Early Hydration Behavior Research Articles

Enhancing strength of cement using aluminium sulfate accelerator with aluminium formate

An alkali-free liquid accelerator was prepared with aluminium sulfate and aluminium formate as the main components. The effects of the accelerator on the setting of paste and the mechanical strength of mortar were studied, and the impact of the accelerator on the early hydration behaviour and hydration products of the paste were investigated by isothermal calorimeter analysis, X-ray diffraction analysis, scanning electron microscopy and thermogravimetric analysis. The results show that the accelerator is excellent for the rapid setting and hardening of the cement. When the content of the accelerator was 8 wt%, the initial setting time and final setting time of the paste were 85 s and 180 s, respectively, and the strengths of the mortar at 1 day and 28 days were 9.52 MPa and 44.42 MPa, respectively. The proposed accelerator can accelerate the dissolution and hydration of tricalcium aluminate and tricalcium silicate and promote the formation of ettringite, formate and portlandite.

Early age hydration behaviour of foam concrete containing a coal mining waste: novel experimental procedures and effects of capillary pressure

Globally, coal mining wastes (CMWs) are associated with significant environmental and economic costs. Processing CMW into an ingredient of foam concrete is a promising solution but the behaviour of this particular construction material has not been sufficiently evaluated, especially during the initial period of cement hydration. The purpose of this paper is to present novel laboratory set-up and experimental procedures designed to investigate the early age behaviour of hydrating foam concrete samples made with a CMW from Poland. Two types of tests were devised to simulate air-curing conditions and water-curing conditions, respectively. These tests were carried out in custom-built unsaturated oedometer cells, and the matric suction in the test samples was monitored for approximately 14 days, using Warwick high capacity tensiometers. Experimental results show that in both curing conditions, a higher matric suction during cement hydration corresponds to a denser sample at the end of the monitoring period. A comparison of water-cured and air-cured samples also reveals different responses to CMW inclusion in their mix designs. The responses can be convincingly explained based on complementary test data and idealised capillary tube models adapted for the hydrating foam concrete samples.

Luminescent Properties of (Ca7ZrAl6O18-Ca3Al2O6-CaZrO3):Eu3+ Composite Ceramics and Tracing in the Hydration Process

In this work, solid-state reaction sintering was used to fabricate Ca7ZrAl6O18-Ca3Al2O6-CaZrO3:Eu3+ ternary composite ceramics and cements. The structural, microstructural, and spectroscopic properties of the ceramics with different Eu2O3 content were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and spectrofluorimetry, respectively. The XRD patterns analyzed with Rietveld refinement confirm the presence of the orthorhombic phase of Ca7ZrAl6O18 and the cubic phase of Ca3Al2O6 in all the samples, indicating that doping of Eu3+ slightly changes the crystalline structure of both aluminate phosphors. EDS analysis revealed that the Eu doping element was strongly concentrated to the two phases, i.e., Ca7ZrAl6O18 and Ca3Al2O6, with the Eu concentrations of 8.45 wt.% and 8.26 wt.%, respectively. The luminescent properties of the ceramics doped with different Eu3+ ion concentrations were investigated by excitation and emission spectroscopy at room temperature. These results were compiled using a laser with an optical parametric oscillator (OPO) system. The obtained spectra indicated changes in the luminescence intensity and shape occurring with phase composition and Eu2O3 concentration. The emission spectra of the ceramics exhibit a strong dependence on the excitation wavelength in the range from 210 to 300 nm, and invariably, five peaks were assigned to the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+. The luminescence spectroscopy was then used to trace the early and long-term hydration behavior of cements. Thus, luminescence spectroscopy may provide a new tool for non-destructive testing of cement-based structures.

