Hydration Of Tricalcium Aluminate Research Articles

Molecular insight into the initial hydration of tricalcium aluminate

Portland cement (PC) is ubiquitously used in construction for centuries, yet the elucidation of its early-age hydration remains a challenge. Understanding the initial hydration progress of tricalcium aluminate (C3A) at molecular scale is thus crucial for tackling this challenge as it exhibits a proclivity for early-stage hydration and plays a pivotal role in structural build-up of cement colloids. Herein, we implement a series of ab-initio calculations to probe the intricate molecular interactions of C3A during its initial hydration process. The C3A surface exhibits remarkable chemical activity in promoting water dissociation, which in turn facilitates the gradual desorption of Ca ions through a metal-proton exchange reaction. The dissolution pathways and free energies of these Ca ions follow the ligand-exchange mechanism with multiple sequential reactions to form the ultimate products where Ca ions adopt fivefold or sixfold coordination. Finally, these Ca complexes reprecipitate on the remaining Al-rich layer through the interface-coupled dissolution-reprecipitation mechanism, demonstrating dynamically stable inner-sphere adsorption states. The above results are helpful in unmasking the early-age hydration of PC and advancing the rational design of cement-based materials through the bottom-up approach.

The Effect of Gypsum/Bassanite on the Retardation of Ethylene Diamine Tetra(Methylene Phosphonic Acid) Sodium in Oil Well Cement Slurry

Summary Organophosphonates are commonly used retarders to prolong the thickening time of oilwell cement slurry at medium and high temperatures. In this paper, the impact of calcium sulfate in cement on the retarding effect of ethylene diamine tetra(methylene phosphonic acid) sodium (EDTMPS) was explored. First, the thickening properties of cements from four different factories were studied in detail with varying additions of EDTMPS. The study revealed diverse thickening phenomena, including retarding, accelerating, and increasing the initial consistency of cement slurries. The heat flow of cement hydration was detected, and the mineral changes of cement slurries at the early stage (1–3 hours) were analyzed. Additionally, the effect of EDTMPS on the hydration of tricalcium aluminate (C3A) and gypsum (GP)/bassanite (BS) slurry was investigated through X-ray diffraction (XRD) and ion concentration test. Finally, two clinkers from the same cement factory were mixed with GP/BS of different dosages to study the effect of calcium sulfate type on the thickening properties of cement slurry with EDTMPS. The results revealed that EDTMPS slowed down the dissolution of GP while promoting the dissolution of C3A. The rapid hydration of C3A increased the consistency of cement slurry without the retarding effect of GP. However, EDTMPS promoted the dissolution of BS, which can retard the hydration of C3A. Therefore, EDTMPS is appropriate for cements containing BS.

Development of CO2-integrated 3D printing concrete

3D printing concrete (3DPC) technology is a promising technique for construction due to its advantages such as no formwork is needed, fast production, automation, and high architectural freedom. However, the layer-by-layer extrusion method has stricter requirements on the rheological properties of concrete. One of challenges of this technology is how to improve the rheological properties of concrete to satisfy the conflicting requirements during pumping and after extrusion. This study proposed to use CO2 as accelerator and rheology modifier by injecting CO2 during secondary mixing to improve the rheological and mechanical properties of 3DPC. The influences of the secondary CO2 mixing on the properties of poured concrete and 3DPC were investigated. After using the secondary CO2 mixing, the setting time and workability of concrete were reduced, which contributed to the significantly improved buildability of 3DPC. This was because CO2 accelerated the hydration of tricalcium aluminate (C3A) and tricalcium silicate (C3S) during the secondary mixing. After that, they were continuously accelerated by the calcium carbonate formed during CO2 mixing. Also, the compressive strength of poured concrete was enhanced by the secondary CO2 mixing because it reduced the volume of larger pores (>200 nm) and promoted the formation of calcium silicate hydrates (C-S-H), which simultaneously slightly increased the drying shrinkage. In addition, after using the secondary CO2 mixing, the compressive strength and interlayer bond strength of 3DPC was enhanced.

