1,235 research outputs found
Optimizing In-Place Density of Asphalt Pavements During Cold Weather Paving in Nebraska
Late season paving is common and often performed in colder temperatures, which is the most challenging environment for attaining optimal in-place density/compaction The in-place density of asphalt pavement greatly affects the lifespan of the pavement. It is also a key factor in preventing major pavement distresses, such as rutting, cracking, stripping (due to water damage) and aging. This research project aims to evaluate and compare the effectiveness of different compaction, delivery, and mix design characteristics to ensure the optimization of in-place asphalt pavement density. To this end, various laydown methods (i.e., Standard Pick-up Machine (SPM) and Material Transfer Vehicle (MTV)) and compaction equipment (i.e., double drum steel rollers, pneumatic rollers, and combination rollers with both steel and pneumatic tires), using both static and vibratory modes were employed. In addition, the effect of different aggregate blend combinations (i.e., using less coarse ledge rock) and asphalt binders (i.e., PG 58V-34, PG 40-40, and PG 52-40) on in-place density were studied. Four test sections were constructed over four separate days of paving, during cold weather conditions. The in- place density was measured using four methods: 1) Conventional/traditional cut roadway cores, 2) Combination of Infrared Continuous Thermal Scanning (ICTS) with conventional/traditional cut roadway cores, 3) Pavement Quality Indicator (PQI), and 4) Rolling Density Meter (RDM) utilizing Ground Penetrating Radar (GPR). The obtained results were compared and contrasted to the current testing, acceptance and construction methods system at Nebraska Department of Transportation (NDOT) and recommendations for future construction specifications and best practices were presented
Asphalt Binder Laboratory Short-Term Aging
The Rolling Thin Film Oven (RTFO) is widely used to simulate asphalt binder short-term aging. However, there is a general interest to improve the current short-term aging protocol especially for reducing the aging time. Besides, there are some doubts about the capability of RTFO in the simulation of aging of highly polymer modified asphalt binders which is mainly due to improper dispersion of such binders in the bottles during rotating and creeping of highly viscous binder out of the bottles during rotation. This work addresses the effect of time, temperature, airflow rate, and weight of asphalt binder on the laboratory short-term aging of asphalt binders and proposes an alternative protocol that can reduce the aging time and resolve some of the current short-term aging protocol shortcomings. In the first part of this study, two asphalt binders, from different sources, were examined in RTFO at different combinations of the above-mentioned test parameters. The high-end continuous performance grading temperature (estimated by dynamic shear rheometer), and carbonyl index (estimated by Fourier transform infrared spectroscopy) were considered as the two responses for quantification and qualification of laboratory aging. The statistical analysis showed that the first order terms of time, temperature, and weight as well as their interactive terms were statistically significant. However, the effect of airflow rate, within the studied range, was insignificant. Based on the findings of the first part of study, an alternative protocol was proposed for the study of short-term aging in a RTFO. One unmodified and three highly modified binders were aged in a RTFO under the current and proposed aging conditions for comparative purposes. According to the obtained rheological (high- and low-end continuous performance grading temperature and viscosity) properties as well as the chemical characteristics (carbonyl index, saturate-aromatic-resin-asphaltene fractions, and oxygen content), it was shown that the proposed laboratory short-term aging protocol not only can reduce the aging time of the conventional protocol, but also that it is applicable to both neat and polymer-modified modern asphalt binders
Quantum phase transition as an interplay of Kitaev and Ising interactions
We study the interplay between the Kitaev and Ising interactions on both
ladder and two dimensional lattices. We show that the ground state of the
Kitaev ladder is a symmetry-protected topological (SPT) phase, which is
protected by a symmetry. It is confirmed by
the degeneracy of the entanglement spectrum and non-trivial phase factors
(inequivalent projective representations of the symmetries), which are obtained
within infinite matrix-product representation of numerical density matrix
renormalization group. We derive the effective theory to describe the
topological phase transition on both ladder and two-dimensional lattices, which
is given by the transverse field Ising model with/without next-nearest neighbor
coupling. The ladder has three phases, namely, the Kitaev SPT, symmetry broken
ferro/antiferromagnetic order and classical spin-liquid. The non-zero quantum
critical point and its corresponding central charge are provided by the
effective theory, which are in full agreement with the numerical results, i.e.,
the divergence of entanglement entropy at the critical point, change of the
entanglement spectrum degeneracy and a drop in the ground-state fidelity. The
central charge of the critical points are either c=1 or c=2, with the
magnetization and correlation exponents being 1/4 and 1/2, respectively. In the
absence of frustration, the 2D lattice shows a topological phase transition
from the spin-liquid state to the long-range ordered Ising phase
at finite ratio of couplings, while in the presence of frustration, an
order-by-disorder transition is induced by the Kitaev term. The 2D classical
spin-liquid phase is unstable against the addition of Kitaev term toward an
ordered phase before the transition to the spin-liquid state.Comment: 16 pages, 18 figure
Symmetry fractionalization: Symmetry-protected topological phases of the bond-alternating spin- Heisenberg chain
We study different phases of the one-dimensional bond-alternating spin-
Heisenberg model by using the symmetry fractionalization mechanism. We employ
the infinite matrix-product state representation of the ground state (through
the infinite-size density matrix renormalization group algorithm) to obtain
inequivalent projective representations of the (unbroken) symmetry groups of
the model, which are used to identify the different phases. We find that the
model exhibits trivial as well as symmetry-protected topological phases. The
symmetry-protected topological phases are Haldane phases on even/odd bonds,
which are protected by the time-reversal (acting on the spin as
), parity (permutation of the chain about a specific
bond), and dihedral (-rotations about a pair of orthogonal axes)
symmetries. Additionally, we investigate the phases of the most general
two-body bond-alternating spin- model, which respects the time-reversal,
parity, and dihedral symmetries, and obtain its corresponding twelve different
types of the symmetry-protected topological phases.Comment: 9 pages, 5 figure
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