Comprehensive analysis of early-stage hydration and microstructure evolution in Sufflaminate cement: Insights from low-field NMR and isothermal calorimetry

This study presented a comprehensive investigation of the early hydration reaction and microstructure evolution of sulfoaluminate cement (SAC) using low-field nuclear magnetic resonance (LF-NMR) and isothermal calorimetry (IC). LF-NMR, combined with total relaxation signal and transverse relaxation time (T2), was employed to characterize the evolution of evaporation water (EW) and the degree of hydration (αlf) during the initial stage of SAC hydration. The hydration process was divided into four phases. The relative content of different EW types within the paste was investigated, and the pore structure and specific surface area evolution of SAC paste were studied based on the T2. The heat release of hydration of SAC was measured using IC, and the hydration kinetics was fitted with the JMAK model. The results demonstrated that the early hydration reaction of SAC was a multidimensional controlled process influenced by various factors. Also, the crystallization nucleation rate of hydration products was inversely related to w/c. Furthermore, a successful nonlinear fitting between the weighted average of T2 and the hydration degree (αt) obtained from IC was established, providing a standard reference curve for studying hydration degree and microstructure. Finally, the hydration products and microstructure were investigated using, SEM, and TG, and the evolution of the compressive strength of SAC was also analyzed. This work gave valuable insights into SAC's early hydration behavior and microstructural development, which can contribute to a better understanding of its performance and potential applications.

Study on Early Hydration Mechanism of Double-Liquid Grouting Material Modified by Composite Early Strength Agent.

To achieve an adjustable setting time and significantly improved early strength of a new type of sulphoaluminate cement-based double-liquid grouting material (SACDL), the effects of calcium formate, sodium sulfate, lithium carbonate, and a composite early strength agent on the setting hardening and early hydration behavior of SACDL paste were studied by means of setting time, fluidity, compressive strength, and viscosity tests. The results showed that the adsorption and osmosis of calcium formate, the complex decomposition of sodium sulfate, the precipitation polarization of lithium carbonate and the synergistic action of the composite early strength agent could accelerate the early hydration rate of SACDL, shorten the coagulation time, and improve the early strength of SACDL. The composite effect of 0.8% calcium formate and 0.5% sodium sulfate is the most significant in promoting coagulation and early strength; the initial setting time and final setting time of the slurry were shortened to 5 min and 10 min, respectively; and the 3 h compressive strength was capable of reaching 16.7 MPa, 31% higher than that of the blank group. In addition, X-ray diffraction and SEM morphology observation were used to study the composition of the hydration products and the evolution of the microstructure, which revealed the early hydration mechanism of SACDL under the synergistic effect of the composite early strength agent: (1) The solubility of tricalcium aluminate (C3A) and dihydrate gypsum (CaSO4·2H2O) increased under the low content composite early strength agent condition, which increased the ettringite (AFt) formation rate. HCOO- was able to penetrate the hydration layers of tricalcium silicate (C3S) and dicalcium silicate (C2S), accelerating the dissolution of C3S and C2S and promoting the early hydration of SACDL. (2) Under the condition of a high dosage of the composite early strength agent, the further increase in Ca2+ concentration promoted the crystallization nodules and precipitation of CH and accelerated the formation of calcium silicate hydrate (C-S-H) gel. C-S-H was filled between a large number of rod-like AFt crystals, thus making the structure more dense.

Effect of acid-activator characteristics on the early hydration behavior and properties of metakaolin-based geopolymer

Effect of acid-activator characteristics on the early hydration behavior and properties of metakaolin-based geopolymer

Effect of seed emulsion on the early hydration behavior of basic magnesium sulfate cement

