Calcium Monosulfoaluminate Hydrate Research Articles

Effect of diethanolisopropanolamine and ethyldiisopropylamine on hydration and strength development of Portland cement

Diethanolisopropanolamine (DEIPA) and ethyldiisopropylamine (EDIPA) are new types of alkanolamines, which can be used in grinding aids or accelerators. Effect of DEIPA and EDIPA at different dosages (0.05 % and 0.5 %) on cement hydration and strength development is studied by compressive strength, heat evolution, X-ray diffraction (XRD), thermogravimetry (TG), 1H nuclear magnetic resonance (1H NMR) and scanning electron microscope (SEM). Results indicate that both dosages (0.05 %, 0.5 %) of DEIPA or EDIPA accelerated the hydration of aluminate (C3A), ferrite (C4AF), alite (C3S) and belite (C2S) due to their complexation effect. The main hydration peak was advanced and enhanced by 0.05 % of DEIPA or EDIPA, while it was significantly weakened with 0.5 % of DEIPA or EDIPA incorporation due to the large formation of calcium monosulfoaluminate hydrate (AFm). Compared with DEIPA, EDIPA under both dosages caused more AFm formation and led to lower hydration degree of C3S and C2S at early ages, and possessed higher air entraining property to cause pore structure degradation. However, EDIPA contributed to higher hydration degree of C3S and C2S at later ages due to its higher steric hindrance than DEIPA. As a result, cement mortars with 0.05 % of DEIPA or EDIPA present higher or comparable compressive strength compared to the reference sample, with DEIPA005 primarily increased the early strength while EDIPA005 mainly increased the later strength. Whereas, DEIPA or EDIPA at higher dosage (0.5 %) considerably decreased early strength of cement mortars, especially EDIPA.

Thermodynamic model for ternary OPC/CAC/Calcium Sulfate binders

Ternary binders combining Portland (OPC) and calcium aluminate (CAC) cements with calcium sulfate (CS-) capitalise on differential setting and hardening properties to compensate for expansion or shrinkage.This study explored hydration over curing times ranging from 1 h to 1 year in nine cements, combinations of OPC, CAC and CS- prepared with a w/c ratio of 0.4. The experimental findings were subsequently applied to corroborate the results of a thermodynamic model for the same compositions.According to the model findings, under thermodynamic equilibrium conditions, in binary blends with a high OPC content, the addition of CS- induces the formation of more ettringite (AFt), but no calcium monosulfoaluminate hydrate (AFm), whereas a higher CAC replacement ratio prompts AFm phase formation and retards OPC hydration. Those two effects were observed to compete in the ternary system, with phase development depending on the initial proportions of the two binders.A thermodynamic hydration model was developed for the OPC/CAC/CS- ternary system in keeping with the experimental data and factoring in cement composition, clinker phase hydration kinetics and geochemical speciation-based thermodynamic equilibrium calculations. The model predictions for phase development correlated well with the experimental findings where hydration was assumed to be ongoing in the 1 year materials.

Effect of nano C–A–S–H seeds on the early-stage hydration and pore structure of Portland cement pastes

Most previous studies have focused on the addition of nanoparticles of silicon dioxide, calcium carbonate, aluminium oxide, tin(IV) oxide or calcium silicate hydrate to speed up cement hydration. In this research, nano seeds of calcium aluminium silicate hydrate (C–A–S–H) were added to Portland cement systems. It was found that, with the addition of 1%, 3% and 5% C–A–S–H seeds, the hydration process was brought forward by about 2 h, 3 h and 7 h, the initial setting time was reduced by 16.4%, 25.5% and 34.5%, and the final setting time was reduced by 16.8%, 35.1% and 41.1%, respectively. However, the paste fluidity was reduced by 11.6%, 21.6% and 28.9%, respectively, resulting in decreased workability. X-ray diffraction analysis showed that adding C–A–S–H seeds accelerated the formation of calcium monosulfoaluminate hydrate (AFm). Compared with a control sample, the compressive strength of the mortar doped with 1% C–A–S–H seeds was increased by 4.6%, 3.4% and 5.2% at 3, 7 and 28 days, respectively. However, an increase in the content of C–A–S–H seeds to 3% and 5% led to decreases in compressive strength. The total porosity declined with the addition of 1% C–A–S–H seeds, whereas the total porosity with 3% and 5% C–A–S–H seeds was higher than that of the control sample.

