Hydration Of Alite Research Articles

Investigation of alite hydration in the presence of low- and high-silica zeolites

Synthetic zeolites that are obtained from the hydrothermal reaction of NaOH with fly ash have a well-defined pore structure and pozzolanic properties. This work examines the effect of the low-silica (Na-A) and high-silica (ZSM-5) zeolite structure on the kinetics of alite hydration and mineralogical characteristics of the reaction products. The addition of the Na-A and ZSM-5 zeolites reduced the rate of heat release during the hydration reaction, which is typical for commonly used pozzolanic additives. The ZSM-5 zeolite had a much higher Si/Al ratio relative to the Na-A zeolite, which translated into a higher pozzolanic activity and resulted in greater stability of the hydration reaction kinetics. The addition of zeolites caused the heat of hydration to decrease compared to the reference pastes (the alite reference paste—206 J/g): Na-A 15%—148.9 J/g; ZSM-5 15%—149.9 J/g. The concentration of calcium ions in the alite solution and the content of active silica were identified as the most important parameters affecting the kinetic, morphological, and structural characteristics of the C–S–H phase. The addition of zeolites increased the amount of C–S–H gel phases formed. At the same time, the proportion of portlandite in the hydration products of the alite–zeolite systems decreased. Pozzolans reduced the ratio of CaO/SiO2 in the C–S–H phase, which for pastes with the addition of the Na-A ranged from 1.61 to 1.37, and for the ZSM-5 from 1.91 to 0.47. This ratio decreased with the dosage and the age of alite paste. In summary, this research has shown that synthetic zeolites are a viable pozzolanic additives.

Mix and measure II: joint high-energy laboratory powder diffraction and microtomography for cement hydration studies.

Portland cements (PCs) and cement blends are multiphase materials of different fineness, and quantitatively analysing their hydration pathways is very challenging. The dissolution (hydration) of the initial crystalline and amorphous phases must be determined, as well as the formation of labile (such as ettringite), reactive (such as portlandite) and amorphous (such as calcium silicate hydrate gel) components. The microstructural changes with hydration time must also be mapped out. To address this robustly and accurately, an innovative approach is being developed based on in situ measurements of pastes without any sample conditioning. Data are sequentially acquired by Mo Kα1 laboratory X-ray powder diffraction (LXRPD) and microtomography (µCT), where the same volume is scanned with time to reduce variability. Wide capillaries (2 mm in diameter) are key to avoid artefacts, e.g. self-desiccation, and to have excellent particle averaging. This methodology is tested in three cement paste samples: (i) a commercial PC 52.5 R, (ii) a blend of 80 wt% of this PC and 20 wt% quartz, to simulate an addition of supplementary cementitious materials, and (iii) a blend of 80 wt% PC and 20 wt% limestone, to simulate a limestone Portland cement. LXRPD data are acquired at 3 h and 1, 3, 7 and 28 days, and µCT data are collected at 12 h and 1, 3, 7 and 28 days. Later age data can also be easily acquired. In this methodology, the amounts of the crystalline phases are directly obtained from Rietveld analysis and the amorphous phase contents are obtained from mass-balance calculations. From the µCT study, and within the attained spatial resolution, three components (porosity, hydrated products and unhydrated cement particles) are determined. The analyses quantitatively demonstrate the filler effect of quartz and limestone in the hydration of alite and the calcium aluminate phases. Further hydration details are discussed.

Clinkering and hydration of alite-belite-ye'elimite cement with increasing ye'elimite percentage

Alite-belite-ye'elimite (ABY) cement is considered to be eco-cements with adequate mechanical properties and fewer CO2 emissions. The phase assemblage and ye’elimite content of ABY cement play a very important role in cement properties. In this study, ABY clinkers with increasing ye'elimite percentage (0.3 wt%-36.4 wt%) were prepared at 1300 °C and the phase composition was characterized by Rietveld Quantitative Phase Analysis combined with energy dispersive X-ray spectrometry. The ye'elimite formed with a calculated composition of Ca3.92Mg0.02Al2.81Fe0.05Si0.04S1.16, incorporating additional sulfur compared to the theoretical value. In addition, the hydration properties of heat evolution, hydration products and compressive strength of ABY cement are studied. The result shows that the increase of ye'elimite content leads to a more intense initial heat release and a higher cumulative heat release. The presence of ye'elimite inhibits the hydration of alite at early ages. ABY mortars with increasing ye'elimite (15.8 wt%) exhibited a higher strength (29.6 MPa) at 3 days by the contribution of ye'elimite hydration, and an increase (47.4 MPa) at 28 days. An adequate proportion of ye'elimite (<15 wt%) is favorable to the performance of ABY cement, and releases 12% less CO2.