Basic magnesium sulphate cement (BMSC) has been known as a lightweight and high strength magnesium-based cementitious material. However, the addition of admixtures (e.g. citric acid) significantly retards the early hydration process of cement, which is not conducive to its actual utilization in construction. In this work, BMSC and fly ash (FA, 50 wt%)-BMSC with extremely high early strength were prepared by addition of the seed emulsion (SE) of BMSC obtained by wet grinding. Meanwhile, the influence of SE on the early hydration behavior of BMSC was investigated and the corresponding hydration mechanism was proposed as well. The results demonstrated that wet grinding can effectively reduce the particle size of crystal seeds and increase their specific surface area. The crystal seeds were emulsified after 3 h of wet grinding, with a particle size of 2–6 μm and a specific surface area of 14.36 m2/g. The SE could provide crystal nuclei to directly induce the generation of 5·1·7 phase, which could significantly accelerate the early hydration process at low temperature (15 °C). The 12 h-strength of BMSC was reached to 33 MPa with a sharply shorten initial setting time of 48 min when adding 6% SE. Moreover, the mechanical properties of FA-BMSC with addition of SE were improved by 30% since FA particles can be tightly encapsulated in the reticulated whisker structures of 5⋅1⋅7 phase. This work provides a theoretical and technical support to better understand and properly use of SE in the production of BMSC.

Early age hydration behavior of portland cement-based binders incorporating fly ash contaminated with flue gas desulfurization products

Fly ash co-mingled with flue gas desulfurization (FGD) products are currently discarded as off-specification materials based on their high SO3 content. However, previous studies have shown that performance of these fly ashes varies significantly based on FGD product type and as such they may be viable for use in low-CO2 concrete as supplementary cementitious materials (SCMs). In this study, fly ashes with three different types of FGD products including calcium sulfite hemihydrate, calcium sulfate (with some unreacted lime), and sodium sulfate (with some unreacted sodium carbonate) were evaluated. The early age hydration behavior in blended cementitious systems at 20% cement replacement level was studied using Vicat setting time tests, isothermal calorimetry, in-situ quantitative X-ray diffraction, and pore solution analysis. The cause of the setting time retardation and flash setting observed in fly ashes with calcium sulfite hemihydrate and sodium carbonate, respectively, were identified and suitable beneficiation options were suggested for the valorized use of these materials in low-CO2 concrete.

Ultrasound Non-Destructive Characterization of Early Hydration of Cement Pastes: The Effects of Water-Cement Ratio and Curing Temperature

A newly developed ultrasound method that acquires at the same time both reflected and transmitted P-waves, at different angles, using two immersion transducers of 0.5 MHz central frequency, is described in this present study. This non-destructive method allows calculating the longitudinal and transverse velocities, and thus, the Young modulus, so that its evolutions is followed in time domain. The closely correlation between the evolution in time domain of those calculated parameters and hydration properties of cement based materials was used to characterize the effects of different water-cement ratio and curing temperatures on early age hydration behaviour of cement pastes. To do so, cement samples were prepared by mixing Portland cement and freshwater. Results indicates that lower water to cement ratio reduces the workability and increases the Young modulus of resulted cement medium. Also, both ultrasound velocities and Young modulus values increases linearly with increasing curing temperature.

On the early hydration of cubic ye’elimite: New insights from time-resolved in situ MAS NMR spectroscopy

Two polymorphs of ye’elimite are known to exist in calcium sulfoaluminate cements, namely, orthorhombic (iron free), C4A3$ and cubic/pseudo-cubic (iron incorporated), C4A3-xFx$ forms. The very early hydration behaviour of cubic ye’elimite (nominal composition: Ca3.8Na0.2Al5.6Fe0.2Si0.2O12SO4) has been investigated using a time-resolved in situ multi-nuclear (1H, 27Al, 23Na and 29Si) MAS NMR spectroscopic approach. The study shows that the reaction pathway and the intermediate species formed are substantially different from those that are observed during the hydration of orthorhombic ye’elimite, and the rate as well as the nature of hydration products are dictated by the presence or the absence of limestone (CaCO3). Furthermore, the detection of diverse transient species as well as the uncovering of different kinetic behaviour during the early hydration of cubic ye’elimite illustrate the advantages of time-resolved in situ MAS NMR experimental approach for fingerprinting hydrated phases.

