Hydration Of Tricalcium Silicate Research Articles

Effect of carboxylic and hydroxycarboxylic acids on cement hydration: experimental and molecular modeling study

Most concrete produced includes chemical admixtures such as air entrainers, set modifiers, water reducers, etc., many of which include organic molecules. Hydroxycarboxylic acids, in particular, retard portland cement hydration. The interaction of such acids with hydrating cement phases is a complex, multi-parameter problem. To elucidate the interaction of hydroxycarboxylic and carboxylic acid retarders on hydration of cement, a combined experimental and molecular-computational approach was used. Glycolic acid, acetic acid, calcium glycolate and calcium acetate were used as model compounds. Molecular dynamics simulations were performed to simulate the interactions of select test compounds with the (001) surface of the portlandite crystal (calcium hydroxide) and the (040) surface of the tricalcium silicate crystal. Hydrogen bond density profiles and binding energies were evaluated. The adsorption isotherm for chelate complexes was determined experimentally by equilibrating aqueous solutions of the agents in the presence of various amounts of solid-phase calcium hydroxide. Finally, isothermal calorimetry experiments were used to quantify effects on hydration rate. The glycolic acid shows significant cement retardation, whereas acetic acid does not retard. Glycolic acid was found to retard hydration via calcium chelation and surface adsorption that involves the adsorption of the calcium chelate complex preferentially on tricalcium silicate. Simulation results reveal that calcium glycolate forms a strong hydrogen bonding network near to calcium hydroxide and hydrated tricalcium silicate surfaces and are responsible for its strong adsorption on these surfaces. While acetic acid forms a strong calcium chelate, it does not associate with calcium hydroxide or unhydrated or hydrated tricalcium silicate surfaces.

A study of cement Type II hydration partially substituted by Brazilian spent cracking catalyst fines

In fluidized catalytic cracking refinery units, two kinds of wastes are generated: the equilibrium catalyst, which is withdrawn continuously from the catalyst regenerator, and the catalyst fines (Epcat), which are dragged by the gas stream leaving the regenerator, being separated by cyclones or electrostatic precipitators. This work aims to study the early cement hydration stages of Type II Portland cement, when substituted partially by Epcat. For this purpose, pastes were prepared with water/(cementitious material) ratio (W/C) of 0.5 and substitution degrees up to 30 mass% of cement per Epcat, which were analyzed during the first 24 h of hydration by non-conventional differential thermal analysis. The results show that the higher is the substitution degree of cement by Epcat, the higher is the formation of ettringite and the higher is the acceleration effect of tricalcium silicate hydration reactions. The deconvolution of the NCDTA curves obtained for the early cement hydration stages indicates that, in the early hydration stages, ettringite and tobermorite have an inverse relationship formation as a function of the degree of substitution, which shows a linearly growing ettringite content, as tobermorite content decreases. The released accumulated energy, calculated from NCDTA curve data, shows that Epcat has pozzolanic activity, which increases with the degree of substitution, also shown from the respective curve deconvolution data.

Analysis of C-S-H growth rates in supersaturated conditions

The growth rate of calcium-silicate-hydrate (C-S-H) was analyzed by following the evolution of calcium and silicon concentrations in supersaturated solutions. In these experiments, the supersaturated solution was produced by mixing a saturated calcium hydroxide solution and a solution obtained from the hydration of tricalcium silicate. A continuous decrease of the silicon concentration over time was observed during the experiments and the C-S-H formation rate was calculated from the amount of silicon that was precipitated between two consecutive analyses.The data obtained in this study demonstrate that the interfacial growth rate of C-S-H depends mainly on the supersaturation with respect to this phase, the availability of calcite as a substrate for heterogeneous nucleation and the calcium concentration in solution. A mean value of approximately 10nmol of C-S-H per m2 per second was obtained for the interfacial growth rate of C-S-H in conditions that are relevant for the hydration of tricalcium silicate.

