Creep models for asphalt under static load
Added on 2021-01-01
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CREEP MODELS INASPHALT1
TABLE OF CONTENTINTRODUCTION...........................................................................................................................3Creeps in asphalt..............................................................................................................................3CREEP ANALYSIS........................................................................................................................4Creep models...............................................................................................................................4Mathematical creep models for asphalt.......................................................................................5Factors affecting creep formation................................................................................................6CREEP DAMAGE PROPERTIES OF ASPHALT UNDER STATIC LOAD...............................6Creep test analysis of static load of asphalt.................................................................................6Observed Results.........................................................................................................................7Micromechanical modeling of asphalt uniaxial creep by using discrete element method..............7Characteristics of Asphalt concrete microstructure.....................................................................7Discrete element approach for micromechanical modeling of uniaxial creep in asphalt............8Axial creeps versus load time......................................................................................................8Log loading duration versus creep compliance...........................................................................8Finite element analysis of creep equation for high modulus asphalt...............................................9Comparison of discrete and finite element models......................................................................9Creep constitutive equation.........................................................................................................9CONCLUSION..............................................................................................................................10REFERENCES..............................................................................................................................112
INTRODUCTION Pavement engineering is defined as the branch of civil engineering which deals with therehabilitation and management of pavements. These structures are concerned with application ofman-made surfaces to ground so that objects are allowed to move across it. This branchemphasizes on designing and maintenance of rigid and flexible pavements (Esfandiarpour,Saman, and Ahmed, 2017). The report aims at evaluation of advance topic in pavementengineering. It will critically evaluate the creep models in asphalt (flexible pavement). Thedocument will analyze the creep damage model of asphalt. It will describe the creep behaviorand stability analysis of this advance technique. The report will highlight the finite elementanalysis on creep constituting high modulus asphalt concrete. Further the report will analyze theresults and advantages obtained from this advance technique. It will compare Burger’s modeland Vander Pool model along with their stability analysis. Creeps in asphalt In asphaltic concrete creep is also called rutting or deformation and is key failuremechanism within infrastructure of road network. In many countries including Australiaconstruction authorities does not focus on minimizing creeps rather they have greater reliabilityon empirical testing methods which rank material performance in testing laboratory. Theadvancements in the creep models in asphalt are effective in predicting creeps and provide highlyefficient methods for simulation of temperature, stress and boundary parameters of pavement infield. Asphalt is mainly used in urban environment and involves huge investment inmaintenance. Structural distresses in asphalt are in the form of creep deformation and fatiguecracking. Creep refers to strain accumulation as a result of traffic loads and is dependent on time.Due to heavy traffic on roads under the wheel paths permanent deformation occurs which isknown as rutting (Moghaddam and et.al., 2014). When load is removed then some deformationscan be easily recovered while some remains permanently in asphalt mixture. The factors liketemperature, stress, properties of material used, duration of load and mix design controls theseverity of deformation. Rutting generation is accomplished by following two mechanisms: Shear deformation: It is defined as the lateral movement of material and is more significant thandensification approach. In this approach asphalt is pushed down under the pressure of tyre orwheel load and is displaced in upward direction on either side of wheel path. Densification: It is the result of inefficient compaction during the process of construction or inearly development stage of pavement. Traffic pressure encourages aggregates to pack moreclosely which is known as post construction compaction. Thus it also reduces air voids. 3
In the initial stages permanent deformation is result of traffic compaction or densificationwhereas during entire life time of pavement shear deformation is the major case for developingrutting.Current practices Current standards of Australian use include quasi or full confining stress so that the betterreplica of field conditions can be obtained. In quasi confinement smaller platen is kept on anoversized sample of asphalt. The lack of proper confining of annulus of asphalt can result inradial splitting (Ma and et.al., 2016). The purpose of this approach is to explore platen to effectsof sample diameter with the help of viscoelastic modeling. However this can be augmented byusing hoop stress which is applied through confining ring. This mechanism is similar togeomechanism of soil consolidation test by odometer method. Performance of creep field inasphalt can be predicted by calibrating viscoelastic model. CREEP ANALYSIS Creep strain in asphalt can be divided into four components by following equation. ε (t) = ε (e) +ε (p) + ε (ve) + ε (vp) Where, ε (t) is the creep strain ε (e) is time dependent and recoverable elastic strainε (p) is called is time dependent and irrecoverable plastic strainε (ve) is known as viscoelastic strain. It can also recover with time and thus can be considered astime dependent. ε (vp) is unable to recover and is called viscoplatic strain. Small stresses can cause asphalt to behave elastically. When load or stress is removedelastic strain is also disappeared. The creep behavior becomes plastic when high stress is applied. It leads to permanentstrain so even after stress is removed recovery is not possible. In viscoeleastic behavior loading first cause elastic action which is followed by gradualincrease of strain at declining rate. Creep models Asphalt concrete belongs to viscoelastic materials. The standard form of Hookean spring modeland Newtonian dashpots is used to explain the creep behavior but it cannot be used in case ofasphalt (Safi and et.al., 2018). Spring model is suitable for purely elastic material. To describethe nature of these materials following models can be used. 4
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