Uptake of Metal Ions by Autoclaved Cement Pastes

1991 ◽  
Vol 245 ◽  
Author(s):  
Caijun Shi ◽  
Robert L. Day ◽  
Xuequan Wu ◽  
Mingshu Tang
Keyword(s):  
Portland Cement ◽  
Metal Ions ◽  
Pore Structure ◽  
Metal Ion ◽  
Room Temperature ◽  
Physical Adsorption ◽  
Total Porosity ◽  
Hydration Products ◽  
Cement Pastes ◽  
Insoluble Compounds

ABSTRACTThis paper deals with the hydration products and pore structure of Portland cement (PC) and alkali-phosphorus slag cement (APSC) pastes, and the uptake of metal ions (Sr2+, Co2+, Cd2+, and Cu2+) in pastes which have been hydrated at 150°C for 25 days. Results indicate that the hydration products of PC are crystalline Ca(OH)2 and C2SH(A); for APSC the products are poorly crystallized low-basic CSH(B) and crystalline tobermorite. The PC pastes have a lower total porosity than APSC pastes, but the PC pastes consist mainly of larger pores with r> 1000Å, while the APSC pastes consist mainly of smaller pores with r< 100Å. The two types of paste were immersed for 19 days at room temperature in Sr2+, Co2+, Cd2+ and Cu2+ solutions with concentrations of 100, 200, 500 and 1000 ppm. It was found that all Ca(OH)2, in the PC pastes was dissolved. Except for Sr2+, the uptake of metal ions by PC paste is mainly due to the formation of insoluble hydroxides. The uptake of metal ions by APSC pastes is due to physical adsorption and the formation of some insoluble compounds. The APSC pastes show a stable structure after immersion in these metal ion solutions.

Pore Structure Development in Portland Cement/Fly Ash Blends

1986 ◽  
Vol 86 ◽  
Author(s):  
David J. Cook ◽  
Huu T. Cao ◽  
Everett P. Coan
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Pore Structure ◽  
Mercury Porosimetry ◽  
Chemical Properties ◽  
Blended Cement ◽  
Total Porosity ◽  
Structure Development ◽  
Cement Pastes ◽  
Diffusion Parameters

ABSTRACTPore structure development in portland cement/fly ash blends was investigated using mercury porosimetry and methanol exchange techniques. The progress of hydration was monitored using compressive strength tests. The specimens were made using four water-cement ratios and were hydrated over a one-year period in lime-saturated water. Mercury porosimetry results indicated that the blended cement pastes generally had higher total porosity than plain cement pastes. The major contribution to this increase in porosity was in the form of smaller pore sizes. With reactive fly ash at 20% replacement, the pore structure of mature paste consists mainly of pores nominally smaller than 0.05 μm in diameter. Diffusion parameters obtained from the methanol exchange results were found to be inversely related to the volume of large pores (nominally >0.05 μm) and also to the volume of small pores (nominally <0.05 μm). The effects of the physical and chemical properties of cements and fly ashes on pore structure development are discussed.

scholarly journals Removal of barium, cobalt, strontium and zinc from solution by natural and synthetic allophane adsorbents

2018 ◽  
Author(s):  
Andre Baldermann ◽  
Andrea Cäcilia Grießbacher ◽  
Claudia Baldermann ◽  
Bettina Purgstaller ◽  
Ilse Letofsky-Papst ◽  
...  
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Physical Adsorption ◽  
Ion Concentration ◽  
Pseudo First Order Reaction ◽  
Uptake Mechanism ◽  
Nano Structure ◽  
Metal Ion Removal ◽  
Ion Removal ◽  
Transmission Electron

