Decomposition Of Ettringite Research Articles

Unraveling the interactive effects of Na2O/Al2O3, SiO2/Al2O3 and calcium on the properties of geopolymers from circulating fluidized bed fly ashes

Circulating fluidized bed fly ash (CFB-FA), generated as solid waste from the thermal power plants with different contents of calcium. The reuse of CFB-FA for construction materials is the most promising method for the large-scale transformation of waste to resource. This paper examines the ratio effects of Na2O/Al2O3 and SiO2/Al2O3 on geopolymers from low-calcium fly ash (CFB-FA1) and high-calcium fly ash (CFB-FA2) by using a mixture of Na2SiO3 and NaOH as the alkali activator. The detailed mechanistic study with XRD, FTIR, SEM, and MAS NMR is also conducted for the roles of silicon, aluminum, and calcium in the reaction process and their mutual interaction mechanism, along with the regulating mechanism for the compressive strength and setting time of geopolymers. The results indicate that the increased ratios of Na2O/Al2O3 and SiO2/Al2O3 are favorable for the reactions and reduce the setting time of CFB-FA1 and CFB-FA2 based geopolymer. In CFB-FA1, the higher silicon and aluminum content is conducive to their dissolution by regulating the Na2O/Al2O3 ratio, forming N-A-S-H and resulting in the increased strength. A small amount of calcium mainly exists in the form of CaSO4, which completely participates in the reaction. In CFB-FA2, the silicon and aluminum contents are relatively low, while the calcium content is high. The compressive strength is achieved by regulating the SiO2/Al2O3 ratio to increase the dissolution of silicon and aluminum, allowing CaSO4 and CaO to react and form C-A-S-H and ettringite, with CaCO3 as unreactive. The low calcium is favorable for the long-term strength, but the high calcium acts oppositely, primarily attribute to the decomposition of ettringite, a critical component for maintaining the compressive strength of CFB-FA2 based geopolymers.

Investigation on the compositional and performance evolution of cement paste subjected to Xenon radiation

This study addresses the critical question of how Xenon radiation, simulating natural solar radiation, affects the compositional, structural, and mechanical properties of cement paste. This aim is to understand the micro-to macro-scale changes in cement paste subjected to such radiation, a key concern for the durability of construction materials in solar-intensive environments. Employing a comprehensive suite of analytical techniques, including XRD, TG, 29Si NMR, 1H NMR, CT, SEM, and Vickers hardness testing, we systematically analyze the changes in phase composition, bound water content, silicate chain length in C–S–H, microstructure, and micro-mechanical behavior before and after radiation exposure. Our research uncovers a substantial decomposition of ettringite and a discernible reduction in the bound water content within the cement paste post-radiation exposure. Crucially, we detected a significant elongation in the C–S–H chain length, with a peak increase observed at 6%. This elongation is coupled with an increase in pore coarseness and a proliferation of internal defects. These alterations collectively lead to a marked decrease in the material's mechanical strengths: we noted a reduction in flexural strength by up to 18% and in compressive strength by as much as 25% at the macroscopic level. This research thus provides essential insights into the design and development of high-durability cementitious materials for solar radiation-intensive environments, contributing to the advancement of sustainable and resilient infrastructure.

Investigation on hydration behavior and microscopic pore structure of early-age cement-based grouting material

The present paper reports an experimental investigation into the hydration behavior and microscopic pore structure evolution of early-age cement-based grouting material (CGM) with the same compressive strength as concrete (C60) at various ages (18 h, 1 d, 3 d, 7 d, and 28 d). The hydration process, hydration products, microstructure, and pore structure changes of early-age CGM were analyzed using isothermal calorimetry, thermogravimetry (TG), X-ray diffraction (XRD), backscattered electron imaging (BSEI), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The results show that the hydration process of early-age CGM can be classified into five stages: pre-induction, induction, acceleration, deceleration, and stabilization. Compared to C60, early-age CGM displays a higher initial heat flow but lower subsequent heat flow, with a cumulative heat release (72 h) only 38 % of that of C60, effectively avoiding temperature shrinkage and ettringite decomposition. During the hydration process, CGM continuously generates portlandite along with substantial quantities of ettringite and calcite. The addition of calcium sulphoaluminate expansive admixture (CSA) is advantageous in facilitating CGM's hydration process, effectively promoting the formation of ettringite and C–S–H gel, thus leading to an enhancement in the microstructure of CGM. At 28 d, the microstructure of CGM displays a relatively compact morphology. The porosity of CGM at 28 d was 13.74 %, with a higher proportion of harmless and less-harmful pores. These research findings contribute to a better understanding of the hydration process and microscopic pore structure evolution of early-age CGM, providing a reliable theoretical basis for the rational application of CGM in engineering and guidance for the improvement and optimization of CGM.

