scholarly journals Effect of Nitrate/Bromide on the Hydration Process of Cement Paste Mixed with Alkali Free Liquid Accelerator at Low Temperature

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1585
Author(s):  
Yongdong Xu ◽  
Tingshu He
Keyword(s):  
Low Temperature ◽  
Mass Loss ◽  
Cement Paste ◽  
Inorganic Salt ◽  
Inorganic Salts ◽  
Hydration Products ◽  
Hydration Degree ◽  
Acceleration Mechanism ◽  
Setting Times ◽  
The Relationship

The effects of different inorganic salt accelerators (CaBr2, NaBr, Ca(NO3)2, NaNO3) and an alkali-free liquid accelerator were researched at a low temperature of 10 °C. The results showed the effects of 1.5% NaBr and 1.5% NaNO3 inorganic accelerator were pronounced. The 1-d compressive strengths of the mortar with these two inorganic salts were increased by 185.8% and 184.2%, respectively, and the final setting times were shortened from 7.74 to 6.08 min and 6.12 min, respectively. The hydration temperatures at 10 °C were measured, and the promotion effects of the inorganic accelerators were calculated: the relationship between the hydration degree was αAS + NN > αAS + NB > αAS + CB > αAS + CN > αAS. In addition, the reaction of C3A with NaBr and NaNO3 was used to analyze the products in an ettringite phase, i.e., Ca4Al2O6Br210·H2O, 3CaOAl2O3Ca(NO3)2X·H2O. The formation of these phases was detected in the hydration products of the cement paste hydration for 12 h, 24 h, and 28 d. Combined with the mass loss of the ettringite phase at 90–120 °C, determined using TG/DTG, the synergetic acceleration mechanism of the inorganic accelerators was comprehensively inferred.

scholarly journals Difference between Internal and External Hydration of Hardened Cement Paste under Microwave Curing

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Guoshun Yan ◽  
Jiazheng Li ◽  
Yuqiang Lin ◽  
Xia Chen
Keyword(s):  
Cement Paste ◽  
Outer Part ◽  
Total Porosity ◽  
Fracture Morphology ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Hydration Degree ◽  
Microwave Curing ◽  
The Difference

In order to investigate the difference between internal and external hydration of hardened cement paste under microwave curing, a comparative study on the hydration products, hydration degree, fracture morphology, and pore structure between the inner part and outer part of hardened cement paste (Φ120 mm × 120 mm) under microwave curing was carried out by XRD-Rietveld refinement, TG-DSC, SEM, and MIP methods. The results show that the total hydration degree of the inner part is lower at early ages, but with the hydration, there is little difference in the hydration degree between inner and outer parts at later ages. Apart from granular AFt crystal formed in the inner part of hardened cement paste, there is little difference in the fracture morphology between internal and external hydration. The total porosity of the outer part is lower than that of the inner part.

Gebirgswaldpflege – es kommt auf den Standort an | Mountain silviculture – it all depends on the site

2001 ◽  
Vol 152 (5) ◽  
pp. 169-176 ◽  
Author(s):  
Monika Frehner
Keyword(s):  
Nature Conservation ◽  
Low Temperature ◽  
Tree Species ◽  
Forest Stand ◽  
Ground Vegetation ◽  
Mountain Forests ◽  
Research Projects ◽  
Snow Mould ◽  
The Relationship ◽  
Protection Forests

The article shows that knowledge of the site of a particular forest stand, together with research results and experience, can provide information that is important for the cultivation of mountain forests, including knowledge of the composition of the tree species and the structure and growth capacity of natural forest. Furthermore, certain sites can, thus, be characterized by factors that influence restocking, such as snow mould,lush ground vegetation or low temperature. The guidelines«minimale Pflegemassnahmen» – «Minimal tending of protection forests» (WASSER und FREHNER, 1996) are based on this principle. For individual sites, warnings about natural dangers such as rock fall or statements concerning nature conservation can be made (e.g., the occurrence of tree species, suitability as a biotope for Capercaille). In conclusion, two research projects on the relationship between site and natural dangers will be presented.

Depression of freezing temperature of water and water solutions in porous materials

1989 ◽  
Vol 54 (10) ◽  
pp. 2644-2647 ◽  
Author(s):  
Petr Schneider ◽  
Jiří Rathouský
Keyword(s):  
Water Vapor ◽  
Porous Materials ◽  
Inorganic Salt ◽  
Freezing Point ◽  
Freezing Temperature ◽  
Inorganic Salts ◽  
Freezing Point Depression ◽  
Salt Solutions ◽  
Water Solutions

In porous materials filled with water or water solutions of inorganic salts, water freezes at lower temperatures than under normal conditions; the reason is the decrease of water vapor tension above the convex meniscus of liquid in pores. The freezing point depression is not very significant in pores with radii from 0.05 μm to 10 μm (about 0.01-2.5 K). Only in smaller pores, especially when filled with inorganic salt solutions, this depression is important.

