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In this paper, the strength development of a pure steel slag (SS) system with various concentrations of N,N,N′,N′-Tetrakis-(2-hydroxyethyl) ethylenediamine (THEED) was investigated. The hydration kinetics, pore structure and microstructure of SS pastes with and without THEED were characterized to underscore the working mechanism of THEED. Results show that THEED additions significantly increase the 3, 7 and 28 days compressive strength of hardened SS pastes. The enhancement effect increases with the dosage of THEED. At a concentration of 2000 ppm, THEED increased the compressive strength by 733%, 665%, and 545% at 3, 7 and 28 days, respectively. It is confirmed that THEED additions improve the hydration degree of SS by accelerating hydration of the aluminum phase (C3A, PDF-38-1429; C12A7, PDF-48-1882) and C2F,(PDF 38-0408) to generate Mc (PDF-41-0219) and Pa (PDF-30-0222) in the presence of CaCO3. Also, the hydration degree of silicates is increased by THEED. In this way, THEED additions refine the pore structure of hardened SS paste by increasing the pore volume with a diameter below 300 nm to achieve enhancement. The chelating effect of THEED results in promoting dissolution of SS, which provides the driving force for accelerating SS hydration. [ABSTRACT FROM AUTHOR]

A blended cementitious material consisting of cement and titanium slag in a mass ratio of 1:1 was prepared and the influence of varying dosages of tetrakis (2-hydroxyethyl) ethylenediamine (Theed) on the strength development and hydration process of the blended systems was investigated. The hydration process, pore structure and microstructure at different ages were characterised by isothermal conduction calorimetry, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry and scanning electron microscopy. The results showed that: the addition of Theed (0·01–0·10%) tended to improve the flexural and compressive strength of the blended mortars; the addition of Theed increased the hydration degree of the blended cement pastes before 28 d while delaying the early (before 6 h) hydration, as indicated by isothermal calorimetry measurement; the pore structure of the blended cement pastes after curing for 28 d was modified by Theed, which is beneficial for strength development; the pozzolanic reaction of the titanium slag was enhanced by the presence of Theed, as confirmed by the portlandite content, pore structure measurements and morphological observation. [ABSTRACT FROM AUTHOR]

In this study, the effect of CO2 concentration on carbonation depth, semi-carbonated zone, pore size distribution and carbonation products in concrete were investigated. The CO2 concentration was increased from 0.035 % to 2 % and 20 % at 70 % relative humidity and 20 °C. The results show that the carbonation process of 2 % CO2 was more similar to natural carbonation than 20 % CO2, as evidenced by the better linearity fitness of carbonation depth. The length of semi-carbonated zone was 6 mm at 2 % CO2 and 8 mm at 20 % CO2 within 16 weeks, a number that cannot be ignored when predicting the service life of concrete under carbonation. CH remained in a small amount in the completely carbonated zone instead of being completely consumed, and CH consumed at 20 % CO2 is about 1.5-2.0 times that of 2 % CO2. The content of CaCO3 in the completely carbonated zone at 20 % CO2 was higher than that of 2 % CO2. CaCO3 could fill in large pores between hydration products, so the porosity, average pore size and aperture decreased with CO2 concentration. [ABSTRACT FROM AUTHOR]

To make effective use of plant leaves as an environment-friendly heat-insulating building material, our research group has tested five poplar leaf modification methods to improve compatibility between leaf fibres and cement-based materials. The work involved testing water absorption of before and after modification of leaf fibres, the setting time and hydration heat of the fibre–cement paste, and analysed the mechanisms and effect of fibre modification methods on compatibility between fibres and cement-based materials. The results show that processing of fibres with surface coating and dipping methods improved compatibility between fibres and cement-based materials to some extent and in different aspects. Overall, the following three methods gave superior performance: pure acrylic polymer emulsion spraying, sodium silicate solution spraying and water dipping. [ABSTRACT FROM AUTHOR]

