178,706 research outputs found
Fabrication and Properties of Blended Calcium Sulfoaluminate Cements Based on Thermally Treated Reservoir Sediments
No full textIn 2021, approximately 4.1 billion tonnes of cement were globally produced and the annual
CO2 emissions from cement plants reached almost 2.8 billion metric tonnes. In recent years, many
efforts have been made to manufacture low-CO2 cements. In this regard, great consideration has been
given towards calcium sulfoaluminate (CSA) binders for both their technical features and sustainable
properties, principally connected to their industrial process. The use of blended cements composed
by CSA binders and supplementary cementitious materials (SCMS) can be an effective way to (a)
reduce the CO2 footprint and (b) produce greener binders. This scientific work studied the utilization
of different amounts (15–35 wt%) of calcined reservoir sediments (RS) as SCMS in blended CSA
binders, where the binders were cured for up to 56 days and characterised by various analytical
techniques. It was found that thermally treated RS were particularly noteworthy as their utilization
allowed for a dilution of the CSA clinker, thus implying a decrease in CO2 emissions and a reduction
in costs related to their production. However, compared to a plain CSA cement, the blended systems
showed rather similar volume stability levels, whilst their compressive strength and porosity values
were, respectively, lower and higher at all the investigated aging periods
The influence of chemical activators on the hydration behavior and technical properties of calcium sulfoaluminate cements blended with ground granulated blast furnace slags
No full textThe manufacture of Ordinary Portland cement (OPC) generates around 8% of the global CO2 emissions related to human activities. The last 20 years have seen considerable efforts in the research and development of methods to lower the carbon footprint associated with cement pro-duction. Specific focus has been on limiting the use of OPC and employing alternative binders, such as calcium sulfoaluminate (CSA) cements, namely special hydraulic binders obtained from non-Portland clinkers. CSA cements could be considered a valuable OPC alternative thanks to their dis-tinctive composition and technical performance and the reduced environmental impact of their manufacturing process. To additionally reduce CO2 emissions, CSA cements can also be blended with supplementary cementitious materials. This paper investigates the influence of two separately added chemical activators (NaOH or Na2CO3) on the technical properties and hydration behavior of four CSA blended cements obtained by adding to a plain CSA cement two different ground granulated blast furnace slags. Differential thermal-thermogravimetric, X-ray diffraction and mercury intrusion porosimetry analyses were done, along with shrinkage/expansion and compressive strength measurements
Calcium sulfoaluminate cement and fly ash-based geopolymer as sustainable binders for mortars
No full textThis work investigates the hydration behaviour and the physico-mechanical properties of mortars based on calcium sulfoaluminate (CSA) cements and fly ash-based geopolymers (GEO) as alternatives to ordinary Portland cement. According to the EN 1504-3, mortars were prepared in order to reach three compressive strength classes, namely R1, R2 and R3 (R1 with Rc ≥ 10 MPa, R2 with Rc ≥ 15 MPa and R3 with Rc ≥ 25 MPa). CSA mortars were prepared by using sulfoaluminate cement alone (R3) or in mixture with a limestone filler (R1 and R2); GEO mortars were manufactured by alkali-activation of coal fly ash and calcium aluminate cement with a sodium silicate and potassium hydroxide water solution. The hydration behaviour was evaluated on pastes submitted to differential thermal-thermogravimetric and X-ray diffraction analyses. Mortars was analysed through mercury intrusion porosimetry; their mechanical properties were evaluated in terms of compressive strength and dynamic modulus of elasticity. Furthermore, capillary water absorption and drying shrinkage tests were carried out in order to evaluate their durability. Due to the rapid ettringite formation, CSA-based mixtures reached their maximum compressive strength values faster than the corresponding GEO mortars. Results showed that the lower modulus of elasticity of GEO mortars causes the higher drying shrinkage. Moreover, the lower porosity exhibited by GEO mortars was responsible for the lower water capillary absorption
Los orígenes del latifundio en Paraguay a fines del Siglo XVII : Una lectura-homenaje a partir de Carlos Pastore y su lucha por la tierra en el Paraguay
No full textEn homenaje a la obra de Carlos Pastore, La Lucha por la Tierra en el Paraguay, este artículo reflexiona sobre el origen del latifundio en el Paraguay, tras la expulsión de los jesuitas a fines del siglo XVIII.Fil: Telesca, Ignacio. Universidad Nacional de Formosa; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Investigaciones Geohistóricas (i); Argentin
Multidimensional indicators for evaluating impacts of climate change and air pollution on human health at local scale: a test case in Southern Italy.