scholarly journals Effect of C-S-H Nucleating Agent on Cement Hydration

2021 ◽  
Vol 11 (14) ◽  
pp. 6638
Author(s):  
Wenhao Zhao ◽  
Xuping Ji ◽  
Yaqing Jiang ◽  
Tinghong Pan
Keyword(s):  
Fractal Dimension ◽  
Cement Hydration ◽  
Nucleating Agent ◽  
Crystal Nucleation ◽  
Enhancement Effect ◽  
Hydration Products ◽  
Hydration Degree ◽  
Hydration Kinetics ◽  
Cement Mortars ◽  
Early Strength

This work aims to study the effect of a nucleating agent on cement hydration. Firstly, the C-S-H crystal nucleation early strength agent (CNA) is prepared. Then, the effects of CNA on cement hydration mechanism, early strength enhancement effect, C-S-H content, 28-days hydration degree and 28-days fractal dimension of hydration products are studied by hydration kinetics calculation, resistivity test, BET specific surface area test and quantitative analysis of backscattered electron (BSE) images, respectively. The results show that CNA significantly improves the hydration degree of cement mixture, which is better than triethanolamine (TEA). CNA shortens the beginning time of the induction period by 49.3 min and the end time of the cement hydration acceleration period by 105.1 min than the blank sample. CNA increases the fractal dimension of hydration products, while TEA decreases the fractal dimension. CNA significantly improves the early strength of cement mortars; the 1-day and 3-days strength of cement mortars with CNA are more than the 3-days and 7-days strength of the blank sample. These results will provide a reference for the practical application of the C-S-H nucleating agent.

scholarly journals Influence of Preaging Temperature on the Indentation Strength of 3Y-TZP Aged in Ambient Atmosphere

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2767
Author(s):  
Ki-Won Jeong ◽  
Jung-Suk Han ◽  
Gi-Uk Yang ◽  
Dae-Joon Kim
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Low Temperature ◽  
Compressive Residual Stress ◽  
Yttria Stabilized Zirconia ◽  
Ambient Atmosphere ◽  
Aged Specimen ◽  
Stabilized Zirconia ◽  
M Phase ◽  
The Relationship

Yttria-stabilized zirconia (3Y-TZP) containing 0.25% Al2O3, which is resistant to low temperature degradation (LTD), was aged for 10 h at 130–220 °C in air. The aged specimens were subsequently indented at loads ranging from 9.8 to 490 N using a Vickers indenter. The influence of preaging temperature on the biaxial strength of the specimens was investigated to elucidate the relationship between the extent of LTD and the strength of zirconia restorations that underwent LTD. The indented strength of the specimens increased as the preaging temperature was increased higher than 160 °C, which was accompanied by extensive t-ZrO2 (t) to m-ZrO2 (m) and c-ZrO2 (c) to r-ZrO2 (r) phase transformations. The influence of preaging temperature on the indented strength was rationalized by the residual stresses raised by the t→m transformation and the reversal of tensile residual stress on the aged specimen surface due to the indentation. The results suggested that the longevity of restorations would not be deteriorated if the aged restorations retain compressive residual stress on the surface, which corresponds to the extent of t→m phase transformation less than 52% in ambient environment.

scholarly journals Performance and Microstructure of Cold Recycled Mixes Using Asphalt Emulsion with Different Contents of Cement

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2548 ◽  
Author(s):  
Yanhai Yang ◽  
Ye Yang ◽  
Baitong Qian
Keyword(s):  
Low Temperature ◽  
Temperature Stability ◽  
Hydration Products ◽  
High Temperature Stability ◽  
Asphalt Emulsion ◽  
Moisture Susceptibility ◽  
Pavement Maintenance ◽  
Maintenance And Rehabilitation ◽  
Low Temperature Cracking ◽  
Temperature Crack

Cold recycled mixes using asphalt emulsion (CRME) is an economical and environmentally-friendly technology for asphalt pavement maintenance and rehabilitation. In order to determine the optimum range of cement contents, the complex interaction between cement and asphalt emulsion and the effects of cement on performance of CRME were investigated with different contents of cement. The microstructure and chemical composition of the fracture surface of CRME with different contents of cement were analyzed in this paper as well. Results show that the high-temperature stability and moisture susceptibility of CRME increased with the contents of cement increasing. The low-temperature crack resistance ability gradually increased when the content of cement is increased from 0% to 1.5%. However, it gradually decreased when the content of cement is increased from 1.5% to 4%. Cold recycled mixes had better low-temperature cracking resistance when the contents of cement were in the range from 1% to 2%. The results of microstructure and energy spectrum analysis show that the composite structure is formed by hydration products and asphalt emulsion. The study will be significant to better know the effects of cement and promote the development of CRME.

