scholarly journals Effect of leaching on the composition of hydration phases during chloride exposure of mortar

2022 ◽  
Vol 153 ◽  
pp. 106691
Author(s):  
Alisa Machner ◽  
Marie H. Bjørndal ◽  
Harald Justnes ◽  
Lucija Hanžič ◽  
Aljoša Šajna ◽  
...  
Keyword(s):  
Hydration Phases

Study of Alternating Current Impedance of Basic Magnesium Sulfate Cement

2017 ◽  
Vol 896 ◽  
pp. 97-103 ◽  
Author(s):  
Wen Hai Chen ◽  
Cheng You Wu ◽  
Hui Fang Zhang ◽  
Wu Yu Zhang ◽  
Bo Kun Chen ◽  
...  
Keyword(s):  
Magnesium Sulfate ◽  
Alternating Current ◽  
Molar Ratio ◽  
Impedance Spectra ◽  
Early Hydration ◽  
Straight Line ◽  
Steel Protection ◽  
Magnesium Oxysulfate ◽  
Solution Resistance ◽  
Hydration Phases

Alternating current impedance has been used to study effects of hydration stages and molar ratio on the pore structure and hydration characters of basic magnesium sulfate cement. The alternating current impedance spectra of at early hydration almost appears as a straight line because none crystal hydration phases form. And it appears high frequency semicircle at late hydration stage because of decreasing of porosity and amount of 5Mg (OH)2 ·MgSO4·7H2O gradually form with ages. Besides, alternating current impedance spectra differences among basic magnesium sulfate, magnesium oxysulfate and magnesium oxychloride cement have been studied. These differences indicate that additives such as citric acid may change the structure and charge characteristics of MgO hydration layer which make tends to form more 5Mg (OH)2 ·MgSO4·7H2O phase in basic magnesium sulfate cement than that in magnesium oxysulfate cement. The higher pore solution resistance of BMS cement is the main factor of better steel-protection.

scholarly journals Application of Automated Image Analysis to the Study of Cement Paste Microstructure

1994 ◽  
Vol 370 ◽  
Author(s):  
David Darwin ◽  
Mohamed Nagib Abou-Zeid
Keyword(s):  
Image Analysis ◽  
Silica Fume ◽  
Cementitious Material ◽  
Automated Image Analysis ◽  
Mineral Admixtures ◽  
Partial Replacement ◽  
Size Distributions ◽  
Cement Pastes ◽  
Backscattered Electron ◽  
Hydration Phases

AbstractDigital acquisition and analysis of backscattered electron images provide powerful tools for the study of cement-based materials. The techniques can provide useful information on hydration phases, size distributions of unhydrated particles and voids, effects of changes in the watercementitious material ratio and the use of mineral admixtures, and the distribution of microcracks. The results of automated analyses of cement pastes with different water-cement ratios and pastes containing silica fume are presented. The analyses demonstrate that microstructural data vary significantly from image to image, requiring multiple images to limit the effects of scatter. The analyses also indicate that, although the pastes exhibit different degrees of hydration, the size distributions of the unhydrated cement particles are nearly identical. In contrast, the size distribution of larger voids differs significantly as a function of water-cementitious material ratio and with the use of silica fume as a partial replacement for cement. The calcium hydroxide content obtained based on image analysis exceeds but generally parallels that obtained with thermogravimetric analysis. The majority of microcracks in both nonloaded and loaded specimens occur through or adjacent to the lowest density hydration phase.