No full textForeshocks or swarms? Insights from theory and statistical analysis
No full textAre foreshocks “fore-shocks” or simply markers of local instability without any prognostic value about future large-scale mainshocks? We try to answer this question using both theoretical modelling and statistical analysis of clusters listed in relocated high quality seismic catalogues. Concerning theory, we show that the combined effect of long-range correlations and fault memory make the system sensitive to both details and history. It results in different future evolutions because of tiny changes in internal parameters or in past occurrences. For this reason, even an identical sequence of events can flow into drastically different future because of a tiny variation in the physical conditions. On the other hand, two completely different seismic patterns can give rise to seismic events with similar features, e.g., the 2009 Mw 6.3 L'Aquila and the 2016 Mw 6.0 Amatrice event, which occurred in the same normal-faulting region in Central Apennines in Italy, were preceded by five months of foreshocks (Papadopoulos et al., 2010) and seismic quiescence (Gentili et al., 2017) respectively. To provide observational evidence for answering our question, we investigate the relationships between several parameters of seismic clusters until the mainshocks in relocated seismic catalogues in California and Italy as a function of their mainshock magnitude (e.g., the involved area, duration, seismic rate, number of events, cumulative nucleated seismic moment, Shannon and Tsallis entropy, inter-event times distribution, global coefficient of variation of interevent times, trend, and fluctuations of magnitudes and interevent times). We find differences in the distributions of some features (e.g., Zaccagnino et al., 2023), although large variability is observed, while others cannot be distinguished. Foreshocks and swarms share the same scaling behaviour and are likely generated by the same physical mechanism; however, statistical analyses highlight that foreshocks spread over larger areas, are featured by larger and more energetic clusters with also higher variance of magnitudes and relative Tsallis and Shannon entropies. We suggest possible explanations for them. On the base of our results, we believe that precursory patterns of accelerated seismic activity can be hardly distinguished by more frequent swarms using the structural and statistical properties of clusters (Zaccagnino et al., 2024). In this sense, foreshocks are likely of limited usefulness for short-term earthquake prediction. Conversely, seismic hazard may benefit of the identification of regions featured by strongly correlated seismic activity, which is likely to be a mark of crustal developing instability.
References:
Gentili, S., Di Giovambattista, R., & Peresan, A. (2017). Seismic quiescence preceding the 2016 central
Italy earthquakes. Physics of the Earth and Planetary Interiors, 272, 27-33.
Papadopoulos, G. A., Charalampakis, M., Fokaefs, A., & Minadakis, G. (2010). Strong foreshock signal
preceding the L'Aquila (Italy) earthquake (M w 6.3) of 6 April 2009. Natural Hazards and Earth System
Sciences, 10(1), 19-24.
Zaccagnino, D., Telesca, L., & Doglioni, C. (2023). Global versus local clustering of seismicity:
Implications with earthquake prediction. Chaos, Solitons & Fractals, 170, 113419.
Zaccagnino, D., Vallianatos, F., Michas, G., Telesca, L., & Doglioni, C. (2024). Are Foreshocks Fore‐
Shocks?. Journal of Geophysical Research: Solid Earth, 129(2), e2023JB027337
Calcium sulfoaluminate and alkali-activated fly ash cements as alternative to Portland cement: study on chemical, physical-mechanical, and durability properties of mortars with the same strength class
No full textThere is an increasing interest towards the development of alternative binders for the manufacture of sustainable mortars and concretes. Ordinary Portland cement (OPC) is the most commonly used material in construction, even if its production process is highly polluting. Both calcium sulfoaluminate (CSA) and alkali-activated cements (AAC) are potential alternative binders to be used in both structural (R3 class, with Rc " 25 MPa) and non-structural applications (R1 and R2 classes, with Rc " 10 MPa and Rc " 15 MPa, respectively) according to UNI EN 1504-3. This paper reports the hydration mechanisms and the evolution of porosity of OPC-, CSA- and AAC-based binders. The properties of fresh and hardened mortars, belonging to the above-mentioned mechanical strength classes, were evaluated and compared with particular emphasis on durability properties in terms of capillary water absorption, drying shrinkage, and resistance to sulfate attack. The results show that CSA-based mortars exhibit the lowest drying shrinkage due to their highest elasticity modulus. AAC mortars are characterized by the highest water vapor permeability and the lowest capillary water absorption for the highest presence of large pores
(>3000 nm)
Tidal sedimentation preserved in volcaniclastic deposits filling a peripheral seaway embayment (early Miocene, Sardinian Graben)
