Influence of superplasticizers on the course of Portland cement hydration

A multicell isoperibolic — semiadiabatic calorimeter was used for the measurement of temperature and the determination of the hydration heat evolution at earlier period of cement pastes setting and hardening. The measurements were aimed at the determination of the effect of superplasticizers (SPs) on the course of the Portland cement hydration. Commercial polycarboxylate SP was added to the mixtures and the heat effect was measured. With the increasing content of SP, the hydration temperature increased up to a certain value and then decreased. In case of a sufficient amount of water in the mixture to achieve complete hydration of cement, samples with the highest values of the maximum hydration temperature reached the highest values of the released total heat. If there is not a sufficient amount of water to achieve complete hydration, the samples with the highest values of the maximum hydration temperature reach the lowest values of the released total heat.     

Effect of pulverization of the bulk powder on the hydration of creatine anhydrate tablets and their pharmaceutical properties

The hydration behavior and expansion properties of untreated and pulverized creatine anhydrate (CRA) tablets were studied under 60 and 75%RH at 25 degrees C by using differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD). The tablet hardness of untreated and pulverized CRA tablets was significantly decreased after hydration. There was a linear relationship between the degree of hydration and the tablet hardness of untreated CRA tablets compressed at 1000 kg/cm2. In contrast, the relationship between the degree of hydration and the tablet hardness of pulverized CRA tablets was nonlinear. These results suggest that the reduction in hardness of pulverized CRA tablets does not depend solely on the hydration level of crystal water. PXRD analysis indicated that the diffraction pattern of the pulverized CRA powder was similar to that of the untreated CRA powder. However, the diffraction intensity of the pulverized CRA powder was slightly lower than that of the untreated CRA powder at high angle. The micropore radius of both untreated and pulverized CRA tablets was significantly increased after hydration, but analysis of the relationship between micropore radius and fractional hydration of crystal water showed that untreated CRA tablets were more affected than pulverized CRA tablets. Therefore, the reduction in tablet hardness depends not only on the hydration behavior but also on the crystal orientation of the CRA powder.     

New solid compounds of Tb(III), Ho(III), Er(III) and Yb(III) with chrysin

The time required for maximum hydration of MgO obtained from the calcination of magnesite was determined. The MgO samples were hydrated for different time intervals in both water and magnesium acetate. A thermogravimetric analysis (TG) method was used to determine the degree of hydration to Mg(OH)₂. Increasing the hydration time, the degree of hydration of MgO and surface area of the formed Mg(OH)₂ increased. A leveling effect was observed on the percentage Mg(OH)₂ obtained from hydration in magnesium acetate, and an optimum amount of 85% was obtained after 500 min. For the hydration in water, the leveling effect was only observed after 800 min giving a maximum of 65% Mg(OH)₂.     

电解质溶液界面结构的分子动力学模拟研究

电解质溶液界面结构的研究不仅具有重要的理论意义, 而且具有一定的实用价值. 采用分子动力学模拟研究了LiCl, LiBr, LiI, NaI, KI, CsI水溶液中阴阳离子在1×105 Pa和300 K下的气液界面分布情况, 探讨离子水化与电解质溶液界面结构的关系, 并分析阳离子水化能力的强弱对共存阴离子在界面富集分布的影响. 通过对模拟结果的分析发现, 离子的水化能力越强, 就越能形成稳定的水化结构而处于本体相中, 水化能力越弱, 则越易在界面富集. 该机理合理地解释了离子在界面的分布现象, 阳离子水化能力一般较其共存阴离子强而处于本体相, 阴离子则趋向在界面处富集; 不同阴离子在界面的密度分布也与阴离子的水化能力相关, 阴离子水化能力越弱, 其在界面富集程度越高, 不同阴离子在界面的富集趋势为Cl－＜Br－＜I－; 阳离子水化能力的强弱也影响其共存阴离子在界面的富集程度, 阳离子的水化能力越弱, 其共存阴离子在界面的富集程度就越低.     

Hydration behaviour of a lime-pozzolan cement containing MSW incinerator fly ash

A lime-pozzolan cement was used to make pastes containing different quantities of MSW fly ash. After setting, the pastes were cured in water at room temperature from 1 h to 260 days. The hydration characteristics and the nature of the hydration products of the various pastes were studied by simultaneous TG/DSC thermal analysis and X-ray diffractometry. The MSW fly ash was found to induce a slowing of the hydration process in lime-pozzolan pastes, and after some days an evident acceleration of hydration reactions occurred. Sulphate and chloride in the MSW fly ash yield hydration products forming a cementitious matrix.The author is grateful to D. Calabrese for assistance with the thermal and XRD analyses.     

