Showing papers on "Ettringite published in 2018"
TL;DR: In this paper, the incorporation of uncarbonated and carbonated hardened cement paste powder into cement affects the hydration and microstructure development of cement, which is classified as a corrosive hazardous material.
144 citations
Katholieke Universiteit Leuven1, Ghent University2, Indian Institute of Technology Madras3, École Polytechnique Fédérale de Lausanne4, RWTH Aachen University5, University of Toronto6, Institut national des sciences appliquées de Toulouse7, Swiss Federal Laboratories for Materials Science and Technology8
TL;DR: In this paper, a round-robin test on the impact of hydration stoppage methods on the composition of hydrated cements was conducted and a regular and a fly ash blended Portland cement hydrated for 90 days were selected.
Abstract: For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)2) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.
135 citations
TL;DR: In this article, the consequences of accelerated carbonation at 3% CO2 were compared with those of natural carbonation (0.04%) in Cement Pastes (CEM I and CEM V/A) and three major constitutive phases (C-S-H of different C/S ratios, portlandite and ettringite).
127 citations
TL;DR: In this article, the impact of NaOH and Na2SO4 on the kinetics and microstructural development of cement hydration was analyzed to better understand their effect on the mechanical properties.
89 citations
TL;DR: The investigated red mud and arsenic sludge can be successfully utilized in cement composites to create a red mud-based cementitious material.
79 citations
TL;DR: In this article, the authors identified temperature ranges on the phases in actual cementitious systems (portland cement (OPC) pastes, blended pastes of ground granulated blast furnace slag (GGBFS) with OPC, and Ca(OH)2-activated GGBFS), by simultaneously using thermogravimetry (TG) and high-temperature X-ray diffraction (HT-XRD).
75 citations
TL;DR: In this paper, the effects of flue gas desulfurization gypsum addition on compressive strength, elastic modulus, resistance to carbonation, chloride ion diffusion and drying shrinkage were examined.
75 citations
TL;DR: In this article, the authors proposed that ettringite (6CaO·Al2O3·SO3·32H2O) is the only hydration product after the initial reaction period and before complete gypsum dissolution.
67 citations
TL;DR: In this article, the authors developed an experimentally validated reactive transport model to investigate the transport behavior of sulfate ions in concrete containing interfacial transition zone (ITZ), taking into account the spatially dependent pore size in ITZ and the change of diffusion coefficient of sulfates due to the formation of ettringite and gypsum in concrete pores resulting from the chemical reaction between sulfate ion and concrete components.
66 citations
TL;DR: In this paper, the effects of chemical admixtures on the workability and strength development of calcium sulphoaluminate cement (CSA) at various temperature were researched, of which mechanisms were analyzed by XRD and TG.
64 citations
TL;DR: In this paper, the authors used OPC to enhance the early performances of calcium sulfoaluminate cement (CSA), and the hydration process of CSA-OPC composite was researched by XRD, TG and SEM.
TL;DR: In this article, the effects of combined attack of drying-wetting cycles and sulphate are investigated and compared to concrete made with natural river sand (NPC), which is natural abundant solid resource on islands in the tropical region.
TL;DR: In this paper, the effects of calcium sulfate additions on hydration, microstructure and performance of composite Portland clinker-slag-limestone cements were investigated, and the results showed that the presence of sulfate influenced the early-age reaction kinetics of the clinker phases and supplementary cementitious materials.
TL;DR: In this article, the composition and microstructure of the AH3 phase in the hydration product system AFt-AFm-AH3 were characterized using X-ray diffraction, Rietveld method, thermogravimetric analysis, 27Al magic angle spinning nuclear magnetic resonance spectroscopy, field emission scanning electron microscopy, and inductively coupled plasma optical emission spectroscope.
TL;DR: In this article, the hydration of metakaolin composite cements containing quartz, natural limestone and dolomite rock is studied using a multi-method approach and modelling, and experimental results supported by the thermodynamic modelling suggest that the silicate mainly precipitates as low Ca/Si C-S-H and additionally the ettringite content is higher.
TL;DR: In this paper, the effects of limestone powder on the resistance of concretes to the chloride ion penetration and sulfate attack with a constant water/binder ratio and a constant 28-day compressive strength were studied.
TL;DR: In this article, an experimental investigation of the microstructure and mechanical properties of graphene-reinforced cementitious composites is presented, which revealed that ettringite, C-S-H gel and other hydration crystals were connected by graphene sheets, which formed a 3D structure that could bridge the cracks and fill the pores in cement matrix.
