INCORPORATION OF SILICA FUME INTO CEMENT BASED COMPOSITES CURED UNDER SPECIFIC HYDROTHERMAL CONDITIONS

2018 ◽  
Author(s):  
Petr Holub
Keyword(s):  
Silica Fume ◽  
Hydrothermal Conditions

Influence of Silica Fume Source on Crystallization of Xonotlite in a New Process Making Medium Density Ca-Silicate Based Products

2018 ◽  
Vol 788 ◽  
pp. 3-12
Author(s):  
Felipe Marti-Montava ◽  
Ann Opsommer ◽  
David Garcia-Sanoguera
Keyword(s):  
Particle Size ◽  
Silica Fume ◽  
Calcium Silicate ◽  
New Technology ◽  
Medium Density ◽  
Hydrothermal Conditions ◽  
Calcium Silicate Hydrates ◽  
New Process ◽  
Different Types ◽  
Dispersion Technique

This paper investigates the influence of different types of silica fume on the crystallization process of medium density calcium silicate based products. The products are formed by a new technology that consists of two steps. In the first step, a mixture containing calcium silicate hydrates (C-S-H) is formed by reaction of lime with special silicas at temperatures below 100°C. This mixture is then molded into boards by a filter-pressing technique. In the second step, the boards are treated in hydrothermal conditions enabling the conversion of the C-S-H into important contents of xonotlite (Ca6Si6O17(OH)2); this is the most stable calcium silicate hydrate phase at high temperatures. In order to make C-S-H in pressure less conditions, the use of reactive forms of silica is required. In this work we used silica fume as reactive silica. To understand the influence of the silica fume on the formation of xonotlite, several properties were studied, such as particle size, purity and specific surface area (BET). It was found that the particle size distribution and degree of agglomeration for the silica fume were the most important properties. A proper dispersion technique must be applied in order to break the silica fume agglomerates, forming particles small enough to react with dissolved lime and to form C-S-H phases that are able to be converted into xonotlite under hydrothermal conditions. Finally, it was also found that the formation of xonotlite is favored by the use of high purity silica fume.

scholarly journals Phase Composition of Silica Fume—Portland Cement Systems Formed under Hydrothermal Curing Evaluated by FTIR, XRD, and TGA

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2786
Author(s):  
Eva Kuzielová ◽  
Michal Slaný ◽  
Matúš Žemlička ◽  
Jiří Másilko ◽  
Martin Tchingnabé Palou
Keyword(s):  
Portland Cement ◽  
Silica Fume ◽  
High Temperature Phase ◽  
Molecular Water ◽  
Temperature Phase ◽  
Polymerization Degree ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Treatment Regimes

Two substitution levels of Portland cement by silica fume (SF; 30 and 50 mass%) and three hydrothermal treatment regimes (0.5, 1.2, and 2 MPa and 165, 195, and 220 °C for 7 days, respectively) were selected for the investigation of high-temperature phase formation. A combination of thermogravimetric, X-ray diffraction, and Fourier transform infrared analyses in the mid-IR region was used to overcome the shortcomings of individual techniques for the identification of these complex systems. Changes in molecular water amounts, the polymerization degree of silicate chains, or their decomposition due to transformations and crystallization of phases at hydrothermal conditions were observed and discussed concerning composition. Contrary to the calciochondrite, hydrogrossular phases, α-C2SH, and jaffeite detected in the systems without SF, a decrease in CaO/SiO2 ratio resulted in the formation of stable tobermorite in the case of 30 mass% SF, whilst calcium hydrogen silicate, gyrolite, and cowlesite were identified as more thermally stable phases in the samples with 50 mass% SF.

