This work analyses the influence of fine concrete fractions (<5 mm) of different natures -calcareous (HcG) and siliceous (HsT)-obtained from construction and demolition waste (C&DW) on the behaviour ...of blended cement pastes with partial replacements between 5 and 10%. The two C&DW fractions were characterised by different instrumental techniques. Subsequently, their lime-fixing capacity and the physico-mechanical properties of the blended cement pastes were analysed. Lastly, the environmental benefits of reusing these fine wastes in the manufacture of future eco-efficient cement pastes were examined. The results show that HsT and HcG exhibit weak pozzolanic activity, owing to their low reactive silica and alumina content. Despite this, the new cement pastes meet the physical and mechanical requirements of the existing regulations for common cements. It should be highlighted that the blended cement pastes initially showed a coarser pore network, but then they underwent a refinement process between 2 and 28 days, along with a gain in compressive strength, possibly due to the double pozzolanic and filler effect of the wastes. The environmental viability of the blended cements was evaluated in a Life Cycle Assessment (LCA) concluding that the overall environmental impact could be reduced in the same proportion of the replacement rate. This is in line with the Circular Economy goals and the 2030 Agenda for Sustainable Development.
Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the ...identification of anhydrous, hydrated, and carbonated phases in cement‐based materials has been demonstrated. In the present work, the application of micro‐Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C12A7, CA2, C2AS, cubic‐C3A, C4AF, and C4A3S¯; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet (C3AH6); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.
The calcium silicate hydrate gel (C–S–H) was synthesized by the double decomposition method because of the simplicity and the quickness of the procedure. The structure of the C–S–H gels after 1 week ...and 4 weeks in contact with the formation solution was studied through micro-Raman, Fourier transformed infrared spectroscopy and
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Si nuclear magnetic resonance. Simultaneous thermodifferential–thermogravimetric analysis and mass spectrometry (DTA/TG/MS) was used to identify the amount of calcium carbonate formed due to the reaction between the calcium and atmospheric CO
2
. With DTA/TG/MS, mass loss due to CO
2
was observed to take place at temperatures below 400 °C, unidentified to date, which might be associated with the CO
2
adsorbed on the C–S–H gel. Thus, in the TG analysis in the 300–430 °C range, both the loss of water due to the decomposition of the amorphous calcium carbonate and the loss of CO
2
adsorbed on the gel must be considered. Additionally, polymerization of the gel and a decrease in the Ca/Si ratio was observed from the samples from 1 to 4 weeks.
Concrete is one of the most fire‐resistant materials, whose resistance depends on the chemical and structural characteristics of the hydrated calcium silicate (C‐S‐H) formed in the hydration and ...hardening process. However, the structure and composition of this C‐S‐H varies with the time of hydration. The effect of the composition of the calcium silicate on the anhydrous material formed has been studied after subjecting it to an accelerated study of the effect of fire, irradiating it with a CO2 laser. Changes in the composition of C‐S‐H can lead to changes in the mechanical properties of the cement. C‐S‐H samples with different chemical composition (Ca/Si ratios 1 and 2) as well as different synthesis processes (double decomposition and hydrothermal) were studied. The crystalline phases obtained after heating were identified through micro‐Raman spectroscopy, which confirmed the formation of anhydrous calcium silicates with the same Ca/Si ratio as the initial one. In C‐S‐H gels with a Ca/Si ratio of over 1.5, stable Ca (OH)2 was formed. Scanning electron microscopy/energy dispersive X‐ray analysis analysis determined that in the process of heating with the laser, water is lost fast, generating porous structures. Such porosity is higher in materials with a lower Ca/Si ratio.
The effect of fire over the composition of the hydrated calcium silicate of cement has been studied. The crystalline phases obtained after irradiation with a CO2 laser were identified through micro‐Raman spectroscopy. Different calcium silicates have been formed as well as stable Ca(OH)2. After the process of heating with the laser, water is lost, generating porous structures.
Raman spectroscopy has been used to follow the hydration of the main calcium aluminate phases present in calcium aluminate cement (CAC) and calcium sulfoaluminate cement (CSA) clinkers, i.e. C3A, CA, ...C12A7, CA2, C4AF and C4A3S¯. We investigate the reaction products induced by hydration on these six compounds. Spectra of anhydrous pure samples and pastes hydrated for 48h were recorded. In order to contrast the Raman analysis results, the samples were also characterized by XRD and FTIR techniques. Hydration of calcium aluminates led to the formation of C3AH6, C2AH8 and aluminum hydroxide, and hydration of ferrite phases led to hydrogarnet phases. Meanwhile the hydration of C4A3S¯ led to the formation of ettringite and AFm phases. The Raman spectra analysis developed gives the details of the vibration of the different functional groups present in the calcium aluminate hydrated samples and our results show the potential of Raman spectroscopy in the study of the aluminate hydration on the cement chemistry. The product identity was confirmed by XRD and infrared spectroscopy.