The capacity and the mechanism of the adsorption of aqueous barium (Ba), cobalt (Co), strontium (Sr) and zinc (Zn) by Ecuadorian (NatAllo) and synthetic (SynAllo-1 and SynAllo-2) allophanes were studied as a function of contact time, pH and metal ion concentration using kinetic and equilibrium experiments. The mineralogy, nano-structure and chemical composition of the allophanes were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and specific surface area analyses. The evolution of adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium between aqueous metal ions and allophane was reached within &lt; 10&thinsp;min. The metal ion removal efficiencies varied from 0.7 to 99.7 % at pH 4.0 to 8.5. At equilibrium, the adsorption behavior is better described by the Langmuir model than by the Dubinin-Radushkevich model, yielding sorption capacities of 10.6, 17.2 and 38.6 mg/g for Ba^(2+), 12.4, 19.3 and 29.0 mg/g for HCoO_2^-, 7.2, 15.9 and 34.4 mg/g for Sr^(2+) and 20.9, 26.9 and 36.9 mg/g for Zn^(2+), respectively, by NatAllo, SynAllo-2 and SynAllo-1. The uptake mechanism is based on a physical adsorption process. Allophane holds great potential to remove aqueous metal ions and could be used instead of zeolites, montmorillonite, carbonates and phosphates for wastewater treatment.

scholarly journals Influence of Pore Structure on Chloride Penetration in Cement Pastes Subject to Wetting-Drying Cycles

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Honglei Chang ◽  
Zhiwu Zuo ◽  
Mingyue Qu ◽  
Fei Wang ◽  
Zhi Ge ◽  
...  
Keyword(s):  
Pore Structure ◽  
Penetration Rate ◽  
Error Function ◽  
Chloride Concentration ◽  
Total Porosity ◽  
Chloride Penetration ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Cement Pastes ◽  
The Matrix

Copious studies have discovered a phenomenon that a chloride concentration peak appears on the surface of concrete under cyclic drying-wetting environments. In such cases, the chloride diffusion coefficient (D) obtained through directly fitting the standard error function of Fick’s second law is no longer accurate. The more reliable D obtained by the method proposed by Andrade is employed in this research to investigate the influence of pore structure on chloride penetration rate of pastes. The results show that both the effective coefficient (Deff) and the apparent coefficient (Dapp) increase with total porosity, the most probable pore size, and water absorption porosity, suggesting that the increase of the three pore structure parameters accelerates chloride penetration rate under cyclic wetting-drying condition. The increase of the three parameters makes more room available and eases the difficulty for salt solution to enter the matrix and thus leads to the augmentation of chloride transporting in matrix.

Estimation and Measurement of Porosity Change in Cement Paste

2010 ◽  
Author(s):  
Eunyong Lee ◽  
Haeryong Jung ◽  
Ki-jung Kwon ◽  
Do-Gyeum Kim
Keyword(s):  
Ionic Strength ◽  
Portland Cement ◽  
Cement Paste ◽  
Thermodynamic Model ◽  
Ordinary Portland Cement ◽  
Type I ◽  
Hydration Products ◽  
Cement Pastes ◽  
Porosity Change ◽  
Dissolution Reaction

Laboratory-scale experiments were performed to understand the porosity change of cement pastes. The cement pastes were prepared using commercially available Type-I ordinary Portland cement (OPC). As the cement pastes were exposed in water, the porosity of the cement pastes sharply increased; however, the slow decrease of porosity was observed as the dissolution period was extended more than 50 days. As expected, the dissolution reaction was significantly influenced by w/c raito and the ionic strength of solution. A thermodynamic model was applied to simulate the porosity change of the cement pastes. It was highly influenced by the depth of the cement pastes. There was porosity increase on the surface of the cement pastes due to dissolution of hydration products, such as portlandite, ettringite, and CSH. However, the decrease of porosity was estimated inside the cement pastes due to the precipitation of cement minerals.