Fabrication and characterization of calcium aluminates cement via microwave-hydrothermal route: Mayenite, katoite, and hydrocalumite

In response to the growing interest in functional building materials, the microwave-hydrothermal (M-H) technique was employed to prepare calcium aluminate-based cement. In this study, aqueous solutions containing active lime and alumina were treated using M-H method for one hour at temperatures of 100°, 120°, and 140 °C. Various starting compositions with calcia to alumina molar ratios (C/A) of 1, 1.3, 1.5, 2, 3, and 4 were investigated. Subsequently, the hydrothermally synthesized powders at 140 °C were subjected to calcination for 2hr at 1150°, and 1350 °C to obtain anhydrous phases. The formed powders were characterized using X-ray diffraction (XRD), differential thermogravimetric analysis (TG-DTG), Raman spectroscopy, and scanning- or transition- electron microscopy (SEM & TEM). The results revealed that for starting C/A molar ratio of 1.00–2.00, M-H treated samples at 100°–140 °C produced stable phases such as katoite and hydrocalumite. As the lime content increased in the C/A mixtures up to a molar ratio of 3.00, the tri-calcium aluminate hydrate was an abundant phase, with its crystallinity increasing with higher hydrothermal temperatures. The M-H treated samples at 140 °C, calcined for 2hr at 1150°, and 1350 °C, yielded mayenite powder (C12A7) with varying degrees of crystallinity. These findings provide valuable insights into the preparation of calcium aluminate-based cement using the microwave hydrothermal method.

Understanding the adsorption of calcium sulfate on tetracalcium aluminoferrite and tricalcium aluminate surfaces

AbstractCalcium sulfate (CaSO4), an essential retarder in cement, retards the hydration of tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) phases. However, its retarding mechanism remains unclear. This paper focused on the adsorption of CaSO4f on C4AF and C3A surfaces based on isothermal calorimetry, the measurement of the ionic concentrations in a diluted system, and density functional theory to enhance the understanding of the retardation mechanism. The results showed that the retarding effect of CaSO4 on C4AF was stronger than that on C3A due to the slower CaSO4 consumption rate, lower driving force for CaSO4 adsorption, and surface coverage of Fe(OH)3 gel. The adsorption of CaSO4 hindered Ca dissolution more markedly on C4AF than C3A, which was pronounced on Fe‐free C4AF surfaces. The adsorption of CaSO4 weakened the affinity of water on C4AF and C3A surfaces, lowering the driving force for H2O adsorption. The adsorption of H2O and CaSO4 promoted the dissolution of Al on the [AlO6] octahedral surface of C4AF, which may be responsible for the maintenance of a higher Al concentration in the solution. Based on the above results, the adsorption of CaSO4 on initial C4AF and C3A hydration was explained.

Investigating the hydration of C3A in the combined presence of anhydrite and limestone using solid-state NMR, XRD and TG techniques

Diverse AFm phases are commonly found during the hydration of calcium sulfoaluminate (CSA), Portland (OPC), and calcium aluminate (CAC) cements. Due to the flexibility in their layered double hydroxide (LDH) structure, they are observed in variable single or multi-anion bearing forms, water contents and transient states. When multiple sulfate and carbonate anion sources, in variable compositions, are available during the hydration of cements, the identity, quantity, and stability of the formed AFm phases vary considerably. They may also precipitate as microcrystalline and/or amorphous phases, rendering their detection by X-ray powder diffraction (PXRD) difficult. In this study the AFm phases have been generated through the hydration of tricalcium aluminate (C3A) in the presence of sulfate (anhydrite) and carbonate ions (limestone) in various compositions. A multi-technique approach involving solid-state nuclear magnetic resonance spectroscopy (ssNMR), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and PXRD has been employed to govern the sequence of hydration reactions, the evolution, structure, and the stability of AFm phases at 1 and 28 days of C3A hydration. The results show that the identity and quantity of AFm phases formed vary considerably according to the nature of the anion sources available during the hydration. Hydration products such as crystalline C3AH6, ettringite and amorphous as well as crystalline/microcrystalline monoanionic AFm phases (monosulfate, monocarbonate, hydroxy-AFm) and bi-anionic phases (hemicarbonate and solid-solutions involving more anions) have been identified and quantified.

