Density and SCB Measured Fracture Resistance of Temperature Segregated Asphalt Mixtures Accepted Manuscript Density and SCB Measured Fracture Resistance of Temperature Segregated Asphalt Mixtures Mink[.]
Accepted Manuscript Density and SCB Measured Fracture Resistance of Temperature Segregated Asphalt Mixtures Minkyum Kim, Louay N Mohammad, Pranjal Phaltane, Mostafa A Elseifi PII: DOI: Reference: S1996-6814(16)30099-2 http://dx.doi.org/10.1016/j.ijprt.2017.01.004 IJPRT 68 To appear in: International Journal of Pavement Research and Technology Received Date: Revised Date: Accepted Date: 18 May 2016 22 November 2016 20 January 2017 Please cite this article as: M Kim, L.N Mohammad, P Phaltane, M.A Elseifi, Density and SCB Measured Fracture Resistance of Temperature Segregated Asphalt Mixtures, International Journal of Pavement Research and Technology (2017), doi: http://dx.doi.org/10.1016/j.ijprt.2017.01.004 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain Density and SCB Measured Fracture Resistance of Temperature Segregated Asphalt Mixtures Minkyum Kim, Corresponding Author Research Associate College of Engineering Louisiana Transportation Research Center Louisiana State University 4101 Gourrier Ave., Baton Rouge, LA 70808 e-mail: mkim@lsu.edu Louay N Mohammad Irma Louise Rush Stewart Distinguished Professor Department of Civil and Environmental Engineering Engineering Materials Characterization Research Facility Louisiana Transportation Research Center Louisiana State University 4101 Gourrier Ave., Baton Rouge, LA 70808 e-mail: louaym@lsu.edu Pranjal Phaltane Graduate Research Assistant Department of Civil and Environmental Engineering Louisiana State University 4101 Gourrier Ave., Baton Rouge, LA 70808 e-mail: pphalt1@tigers.lsu.edu Mostafa A Elseifi Associate Professor Department of Civil and Environmental Engineering Louisiana State University 3526c Patrick Taylor Hall, Baton Rouge, LA 70803 e-mail: elseifi@lsu.edu Density and SCB Measured Fracture Resistance of Temperature Segregated Asphalt Mixtures Abstract: Segregation is a serious challenge for high quality constructions of asphalt pavements Temperature segregation (or temperature differential) in uncompacted asphalt mats has been identified with the use of infrared thermal cameras at the paving site Four Louisiana asphalt rehabilitation projects were selected for investigating the effects of temperature segregation on the quality and performance of asphalt pavements A multi-sensor infrared temperature scanning bar (IR-bar) system mounted behind the paver measured the real-time thermal profile The quality of paving mats was measured by the density of field cores while the performance was measured by the mix’s intermediate temperature fracture resistance using the semi-circular bend (SCB) test Results showed that temperature-segregated samples generally had lower densities than the control samples, although the differences were mostly statistically insignificant On the other hand, temperature segregated samples generally had lower fracture resistance than the control samples measured by the SCB Jc values Four out of six comparison cases showed the differences were statistically significant Further verification effort was recommended for confident implementation of the IR thermal imaging technology to the asphalt pavement construction specification Keywords: temperature segregation, temperature differential, thermal profile, infrared thermal camera, density, semi-circular bend (SCB), fracture resistance 1 INTRODUCTION Segregation has been a serious concern for the asphalt paving industry for decades Brock (1986) described segregation in asphalt mixtures as “a concentration of coarse materials in some areas and fine materials in others, which result in non-uniform mixes that not duplicate the original design, grading, or asphalt cement.” He suggested that the segregated areas would develop localized premature distresses such as fatigue cracking, rutting, raveling, pothole, etc A number of research efforts on the topic was conducted in the past decades (Brown et al 1989, Cross and Brown 1992, Webb and Day 1995, Khedaywi and White 1995, Khedaywi and White 1996, Williams et al 1996, Cross et al 1997, Wolff et al 1997) Stroup-Gardiner et al (2000) further identified segregation as (1) gradation segregation, (2) 10 temperature segregation, and (3) aggregate-asphalt segregation (a.k.a drain-down in stone matrix 11 asphalt) 12 Gradation segregation results in either coarse aggregate-rich or fine aggregate-rich spots and has 13 been the most common type of segregation; therefore, many remedies have been introduced and resulted 14 in significant reductions of the problem Common remedies for reducing the chances of gradation 15 segregation include multiple pile truck loading from the storage bin at the plant, and use of Material 16 Transfer Vehicle (MTV) from the truck bed to the paver Temperature segregation is a phenomenon