Study on the hydration product of ettringite in cement paste with ethanol-diisopropanolamine

Ettringite (AFt) is a very important hydration product of hardened cement pastes in the early stage. The effect of ethanol-diisopropanolamine (EDIPA) on the formation and transform process of AFt in cement pastes was systematically investigated in this paper. The results indicate that the AFt content in hardened cement pastes notably decreases due to the inhibition effect of EDIPA on the dissolution of gypsum. In addition, EDIPA promotes the transformation of AFt into calcium monosulfoaluminate hydrate and considerably alters the morphology of AFt crystals from the acicular crystals to stubby rods crystals. The mechanism of the formation of EDIPA-Ca2+ complex by the interaction between Ca2+ in ettringite and the oxygen atoms in EDIPA molecule was proposed. EDIPA-Ca2+ complex can slow down or prevent the crystal growth process of AFt and lead to altering the morphology of AFt crystals.

The effect of using supplementary cementitious materials on damage development due to the formation of a chemical phase change in cementitious materials exposed to sodium chloride

Abstract It has been reported that concrete can chemically interact with high-concentrated sodium chloride solution to form a new chemical phase change at temperatures between 0 °C and 10 °C. The formation of the chemical phase change has been found to be destructive and can cause damage in concrete. The chemical phase change appears to be the result of reactions between the sodium chloride, the tricalcium aluminate and the calcium monosulfoaluminate hydrate in the concrete matrix. This paper reports results of a study conducted to determine the effects of using supplementary cementitious materials as a partial replacement of the cement on reducing the chemical phase change amount and the associated damage development. Class C fly ash, class F fly ash, slag, and silica fume were used in this study. The amount of the chemical phase change was quantified using low-temperature differential scanning calorimetry. The damage development was monitored and quantified using a low-temperature longitudinal guarded comparative calorimeter equipped with acoustic emission technique. The results indicated that the addition of silica fume, class F fly ash, and slag can reduce the chemical phase change amount and the associated damage development while the addition of class C fly ash showed the opposite effect. X-ray diffraction analysis coupled with thermogravimetric data were also used to estimate the chemical compositions of cementitious pastes in order to determine the relationship between the amounts of the chemical phase change and the chemical constituents present in the cementitious systems. It was found that the formation of the chemical phase change is well correlated with the amounts of tricalcium aluminate and calcium monosulfoaluminate hydrate while a poor relationship existed for other chemical constituents available in cementitious systems. The beneficial aspects of supplementary cementitious materials based on their replacement levels, such as dilution effect and pozzolanic activity were also discussed. The best mitigation strategy to limit the formation of the chemical phase change and the associated damage is to utilize Type V cement or partially replace the Type I cement with silica fume, slag, or class F fly ash. The use of class C fly ash was found to increase the chemical phase change and the associated damage. Therefore, it should not be recommended in concrete exposed high-concentrated NaCl solution.

Can calcium aluminates activate ternesite hydration?

Aluminum hydroxide (AH3) has recently been shown to be able to activate hydration in ternesite, a phase found in some calcium sulfoaluminate (CSA) cements.This study explored the capacity of a number of calcium aluminates (C3A, C12A7, CA and C4A3S¯) to activate ternesite hydraulic reactivity. After laboratory synthesis, the aluminates were blended with ternesite at a ratio of 1:2 and their hydration was monitored with isothermal conduction calorimetry for 7days at 25°C. The resulting pastes were analysed with XRD, FTIR and DTA. The presence of ternesite in the pastes altered the aluminate heat flow curves, shortening the induction period and bringing the reaction peak forward, an indication of hastened hydration. Ternesite also altered the reaction products, which included calcium monosulfoaluminate hydrate and strätlingite.