A series of novel comb-like poly(butyl acrylate)-g-poly(dimethylaminoethyl methacrylate) (PBA-g-PDMAEMA) with different side chain lengths were designed and successfully synthesized by the "first main chain then side chain" method. Infrared Spectroscopy (IR), 1H Nuclear Magnetic Resonance (1H NMR), and gel permeation chromatography (GPC) were used for structural confirmation and molecular weight characterization. This polymer exhibited responsive behavior from hydrophilicity to hydrophobicity under the alkaline environment of cement-based materials, with the contact angle of 105.6°, a decreased evaporation rate, and a hydrophile–lipophile balance (HLB) value. A significant internal hydrophobic effect on cement mortar was shown in the water absorption rate, which decreased by 75.2%, and a dry shrinkage-reducing rate of more than 30%. Furthermore, this polymer can effectively slow the exothermic rate, reduce the heat release, and delay the exothermic peak of cement hydration. It was interesting that these properties showed a direct correlation with the side chain length of the comb polymer. The aims of this study are to provide a new avenue to synthesize polymers with the spontaneous hydrophilicity–hydrophobicity transition in the cement system, achieving excellent internal hydrophobicity of cement-based materials, and to offer a promising alternative to resist external erosion for improving the durability and service life of cement-based materials. [ABSTRACT FROM AUTHOR]

In the cement industry, SO2 and NOx are generally removed separately. There are many problems, such as large area, high investment cost, secondary pollution and so on. Desulfurization and denitrification technology have become a frontier research direction in the field of air pollution control. In this paper, rice husk ash and carbide slag were compounded and modified to prepare modified rice husk ash-carbide slag composite absorbent, and its desulfurization and denitrification performance and mechanism were studied. The results showed that the NO conversion and SO2 conversion of the modified rice husk ash-carbide slag composite absorbent increased by 44% and 2%, respectively, at 700 °C. Fibrous calcium silicate and calcium silicoaluminate hydrates were formed during the hydration process, which made the specific surface area of the absorbent larger and provided more reactive sites. The hydration process increases the content of oxygen-containing functional groups, decreases the hydroxyl/ether C–O functional groups, and increases the content of carboxyl–COO functional groups are conducive to the denitrification reaction. [ABSTRACT FROM AUTHOR]

Sulphoaluminate cement has the advantage of low-temperature application performance, but its hydration mechanism at low temperatures is not yet clear. Anhydrous calcium sulfoaluminate (C4A3 S) is the main mineral in the composition of sulfoaluminate cement clinkers. In this paper, C4A3 S mixed with gypsum (CaSO4∙2H2O) to form a C4A3 S -C S H2 cement system; X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM) and mercury intrusion analysis (MIP) to clarify the effect of temperatures on the hydration properties of C4A3 S -C S H2 cement system. The results showed that hydration of the C4A3 S -C S H2 cement system could carry on at low temperatures, even at −15 °C. The main hydration product was ettringite. Low temperatures did not change the types of the hydration products, but the low temperature of 0 °C was more favorable for the formation of ettringite. The early hydration of the C4A3 S -C S H2 cement system was inhibited by the decrease in temperature. However, hydration of the cement at 0 °C continued at a high rate after one day. Morphologies of the ettringite for the C4A3 S -C S H2 cement system at −15 °C were needle-like structures, while they were of columnar structure at 0 °C. The compressive strength of samples at 0 °C reached 82 MPa, which is significantly higher than that at 20 °C. [ABSTRACT FROM AUTHOR]

The slag obtained in the process of pig iron smelting has been widely used, but the variational hydration activity always is a significant factor affecting its quality. In this experiment, the laboratory simulated slag was prepared by adjusting the chemical composition and cooling method. The experiment primary characterized the structure and hydration process with different types of slag by using MAS NMR, XRD, compressive strength, ICP, SEM, and hydration heat, then obtained the influence of the composition of the network former S/A (the mass ratio of SiO2 and Al2O3 in chemical composition) and amorphous phase content on its structure and hydration activity. The result shows that lowering the S/A value can reduce the degree of vitreous polymerization in the slag; reducing the S/A value of the slag can make the slag hydration time advance, and consequently, the cumulative exotherm increases, the liquid phase Ca/Si and Al/Si ionic ratio increases, and the hydration product changes from C–S–H gel to C–A–S–H gel, which ultimately leads to an increase in compressive strength. In the high S/A value slag, the formation of the trace crystal phase of gehlenite is beneficial to reduce the degree of polymerization of the amorphous. [ABSTRACT FROM AUTHOR]