Hydrate assemblage stability of calcium sulfoaluminate-belite cements with varying sulfate content

To assess the feasibility of employing calcium sulfoaluminate (CSA)-belite cements for radioactive waste encapsulation purposes, a series of 40 mixes were conducted on a 3-litre scale. This series of tests incorporated two commercially available CSA-belite clinkers, gypsum or anhydrite addition at 15, 25 or 35 wt%, a water to solids ratio of 0.5, 0.6 or 0.7, and a high or low mixing shear regime. CSA clinkers chosen contain predominantly ye’elimite, with some belite, and a small quantity of calcium sulfate as anhydrite. This paper outlines the effect of these parameters upon the phase composition and structure of these CSA samples tested at 7, 28, and 90 days. The development of the hydrate assemblage was monitored in order to assess the suitability of these grouts for use in encapsulation processes. The trends in phase development and evolution are consistent across both clinkers tested. The levels of ettringite formed as a hydration product are dependent upon the levels of calcium sulfate addition and the availability of water, with ettringite production evident, though at a decreasing rate, from between 7 and 90 days. Throughout the entire catalogue of mixes, no ettringite decomposition was detected. The majority of belite within both clinkers appears to remain unreacted, with a small increase in mixes producing less ettringite. Simulations also show similar phase assemblages to those encountered experimentally, with little phase development after 90 days.

Drying shrinkage behavior of cement mortar under low vacuum conditions

In this work, the time-dependent drying shrinkage behaviors of cement mortar under low vacuum and standard drying conditions were tested and compared, in which the specimens were prepared based on various mixtures. Also, a series of microscopic tests were conducted to investigate the hydration and microstructure of the prepared specimens, and thus, to explain the drying shrinkage behavior of different specimens. The results showed that compared with standard drying condition, the specimens under the low vacuum condition exhibited higher drying shrinkage and mass loss, but lower sensitivity of drying shrinkage to mass loss. Under both conditions, the incorporation of fly ash and silica fume or shrinkage-reducing agent could greatly decrease the drying shrinkage, with the better performance identified in the case of fly ash and shrinkage-reducing agent; while the addition of sulphoaluminate cement had no inhibiting effect on the drying shrinkage deformation. Although the specimen solely based on sulphoaluminate cement showed the lowest drying shrinkage under standard drying condition, it exhibited greater drying shrinkage than the Portland cement specimens under low vacuum conditions. The microscopic test results suggested that low vacuum treatment could decrease the hydration degree while the decomposition of ettringite in the sulphoaluminate cement could be observed under low vacuum conditions. Besides, the gel pore volume fractions decreased while the cumulative total pore volume increased after low vacuum treatment, which resulted in a loose and porous microstructure with high vulnerability to drying shrinkage.

Recycling of hazardous and industrial solid waste as raw materials for preparing novel high-temperature-resistant sulfoaluminate-magnesia aluminum spinel cement

Secondary aluminum dross from aluminum smelter plants is a hazardous waste with no effective method for realizing its disposal and utilization safely. This research evaluated the potential of preparing novel high-temperature-resistant sulfoaluminate-magnesia aluminum spinel (SAC-MA) cement using secondary aluminum dross, carbide slag, magnesite tailings and desulfurization gypsum as the raw materials for the replacement of natural resources. Furthermore, the leaching toxicity of unroasted and preroasted secondary aluminum dross was analyzed. The mineral phase and microstructure of clinkers and hydration products were also considered and their effect on the mechanical properties and microstructure of the high-temperature-resistant SAC-MA samples was researched. The experimental results showed that roasting detoxification was effective in realizing the safe disposal of secondary aluminum dross and magnesia aluminum spinel, dicalcium silicate and Fe→Al substitutional ye'elimite formed in the SAC-MA clinker after the sintering using hazardous and industrial solid waste. Improved high temperature resistance of SAC was also observed. High temperature induced the decomposition of ettringite and led to its structural relaxation. Surprisingly, the existence of magnesia aluminum spinel made the structure of ettringite smaller and decreased the decomposition degree of ettringite, as well as improving the high temperature resistance of SAC. Changes in the main skeletal structures of ettringite and AH3 gel were not noticeable, which still had good stability at 200 °C for the SAC-MA sample. However, ettringite gradually became amorphous at 200 °C for the SAC sample. These results strongly indicated that using hazardous waste, including secondary aluminum dross, as raw materials for preparing SAC-MA was far superior to SAC with regards to high temperature resistance. This study contributed a novel example of converting hazardous and industrial solid waste into high value-added materials and may open a new approach for synthesizing high temperature-resistant SAC-MA cement from low-cost feedstocks.