that 17 has been identified with the introduction of high-precision portable infrared thermal cameras at the paving 18 site Many state agencies and researchers have investigated this phenomenon in recent years (Stroup- 19 Gardiner and Brown 2000, Willoughby et al 2001, Henault et al 2005, Amirkhanian and Putman 2006, 20 Song et al 2009, Sebesta and Scullion 2012a, Sebesta and Scullion 2012b, Cho et al 2012) A common 21 finding of these research studies is that temperature segregation (or temperature differential) during the 22 laydown operation of asphalt mixtures can cause a compaction problem that leads to the lower-than- 23 desirable pavement density, which consequently results in a considerable reduction of pavement service 24 life In Louisiana, asphalt construction contractors are required to follow some operational practices such as the truck loading/hauling methods and use of MTV in order to prevent segregations (Louisiana DOTD 2013) Hence, it is generally expected that the uniformity of Louisiana asphalt mixtures is appropriate to the required quality However, investigations concerning temperature segregation and its associated problems have not been thoroughly conducted Therefore, it is necessary to identify how often and under which conditions temperature segregation is likely to occur in Louisiana asphalt paving projects Moreover, understanding the ultimate link between temperature segregation and asphalt pavement performance via mechanical properties of asphalt mixtures would enable Louisiana pavement engineers to tailor the solutions to fix the problem 10 11 OBJECTIVES AND SCOPE 12 The objective of this study was to identify the relationship between temperature segregation and the 13 quality of asphalt pavements The quality of asphalt pavements was measured primarily by the density of 14 field cores In addition, selected field cores were tested in the lab using the semi-circular bend (SCB) test 15 to evaluate the fracture resistance of mixtures at intermediate service temperatures 16 17 BACKGROUND 18 A comprehensive study on segregation problems in asphalt pavement construction was conducted by 19 Stroup-Gardiner et al (2000) through the national cooperative highway research program (NCHRP) 9-11 20 The objectives of this study were to develop procedures for defining, detecting, and measuring 21 segregation, and to evaluate the effects of segregation on hot-mix asphalt (HMA) pavement performance 22 Nondestructive technologies capable of evaluating the characteristics of the entire mat during construction 23 were considered the most desirable methods The best candidate technologies were expected to produce 24 measurements strongly correlated with changes in key performance-related mixture properties Two main types of segregation have been thoroughly investigated in the literature: gradation segregation and temperature segregation Gradation segregation is the most common type and can occur as the result of aggregate stockpiling, handling, asphalt mixture production, storage, truck loading practices, construction practices, and equipment adjustments Temperature segregation was identified as occurring as the result of differential cooling rate of portions of the mix in the exposed part of the mix in the haul truck, along the sides of the truck bed, in the wings of the paver, etc An additional type, aggregate-asphalt segregation, common in stone matrix asphalt (SMA), was also suggested Segregation may be defined as a lack of homogeneity in the HMA constituents of the in-place mat of such a magnitude that there is a reasonable expectation of accelerated pavement distresses “Constituents” 10 11 should be interpreted to encompass asphalt cement, aggregates, additives, and air voids A thorough evaluation of temperature differential (TD) phenomenon was performed by 12 Willoughby et al (2001) from 1998 through 2000 The objectives of the study were to identify the 13 problems experienced by the Washington Department of Transportation (WSDOT) with hot-mix paving, 14 and whether temperature or aggregate segregation could be the possible causes of these problems The 15 authors found that the temperature segregation occurred more frequently than the aggregate segregation 16 did, and the temperature segregations caused reduced density of pavement areas, which would eventually 17 result in reduced pavement life In this study, TD less than 14°C (25°F) did not result in significant 18 density differentials, while TD greater than 14°C resulted in density differentials more frequently It was 19 also found that the use of material transfer vehicles, pneumatic rollers as breakdown or intermediate 20 rollers, and timely compaction can reduce the temperature segregation related density differentials 21 In 2005, the Connecticut Department of Transportation (ConnDOT) published guidelines for 22 reduction of Temperature Differential Damage (TDD) for HMA (Henault et al 2005) After five