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A Critical Review of Endurance Limits of Bituminous Mixes for Developing Countries Transportation Research Procedia 17 ( 2016 ) 438 – 444 2352 1465 © 2016 The Authors Published by Elsevier B V This is[.]
Available online at www.sciencedirect.com ScienceDirect Transportation Research Procedia 17 (2016) 438 – 444 11th Transportation Planning and Implementation Methodologies for Developing Countries, TPMDC 2014, 10-12 December 2014, Mumbai, India A Critical Review of Endurance Limits of Bituminous Mixes for Developing Countries Gagandeep Singha*, Devesh Tiwarib, P.K.Jainc and A.K.Swamid a Scientist, bPrincipal Scientist, cChief Scientist CSIR-CRRI, New Delhi, 110025, India d Assistant Professor IIT Delhi, New Delhi, 110025, India Abstract Fatigue failure of any kind of material is of great concern while designing any component of Civil Engineering Structure A fluctuating stress i.e with positive and negative phase is the root cause of fatigue failure Even controlling the peak amplitude stress, failure may take place due to fatigue, by initiating micro cracks due to fluctuating stress This control in peak amplitude stress transform to number of cycle which material can take Thus, there is existence of hypothesis that there exists stress amplitude below which it can take infinite number of load cycles; this limit is defined as endurance limit or fatigue endurance limit (FEL) Literature has records of bituminous concrete pavement which have been performing for 40 years without exhibiting any fatigue damage It is the endurance limit of bituminous mixes, in these long lasting pavements which has controlled the damage due to fatigue But still this concept is not fully established because establishment of endurance limit for different bituminous mixes itself is a challenging task reason being that many parameter and test methods control it Different test methods like Four Point Bending Beam Test, Uniaxial tension test are followed in laboratory for establishment of endurance limits Different test methods have their own test methodology and failure criteria So depending upon, kind of available expertise/equipment the test method is selected, but mostly bending beam fatigue test method is adopted because of more control in data capturing and easy to analyze © Published by by Elsevier B.V.B.V This is an open access article under the CC BY-NC-ND license © 2016 2015The TheAuthors Authors.Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the Department of Civil Engineering, Indian Institute of Technology Bombay Peer-review under responsibility of the Department of Civil Engineering, Indian Institute of Technology Bombay Keywords: Endurance Limit, Flexible Pavement, Modulus * Corresponding author Tel.: +91-9654384348 E-mail address:singh1830@gmail.com 2352-1465 © 2016 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the Department of Civil Engineering, Indian Institute of Technology Bombay doi:10.1016/j.trpro.2016.11.085 Gagandeep Singh et al / Transportation Research Procedia 17 (2016) 438 – 444 Introduction Fatigue failure of any kind of material is of great concern while designing any component of Civil Engineering Structure A fluctuating stress i.e with positive and negative phase is the root cause of fatigue failure Even controlling the peak amplitude stress, failure may take place due to fatigue, by initiating micro cracks due to fluctuating stress This control in peak amplitude stress transform to number of cycle which material can take Thus, there is existence of hypothesis that there exists stress amplitude below which it can take infinite number of load cycles; this limit is defined as endurance limit or fatigue endurance limit (FEL) Various components of the machines are properly designed to take care of fatigue Same is with the bituminous layer provided in the flexible pavement As per Mechanistic- Empirical design approach, horizontal tensile strain at the bottom of the bituminous mix and vertical compressive strain at the top of the subgrade are two main critical strains To prevent the failure due to bottom up cracking, it is very important to control these tensile strains Many researchers have suggested that bituminous mixes exhibit fatigue endurance limit, when applied strain is sufficiently low that no or minor damage occurs in bituminous mixes where rate of healing is more as compare to rate of damage accumulation This concept is used in developed countries to design long- lasting or perpetual pavements having life of 40 years or more Literature has records of bituminous concrete pavement which have been performing for 40 years without exhibiting any fatigue damage It is the endurance limit of bituminous mixes, in these long lasting pavements which has controlled the damage due to fatigue Illustrations Originally the concept of endurance limit was developed for metals To control the fatigue failure in metals, strains developed in uncracked metal are kept below one level Barret et al (5) describe the endurance limits for uncracked metals, the strain below which the plot of strain versus number of load cycles becomes asymptotic and fatigue does not occur The theoretical concept of FEL is illustrated in Figure1 Figure:1Theoretical Concept of Endurance Limit To control the bottom up cracking in the bituminous pavement, it is important to keep the strain values below particular level so that no damage accumulation takes place This can be achieve either by increasing the thickness of the bituminous pavement or stiffness of the bituminous mixes Monismith, Epps, Kasianchuk and McLean (1972) first proposed the value of endurance limit i.e 70 μ for bituminous mixes The existence of fatigue can easily be established via laboratory test on bituminous mixes Various testing possibilities exist in the laboratory for example four point bending test, indirect tensile test, two point bending, uniaxial tension/compression test etc Also it is possible to change