Mineralogical evolution of cement pastes at early ages based on thermogravimetric analysis (TG)

Ordinary thermogravimetric analysis (TG) and high-resolution TG tests were carried out on three different Portland cement pastes to study the phases present during the first day of hydration. Tests were run at 1, 6, 12 and 24 h of hydration, in order to determine the phases at these ages. High-resolution TG tests were used to separate decompositions presented in the 100–200 °C interval. The non-evaporable water determined by TG was used to determine hydration degree for the different ages. The effect of particle size distribution (PSD) on mineralogical evolution was established, as well as the addition of calcite as mineralogical filler. Finer PSD and calcite addition accelerate the hydration process, increasing the hydration degree on the first day of reaction between water and cement. According to high-resolution TG results, it was demonstrated that ettringite was the only decomposed phase in the 100–200 °C interval during the first 6 h of hydration for all studied cements. C-S-H phase starts to appear in all cements after 12 h of hydration.     

磷酸钙骨水泥水化过程的XRD实时分析

采用ＸＲＤ实时分析方法,研究了磷酸钼骨水泥水化过程中反应物磷酸四钙（ＴｅｔｃＰ）和二水磷权氢钙（ＤＣＰＤ）的消失过程,以及生成物羟基磷灰石（ＯＨＡｐ）的形成过程。结果表明,ＤＣＰＤ比ＴｅｔＣＰ溶解速度快而先耗尽,水化反应的速度受ＴｅｔＣＰ控制,水化产物的主晶相为结晶ＯＨＡＰ。方法简单易行,合理可靠,能够准确实时体现水化反应的动态过程。     

Structure and dynamics of the CrIII ion in aqueous solution: Ab initio QM/MM molecular dynamics simulation

Structural and dynamical properties of the Cr(III) ion in aqueous solution have been investigated using a combined ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulation. The hydration structure of Cr(III) was determined in terms of radial distribution functions, coordination numbers, and angular distributions. The QM/MM simulation gives coordination numbers of 6 and 15.4 for the first and second hydration shell, respectively. The first hydration shell is kinetically very inert but by no means rigid and variations of the first hydration shell geometry lead to distinct splitting in the vibrational spectra of Cr(H(2)O)(6) (3+). A mean residence time of 22 ps was obtained for water ligands residing in the second hydration shell, which is remarkably shorter than the experimentally estimated value. The hydration energy of -1108 +/- 7 kcal/mol, obtained from the QM/MM simulation, corresponds well to the experimental hydration enthalpy value.     

Preferential hydration and the exclusion of cosolvents from protein surfaces

Protein stability is enhanced by the addition of osmolytes, such as sugars and polyols and inert crowders, such as polyethylene glycols. This stability enhancement has been quantified by the preferential hydration parameter which can be determined by experiments. To understand the mechanism of protein stability enhancement, we present a statistical mechanical analysis of the preferential hydration parameter based upon Kirkwood-Buff theory. Previously, the preferential hydration parameter was interpreted in terms of the number of hydration waters, as well as the cosolvent exclusion volume. It was not clear how accurate these interpretations were, nor what the relationship is between the two. By using the Kirkwood-Buff theory and experimental data, we conclude that the contribution from the cosolvent exclusion dominantly determines the preferential hydration parameters for crowders. For osmolytes, although the cosolvent exclusion largely determines the preferential hydration parameters, the contribution from hydration may not be negligible.     