Dynamics of CO2 emission from chernozems under agricultural use

2017 ◽  
Vol 4 (3) ◽  
pp. 43-49
Author(s):  
M. Miroshnychenko ◽  
O. Siabruk
Keyword(s):  
Carbon Dioxide ◽  
Agricultural Practices ◽  
Growing Season ◽  
Warm Period ◽  
Direct Seeding ◽  
Soil Tillage ◽  
Plant Residues ◽  
Hydrothermal Conditions ◽  
Organic Mineral ◽  
Mineral System

Aim. The comparison of the effect of hydrothermal conditions and various agricultural practices on the emission of CO 2 from chernozems in the Left-Bank Forest-Steppe of Ukraine. Methods. The dynamics of the intensity of carbon dioxide emissions from chernozem calcic (typical chernozem – in Ukrainian classifi cation) was studied during the growing season of 2011–2012. The observations were based on two fi eld experiments with various methods of soil till- age (6–7 years from the beginning of the experiment) and fertilization systems (21–22 years from the beginning of the experiment). Particularly, plowing at 20–22 cm, disking at 10–12 cm, cultivation at 6–8 cm and direct seeding using Great Plains drill were studied among the soil tillage methods. Mineral system (N 45 P 50 K 45 ), organic system (manure 8 t/ha) and combined organic-mineral system (manure 8 t/ha + N 45 P 50 K 45 ) were studied among fertilization systems. The intensity of CO 2 fl ux was determined using the non-stationary respiratory chambers by the alkaline absorption method, with averaging of the results during the day and the frequency of once a month. Results. During the warm period, the emission of carbon dioxide from the soil changes dynamically depending on temperature and humidity. The maximum of emission coincides with the periods of warm summer showers in June-July, the minimum values are characteristic for the late autumn period. The total emission losses of carbon in chernozems over the vegetation period ranged from 480 to 910 kg/ha and varied depending on the methods of tillage ± (4.0–6.0) % and fertilization systems ± (3.8–7.1) %. The changes in the intensity of CO 2 emission from the soil under different methods of soil tillage are associated with hydrothermal regime and the depth of crop residues location. The biggest difference is observed im- mediately after tillage, but in the spring period the differences are only 12–25 %, and after drying of the top layer of soil become even less. Direct seeding technology provides the greatest emission of CO 2 from chernozem, which is fa- cilitated by better water regime and more complete mineralization of plant residues on the soil surface. Annual losses of carbon are the least under disking of soil at 10–12 cm. The changes in the intensity of CO 2 emission from the soil under different fertilization systems are associated with the involvement of the additional organic matter from plant residues and manure to the microbiological decomposition. The greatest emission was observed under the organic- mineral fertilization system, which increased the loss of carbon by 7–8 % in comparison with the mineral system in the unfavorable hydrothermal year and by 11–15 % in the more favorable year. These differences are observed mainly during the fi rst half of the growing season when there is a clear tendency to increase the intensity of soil respiration. Conclusions. The hydrothermal conditions of the warm period of the year are decisive in the formation of the CO 2 emission fl ow from chernozems. Due to the improvement of agricultural practices, emissions might be reduced but not more that by 15 % of natural factor contribution.

Effect of Copper Slag as a Fine Aggregate on the Durability Characteristics of High-Performance Concrete (HPC) Containing Silica Fume

2020 ◽  
Vol 07 (02) ◽  
pp. 1-10
Author(s):  
Rizwan Ahmad Khan ◽  
Keyword(s):  
Silica Fume ◽  
High Performance ◽  
High Performance Concrete ◽  
Copper Slag ◽  
Chloride Penetration ◽  
Interfacial Transition Zone ◽  
Fine Aggregate ◽  
Fresh Properties ◽  
Fine Aggregates ◽  
Effect Of Copper

This paper investigates the fresh and durability properties of the high-performance concrete by replacing cement with 15% Silica fume and simultaneously replacing fine aggregates with 25%, 50%, 75% and 100% copper slag at w/b ratio of 0.23. Five mixes were analysed and compared with the standard concrete mix. Fresh properties show an increase in the slump with the increase in the quantity of copper slag to the mix. Sorptivity, chloride penetration, UPV and carbonation results were very encouraging at 50% copper slag replacement levels. Microstructure analysis of these mixes shows the emergence of C-S-H gel for nearly all mixes indicating densification of the interfacial transition zone of the concrete.

