Eco-efficient cements based on industrial wastes constitute a priority line of research for the sustainability of the cement sector, in response to the challenges of the circular economy at a ...European level. Eco-innovation and investigation of new alternative sources of primary materials from waste arise as potential actions directed at the achievement of greater efficiency in the use of resources. From among the broad range of industrial wastes, those that contain kaolinite (K) and phyllosilicates are ideal as active additions in the manufacture of cements, having previously undergone a process of thermal activation. Earlier works have indicated that the chemical reactivity of natural K (untreated kaolin) may be increased through the addition of ZnO as a chemical agent. In this study, the effect of ZnO as a chemical agent is for the first time studied, when added to coal waste in proportions of 0.5, 1.0, 1.5 and 3.0% by weight, prior to the thermal activation process of the waste that is calcinated at 550°, 600°, and 650°C for 2h. The mineralogy and the pozzolanic activity of the activated products are considered, and their influence on the evolution of the hydrated phases at 1, 7, and 28days of reaction in the pozzolan/lime system. Subsequently, the results are compared with those obtained from pure natural kaolinite activated at 600°C/2h, with ZnO addition and without chemical agent ZnO, with an added quantity of 1.0% in weight. The results showed important variations when the chemical activator (ZnO) was used for the natural kaolinite (NK) and the industrial waste. The chemical activator favors the disaggregation of the phyllosilicates from the aggregates, strengthening the pozzolanic reaction in the natural/lime kaolinite system. However, the activator in the coal waste/lime system, in addition to favoring the disaggregation of the aggregate, leaves epitaxial deposits on the surface and on the edges of the materials, saturating the substrate surface loading, with an inhibitory effect on the pozzolanic reaction. The abundance of metakaolinite (MK) and the partial dehydroxylation of the mica with its subsequent reorganization, explains the appearance of these minerals as one of the products of the reaction. With SEM/EDX, the existence of CSH gels of a spongy appearance may be observed following thermal activation of the coal waste; while if the activation is done under the combined effect of temperature and the addition of 1.0% ZnO, then the chemical activator favors the formation of long fibers and the appearance of gels, with compositions similar to LDH and calcium aluminates.
•The calcination of coal waste was producing, at 600°C/2h, the dihydroxylation of K.•The dehydroxylation of K and mica generated spongy aggregates and scaly surfaces.•CSH gels, St, mica and LDH was the principal products in the natural K/lime system.•ZnO inhibited the formation of layered compounds.•ZnO favored the formation of fibers with similar composition to LDH and Ca aluminates.
The arrival of Christopher Columbus in America stimulated the creation of new settlements in which the materials and construction methods coming from Spain and those existing in the area were used. ...The first village built was La Isabela (1494) where the Spaniards found good limestone for ashlars and were able to make lime as well as good clay for earth walls, masonry walls, etc. After La Isabela, the cities of La Vega (1495) and Santo Domingo (1498) were established. These villas still include vestiges of these building materials that are a source of information about their composition. The study is focused on the ruins of the fortress of Concepcion de La Vega that survived the earthquake in 1562 that destroyed the city. The aim of this research was to characterize the mortar and plasters of the fortress of Concepcion de La Vega on the Hispaniola Island. To determine their chemical and mineralogical composition optical microscopy (OM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and a thermogravimetric differential thermal analysis (TG-DTA) were used. The results showed that the major component of the mortars was CaCO3 (95 %), indicating that there is lime mortar. The plaster is lime based with iron oxide.
Carbonation of ternary cement systems Martínez-Ramírez, Sagrario; Fernández-Carrasco, Lucía
Construction & building materials,
02/2012, Letnik:
27, Številka:
1
Journal Article
Recenzirano
► We study the formed ettringite in ternary systems (fly ash, CaSO
4, CAC). ► We study the evolution of ettringite after carbonation. ► We observed that carbonates decomposed ettringite giving ...gypsum, CaCO
3 and Al(OH)
3. ► Carbonates incorporated into the gypsum forming rapidcreekite.
The main hydration reaction product in the ternary system fly ash, calcium sulphate and calcium aluminate cement (40/20/40) at 20
°C is a hydrated calcium sulfoaluminate compound, an AFt phase slightly different from “traditional ettringite”. The carbonation of ettringite develops gypsum but in this case rapidcreekite is formed. For the first time it has been observed that carbonation of the mentioned calcium sulfoaluminate compound (AFt), an hydrated calcium sulphate carbonated phase (Ca
2(SO
4)(CO
3)·4H
2O) is formed with the replacement of an SO
4 row in a (0
4
0) layer of the gypsum by CO
3 groups. The developed carbonated phase has been studied and analyzed through XRD, FTIR, Raman spectroscopy, and scanning electron microscopy.
Fire-induced compositional changes lead to strength loss and even failure in cement and concrete. Calcium silicate hydrate (C–S–H) gel, the main product of cement hydration, dehydrates at 25–200 °C, ...while temperatures of 850–900 °C alter its structure. A Raman spectroscopic study of the amorphous and crystalline phases forming after CO
2
laser radiation of cement mortar showed that C–S–H dehydration yielded tricalcium silicate at higher, and dicalcium silicate at lower, temperatures. Post-radiation variations were identified in the position of the band generated by Si–O bond stretching vibrations.