Effects of Nanoalumina and Graphene Oxide on Early-Age Hydration and Mechanical Properties of Cement Paste

The effects of nanoalumina (NA) and graphene oxide (GO) on the early-age hydration and mechanical properties of portland cement pastes were investigated in this study. The hydration heat release rate and cumulative heat of cement pastes incorporating different dosages of NA and GO were evaluated using an isothermal calorimeter measurement method. Early-age electrical resistivity development was investigated by a noncontact electrical resistivity technique. The results show that both NA and GO could efficiently accelerate cement hydration. As a physical filler, NA significantly accelerates the hydration of tricalcium aluminate (CA) in cement. On the other hand, GO is able to obviously reduce the dormant period of cement hydration and shift the heat flow peaks to the left by accelerating the hydration of tricalcium silicate (CS) in cement. Compared to plain cement pastes, both the compressive and flexural strengths of cement pastes incorporating NA or GO are significantly increased. However, when NA and GO contents exceed the optimal amounts, improvements in flexural strength tend to decline, which is probably due to particle agglomeration. NA-cement paste exhibited slightly higher electrical resistivity than plain cement paste during hydration acceleration and deceleration stages. But GO-cement paste clearly showed lower electrical resistivity, which might be attributed to iron diffusion caused by GO with large surface areas.

The filler effect: The influence of filler content and type on the hydration rate of tricalcium silicate

AbstractThe partial replacement of ordinary portland cement (OPC) by fine mineral fillers accelerates the rate of hydration reactions. This acceleration, known as the filler effect, has been attributed to enhanced heterogeneous nucleation of C‐S‐H on the extra surface provided by fillers. This study isolates the cause of the filler effect by examining how the composition and replacement levels of two filler agents influence the hydration of tricalcium silicate (T1‐Ca3SiO5; C3S), a polymorph of the major phase in ordinary portland cement (OPC). For a unit increase in surface area of the filler, C3S reaction rates increase far less than expected. This is because the agglomeration of fine filler particles can render up to 65% of their surface area unavailable for C‐S‐H nucleation. By analysis of mixtures with equal surface areas, it is hypothesized that limestone is a superior filler as compared to quartz due to the sorption of its aqueous CO32− ions by the C‐S‐H—which in turn releases OH− species to increase the driving force for C‐S‐H growth. This hypothesis is supported by kinetic data of C3S hydration occurring in the presence of CO32− and SO42− ions provisioned by readily soluble salts. Contrary to prior investigations, these results suggest that differences in heterogeneous nucleation of the C‐S‐H on filler particle surfaces, caused due to differences in their interfacial properties, have little if any effect on C3S hydration kinetics.

Analysis of aluminum concentrations in the pore solution during hydration of tricalcium silicate

The hydration of two batches of tricalcium silicate was followed by isothermal heat conduction calorimetry and analysis of pore solution composition. These two samples were different in Al2O3-content and free lime concentration. It was observed that the material containing aluminum reacts slower than the pure one. The reactivity was also analyzed in the presence of ettringite, gypsum and tricalcium aluminate, respectively.The aluminum concentration in the pore solution was always below the limit of detection during hydration of the samples independent of the presence of aluminum in tricalcium silicate or the addition of most supplementary phases. Elevated aluminum concentrations were only observed in the presence of tricalcium aluminate.The experimental investigations confirm earlier results that aluminum can reduce the reactivity of tricalcium silicate. It is shown in this study that this mechanism is not based on elevated aluminum concentrations in the pore solution.

Quantification and characterization of C-S-H in silica nanoparticles incorporated cementitious system

This paper presents the quantification and nanomechanical properties of calcium silicate hydrate (C-S-H), formed at early stage hydration of tricalcium silicate (major cement phase) in presence of silica nanoparticles (SNPs). SNPs showed dominant nucleation effect at 8 h and pozzolanic effect at 24 h and accelerate the hydration rate (∼83% at 8 h and ∼51% at 24 h) due to the formation of additional C-S-H nuclei. Further, 29Si-NMR and FTIR techniques showed the acceleration in polymerization of silicate chain leading to the formation of tobermorite like structure. Formation of polymerized and crystalline C-S-H gel in presence of SNPs increases the percentage of high density C-S-H (∼40%) and lowers the low density C-S-H (∼52%) at 24 h of hydration, as observed in nanoindentation results.