Drift-dissipative instability of the electromagnetic convection mode in a low-temperature plasma

1992 ◽  
Vol 47 (3) ◽  
pp. 439-443 ◽  
Author(s):  
Hamid Saleem ◽  
M. Y. Yu
Keyword(s):  
Low Temperature ◽  
Collisional Plasma ◽  
Low Temperature Plasma ◽  
Temperature Plasma ◽  
Electromagnetic Effects ◽  
Dissipative Instability ◽  
Low Temperature Plasmas ◽  
The Relationship

The convection mode in a collisional plasma is investigated, with the inclusion of electromagnetic effects. It is shown that a dissipative instability can occur. The relationship to several well-known modes as well as applications to typical low-temperature plasmas are discussed.

Near-infrared spectroscopy investigation on the hydration degree of a cement paste

2010 ◽  
Vol 45 (12) ◽  
pp. 3169-3174 ◽  
Author(s):  
D. Gastaldi ◽  
F. Canonico ◽  
S. Irico ◽  
D. Pellerej ◽  
M. C. Paganini
Keyword(s):  
Infrared Spectroscopy ◽  
Cement Paste ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Hydration Degree

Study of the pozzolanic activity and hydration products of cement pastes with addition of natural zeolites

Clay Minerals ◽  
2011 ◽  
Vol 46 (2) ◽  
pp. 241-250 ◽  
Author(s):  
V. Lilkov ◽  
O. Petrov ◽  
V. Petkova ◽  
N. Petrova ◽  
Y. Tzvetanova
Keyword(s):  
Surface Area ◽  
Cement Paste ◽  
Chemical Reactions ◽  
Natural Zeolite ◽  
Early Stage ◽  
Pozzolanic Activity ◽  
Large Surface Area ◽  
Natural Zeolites ◽  
Hydration Products ◽  
Cement Pastes

AbstractThis paper presents results from comparative thermogravimetric, calorimetric and pozzolanic activity analyses of five natural zeolite samples from Bulgaria, Slovakia, Philippines, USA and North Korea. The zeolites actively participate in the hydration processes of cement. Their activity in the early stage of hydration is based mainly on the large surface area of the particles while, in the later stages of activation, chemical reactions occur between the products of the hydration of cement and the soluble SiO2 that is present in the bulk of the zeolites. It has been shown that in all cement pastes which contain zeolite additives, the quantity of portlandite is lower than that in pure cement paste or is even totally absent. The amounts of hydration products are greater when 30% zeolite is used than when 10% zeolite is added (excluding the sample with chabazite). The lowest pozzolanic activity is shown by chabazite, which possessed the lowest SiO2/Al2O2 ratio.

scholarly journals Liquid–liquid phase separation in particles containing organics mixed with ammonium sulfate, ammonium bisulfate, ammonium nitrate or sodium chloride

2013 ◽  
Vol 13 (23) ◽  
pp. 11723-11734 ◽  
Author(s):  
Y. You ◽  
L. Renbaum-Wolff ◽  
A. K. Bertram
Keyword(s):  
Phase Separation ◽  
Sodium Chloride ◽  
Liquid Phase ◽  
Relative Humidity ◽  
Ammonium Sulfate ◽  
Inorganic Salt ◽  
Liquid Phase Separation ◽  
Inorganic Salts ◽  
Organic Species ◽  
Liquid Liquid Phase Separation

Abstract. As the relative humidity varies from high to low values in the atmosphere, particles containing organic species and inorganic salts may undergo liquid–liquid phase separation. The majority of the laboratory work on this subject has used ammonium sulfate as the inorganic salt. In the following we studied liquid–liquid phase separation in particles containing organics mixed with the following salts: ammonium sulfate, ammonium bisulfate, ammonium nitrate and sodium chloride. In each experiment one organic was mixed with one inorganic salt and the liquid–liquid phase separation relative humidity (SRH) was determined. Since we studied 23 different organics mixed with four different salts, a total of 92 different particle types were investigated. Out of the 92 types, 49 underwent liquid–liquid phase separation. For all the inorganic salts, liquid–liquid phase separation was never observed when the oxygen-to-carbon elemental ratio (O : C) &amp;geq; 0.8 and was always observed for O : C < 0.5. For 0.5 &amp;leq; O : C < 0.8, the results depended on the salt type. Out of the 23 organic species investigated, the SRH of 20 organics followed the trend: (NH4)2SO4 &amp;geq; NH4HSO4 &amp;geq; NaCl &amp;geq; NH4NO3. This trend is consistent with previous salting out studies and the Hofmeister series. Based on the range of O : C values found in the atmosphere and the current results, liquid–liquid phase separation is likely a frequent occurrence in both marine and non-marine environments.

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