Minutes Of Hydration Research Articles

Analysis of cementitious pore solutions with very high time resolution by coupling cross flow filtration and ICP-OES

Pore solution analysis is a powerful tool for understanding reactions that occur during the cement hydration. Crossflow filtration of cement paste provides more detailed insight into reactions and reaction pathways compared to standard methods for gaining pore fluid. In particular, the large time resolution for the analysis enables the characterization of fast processes like adsorption kinetics and hydration reactions of aluminate phases in unprecedented detail. A direct comparison of the crossflow filtration results with those obtained using a filter press showed no significant difference in pore solution composition. With this method, it is possible to analyze the complex reaction patterns of cementitious reactions in great detail during the first minutes of hydration. This is especially important for chemically admixed systems.

Early-age hydration mechanism of ternary binders: Quantitative relation between microstructure evolution and strength build-up

The goal of this study is to develop a better understanding of the working mechanisms of CACC$ acceleration of OPC in the first hour and establish a quantitative link between the progress of hydration, strength build-up and associated microstructure evolution. Monitoring the progress of reaction using isothermal calorimetry in the first few minutes of hydration is difficult owing to the limitations associated with the measurement method. We have developed a method to correct the heat data in the first minutes, which along with ICP data of elements Ca, Al and S, enables a quantification of the amounts of various phases dissolving and/or precipitating at different times after acceleration. It is concluded that strength build-up is directly proportional to heat of hydration up to a certain point, irrespective of accelerator dosage. However, beyond this point, there is a change of mechanism which is likely attributed to physical effects rather than chemical ones. Additionally, it was also found that the amount of available CA controls the rate of reaction and that the impact of CAC addition to OPC follows a decay function type heat release.

Early hydration of belite-ye’elimite-ferrite cements: Role of admixtures

The effect of TIPA and CaCl2 on early hydration, i.e. 24 h, of a B-BYF cement has been studied by in situ synchrotron X-ray powder diffraction, calorimetry, thermal analysis, NMR, and rheological measurements of the pastes and mechanical strength of the corresponding mortars. The addition of 0.05 %bwc (by weight of cement) of TIPA reduced the viscosity of the paste during the first minutes of hydration but, after the end of the induction period, ∼7 h, it favored the formation of AFt compared to the reference paste. The latter is likely due to the acceleration of the dissolution of the amorphous aluminates and sulfates by the presence of TIPA. These results correlate with the increase of ∼169% of the 1-day mechanical strengths. The addition of 2.0 %bwc of CaCl2 accelerated the dissolution rate of ye’elimite, causing an increase of the amount of precipitated ettringite even before the end of the induction period, which has been shorted to ∼6 h. The 1-day mechanical strengths of the mortars with this admixture outperforms that of the reference mortar by 181%. Finally, ferrite and α’H-belite reactivities were not affected by the addition of any of these admixtures during the first 24 h of hydration of this cement.

Rheology, calorimetry and electrical conductivity related-properties for monitoring the dissolution and precipitation process of cement-fly ash mixtures

The process of dissolution and precipitation of hydrated cement-fly ash mixtures is the basis of rheological behaviour and the establishment of mechanical strength over time. In this paper, the dissolution and precipitation process of cement-fly ash mixtures was monitored by rheology, calorimetry and electrical conductivity measurements.Two FAs supplied from different thermal power stations are used.The physical and chemical properties of FAs, including particle size and glassy phase, are shown to have various effects on the rheology and hydration kinetics of modified cement pastes.Calorimetry and electrical conductivity findings are in agreement to corroborate the dissolution process during the first minutes of hydration, followed by the precipitation of hydrated products, mainly portlandite, during the acceleration period. The addition of FAs leads to the prolongation of the dormant period and the slow dissolution of cement species by diffusion through the formed hydrate layer around the surface of cement particles. • Cement partially (10, 20, 30, 40%wt) replaced with altered FAs. • FA type affected the hydration degree and electrical conductivity. • The rheological properties are more related to the FA particle size. • The glassy phase has higher influence on the mechanical performance than the fineness of FA.