Effects of early hydration of alite and belite phases on subsequent accelerated carbonation

To better understand the early hydration impact of cement phases on subsequent accelerated carbonation, this study mixed alite (C3S) and belite (β-C2S) with 40 wt% of water for 2, 4, 8, 18 h hydration before exposing to 2 h accelerated carbonation. The results indicated that early hydration exerted a significant impact on C3S (particularly 4–8 h), which accelerated the subsequent carbonation degree (CD) with maximum of 57.27%. Over 8 h, however, packed hydrates impeded CO2 ingress, leading to a decelerated CD and co-existence of different calcium carbonate polymorphs: calcite (dominant for short hydration), aragonite and vaterite (dominant for long hydration). Differently, β-C2S samples with marginal hydrates continuously accelerated CD with time (32.23% after 18 h), and indicated a direct β-C2S carbonation. Detection of calcite and vaterite in carbonated β-C2S samples revealed that carbonates polymorphs varied with calcium silicate and their resulting hydrates participation. This study provides a viable strategy for CO2 storage and microstructure densification, distinct from conventional cement carbonation regime.

Sulfate consumption during the hydration of Alite and its influence by SCMs

AbstractSCMs with a large specific surface area, such as calcined clays or fine limestone powder, can significantly accelerate the occurrence of the aluminate heat flow peak during the early hydration of blended cements. These systems therefore require a higher amount of sulfate. While this effect has been drawn back to the sulfate incorporation into C‐S‐H, which is formed more rapidly due to the filler effect, it has been recently shown that in systems with high amounts of metakaolin, the sulfate balance is influenced by further mechanisms. This study provides new results on the influence of aluminum‐rich and aluminum‐free SCMs on the early hydration of alite in presence of calcium sulfate. A synthesized alite was blended with 5 wt% of anhydrite and its hydration was investigated by isothermal calorimetry and in‐situ XRD at a w/b ratio of 0.5. It was shown that the formed C‐S‐H is able to take up the calcium and sulfate ions, indicated by a depletion of the solid anhydrite after approximately 20 hours. This process is significantly accelerated by incorporating 30 wt% of a fine limestone filler. The addition of metakaolin leads to an acceleration of the alite hydration compared to the reference as well, but to a significantly lower extend compared to the limestone. However, this system requires a lower degree of alite reaction to reach sulfate depletion. This indicates that in metakaolin‐rich systems, the sulfate demand is influenced by further effects. The results from in‐situ‐XRD reveal that significant ettringite formation is taking place in the metakaolin‐blended system already during the first hours of hydration. Correlations between the degree of alite hydration and the rate of sulfate depletion provide new insights into the mechanisms affecting the sulfate balance and early hydration of blended cements.

Reaction kinetics during early hydration of calcined phyllosilicates in model cement systems

Model cement systems form the basis for investigating the influence and behavior of three calcined phyllosilicates during early hydration. Metamuscovite acts as pure filler, accelerates alite hydration and leads to an increased degree of hydration of alite compared to the reference. A different picture emerges for metaillite and metakaolinite. They influence in addition the alite hydration which reaches at the onset of the aluminate clinker reaction as well as after 2 days of hydration significantly lower degrees of hydration. This indicates interaction of the negatively charged calcined clay surfaces with the sulfate from the pore solution. Chemical reactivity of the metaillite and metakaolinite during early hydration can be demonstrated by direct quantification as well as determination of portlandite consumption and C-S-H formation. This leads to a better understanding of the effect of individual calcined phyllosilicates and help to predict the influence of complex calcined clays on early hydration.