Effects of nano-limestone on hydration properties of tricalcium silicate

In this research, the influences of nano-limestone (NC) on tricalcium silicate (C3S) hydration, including early hydration rate, setting time, Ca(OH)2 content, quantification of C–S–H, micrographs of hydration products and compressive strength, were investigated by different methods. Calorimetry results show that the first and second exothermic peak of C3S with 1 mass% NC is ~29 and ~5% higher than that of control sample and the second peak appears 32 min in advance. Besides, the total hydration heat of C3S with 1 mass% NC increases by 10.08% compared to control sample at 72 h. The initial and final setting time of C3S with 1 mass% NC shortens by 23 and 17 min, respectively. In addition, thermal analysis results show that adding NC leads to higher Ca(OH)2 and C–S–H content at all ages (1, 3 and 28 days). All of the above results imply that the hydration progress of C3S is accelerated by NC. Correspondingly, the compressive strength of C3S with 1 mass% NC increases by 9.88% at 28 days. Besides, EDS results reveal that the Ca/Si ratio of C–S–H gel decreases after NC modification. However, excessive content NC (4 mass%) reduces the acceleration effect of NC on C3S hydration and finally leads to relative low content of Ca(OH)2 and C–S–H compared with C3S sample containing 1 mass% NC.

Modeling the effect of fineness and filler in early‐age hydration of tricalcium silicate

Alite (impure C3S) being the major and most reactive phase in ordinary portland cement has been studied extensively. This paper focuses on the mathematical modeling of new hypothesis developed, densified volumetric growth, applied to the main hydration peak in alite hydration. This hypothesis assumes a time and particle size‐dependent growth rate and densification rate of C–S–H controlled by its internal surface area. To test this hypothesis, a new microstructural modeling platform (Cementitious Reactions Simulator) has been developed. The model was used to calibrate and predict the isothermal calorimetric results from the literature and two sets of original experimental results with alite replaced with different replacement fractions of quartz, fly ash, and slag of different fineness. The model is able to capture and predict the effect of fineness and fillers without the need of varying the parameters for the particular set of simulations. The values of the parameters of simulation reflect the current experimental evidence from the literature and thus provide validation of the hypothesis which suggests that the main hydration period including deceleration period in the alite hydration is induced by the densification and reducing outer growth rate of C–S–H.

In Situ Soft X-ray Spectromicroscopy of Early Tricalcium Silicate Hydration.

The understanding and control of early hydration of tricalcium silicate (C3S) is of great importance to cement science and concrete technology. However, traditional characterization methods are incapable of providing morphological and spectroscopic information about in situ hydration at the nanoscale. Using soft X-ray spectromicroscopy, we report the changes in morphology and molecular structure of C3S at an early stage of hydration. In situ C3S hydration in a wet cell, beginning with induction (~1 h) and acceleration (~4 h) periods of up to ~8 h, was studied and compared with ex situ measurements in the deceleration period after 15 h of curing. Analysis of the near-edge X-ray absorption fine structure showed that the Ca binding energy and energy splitting of C3S changed rapidly in the early age of hydration and exhibited values similar to calcium silicate hydrate (C–S–H). The formation of C–S–H nanoseeds in the C3S solution and the development of a fibrillar C–S–H morphology on the C3S surface were visualized. Following this, silicate polymerization accompanied by C–S–H precipitation produced chemical shifts in the peaks of the main Si K edge and in multiple scattering. However, the silicate polymerization process did not significantly affect the Ca binding energy of C–S–H.

Effects of hexitols on the hydration of tricalcium silicate

The hydration of tricalcium silicate (C3S) in presence of hexitols (d-glucitol, d-galactitol and d-mannitol) which only differ by their stereochemistry was followed by using calorimetric and conductometric measurements of the pastes and of the diluted suspensions respectively. Hexitols delay the acceleration of the growth of C-S-H and enhance the quantity of C-S-H when the maximum rate of C3S hydration is reached in relation to the stereochemistry of their hydroxyl groups: d-glucitol>d-galactitol>d-mannitol. Their relative retarding effect is shown to change depending on their sensitivity to calcium ions at pH found in cement paste. In diluted suspension in solutions representative to a cement paste, alditols are shown to retard C3S hydration whereas its dissolution is not limited suggesting an impact of the molecules on the precipitation of C-S-H.