Study on early hydration and properties of basic magnesium sulfate cement using electrodeless resistivity measurements

The effect of early hydration behaviour on the long-term performance of cement is profound, but such studies are lacking. The early hydration behaviour and mechanical properties of basic magnesium sulfate (BMS) cement were investigated using an electrodeless resistivity test combined with compressive strength measurement, X-ray diffraction analysis, scanning electron microscopy and mercury intrusion porosimetry. According to the resistivity variation curve, the early hydration process of BMS cement can be divided into three stages (induction period, acceleration period and deceleration period). A linear correlation between resistivity and setting time was established. The initial and final setting times of BMS cement could thus be estimated using two points on the differential resistivity curve – the time when the resistivity growth rate starts to increase and the time of maximum resistivity, respectively. A linear fitting equation between resistivity at 24 h and compressive strength of the BMS cement after curing for 28 days was determined. The correlation coefficient was high (0.9979). Using the equation, the long-term strength (28 days) of BMS cement could be precisely predicted from the measured resistivity at 24 h. This study provides a feasible, accurate and in situ method for understanding the early hydration behaviour and quality monitoring of BMS cement.

The Influence of Alkali-Free Shotcrete Accelerators on Early Age Hydration and Property Development within Cement Systems.

Fluoride-containing alkali-free setting accelerators are a common type of admixture used in tunnel shotcrete but few studies in the literature focus on the effect of their fluoride compounds on the setting and hardening properties of accelerated cement paste under low environment temperatures. Tunnel shotcrete in cold regions or winter construction periods would be obviously influenced by low environment temperatures, especially for its fast setting and quick support applications. The objective of this work is to evaluate the early age hydration behavior of different accelerated cement pastes under 20 °C and 5 °C environment temperatures. In this study, setting time measurement, early age strength development, hydration ion leaching concentration, isothermal calorimetry, X-ray diffraction, and ESEM were performed on cement systems prepared with a non-fluoride alkali-free accelerator (aluminum sulfate solution with over 60% solid content) and a designed fluoride-containing alkali-free setting accelerator (aluminum sulfate and fluoride compound). The results showed that the fluorides obtained in alkali-free accelerators promote C3S dissolution and massive ettringite needles together with monosulfoaluminate (AFm) hydrate formation, thus leading to a quicker setting effect and low sensitivity to low environment temperatures than in non- fluoride groups. However, the rate of mechanical strength development of cement pastes hydrated within 24 h was decreased obviously when fluorine-containing alkali-free accelerator was used. This phenomenon is mainly related to the crystallization of thin-plate shape calcium fluoride (CaF2) formations and promoted conversion of ettringite to monosulfoaluminate hydrate in the accelerating period, thus weakening the denseness of C-S-H gel and inhibiting alite further hydration.

Effects of Limestone Powder on the Early Hydration Behavior of Ye'elimite: Experimental Research and Thermodynamic Modelling.

To investigate the effects of limestone powder and gypsum on the early hydration of ye’elimite, the hydration behavior of C4A3-LP-CaSO4·2H2O-H2O systems are researched. The hydration behavior of systems are researched by employing isothermal calorimetry, XRD technique and chemical shrinkage. The thermodynamic modelling method is employed to predict the equilibrium phase assemblages. The results show that the system with 5 wt.% LP has a comparable hydration heat evolution to limestone powder-free systems. Limestone powder can take part in the reaction to produce monocarboaluminate in the system with M-value (molar ratio of gypsum to ye’elimite) of 1, but monocarboaluminate is not found in the system with M-value of 2. The level off time of chemical shrinkage shortens with the increase of limestone powder dosage. Thermodynamic modelling results show that monocarboaluminate is no longer formed in all systems when M-value exceeds 1.27, which corresponds to the XRD results. This study can provide theoretical guidance for the rational utilization of limestone powder in calcium sulphoaluminate cement.

