Na3V2(PO4)3/C cathode and commercial hard carbon anode materials are coated with a roll-to-roll coater on an aluminum current collector. Sodium-ion pouch and coin cells are assembled. The degradation ...mechanism, cycle stability, morphology of cycle-aged material, and aging influence on the heat generation during cycling are thoroughly investigated. Electrochemical impedance spectroscopy permits resistance assignment to the specific electrodes by using the distribution of relaxation times. Comparison of pristine and cycle-aged cells allows separating the degradation contributions of the particular electrodes. The generated heat during charging and discharging is determined by means of an advanced highly sensitive MS80 3D Tian-Calvet calorimeter under isothermal conditions at 25 °C and the heat generation mechanisms are elucidated. It is observed that less heat is generated during charging than discharging process. Furthermore, the cell balancing reveals a pronounced effect (approximately 50% in charging and 20% in discharging) on the amount of generated heat, which is valuable feedback for the material developers and cell designers. These analyses represent a fingerprint for the underlying electrochemical processes at the electrodes and are very essential for state of health, aging prediction as well as the subsequent tackling of safety-related issues in sodium-ion batteries.
•Na3V2(PO4)3/C vs HC in coin and pouch cell formats are studied.•The heat generation is measured both on pristine and cycled-aged cells.•Identification and contribution of various resistances from cathode and anode.•Describe the relationship between generated heat and the degradation of materials.•The cell balancing shows a pronounced effect on the amount of generated heat.
Tests to determine the reactivity of supplementary cementitious materials (SCMs) by using isothermal calorimetry and thermogravimetric analysis have been proposed. In one such test, the heat release ...and calcium hydroxide consumption of SCMs mixed with calcium hydroxide (3:1 ratio of calcium hydroxide and SCM) at 50 °C in a 0.5 M potassium hydroxide environment are measured. In this study, we show the results of such testing for a large variety of SCMs and fillers, ranging from conventional materials such as fly ash, slag, silica fume, quartz, and limestone, to alternative materials such as calcined clays, municipal solid waste incineration fly ash, basic oxygen furnace slag, ground lightweight aggregates, ground pumice, ground glass pozzolan, and basalt fines. A total of 54 SCMs are tested using this approach. Results show that even among SCMs of the same type, there is considerable difference in the heat release and calcium hydroxide consumption, likely due to differences in amorphous content, chemical composition, and fineness, leading to different reactivities. Based on the response in the test, SCMs are classified into inert, pozzolanic, and latent hydraulic; the pozzolanic and latent hydraulic materials are further classified into less reactive and more reactive. The relationship between heat release and calcium hydroxide consumption depends on the chemical composition of the SCMs, and SCMs with high calcium, high alumina, and high silica contents show different relationships (determined by the slope of the heat release vs. calcium hydroxide plot).
Early-age reaction kinetics of geopolymers is one of the challenging issues associated to their mechanical performances and durability. In this work, the early-age reaction of metakaolin geopolymer ...prepared by activators with various silicate moduli was studied. Compared to conventional methods, a novel approach was firstly proposed to evaluate the early-age reaction of geopolymer by using 1H low-field nuclear magnetic resonance (NMR) and isothermal calorimetry. The state and relative quantity of water in geopolymer pastes were detected by NMR during reaction process. While in this timescale, the heat release of pastes was recorded by isothermal calorimetry. A good consistency to the measurement of reaction process between these two testing methods can be observed. Activator with low silicate modulus (i.e., high alkalinity) deepens the reaction degree at the same timescale and the gel pore volume is increased with the alkalinity of activator. This method is useful to monitor the early-age reaction process of geopolymer, which is expected to offer new insights into the early-age reaction kinetics of geopolymer.