No full textThe Sardinian Graben System was a part of a NE-SW-oriented extensional basin, rotated counter-clockwise into a N-S-elongate basin, as consequence of the eastward migration of the Apennine orogenic front, in the western Mediterranean during the Neogene. Starting from the early Miocene, the Sardinian Graben was inundated by marine waters, turning progressively into a seaway, characterized by a tidal circulation as consequence of the connection between the Atlantic Ocean to the west and the Paratethys Ocean to the east. In this work, we investigate an area located marginally to the mid-seaway, whose well-exposed volcaniclastic deposits record the local expression of a tidal amplification occurring in a coastal peripheral embayment of the wider Sardinian Seaway. The studied succession is ca. 140 m thick and includes three main units: (i) the 20-m-thick lowermost unit consists of fluvio-lacustrine sandstones and conglomerates belonging to lower delta-plain and delta-platform environments; (ii) the second unit is 60–70 m thick and includes heterolithic sandstones and mudstones, exhibiting a variety of tidal sedimentary structures, and lies on the previous deposits through a tidal ravinement surface; these two units are mostly volcaniclastic in composition, reflecting the dominance of a magmatic source over other extrabasinal components; (iii) the uppermost unit is ca. 50 m thick, erosionally overlies the previous deposits and is made up of shoreface sandstones and open-shelf mudstones, whose composition indicates even less volcaniclastic elements and the prevalence of other clastic alongshore-derived components. Based on the results of the facies analysis, the study succession is interpreted as the infill of an incised valley along the southern flank of a structural high. The valley was excavated during a phase of relative sea-level lowstand (Aquitanian?) preceding a subsequent stage of major transgression (Burdigalian). Initially, a fluvial system impinged the valley from the west favoring the progradation of a deltaic system in a shallow-marine embayment. During an early stage of transgression, the isolation of a part of this coastal area generated by the building of a barrier island, produced the onset of a tidal-flat sedimentation over the previous deposits. A late transgression occurred through the inundation of this coastal area by marine waters and the consequent back-stepping of beach-barrier and open-shelf strata. The sedimentological features of this stratigraphic succession indicate as this valley was filled in a tectonic setting with a high rate of accommodation, where the tidal influence progressively increased during sediment accumulation, possibly due to the marginal position respect to a wider tide-dominated marine conduit. The present paper thus: (i) documents for the first time a tidal signature in the lower Miocene strata of Sardinia; (ii) indicates new possible relationships with other, coeval seaway successions of the western and northern Mediterranean area; (iii) suggests constrains for palaeogeographic reconstructions; (iv) and throws the basis for future researches on the Sardinian Seaway
Enhancement of the environmentally friendly features of calcium sulfoaluminate cements through the use of a calcium looping spent sorbent as a raw material
No full textReduced CO2 emission, increased energy saving and potential use of several industrial by-products as raw mix components are well-recognized features associated with the calcium sulfoaluminate (CSA) clinker manufacture which, compared with that of Portland clinker, requires less limestone in the kiln feed as well as lower burning temperature, fuel consumption and grinding energy in the cement mill. The above-mentioned environmentally friendly characteristics can be further improved through a total replacement of limestone, on which both the CO2 emission and kiln thermal input are strongly dependent, with a poorly carbonated source of lime.
In this work, a CaO-rich spent sorbent, generated during a calcium looping (CaL) process and purged after 60 calcination/carbonation cycles from a 200 kWth dual fluidized bed pilot facility, was tested as a raw material together with other industrial by-products. These were (1) flue gas desulfurization (FGD) gypsum, as a source of CaSO4, (2) anodization mud (AM), as a source of Al2O3 and additional sulfate, (3) fluidized bed combustion (FBC) fly ash and (4) FBC bottom ash or both of them, as a source of CaSO4 plus additional alumina and uncarbonated lime.
Eight CSA clinker-generating raw mixes were heated in a laboratory electric oven at temperatures ranging from 1200° to 1350°C: one included only natural materials (40.4% bauxite, 30.4% limestone, 29.2% gypsum) and was taken as a reference term; the others contained CaL spent sorbent in a measure comprised between 20.0 and 28.3% by mass, bauxite (42.6–47.3%) or AM (53.6–65.6%), natural (15.3–30.7%) or FGD (11.6–24.4%) gypsum, FBC fly- (26.4%) or bottom- (17.6%) ash or a mixture of them (13.2 and 8.8%, respectively).
Basically, the X-ray diffraction (XRD) analysis on the burning products showed high conversion of reactants and good selectivity toward the main cement component (C4A3$), especially at 1250° or 1300°C. CSA cements based on different synthetic clinkers, investigated by means of both XRD and differential thermal–thermogravimetric (DTA–TG) analyses, generally displayed a similar hydration behavior
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