration products detected by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were ettringite (AFt), calcium silicate hydrate (C-S-H), and calcium aluminosilicate hydrate (C-A-S-H). The scanning electron microscope (SEM) micrograph showed these hydration products formed dense microstructure for SCA pastes. As a result, the SCA materials had sufficient compressive strength for practical applications in building materials and civil engineering structures. The compressive strengths of th...

Hydration characteristics of calcium sulfoaluminate (CSA) cement/portland cement blended pastes

Abstract: The hydration characteristics of calcium sulfoaluminate cement (CSA) and ordinary Portland cement (OPC) blended pastes incorporating calcium sulfate (C S ‾ ) are investigated. The experimental characterization techniques were employed and complemented with thermodynamic calculations to provide in-depth understanding of the hydration of CSA/OPC blended system. The results showed that the hydration of C3S in the CSA/OPC blended pastes was significantly delayed in comparison with the sole OPC paste. The delayed hydration of C3S negatively affected the strength development of the CSA/OPC pastes. As the amount of C S ‾ increases, the induction period occurring between the initial peak and the intermediate peak was extended, thus increasing the initial setting time. The addition of C S ‾ to the CSA/OPC blends led to the two phenomena in the hydration of C4A3 S ‾ , (1) retardation of C4A3 S ‾ hydration, and (2) formation of more ettringite after a few hours of hydration. The thermodynamic calculations indicated that the setting of the CSA/OPC blended system is mainly facilitated by hydration of C4A3 S ‾ and by the formation of ettringite, while the major strength-giving phase is C–S–H that originates from the hydration of C3S.