Mössbauer and calorimetric studies of portland cement hydration in the presence of black gram pulse

Effect of different concentrations of naturally occurring admixture in the form of fine powder of black gram pulse (BGP) on the hydration of Portland cement was studied by isothermal calorimetry and ⁵⁷Fe Mössbauer spectroscopy. The spectra were recorded for anhydrous cement and the hydration products at room temperature and 77 K. In the presence of BGP, the spectra showed superparamagnetic doublets at room temperature and the sextet at 77 K, due to the presence of fine particles of iron containing component. Mössbauer studies of hydration products confirmed the formation of nanosize hydration products containing Fe^3?+?. The isomer shift (δ) and the quadrupole splitting (ΔE _Q) values of C₄AF in the cement confirmed iron in an octahedral and tetrahedral environment with +3 oxidation state. The high value of quadrupole splitting showed the high asymmetry of the electron environment around the iron atom. The overall mechanism of the hydration of cement in presence of BGP is discussed.     

A remark on nano-particle stability of cement C-S-H gel

Hydrated pastes of ordinary Portland cement prepared with different water-to-cement ratios were investigated by using the small-angle neutron scattering technique in the region of Q ∈ (0.0045, 0.11) Å^?1. Samples of cement pastes were subjected to non-standard hydration conditions using a mix with D₂O, low RH, and water-to-cement ratios spread over a very wide interval (0.4; 1.4). The investigation was focused on testing the structural stability of nano-metric particles in the cement C-S-H gel. Owing to the high structural stability of these nano-particles, their average diameter might be used as a microscopic parameter characterizing the nano-metric structure of C-S-H gels. The average diameter of the nano-particles of the studied ordinary Portland cement CEMI 42.5 R-SC was found to be close to the value of 4.2 nm and independent of the water-to-cement ratios.     

Electron paramagnetic resonance study on metakaolin-admixtured cement paste at different hydrated periods

The present work reports the effect of metakaolin (MK) on the properties of Portland cement through electron paramagnetic resonance study. Cement pastes containing 0%, 10%, 20% and 30% replacements of MK with cement and a water to cement ratio of 0.4 have been prepared. The g factors of Fe(III) and Mn(II) impurities at different hydration ages have been related to changes in the setting time of cement. The increase in g _Fe values and simultaneous decrease in g _Mn values with an increase in the replacement percentage of MK are explained due to pozzolanic reaction.     

Factors Affecting Early-Age Hydration of Ordinary Portland Cement Studied by NMR: Fineness,Water-to-Cement Ratio and Curing Temperature

The aim of the present study was to apply nuclear magnetic resonance (NMR) relaxation measurements for understanding the microstructure evolution of cement paste during hydration. Ordinary Portland cement powder was mixed with double-distilled water, and hydration process was analyzed via ¹H proton NMR spin–spin relaxation time. In order to induce strong modification of the rate of hydration, water-to-cement ratio, curing temperature and cement fineness were varied. The evolution of the NMR spin–spin relaxation time, T ₂, of hydrating water versus the hydration time was monitored from the very first few minutes after the mixing up to several hours. Authors' address: Marcella Alesiani, Department of Physics, University La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy     

The hardening of Portland cement observed by1H spin-lattice relaxation and single-point imaging

The nature of hydration in ordinary Portland cement samples from different Polish factories was investigated by the proton spin-lattice relaxation timeT ₁ and single-point imaging (SPI). The time dependence of the spin-lattice relaxation timeT ₁ shows the usual behavior:T ₁ is constant at the beginning of hydration (the dormant period), then, during the setting process, decreases to the constant value in the hardening period of hydration. However, there are some anomalies inT ₁ connected with the different amount of the mineral components in the cement sample. The unusual behavior of the stretched parameterα, after about 20 h of hydration, is observed and connected with the microcracking of the cement matrix. The 1-D and 2-D SPI images of the cement paste taken at various times of hydration show the distribution of the water throughout the sample and clearly demonstrate the usefulness of SPI in the study of the internal structure of the porous system.     