Understanding the role of C–S–H seed/PCE nanocomposites, triethanolamine, sodium nitrate and PCE on hydration and performance at early age

Compared to thermal curing, the application of C–S–H/PCE nanocomposites (CPNs) and triethanolamine (TEOA) compound admixture is a green and highly efficient hydration acceleration strategy. Commercial CPNs usually contain polycarboxylate (PCE) and residual sodium nitrate (NN). It is still uncertain whether their presence has some influence on the hydration of cement with this admixture. The experimental results show that TEOA-NN promotes hydration, and then the setting times are shortened and the early compressive strength is increased; it advances the start of the acceleration period, slightly increases tricalcium silicate (C3S) hydration, or further improves tricalcium aluminate (C3A) hydration. TEOA-PCE significantly retards C3S and C3A hydration at 1 d. In contrast, TEOA-CPNs exhibit excellent mechanical properties and hydration heat owing to its strong promotion of the hydration of C3S and C3A. These results can provide guidance for the formulated design of CPNs-based admixtures.

Role of ionic diffusion in heat flow and chemical shrinkage of tricalcium aluminate hydration subjected to thermo-chemo-electrical coupled fields

The role of ion diffusion in the heat flow and chemical shrinkage of tricalcium aluminate (C3A) hydration was investigated using the proposed multi-ionic reactive transport model for C3A hydration. Ion diffusion, dissolution, and precipitation reactions were coupled in the governing equation of the chemical field during C3A hydration in the presence of gypsum. Ion diffusion and chemical reactions were also governed by the electric and temperature fields in the model. Theoretical computations were performed relating ion diffusion to heat flow and chemical shrinkage during all stages of C3A hydration. Excellent agreement was achieved by comparing the simulation results and the experimental data under various conditions. The effects of the gypsum content, specific surface area (SSA), and curing temperature on the ion diffusion, electrical potential, heat flow, and chemical shrinkage were numerically studied. The results indicated that (1) higher gypsum contents, SSAs, and curing temperatures increased the ion concentration gradient and improved the supersaturation concentration of sulfate near the C3A surface; (2) higher gypsum contents led to faster decreases in the Ca2+ and SO42− concentrations before the depletion of gypsum; and (3) the gypsum content affected the phase assemblage through spatial and temporal evolution of the ionic species. The proposed model may guide the design of the C3A-gypsum system and can be extended to optimize the fluidity and setting properties of the cement paste.

Chloride binding behaviors and early age hydration of tricalcium aluminate in chloride-containing solutions

Understanding the hydration kinetics and interactions of hydration products of cement components with chlorides is crucial for designing durable cement-based materials. The most reactive component of ordinary Portland cement (OPC), tricalcium aluminate (C3A), was investigated on its hydration kinetics, chloride binding behaviors and hydrated phase assemblages through multiple ex-situ and in-situ methods. The hydrated phases of C3A demonstrated different chloride binding isotherms in NaCl and CaCl2 solutions at different ages. Chloride ions can suppress the formation of calcium aluminate hydrates (OH-AFm and C3AH6) while calcium ions were favorable to increase the content of hydrocalumite (Cl-AFm) and regulate its crystal structure. The carbonation process deteriorated the chloride binding capacity of C3A pastes through producing more calcium mono/hemi-carboaluminate phases (Mc/Hc) or forming a solid solution between Mc and Cl-AFm. These findings can be used as a guide for corrosion protection design of cement-based materials.

Mechanisms of hydration heat inhibitors on the early heat release process of cement

We evaluated the effects of hydration heat inhibitors on the early hydration heat release process of cement and its main mineral components. We used a microcalorimetric method to determine the effects of various proportions and properties of hydration heat inhibitors on the hydration of portland cement, tricalcium silicate, and tricalcium aluminate: concentration (C) = 40% m/m hydroxydiphosphonic acid (HEDP) (1-hydroxyethylidene-1,1-diphosphonic acid) and C = 40% m/m diethylene triamine pentonyphosphonic acid (DTPMPA) (diethylenetriaminepentamethylene phosphonic acid). We also analyzed and tested the heat release rate and cumulative heat release during the hydration of cement and its main mineral components. The hydration heat inhibitors decreased the heat release rate of cementitious materials by means of adsorption, chelation, precipitation, complex formation, and control of calcium hydroxide crystals. Among these materials, the hydration heat inhibitor had the most substantial effect on the composition of tricalcium silicate clinker, reducing the peak temperature at the initial stage of hydration and delaying its occurrence time. These results are pertinent to controlling and selecting the early hydrothermal release process of cement systems.