Tertiary alkanolamines play an essential role in the hydration of cement-based materials as one of the main components of cement grinding aids and concrete admixtures. Although the field has been well-studied, the significant effects of slight variations in alkanolamine type and dosage make it imperative for researchers to fully understand alkanolamines before using them. Therefore, it is necessary to understand in detail the mechanism of different alkanolamines affecting the hydration of cement-based materials and their effects on setting and hardening. Based on the synthesis and chemical characteristics of alkanolamines, the complexation between alkanolamine and metal ions is discussed in this paper. The influence of alkanolamines on hydration of cement-based materials and the role of complexation in hydration are studied. Various properties of cement-based materials in the presence of alkanolamines are rigorously reviewed. The synergistic effects of alkanolamine and other admixtures are also considered in this review. The research findings prove that the complexation of alkanolamines plays an essential role in hydration and further interferes the microstructure and properties of the cement-based materials. Variations in the molecular structure and dosage of alkanolamines can lead to significant differences in hydration. The modification of alkanolamines at the molecular level and their use in combination with other admixtures are the future research directions. The working mechanism of alkanolamines in the hydration process of cement-based materials still needs to be further explored. • Complexation of alkanolamines significantly affects cement hydration. • Different alkanolamines have different effects on mineral phase hydration. • Alkanolamines significantly affect the morphology of C-S-H gels and Ca(OH) 2. • The right dosage of alkanolamine could improve compressive strength. • TEA has a significant effect on setting time. [ABSTRACT FROM AUTHOR]

Steel slag (SS) as a supplementary cementitious material has low cementitious activity. Diethanol-isopropanolamine (DEIPA) is an organic admixture that can enhance the cementitious activity of cementitious materials. This work aimed to investigate the hydration characteristics of SS under the complexing of DEIPA. The hydration process of SS, the complexation of DEIPA with metal ions, and the dissolution process of C 3 A and C 3 S in the presence of DEIPA were systematically investigated. The results showed that DEIPA enhanced the hydration of aluminate (C 3 A and C 12 A 7), ferrate (C 2 F) and silicate phases (C 3 S and C 2 S), which formed a large amount of monocarboaluminate, paraalumohydrocalcite and C–S–H gels. In the early stages of hydration, the hydration products were mainly C–S–H gels, monocarboaluminate and paraalumohydrocalcite, and in the later stages of hydration, the hydration products were mainly C–S–H gels, paraalumohydrocalcite. The monocarboaluminate may be transformed to paraalumohydrocalcite at a later stage. This hydration-promoting effect was related to the complexation of DEIPA. DEIPA facilitated the dissolution of mineral phases and the precipitation of complexed metal ions by complexing with metal ions. The stronger complexation of Al3+ by DEIPA made it more solubilizing for C 3 A. As a result, more aluminum-containing hydration products were formed. The weaker complexation of Ca2+ by DEIPA made it a weaker solubilizing for C 3 S, which also led to a weaker promotion of silicate hydration by DEIPA. The solubilization of DEIPA to minerals enhanced the cementitious activity of SS, which ultimately led to the increase in the compressive strength of the hardened SS paste at each age. [ABSTRACT FROM AUTHOR]

Air quenched slag is processed by a fast air cooling method which is developed with the advantages of recovering heat from molten slag and water conservation compared to the water quenching method. Air quenched slags with different chemical compositions are synthesized in the lab by designing three chemical composition ratios: (CaO + MgO)/(SiO2 + Al2O3), CaO/MgO and SiO2/Al2O3, which are donated as CM/SA, C/M and S/A, respectively. The effect of different chemical compositions on the phase compositions of synthetic air quenched slag, the strength and hydration properties of slag blends were investigated by using various characterization techniques. The results show that the amorphous content of air quenched slag decreased with the increasing basicity CM/SA of slag. The S/A ratio of slag was the dominant factor for the compressive strength of slag blends at 28 days and negatively correlated with strength. Decreasing the S/A ratio of slag increased the reactivity of slag and its reaction degree indicated by higher hydration heat release, lower CH content, greater chemical combined water amount and denser microstructure. Moreover, thermodynamic modelling revealed that a higher S/A of slag leads to the increase of C-(A)-S-H and AFt contents, whilst decreasing the amounts of Ht, AFm-SO4 phases and the total volume of hydrates. [ABSTRACT FROM AUTHOR]