Hydration of shrinkage-compensating binders with different compositions and water-binder ratios

The calorimetric data of blended shrinkage-compensating binders with different compositions were measured at 25°C at different water-binder ratios using an isothermal calorimeter. The hydration characteristics of shrinkage-compensating binders were evaluated and their influence on the expansive properties of blended shrinkage-compensating binders was determined. Composition and w/b ratio significantly affect the hydration rate and degree of shrinkage-compensating binders, as well as their expansive and mechanical properties. The total heat of hydration of binders decreases with w/c ratios. Its final hydration degree also decreases with w/c ratio. The ternary binders composed with Portland cement, mineral admixture and expansive agent show low hydration heat and rate of heat evolution, but their total heat of hydration increases continuously and surpasses that of binary binder in later period at low w/b ratio. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influences of fly ash and fluorgypsum on the hydration heat and compressive strength of cement

The hydration heat of pure cement, fly ash single-doped cement, as well as fly ash and fluorgypsum co-doped cement were investigated by means of micro-calorimetry with an eight-channel micro-calorimeter. The results showed that the hydration heat and the hydration rate could be reduced significantly by fly ash and fluorgypsum. However, the reduction was not proportional to the loading of dopant. The exothermic peak of the co-doped cement was appeared earlier than that of the single-doped cement. As the temperature decreased, the hydration heat and the hydration rate of both the doped cement were reduced, and the exothermic peak appeared later. The effect of fly ash and fluorgypsum on the compressive strength of cement was also investigated. The results revealed that the early compressive strength of concrete made up of the co-doped cement was largely higher than that of the single-doped cement. Based on the experiment results obtained in this article, we could conclude that fluorgypsum is a suitable additive for the single-doped cement.     

Theoretical and Experimental Interpretation of the Signals From ΔITA

Computer modelling of time dependences of radon release rate during hydration of 3CaO·SiO₂ was carried out. It was demonstrated that the emanation thermal analysis (ETA) can be used for the characterisation of morphology changes during hydration of Portland cement clinker minerals. The presence of various additives and increased temperature affecting kinetics of hydration were simulated by the mathematical model of the radon release rate during hydration of 3CaO·SiO₂. A good agreement between the mathematical model and ETA experimental results was found.This revised version was published online in November 2005 with corrections to the Cover Date.     

Calorimetric and thermogravimetric study on the influence of calcium sulfate on the hydration of ye’elimite

Calcium sulfoaluminate (CSA) cements, which represent a CO₂-friendly alternative to conventional Portland cements, are produced by blending CSA clinker with gypsum and/or anhydrite. The hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye’elimite (calcium sulfoaluminate) with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling. Two calcium sulfates with different reactivities (gypsum and anhydrite) were applied. It was found that the pure phase without any calcium sulfate addition exhibits very slow hydration kinetics during the first 10 h. The hydration can be accelerated by the addition of calcium sulfate or (less effective) by increasing the pH of the aqueous phase. The amount of the calcium sulfate determines the ratio between the hydration products ettringite, monosulfate and amorphous aluminium hydroxide. The reactivity of the added calcium sulfate determines the early hydration kinetics. It was found that the more reactive gypsum was better suited to control the hydration behaviour of ye’elimite.     

Extended solvent-contact model approach to SAMPL4 blind prediction challenge for hydration free energies

Extended solvent-contact model was applied to the blind prediction of the hydration free energies of 47 organic molecules included in the SAMPL4 data set. To obtain a suitable prediction tool, we constructed a hydration free energy function involving three kinds of atomic parameters. With respect to total 34 atom types introduced to describe all SAMPL4 molecules, 102 atomic parameters were defined and optimized with a standard genetic algorithm in such a way to minimize the difference between the experimental hydration free energies and those calculated with the hydration free energy function. In this parameterization, we used a training set comprising 77 organic molecules with varying sizes and shapes. The estimated hydration free energies for the SAMPL4 molecules compared reasonably well with the experimental results with the associated squared correlation coefficient and root mean square deviation of 0.89 and 1.46 kcal/mol, respectively. Based on the comparative analysis of experimental and computational hydration free energies of the SAMPL4 molecules, the methods for further improvement of the present hydration model are suggested.     

Quantum-mechanical studies of environmental effects on biomolecules VI.Ab initio Studies on the hydration scheme of the phosphate group

Ab initio SCF computations using the STO 3G basis set have been performed on the hydration scheme of the dimethylphosphate anion (DMP^?) within the “supermolecule” approach. This model compound represents the phosphate group in nucleic acids, phospholipid components of membranes and a number of other important biological structures. In the first place the principal hydration sites for the fixation of a water molecule have been established and this was followed by the determination of the polyhydration scheme of the first solvation shell, which may involve up to six water molecules. The effect of hydration on the relative stabilities of thegg,gt andtt forms of (DMP^?) was evaluated. The study was extended to the computation of the energies of interaction in the second and third hydration shells and the conclusion was reached that organized hydration around (DMP^?) is essentially limited to two hydration shells with possible residual organization of a third shell around specific sites. The structure of the bound water was investigated. Charge transfer is observed from (DMP^?) to the bound water, the perturbation extending essentially to the first and with decreasing intensity, to the second hydration shell.     