CaL2,3-edge near edge X-ray absorption fine structure of tricalcium aluminate, gypsum, and calcium (sulfo)aluminate hydrates

Author(s): Geng, G; Myers, RJ; Kilcoyne, ALD; Ha, J; Monteiro, PJM | Abstract: Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoaluminate hydrate (abbreviated as kuzelite) are the major minerals in the hydration reaction of tricalcium aluminate in the presence of gypsum and have critical impacts on the kinetics and thermodynamics of early-age cement hydration mechanisms. Here, spectroscopic analysis of these minerals is conducted using scanning transmission X-ray microscopy (STXM). Their Ca L2,3-edge near edge X-ray absorption fine structure (NEXAFS) spectra are measured and correlated to the known Ca coordination environments. The results indicate that these minerals have unique Ca environments that can be differentiated from one another based on the intensities and positions of the absorption peaks at 346.5-348.5 and 350.5-351.5 eV. It is concluded that Ca in tricalcium aluminate (cubic and orthorhombic polymorphs) and katoite is in cubic-like coordination with negative 10Dq, whereas Ca is in an octahedral-like coordination with positive 10Dq in ettringite, gypsum, and kuzelite. For tricalcium aluminate, the Ca atoms in both polymorphs are in similar chemical environments with slightly more distortion in the orthorhombic polymorph. As a common issue in STXM experiments, absorption saturation of NEXAFS spectra is also investigated. It is demonstrated that the optical density difference between pre- and post-edge absorption levels provides a reliable indication of the sample thickness in the systems studied. The present work provides a reference for the STXM study of the calcium (sulfo)aluminate reactions in cement hydration and natural aqueous environments, and in the former case, provides a more complete understanding of a system that may serve as a low-C alternative to Portland cement.

Uptake of chloride and carbonate ions by calcium monosulfoaluminate hydrate

Decommissioning of old nuclear reactors may produce waste streams containing chlorides and carbonates, including radioactive 36Cl− and 14CO32−. Their insolubilization by calcium monosulfoaluminate hydrate was investigated. Carbonates were readily depleted from the solution, giving at thermodynamic equilibrium monocarboaluminate, monocarboaluminate+calcite, or calcite only, depending on the initial ratio between the anion and calcium monosulfoaluminate hydrate. Chloride ions reacted more slowly and were precipitated as Kuzel's salt, Kuzel's and Friedel's salts, or Friedel's salt only. Rietveld refinement of X-Ray powder diffraction patterns was successfully used to quantify the phase distributions, which were compared to thermodynamic calculations. Moreover, analysing the lattice parameters of Kuzel's salt as a function of its chloride content showed the occurrence of a restricted solid solution towards the sulfate side with general formula 3CaO·Al2O3·xCaCl2·(1−x)CaSO4·(12−2x)·H2O (0.36≤x≤0.50).

Influence of some admixtures on the formation of primary and secondary ettringite

Different types of admixtures (2% each of superplasticiser, barium nitrate and stearic acid) were added to examine their effect on the hydration reactions of pure tricalcium aluminate (C3A) in presence of gypsum (G). The effect of 5% magnesium sulfate solution on the formation of secondary ettringite was examined for different time intervals, 3, 7, 28, 60 and 90 days. The hydration products were investigated using X-ray diffraction, Fourier transform infrared and scanning electron microscopy. The time taken for ettringite formation was determined without admixture and in the presence of admixtures. The results showed that superplasticiser, barium nitrate and stearic acid retard ettringite formation whereas they accelerate the formation of calcium mono-sulfoaluminate hydrate phase and tetracalcium aluminate.