Production, Composition, and Ecological Function of Sweet-Basil-Seed Mucilage during Hydration

The sweet-basil (Ocimum basilicum L.) fruit/pericarp produces mucilage that engulfs the fruit and seed within minutes of hydration. Seed mucilage is produced by plant species that have adapted to arid, sandy soils. This study was conducted to determine how basil-seed mucilage improves ecological fitness. A second objective was to find ways to remove mucilage, which may interfere with commercial planting. Basil fruit/seeds were examined using light and environmental scanning electron microscopy. Columnar structures of basil mucilage rapidly unfolded from the pericarp upon initial hydration. Dilute hydrochloric acid removed the mucilage, which decreased the water content four-fold but did not inhibit seed germination in a laboratory test. Nondestructive Fourier-transform mid-infrared (FTIR) spectroscopy confirmed that the mucilage was primarily composed of hemicellulose that anchored the basil seed to resist movement. The fully hydrated seeds approached zero water potential, so the mucilage did not interfere with hydration. The seeds that were planted in growing media with mucilage had from 12 to 28% higher seedling emergence and survival percentages after 10 days than seeds without mucilage. Basil-fruit/seed mucilage provides a reservoir of loosely bound water at high water potential for seed germination and early seedling development, thus improving survivability under low moisture.

High- and ultra-high-performance concrete produced with sulfate-resisting cement and steel microfiber: Autogenous shrinkage, fresh-state, mechanical properties and microstructure characterization

High-performance concrete (HPC) and ultra-high-performance concrete (UHPC) are cement-based composites that present improved mechanical performance and durability. However, their low water/binder ratio and high binder content lead to significant autogenous shrinkage. This work investigated the autogenous shrinkage of HPC and UHPC produced with sulfate-resisting cement and steel microfiber in volumetric fractions (Vf) of 0–1.5%, from the first minutes of hydration. In addition, fresh performance (mini slump flow), hardened properties (dynamic modulus of elasticity – Ed, compressive and flexural strength at 28 days) and microstructure (SEM-EDS) were evaluated. Results showed that steel microfiber incorporation progressively reduced the autogenous shrinkage of both HPC and UHPC (by up to 11% and 22%, respectively) because of the increased resistance to volumetric reduction caused by the capillary pressure. The fresh-state performance of UHPC was not affected by microfiber incorporation (mini slump flow of 305–310 mm), while increasing Vf progressively reduced the mini slump flow of HPC from 305 mm (Vf 0%) to 262 mm (Vf 1.5%); this behavior was associated with the viscosity of the mixes. Furthermore, increasing Vf progressively increased the compressive strength (by up to 8% for HPC and 23% for UHPC) and the flexural strength (by up to 23% for HPC and 47% for UHPC) due the inhibition in propagation and opening of microcracks, while no significant differences were observed in the Ed. In turn, 0.75% microfiber incorporation in UHPC increased the air content by 80%, thus reducing its flexural strength. SEM-EDS analysis indicated the absence of chemical bond between the fiber and the cementitious matrix, suggesting that this interaction was essentially mechanical. Overall, steel microfibers incorporation was effective in reducing the autogenous shrinkage of HPC and UHPC produced with sulfate-resisting cement, in addition to keeping or even improving the mechanical performance of the composites.

Reaction of clinker surfaces investigated with atomic force microscopy

The application of microscopy to investigate cement hydration has widely spread in the last decades. For instance, scanning electron microscopy (SEM) is of primary importance to detect the formation of microstructures and detect their chemical composition. In this work, atomic force microscopy (AFM), which is a relatively less diffused technique, is applied to illustrate and estimate changes of the surface roughness of a clinker substrate, treated with different electrolytic solutions, with and without superplasticizer, at different times of hydration. Furthermore, SEM images are collected to characterize the chemical composition of hydration products formed on the clinker surface. It is shown that surface reaction increases drastically with the increase of the pH, and that surface roughness changes occur mainly in the first minutes of hydration. Moreover, the formation of hydration products is reduced when the clinker is treated with solutions containing polycarboxylate ether-based superplasticizer. Additionally, AFM images collected in tapping mode revealed the presence of nano-structures on calcium silicate phase.