Influence of the availability of calcium on the hydration of tricalcium aluminate (C3A) in seawater‐mixed C3A–gypsum system

AbstractThis work examined the effects of seawater (SW) on the hydration of tricalcium aluminate (C3A) in C3A–gypsum and C3A–gypsum–Ca(OH)2 systems through the characterization of hydration heat release, the evolution of aqueous phase composition and hydration products with the hydration time. It was found that SW increased the dissolution driving force of C3A and solubility of gypsum, which accelerated the early hydration of C3A and the formation of ettringite (AFt), leading to a higher hydration degree of C3A at an early age compared with the deionized (DI) water–mixed pastes. After gypsum depletion to form AFt, and in the absence of Ca(OH)2, the formation of chloroaluminate hydrates was slower due to the insufficient Ca resulted in an accumulation of Al in solution. This would delay the subsequent transformation of AFt to monosulfate (SO4–AFm) and the formation of hydrogarnet (C3AH6), which would further reduce the hydration degree of the C3A at the later ages. However, in the presence of Ca(OH)2, the hydration degree of C3A–gypsum–Ca(OH)2 at later ages was increased, which was similar to that of the corresponding DI pastes. This can be inferred that the amount of Ca available in SW‐mixed cement concrete can affect the hydration degree of C3A in cement.

Mineralogy of tricalcium aluminate hydration with silica nanoparticles

Formation of siliceous-hydrogarnet (Si-hydrogarnet) and stability of katoite (C3AH6) in tricalcium aluminate (C3A) system in presence of silica nanoparticles (n-SiO2) have been examined in the present study. C3A hydration in presence of n-SiO2 upto 24 h show retardation in hydration due to the surface coverage of C3A grain through calcium-silicate-hydrate (C-S-H)/calcium-alumino-silicate-hydrate (C-A-S-H) (previous study). However, in the present investigation, hydration was studied upto 10 days using QXRD, TGA, FTIR, FESEM, EDS and Mapping and 29Si NMR techniques. QXRD results show that in case of control samples, the katoite content increases from 61 to 73%, while in n-SiO2 incorporated C3A samples, it decreases from 28 to 15% as the hydration proceeds showing katoite phase destabilization in presence of n-SiO2. Further, FTIR results show symmetric stretching vibration of Si-O-Si at ∼784 cm−1 and ∼818 cm−1, while asymmetric stretching vibration of Si–O–Si/Si-O-Al at ∼1028 cm−1 indicating the formation of C-S-H/C-A-S-H and Si-hydrogarnet in presence of n-SiO2. In 29Si NMR results, Q2u peak at −89 ppm confirm the formation of Si-hydrogarnet at 10 days of hydration. The present study is important from performance and durability point of view as formation of C-A-S-H and Si-hydrogarnet can act as an aluminum reservoir, which may prevent severe chloride and sulphate attack.

Study on the Strength and Hydration Behavior of Sulfate-Resistant Cement in High Geothermal Environment.