Calcium sulfoaluminate cement blended with OPC: A potential binder to encapsulate low-level radioactive slurries of complex chemistry

Investigations were carried out in order to solidify in cement a low-level radioactive waste of complex chemistry obtained by mixing two process streams, a slurry produced by ultra-filtration and an evaporator concentrate with a salinity of 600 gxL − 1 . Direct cementation with Portland cement (OPC) was not possible due to a very long setting time of cement resulting from borates and phosphates contained in the waste. According to a classical approach, this difficulty could be solved by pre-treating the waste to reduce adverse cement–waste interactions. A two-stage process was defined, including precipitation of phosphates and sulfates at 60 °C by adding calcium and barium hydroxide to the waste stream, and encapsulation with a blend of OPC and calcium aluminate cement (CAC) to convert borates into calcium quadriboroaluminate. The material obtained with a 30% waste loading complied with specifications. However, the pre-treatment step made the process complex and costly. A new alternative was then developed: the direct encapsulation of the waste with a blend of OPC and calcium sulfoaluminate cement (CS̄̄A) at room temperature. Setting inhibition was suppressed, which probably resulted from the fact that, when hydrating, CS̄̄A cement formed significant amounts of ettringite and calcium monosulfoaluminate hydrate which incorporated borates into their structure. As a consequence, the waste loading could be increased to 56% while keeping acceptable properties at the laboratory scale.

Early Hydration Properties of Calcium Aluminosulfate (3CaO · 3Al2O3· CaSO4) Prepared by Chemical Synthesis

Calcium aluminosulfate (3CaO.3AlO.CaSOor AS) was prepared by chemical synthesis from the nitrate salts and aluminum sulfate. AS was the main phase after calcination at 110. The specific surface areas after calcination at 110 and 130 were about 2.5 and 1.0 /g, respectively. Hydration was investigated by XRD, DSC, SEM, EDS, conduction calorimetry and analysis of the liquid phase. Calorimetry showed that the induction period was longer than that of a sample prepared by conventional solid state sintering and this was attributed to the formation of amorphous coatings in abundance of O and SO. Crystalline hydration products, principally calcium monosulfoaluminate hydrate and Al(OH), appeared subsequently.ᜎࠀࠀ㘲㌮㠵㘻Ԁ䭃䑎䷕᜕ఽ0〳⸵㬅K䍄乍븗ጊ缀Ѐ㘰〻Ԁ䭃䑎䶩᜖ഏ3㠴⸰㠻Ԁ䭃䑎䴀

The structure and influence of ferric oxide on the properties of 3CaO·3Al 2O 3·BaSO 4

The structure of 3CaO · 3Al 2O 3 BaSO 4 was determined by computer programs which are based on the single-crystal structure of 3CaO ·3Al 2O 3·CaSO 4 as T 5−123; a = b = c = 9.303 ±0.002 Å, α = β = γ = 90°, density 3.01 g cm −3. The maximum amount of ferric oxide in 3CaO·3Al 2O 3·BaSO 4 by replacement of Al 2O 3 was determined by electron microprobe analysis which led to the proposed formula, 3CaO·2.71Al 2O 3·0.29Fe 2O 3·BaSO 4. The physical properties of the compound with and without ferric oxide were measured together with the analysis of the hydration process and products using XRD, DTA and equipment to determine the heat of hydration, etc. The results show that the presence of barium sulfate has the ability to prevent the transformation of calcium aluminate decahydrate (CaO·Al 2O 3·10H 2O) to tricalcium aluminate hexahydrate (3CaO·Al 2·6H 2O). Also there is a new phase present in the hydration products which has a DTA peak similar to that of the calcium monosulfoaluminate hydrate (3CaO·Al 2O 3·CaSO 4·12H 2O).

Hydration kinetics and microstructural development in the 3 CaO. Al2O3-CaSO4.2H2O-CaCO3-H2O system

Hydration and microstructural characteristics of mixtures containing C3A and CaSO4.2H2O (0, 12.5, 25%) with or without addition of CaCO3 (0, 12.5, 25%) are followed by X-ray diffraction, differential scanning calorimetry, differential thermogravimetry, scanning electron microscopy and conduction calorimetry. Depending on the length of hydration, products formed at different periods from 5 min to 3 days consisted of hexagonal calcium aluminate hydrate, cubic calcium aluminate hydrate, calcium monocarboaluminate hydrate, etrringite, calcium monosulfoaluminate hydrate and possibly a solid solution of hexagonal calcium aluminate hydrate with monocarbo-and sulfo-aluminate hydrates.