Cooperative hydration effect on the binding of organic vapors by a cross-linked polymer and beta-cyclodextrin

A cooperative hydration effect being favorable for the binding of organic vapors by cross-linked poly(N-6-aminohexylacrylamide) and beta-cyclodextrin was observed in ternary systems in the absence of liquid phase. For these systems the vapor sorption isotherms were determined by the static method of headspace gas chromatographic analysis at 298 K. The obtained isotherms show an increase of binding affinity for vapor of hydrophobic sorbates above a threshold value of receptor hydration. Further hydration gives a saturation of this affinity for the studied hydrophilic polyacrylamide derivative, while the affinity of beta-cyclodextrin for the hydrophilic sorbate ethanol even decreases. A similar behavior of this polymer and beta-cyclodextrin at the change of their hydration helps to explain the observed cooperative hydration effect in terms of clathrate formation.     

Thermoanalytical studies on hydrated tricalcium silicate

The thermal decomposition of the hydration products of tricalcium silicate has been studied by TG, DTG and DTA. The thermal decomposition characteristics of the CSH-phase formed changed, as the hydration progressed. The heat requirement for thermal decomposition of the calcium hydroxide formed in the hydration process was lower than the one of a pure crystalline material.     

Early stages hydration of high initial strength Portland cement

Thermogravimetry (TG) and derivative thermogravimetry (DTG) were used to analyze the early stages of hydration of a high-initial strength and sulphate resistant Portland cement (HS SR PC) within the first 24 h of setting. The water/cement (W/C) mass ratios used to prepare the pastes were 0.35, 0.45, and 0.55. The hydration behavior of the pastes was analyzed through TG and DTG curves obtained after different hydration times on calcined cement mass basis to have a same composition basis to compare the data. The influence of the W/C ratio on the kinetics of the hydration process was done through the quantitative analysis of the combined water of the main hydration products formed in each case. TG and DTG curves data calculated on calcined mass basis of all the results were converted to initial cement mass basis to have an easier way to analyze the influence of the W/C ratio on the free and combined water of the different main hydrated phases. The gypsum content of the pastes was totally consumed in 8 h for all cases. A significant part of the hydration process occurs within the first 14 h of setting and at 24 h the highest hydration degree, indicated by the respective content of formed calcium hydroxide, occurs in the case of the highest initial water content of the paste.     

水溶性聚合物改性水泥的研究 Ⅱ.水溶性聚合物对水泥水化过程的影响

从聚合物改性水泥的水化速率、水化热及水化生成物三方面讨论了聚合物对水泥水化的影响。水泥溶液ｐＨ 值和电导率及水泥凝结时间的研究结果表明,非离子聚合物聚丙烯酰胺、聚乙烯醇减慢水泥的初期水化,具有缓凝作用,而阴离子聚合物水解聚丙烯酰胺、聚丙烯酸、磺化聚丙烯酰胺及磺化聚苯乙烯则加速水泥的初期水化,具有促凝作用;水化放热测量结果表明,掺加聚合物均滞缓水泥的后期水化;ＸＲＤ 分析表明,ＨＰＡＭ 抑制水泥中晶体的早期生长,有利于晶体后期形成。在水泥中掺加１ ％ ～２ ％ 的ＨＰＡＭ、ＰＡＡ、ＳＰＳ或ＰＶＡ,抗折强度和抗压强度均有明显提高。     

耐高温阴离子交换树脂的合成及在环氧乙烷催化水合反应中的应用

我们合成了一种新型结构的季铵型阴离子交换树脂催化剂(NC-1),并将其转型为碳酸氢根型应用于环氧乙烷(EO)催化水合反应.并用NC-1、D201树脂催化EO水合反应进行了考察.NC-1型离子交换树脂催化剂,因具有较好的热稳定性,其使用寿命比D201树脂提高到数十倍.同时,还设计了一种“二步法”新型水合工艺,与传统水合工艺相比,这种工艺有效地抑制了树脂催化剂的膨胀.在使用105h后,催化剂的膨胀率由原来的76%下降到5%左右.