Microstructure and properties of Pb(Mg1/3Nb2/3)O3–Portland cement composites

Lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), ceramics particles was mixed with Portland Cement (PC) using a water to cement ratio of 0.50 and PMN content at 40% and 60% by weight to produce 0–3 Pb(Mg_1/3Nb_2/3)O₃–Portland cement (PMN–PC) composites. Microstructure and hydration of the composites were investigated. Calcium silicate hydrate gel can be seen surrounding the PMN particles. Dielectric constant of the composites was found to increase with PMN content. Successful poling of the composites was achieved. Interestingly, SEM micrographs of the PMN40 composite clearly showed calcium silicate hydrate gel (an essential hydration product of Portland cement) surrounding the PMN particles. In PMN60 composite, the gel can also still be seen but of less quantity. This is thought to be due to the increase in the volume ratio of the ceramics where the amount of calcium silicate hydrate gel was reduced in relation to the overall volume.     

Behavior of multi-walled carbon nanotubes on the porosity and microstructure of cement-based materials

The porosity and microstructure of a Portland cement-multi-walled carbon nanotube composite were investigated. Multi-walled carbon nanotubes (CNTs), up to 1 wt.% of cement, synthesized by infusion chemical vapor deposition, and Portland cement type I (PC) were used to produce pastes with a water to cement ratio of 0.5. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to characterize Portland cement-CNTs systems. MIP analysis of the results indicates that total porosity of the mixes with CNTs was found to decrease with increasing CNTs content. Moreover, an important effect of additional CNTs was a reduction in the number of mesopores, while SEM technique showed dispersion of CNTs between the hydration phases of Portland cement pastes.     

Two-dimensional correlation relaxation studies of cement pastes

Two-dimensional nuclear magnetic resonance relaxation correlation studies of cement pastes have been performed on a unilateral magnet, the Surface GARField. Through these measurements, the hydration process can be observed by monitoring the evolution of porosity. Characteristic relaxation time distributions have been observed in different cement pastes: fresh white cement, prehydrated white cement and ordinary Portland cement. The observed T(1)/T(2) ratio in these cements has been shown to agree with expectations based on high field values.     

Theoretical and experimental study of structures and properties of cement paste: The nanostructural aspects of C-S-H

Ordinary Portland cement (OPC) paste with water to cement ratio 0.5 has been studied by FTIR spectroscopy and TEM/SAED techniques. The progressive shift in frequencies and change in intensity of characteristic peaks in the FTIR spectra of cement powder indicate polymerization of silicates due to hydration reaction. The appearance of new peaks around 975-985 and 3640-3650 cm⁻¹ in FTIR spectra of cement paste has been attributed to the formation of two principal hydration products (C-S-H) and Ca(OH)₂, respectively. There is a strong resemblance of peak shape at 980 cm⁻¹ of cement paste with that of synthesized 1.1 nm Tobermorite. TEM/SAED techniques reveal the presence of three distinct types of C-S-H nanostructures viz. spherical particles, fibres and bundle of fibres, and nano tubes in cement paste. Theoretical study of two C-S-H clusters by MNDO and Density Functional Techniques shows excellent agreement between computed structural data and reported experimental results of Tobermorite and Jennite. The computed interplanar Ca-Ca distance (11.162 Å) of C-S-H cluster (Ca/Si=1.125) indicates greater structural similarity of this cluster to 11 Å Tobermorite. There is a strong similarity of IR profile of C-S-H cluster (Ca/Si=1.125) with 1.1 nm Tobermorite. Above study indicates that this cluster is probably the most likely basic unit of C-S-H phases formed during the early stage of OPC cement hydration.     

Dielectric and piezoelectric properties of PZT–silica fume cement composites

PZT–silica fume cement (PZT–SFC) composites were produced using PZT (at 50% and 60% by volume) and silica fume cement (cement containing silica fume of 5% and 10% by weight). PZT–Portland cement with no silica fume was also produced to allow comparison of the results. Dielectric constants of PZT–SFC composites are found to be higher than that of PZT–PC composite where ε_r value was found to increase with increasing SF content (ε_r values of composite with SF at 0%, 5% and 10% are 117, 125 and 178, respectively). PZT–SFC composites were successfully poled and d₃₃ results of PZT–SFC composites (d₃₃ = 18 pC/N) were found to be marginally higher than that of PZT–PC composite (d₃₃ = 17 pC/N). SEM micrograph also shows a dense matrix of SFC hydration product surrounding the PZT particles. From the results, these PZT–SFC composites are therefore promising materials for use in structural applications and should be ideal for high strength structures where SFC is used in the host structure.     