Effects of nano-silica on hydration properties of tricalcium silicate

In order to evaluate the influence of nano-silica on tricalcium silicate (C3S) hydration, hydration rate, Ca(OH)2 content, quantification of C–S–H, pore size distribution and micrographs of hydration products were measured. Results revealed that with the increase content of nano-silica, the hydration of C3S is accelerated before hydration for 3d but slows down in the later age (7d, 28d and 60d). C–S–H content increases with the increase content of nano-silica. However, an obvious reduction in C–S–H increment occurs at 7d, 28d and 60d. In addition, the hydration products morphology changes from rod-shape to dense matrix at 28d after nano-silica modification, and the Ca/Si ratio of C–S–H gel decreases. Besides, the addition of 3wt.% nano-silica can reduce the total porosity of C3S by 4.04% and optimize the pore structure. Furthermore, the density of paste increases by 4.22%, which finally leads to the more compact structure of hardened paste.

Effects of functionality and stereochemistry of small organic molecules on the hydration of tricalcium silicate

The retardation and the maximum rate of tricalcium silicate (C3S) hydration induced by organic molecules were rarely measured as a function of their molar concentration and prevent us to identify the effect of specific functional groups carried by the molecules. In this study, the maximum rate of C3S hydration which is proportional to the maximum heat flow and the retardation led by different concentrations of organic molecules was determined using the monitored calorimetric curves of the C3S pastes. The effect of the charge, functionality and stereochemistry was studied by using a set of sugar alcohols (d-glucitol, d-galactitol…), sugar acid anions (d-gluconate, d-galactarate…), carboxylate (adipate) and amines with functionalized sulfonate, carboxylate and phosphonate groups (EDTA, EDTMP…).This study reveals that the maximum rate of C3S hydration is enhanced in the presence of the organic molecules and that the retardation is increased with their concentration. The nature of the ending functional group of the molecules (hydroxyl, hydroxy-carboxylate, carboxylate, sulfonate or phosphonate), their main chain group (hydrocarbon or polyol chain) and the stereochemistry of their hydroxyl groups are shown to play a role.

A new view on the kinetics of tricalcium silicate hydration

C3S hydration is an interesting example of chemical coupling between C3S dissolution, C–S–H and portlandite precipitation. It occurs because Ca2+, OH− and silicate ions are present in C3S, in both hydration products and in the surrounding solution. Various experimental data sets reveal that the undersaturation with respect to C3S always increases when C3S hydration enters into the deceleratory phase, leading to the conclusion that C3S dissolution is at the origin of this deceleration, not C–S–H growth. In addition, as soon as portlandite precipitates, the dissolution limits the hydration already in the acceleratory hydration step. The evolution of the undersaturation cannot account for the hydration peak. Rather, it results from an extension and subsequently a decrease of the C3S reactive surface area. The formation and coalescence of dissolution etch-pits can provide a reasonable explanation for the C3S hydration kinetics.

State of Water in Hydrating Tricalcium Silicate Pastes: The Effect of a Cellulose Ether

Time-dependent quasi-elastic neutron scattering (QENS) and differential scanning calorimetry (DSC) were applied to study water dynamics and hydration kinetic of the hydration reaction of tricalcium silicate in the presence of a methyl hydroxyethyl cellulose (MHEC) additive. The translational dynamics of the water confined in the developing hydrated calcium silicate matrix was probed at the molecular scale by QENS during the first 4 days, while the evolution of the matrix porosity and the hydration kinetics were determined up to 28 days of hydration by differential scanning calorimetry. The application of the boundary nucleation and growth model consistently improved the hydration kinetics picture, usually obtained from the application of the classical Avrami-Erove’ev model, allowing the evaluation of the individual contributions of nucleation and growth over the entire hydration process. In the presence of the cellulose ether the nature of the nucleation process is strongly modified, approaching a “spatia...

