Main Hydration Peak Research Articles

Retarding Effect of Hemp Hurd Lixiviates on the Hydration of Hydraulic and CSA Cements.

Wood wool panels are widely used in the construction industry as sustainable cementitious composites, but there is a growing need to replace traditional Portland cement with a binder that has a lower embodied carbon footprint. In addition, the sustainability of these panels may face serious impediments if the required amount of wood for their production needs a harvest rate higher than the rate at which the tree sources reach maturity. One solution is to use the wooden part of fast-growing plants such as hemp. However, the compounds extracted from the mixture of plants and water are the main cause of the delay observed during the hydration process of hydraulic binders in these cementitious composites. The objective of this study is to evaluate the effect of bio-aggregate lixiviates (hemp hurd) on the hydration kinetics of calcium sulfoaluminate (CSA) cement as a low-embodied-carbon alternative to ordinary Portland cement (OPC). The isothermal calorimeter showed that the hemp hurd lixiviate caused a greater delay in GU's hydration process than CSA's. At a 5% concentration, the main hydration peak for GU cement emerged after 91 h, whereas for CSA cement, it appeared much earlier, at 2.5 h. XRD and TGA analysis showed that after 12 h of hydration, hydration products such as calcium silicate hydrates (C-S-H) and portlandite (CH) were not able to form on GU cement, indicating low hydration of silicate products. Moreover, at 5% concentration, the carbonation of ettringite was observed in CSA cement. The compressive strength values obtained from the mixes containing hemp hurd lixiviate consistently showed lower values compared to the reference samples prepared with distilled water. Furthermore, the CSA samples demonstrated superior compressive strength when compared to the GU samples. After 28 days of hydration, the compressive strength values for CSA cement were 36.7%, 63.5% and 71% higher than GU cement at a concentration of 0.5%, 2% and 5% hemp hurd lixiviate, respectively.

Properties of Polycarboxylate Superplasticizers with Different Molecular Structure: A Comparative Study

Polycarboxylate superplasticizers (PCEs) with different molecular structure had been synthesized and characterized by FT-IR. PCEs were mainly included polyester (Type A), polyether (Type B) and ester ether copolymer (Type C). The application properties, adsorption behaviors and hydration process were investigated. The TOC was used to measure the adsorption amount, and crystal components in the hydration products were detected by XRD analysis. Test showed that Type B had the excellent performance, including large water reduction rate and strong adsorption capacity. The ester group in the molecular structure of Type A and C could improve the fluidity retention of cement paste, but the hydrolysis of ester group also weakened adsorption capacity on cement particles. In addition, in the cement-water-PCEs system, the difference of molecular structure would affect the early hydration process of cement slurry. For example, research indicated that the main hydration peak and maximum elevated temperature was delayed by adding PCEs. Through the examination of hydration products, it revealed that the intensity of calcium hydroxide (CH) and ettringite (AFt) peaks with Type B was higher than the other. The concrete application performance results indicated that PCEs had the basically equal contribution to the compressive strength. Keywords molecular structure; ester group; adsorption; hydration products; compressive strength

Effects of controlled release silica nanocapsules containing sucrose on the heat release of cement hydration

The usage of chemical admixtures, such as starch-based materials, is a common approach to addressing the thermal cracking problem of cementitious materials. Capsule-based controlled release technique enables the adjustable action time of loaded chemical admixture and thus reveals the potential on inhibiting the exothermic process of cement hydration. Three types of silica-based nanocapsules loaded with 53–63% sucrose retarder are firstly prepared by interfacial polymerization in water-in-oil (W/O) emulsion. The release characteristics of three types of nanocapsules are precisely tuned by varied preparation conditions. The effects of nanocapsules on the exothermic process of cement hydration have been investigated through calorimetry measurements. All prepared nanocapsules not only delay the appearance of the main hydration peak as the retardation effect but also reduce the maximum heat flow of the main hydration peak, to some extent, as the depression effect. The depression and retardation effects are improved with the increased dosage and slower release rate of added nanocapsules. The relationship between the two effects and the action time of loaded sucrose suggests the importance of persistently inhibiting the cement hydration over the entire accelerating and decelerating processes, which can be estimated by the time window between the action of sucrose (50% release time) and occurrence of main hydration peak.