Alite hydration at the single grain level

Understanding cement hydration processes is crucial for achieving the desired properties in concrete. However, the nanoscale mechanism whereby calcium silicate hydrate (C–S–H) transforms, particularly regarding morphology, structure, and composition evolution, remains unclear. Here, we employed multimodal transmission electron microscopy (TEM) to investigate the hydration kinetics of alite at the single grain level, extracting comprehensive chemical and structural information. Our findings reveal that rapid nucleation of C–S–H occurs at the boundaries within minutes, followed by subsequent C–S–H growth. The development of C–S–H fibrils can be categorized into two distinct stages: needle elongation and texture densification. Through quantitative analysis, we estimated the growth rate of C–S–H needles to be 7 nm/min, while observing a decrease in the intrinsic porosity of C–S–H from 7.9% to 3.1% concurrent with the thickening of C–S–H lamella. Electron diffraction analysis further demonstrates the homogenization of C–S–H throughout hydration, involving structural compaction and silicate polymerization. Our work provides valuable insights into the origins of C–S–H nucleation and growth, thereby enhancing our understanding of hydration mechanisms at a fundamental level.

Understanding the longer-term effects of C–S–H seeding materials on the performance of limestone calcined clay cement

The application of C–S–H seeding offers great potential for improving the early age strength of cement. However, the fundamental understanding of longer-term effects of C–S–H seeding on the properties of cementitious materials is still limited, partly due to the complex composition of C–S–H seeding materials. This paper studied the effects of purified C–S–H seeding and impurities separated from synthesized C–S–H seeding suspensions on the hydration and strength of limestone calcined clay cement (LC3) over a period of 90 days. The results showed that compared to reference, the addition of purified C–S–H seeding leads to an average increment of 16.5% in the compressive strength of LC3 at the first 7 days and does not significantly affect the strength development afterwards, while the presence of impurities can cause a 5.7% decrease in compressive strength at 90 days. The reason for this later-age discrepancy was attributed to the lower degree of hydration of alite and less reaction of metakaolin in the system with impurities compared to the system without impurities. The findings offer a new perspective to better understand the longer-term effects of C–S–H seeding materials on the performance of cementitious materials.

Recent Advances in C-S-H Nucleation Seeding for Improving Cement Performances.

Reducing cement CO2 footprint is a societal need. This is being achieved mainly by replacing an increasing amount of Portland clinker by supplementary cementitious materials. However, this comes at a price: lower mechanical strengths at early ages due to slow pozzolanic reaction(s). This is being addressed by using accelerator admixtures. In this context, calcium silicate hydrate nucleation seeding seems to have a promising future, as it can accelerate cement and pozzolanic reactions at early ages, optimising their microstructures, without compromising late strength and durability performances. In fact, these features could even be improved. Moreover, other uses are low temperature concreting, precasting, shotconcrete, etc. Here, we focus on reviewing recent reports on calcium silicate hydrate seeding using commercially available admixtures. Current knowledge on the consequences of nucleation seeding on hydration reactions and on early and late mechanical strengths is discussed. It is noted that other features, in addition to the classic alite hydration acceleration, are covered here including the enhanced ettringite precipitation and the very efficient porosity refinement, which take place in the seeded binders. Finally, because the seeded binders seem to be denser, durability properties could also be enhanced although this remains to be properly established.

Enhanced alite dissolution by CAH10 addition

The influence of varying Al addition in the form of CAH10 on the hydration of alite was studied to gain further insights into the alite hydration mechanisms in the presence of increased Al concentration in pore solution. Therefore, pure alite and mixtures of alite and CAH10 were investigated by means of isothermal heat flow calorimetry, XRD and pore solution chemistry analysis. The two occurring hydration events can be attributed to the precipitation of two different silicate-bearing hydrate phases, C2ASH8 and C-(A)-S-H. In this case, the consumption and removal of Al in pore solution initiated the change to C-(A)-S-H-forming hydration. Furthermore, the formation of C2ASH8 and the alite reaction rate and reaction were directly influenced by the amount of Al provided by CAH10 addition, leading to an alite reaction turnover of up to 68–86 % within 48 h.

Belite clinkers with increasing aluminium content: Effect of calcium aluminates on calcium silicate hydration