Translational diffusion of water in compacted clay systems

The translational diffusion of water in compacted clays at a high hydration level has been investigated by quasielastic neutron scattering at a time-of-flight spectrometer FOCUS (SINQ). Four compacted clays with systematic structural differences have been studied: Na-montmorillonite, Na-illite, kaolinite and pyrophyllite. The QENS experiments were performed using two different incident wavelengths in order to access a larger Q range and verify the data analysis. The translational diffusion coefficient for water in Na-montmorillonite and Na-illite are lower than those for bulk water, whereas the preliminary results for kaolinite and pyrophyllite show larger diffusion coefficient.     

Acoustical properties of aerated autoclaved concrete

This work analyses acoustic qualities of autoclaved aerated concrete (AAC). Three the most widely used types of AAC are chosen for the analysis: gas cement concrete, gas cement concrete with combined binder (Portland cement and lime), and foam cement concrete. The procedure and technique of the materials’ formation is presented in this work. The evaluation of acoustic qualities of AAC is based on the material’s air permeability and porosity (i.e., ratio of the volume of the interconnected pores to the total volume of pores). For this purpose the measurements obtained by an acoustic interferometer are used. The results of the experiment show that regression equations for the AAC types, which density ranges from 250 to 500 kg/m³, may be used to estimate the materials’ normal incidence absorption coefficient values, which depend on the air permeability and porosity. Results show that absorption coefficient of not specially treated AAC is rather low. According to the measurements obtained in a special reverberation room of 202 m³, a sound absorption coefficient may increase up to 0.6, provided that slits of Helmholtz resonator’s type are made in the slabs of AAC gas cement concrete with combined binder.     

119Sn and121Sb Mössbauer studies of BaSn1−x Sb x O3 Perovskite system

The relations between the electrical characteristics of BaSn_1?x Sb _x O₃ perovskite system and the contents of BaO, Sb₂O₃ and silicate sintering agent were studied by X-ray diffraction analysis and Mössbauer spectroscopy. It was found that the electrical conductivity is related to the substitution of Sb³⁺ for Sn⁴⁺, the content of sintering agent and the phase constitutents in samples. BaSnO₃, Ba₃Sn₂O₇, Ba₂SnO₄ and SnO₂ phases might appear in different fractions when the contents of BaO change from 0.5 mole to 3.5 mole. In low antimony percentage condition, pentavalent Sb³⁺ ions inserted in Sn⁴⁺ sites and formed the donor center. In high antimony percentage (x≥0.20) condition, the existence of an insulating phase (BaSb₂O₆) was confirmed.     

Follow up of the glassy phase formation as silicon oxide was added to Brownmillerite phase of Portland cement clinker

Brownmillerite phase is one of the four main phases of Portland cement clinker. It was prepared as pure C₄AF¹ and C₄AF with different amount of SiO₂, (5, 10, 15, 20, 25, and 40 mol%) by addition. Pure C₄AF was prepared using CaO, Al₂O₃ and Fe₂O₃ according to the ratios 4:1:1. Each sample mixture was fired at 1,400°C for 1 h then ground and introduced again to 1,400°C for 1/2 h then quenched in air. The prepared samples were ground and measured using x-ray diffraction, scanning electron microscope, A.C. conductivity and Mössbauer spectroscopy. The results were correlated and discussed. The main finding is the formation of a glassy phase besides the C₄AF structure, in addition to the formation of the C₂S phase of cement clinker as SiO₂ addition was upgraded. The electrical conductivity results showed that the 20 mol% SiO₂ sample has the lowest (σ) value.     

Speeds of sound and isentropic functions of n-alkoxypropanol with 1-butanol and 2-butanol at 298.15 K

Speeds of sound have been measured as a function of composition for binary mixtures of propylene glycol monomethyl ether (1-methoxy-2-propanol), propylene glycol monoethyl ether (1-ethoxy-2-propanol), propylene glycol monopropyl ether (1-propoxy-2-propanol), propylene glycol monobutyl ether (1-butoxy-2-propanol), and propylene glycol tert-butyl ether (1-tert-butoxy-2-propanol), with 1-butanol, and 2-butanol, at 298.15 K and atmospheric pressure. The speeds of sound values were combined with those of our previous results for excess molar volumes converted to densities to obtain isentropic compressibility κ_S. Deviation in isentropic compressibility Δκ_S was evaluated using volume fraction weighting of the individual component properties to estimate ideal mixture behavior. The deviations u^D of the speed of sound from their values in an ideal mixture were also evaluated for all measured mole fractions. The speeds of sound results have been used to estimate the apparent molar isentropic compressibility at infinite dilution.     