Influence of sodium chloride on the hydration of C3S blended paste

Understanding the chloride influence mechanism on the hydration kinetic of cementitious materials is meaningful for the application of chloride rich raw materials. This paper explored the main hydration peak and AFm peak evolution for various chloride content in C3S systems blended with metakaolin and limestone. Calorimetry test was applied to reveal the hydration process under chloride condition. Phase assemblage evolution was analyzed through X-Ray powder diffraction (XRD)/Rietveld analysis. It was observed that the hydration rate was accelerated and enhanced for both silicate and aluminate peaks when chloride was present. Silicate peak change comes from the ions effect of the pore solution owing to chloride. AFm peak heat release presents linear relation with chloride content. In addition, MK and LS shows little effect at the beginning and then some chemical reaction effect after the main peak. Therefore, pure Friedel’s salt is formed at the beginning of hydration in all systems, while solid solution of Friedel’s salt would be produced after the silicate peak in systems with limestone, which is controlled by the carbonate in the system.

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.

An insight of carbonation-hydration kinetics and microstructure characterization of cement paste under accelerated carbonation at early age

Accelerated carbonation of cement and concrete at early age is an essential technique for both of carbon sequestration and performance improvement, while the core carbonation heat and the interplay with the subsequent hydration process remain unclear. This study aims to develop a method to explore carbonation-hydration heat evolution using a modified isothermal calorimeter, microstructure characterization of carbonated pastes was revealed by multi-techniques of TG/DTG, XRD, SEM and thermodynamic modelling. Carbonation heat was confirmed and the intensity of this heat was much higher than that of hydration heat. Interestingly, the main hydration peak flow overlapped with the front carbonation flow, while three factors including prior-hydration time, w/c ratio and superplasticizer (SP) were found to be the key factors to obtaining independent carbonation-hydration flow in this process. Furthermore, prior-hydration of 2 h promoted CO2 uptake of paste to 14.9%, and the generation of 1–4 μm calcium carbonate crystals with irregular graininess and rhombohedral-like shape were also observed in carbonated pastes.

Deconvolution of main hydration kinetic peaks in properly sulfated Portland cements with boundary nucleation and growth models and relation to early-age concrete strength development

When the hydration kinetics of properly sulfated Portland cements is monitored by heat flow calorimetry, the initial dissolution peak and the dormant period is followed by the main hydration peak – formation of calcium-silicate-hydrates and portlandite, the so-called silicate peak. This main peak is superimposed by a peak associated to further tricalcium aluminate dissolution and a surge in precipitation of sulfoaluminates (the so-called sulfate depletion peak) right after sulfate added for setting control is depleted in the material system. In this paper strategies for the deconvolution of silicate peak and sulfate depletion peak are presented. Hereby, the boundary nucleation and growth model and the classical bulk nucleation and growth model serve as tools for deconvolution of calorimetric data. We discuss obtained kinetic parameters and their temperature dependency. The boundary nucleation and growth model for constant nucleation rate emerged as the most suitable model for the silicate reaction, the bulk nucleation and growth model with an order of three, indicating site saturation, as adequate for the sulfate depletion peak. The reaction enthalpy for tricalcium silicate hydration was obtained as 503 J/g, remarkably close to literature values. Calorimetric data related to the sulfate depletion peak is corroborated by X-ray diffraction analysis of formation history of crystalline hydration products. Furthermore, the history of the (silicate) degree of reaction as predicted by the boundary nucleation and growth model for different temperature histories is related to experimentally obtained early-age strength histories. • Investigation of hydration kinetics of commercial, well-sulfated Portland cement. • Main peak (C-S-H and portlandite formation) superimposed by sulfate depletion peak. • Strategies for deconvolution of peaks with Avrami–Cahn models as tools for analysis. • Degree of silicate reaction history is linked to early-age strength gain.

Impact of trace metals Zn, Cu, Cd and Ni on the reactivity of OPC and GGBS-based hydraulic binders at early age for sediment stabilization