Influence of liquid accelerator based on sodium aluminate on the early hydration of cement, C3A and C3S pastes

The objective of this study was to explore the influence of an alkali liquid accelerator based on sodium aluminate (ASa) on the early hydration behaviour of cement paste, tricalcium aluminate (C3A) and tricalcium silicate (C3S) and identify its accelerating mechanism. The setting times and mechanical properties of cement paste and mortar mixed with different amounts of ASa were determined. Isothermal calorimetry showed that the addition of ASa increased the first exothermic peak of cement hydration and advanced the second exothermic peak. The morphology of hydration products was analysed by scanning electron microscopy (SEM) and a model for the early hydration of cement paste was established. X-ray diffraction and SEM were also used to analyse the phase composition and morphology changes of C3A and C3S with or without ASa and early hydration models were established. Analysis of the experimental results revealed that the sodium hydroxide produced by ASa hydrolysis had the function of consuming gypsum, breaking calcium silicate hydrate gel film and increasing the calcium hydroxide concentration in the cement paste. The ettringite in the hydration products interweaved together to form a skeleton structure, which was conducive to cement paste hardening.

Particle characteristics of calcined clays and limestone and their impact on early hydration and sulfate demand of blended cement

Supplementary cementitious materials (SCMs) can alter significantly the early hydration behavior of blended cement. While the underlying mechanisms have been intensively discussed in literature, they need to be extended regarding SCMs with complex mineralogy and surface properties, such as calcined clays. In this study, a blended Portland limestone cement was monitored during the first 48 h of hydration using in situ X-ray diffraction and isothermal calorimetry. The influence of a fine limestone and four different calcined clays, which vary in mineralogical composition and particle properties, was investigated at a replacement level of 30 wt%. The sulfate content was gradually adjusted and its influence on heat evolution and phase development was examined. It was shown, that depending on their particle properties, the investigated SCMs influence the aluminate and silicate clinker reaction by different mechanisms and to varying extents. The results underline the importance of proper sulfation of blended cements.

Early hydration behavior of novel amphoteric polymer in cement paste

The development of the early strength of the concrete mainly depends on the early hydration process of the cement, and there are many factors influencing the early hydration process of the cement. It is of great significance to study the mechanism of the polymer on the cement hydration for the development of the product. The amphoteric polymer was synthesized by (2-propenyloxyethyl) trimethyl ammonium chloride, acrylic acid and isopentene polyoxyethylene ether with different molar ratio. The chemical structure of polymer was characterized by GPC, and the performance of cement with polymers was observed by isothermal calorimetry and compressive strength of mortar. The results showed that the new amphoteric polymer has a strong promoting effect on the early hydration of cement. With the increase of the amount of (2-propenyloxyethyl) trimethyl ammonium chloride, the hydration speed is faster, but the addition of amphoteric polymer results in the decrease of fluidity of cement paste, so it is necessary to control its amount reasonably.

Early hydration of blast furnace slag in the presence of sodium chromate

Blast furnace slag (BFS) is a potential candidate for the immobilization of chromium-bearing wastes. This paper investigated the effect of soluble hexavalent chromium (Na2CrO4) on the early hydration behavior of BFS by means of isothermal calorimetry, X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM) and pH measurement of pore solution. Meanwhile, the compressive strength of BFS pastes in the presence of different dosage of chromate was tested for the structural study. The primary aim was to verify the alkaline activation of Na2CrO4 on the BFS. It was found that the BFS in water had scarcely hydrated in the first 7 days, whereas the addition of Na2CrO4 greatly accelerated the hydration of BFS and promoted the hardening. Increasing the Na2CrO4 dosage could significantly improve the compressive strength, which was sufficient to meet the requirement for immobilization of wastes. The hydration products of BFS in Na2CrO4 solutions were mainly C-(A)-S-H and CrO4-U phase. The CrO4-U phase played a key role in Cr(VI) binding due to its layered structure. During the formation of CrO4-U phase, a large number of alkalis was released, which largely increased the pH of pore solution, thus greatly promoting the BFS hydration. The results indicated that the Na2CrO4 had a strong alkaline activation on blast furnace slag.