Investigation the properties of sustainable ultra-high-performance basalt fibre self-compacting concrete incorporating nano agricultural waste under normal and elevated temperatures

Producing sustainable concrete using waste materials has a noticeable impact on the environment. From another aspect, understanding the effect of high temperature on concrete can help in reduce the environmental fire impact and lower rehabilitation costs. This study presents a systematic experimental investigation to produce sustainable ultra-high-performance basalt fibre self-compacting concrete (UHPBF-SCC) using agricultural waste materials including nano sugar cane bagasse, nano cotton stalk ash and nano rice straw ash as cement replacement. The three dosages of nanoparticles are mechanically produced after heat treatment at 700°C. The performance of the three dosages of nanoparticles (partially replacing 1–5% of cement) was investigated in the presence of basalt fibre. This study also examines the effect of elevated temperatures of 300°C and 600°C on the behaviour of UHPBF-SCC. The physical properties, including passing ability, flowability and segregation resistance, were studied. Compressive strength, strength loss at elevated temperature, mass loss, ultrasonic pulse velocity, splitting, and flexure strength were also investigated. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) analysis were conducted to show the microstructure of the mixes. Mechanical characteristics are significantly increased in the presence of nanoparticles, more than 18% in compressive, 32% in tensile strength and 28% in flexure strength compared with the reference mix. SEM analysis showed compacted sections with high bonded matrix and high ITZ at normal conditions, but microcrack propagation appeared at 300°C and 600°C due to ettringite decomposition and evaporation of capillary and adsorbed water. EDX analysis showed high Ca/Si with the addition of nanomaterials.

Degradation mechanism of cement-based materials under the effects of stray current, chloride and sulfate

When infrastructure is exposed to a complicated environment containing stray current, chloride and sulfate, it may be subjected to severe degradation. In order to analyze the interaction of different factors and the degradation mechanism of cement-based materials in a complicated environment, the blended solution with four molar concentration ratios of Cl-/SO42- (0, 0.5, 1, and 2) were prepared to simulate a range of aggressive medium. Meanwhile, 40 V DC (direct current) electrical field was applied to cement-based materials to simulate stray current. After exposure, the transport properties, macro-properties, and microstructures of specimens were observed and measured. Additionally, the types and amounts of degradation products were tested to further analyze the degradation mechanism of cement-based materials. Experimental results show that chloride in the blended solution could inhibit SO42- transport into cement-based materials, causing the SO42- concentration in a specimen to decrease with the increase of Cl-/SO42- ratio. Therefore, the specimens appeared less degraded in terms of macro-properties. But the results of microstructural analysis showed that degradation products and cracks were generated in the interior of specimens. Friedel’s salt was detected in the specimens exposed to the solutions containing chloride. The formation of Friedel’s salt consumed calcium aluminate hydrate, which caused the amount of Al-phase involved in the formation of ettringite to reduce. Consequently, the amount of ettringite was reduced, and the degradation of compressive strength and appearance was also reduced. Additionally, an electrical field could induce the ion concentration in pore solution to change and even break the ion chemical equilibrium, which resulted in the decomposition of ettringite and Friedel’s salt. However, Friedel’s salt can also transform into ettringite at a specific condition. Therefore, the amounts of ettringite and Friedel’s salt in specimens were changed over the exposure time.