The solidification/stabilization method was demonstrated to be an effective remediation technology for hazardous waste treatment. Three types of binding agents were tested in the present study in view of their potential use in solidification of contaminated sediments and soils – ordinary Portland cement (OPC), granulated ground blast furnace slag (GGBS) activated by OPC and a Supersulfated (SSC) binders. An investigation into the impact of trace metals Zn, Cu, Ni and Cd on the hydration of the binders was performed by adding them into pure binders’ systems. Hydration heat evolution of the binders was assessed through isothermal calorimetry and hydration products were analysed through XRD, NMR and XAFS analysis. Copper and zinc present the most perturbing effect on the early hydration delaying the main hydration peak occurrence while nickel and cadmium ions do not perturb or accelerate it. For example, the GGBS/OPC formulation without any metal addition has its MHP at 13.5 h, with the addition of 0.5%Zn the MHP appears 37 h later, with 0.5%Cu 11.5 h later, but with Ni and Cd 5 h earlier. The SSC formulation was shown to be the most sensitive on the trace metals (TM) addition. The electrokinetic and conductivity measurements of the binders using Zeta Potential apparatus showed a decrease in obtained values in the presence of Cu and Zn and an increase in the presence of Ni and Cd confirming the different behaviours of TM in the considered systems.

Effect of tartaric acid on the hydration of oil well cement at elevated temperatures between 60 °C and 89 °C

In order to study the abnormal viscosity evolution behavior of oil well cement slurries containing tartaric acid, the influence of tartaric acid on the early-age hydration of oil well cement at high temperatures was investigated by isothermal calorimetry (IC), thermogravimetric analysis (TGA) and quantitative XRD (QXRD) analysis in the temperature range of 60 °C to 89 °C. Results show that, a high dosage of tartaric acid can fundamentally change the typical shape of the cement hydration heat flow curve - two additional exothermic peaks associated with aluminate phase hydration (C3A and C4AF) appear before the main hydration peak. The unsynchronized hydration of the aluminate phases and the silicate phases was found to be the cause of premature setting. Additionally, long-term curing study (up to 28 d) showed that increasing the dosage of tartaric acid decreased the ultimate hydration extent of C2S while it increased the ultimate hydration extent of C4AF.

Early age hydration of model slag cement: Interaction among C3S, gypsum and slag with different Al2O3 contents

A deeper insight into SO3/Al2O3 ratio including the contribution of alumina in slag at early age is required to ensure a properly sulfated slag cement. In this paper, to investigate the effect of gypsum and alumina of slag, emphasis was laid on the hydration characteristics of C3S-gypsum-slag system during the early age, of which slag was synthesized in the laboratory with varying Al2O3 contents from 3.69 to 18.19 wt%.The duration of dormant period during the hydration of C3S depended on Al2O3 content of slag significantly; however, the amount of silicate reaction before the onset of aluminate reaction was independent of slag chemistry and gypsum content added. The rate of aluminate reaction was controlled by the availability of reactants, SO42− and Al3+ ions in particular, which were sourced from gypsum and slag, respectively. Calcium monosulfoaluminate only occurred in mixture when slag contained a high amount of Al2O3 (18.19 wt% in this study) at early age, and its formation proceeded continuously at the expense of ettringite. Sulfur rich species incorporated in slag started to participate into aluminate reaction after the main hydration peak of C3S, and it played a similar role to gypsum.

Determining hydration mechanisms for initial fall and main hydration peak in tricalcium silicate hydration using a two-scale hydration simulation model

This study aimed to determine the hydration mechanisms of the initial fall and main hydration peak in tricalcium silicate (C3S) hydration using a two-scale hydration simulation model. The model could consider the coalescence of etch pits, the dependence of the interfacial dissolution rate on solution undersaturation, and the boundary nucleation and growth of calcium silicate hydrate (CSH). The results indicated that (1) the dissolution theory could reproduce the initial fall of the hydration rate in C3S hydration; (2) when only the dissolution theory was considered, a discrepancy in Si concentration at the very early age of hydration was found between the results obtained from simulation and experiment; and (3) the main hydration peak could be ascribed to the combined effect of the dissolution of C3S with the coalescence of etch pits, the nucleation and growth of CSH, and the shrinkage of particles.

Embedded dual PZT-based monitoring for curing of concrete

Monitoring the hardening of concrete during construction, is important to ensure proper strength gain and timely removal of formwork without compromising safety. Existing non-destructive testing (NDT) techniques mostly require sophisticated equipment and technical expertise, which makes it less applicable for field monitoring. Alternatively, lead zirconate titanate (PZT)-based electromechanical impedance (EMI) technique is under research, as an option for monitoring the hydration of concrete. The current study proposes a transducer design using an innovative configuration of PZT patches on metal plate, which enables segregation of flexural and axial modes while measuring EMI. The resultant peaks are more prominent, making its variation easier to track. The effectiveness of this configuration is studied by embedding the smart piezoelectric-based plate in the concrete during casting and recording the electromechanical admittance throughout the curing period. The frequency shift of the first flexural/axial peak, is a good indicator of the strength gain during this period. This has been verified for ordinary Portland cement (OPC) and fly ash-based geopolymer (GP). The results show that the frequency shift curve follows the isothermal calorimetry curves beyond the main hydration peak.