Fingerprinting the Hydration Products of Hydraulic Binders Using Snapshots from Time-Resolved In Situ Multinuclear MAS NMR Spectroscopy

The very early hydration behavior of a hydraulic binder phase, ye’elimite, Ca4Al6O12SO4, in the absence and in the presence of calcium sulfate, has been investigated. A time-resolved in situ multinuclear magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic suite involving 1H and 27Al MAS as well as two-dimensional 27Al multiple quantum MAS (MQMAS) experiments has been employed to detect the transient species and to govern the sequence of hydration reactions and the subsequent formation of the hydration products. The results of the study show that the rates of formation of ye’elimite hydration products vary substantially according to the absence or the presence of calcium sulfate. Hydrated calcium sulfoaluminate phases such as ettringite and monosulfate as well as aluminum hydroxide gel have been detected during the various stages of hydration. The direct observation of various transient species during the hydration stages of calcium aluminates and calcium sulfoaluminates illustrates the potential of a newly designed time-resolved in situ 1H MAS NMR experimental approach for fingerprinting phases and offers significant advantages over other established techniques in detecting transient species.

Effect of iron on the preparation of iron-rich calcium sulfoatablluminate cement using gypsum as the sole calcium oxide source and its incorporation into mineral phases

Iron-rich calcium sulfoaluminate (IR-CSA) cement is a low-carbon cement that contains small amount of aluminum. In this study, IR-CSA cement preparation method using gypsum as the source of calcium oxide was developed. The effects of iron on the decomposition of gypsum, formation of phases, microstructure of the clinker, and hydration of cement paste were investigated. The results indicated that the decomposition of gypsum and the formation of the target phase were first slightly promoted and then hindered when the iron content in the raw material increased. The presence of iron enhanced the growth of crystal grains and densification of the microstructure in the clinker. The early hydration behavior of IR-CSA cement mainly depended on the hydration of the iron-bearing ye’elimite and ferrous phases. Furthermore, the incorporation of iron into mineral phases was studied. The maximum incorporation content of Fe2O3 in ye’elimite and belite phase reached 19.36 wt%, expressed as C4A2.61F0.39S-, and 2.83 wt%, respectively. The chemical composition of the ferrous phase was similar to that of C4AF, and its mineral phases were C2F, C6AF2, C4AF, and C6A2F from the center to the edge. Finally, the feasibility of preparing IR-CSA cement using phosphogypsum as the sole calcium oxide source was evaluated for engineering applications. This unique preparation method reduces the use of aluminum in raw materials and thus promotes recycling of iron-containing or low-aluminum-containing industrial solid waste materials.

Preparation and Performance of a Fluorine-Free and Alkali-Free Liquid Accelerator for Shotcrete

Based on aluminum sulfate, a fluorine-free and alkali-free liquid accelerator (FF-AF-A) was prepared in this study. The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully investigated. The compatibility of the FF-AF-A with the superplasticizers were also investigated, and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat, X-ray diffractometry (XRD), and scanning electron microscopy (SEM). Test results indicated that adding the FF-AF-A at 8 wt% of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting time. The 1-day compressive strength of the cement mortar with 8 wt% of FF-AF-A reached 13.5 MPa, which represents an increase of 35% as compared to the strength of cement mortar without the FF-AF-A, and the 28-day compressive strength ratio was 119%. In addition, the FF-AF-A also showed good compatibility with different superplasticizer dosages. The results show that, when the FF-AF-A was added to the cement paste, it promoted the formation of ettringite crystals due to the aluminum ions (Al3+) and sulfate ions (SO4 2-) reacted with gypsum in the cement, as well as promoted the hydration of tricalcium aluminate (C3A) and tricalcium silicate (C3S) leading to the overall structure becomes more compact. As a consequence, the hydration heat rate of the cement sharply increased, the cement paste setting time is shortened, and the compressive strength of cement mortar is improved.