Effects for partial replacement of Portland cement by low water absorption porcelain insulator

The side effects caused by the low water absorption capacity of ground electrical porcelain insulator (GEPI) as a partial substitute for ordinary Portland cement (OPC) was evaluated. Despite the wide use of alternative eco-friendly materials in order to minimize the carbon footprint of the cement industry, the complex chemistry of cement hydration requires deeper studies to comprehend the influence of such admixtures. GEPI was characterized by granulometric analysis, as well as by XRF, PXRD and SEM. Its pozzolanic activity was determined by the Modified Chapelle assay, and the mechanical tests were performed in order to measure the compressive and flexural strengths of the specimens. For this reason, prismatic specimens were prepared by the replacement of 5.0, 10.0 and 20.0 wt.% of OPC by GEPI. The specimen strength showed a dependence on the level of substitution and a delay in the strength gain was observed over time. PXRD allowed the analysis of the variation in the quartz peaks intensities and to monitor the role played by the low water absorption of porcelain in the ettringite decomposition. A crystalline phase of γ-Al2O3, which was formed by the dehydration of the gel-like Al2O3, was identified. SEM images allowed us to indicate a fibre bundle-shaped C-H-S massive phase embedded in the mortar, as well as portlandite plates and angular crystallites of quartz. GEPI influenced the OPC hydration process and did not drastically compromise the strength of the mortar; therefore, it may be further investigated as a support material to prevent early OPC stiffening.

The impact of carbonation at different CO2 concentrations on the microstructure of phosphogypsum-based supersulfated cement paste

This study investigates mechanisms of carbonation on the microstructure of phosphogypsum-based supersulfated cement (PSSC) paste at different CO2 concentrations (atmospheric, 5% and 20%). The products was characterized using XRD, TGA, FTIR and 27Al MAS NMR. It is observed that the main hydration products of PSSC are ettringite, C-A-S-H gels and third aluminate hydrate (TAH), and the carbonation products are calcium carbonate (mainly vaterite and calcite), secondary gypsum, and C-A-S-H gels and separate TAH with varying degrees of decalcification. The quantitative analysis of BSEM images shows that the volume change of products occurring on carbonation significantly increases porosity and pore size of the PSSC paste. Results indicate that the carbonation of PSSC at different CO2 concentrations results in a progressive carbonation degree, 5% CO2 supports the accelerated carbonation experiment in PSSC to simulate the natural carbonation process due to the same phase composition and similar microstructure with atmospheric CO2 and 20% CO2 further loosens the microstructure of PSSC for the complete decomposition of ettringite and the severe decalcification of gel products.

A study of variables that affect the process of sulfate attack of cement‐based materials subjected to stray current

AbstractDurability is one of the most important considerations for subway structures. However, the cement‐based materials used in subway engineering can be jeopardized by sulfate and the stray current and therefore can be subjected to severe damage during service. This study aims to investigate the degradation process of cement‐based materials exposed to stray current and external sulfate. In particular, the effects of three key variables were evaluated: concentration of external sulfate solution, level of stray current and cement type. After exposure, the visual appearance, compressive strength, SO42− profiles and microstructure of cement‐based materials were analyzed. Moreover, the amounts of degradation products were measured to evaluate the influencing degree of different variables and further explain the degradation mechanisms. Experimental results of this study reveal that (a) sulfate attack was related to the external sulfate concentration, but the relation was changed due to the presence of stray current. One explanation is that sulfate ions can be quickly accumulated in the pores of cement‐based materials under the effect of stray current, which makes the chemical reaction of sulfate attack exchange from diffusion control to reaction control. (b) Stray current could accelerate external sulfate attack of cement‐based materials, and the greater the stray current, the more severe sulfate attack was induced. (c) Compared with P·I type cement, high sulfate resistant (HSR) cement showed a better resistance to external sulfate attack. (iv) And, the main degradation products, ettringite and gypsum, were observed in specimens after exposure. Additionally, stray current might induce the decomposition of ettringite. It should be paid more attention on the durability of cement‐based materials exposed to the coupled conditions of stray current and sulfate.

Effects of cyclic seawater exposure on the mechanical performance and chloride penetration of calcium sulfoaluminate concrete

Calcium sulfoaluminate (CSA) cement distinguishes itself from Ordinary Portland cement (OPC) by a rapid strength gaining and a shrinkage reduction, however, its performance in a marine environment is still not fully comprehended. Therefore, to clarify this issue, the effects of cyclic seawater exposure on the mechanical performance and chloride penetration of CSA concrete were investigated via the accelerated drying-wetting cyclic tests in the laboratory, facilitated by the use of seawater and 2.5% NaCl solution, and the results were further interpreted by the microstructural analysis. The outcomes indicate that resulted from the drying-wetting cycles (i.e., cyclic seawater and NaCl solution exposure), the decomposition of ettringite led to a coarse concrete surface, where a large number of chloride ions accumulated in this region, however, the coupling of multi-ions such as SO42- and Ca2+ in the seawater could enhance the stability of ettringite, along with a regeneration of the new ettringite that would fill in the concrete pores, which alleviated the damages owing to the chloride penetration into concrete, indicating the suitability of CSA cement usage in a marine environment.