The Influence of Water Activity on the Hydration Rate of Tricalcium Silicate

Tricalcium silicate does not undergo hydration at relative humidities (RH's) below 80%. But, the rate at which its hydration rate decreases as a function of the RH has not yet been elucidated. By invoking correspondence between RH and water activity (aH, unitless), both of which are related to the chemical potential of water, the reaction evolutions of triclinic tricalcium silicate (i.e., T1‐Ca3SiO5 or C3S) are tracked in water + isopropanol (IPA) mixtures, prepared across a wide range of water activities. Emphasis is placed on quantifying the: (a) rate of hydration as a function of aH, and (b) the critical (initial, aH0c or the achieved) water activity at which hydration effectively ceases, i.e., does not progress; here identified to be ≈ 0.70. The hydration of tricalcium silicate is arrested even when the system remains near saturated with a liquid phase, such that small, if any, capillary stresses develop. This suggests that changes in chemical potential induced via a vapor‐phase or liquid‐phase route both induce similar suppressions of C3S hydration. A phase boundary nucleation and growth (pBNG) model is fit to measured hydration rates from the onset of the acceleration period until well beyond the rate maximum when the water activity is altered. The simulations suggest that for a fixed hydrate nucleation density, any water activity reductions consistently suppress the growth of hydration products. Thermodynamic considerations of how water activity changes may influence reactions/hydrate evolutions are discussed. The outcomes improve our understanding of the chemical factors that influence the rate of Ca3SiO5 hydration.

Effect of Carbon‐Based Materials on the Early Hydration of Tricalcium Silicate

Two types of carbon‐based materials, i.e., mesoporous carbon and HNO3‐oxidized carbon nanotubes, with nearly the same specific surface area and abundant in surface oxygen‐containing functional groups were selected in order to examine their effect on the hydration of tricalcium silicate (C3S), the main portland cement component, in early stages. Different methods, including XPS and TG‐MS analyses, electrokinetic potential measurements, as well as determination of adsorption capacity for calcium ions from aqueous solutions, were used to investigate the physicochemical surface properties of the selected carbon‐based materials. It was found that the carbon‐based materials with high specific surface area and rich in oxygen‐containing functional groups on their surfaces have a catalytic effect on early C3S hydration. It was observed that the modification of C3S paste with the selected materials added in high concentrations (1 wt% and higher) led to an increase in the rate and degree of C3S hydration in the early stages. The mechanism of early C3S hydration accelerated by carbon‐based materials rich in surface functional groups was clarified by the example of the mesoporous carbon. It was found that the oxygen‐containing functional groups present on the carbon surface have both an influence on the content of calcium ions in the aqueous phase of the C3S paste and an indirect positive effect in relation to the specific surface of C3S.

Calorimetric study of the early stages of the nanosilica - tricalcium silicate hydration. Effect of temperature

The pozzolanic reaction of nanosilica in contact with C3S was monitored via isothermal conduction calorimetry. Since that reaction is affected by heat, its variations with curing temperature (25, 40 and 65 °C) were also analysed. The findings showed that while C3S hydration was accelerated by both nSA and higher curing temperature, the former impacted the reaction more intensely. Moreover, the presence of nSA was observed to shorten the acceleration stage during C3S hydration, inducing earlier precipitation of portlandite and earlier C-S-H precipitation and nucleation.

Composition, silicate anion structure and morphology of calcium silicate hydrates (C-S-H) synthesised by silica-lime reaction and by controlled hydration of tricalcium silicate (C3S)

The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesised via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/without accelerators. The silicate anion structure of the samples was studied by 29Si magic angle spinning nuclear magnetic resonance spectroscopy and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]<22 mmol L− and fibrillar C-S-H for [CaO]>22 mmol L−1. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators.

Soft X‐ray Ptychographic Imaging and Morphological Quantification of Calcium Silicate Hydrates (C–S–H)

Morphological details of calcium silicate hydrate (C–S–H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC‐based systems but are still only partially known. Here we introduce the first soft X‐ray ptychographic imaging of tricalcium silicate (C3S) hydration products. The results are compared using both scanning transmission X‐ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C–S–H of fully hydrated C3S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high‐resolution ptychrography image enables us to perform morphological quantification of C–S–H, and, for the first time, to possibly distinguish the contributions of inner and outer product C–S–H to the small angle scattering of cement paste. The results indicate that the outer product C–S–H is mainly responsible for the q−3 regime, whereas the inner product C–S–H transitions to a q−2 regime. Various hypotheses are discussed to explain these regimes.