Phase transition characterization in low hydration phases of dilauroylphosphatidylcholine

1990 ◽  
Vol 139 (2) ◽  
pp. 586-588 ◽  
Author(s):  
J.M Collins ◽  
L.J Lis ◽  
S Qadri ◽  
W Tamura-Lis ◽  
P.J Quinn
Keyword(s):  
Phase Transition ◽  
Hydration Phases

Quantification of hydration phases in supersulfated cements: review and new approaches

2011 ◽  
Vol 23 (6) ◽  
pp. 265-275 ◽  
Author(s):  
Astrid Gruskovnjak ◽  
Barbara Lothenbach ◽  
Frank Winnefeld ◽  
Beat Münch ◽  
Renato Figi ◽  
...  
Keyword(s):  
New Approaches ◽  
Hydration Phases

Investigation of hydration phases in the system CaO–SiO2-P2O5-H2O

1988 ◽  
Vol 3 (4) ◽  
pp. 772-780 ◽  
Author(s):  
Jiashan Hu ◽  
D. K. Agrawal ◽  
R. Roy
Keyword(s):  
Room Temperature ◽  
Sol Gel ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Sol Gel Process ◽  
Structural Nature ◽  
Amorphous Powders ◽  
Hydration Phases

Hydration reactions and their rates have been studied qualitatively in CaO-and P2O5-rich compositional regions of the system CaO–SiO2-P2O5-H2O. Using aqueous solutions of Ca (NO3)2–4H2O, Ludox, and H3PO4 as starting materials, amorphous powders made by the sol-gel process were reacted with water. Some “curing” reactions were carried out at several temperatures: room temperature, 90 °C, and under hydrothermal conditions. Some glasses in the phosphate-rich region of the system were also made and hydrated. The hydration products are OH–Ap [OH–Ap = Ca10(PO4)6-(OH)2], Ca(OH)2 [CH = Ca(OH)2],C–S–H crystalline, C–S–P–H (C = CaO,S = SiO2,P = P2O5,H = H2O) crystalline, C–S–H gel, C–S–P–H gel, Ca(H2PO4)2·H2O, and CaHPO4. All phases have been identified and characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray analysis (EDAX). The reactivities of the precursor materials and the compositional-structural nature of the hydration products formed are discussed. Some new compositions for “cementlike behavior” have been discovered.

scholarly journals THERMODYNAMIC ANALYSIS OF TRICALCIUM SILICATE HYDRATION

2021 ◽  
Vol 6 (4) ◽  
pp. 75-81
Author(s):  
S. Rahimbaev ◽  
N. Onoprienko ◽  
O. Sal'nikova
Keyword(s):  
Thermodynamic Analysis ◽  
Water Solubility ◽  
Hydration Product ◽  
Tricalcium Silicate ◽  
Enthalpies Of Formation ◽  
Free Energy Of Formation ◽  
Calcium Hydrosilicates ◽  
Calculated Solubility ◽  
Hydration Phases ◽  
Mineral Additives

Thermodynamic analysis of the hydration processes of tricalcium silicate 3CaO•SiO2 is difficult due to the unreliability of the initial data for hydration products. In addition, there are disagreements about the basicity of the hydration phases (3CaO•SiO2•3H2O or 2CaO•SiO2•2H2O). For the latter, there is no free energy of formation in the reference literature. There are also no data on the water solubility of these calcium hydrosilicates. The proposed values of ∆G0298 for these hydrosilicates, equal to 1064,3 and 639,7, as well as the enthalpies of formation (∆Н0298), equal to 1157,2 and 696,9 kcal/mol, re-spectively. Further thermodynamic calculations were performed using these values. To calculate the composition of the liquid phase, a simplified Born-Haber cycle is used. The values of the calculated heat release of tricalcium silicate with the formation of C3S2H3 and C2SH2, obtained using the pro-posed values of enthalpies, differ little from each other and are close to the experimental data. The calculated solubility of C3S2H3 is 0,7 g/l CaO, and C2SH2 is 0,92 g/l CaO. Since the solubility of C3S2H3 is much lower than of Ca(OH)2 (portlandite), which is formed during hydration of tricalcium silicate in large quantities, C3S2H3 is unstable under these conditions and its basicity increases. It is suggested that C3S2H3 is the main hydration product of CEM III and other cements with a high content of active mineral additives, and C2SH2 is CEM I and CEM II.

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