Sulfate removal from lignite coal mine drainage in Thailand using ettringite precipitation

This research was studied the optimum conditions for sulfate removal from lignite coal mine drainage in Thailand by ettringite precipitation using Central Composite Design. The effects of Ca/S and Al/S ratio (mole basis), reaction time and temperature on the sulfate removal efficiency were investigated. The statistical analysis showed that the Al/S ratio and reaction time had a significant effect on sulfate removal efficiency. The sulfate removal efficiency increases when Al/S ratio and reaction time are increased. The Ca/S ratio in the range of 1–7 was found to have no significant effect on sulfate removal efficiency. The optimal reaction time obtained from the predicted equation was 6.14 h, while the Ca/S and Al/S ratios were fixed at 4 and 4.5, respectively, at ambient temperature. Under the optimum conditions, sulfate removal of 99.6 and 99.0% was achieved in both Lamphun and Lampang mine drainage, respectively, which is very close to the predicted value (100%). This study showed that the sulfate removal efficiencies of Lamphun and Lampang mine drainage sharply increased from 33.3 to 89.9% and 42.3 to 81.8%, respectively, when the temperature was increased from 25 to 80 ○C during a 3 h reaction time. XRD results match well with a majority of ettringite and a minority of calcium carbonate when the precipitation was done at ambient temperature. However, monosulfate was found to be the majority when the precipitation was done at 80 ○C due to the decomposition of ettringite to monosulfate at the high temperature.

Characterization of reactive MgO-modified calcium sulfoaluminate cements upon carbonation

This study characterizes reactive MgO-modified calcium sulfoaluminate (CSA) cement upon carbonation. Paste samples were fabricated by replacing CSA cement with reactive MgO at levels of 0, 5, 10, and 20 wt%. The samples were cured for 56 days and further cured at a CO2 concentration of 3% for 28 days. MgO incorporation into the CSA cement favored the formation of monosulfate over ettringite. Externally supplied MgO in the CSA cement reduced Al uptake in C-A-S-H and formed hydrotalcite as a secondary phase, which is associated with a reduction in the carbonation degree. In addition, the incorporated MgO inhibited the carbonation of ettringite and monosulfate, while more C-A-S-H and aluminum hydroxide were formed in neat CSA cement upon carbonation, showing the nearly full decomposition of ettringite and monosulfate. The tetrahedral Al network of the MgO-modified sample was not altered upon carbonation, indicating that MgO modified the route of carbonation.

Understanding the sulfate attack of Portland cement–based materials exposed to applied electric fields: Mineralogical alteration and migration behavior of ionic species

The magnesium and sodium sulfate attacks on Portland cement paste in the presence of applied electric fields were studied, and the mineralogical alterations were investigated by both experiments and thermodynamic modeling. When an electric current flows out of the cement paste, the electric migration of ions induced sulfate ingress and decalcification. Compared with the specimen exposed to Na2SO4, that exposed to MgSO4 for 28 d proceeded to a later degradation stage, which is characterized by the decomposition of ettringite, portlandite, and AFm phases, and the formation of CaSO4. Thermodynamic modeling indicates a neutralization process induced by the electric migration of OH−, which is potentially responsible for the decomposition of ettringite. When an electric current flows into the cement paste, the Mg2+ and Na+ showed different migration behavior. Mg2+ was incorporated to form brucite and M-S-H–like products in a shallow area (~100 μm) on the surface of the specimen, whilst a part of the Na+ could be bonded to form Na-rich silica gel with the other part penetrating through the specimen. By coupling the pore solution chemistry obtained from thermodynamic modeling with the Nernst-Planck equation, the migration behaviors of the ionic species (SO42-, Mg2+, and Na+) were analyzed.

The Effect of Elevated Curing Temperatures on High Ye'elimite Calcium Sulfoaluminate Cement Mortars.

