12 results on '"Bignozzi, Maria Chiara"'
Search Results
2. Fly ash-based lightweight geopolymer mortars for fire protection
- Author
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Carabba, Lorenza, Gluth, Gregor J. G., Pirskawetz, Stephan M., Krüger, Simone, Bignozzi, Maria Chiara, Vyatcheslav Falikman, Roberto Realfonzo, Luigi Coppola, Petr Hàjek, Paolo Riva, Carabba, Lorenza, Gluth, Gregor J.G., Pirskawetz, Stephan M., Krüger, Simone, and Bignozzi, Maria Chiara
- Subjects
Standard fire curve ,Passive fire protection ,Room temperature curing ,Fly ash ,Building and Construction ,Materials Science (all) ,Alkali activated material ,Geopolymer ,Expanded perlite ,Civil and Structural Engineering - Abstract
The present study aims to investigate the use of geopolymer mortars as passive fire protection system for steel structures. Coal fly ashes were used as aluminosilicate source and perlite was employed as aggregate to obtain a lightweight system. In addition, a geopolymer mortar containing quartz aggregate was produced for comparison. The geopolymer mortars were applied on stainless steel plates and exposed to both, cellulosic and hydrocarbon standard fire curves, according to ISO 834-1 and EN 1363-2, respectively. Acoustic emission measurements were conducted to analyze cracking phenomena during the high temperature exposure. The resulting temperature-time curves showed that the investigated system is effective in retarding the temperature rise of the steel plates. When the cellulosic fire curve was applied, a 20 mm [0.79 in.] thick layer of lightweight geopolymer mortar protected the steel substrate from reaching the critical temperature of 500 ?C [932 ?F] for at least 30 minutes, avoiding the rapid decrease of its mechanical properties and thus representing an important safety measure against accidental fires. No spalling phenomena on heating were detected; however, significant cracking was observed on cooling.
- Published
- 2018
3. Superplasticizer Addition to Carbon Fly Ash Geopolymers Activated at Room Temperature.
- Author
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Carabba, Lorenza, Manzi, Stefania, and Bignozzi, Maria Chiara
- Subjects
CARBON ,SUPERPLASTICITY ,FLY ash ,POLYMERS ,GLOBAL warming ,EMISSIONS (Air pollution) ,PORTLAND cement - Abstract
Present concerns about global warming due to the greenhouse emissions in the atmosphere have pushed the cement industry to research alternatives to ordinary Portland cement (OPC). Geopolymer binder may constitute a possible breakthrough in the development of sustainable materials: understanding the effectiveness and the influences of superplasticizers on geopolymer systems is one of the essential requirements for its large-scale implementation. This study aims to investigate the possibility of using commercially available chemical admixtures designed for OPC concrete, to improve fresh properties of fly ash-based geopolymers and mortars. A special emphasis is laid upon evaluating their influence on mechanical and microstructural characteristics of the hardened material realized under room-temperature curing conditions. Results indicate that the addition of a polycarboxylic ether-based superplasticizer, in the amount of 1.0 wt. % by mass of fly ash, promotes an improvement in workability without compromising the final strength of the hardened material. Moreover, the addition of the polycarboxylic ether- and acrylic-based superplasticizers induces a refinement in the pore structure of hardened mortar leading to a longer water saturation time. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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4. Room temperature alkali activation of fly ash: The effect of Na2O/SiO2 ratio.
- Author
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Bignozzi, Maria Chiara, Manzi, Stefania, Natali, Maria Elia, Rickard, William D.A., and van Riessen, Arie
- Subjects
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TEMPERATURE effect , *ALKALI metals , *FLY ash , *SILICA , *BINDING agents , *HYDRAULICS - Abstract
Alkali activation of fly ash can be considered as one of the more promising alternative systems to traditional hydraulic binders, particularly if the process can be carried out at room temperature. With the aim of finding the best solution chemistry for room temperature activation, two types of fly ash have been activated using Na 2 O/SiO 2 molar ratio ranging from 0.12 to 0.20. It was found that the behaviour of the resultant geopolymer and mortars in the fresh and hardened state is more influenced by the type of fly ash, in particular by their fineness and mineralogical composition, than by the increasing proportion of sodium silicate solution in the mix. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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- View/download PDF