Composition and properties of cement system with glutaraldehyde

The experience of operating livestock farms shows that periodic reorganization does not prevent biological corrosion of building structures. In this work, the possibility of using glutaraldehyde as a fungicide for volumetric administration in the preparation of biostable concrete was investigated. The study aims to minimize the adverse effects of the components of commercial biocidal products on the physical and mechanical characteristics of products. For research, we used an aqueous solution of glutaraldehyde with an active substance concentration of 0.5 and 1 %, which was introduced into Portland cement CEM I 42.5 N as mixing water. The degree of influence of the active substance on the properties of cement paste and mortar was estimated according to data on heat release during hydration, strength, and phase composition. The fungicidal activity evaluation of glutaraldehyde in cement systems and the degree of their growth with the Aspergillus niger test culture were evaluated. It was established by isothermal calorimetry that, in mixtures with glutaraldehyde, a delay in the achievement of the main hydration peak is observed-by 30 minutes for 0.5 %, by 1 hour for 1 %. After 72 hours of hydration, a lower total amount of released heat of hydration is observed-for 0.5 and 1% solutions by 6.8 and 5.8 %, respectively. According to X-ray phase and differential thermal analyzes, the phase composition of the initial and aldehyde-modified cement stone on day 28 does not differ and consists of the following phases: ettringite, portlandite, calcite and clinker minerals. Varying the phase composition leads to a change in strength: when using a 0.5 % solution of aldehyde, the power of the cement-sand mortar increases by 6.5 %, and a 1 % solution decreases by 6.7 %. The use of a 0.5 % solution of glutaraldehyde provides a decrease in the intensity of fungal development and the formation of a fungistatic effect. Based on the results, a 0.5 % solution of glutaraldehyde can be recommended for the development of cement composites with prolonged bioresistance.

Effect of starch-based admixtures on the exothermic process of cement hydration

The effect of three types of starch-based admixtures, namely glucose and its derivatives, soluble dextrin with various degree of polymerization and a novel starch-based temperature rise inhibitor (TRI) with various degree of starch acidification on the exothermic process of cement hydration has been investigated through the calorimetry measurements. Except delaying the appearance of the main hydration peak as the retarding effect, starch-based admixtures can also reduce the heat flow during the acceleration period and induce a lower maximum heat flow as the depressing effect. Together with the dissolution and adsorption results, it can be concluded that the relationship between these two effects is determined by the action time of molecule in the cement paste. The soluble admixtures with fairly short action time focus mainly on disturbing the cement hydration during the induction period but have minor effect on depressing the main hydration peak. TRI with limited dissolution can persistently inhibit the cement hydration over a longer period of action time, inducing negligible retarding effect but apparent depressing effect.

Prehydration of calcium sulfoaluminate (CSA) clinker at different relative humidities

The use of CSA cement in practice has been hindered by its unstable performance and short shelf-life caused by the prehydration of CSA clinker. In this study, the effect of ambient humidity on the prehydration rate and process of CSA clinker was investigated. The prehydration degree, ageing progress, and the dynamic change of mineral composition of CSA clinker exposed to five different relative humidities (ranging from 23% to 98%) for up to 180 days were studied. Experiments revealed that the ambient humidity of 60% RH can be considered a threshold value for storage of CSA clinker. Exposure of CSA clinker to RH higher than 60% will not only result in a significant decrease of hydraulic reactivity, but also in agglomeration of the clinker. Although the exposure of CSA clinker to RH lower than 60% has little effect on the hydraulic reactivity, the main hydration peak was found to be slightly delayed with the increase of RH.

Effect of a novel starch-based temperature rise inhibitor on cement hydration and microstructure development: The second peak study

Temperature rise inhibitor (TRI) modifies the exothermic process of cement hydration at early age and mitigates the buildup of cumulative heat, which sheds new light on solving the thermal cracking issue. After the main hydration peak, a broader “second peak” appears and brings the cumulative heat back to normal level within 7 days (for additions less than 0.15%). This study shows that the “second peak” can be attributed, almost exclusively, to C3S hydration while triggered by C3A hydration. In a pure C3S system, the heat flow is depressed by TRI during the main hydration peak but never recovers after. In a monophase system composed of C3S, C3A and gypsum or a real cement paste, the ongoing precipitation of ettringite helps to pump out TRI polymer from the pore solution and eliminate the restriction on C-S-H nucleation. Afterwards, the precipitation of C-S-H accelerates again to form the “second peak”.

