1,721,083 research outputs found
Recycling of milled asbestos containing waste as mineral addition in manufacturing of hydraulic mortars
No full textDiffuse reflectance infrared fourier transform spectroscopy for the determination of asbestos species in bulk building materials
No full textDiffuse reflectance infrared Fourier transform (DRIFT) spectroscopy is a well-known technique for thin film characterization. Since all asbestos species exhibit intense adsorptions peaks in the 4000–400 cm−1 region of the infrared spectrum, a quantitative analysis of asbestos in bulk samples by DRIFT is possible. In this work, different quantitative analytical procedures have been used to quantify chrysotile content in bulk materials produced by building requalification: partial least squares (PLS) chemometrics, the Linear Calibration Curve Method (LCM) and the Method of Additions (MoA). Each method has its own pros and cons, but all give affordable results for material characterization: the amount of asbestos (around 10%, weight by weight) can be determined with precision and accurac
Impiego di resine a basso peso molecolare nel risanamento dei locali della Gypsoteca dell'accademia delle Belle Arti di Napoli
No full textLyfe Cycle assessment (LCA) nel settore delle costruzioni: possibili scenari ed elementi di criticità
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Strain engineering of two-dimensional materials
No full textGraphene displays a range of remarkable properties that have catalyzed
an impressive interest in the scientific community
. Its unique
electronic behavior stems from the hexagonal honeycomb structure of the
one-atom thick carbon lattice, which forces low-energy conducting electrons to
assume linear dispersions mimicking the one of massless relativistic fermions
.
After graphene, the past few years have been marked by the discovery
and characterization of plenty of other two-dimensional (2D) materials
and most of them share with graphene the hexagonal atomic network and
have as many peculiar electrical and optical properties. Among this wide
family, many of transition metal dichalcogenides (TMDs) have a gapped
electronic structure and efficiently emit light, even at room temperature.
Tungsten disulfide (WS2)
belongs to the TMD family and has gained a
preferential attention due its interesting features, including a strong, wide-band
exciton photoluminescence (PL) around 630 nm when a monolayer is
considered. Mechanical characterization of 2D materials revealed that they
display an unusual good elasticity and high mechanical strength; for example,
graphene crystals can sustain strain well beyond 10% without undergoing
plastic deformation
. In addition to that, it has been predicted
, and
in part experimentally demonstrated
, that mechanical deformations in a
2D hexagonal system can significantly impact its physical properties. Random
deformations are typically detrimental, but intriguing effects can emerge if
proper strain fields are implemented in these systems
. Strain gradients
can be engineered to mimic the presence of a external magnetic field[18,19]
applied perpendicularly to the 2D material plane. Such strain-induced field
has been defined pseudo-magnetic field (PMF) since, at odd of the real
magnetic field, it conserves the time reversal symmetry and has a pseudo-spin
dependent orientation. The fact that 2D materials can sustain large strain,
implies that large PMFs can be induced and used to dramatically change the
material local energy spectrum. Strain can be also used to modulate the
optoelectronic properties of TMDs by controlling the excitons PL wavelength
with strain intensity and the excitons diffusion dynamics with strain
gradients
. However, these intriguing possibilities demand a control of
strain that, while validated by artificial-lattice studies, to date remains elusive
in the case of atomic lattices
. Preliminary and remarkable results were
obtained on self-assembled graphene nanobubbles and nano-wrinkles
,
using scanning probes or nano-patterned substrate
, and in twisted bilayer systems
. Micro-scale strain devices were implemented
exploiting deformable substrates
, uniform external loads
, thin-film
shrinkage or complex micro-actuation technologies, including in particular
inorganic microelectromechanical systems (MEMS)
. Nevertheless, in
order to master the physical properties through deformations, a more accurate
control and investigation of the 2D material strain field is required; the existing
techniques lack of flexibility, they can be exploited on one flake at a time, and
are in practice poorly suited to obtain arbitrary and reconfigurable strain fields.
In this Thesis, I will demonstrate an innovative technique to strain
2D materials which deals with these limitations. The technique is based
on polymeric micrometric artificial muscles (MAMs) which contract upon a
high-dose electron beam exposure and can be used to induce a local deformation
in the 2D material crystal. I will show that MAMs are patternable, therefore
they are perfectly suited to create arbitrary strain patterns and the method
will be first of all demonstrated on a set of suspended graphene devices.
Moreover, I will show that by employing a clean and atomically flat substrate
as a “low-friction” platform, the same technique can be applied to strain
2D materials while avoiding the critical steps of crystal transfer and suspension.
To this end, I employed WS2 grown by chemical vapor deposition (CVD)
directly on top of graphene obtained by thermal decomposition of silicon
carbide (SiC). I investigated the WS2/graphene heterostructures combining a
simple and scalable fabrication protocol with all the benefits of the MAMs-based
strain engineering technique. I will demonstrate a local strain-controlled tuning
of the WS2 photoluminescence wavelength as a proof of concept
Mechanical properties and durability of mortar containing fine fraction of demolition wastes produced by selective demolition in South Italy
No full textRecycling of construction and demolition waste (CDW) has to be encouraged. Structural concrete and mortar is one of the possible applications, but requires a good quality of the aggregates to be used.The use of wastes treated by mobile plants in the above application is possible only if an accurate selective demolition is conducted. The goal of this study is to produce self-levelling mortars containing high amount of CDW fine fractions that are problematic waste materials. This research investigate the physical and mechanical characteristics of different kind of CDW obtained from selective and traditional demolition techniques. Comparison between the properties of the mixtures obtained from different kind of aggregates offers the possibility to understand the advantages in using selective demolition. The results show that the use of superplasticizer, combined with selective demolition, can improve significantly the mechanical properties of mortars produced with CDW aggregate. In particular aggregate coming from bricks can improve mechanical strength, probably because of their pozzolanic effect
Recycling of stabilized municipal solid waste incinerator fly ash in civil engineering applications
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