This study investigated the material properties and hydration characteristics of calcium sulfoaluminate cement (CSA) based mortars cured under 3 different initial curing temperatures. Two CSA cements with different M-values were selected. Obtained experimental results of mechanical properties, dimensional stability, and heat release were explained by hydration characteristics from X-ray diffraction, thermal gravimetric analysis, porosimetry, and thermodynamic modeling. Decomposition of ettringite decreased compressive strength but re-formation of ettringite after additional curing at 30 °C helped to recover the strength in CSA cement with a high amount of calcium sulfate. CSA cement with a low amount of calcium sulfate which was designed to predominantly have monosulfate as the main hydration product, showed increased 1-day strength after higher temperature curing but this occurred was at the expense of decreased 28-day strength.

Study of the Hydration Process of Synthetic Preparation of Ettringite by Direct Addition of Aluminum Sulfate and Calcium Hydroxide

The stability of ettringite as high-watery mineral is highly dependent on the ambient temperature. Under standard laboratory conditions, onset of decomposition of this phase occurs at temperature of 80°C already and the theoretical temperature of the complete decomposition of ettringite is 180°C. Ettringite decomposition can occur at significantly different temperatures under humidity conditions other than the laboratory ones. Within the work verification of the possibility of synthetic preparation of ettringite by direct addition of aluminum sulfate, Al2(SO4)3·18H2O, and calcium hydroxide, Ca (OH)2, as an alternative method to the yeelimite hydration procedure was carried out. The stability of the resulting systems was examined in two different environments, namely in a laboratory environment and the environment of saturated water vapour. The phase composition of the samples was determined by X-ray diffraction (XRD) analysis, thermal analysis and scanning electron microscopy (SEM).

On shrinkage and structure changes of pure and blended Portland concretes

AbstractThis research investigates the long‐term shrinkage and Relative Mass Loss (RML) of mature Portland concretes (pure CEMI and blended CEMV/A), at temperatures of 20°C and 80°C. When placed at 80°C and at relative humidities (RH) below 50‐60%, concrete shrinkage increases with very slow stabilization kinetics by several hundreds of μm/m, while RML remains of about 0.2%. The origins of this continued shrinkage, simultaneously with limited RML, are investigated through the changes in (i) the pore structure of the concretes (by Mercury Intrusion Porosimetry and nitrogen adsorption) and in (ii) their solid phases (by TGA/DTA, FTIR spectroscopy coupled to DVS, quantitative X‐Ray Diffraction by Rietveld analysis, and 29Si and 27Al MAS NMR). While the pore structure coarsens during continued shrinkage, several phase transformations occur, namely ettringite decomposition and changes in the silicate chain length of the C–A–S–H. While these structural changes are documented, their relationship with shrinkage/RML and to the pore structure is novel.

Stability and decomposition mechanism of ettringite in presence of ammonium sulfate solution

The formation and transformation characteristics of ettringite play an extremely important effect on the accelerated hardening and expansion of concrete as well as its long term durability. In alkaline condition, ettringite can be existed stably; but when the alkalinity exceeds a certain value, ettringite can be decomposed into calcium monosulfoaluminate (AFm). In this paper, the stability and its decomposition mechanism of ettringite in alkaline (NH4)2SO4 solution were then investigated. The results show that in alkaline environment, decomposition of ettringite can be occurred and main produces were gypsum and Al(OH)3 as long as the concentration of (NH4)2SO4 reached to a certain extent. Based on experiment data, a kind of NH4+ involved decomposition mechanism of ettringite had been proposed by method of quantum mechanics combined with frontier molecular orbital theory and thermodynamic theory.

Kinetic and thermal decomposition of ettringite synthesized from aqueous solutions

The kinetics of the thermal decomposition of a synthetic ettringite sample was studied between 298 and 820 K in an inert atmosphere for the present work. The ettringite and its thermal decomposition products were characterized using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Four endothermic events were observed with thermogravimetry curves, the maxima of which occurred at 366, 397, 537, and 641 K. All events were associated with the loss of water molecules with different degrees of interaction within the ettringite structure. Chemical equations for each decomposition step were proposed based on the percentages of mass loss observed. In addition, for the first time, the activation energies of each ettringite decomposition events were determined by the isoconversional methods of Ozawa–Flynn–Wall, Friedman, and Kissinger–Akahira–Sunose. The modeling revealed that the activation energy varied from ~50 kJ mol−1, characteristic of mass transfer control steps, to ~150 kJ mol−1, which is typical of chemical control, as the temperature increased and the ettringite structure lost water. A total of 32 mol of water was released equivalent to 43.1 % of the initial sample mass.