The impact on hydration of four kinds of alkanolamines (triethanolamine (TEA), triisopropanolamine (TIPA), diethanol-isopropanolamine (DEIPA) and methyldiethanolamine (MDEA)) in a steel slag cementitious system was reviewed. Isothermal calorimetry studies provided information on the hydration heat release rate and the cumulative energy released by blend cement systems. Mortar strength, quantitative X-ray diffractometry, mercury intrusion pore size distribution analysis, scanning electron microscopy and thermogravimetric analysis were used to analyze the mechanism of strength enhancement and micro-structure of hydrates that were impacted by alkanolamines. Alkanolamines prolonged the hydrated induction period in the steel slag–cement system, and enhanced the second exothermic peak of hydration at dosages of 0.01%, 0.03% and 0.05%. The second hydration rate was decreased by TEA, DEIPA and MDEA, and increased by TIPA at alkanolamine dosages of 0.1% and 0.2%. The compressive strength and non-evaporable water content were enhanced by the four types of alkanolamines (dosage of 0.03%) at 3 d, 7 d and 28 d, which allowed TEA and DEIPA to contribute to strength development and the hydration reaction over TIPA and MDEA. The CH content, porosity and pore size were decreased by alkanolamines at different ages. Alkanolamines promoted the formation of ettringite and an alumina–ferric oxide–monosulfate phase, and the C–S–H morphology was also changed by different kinds of alkanolamines. [ABSTRACT FROM AUTHOR]

Although the side chain ionizability (the adsorption group density and adsorption space are changed) of polycarboxylate superplasticizer (PCE) serve as the key structural parameter in affecting the cement hydration, its effect on cement hydration is unclear. Based on PCE with nonionizable side chain (NSC-PCE) and the PCE with ionizable side chain (ISC-PCE), the influence of the side chain ionizability of PCE on the hydration behavior of cement was studied. Compared with NSC-PCE, ISC-PCE has a stronger ability to change the migration of water and ions, thus delaying the crystal nucleation and growth of cement hydration (better morphology and distribution, the crystal size was reduced by more than 20 %), increasing the crystal growth index (tendency toward spherical growth), prolonging the phase boundary reaction (reduce micro-cracks), which was conducive to the formation of more uniform and dense crystals (good strength, ISC-PCE: 50.0 MPa > NSC-PCE: 49.2 MPa > Blank: 48.7 MPa). These findings provide the design basis and theoretical guidance for the innovative development of PCE. [Display omitted] • ISC-PCE decreases the hydration rate and hydration degree of cement. • The effect of PCE on the hydration process was studied by the hydration kinetics model. • ISC-PCE has a stronger ability to change the migration of water and ions. • Proposes working mechanism in viewpoints of dissolution-precipitation equilibrium. • Tailoring the side chain ionizability was a new strategy to tune the performance of PCE. [ABSTRACT FROM AUTHOR]

In this study, the impacts of CO 2 -absorbed triethanolamine solutions (TEA-CO 2) on the mechanical property, phase composition and micro-structure of cement mortars were investigated. The results showed that TEA-CO 2 addition increased the 1d, 3d, and 28d compressive strength by 47%, 19%, and 4%, respectively, which suggests a synergistic effect of triethanolamine and absorbed CO 2 on strength development of cement mortars. The enhancement is due to TEA-CO 2 accelerates hydration of aluminate and silicate phases in early age. TEA-CO 2 facilitated CaCO 3 formation to increase cement hydration degree and modify the pore structures. However, the hydration of silicate phases was delayed slightly by TEA-CO 2 at 28d. The above results provide theoretical support for further utilization of CO 2 in cementitious materials. • Effect of TEA-CO 2 on strength development of mortars was investigated. • TEA-CO 2 addition increases flexural and compressive strength of mortars. • TEA-CO 2 accelerates the hydration of aluminate phase and silicate phase at early age. • A synergism of cement hydration and carbonation in the presence of TEA-CO 2 was proposed. [ABSTRACT FROM AUTHOR]

