1,215 research outputs found
Cracking in asphalt materials
This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.Peer ReviewedPostprint (author's final draft
ASSESSMENT OF ASPHALT MATERIALS TO RELIEVE REFLECTION CRACKING OF HIGHWAY SURFACINGS
The thesis investigates the mechanisms and restraints which influence
transverse crack propagation through the bituminous surfacings of
semi-flexible pavements. These pavements incorporate continuously
laid cement bound roadbases which, during curing, crack into slabs of
varying length, ranging from 4-25m.
Reciprocal crack growth can occur in the surfacing, known as
'reflection cracks', located through stresses concentrated at the
discontinuities within the roadbase .
Three mechanisms have been identified and are described as
contributing to reflection crack propagation. They have been
analysed independently although the majority of conclusions drawn are
applicable to their combined action. Their relative importance will
vary with respect to pavement geometry, material properties,
environmental conditions and traffic intensity.
The first mechanism, 'tensile fatigue', induces crack propagation
vertically upward through the surfacing. Tensile strains are
developed during daily and ru1nual fluctuations of temperature, which
cause expansion and contraction of the cement bound roadbase. This
mechanism is most prominent on pavements with thin surfacings and
long slab lengths. The rate of crack growth is dependent on the
range of temperature within the roadbase , slab length, thermal
characteristics of the roadbase material and resistance of the
surfacing to this form of fatigue .
A model has been developed based on a combination of results from an
extensive testing programme, the use of fracture mechanics theory and
computer simulation of the condition. The results quantify the
resistance shown by conventional bituminous mixes to reflection
cracking in terms of their mix parameters. Also considered are the
use of stress relieving membranes, reinforcement material and
modified binders to inhibit crack growth.
The second mechanism, 'tensile yield' is also thermally induced but
associated with cold weather conditions. Temperature gradients
through the pavement structure induce warping and contraction within
the uppermost layers. Tensile strains developed at the surface can,
under U.K. winter temperatures, exceed the ultimate yield strain of
the wearing course material.
Preliminary. investigations of four pavements constructed in the early
1970's to motorway specifications indicate that reflection cracking
will initiate at the surface if the yield strain, as defined through
tensile creep tests, is reduced through binder oxidization to a value
of 0.5%. This mechanism will operate on pavements with greater
structural layer thicknesses and is only partially dependent on slab
length.
The influence of a further mechanism, 'shear fatigue' induced through
trafficking of the pavement, has been shown to be confined to the
acceleration of crack growth in the final stages of propagation
unless a breakdown of interlock occurs between adjoining roadbase slabs .The Transport
and Road Research Laboratory (TRRL) U.
Quasi-Brittle Fracture Modeling of Preflawed Bitumen Using a Diffuse Interface Model
Fundamental understandings on the bitumen fracture mechanism are vital to improve the mixture design of asphalt concrete. In this paper, a diffuse interface model, namely, phase-field method is used for modeling the quasi-brittle fracture in bitumen. This method describes the microstructure using a phase-field variable which assumes one in the intact solid and negative one in the crack region. Only the elastic energy will directly contribute to cracking. To account for the growth of cracks, a nonconserved Allen-Cahn equation is adopted to evolve the phase-field variable. Numerical simulations of fracture are performed in bituminous materials with the consideration of quasi-brittle properties. It is found that the simulation results agree well with classic fracture mechanics
THE DETERMINATION OF CRACK PROPAGATION RATES OF REFLECTION CRACKING THROUGH ASPHALT SURFACINGS
Merged with duplicate record 10026.1/855 on 06.20.2017 by CS (TIS)A large proportion of the U.K. highway network constructed in the
1960's and 1970's contains lean concrete roadbase with bituminous
surfacing. Pavements containing relatively high strength lean concrete
have rarely required structural maintenance (thick overlay or reconstruction)
but have required maintenance because of reflection cracking
where the surfacing cracks above cracks in the lean concrete. The
time of appearance of this cracking is very variable (2-20 years).
Field observations indicate that roadbase transverse crack spacings
are often greater than 5m. Reflection cracking at these long spacings
can be caused by thermal stresses. This project identifies
conditions under which thermal reflection cracking will occur and
develops a predictive model that allows estimation of the combined
effect of thermal and traffic stresses. Finite element analyses
indicate that initial crack development is likely to be caused by
thermal stresses and final cracking will be assisted by traffic
stresses.
A temperature model has been developed to determine roadbase daily
temperature range and surfacing temperature on a mean monthly basis.
Thermal reflection cracking is considered to result from daily cycle
fatigue rather than an extreme low temperature mechanism. A test
rig has been developed to apply cyclic crack opening movements and
simulative tests have been accelerated to 0.1Hz by using a "bitumen
stiffness", fatigue criterion.
Finite element results, displacements recorded during tests and tensile
creep tests to determine mix stiffness, enable dc/dN and K1 values
and material constants (A, n) to be determined. This fracture mechanics
interpretation of test results serves as the basis of the predictive
model for thermal reflection cracking that is consistent with observations
from an untrafficked road.