The hydration process and compressive strength and flexural strength development of sulphate-resistant Portland cement (SRPC) curing at 20 °C, 40 °C, 50 °C, and 60 °C were studied. In addition, MIP, XRD, SEM, and a thermodynamic simulation (using Gibbs Energy Minimization Software (GEMS)) were used to study the pore structure, the types, contents, and transformations of hydration products, and the changes in the internal micro-morphology. The results indicate that, compared with normal-temperature curing (20 °C), the early compressive strength (1, 3, and 7 d) of SRPC cured at 40~60 °C increased by 10.1~57.4%, and the flexural strength increased by 1.8~21.3%. However, high-temperature curing was unfavorable for the development of compressive strength and flexural strength in the later period (28~90 d), as they were reduced by 1.5~14.6% and 1.1~25.5%, respectively. With the increase in the curing temperature and curing age, the internal pores of the SRPC changed from small pores to large pores, and the number of harmful pores (>50 nm) increased significantly. In addition, the pore structure was further coarsened after curing at 60 °C for 90 d, and the number of multiple harmful pores (>200 nm) increased by 17.9%. High-temperature curing had no effect on the types of hydration products of the SRPC but accelerated the formation rate of hydration products. The production of the hydration products C-S-H increased by 13.5%, 18.6%, and 22.8% after curing at 40, 50, and 60 °C for 3 d, respectively. The stability of ettringite (AFt) reduced under high-temperature curing, and its diffraction peak was not observed in the XRD patterns. When the curing temperature was higher than 50 °C, AFt began to transform into monosulfate, which consumed more tricalcium aluminate hydrate and inhibited the formation of “delayed ettringite”. Under high-temperature curing, the compactness of the internal microstructure of the SRPC decreased, and the distribution of hydration products was not uniform, which affected the growth in its strength during the later period.

Effects of limestone powder on the early hydration of tricalcium aluminate

Effects of limestone powder on the early hydration of tricalcium aluminate

New scientific evidence of the effect of high temperatures and long curing times on MK-blended cement paste mineralogy

This article reports new scientific evidence on the hydrated phases present in blended cement pastes formulated with 10%, 20% or 25% metakaolin (MK) and stored at 60 °C for 15 years. XRD-Rietveld, SEM/EDX, NMR, FT-IR and TG/DTG findings attested to substantial difference in the mineralogy and morphology of the phases present (C2ASH8, C4AH13 and hydrogarnet) between long-term and short-term curing. The predominant crystalline phases in OPC and 10% MK-blended pastes, portlandite, calcite and γ-C2S, were characterised by small, laminar crystals. Stable katoite and hydrogrossular were observed in the pastes with MK content ≥20%, although the cubic phase of the latter (tricalcium aluminate hydrate, Ca3Al2(OH)12) was found only in pastes with an MK content of 25%.

Effects of Nano-CSH on the hydration process and mechanical property of cementitious materials

Nanomaterials are widely used in cement to improve the various properties of cement-based materials. Nano-CSH is considered as an effective accelerator for the hydration of cement. This paper studied the effects of nano-CSH on the hydration behavior and compressive strength of cementitious materials with various mineral admixtures. Isothermal calorimetry test was used to study the early hydration of cement paste. Thermogravimetric and X-ray diffraction tests were used to study the evolution of hydration product and unhydrated mineral phases in the hydrated cement paste. The presentation of compressive strength can evaluate the influence of nano-CSH on the property of cement-based material at the macro level. The obtained results show that the used nano-CSH can promote the hydration of tricalcium silicate (C3S), and is more active on the hydration of tricalcium aluminate (C3A) in the samples with GGBFS. The presence of nano-CSH can definitely accelerate the secondary hydration reaction of mineral admixtures.

Effect of seawater as mixing water on the hydration behaviour of tricalcium aluminate

This study explored the mechanism of the effect of seawater on tricalcium aluminate (C3A) hydration. The results showed that seawater retarded C3A hydration and reduced the reaction degree of C3A. The co-existence or ion pairing of Ca2+ and SO42− onto the surface of C3A poisoning the reactive sites is the main reason for this retardation. Besides, the precipitation of Mg(OH)2 on the surface of C3A would prolong the induction period for another 30 min and then consequently decrease the dissolution rate of C3A hydration. Trace amounts of MgSO40 and Mg2+ present in the alkaline solution had little retardation effect. It was also found that Cl− would preferentially react with C3A to form Friedel's salt, rather than forming hydroxy-AFm as that in the C3A-deionized water paste. The direct formation of Friedel's salt resulted in an accumulation of Al3+ in solution, which would also hinder the subsequent dissolution of C3A.