End-of-life tire (ELT) rubber has been widely researched to replace fine or coarse aggregates in cementitious composites. While most studies paid attention to its effect on the engineering ...properties, very few considered chemical reactions with pore solution and the potential for environmental leachate. Recently the authors developed a methodology to remove zinc from the ELT rubber, since zinc can be toxic if it is leached into the environment. In this study, the authors utilized ELT rubber before and after the zinc extraction process to partially replace fine aggregate in a mortar. Flowability, compressive strength, flexural strength, and ultrasonic pulse velocity were measured for the engineering properties of rubberized mortars. Simultaneously, isothermal calorimetry was also employed to investigate the effects of ELT rubber on the hydration process of the rubberized mortars. In addition, the pore solution and leaching solutions were taken at different curing ages and then analyzed for elemental and total organic carbon (TOC) contents. The results showed a remarkable loss in engineering properties of rubberized mortar when ELT rubber was utilized, and the decrease in performance was more pronounced in the samples with zinc-extracted ELT rubber. The pore solution was found to contain significant quantities of zinc and TOC. However, the authors also found that using silica fume to partially replace cement could effectively recover the loss in strength and could reduce the leachability of zinc and TOC.
•A metallurgical processing technique is implemented to leach zinc from end-of-life tire rubber.•The fate of zinc and organic carbon leached from end-of-life tire rubber is studied.•Cement-based materials are proven effective to immobilize zinc and organic carbon leached from tire rubber.
In the quest for environmentally sustainable binders within the construction industry, metakaolin (MK) has emerged as a highly promising material. Its reactivity and hardening performance encompass a ...wide range of applications, spanning from lime to cement-based materials. This performance is primarily underpinned by the pozzolanic reaction with calcium hydroxide (CH), leading to the formation of various calcium aluminate silicate hydrates. The intricacies of the hydration kinetics and resultant reaction products hinge on several factors woven into the specifics of the binder type. This study investigates the influence of CH availability, explored through initially mixed MK/CH weight ratios of 0.33 and 1.0. Furthermore, the study examines the impact of introducing alkali hydroxides (KOH and NaOH) and/or sulfates (K2SO4 and Na2SO4) on the pozzolanic reactions. Short-term analysis employed inductively coupled plasma optical emission spectrometry (ICP-OES), and pH measurements for pore solution as well as isothermal calorimetry, and in-situ X-ray diffraction (XRD) on paste samples. Long-term investigations extended to 245 days at 40 °C, incorporating XRD, thermogravimetric (TGA) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX). Results provide insights into the kinetics of phase assemblage and compositions of C-A-S-H gels, highlighting the transformation of metastable C2ASH8 and C4AH13 to stable Si-rich hydrogarnet phases, incorporating sulfate, under excess CH conditions. Higher MK/CH enriches Si/Ca, Al/Ca, enhancing C-A-S-H gels, while KOH addition further boosts Al/Ca ratios.
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•High OH-/CH weight ratio (0.0307) promotes formation of alkaline aluminosilicates.•For higher MK/CH (1.0), sulfate addition slows pozzolanic reactions.•Excess CH transforms C4AH13 and C2ASH8 into hydrogarnet phases.•Sulfate localizes in aluminum-rich phases: AFt, AFm and hydrogarnet.•Higher MK/CH boosts Si/Ca, Al/Ca, enhancing CASH phases, while KOH increases Al/Ca.
•An experimental study was conducted to investigate seawater-mixed concrete.•A wide range of fresh and hardened properties of concrete were investigated.•Results were corroborated by isothermal ...calorimetry and SEM analytical techniques.•Remedial measures were proposed to improve the properties of seawater concrete.
Using seawater for mixing concrete is potentially advantageous from a sustainability perspective. However, the presence of high concentrations of chloride in the seawater can lead to corrosion of steel reinforcement. This issue can be addressed by using non-corrosive reinforcement; e.g., fiber reinforced polymer (FRP) bars. Moreover, the global threat of freshwater scarcity suggests that the use of seawater in concrete mixtures becomes plausible in the future. This paper reports on the results of an extensive experimental study to compare the fresh and hardened properties of freshwater- and seawater-mixed concretes. The experimental program included the following tests: (a) characterization of fresh concrete (slump flow, density, yield, air content, and setting time); (b) mechanical characterization of hardened concrete (compressive strength, splitting tensile strength, and shrinkage); and (c) permeability performance of hardened concrete (rapid chloride permeability, chloride migration, and water absorption). The use of seawater had a notable effect on the fresh concrete properties. Mechanical performance of seawater concrete was slightly lower than that of the freshwater-mixed concrete. The permeability performance of hardened concrete in the two mixtures was similar. Scanning electron microscopy and isothermal calorimetry were used as supplementary tools to better explain the experimental observations. Finally, remedial measures were proposed based on lab trials to improve the properties of seawater concrete.
