Effect of Moisture on Low-Temperature Asphalt Mixture Properties and Thermal Cracking Performance of Pavements

Transcription

1 82 TRANSPORTATION RESEARCH RECORD 144 Effet of Moisture on LowTemperature Asphalt Mixture Properties and Thermal Craking Performane of Pavements NAMHO KIM, REYNALDO ROQUE, AND DENNIS HILTUNEN Effets of moisture on asphalt mixtures were evaluated by determining the fundamental lowtemperature properties of field ores from 22 field test setions at two different levels of moisture, to get an indiation of how muh these properties may have hanged during the pavements' servie. The idea was to introdue moisture into the mixtures without ausing signifiant breakdown of the mixtures from stripping or disintegration. The indiret tensile reep and failure test at low temperature, whih was seleted by the Strategi Highway Researh Program (SHRP) to support the mixture speifiation for thermal raking, was performed on field ores at two temperatures and two levels of moisture. Master ompliane urves and frature properties were generated and ompared to evaluate hanges in fundamental lowtemperature properties at two different levels of moisture. The properties were input into a thermalraking model that was developed at Penn State and is now part of the SHRP SUPERPAVE software in order to determine whether the differenes in properties had an effet on thermalraking performane in the field. The key finding was that hanges in moisture ondition within asphalt mixtures have a signifiant effet on the lowtemperature properties of asphalt mixtures and may have a signifiant effet on the thermalraking performane of asphalt pavements. Changes in properties and performane our even when moisture does not damage the mixture signifiantly. Moisture damage of asphalt mixtures is a ombined result of moistureindued hanges in mixture harateristis and indued stress in the mixture (J). Moisture damage resulting from these two effets, primarily stripping, has been a subjet of muh researh. Even so, there is limited understanding of moistureindued hanges in asphalt mixtures in the absene of stress effets. Some evidene in the literature indiates that moisture hanges in the mixture indue hanges in mixture properties even when the moisture does not result in mixture damage or disintegration (2,3,4). Suh moistureindued property hanges may signifiantly affet the field performane of pavements. Aurate haraterization of lowtemperature properties of asphalt mixtures is important to evaluating the thermalraking performane of pavements. However, investigations into hanges in fundamental lowtemperature properties of asphalt mixtures indued by moisture have not been onduted. Therefore, this study was undertaken to evaluate the effets of moisture on the lowtemperature properties of asphalt mixtures; the study is part of researh being onduted at the Pennsylvania State University as part of a Strategi Highway Researh Program (SHRP) researh projet titled, "Performane Models and Validation of Test Results." Objetives of the work presented in this paper are as follows: N. Kim, N onhyundong, KangnamGu, Seoul, Korea. R. Roque and D. Hiltunen, Pennsylvania Transportation Institute, Pennsylvania State University, Researh Offie Building, University Park, Pa To investigate the effets of moisture on the lowtemperature reep ompliane of asphalt mixtures; To investigate the effets of moisture on the lowtemperature failure limits of asphalt mixtures; and To ondut a preliminary evaluation to determine the effets of these hanges on thermalraking performane. RESEARCH APPROACH The study was based on the evaluation of 22 fieldtest setions that were seleted as part of an SHRP thermalraking validation effort to provide data on a wide range of materials and environmental onditions in United States. Effets of moisture were evaluated by determining the fundamental lowtemperature properties of the field ores from the test setions at two different levels of moisture to get an indiation of how muh these properties may have hanged while the pavement has been in servie. The idea was to introdue moisture into the mixtures without ausing signifiant breakdown of the mixtures from stripping or disintegration. The goal was to determine how the presene (or lak) of moisture affeted properties, not to ause damage to the mixtures. Visual observations of the field ores learly indiated that the mixtures had not stripped or disintegrated in servie. Field ores were tested in two ways, either as dry speimens or wetted speimens. Dry speimens are those speimens that were tested in theasreei ved ondition, exept that they were kept in a hamber at onstant low, relative humidity (3 perent) for at least 3 days before testing. Wetted speimens are those speimens to whih moisture was introdued by applying the wetting portion of Lottman moisture onditioning proedure AASHTO T283, (i.e., they were vauum saturated at 26 in. of merury for 3 min, then left submerged for an additional 3 min.). The proedure was the most effetive way of introduing moisture into the speimens without induing damage in them. After wetting, the speimens were also plaed in a 3 perent relative humidity hamber for at least three days before testing. The following response variables were measured: Creep ompliane; Tensile strength and strain at failure; and The mvalue, whih is the slope of the linear portion of the master reep ompliane urve on a loglog sale and is related to the frature parameters of visoelasti materials ().