This paper explores the potential of three industrial alkaline waste materials – concrete construction and demolition waste (CDW-C), white ladle furnace slag (LFS) and biomass ash (BA) – for use as ...secondary raw materials in the manufacture of future eco-cements with a reduced carbon footprint. Circularity is one of the key strategies behind the circular economy, the cement industry roadmap and the climate neutrality targets set for 2050. The three materials were characterised using various instrumental techniques (XRF, laser, BET, XRD–Rietveld, SEM/EDX, FTIR, TG/DTA and NMR) and their chemical reactivity, the changes in their mineralogical phases and the thermodynamic stability within the pozzolan/lime system were determined. Finally, their physical and mechanical behaviour in binary cement pastes at replacement proportions of 7 % and 20 % over 90 days of curing were analysed. The results obtained show that these alkaline waste materials are different in nature and composition to standard pozzolans, with the LFS containing fluorine and the BA containing sulphates, potash and chlorides. The standard combined water test showed different levels of chemical reactivity (BA > LFS > CDW-C). Analysis of the materials’ composition, mineralogical phases and thermodynamic stability over 90 days of reaction in the pozzolan/Ca(OH)2 system revealed that hydrogarnet was the stable phase in the LFS cement paste, while in the BA and CDW-C pastes ettringite and CSH and C-(A)-SH gels, among others, were the stable phases. All the blended cement pastes with 7 % and 20 % replacement content met the physical requirements and maintained the strength category of the starting cement.
•Generation of new knowledge on alkaline waste such as ecopozzolans.•Characterisation of the starting ecopozzolans by different instrumental techniques.•Chemical reactivity in different systems.•Evolution of mineralogical phases with reaction time and thermodynamic model.•Physical-mechanical behaviour of cement ecopastes
Weathering steels are widely used in civil engineering, architecture and contemporary art due to their mechanical properties, their enhanced resistance to atmospheric corrosion as well as their ...aesthetic properties. Artists and blacksmiths often apply chemical treatments to obtain the appealing colors of a patina in a shorter period of time. However, the development of an accelerated patina may have an effect on the final appearance and color of the surface. With the aim of evaluating differences in color and studying the evolution of the surface, eight accelerated patinas were made and exposed to the atmosphere for periods of time of up to 24 months and were compared to a natural patina. The characterization studies showed the presence of lepidocrocite on the surface. A close inspection of the X-ray diffraction patterns showed the displacement of the (020) lepidocrocite reflection and asymmetric broadening of selective lines of this phase that were associated to stacking and twins faults, respectively. These faults decrease with the exposure time and are related to a maximum at 630 nm in the reflectance spectrum and the stabilization of the b* coordinate (yellow color). The colors of the accelerated patinas differ from the natural patina at short exposure times. However, they tend to converge at longer exposure times.
Spent activated carbon is a by-product of potabilization plants. The present study explored the feasibility of valorizing this waste as an alternative fuel to replace oil coke in portland clinker ...furnaces. This involved determining its composition, calorific value, and ash and heavy metal content. Since the ash generated by spent activated carbon firing is taken up by the clinker, the possible effect of such uptake on clinkerization or the properties of the clinker obtained were also ascertained.
Although spent activated carbon has an 18% lower calorific value than oil coke, one of the traditional cement kiln fuels, it was found to be apt for the purpose envisaged. Its ash content (10 wt%) is one order of magnitude higher than the ash content in coke.
Spent activated carbon ash contains substantial proportions of anhydrite and quartz, hematite and augite, but consists primarily of amorphous matter (59 wt%).
The effect of this ash on clinker phases was studied by clinkerizing raw meal in which it was used as a replacement for clay. Such meal exhibited high burnability and yielded clinkers with a composition and mineralogy comparable to the properties found in the industrial product. The sulfate present in the ash induced substantial alite crystal growth in the clinker. The loss of minority elements during clinkerization was likewise studied.
•A waste material (Spent activated carbon) is proposed as alternative fuel in cement production.•Incorporation of new fuel ashes in raw mixes improved its burnability.•Modification in composition and microstructure of clinker phases due to the new fuel ashes has been established.
White cement pastes were hydrated in the presence or absence of amorphous nanosilica (nSA) and cured at 25 or 65 °C. The findings showed that at the higher curing temperature the initial belite ...hydration rate rose substantially and that this effect was more accentuated in the pastes containing nSA. The C–S–H gel formed in the presence of nSA was more uniform and had a consistently longer mean chain length (MCL) than in the gels formed in the absence of the addition. Moreover, the C–S–H gel formed in nSA-bearing paste cured at the higher temperature had a longer MCL and a higher Al3+ uptake than the gels in the other pastes studied. Lastly, at 65 °C, the presence of nSA stabilized ettringite formation during the first 28 days of paste hydration; while no calcium hemicarboaluminate, which was the sole crystalline aluminate hydrate identified in the unblended pastes, was detected in the nSA-containing pastes.
The requirements for the formation of a protective patina on conventional weathering steels (WS) are well known in the scientific literature related to civil structures. However, these criteria are ...not always given due consideration when WS is used in cultural heritage, as in the case of sculptural work. An artificial patina was produced simulating artists’ working procedures using a direct patination technique, applying a solution of 10% H2SO4 on WS specimens. These were exposed for two years in the urban atmosphere of Madrid along with weathering steel specimens without artificial patina, called natural patina. The patinas generated have been analyzed using colorimetry, micro-Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and thickness measurements.The artificial patina color formed hardly differs from the color that the natural patina acquires from practically the beginning of its formation in the atmosphere of Madrid. After two years, the atmospheric corrosion rate of patinated WS is lower than 6 µm/year. The sulfuric acid treatment accelerates the protective ability of the patina with respect to the natural patina according to the ratio goethite to lepidocrocite (α/γ). Chromium-rich goethite is located in the inner part of the artificial patina as well as chromium-rich ferrihydrite. Ferrihydrite may act as a precursor of nanophasic goethite.
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