Density Functional Theory was applied to obtain a refined IR and Raman theoretical vibrational spectra of the major silicate phases of Portland cement, i.e. dicalcium silicate (β-C2S) and tricalcium ...silicate (C3S). We investigate the crystal structure and vibrational frequency values in the electronic ground state using a plane wave density functional method with new norm-conserving pseudopotentials. The calculated results show that the optimized geometry can reproduce the crystal structure well, and the theoretical vibrational frequency values show good agreement with the experimental values and allow us to describe some uncertainties in the experimental assignments previously described. The assignment performed for 100–1200 cm−1 region shows that the vibrations of C2S and C3S are presented in the IR spectra, while the vibrations with a minor contribution from the silica groups are observed in the Raman spectra. Satellite bands from C3S are observed in the experimental spectra but there not in the calculated one.
•C2S and C3S compounds has been synthetized, X-ray analysis and infrared together with Raman spectroscopy studied.•Monoclinic β-C2S and C3S monoclinic and triclinic atomistic models describe the analyzed compounds.•The ν1-like, ν3-like mode of SiO44− has been assigned with accuracy.•AlO and MgO bands from C3S stabilizer have been identified.
The main component of the cement hydration, are both, the calcium silicate hydrate (C–S–H) and calcium silicate hydrate with Al (C–S(A)–H), whose composition is characterized by its calcium to ...silicon ratio (Ca/Si), which normally varies from 0.6 to 1.6. The theoretical Ca/Si ratios of the synthesized gels were compared with those of the experimental gels, which were determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES). In addition, the microstructure of the gels was studied by spectroscopic techniques: infrared and Raman spectroscopy and nuclear magnetic resonance. By the double-decomposition method used in this work (1 day at 25 °C, inert atmosphere and pH = 12.3), only C–S–H and C–S(A)–H gels with a maximum Ca/Si ratio ranging from 0.8 to 1.0 were synthesized. However, the structures of the gels are slightly different as the Ca/Si ratio increases.
Calcium silicate hydrate, with and without Al has been synthetized following double decomposition method, with different Ca/Si ratio. Analyzing Ca/Si ratio of the formed compounds, indicate that C–S(A)-H with Ca/Si ratios from 0.6 to 1.1 can be formed.
Highlights
Calcium silicate hydrate, with and without aluminum, was synthesized by the double-decomposition method with different nominal Ca/Si ratio.
Ca/Si ratio ranging from 0.8 to 1.0 in the C–S–H synthesized by the double-decomposition method.
C–S(A)–H gel with Ca/Si ratio <0.6, cannot be synthesizes by the double-decomposition method.
As nominal Ca/Si ratio increases, Q
1
units increases in the C–S–H gel structure.
The arrival of Spaniards in the Caribbean islands introduced to the region the practice of applying pigments onto buildings. The pigments that remain on these buildings may provide data on their ...historical evolution and essential information for tackling restoration tasks. In this study, a 17th-century mural painting located in the Cathedral of Santo Domingo on the Hispaniola island of the Caribbean is characterised via UV–VIS–NIR, Raman and FTIR spectroscopy, XRD and SEM/EDX. The pigments are found in the older Chapel of Our Lady of Candelaria, currently Chapel of Our Lady of Mercy. The chapel was built in the 17th century by black slave brotherhood and extended by Spaniards. During a recent restoration process of the chapel, remains of mural painting appeared, which were covered by several layers of lime. Five colours were identified: ochre, green, red, blue and white. Moreover, it was determined that this mural painting was made before the end of the 18th century, because many of the materials used were no longer used after the industrialisation of painting. However, since both rutile and anatase appear as a white pigment, a restoration may have been carried out in the 20th century, and it has been painted white.
The study described sought further understanding of the synergies in a mix of CDW pozzolans, containing (calcareous and siliceous) concrete and glass waste, used to prepare ternary eco-cement paste ...bearing 7% of the binary blend at concrete/glass ratios of 2:1 and 1:2. The mineralogical phases in the 2-day, 28-day, and 90-day cement matrices were identified and monitored using XRF, XRD-Rietveld, SEM-EDX, FT-IR, and NMR. The findings showed that changes in the reaction kinetics in the ternary blended pastes relative to OPC pastes depended on the nature of the recycled concrete and the glass content. Adding the binary mix bearing calcareous concrete (at a ratio of 2:1) favoured ettringite, portlandite, and amorphous phase formation, whilst the blends with siliceous concrete favoured C-S-H gel formation. Monocarboaluminate was detected in the 90-day siliceous concrete and glass pastes in amounts similar to those found in the reference OPC paste.
A convenient ligand‐free catalytic system has been developed for the chemoselective cyclization reaction of various α‐allenol derivatives by palladium nanoparticles (PdNPs) in an aqueous reaction ...medium.
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