Effect of nano C–A–S–H seeds on the early-stage hydration and pore structure of Portland cement pastes

2020 ◽  
pp. 1-9
Author(s):  
Han Zhou ◽  
Shupeng Zhang ◽  
Bao Liu ◽  
Qingchao Li ◽  
Cheng He ◽  
...  
Keyword(s):  
Portland Cement ◽  
Pore Structure ◽  
Early Stage ◽  
Cement Pastes ◽  
Early Stage Hydration

Cu3(µ2-Cl)3 and Ag3(μ2-Cl)3 Complexes Supported by Tetradentate Trisphosphino-stibine and -bismuthine Ligands: Structural Evidence for Triply Bridging Heavy Pnictines

2013 ◽  
Vol 66 (10) ◽  
pp. 1281 ◽  
Author(s):  
Iou-Sheng Ke ◽  
François P. Gabbaï
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Room Temperature ◽  
Natural Bond Orbital ◽  
Orbital Method ◽  
Bonding Analysis ◽  
Bonding Mode

The tetradentate stibine and bismuthine ligands (o-(iPr2P)C6H4)3Sb (LSbP3) and (o-(iPr2P)C6H4)3Bi (LBiP3) react with CuCl and AgCl in THF at room temperature to afford (o-(iPr2P)C6H4)3SbCu3(μ2-Cl)3 (1), (o-(iPr2P)C6H4)3SbAg3(μ2-Cl)3 (2), (o-(iPr2P)C6H4)3BiCu3(μ2-Cl)3 (3), and (o-(iPr2P)C6H4)3BiAg3(μ2-Cl)3 (4), respectively. These complexes, which have been fully characterised, feature a central M3(μ2-Cl)3 cluster (M = Cu or Ag) supported by coordination of a LSbP3- or LBiP3-phosphino group to each group 11 metal ion. The heavy pnictogen atom (Pn) interacts simultaneously with the three group 11 metal ions of the M3(μ2-Cl)3 cluster leading to formation of a tetrahedral PnM3 core. Bonding analysis using the Natural Bond Orbital method indicates the presence of a four-centre two-electron Pn→M3 interaction whose strength is the highest in 1 and the lowest in 4. The triply bridging bonding mode of the stibine and bismuthine ligands observed in these complexes is, to our knowledge, unprecedented. We also note that the central M3(μ2-Cl)3 clusters found in these complexes are related to the cyclo-trimers observed in vapours of CuCl and AgCl.

Hardened portland cement pastes of low porosity IV. Surface area and pore structure

1972 ◽  
Vol 2 (5) ◽  
pp. 577-589 ◽  
Author(s):  
Ivan Odler ◽  
Julius Hagymassy ◽  
Edward E. Bodor ◽  
Marvin Yudenfreund ◽  
Stephen Brunauer
Keyword(s):  
Portland Cement ◽  
Pore Structure ◽  
Surface Area ◽  
Cement Pastes ◽  
Low Porosity

Effect of temperature on the pore solution, microstructure and hydration products of Portland cement pastes

2007 ◽  
Vol 37 (4) ◽  
pp. 483-491 ◽  
Author(s):  
Barbara Lothenbach ◽  
Frank Winnefeld ◽  
Corinne Alder ◽  
Erich Wieland ◽  
Peter Lunk
Keyword(s):  
Portland Cement ◽  
Pore Solution ◽  
Effect Of Temperature ◽  
Hydration Products ◽  
Cement Pastes

Diffusion and Pore Structure in Portland Cement Pastes Blended with Low Calcium Fly Ash

1985 ◽  
Vol 65 ◽  
Author(s):  
Amitabha Kumar ◽  
Della M. Roy
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Pore Structure ◽  
Pore Size ◽  
Size Distributions ◽  
Cation Diffusion ◽  
Cement Pastes ◽  
Effective Coefficients ◽  
Pore Size Distributions ◽  
Diffusion Rates

ABSTRACTEffective coefficients for the diffusion of Cs+ and Cl− ions accross hardened plates of Portland cement and Portland cement-fly ash blend pastes were measured at 27°, 38° and 60° for samples cured up to 28 d. The porosity and pore size distributions of the same hardened plates were also determined. The fly ash blends show lower anion and cation diffusion rates at higher temperatures, although the porosity is not significantly different from the neat paste. The finer pore size is considered responsible for the slower diffusion in the blends. The electronegative nature of the pore surfaces also contributes to the slower cation diffusion.

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