The addition of carbon nanotubes (CNTs) to cementitious nanocomposites have demonstrated significant mechanical performance enhancements, however, there has been only limited research of the effects ...of CNTs upon hydration kinetics. Isothermal calorimetry was used to study in detail (i) CNT dispersion with and without a polycarboxylate-based superplasticiser, (ii) CNT dose at 0.05–0.25 wt% of cement, and (iii) CNT dispersion quality upon cement hydration. Results show a 45-min acceleration and 17% increase in principal hydration peak at a CNT dose of 0.1 wt% without superplasticiser, indicating enhanced nucleation with CNTs. Varying CNT dose, delaying effects of the superplasticiser dominated, although there was an increase in hydration peak of 17% with 0.25 wt% CNTs. Finally, it was found that CNT content, not ‘good’ or ‘poor’ dispersion quality, had a greater effect upon the overall nanocomposite hydration and microstructural development, facilitating further optimisation of CNT dispersion and microstructural development for CNT-cement nanocomposites.
The early age reaction kinetics and microstructural development in alkali-activated slag binder are discussed. In-situ isothermal calorimetry was used to characterize the reaction progression in ...sodium hydroxide and sodium silicate-activated slag binders cured at ambient temperature. Microstructure and strength development were monitored to correlate the heat evolution with the property development. In-situ isothermal calorimetric data for sodium hydroxide-activated systems exhibited only one major heat evolution peak with no dormant period. Sodium silicate-activated pastes exhibited multiple peaks and extended dormant periods. Microstructural evolution, monitored using BSE–SEM, showed rapid product formation on the surface of slag grains in sodium hydroxide-activated systems, forming thin reaction shells—the thickness of which was related to the activator concentration—and leading to diffusion controlled hydration at a very early stage. Sodium silicate-activated systems exhibited slow and progressive product formation, predominately nucleated from the solution. These results are supported by electron mapping and electron dispersive X-ray spectroscopy.
•The influences of FA and SL on the nucleation and growth of cement paste were studied.•FA retards the early hydration of cement at 20℃ due to its hindering nucleation.•SL has stronger seeding effect ...than FA because it produces more additional C-S-H gel.
In this study, isothermal calorimetry and the boundary nucleation and growth model (BNG model) were adopted to investigate the influence of fly ash (FA) and slag (SL) on the nucleation and growth of cement hydrates at early-stage. Afterwards, the mechanism was discussed by analyses of instantaneous activation energy and microtopography. The results show that the hinderance of FA on the early hydration at 20℃ is possibly contributed by the inhibition of nucleation, while SL promotes nucleation at both 20℃ and 60℃. Moreover, it is found that the paste containing FA has the lowest activation energy at early-stage, while the paste containing SL has the highest activation energy, which further indicate that the nucleation of the paste containing FA is more difficult. Besides, the surface microtopography analysis of particles confirm that SL has higher reactivity than FA in paste to generates more additional C-S-H gel to provide stronger seeding effect for producing C-S-H.
We used a combination of experimental and modelling techniques to study the effect of NaAlO2 on C3S hydration. pH sensitive inhibition of C3S hydration occurred at an early age of reaction, but was ...followed by an increased amount of hydrates formed later. Most results suggest that aluminates hinder C3S dissolution. It is hypothesised that this takes place in active dissolution areas, present with a higher density on finer particles. Annealing reduces their number and increases retardation for a given dosage of aluminates. The view that aluminates act by hindering dissolution is supported by molecular dynamics (MD) simulations. They establish that aluminates can adsorb on the hydroxylated C3S mainly through strong ionic interactions between aluminate and calcium ions on the surface of silicate. Upon progress of hydration and at higher pH values, the binding strength of aluminates to the hydroxylated C3S decreases so that its passivating effect, and retardation, are reduced.