Abstract: An experimental investigation of the microstructure and mechanical properties of graphene-reinforced cementitious composites is presented. The early-age microstructure of the grapheme/cement composites was examined by scanning electron microscopy (SEM). The SEM images revealed that ettringite, C-S-H gel and other hydration crystals were connected by graphene sheets, which formed a 3-D structure that could bridge the cracks and fill the pores in cement matrix. With the increase of hydration ages, the 3-D structure became more complicated and connection between the graphene and cement hydrates became stronger. The X-ray powder diffraction (XRD) analysis suggested that the amount of ettringite increased with the increase of graphene content, indicating that graphene sheets could promote the formation of ettringite. In addition, the mechanical strength of graphene/cement matrix was measured. The reinforcing effect of graphene is most obvious with the addition of 0.03 wt.% graphene, with which the flexural strength increased by 40%.
TL;DR: In this article, the effect of the S-ettringite on hydration, microstructure and properties of CSA cement-based grouting materials (CBGM) was experimentally investigated.
TL;DR: In this article, 29Si and 27Al MAS NMR spectroscopy combined with SEM-EDS techniques were utilized to investigate the microstructure of Portland cement paste (PC) and PC with granulated blast furnace slag (PC-GBFS) curing in both water and the sulfate sodium solution during 365 days.
TL;DR: In this paper, a lime-based low carbon cementitious material (LCM) was designed and prepared using low contents of hydrated lime and Portland cement and a high content of mineral admixtures.
TL;DR: In this paper, the effects of thermal treatment on the reactivity of the tailings and the use of different activating solutions on the physical properties, microstructure and leaching of harmful components are reported.
Abstract: Gold mining produces hazardous tailings wastes with elevated sulfur content and high levels of heavy metals including oxyanion elements such as V and As. This research investigated activation of these tailings with calcium hydroxide and sodium hydroxide/sodium silicate as a way to stabilize the material and limit leaching of harmful components. The effects of thermal treatment on the reactivity of the tailings and the use of different activating solutions on the physical properties, microstructure and leaching of harmful components are reported. The effect of adding ground granulated blast furnace slag to the tailings is also assessed. The use of 5 wt % Ca(OH)2 activating solution produces optimum performance increasing the immobilization efficiency of sulfates, arsenic and the other harmful elements. Heat-treating mine tailings at 900 °C slightly improves the reactivity but did not improved the immobilization efficiency. Microstructural analysis by TEM and XRD confirmed that stabilization is based on calcium sulfate and/or ettringite formation during alkali-activation. All materials achieved reasonable compressive strength after 28 days of curing and the potential for using alkali activation as a method to treat tailings from mining is discussed.
TL;DR: In this paper, phase characterizations, physical properties and strength of environment-friendly cold-bonded fly ash lightweight aggregates were investigated using thermogravimetry results.
TL;DR: In this article, the effects of lithium carbonate on the properties of dual liquid high water material have been studied through micro testing, including hydration heat tests, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis.
TL;DR: In this article, the authors investigated the evolution of a binder gel in carbonation-cured Portland cement in an acidic medium and found that the carbonation products of belite were more stable than those of alite, with less gypsum formation under H2SO4 or HCl.
TL;DR: The main objectives of this work were to manufacture adobes with good mechanical properties, even in a wet environment, and low thermal conductivity so as to give the population homes that provided better thermal comfort than cement-based constructions.
TL;DR: In this paper, three different types of concrete were produced depending on mineral admixture type, ettringite, portlandite, and C-S-H, which undergo phase changes by forming some active products such as lime and calcium silicates during heating.
TL;DR: In this paper, the effects of both CS and alkali activator (KOH) contents were studied, and the main results showed that the compressive strength, heat of hydration, and consumption of anhydrite phase were strongly influenced by the alkaline content.
Abstract: Considerable attention has been given to special cements, capable of reducing CO2 emissions, energy and limestone consumption. Supersulfated cements are made of blast furnace slag (GBFS), calcium sulfate (CS), and small quantities of activator, but achieving their optimal proportions is complex. In this paper, the effects of the both CS and alkali activator (KOH) contents were studied. The main results showed that the compressive strength, heat of hydration, and consumption of anhydrite phase were strongly influenced by the alkaline content, while low calcium sulfate or alkaline content increased the formation of CSH. The instability of ettringite was verified: with low CS, the probable hypothesis was its conversion into monosulfate due to the scarcity of sulfate; with high CS, it was associated with intense, rapid consumption of anhydrite with high KOH content, followed by the precipitation of ettringite on the surface of slag grains and its conversion into monosulfate.
TL;DR: In this article, the pore size distribution, internal structure and compressive strength of mortar with ion chelating agent before and after freeze-thaw as well as self-healing were investigated by nuclear magnetic resonance, scanning electron microscope and mechanical property test.
TL;DR: In this article, a chemical-reactive transport model is used to simulate the sulfuric acid attack of cement pastes based on ordinary Portland cement, blended Portland cements (CEM III, CEM IV, and CEM V), and calcium aluminate cement (CAC).
TL;DR: In this article, the effect of a softwood calcium lignosulfonate, LSs, on the ettringite formed in cement paste was investigated, by adding either the LSs immediately with the mixing water or after 10min of hydration.