the test conditions (temperature, magnitude of load, rest period) Therefore, different test geometrics result in different fatigue cycles thus different FEL Different test methods have their own test methodology and failure criteria Most commonly used failure criteria are flexural stiffness reduction; energy ratio The Energy Ratio is based on stress-controlled which is obtained by multiplying stiffness by corresponding number of cycle which claims to identify the point at which micro-cracking becomes a 439 440 Gagandeep Singh et al / Transportation Research Procedia 17 (2016) 438 – 444 macro-crack (defined as fatigue failure) Laboratory fatigue testing is conducted until flexural stiffness is reduced to at least 50 percent and graph is plotted between flexural stiffness and number of cycle to define failure of sample 3.0 Laboratory Test Methods 3.1 Flexural Beam Fatigue Testing Bending Beam fatigue testing as per American Association of State Highway and Transportation (AASHTO) T 321 involves the application of sinusoidal loading on beam fatigue sample till fifty percent reduction in initial flexural stiffness value takes place This test is easy to conduct but testing hours are long Failure criteria of flexural stiffness reduction is applied i.e fifty percent reduction in initial flexural stiffness value which is stiffness corresponding to 50th cycle It is most commonly used form of fatigue test in United States Testing was done in a constant strain mode starting from higher to lower to draw complete fatigue graph At lower strains level, test last upto two days for completion It is not possible always to test run till fifty percent reduction in initial stiffness value reached So, extrapolation techniques are applied to predict the number of cycles to failure such as exponential model, logarithmic model, Weibull function, three-stage Weibull function, and ratio of dissipated energy change (RDEC) As per National Cooperative Highway Research Program (NCHRP) report 646: “Validating the Fatigue Endurance Limit for Hot Mix Asphalt” exponential and single-stage Weibull function produced the most accurate fatigue life predictions 3.2 Uniaxial Testing The testing includes complex modulus, monotonic, and fatigue tests in uniaxial tension The basis of this testing lies in characteristic curve which define the reduction in material integrity as damage increases The fatigue endurance limit of bituminous mixtures is predicted with help of characteristic curves The complete testing includes the dynamic modulus testing, monotonic testing for development of characteristic curve, fatigue tests and finally the prediction of endurance limit using viscoelastic and continuum damage mechanics principles Thus it is not a straight forward approach of determination of FEL Uniaxial testing does not required any special casting of sample and haversine pulse loading is applied during testing But the determination of FEL is difficult as data is more complicated to analyze So depending upon, kind of available expertise/equipment the test method is selected, but mostly bending beam fatigue test method is adopted because of more control in data capturing and easy to analyze Molenaar et all studied the effect of two test on FEL They have considered different specimen size to check the effect on FEL under different test methods Table-1 presents the different specimen size used while doing testing Figure shows the test results of different fatigue test performed It can easily predict from Figure that specimen size has more effect while determining FEL through beam fatigue test as compare to uniaxial testing This can be easily explained as the stress generated during uniaxial testing is same over the entire cross sectional area The specimen size will not come into picture till the stress on the cross sectional area is same for both small and large specimen size But this thing is not happening during beam fatigue testing Table: 1- Different specimen size used during testing Test type Specimen shape specimen size size 0.5 Dimension [mm] Φ × h = 25×62.5 Gagandeep Singh et al / Transportation Research Procedia 17 (2016) 438 – 444 UT/C fatigue Beam Fatigue cylinder size 1.0 Φ × h = 50×125 size 1.5 Φ × h = 75×187.5 size 2.0 Φ × h = 100×30 size 0.5 l × w × h = 400×50×25 size 1.0 l × w × h = 400×50×50 Beam Figure – Test Results (Molenaar et al) Besides test method and their related parameters, the FEL for bituminous mixes get change with change in binder type, aggregate characteristic such as size, texture; gradation of mix, type of loading such as haversine or sinusoidal, test temperature, sample dimensions etc This seems different test methods are presenting specimen property rather giving material property Besides this all these laboratories method are not simulating actual field condition in the laboratory For example during testing no redistribution of stress is take care as happening in actual field due to support given by lower layer to bituminous layer , healing and lateral distribution of traffic loads also effect the fatigue performance of in situ bituminous mixtures but these factors are not taken into account during laboratory testing This implies that some kind of shift factor is to be applied to laboratory results for design of pavement Thus establishment of endurance limit for different bituminous mixes itself is a challenging task reason being that many parameter and test methods control it 4.0 Correlation of Laboratory and Field Fatigue Fatigue equation can easily be developed through any fatigue testing but important thing is how to apply it for design of pavement thickness One of the easy ways is to know the strain values coming in pavement and finding the number of load repetitions it can take But this is not easy, as laboratory developed equation has so many limitations in terms of parameters or way actual pavements faced in reality Shift factor is required to correlate the laboratory developed fatigue to those with field