years of 23 field survey and distress analysis, it was recommended that TD alone should not be used as a quality 24 acceptance characteristic (QAC) to award incentive or to punish contractors, but the identified TD areas 25 should be sampled for further evaluations to ensure the quality of the paving mat Furthermore, use of proper insulations for hauling trucks, minimizing waiting time, use of MTV, and careful hopper wing control were recommended as best practices to avoid TDD The South Carolina Department of Transportation (SCDOT) also evaluated thermal differential in HMA and its effects on the laboratory test results (Amirkhanian and Putman 2006) Results showed that the most identifiable cause of temperature segregation within a pavement appeared to be due to either material segregation at the end of a truck load or the introduction of cooler material as the result of dumping the paver wings Proper utilization of a MTV appeared to be the most effective means to minimize thermal differentials in the pavement mat for many mixtures Results also showed that haul time appeared to be one of the largest factors contributing to TDD With haul times greater than 70 minutes, 10 the occurrence of temperature segregation increased 11 The North Dakota Department of Transportation (NDDOT) investigated the use of thermal 12 cameras in asphalt pavement construction in order to determine whether thermal segregation occurs in the 13 state (Song et al 2009) Observations suggested that thermal segregation, if defined as the freshly laid 14 mat having an area 13.9°C (25°F) colder than adjacent areas, does occur in North Dakota asphalt 15 pavement The correlation between temperature and density was compared to that between TD and 16 density It was reported that the density was more dependent on temperature than on TD Authors 17 suggested that it may also be possible to determine limiting mat temperatures, below which pavement 18 density would be significantly affected 19 In Texas, the Pave-IR system was first proposed more than a decade ago and the system was 20 implemented after the system was developed in a commercial version by MOBA, INC in Germany 21 (Sebesta and Scullion 2012a) Using the device, performance of 14 asphalt pavement projects in Texas 22 were monitored from 2004 to 2009 (Sebesta and Scullion 2012b) With projects ranging in age from two 23 to seven years, most projects did not exhibit distress at locations of known thermal segregation On some 24 projects, the Ground Penetrating Radar (GPR) data suggested traffic action may have homogenized the 25 pavement surface density However, on several projects, evidence of thermal segregation still existed, generally noted by differences in surface appearance and localized decreases in the surface dielectric constants measured from the GPR Performance testing cores after some years of service indicated that thermal segregation did not impact the Hamburg test results but may lead to a higher susceptibility to cracking It was concluded that the presence of thermal segregation at the time of construction does not guarantee failure within two to seven years, but the results show that thermally-segregated locations may remain anomalies in the mat that deteriorate due to cracking when on the surface, or contribute to failures of subsequent overlays Cho et al (2012) studied the relationship between thermal differential and the density of compacted mat using a thermal camera device with a handheld GPS system It was shown that a 10 significant relationship existed between TD and pavement density as the level of TD increased Haul time 11 was not found to be significant in creating TD within the observed time range The authors suspected that 12 TD created during transport was caused by the type of truck used The use of a belly dump truck with 13 material pick-up machine appeared to contribute to more uniform mat temperatures Almost one-third of 14 all investigated TD locations are showing signs of deterioration between months and 1.5 years after 15 construction, which led the authors to believe that TD was clearly causing premature distresses 16 17 METHODOLOGY 18 Field projects and Asphalt Mixtures 19 Four asphalt rehabilitation projects in Louisiana were selected for evaluation (Table 1) Each of the four 20 projects was constructed by a different contractor A slightly smaller sized paver was utilized in LA30 21 project, while the other three projects used the same paver model A different model of MTV was used in 22 LA1053, but both models of MTV, i.e., Roadtec Shuttle Buggy and Weiler E2850, were similar in size 23 Travel times of hauling trucks ranged from less than 10 minutes to up to 50 minutes The target laydown 24 temperatures were 135°C (275°F) in LA1058 and 149°C (300°F) in LA30, US165, and LA1053 Table Field Projects Investigated Route Contractor Paver Model MTV Model Haul Time Paving Time Target Temperature LA30 A CAT AP655 Shuttle Buggy