5. Elucidating the atomic structures of different sources of fly ash using X-ray and neutron PDF analysis.
- Author
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Natali, Maria Elia, White, Claire E., and Bignozzi, Maria Chiara
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ELECTROMAGNETIC waves , *CATHODE rays , *IONIZING radiation , *COAL ash , *NEUTRONS - Abstract
This paper presents the comparative results obtained from X-ray and neutron pair distribution function (PDF) analysis aimed at determining the variability in aluminosilicate glass chemistry in five types of class F fly ash (FA). Results have been discussed in light of the complementary information provided by the two methods in order to give a comprehensive overview of FA structure at the nanoscale. The analysis of short range correlations reveals that the bulk glassy structure of FA sources differing in chemical composition are relatively similar, but some specific distinctions in atomic structure are visible in those containing high levels of amorphous VI-coordinated aluminum (e.g., amorphous mullite/alumina), iron and/or carbon (with similar local bonding environment to graphite). The obtained experimental results fill a deficit in literature in the atomic structure and associated variability for class F FA, which is extensively used in several industrial applications including as raw material in alkali-activated cements. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
6. Acoustic emission study of heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars.
- Author
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Carabba, Lorenza, Pirskawetz, Stephan, Krüger, Simone, Gluth, Gregor J.G., and Bignozzi, Maria Chiara
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ACOUSTIC emission , *GLASS transition temperature , *MORTAR , *FLY ash , *HIGH temperatures , *FLIES - Abstract
Alkali-activated fly ashes have been proposed for various applications where resistance against high temperatures is required, yet several details regarding the response of these materials to heat-exposure need to be clarified. In the present study, heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars was analyzed by in-situ acoustic emission (AE) detection during complete heating-cooling cycles (up to ∼1100 °C), augmented by thermogravimetry and ex-situ SEM and XRD analyses. The applicability of the lightweight mortars as passive fire protection coatings was assessed by recording temperature-time curves of mortar-coated steel plates. Cracking during heating was limited and associated exclusively with the dehydration of the materials in the temperature range ∼90–360 °C. However, samples heated to temperatures above ∼600 °C exhibited intense cracking on cooling. This was attributed to differential deformations caused by local sintering and partial melting at the glass transition temperature, and subsequent quenching on cooling. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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7. Alkali activated lightweight mortars for passive fire protection: A preliminary study.
- Author
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Carabba, Lorenza, Moricone, Raffaela, Scarponi, Giordano Emrys, Tugnoli, Alessandro, and Bignozzi, Maria Chiara
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ALKALI metals , *LIGHTWEIGHT materials , *FIRE prevention , *CEMENT - Abstract
Graphical abstract Highlights • Fly ash was successfully alkali activated at room temperature. • The use of expanded perlite and H 2 O 2 allowed obtaining lightweight mortars. • Numerical simulations predicted a satisfactory fire behaviour. • Alkali activated lightweight mortars were able to outperform cement-based ones. Abstract Alkali activated lightweight mortars, obtained by room temperature activation of coal fly ash, were studied as passive fire protection systems for steel elements. Physical, mechanical and thermal properties were investigated as a function of the compositional Si/Al molar ratio and of the amount of lightweight aggregate and foaming agent. Experimental findings were used as input data to assess their fire resistance by finite volume simulations. Results pointed out that the optimized alkali activated lightweight mortars are able to outperform alternative commercial cement-based mortars, thus representing a promising technology. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
8. Steel fiber reinforced geopolymer matrix (S-FRGM) composites applied to reinforced concrete structures for strengthening applications: A preliminary study.
- Author
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Carabba, Lorenza, Santandrea, Mattia, Carloni, Christian, Manzi, Stefania, and Bignozzi, Maria Chiara
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FIBROUS composites , *REINFORCED concrete , *MECHANICAL behavior of materials , *CONCRETE waste , *CONCRETE construction , *STRENGTHENING mechanisms in solids - Abstract
Steel fiber reinforced geopolymer matrix (S-FRGM) composites are explored as a new tool in strengthening applications of reinforced concrete (RC) structures. The suitability of fly ash geopolymers as the matrix employed in S-FRGMs is investigated in this paper. Geopolymer matrix is used to embed galvanized steel fibers and bond the composite to a concrete substrate. By varying the molar concentration of the NaOH activating solution, three different geopolymer matrices are obtained and the influence of the alkaline environment on the bond behavior between fibers and matrix is examined. Physical, mechanical, and microstructural properties of the three matrices are measured and related to the interfacial bond behavior of S-FRGM-concrete joints. Results show that the decrease of the molar concentration of the NaOH activating solution leads to an increase of the interfacial bond behavior between matrix and fibers, which in turn improves the effectiveness of the composite action of the strengthening system. [ABSTRACT FROM AUTHOR]
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- 2017