fatigue Shell in 1970,s first tried to develop correlation between the two For 441 442 Gagandeep Singh et al / Transportation Research Procedia 17 (2016) 438 – 444 this, three point bending test was done to develop the fatigue equation and correlated this with the help of wheel tracking test (WTT) WTT involved test slabs of 950 mm long, 440 mm wide and 40 mm thick They have developed a nomograph correlating the three point beam results with WTT But now, three point bending test is no longer used It is being replaced by four point bending test or uniaxial test In order to get idea of effect of foundation on fatigue, the four point bending test and fatigue test on beams on rubber foundation were done The principal of test on elastic foundation was presented in figure The beam size for both the test i.e Four Point Bending Test (FPBT) and Beam Test on Elastic Foundation (BOEF) was same The test results are reproduced in figure Figure – Principle of Beam Testing on Elastic Foundation (Molenaar et al) Gagandeep Singh et al / Transportation Research Procedia 17 (2016) 438 – 444 443 Figure – Comparison of Fatigue Life (Molenaar et al) It is clear from the figure there is huge difference between the fatigue life predicted from the two methods The fatigue life predicted from beam tested on elastic foundation is 20 to 30 times more those predicted from normal four point bending test 5.0 Field Studies Many studies presented the existence of FEL for different mixes, FEL range from 75 to 200 μ But this required validation through field studies before in corporating in design as fatigue model Many field studies presented the shift factor value of 10 to 100 correlating the lab and field results Various agencies had conducted field studies and incorporated FEL in their design National Center for Asphalt Technology (NCAT) in conjunction with the Asphalt Pavement Alliance (APA) developed a procedure for the mechanistic-based design of flexible long-life pavements and developed a program PerRoad, 2002 NCHRP is currently under research stage to incorporate the concept of an FEL into a mechanistic-empirical pavement design procedure for AASHTO In 1984, UK was first to publish design procedure for full flexible pavement with revision in 1997 At present UK is the only country which has published design procedure for long life pavements Design of pavement based upon the FEL will prevent the overdesigning of flexible pavements FEL will definitely provide a bench mark to designer but applying design procedures of UK or any other countries in India will not effectively work For example temperature of London is 20.8 C, which is considered for taking modulus value for design and the modulus value range is from 3,100 – 7,000 MPa where as Bituminous Concrete (BC) surface layer followed in India is having modulus in the range of 1500 to 2000 MPa at pavement design temperature of 35 C But the healing potential of bituminous mix will be more at 35 C It is necessary to define FEL for different temperature and correlating with modulus values and finally incorporating in pavement design 6.0 Conclusion 444 Gagandeep Singh et al / Transportation Research Procedia 17 (2016) 438 – 444 The fatigue life determined from point bending test is specimen dependant fatigue characteristics Test results change with specimen size The fatigue life determined from uniaxial testing does not depend upon specimen size It gives material fatigue characteristics rather specimen property Fatigue life determined from beam tested on elastic foundation is 20 to 30 times more as compare to beam tested in point bending test Shift factor is required for use of fatigue equation for determination of pavement thickness Endurance limit based designs are more mechanistic and economical 7.0 References NCHRP Report 646: Validating the Fatigue Endurance Limit for Hot Mix Asphalt Andre A.A.A Molenaar, Ning Li, Pungky Pramesti “Fatigue Characterization of Asphalt Mixtures for Designing Long Life Pavements” Asphalt Fatigue Endurance Limit AUSTROADS TECHNICAL REPORT AP-T131/09 Ramsamooj, D V Prediction of Fatigue Life of Asphalt Concrete Beams from Fracture Tests Journal of Testing and Evaluation, JTEVA, Vol 19, No 3, May 1991, pp 231-239 Brian D Prowell Assistant Director National Center for Asphalt Technology Methods for Determining The Endurance Limit Using Beam Fatigue Tests NCHRP Report 762: Laboratory Validation of an Endurance Limit for Asphalt Pavements Giovanni Parmeggiani Design of long life flexible composite and deep strength asphalt pavements 25th ARRB Conference Monismith, CL; Epps, JA; Kasianchuk, DA & McLean, DB 1972, Asphalt mixture behaviour in repeated flexure, TE 70-5, Soil Mechanics and Bituminous Materials Research Laboratory, University of California, Berkeley, USA Damien Bateman Laboratory investigation of fatigue endurance limits in asphalt concrete Doctor of Philosophy Engineering The University of New Mexico Albuquerque, New Mexico May 2012 A.A.A Molenaar Prediction of fatigue cracking in asphalt pavements TRR: Journal of the Transportation Research Board, No.2001, Tranportation Research Board of the National Academics, Washington, D.C.,2007, pp 155-162 Carp enter, Ghuzlan, and Shen A Fatigue Endurance Limit for Highway and Airport Pavements Submitted for Possible Presentation and publication at the Annual Meeting of the Transportation Research Board, January, 2003 ... Validating the Fatigue Endurance Limit for Hot Mix Asphalt Andre A. A .A Molenaar, Ning Li, Pungky Pramesti “Fatigue Characterization of Asphalt Mixtures for Designing Long Life Pavements” Asphalt... A. A .A Molenaar Prediction of fatigue cracking in asphalt pavements TRR: Journal of the Transportation Research Board, No.2001, Tranportation Research Board of the National Academics, Washington,... Carp enter, Ghuzlan, and Shen A Fatigue Endurance Limit for Highway and Airport Pavements Submitted for Possible Presentation and publication at the Annual Meeting of the Transportation Research