The combined estimate of thermal and traffic stresses cannot however
explain reflection cracking at <5m spacings. This cracking apparently
initiates at the surface and is probably influenced by other mechanisms.University
of Birmingham, the Transport and Road Research
Laboratory (TRRL), U.K. and Devon and Cornwall
County Council Highways Department
Advanced Testing and Characterization of Bituminous Materials, Two Volume Set
Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin
Fracture and shakedown of pavements under repeated traffic loads
Thesis (Ph.D.) University of Alaska Fairbanks, 1998Under repeated external loads, engineering structures or objects may fail by large plastic deformation or fatigue. Shakedown will occur when the accumulation of plastic deformation ceases under repeated loads; the response of the system is then purely elastic. Fatigue and shakedown have been individually studied for decades and no attempt has been made to couple these two mechanisms in the mechanics analysis. In this study, an attempt is made to couple shakedown and fatigue in pavement mechanics analysis using numerical simulation. The study covers three main areas: fatigue, static shakedown, and kinematic shakedown analysis. A numerical approach to fatigue analysis is proposed based on elastic-plastic fracture mechanics. The amount of the crack growth during each load cycle is determined by using the J-integral curve and \rm R\sb{-}curve. Crack propagation is simulated by shifting the \rm R\sb{-}curve along the crack growth direction. Fatigue life is predicted based on numerically estabiished fatigue equation. The numerical results indicate that the algorithm can be applied to fatigue analyses of different materials. A numerical algorithm based on the finite element method coupled with the nonlinear programming is proposed in static shakedown analysis. In this algorithm, both the inequality and equality constraints are included in the pseudo-objective function. These constraints are normalized by the material yield stress and the reference load, respectively. A multidirectional search algorithm is used in the optimization process. The influence of finite element mesh on shakedown loads is investigated. An algorithm that utilizes eigen-mode to construct the arbitrary admissible plastic deformation path is proposed in kinematic shakedown analysis. This algorithm converts the shakedown theorem into a convex optimization problem and can be solved by using a multidirectional search algorithm. Fatigue behavior of a two-layer full-depth pavement system of asphalt concrete is analyzed using the proposed numerical algorithm. Fatigue crack growth rate is estimated and fatigue life is predicted for the system. Shakedown analyses are also carried out for the same pavement system. The comparison between the shakedown load and the fatigue failure load with respect to the same crack length indicates that the shakedown dominates the response of the pavement system under traffic load
Advanced Testing and Characterization of Bituminous Materials, Two Volume Set
Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin
Performance of Tencate Mirafi PGM-G4 Interlayer-Reinforced Asphalt Pavements in Alaska
Geosynthetics has been used in hot mix asphalt (HMA) overlays in a variety of design and
construction situations for more than three decades. A number of positive benefits have been identified such as waterproofing control for base and subgrade protection, improved fatigue resistance and reduced propagation of reflective cracks. In cold regions such as Alaska and other northern states, pavements are more prone to distresses due to extreme climatic conditions. Research is needed to explore how interlayers functions in asphalt pavements in cold regions. The interlayers used for pavement reinforcement applications and available in the market are primarily biaxial. Biaxial grids with equal strength in both the machine and cross machine directions allow stress transfer at low strain mainly in longitudinal and transverse directions. The new PGM-G4 paving composite developed by Tencate Geosynthetics contains multi-axial fiberglass filament yarn, which changes the aperture geometry from a rectangular to a quad angular grid structure. This unique feature improves the structure radial stiffness and efficiently distributes stress from surface layer to the geogrid throughout the full 360o. This isotropic feature could deliver optimal asphalt concrete (AC)/grid interaction and more efficient reinforcement. There is a need to identify/validate its expected performance and added value over conventional biaxial grids. Hence, a study has been conducted on interlayer-reinforced asphalt pavements in Alaska that included two phases: laboratory index testing (Phase I) and field performance evaluation (Phase II). Phase I focused on laboratory evaluation of engineering properties of PGM-G4 composite paving grid-reinforced asphalt pavement structure and comparison with other types of interlayers. Five types of interlayers were evaluated in this study for various laboratory tests and they were PGM-G4 (multi-axial composite grid), PGM-G100/100 and PGM-G50/50 (bi-axial composite grid), TruPave® (engineered paving fiberglass and polyester hybrid mat), and MPV500 (conventional polypropylene interlayer). The performance tests included asphalt retention and grab strength tests of interlayers, and shear strength, permeability and indirect tension (IDT) tests of interlayer-reinforced asphalt mixtures. Further, a typical Alaska flexible pavement structure was used, and pavement structure analyses and simulation were conducted by Bisar, Alaska Flexible Pavement Design (AKFPD) and ABAQUS programs to investigate the effects of paving interlayers on the pavement performance.Tencate Geosynthetics North Americ
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