Nano-carbide slag seed as a new type accelerator for Portland cement

In present work, a novel nano-CS seed was prepared by wet-grinding method and added to cement to accelerate the early hydration. With 5% nano-CS seed, the initial and final setting time was clearly shortened by 61.4% and 51.7% respectively; the dormant period and the main hydration peak was notably advanced by 52.9% and 43.5% respectively. Early compressive strength, especially the 8-hour strength, was greatly promoted by the nano-CS seed by 3350%, with 5% nano-CS seed. It was speculated that the early-hydration and early-strength was accelerated by weakening the electrical double layer shielded around the silicate phase, thus shortening the dormant period. Results highlighted that the prepared nano-CS seed in present work is expected to be practically used as a new type accelerator.

Study on the influences of silica and sodium in the alkali-activation of ground granulated blast furnace slag

Slag is activated with alkali-silicate solutions made with nano-silica and waterglass. The reaction kinetics and the reaction products formed are evaluated for different silica and sodium contents. Isothermal calorimetric measurements with in-situ mixing reveal increased early reactivity with added silica, while the main hydration reaction is delayed. The presence of Na with dissolved silica in the activating solution does not influence the initial dissolution and early reactivity of slag. At the same time, it has an accelerating effect on the main hydration peak of slag. Dissolution studies of slag in alkaline solution with added silica indicate the immediate formation of calcium silicate hydrates after dissolution contributes to the early reactivity. The enhanced early reaction product formation in the presence of dissolved silica leads to the very rapid development of the internal structure. Rheological measurements indicate an early loss of workability due to increased early reactivity. The increase in time for the main hydration reaction of slag in the presence of added silica, however, delays the setting behavior. The primary reaction product in alkali-activated slag is calcium silicate hydrate with aluminum uptake, C-(A)-S-H. The addition of silica in the activating solution leads to its larger incorporation in the C-(A)-S-H and higher compressive strength. The sodium content in the activating solution does not contribute to the ultimate strength. The sodium in the alkali-activated slag is present in the form of a water-soluble amorphous product.

Measuring chemical shrinkage of ordinary Portland cement pastes with high water-to-cement ratios by adding cellulose nanofibrils

Chemical shrinkage is an important way to study the hydration kinetics of cement. However, the measurement of chemical shrinkage for cement pastes with high water-to-cement ratio (w/c) faces a significant bleeding issue. This study demonstrates the use of cellulose nanofibrils (CNF) to create a stable structure that can support cement particles and let them be hydrated without settling. The measured chemical shrinkage curves for the 0.5 w/c cement pastes with and without CNF are very similar at early ages (e.g., 3 d), which implies that the chemical effect of CNF on cement hydration is small in the short term; therefore, the use of CNF allows study of chemical shrinkage for high w/c cement pastes at the early ages. The results show that with the increase of w/c, the main hydration peak is delayed and the post-peak stage is prolonged. In the long term (e.g., after 3 days), the measured chemical shrinkage for high w/c is higher than the low w/c. Similarly, the degree of hydration curves show that, with more water, cement hydration is eventually much enhanced.

Towards a further understanding of cement hydration in the presence of triethanolamine

The acting mechanism of triethanolamine (TEA) on cement hydration was studied by combination of techniques including calorimetry, in-situ XRD and pore solution analysis. Results show that, a high dosage of TEA (0.5%) results in accelerated aluminate reaction and retarded silicate reaction during hydration of ordinary Portland cement (OPC). The initial dissolutions of C3S, C3A, C4AF and gypsum are greatly facilitated by TEA. The secondary fast reactions of C4AF and C3A triggered by the earlier sulfate-depletion produce a new exothermic peak before the main hydration peak of C3S that usually presents as a shoulder after the main hydration peak in the reference sample. TEA retards the hydration of pure C3S, but much more severely delays the silicate reaction in OPC system, attributed to the negative interference of aluminate reaction on silicate reaction. The new insights into the interaction between TEA and OPC contribute to the theoretical base for regulating cement hydration.