• The hydration of glass is heterogeneous due to phase-separation structure; • The heterogeneous hydration of glass impact the formation of calcium hydroxide; • The hydration rate advantage of calcium-rich and silicon-rich phase can be reversed; • The heterogeneous hydration is suitable for thermodynamic simulation of cement paste; Supplementary cementitious materials (SCMs) affect the hydration process and long-term properties of cementitious systems. Since a large percentage of SCMs belong to alkaline-earth aluminosilicate glasses that possess a phase-separated structure, further research into their hydration characteristics is essential. This study investigated the effects of the hydration characteristics of synthetic glasses with various phase-separated structure on the phase evolution of cementitious systems by combining simulations with experiments. The results showed that with the increasing degree of phase separation, the hydration of synthetic glass transitions from homogeneous to heterogeneous hydration. The phase evolution of hardened paste, particularly for calcium hydroxide, is influenced by the difference in hydration rates among each separated glassy phase. Compared to homogeneous hydration, the rapid hydration of the Ca-rich phase reduced the consumption of calcium hydroxide, while the rapid hydration of the Si-rich phase accelerated calcium hydroxide consumption. For glasses exhibiting phase separation characteristics, the consistency between thermodynamic simulations employing a heterogeneous hydration model and experimental results exhibits a notable enhancement. [ABSTRACT FROM AUTHOR]

• A certain dosage of DEA or TEA helps to increase the application performance of accelerator. • The complexation effect of DEA and TEA in accelerator have a significant difference. • DEA in accelerator promote the C 3 S hydration in the initial stage of hydration. • High dosage of TEA in accelerator increases the formation rate of AFt and inhibit the hydration of C 3 A and C 3 S. • Transformation of DEA-Al to DEA-Ca occurred in the cement hydration when accelerator containing DEA. In this study, diethanolamine (DEA) and triethanolamine (TEA) were used to prepare a series of liquid alkali-free accelerators to investigate the different effects of complexation of DEA and TEA in accelerators towards the initial stage of cement hydration. Two types of accelerators respectively containing DEA (dosages of 0, 6, 8, 10, 12%) and TEA (dosages of 0, 0.25, 0.5, 0.75, 1, 8%) were prepared, and after addition, the setting time of cement pastes and compressive strength of mortars were tested. The result showed that the optimum dosage of DEA and TEA in accelerators was 8% and 0.25% respectively, and the early-strength effect of TEA was stronger than that of DEA. The mechanisms of DEA and TEA in accelerators were further revealed in terms of complexation capacity, concentration of Ca2+, and hydration products and microstructure morphology of cement pastes. DEA and TEA complexed with Al3+ in accelerators and promoted the formation of ettringite (AFt) in cement pastes, and the complexation capacity of TEA to Al3+ was stronger than that of DEA, causing that high dosage of TEA in accelerator promoted the formation of AFt more than DEA and covered at the surfaces of C 3 A and C 3 S, which inhibited the hydration. DEA in accelerator could promote the hydration of C 3 S in the initial stage due to the transformation of complex DEA-Al to DEA-Ca. This study aims to interpret the different influences of complexation effects of DEA and TEA in accelerators on the properties of cement-based materials and their working mechanisms. [ABSTRACT FROM AUTHOR]

Effects of disodium EDTA (EDTA-2Na) on hydration and mechanical properties of calcium sulphoaluminate-belite cement (CSBC) were investigated systematically. Results show that EDTA-2Na addition leads to visible changes in CSBC strength development. 0.50 % EDTA-2Na significantly enhances the compressive strength by 18 % and 23 % compared with the blank specimens at 7 d and 28 d, while reducing the strength at 8 h and 1 d. The content of the main hydration product (AFt) determines the strength development. At the early hydration stage, EDTA-2Na delays hydration of ye'elimite to form AFt, thus decreasing the early hydration degree of CSBC and increasing the porosity to reduce strength. In the presence of EDTA-2Na, the morphology changes of amorphous aluminum hydroxide (AH 3) facilitate the AH 3 -C 2 S-CaSO 4 reaction to increase AFt content and form a more condensed structure, thus enhancing the late strength. In this way, the strength development of CSBC mortars can be modified and regulated by EDTA-2Na. [ABSTRACT FROM AUTHOR]