Belite cements (BCs) could have advantages over Portland cements concerning durability, low heat development and the use of less demanding raw materials. The activation of BCs by sulfur addition at the clinkering stage and by fast cooling is well established. However, the reaction rates of the calcium silicate phases, mainly belite, are still not fully understood. This is partly due to the interplay between factors including: i) belite activation during clinkering; ii) role of the calcium aluminates at early hydration ages; and iii) role of the sulfates. In the research reported here, three belite clinkers were prepared with constant values of lime saturation factor, and SO3, Fe2O3 and CaF2 contents. The varied parameter was the amount of Al2O3. The resulting clinkers have overall crystalline reactive calcium aluminate contents of 0.4, 7.9 and 16.7 wt%, respectively. Cements were prepared with similar particle sizes and constant anhydrite content. Here, it is shown that calcium silicate reactivities, both alite and belite, strongly depend upon the calcium aluminate contents. As these amounts increase, the degree of hydration of alite at 1 day decreases: 85, 65 and 50 %. Furthermore, the degree of hydration of belite at 7 days was 50, 35 and 0 %. Thus, there is a strong influence of aluminates in calcium silicate rates of hydration. Moreover, comparing the mechanical properties of the cements with 0.6 and 8.2 wt% amounts of calcium aluminates, the improvements due to the higher reactivity of calcium aluminates at very early ages, seem to be counterbalanced by the lower reactivity of the silicate phases. The reported findings may allow further optimization of early age reactivity of active BCs.

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.

Working mechanism of calcium nitrate as an accelerator for Portland cement hydration

AbstractPrecast concrete, cold weather concreting, and the emerging technique of concrete additive manufacturing are applications in which the acceleration of cement hydration plays a critical role. To allow precise control of early cement hydration in these applications, a thorough understanding of the working mechanisms of cement hydration accelerators is required. This study contributes to the understanding of the mechanism by which calcium nitrate (Ca(NO3)2) influences early cement hydration. The influence of Ca(NO3)2 on the hydration of an ordinary Portland cement has been followed by isothermal calorimetry, in situ X‐ray diffraction (XRD), quantitative XRD, compressive strength testing, and the analysis of the pore solution composition. Further, the initial pore solution, the initial phase composition, and the phase composition in the fully hydrated cement have been estimated by thermodynamic calculations to corroborate the experimentally obtained results. The results indicate that Ca(NO3)2, especially at the highest analyzed dosage of 5 wt.%, enhances the formation of ettringite and a nitrate‐containing AFm phase. Furthermore, Ca(NO3)2 accelerates alite hydration. Besides the increased Ca concentration in solution, it has been found that a reduction of the Al concentration in the initial pore solution by Ca(NO3)2 possibly contributes to the accelerating effect of Ca(NO3)2 on alite hydration.

Insights into the “accelerating effect” of sucrose on cement pastes

Sugars have been widely used as setting retarders due to their efficiency and low cost. At low levels, they delay the hardening of the cement paste, reducing the hydration rate of the cement paste, especially alite. Some studies, however, have observed an accelerating effect through rheological tests, depending on the additive content and the water to cement (w/c) ratio, among other factors. So far, there is no explanation of the reason for this phenomenon supported by solid evidence. In this context, this work investigates the effect of sucrose on the structure (through in situ XRD and isothermal induction calorimetry) and on the rheological behavior (stationary rotational rheometry) of cement pastes. The results show that sucrose acts as an efficient setting retarder at low concentrations, delaying the setting time of the pastes with the reduction of the alite hydration rate, and without significant changes in the yield stress evolution. At high concentrations, the hydration delay of alite is even longer, followed by an intense formation of ettringite, whose main precursor is the ferrite phase. The formation of needle-shaped crystals of ettringite is the reason behind the acceleration phenomenon.

Experimental and mesoscale simulation studies of micro-mechanical properties of alite mixed with NaCl solutions

To conserve freshwater resources, seawater may be used for concrete production. As sodium chloride (NaCl) is the most abundant mineral found in seawater, in this study, we focused on the effects of NaCl on the hydration of alite, which is the major clinker phase in Portland cement, and its hydration dominates the mechanical behaviour of cement pastes. NaCl solutions with varying concentrations were mixed with alite at a solution-to-binder ratio of 0.5. Then, a combination of experiments and mesoscale simulation was utilized to study the influence of NaCl on the micro-mechanical properties of alite pastes. The nanoindentation test showed the improving micro-mechanical properties of alite pastes with increasing NaCl concentration. The pore size distribution analysis agreed with mesoscale simulation on the reduced porosity, and the latter showed increased cohesion. The porosity and cohesion changes were initiated by the ionic effects of Na+ and Cl− that modify the Debye length of C-S-Hparticle and dielectric constant of the C-S-Hgel pore solution.