The role of Cl− in pollen germination and tube growth

The involvement of Cl− in cytoplasm polarization in the pollen tube and membrane potential control during pollen germination in vitro was studied by fluorescence techniques in Nicotiana tabacum. Cl− release from cells was blocked by the anion channel inhibitor nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) or by the addition of Cl− to the incubation medium. The concentrations of the inhibitor (40 μM) and extracellular Cl− completely inhibiting pollen germination (200 mM) and pollen tube growth (100 mM) were used. The release of anions from the pollen grain has been revealed in the first minutes of hydration also in the presence of 200 mM Cl−. The inhibitor blocked this process completely, which points to the significance of the NPPB-sensitive anion channels in the transmembrane Cl− transport at the early activation stage. The pollen tube membrane was hyperpolarized in the presence of 100 mM Cl−; however, exogenous Cl− had no effect on the compartmentalization and organelle movement in the tube. The inhibitor depolarized the plasma membrane in the pollen grain and tube and affected the polar organization of the cytoplasm and organelle movement. Thus, activity of NPPB-sensitive chloride channels was required to regulate the potential on the plasma membrane and to maintain the functional compartmentalization of the cytoplasm, which provides for the polar growth.

Proton NMR relaxation as a probe for setting cement pastes

We report a 20-MHz proton nuclear magnetic resonance T1 relaxation study of cement paste hydration in the early stages of setting, using different centimeter-sized samples of cements of various origins and different water-to-cement ratios. In every sample, during the first few minutes of hydration, it is found that inverse Laplace processing of inversion-recovery measurements systematically exhibits at least two T1 values: a long one, around 100 ms, whose value correlates well with water content and which may be attributed to bulk water surrounding cement grains; and a short one, around 2 ms, which is quite insensitive to water-to-cement ratio and which may be attributed to water embedded in floculated cement grains before setting occurs. The time evolution of the longest T1 value for several hours is also shown to exhibit a characteristic five-stage behavior that is well correlated with known stages of the hydration process: initial reaction, induction period, acceleration period, deceleration period and slow hydration reaction. These results are compared with calorimetric measurements and electrical conductivity literature.

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The application of microscopy to investigate cement hydration has widely spread in the last decades. For instance, scanning electron microscopy (SEM) is of primary importance to detect the formation of microstructures and detect their chemical composition. In this work, atomic force microscopy (AFM), which is a relatively less diffused technique, is applied to illustrate and estimate changes of the surface roughness of a clinker substrate, treated with different electrolytic solutions, with and without superplasticizer, at different times of hydration. Furthermore, SEM images are collected to characterize the chemical composition of hydration products formed on the clinker surface. It is shown that surface reaction increases drastically with the increase of the pH, and that surface roughness changes occur mainly in the first minutes of hydration. Moreover, the formation of hydration products is reduced when the clinker is treated with solutions containing polycarboxylate ether-based superplasticizer. Additionally, AFM images collected in tapping mode revealed the presence of nano-structures on calcium silicate phase.

Importance of adequate soluble alkali content to ensure cement/superplasticizer compatibility

The effect of soluble alkalis on cement/superplasticizer compatibility has not yet been thoroughly understood. This paper establishes the impact that soluble alkalis have on the compatibility of cement and polynaphthalene sulfonate superplasticizer during the first few minutes of hydration. The amount of soluble alkalis that go into solution during the first few minutes is a key parameter in controlling fluidity and fluidity loss of a cement paste made with superplasticizer. The optimum soluble alkali content for increasing initial fluidity and decreasing fluidity loss with time was found to be on the order of 0.4%–0.5% Na 2O equivalent in the six cements under study. Furthermore, this optimum alkali content is independent of the superplasticizer dosage and cement type. In cement with an optimum amount of soluble alkalis, the C 3A content has practically no effect on fluidity loss.

Enlarging pediatric i.v. catheters.