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9. Fly ash-based one-part alkali activated mortars cured at room temperature: Effect of precursor pre-treatments
- Author
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Giulia Masi, Maria Chiara Bignozzi, Alessandro Filipponi, Masi, Giulia, Filipponi, Alessandro, and Bignozzi, Maria Chiara
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Pre treatment ,Precursor pre-treatment ,Heat curing ,Materials science ,Room-temperature curing ,One-part geopolymer ,Metallurgy ,Clay industries. Ceramics. Glass ,Mechanical properties ,Fly ash ,Electronic, Optical and Magnetic Materials ,Biomaterials ,TP785-869 ,Alkali activation ,Materials Chemistry ,Ceramics and Composites ,Alkali activated ,One-part geopolymers ,Caustic (optics) ,Mortar ,Mechanical propertie ,Microstructure - Abstract
One-part or “just add water” alkali activated materials (AAMs) have attracted a lot of attention thanks to the use of solid alkaline activators that makes these materials more suitable to commercialization compared to conventional AAMs (two-part). This is mainly because large quantities of caustic solutions should be handled for producing conventional AAMs. So, one-part AAMs have a great potential for in-situ applications. However, heat curing (
- Published
- 2021
10. Alkali activated lightweight mortars for passive fire protection: A preliminary study
- Author
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Raffaela Moricone, Lorenza Carabba, Alessandro Tugnoli, Giordano Emrys Scarponi, Maria Chiara Bignozzi, Carabba, Lorenza, Moricone, Raffaela, Scarponi, Giordano Emry, Tugnoli, Alessandro, and Bignozzi, Maria Chiara
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Materials science ,0211 other engineering and technologies ,020101 civil engineering ,Foaming agent ,Fly ash ,02 engineering and technology ,Geopolymer ,0201 civil engineering ,Thermal conductivity ,Passive fire protection ,021105 building & construction ,Fire resistance ,General Materials Science ,Composite material ,Civil and Structural Engineering ,Cement ,Waste processing ,Aggregate (composite) ,Building and Construction ,Alkali activated material ,Materials Science (all) ,Mortar - Abstract
Alkali activated lightweight mortars, obtained by room temperature activation of coal fly ash, were studied as passive fire protection systems for steel elements. Physical, mechanical and thermal properties were investigated as a function of the compositional Si/Al molar ratio and of the amount of lightweight aggregate and foaming agent. Experimental findings were used as input data to assess their fire resistance by finite volume simulations. Results pointed out that the optimized alkali activated lightweight mortars are able to outperform alternative commercial cement-based mortars, thus representing a promising technology.
- Published
- 2019
11. A comparison between different foaming methods for the synthesis of light weight geopolymers.
- Author
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Masi, Giulia, Rickard, William D.A., Vickers, Les, Bignozzi, Maria Chiara, and van Riessen, Arie
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COMPARATIVE studies , *SURFACE active agents , *POLYMERIZATION , *THERMAL insulation , *HYDROGEN peroxide , *FLY ash - Abstract
Foaming to reduce the density of geopolymeric materials is increasingly being reported in the literature as it has been shown to be effective in improving their insulating properties. However, there is no consistency in foaming methods and as such this study was performed to compare methods in order to better understand their effect on the properties of geopolymers. A surfactant and two chemical foaming agents (hydrogen peroxide and aluminium powder) were added to a fly ash based geopolymer matrix. Surfactant was also combined with each of the chemical foaming agents in order to stabilise the foam in the geopolymer matrix and to reduce coarse pores. The physical, mechanical and microstructural properties of the low density geopolymers are presented and the effects of the foaming agents' characteristics on the hardened product is discussed, as well as the relative merits of the different procedures to synthesise the foamed geopolymer. It was found that homogeneous microstructures with small pores can be obtained by adding surfactant and hydrogen peroxide. The combination of hydrogen peroxide (0.1wt%) and surfactant (1.0wt%) produced geopolymer foams with density and compressive strength values of 0.94g/cm³ and 4.6MPa, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
12. Use of digital image analysis to determine fracture properties of alkali-activated mortars.
- Author
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Baietti, Giulia, Quartarone, Giovanni, Carabba, Lorenza, Manzi, Stefania, Carloni, Christian, and Bignozzi, Maria Chiara
- Subjects
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MORTAR , *IMAGE analysis , *DIGITAL image correlation , *FLY ash , *ALKALIES , *DIGITAL images - Abstract
• The fracture properties of three alkali-activated mortars are studied. • Low values of fracture energy might be associated with the presence of unreacted FA. • The fracture energy depends on the type of aggregate used. • Digital image correlation can be used to estimate the size of the FPZ. Results of three-point bending tests on notched beams cast with three alkali-activated mortars that differ by the type and size of the aggregates are presented. Digital image correlation is used to estimate the size of the fracture process zone. The fracture energy is computed by means of the work-of-fracture method and found to be strongly dependent on the type of aggregate used and does not differ whether the LDVT or DIC load-deflection curves are used. Finally, low values of the fracture energy in alkali-activated mortars might be associated with the presence of unreacted fly ash. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
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