Properties of Sr- and Sb-doped PZT–Portland cement composites

Lead zirconate titanate (PZT) ceramic-cement-based composites have increasingly been recognized as an attractive new composite material for use as a sensor in structural applications. In this work, PZT was doped with Sr and Sb (PSZT) to give it greater dielectric constant (ε _r) and higher piezoelectric coefficient (d ₃₃) values than normal PZT and is the first time that it is mixed with normal Portland cement to produce a 0–3 connectivity PSZT–Portland cement composite using PSZT contents of 50% and 70% by volume. Scanning electron micrographs show PSZT ceramic particles closely surrounded by the hydrated cement matrix where a dense microstructure can be observed in the interfacial zone. Both the ε _r and d ₃₃ values were found to increase with PSZT content and the values are amongst the highest so far for these types of composites, where the ε _r and d ₃₃ values reached 590 and 48 pC/N, respectively.     

The effect of silica nanoparticles on the pore structure of hydrating cement paste: a spatially resolved low-field NMR study

ABSTRACT

The hydration process of four different cement-based materials at different depths inside the sample was investigated using localised nuclear magnetic resonance relaxation measurements. All the samples are based on white Portland cement (CEM I 42.5 R), with a water-to-cement ratio of 0.5. One sample is a simple cement paste and the other three additionally contain 5% (by mass of cement) silica nanoparticles (50–200?nm size), silanised silica nanoparticles (with silane A 174) or silica fume (80% silica; 0.15?µm average size). The localised transverse relaxation measurements were performed using a single-sided NMR instrument. The relaxation rates were monitored for 48?h during the hydration process at different depths inside the sample. The results showed that the presence of nanoparticles influences not only the speed of hydration overall, but also the homogeneity of the materials.     

Natural radiative lifetimes in the1 P 1 and1 F 3 sequences of Sr I

We have measured radiative lifetimes in the 5s n p ¹ P ₁ (n=5–29) and 5s n f ¹ F ₃ (n=4–11) Rydberg series in neutral strontium. The measurements were performed with single-step laser excitation starting from the ground state or from a metastable state populated by collisions. The decay photons were detected using delayed coincidence technique or a transient recorder. The presence of configuration interaction in the 5s n p ¹ P ₁ series can be observed aroundn=8. The perturbation in the 5s n f ¹ F ₃ series is not reflected in the behaviour of the lifetime values.     

Stark interaction in then s n p z 3 P 1 levels of zinc and cadmium

The tensor polarizabilities of then s n p z ³ P ₁ levels of Zn and Cd were measured using optical double resonance. From the rf-resonance signals in parallel electric and magnetic fields, the following tensor polarizabilities were deduced: Zn,α _ten(4s4pz ³ P ₁)=1.83(8) kHz/(kV/cm)²; Cd,α _ten(5s5pz ³ P ₁)=1.77(8) kHz/(kV/cm)². Theoretical values were calculated using Coulomb approximation. The results were then compared with previous theoretical and experimental values and, in addition, with values for Hg. Theoretical results obtained by a modified Sternheimer method (E.J. Robinson: J. Opt. Soc. Am.59, 782 (1969)) are in better agreement with the experimental values than the results of the Coulomb approximation calculations.     

Internal dynamics and hydration of solid proteins by1H NMR relaxation and FTIR spectroscopy

Temperature dependences of¹H nonselective nuclear magnetic resonanceT ₁ andT ₂ relaxation times measured at 27 MHz have been studied on solid human serum albumin (HSA) samples at various hydrations. The data were interpreted in terms of three kinds of internal motions in a protein and microdynamic parameters of the motions were obtained by a “model-free” approach. Two fast motions with correlation times lying in the range of tens to hundreds picoseconds were shown to be essentially insensitive to hydration. Unlike lysozyme and bovine albumin, HSA reveals relaxation transition due to slow motion in the room temperature range thus allowing one to obtain microdynamic parameters more precisely. Hydration leads to a shortening of the correlation time from hundreds to tens nanoseconds and to a less restricted movement. The comparison of the hydration dependence of relaxation parameters with infrared spectra of HSA side chain groups clearly shows that methyl protons are evidently involved in a slow motion, following the saturation of the protein globule surface by water. The same dependence correlating with solvent accessible surface areas was shown to exist for some other proteins. In addition to the main set of protons performing a solidlike movement, a small amount of much more mobile protons is also present with its proportion rising steeply with hydration and temperature. The origin of these protons is discussed.