The Streamline (Menlo Care, Menlo Park, CA) intravenous catheter is constructed of an elastomeric hydrogel (Aquavene) that softens and increases in diameter when exposed to aqueous solutions. The flow rates of 22-gauge x 1'', 24-gauge x 0.7'', and 26-gauge x 0.625" catheters were ascertained during 90 minutes of hydration in 37 degrees C normal saline. Ten tests of each size catheter were performed every 15 minutes starting at 0 minutes and continued throughout the 90-minute period of hydration. Each test consisted of measuring the time for 10 ml of saline to flow through the catheter. All three gauges had a significant increase in flow and reached a maximum at the 75 minute test. Maximum increase in flow rates were 43, 39, and 32% for the 22-, 24-, and 26-gauge catheters, respectively. None of the catheters exceeded the initial flow rate of the next larger gauge catheter.

Early hydration of large single crystals of tricalcium silicate

A reaction product believed to be an initial hydrate layer was observed to have formed on large pure C 3S single crystals after 5 minutes of hydration. This layer then increased in thickness and became covered with micrometer-sized spheres of poorly crystallized Ca(OH) 2 within 30 minutes. Subsequently, the formation of a new hydrate of acicular morphology was observed to occur on the surface of the first-formed hydrate. This transformation was accompanied by the disappearance of the first hydrate layer and the calcium hydroxide spheres. The observation of a transient initial hydrate is in accord with the view that the rate of early C 3S hydration is controlled by the formation and subsequent disappearance of a barrier layer.

Calcium and silicon concentrations in solution during the early hydration of portland cement and tricalcium silicate

The solution chemistry of Portland cement and C 3S pastes has been studied with particular attention to the concentrations of calcium and silicon in the aqueous phase during early stages of hydration. Results are discussed in relation to solubility data available from studies of OPC and C 3S pastes and from the CaOSiO 2H 2O system. It is shown that under normal conditions the concentration of silicon in solution is extremely low (<2ppm) and this remains unchanged even when hydration is accelerated in the presence of CaCl 2. However, retarding admixtures such as oxalic acid and EDTA, which are strong calcium binding agents, release a flush of silicon into solution within the first few minutes of hydration. The results lend support to the osmotic membrane model of cement hydration and also provide insight into the mechanisms by which accelerating and retarding admixtures function.

Dimensional stability of two gas-permeable,hard contact lens materials: Some preliminary findings

Dimensional stability of a contact lens has been defined by Gordon' as the ability to maintain the original back central optic radius (B. C. O. R.) over an extended period. The curvature of hard corneal lenses is known to change when they are immersed in fluid and become hydrated. Corneal lenses manufactured of poly (methyl methacrylate) (P.M.M.A.) of low minus and of plus power flatten in the course of hydration. Minus lenses of moderate and high power undergo an initial phase of steepening before flattening. If the lenses are subsequently allowed to dehydrate, plus power lenses undergo an initial steepening and minus lenses an initial flattening prior to reverting to their original curvature. ~ 2 a It has been noted that the magnitude and time course of curvature changes during 168 hours of hydration varied with different materials and that cellulose acetate butyrate (C.A.B.) lenses were subject to marked flattening. 4 Stone s reported that lathe-cut C.A.B. lenses underwent rapid and extensive changes in curvature in the course of 24 hours of hydration and 22 hours of dehydration. Difficulty has been encountered in the measurement of the B.C.O.R. of C.A.B. lenses by means of the radiuscope since changes in curvature occurred in the course of measurement. 4 s To overcome this problem, Pearson 6 has measured changes in the B. C.O.R. of lathe-cut bi-curve C.A.B. lenses in the course of 336 hours of hydration using the wet cell and keratc meter method commonly used for soft lenses. Minus lenses of moderate to high power were found to steepen maximally after six minutes of hydration. After several hours of hydration, most lenses had flattened from their original curvature by about 0.05 mm. but after 48 hours, further changes occurred, the two high minus powered lenses flattening by 0.40 ram. The purpose of the present study was to investigate the dimensional stability of moulded C.A.B. lenses and to make a comparison with a modifed P.M.M.A. material of similar oxygen permeability.