[Display omitted] • EDIPA greatly improves compressive strength and shortens setting time of SS paste. • Chelation of EDIPA promotes the formation of monocarboaluminate (C(A,F) C ¯ H) • The chelating ability of EDIPA to Al3+ and Fe3+ is stronger than that of Ca2+. • The chelation of EDIPA changes the crystal structure and morphology of Ca(OH) 2. The low cementitious activity of steel slag (SS) limits its application in cement-based materials. The effects of ethanol-diisopropanolamine (EDIPA) on the hydration and mechanical properties of pure basic oxygen furnace SS were investigated. The hydration kinetics and pore structure of SS pastes incorporated with EDIPA and the chelation of EDIPA were analyzed to reveal the working mechanism of EDIPA. The results show that EDIPA improves the compressive strength of the hardened SS paste and greatly shortens the setting time of SS paste, which is related to the chelation of EDIPA. EDIPA could chelate with Ca2+, Al3+, and Fe3+ to form metal chelates, and the chelating ability of EDIPA to Al3+ and Fe3+ is stronger than that of Ca2+. The chelation of EDIPA simultaneously promotes the hydration and carbonation of aluminate and ferrite phases (C 3 A, C 12 A 7 , and C 2 F), resulting in a large amount of monocarboaluminate (C(A,F) C ¯ H), thus improves the hydration degree of SS paste. EDIPA could refine the pore structure of hardened SS paste, which is mainly manifested as the decrease in the amount of macropores and pore size, and the increase in the amount of small pores. The chelation of EDIPA changes the crystal structure and morphology of Ca(OH) 2 , which is potentially helpful to weaken the negative effect of Ca(OH) 2 on strength. This study reveals the effect of chelation of EDIPA on the hydration of SS, which is a valuable guide for the resource utilization of SS. [ABSTRACT FROM AUTHOR]

This work aims to investigate the solubilizing ability of alkanolamines on steel slag (SS) and the chelating ability of alkanolamines with metal ions. In this paper, the chelation effect of four alkanolamines, including triethanolamine (TEA), triisopropanolamine (TIPA), diethanol-isopropanolamine (DEIPA), and methyl diethanolamine (MDEA), and metal ions on the dissolution of SS was investigated. The conductivity meter, pH meter, X-ray powder diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), total organic carbon (TOC) and isothermal calorimetry were used to investigate the solubilizing ability of SS impacted by alkanolamines. Additionally, the conductivity meter and chemical precipitation method (CPM) were used to investigate and explore the chelating ability of alkanolamines interacting with the metal ions. Finally, the nuclear magnetic resonance hydrogen (1HNMR) spectroscopy was adopted to investigate the chelating mechanism between alkanolamines and metal ions. The results showed that the alkanolamines increased the elemental concentrations of [Ca], [Al], [Fe] and [Si] in the liquid phase of SS through chelating and promoted the dissolution of the mineral phase of C 3 S, C 2 S and C 4 AF in SS. Among the different alkanolamines, DEIPA was present in the liquid phase for the longest time and possessed a more sustained ability to chelating metal ions. The result also shows that alkanolamines can chelate the Ca2+, Al3+ and Fe3+ in solution. The chelating ability of tertiary alkanolamines were stronger than the secondary alkanolamine. And the alkanolamine with asymmetric molecular structure have stronger chelating ability than those with symmetric molecular structure. Tertiary alkanolamines form ternary five-ring structure with metal ion through nitrogen and oxygen atoms. • Alkanolamines promoted the dissolution of the mineral phase in steel slag. • DEIPA possessed a more sustained ability to chelating metal ions. • Alkanolamine with asymmetric molecular structure have stronger chelating ability. • Ternary five-ring structure formed between the ternary alkanolamine and metal ion. [ABSTRACT FROM AUTHOR]