Influence and mechanisms of active silica in solid waste on hydration of tricalcium aluminate in the resulting composite cement

Many industrial solid wastes are rich in silica (SiO2) which can be used as supplementary cementitious material (SCM) to replace part of Portland cement. Existing studies mainly focus on the impact of solid waste on tricalcium silicate (C3S) hydration. Since tricalcium aluminate (C3A) is the most reactive component of the Portland cement, it is of great interest t to investigate the effect of solid waste containing SiO2 on the hydration process of C3A. In this study, different amounts of nano-silica (nano-SiO2) were mixed with C3A and the hydration products after 72 h of hydration were analyzed by means of X-ray diffraction (XRD), Fourier Transform Infrared analyzer (FT-IR), Environment Scanning Electronic Microscope - Energy Dispersive Spectrometer (ESEM-EDS), X-ray Photoelectron Spectroscopy (XPS) and Solid-state Nuclear Magnetic Resonance (NMR). The results showed that nano-SiO2 can promote the hydration of C3A and stabilize the hydration products of C3A in the form of crystalline hydrogarnet (C3AH6). The formation of Si-O-Al bonds was also found in the hydration products. ESEM results revealed that the surface of the crystalline hydration products (C3AH6 particles) was covered by gel-like products. The results from the XPS and NMR analyses further confirmed that the negatively charged nano-SiO2 and the silicate anions can literally interact with C3A to produce calcium silicoaluminate hydrate (C-A-S-H) gel, whereas the formation of C-A-S-H is attributed to the substitution reaction of Al in the Si-O-Si network occurring on the surface of C3A. In addition to the reactive silica-aluminum component reacting with Ca(OH)2 to form additional calcium silicate hydrate (C-S-H) and C-A-S-H gels, the reactive silicon in solid waste can also undergo pozzolanic reaction with C3A to form C-A-S-H gel.

Hydration of cubic tricalcium aluminate in the presence of calcined clays

AbstractCalcined clay blended cements play a major role in cement industry's strategy to reduce CO2 emissions. During their hydration, an accelerated aluminate reaction is often observed to affect the sulfate balance. The objective of this study was to provide insights into the influence of different calcined clays on the hydration of cubic tricalcium aluminate (C3A). A cementitious model system consisting of cubic C3A, quartz powder, calcium sulfate and a model pore solution was investigated. The influence of three different calcined clays and one nanolimestone was examined by a successive replacement of the quartz powder and variation of the calcium sulfate. Heat flow and hydrate phase development were followed by isothermal calorimetry and quantitative in‐situ X‐ray diffraction. Accelerated ettringite formation and sulfate depletion were observed for all calcined clays, while the nanolimestone exhibited the opposite effect. It was found that adsorption of SO4 ions and/or Ca‐SO4‐complexes at the surface of calcined clay particles is the main factor inhibiting retardation of the C3A hydration in absence of a silicate reaction. In the Al‐rich systems a retardation through sulfate adjustment seems to be impeded by additional Al ions, which react with Ca adsorbed onto and leached from the C3A surface.

Effect of carboxylated styrene–butadiene copolymer on the hydration of tricalcium aluminate in the presence of gypsum and calcium hydroxide

The clinker mineral tricalcium aluminate (C3A) determines largely the early hydration characteristics of Portland cement. Therefore, understanding the influence of the polymer on the hydration of C3A is contributed to clarify the mechanism of polymer on the early hydration of cement-based material. The hydration environment of C3A in Portland cement was simulated by using C3A mineral, gypsum ( $${\rm C}\bar{S} \cdot {\text{H}}_{2}$$ ) and calcium hydroxide (CH). The specimens, whose water cement ratio (mw/mc) was 0.4 and carboxylated styrene–butadiene (SB) copolymer cement ratio (mp/mc) was 0, 5, 10, 15 and 20%, were cured at 20 ℃/RH90% for 6 h, 12 h, 1 day, 3 days, 7 days and 28 days, respectively. The effect of SB copolymer on the system of C3A– $${\rm C}\bar{S}\cdot{\text{H}}_{2}$$ –CH was investigated by the combination of isothermal calorimetry, X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM). It was found that the SB copolymer retards C3A hydration and reduces the heat of hydration. The XRD results revealed that addition of SB copolymer inhibits the consumption of C3A, delays the conversion of ettringite (AFt) to calcium monosulfate aluminate hydrate (AFm), promotes the formation of hydrated calcium aluminate (C4AH13), and reduces the crystallinity of AFm.