Time-varying structure evolution and mechanism analysis of alite particles hydrated in restricted space

Restricted space could lead to the structure evolution of calcium silicate hydrate (C–S–H) especially during the later hydration stage, which essentially affects the strength and durability of Portland cement based materials. In order to get insights into the effect of restricted space on C–S–H microstructure, the alite powders were pressed into discs for hydration. The pre pressing treatment provides a relatively denser microstructure, which simulates the restricted space during the late hydration of alite or cement. The structure of hydrates grown in restricted space was revealed by Fourier transform infrared spectra, Raman spectra, 29Si nuclear magnetic resonance spectra, scanning electron microscope and energy dispersive X-ray spectroscopy. The results show that restricted space leads to the formation of unstable Ca–O bonds and Si–O bonds in early hydrates, and influences the silicate chains in C–S–H by the formation of high polymerized hydrates (Q3 silicates) at early stage. The content of Q3 silicates in the hydrates of restricted space is the highest at 7 d and then decreases, which is opposite to the control with the lowest Q3 silicates content at 7 d and the highest content at 28 d. The hydrates which form at 28 d show a remarkable higher chemical shift of Q3 sites and a lower Ca/Si ratio than that of the control. The findings indicate that the restricted space may lead to stress, which rearranges the nanostructure of C–S–H and induces a varied structure in Q3 silicates of C–S–H. This work lies a theoretical foundation for exploring the structure evolution of C–S–H in cement concrete after long service.

Formulation of an alkali-free accelerator and its effects on hydration and mechanical properties of Portland cement

An alkali-free accelerator (AMD) mainly composed of aluminum sulfate, magnesium sulfate and diethanolamine (DEA) was formulated and its effects on hydration and mechanical properties of Portland cement were investigated. Results indicate that AMD accelerator can efficiently shorten the setting time and enhance the early strength of Portland cement. The rapid setting and hardening properties were achieved by promoting the formation of ettringite (AFt), Mg(OH)2 and MgAl-hydrotalcite (MgAl-LDHs). Although AMD accelerator retarded early hydration of alite due to the accelerated hydration of C3A and caused higher porosity, it had no negative effect on or even slightly increased long-term strength development. Except for environmentally-friendly advantage, this type of alkali-free accelerator is more beneficial to strength development compared to accelerators with fluoride salts.

Hydration of Hybrid Cements at Low Temperatures: A Study on Portland Cement-Blast Furnace Slag-Na2SO4.

Replacement of Portland cement with high volumes of blast furnace slag is known to negatively affect the early-age properties of concrete, particularly at low temperatures. In this study, the effectiveness of Na2SO4 on the mechanical properties, hydration kinetics and microstructure development of a commercial CEM III/B (~69% slag) is investigated at 10 and 20 °C. Na2SO4 enhances compressive strength at both 10 and 20 °C, and at both early (1 and 7 days) and later ages (28 and 90 days). QXRD shows an increase in the degree of alite hydration at 1 day with Na2SO4 addition, while the degree of clinker and slag hydration is similar for all the systems from 7 to 90 days. An increase in ettringite content is observed at all ages in the systems with Na2SO4. Microstructure and pore structure shows densification of hydrates and reduction in porosity on addition of Na2SO4.

Effects of Early Hydration of Alite and Belite Phases on Subsequent Accelerated Carbonation

Effects of Early Hydration of Alite and Belite Phases on Subsequent Accelerated Carbonation

Strength degradation of seawater-mixed alite pastes: an explanation from statistical nanoindentation perspective

Interest in investigating seawater concrete has been increasing in recent years, but most studies of the strength degradation of seawater mixed concrete have only been carried out on the macro-scale. In this study, alite, the main phase in ordinary Portland cement, was hydrated with various salt solutions (NaCl, MgCl2, CaCl2 and simulated seawater) with a solution-to-binder ratio of 0.5 to explore the effects of common cations in seawater on the micro-mechanical performance of alite pastes. Nanoindentation-energy dispersive X-ray spectroscopy analysis, porosity analysis, and phase evolution tests were carried out to reveal the microstructure evolution of salt-added alite systems. The results showed that in addition to the acceleration of alite hydration by the salt solutions, more low-density (LD) C-S-H in the hydration products was formed. All the cations used in this study were able to enter the mesopores in the C-S-H particles, which improved the micro-mechanical performance of alite pastes. However, the deleterious effects of simulated seawater on the modulus and hardness of C-S-H were noticed, mainly attributed to the presence of Mg2+ in seawater.