Special Binding for Refractory Concretes

2019 ◽  
Vol 17 (17) ◽  
pp. 11-16
Author(s):  
Elena Valentina Stoian ◽  
Dan Nicolae Ungureanu ◽  
Florin Toma ◽  
Alexandru Gabriel Colţa ◽  
Daniel Anculescu ◽  
...  
Keyword(s):  
Silica Fume ◽  
Ph Value ◽  
Concrete Structures ◽  
Hydrated Alumina ◽  
Binding System ◽  
Hydraulic Binder ◽  
Aluminous Cement ◽  
Mechanical Strengths ◽  
Condensed Silica Fume ◽  
New System

AbstractThe paper shows data related to coexistence of various binding systems, which could be present during the hardening of special concretes. It is taken into account the Ultra Low Aluminous Cement Concretes additivated with different materials (phosphates and mineral ultra dispersed powders - Condensed Silica Fume, Hydrated Alumina etc). In correlation to the pH-value, these substances can favour the forming of new binding systems besides the hydraulic binder (which is not important in this case). The new system is the coagulation binding form. The coagulation binding system has a very important role in the advanced compactness and in the increasing mechanical strengths of concrete structures.

A common precursor to both prebiotic and biological pathways to RNA nucleotides

2018 ◽  
Author(s):  
Andrea Pérez-Villa ◽  
Thomas Georgelin ◽  
Jean-François Lambert ◽  
Marie-Christine Maurel ◽  
François Guyot ◽  
...  
Keyword(s):  
Enzymatic Synthesis ◽  
De Novo ◽  
Life Forms ◽  
Hydrothermal Conditions ◽  
Modern Life ◽  
Ab Initio Simulations ◽  
Spontaneous Formation ◽  
Common Precursor ◽  
Open Issue ◽  
Anomeric Carbon

Understanding the mechanism of spontaneous formation of ribonucleotides under realistic prebiotic conditions is a key open issue of origins-of-life research. In cells, <i>de novo</i> and salvage nucleotide enzymatic synthesis combines 5-phospho-α -D-ribose-1-diphosphate ( α-PRPP) and nucleobases. Interestingly, these reactants are also known as prebiotically plausible compounds. Combining ab initio simulations with mass spectrometry experiments, we compellingly demonstrate that nucleobases and α -PRPP spontaneously combine, through the same facile mechanism, forming both purine and pyrimidine ribonucleotides, under mild hydrothermal conditions. Surprisingly, this mechanism is very similar to the biological one, and yields ribonucleotides with the same anomeric carbon chirality as in biological systems. These results suggest that natural selection might have optimized – through enzymes – a pre-existing ribonucleotide formation mechanism, carrying it forward to modern life forms.

A common precursor to both prebiotic and biological pathways to RNA nucleotides

2017 ◽  
Author(s):  
Andrea Pérez-Villa ◽  
Thomas Georgelin ◽  
Jean-François Lambert ◽  
Marie-Christine Maurel ◽  
François Guyot ◽  
...  
Keyword(s):  
Enzymatic Synthesis ◽  
De Novo ◽  
Life Forms ◽  
Hydrothermal Conditions ◽  
Modern Life ◽  
Ab Initio Simulations ◽  
Spontaneous Formation ◽  
Common Precursor ◽  
Open Issue ◽  
Anomeric Carbon

Understanding the mechanism of spontaneous formation of ribonucleotides under realistic prebiotic conditions is a key open issue of origins-of-life research. In cells, <i>de novo</i> and salvage nucleotide enzymatic synthesis combines 5-phospho-α -D-ribose-1-diphosphate ( α-PRPP) and nucleobases. Interestingly, these reactants are also known as prebiotically plausible compounds. Combining ab initio simulations with mass spectrometry experiments, we compellingly demonstrate that nucleobases and α -PRPP spontaneously combine, through the same facile mechanism, forming both purine and pyrimidine ribonucleotides, under mild hydrothermal conditions. Surprisingly, this mechanism is very similar to the biological one, and yields ribonucleotides with the same anomeric carbon chirality as in biological systems. These results suggest that natural selection might have optimized – through enzymes – a pre-existing ribonucleotide formation mechanism, carrying it forward to modern life forms.

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