2 Kim et al. 83 The indiret tensile reep and failure test at low temperature (ITL T), developed by R. Roque and his oworkers at Penn State ( 6, 7), was onduted at three temperatures ( C, 1 C, and 2 C) for dry speimens, and at two temperatures ( C and l C) for wetted speimens. The reep portion of the test involved applying stati ompressive loads on the diametral speimens for 1, se and measuring horizontal and vertial reep strains near the enter of both fiat faes. Loads were seleted aording to preestablished protools in order to keep strains in the linear visoelasti range. The stre 'gth portion of the test immediately followed the reep portion. Without releasing the reep load, the speimen was failed by applying loads at a onstant rate of vertial displaement. Master ompliane urves and frature properties were generated for both of these sets of tests, as desribed elsewhere (7). The results were ompared to evaluate the hanges in fundamental lowtemperature properties between dry and wetted mixtures. The properties were input to the thermalraking model developed at Penn State as part of a researh ontrat to determine the effet of the differenes in properties on predited thermalraking performane (7). MATERIALS AND SAMPLE PREPARATION Seletion of Field Speimens Used in Testing Thirtysix ores eah 6 in. in diameter, from eah of the 22 field setions, were inluded in the thermalraking validation study, whih was onduted at the Pennsylvania Transportation Institute. Nine ores were randomly seleted for testing in the dry ondition and six ores for testing in the wetted ondition. At eah temperature, 69 tests were performed (23 setions times 3 repliates). The order at whih eah test was performed was seleted at random. Sliing of Field Core Speimens The speimens, 6 inh diameter were slied to a thikness of 2 in. with a waterooled masonry saw equipped with a diamondtipped blade. The ut provided the smooth surfae neessary to mount gage points on a speimen's fiat faes. Speimen Humidity Conditioning While making field ore speimens for mehanial property tests moisture is introdued into the test speimen. A series of proedures is used, inluding oring, ore sliing, and speifi gravity measurement. Even though all the ores were stored in sealed plasti bags, the ore storage period of the eah test setion before testing varied by as muh as one year. As a result, there was high probability that different moisture effets were indued. A way to standardize the moisture effet throughout the test setions was needed. A smallsale experiment was onduted to monitor the hanges in moisture in speimens stored in the humidityontrolled hamber. Changes in moisture were monitored for laboratoryompated speimens wetted using Lottman's shortterm onditioning proedure (8). Changes in moisture were also monitored in field ores after they were submerged for speifi gravity determination. Changes in sample weights are plotted in Figure 1. The weight of a saturated speimen hanged rapidly for the first 2 days after wetting,,..._ II.I E '<:) II.I.. C/l. II.I 2+,,==j 1st=:::::::::=::::=:f:======::::::::= "' II.I o ;. ==""'====:.:.!.::..:::::=.Measurement'l u Storage Period (day) I Lab. Speimen Field Core FIGURE 1 Changes of moisture in speimen during humidity onditioning. after whih a slow onstant rate of weight hange was observed through the 1th day. The weight of most field ores also hanged rapidly for the first 2 days. On the basis of results presented in Figure 1, it is expeted that the moisture level at 3 days after a minute soaking (as required for speifi gravity measurement) will be very lose to the moisture level before the minute soaking. The fast hange in weight during the first few days appears to be aused by evaporation of water entrapped in the surfae region of the speimen, whereas the slow hange in weight after the first few days appears to be related to permeability or the airvoid struture of a speimen. Therefore, after bulk speifi gravity was measured, all speimens were plaed in a onstanthumidity environment for a minimum of 3 days before testing. Speimens were onditioned at 3 perent relative humidity and at room temperature (2 C). Speimen Load Conditioning In order to minimize speimenseating effets during testing, a preonditioning load sequene was applied to eah ore during the humidityonditioning period. The proedure onsisted of 1 yles of loading at 2 C. Eah load yle onsisted of a.1 se inverse haversine (ompression) followed by a.9 se rest period. The amplitude of the haversine pulse was set to the load orresponding to a horizontal tensile stress of 6.9 kpa (1 psi). Speimen Temperature Conditioning Speimens were kept at the onstant test temperature for no less than 6 hr before testing. Beause little is known about the effets of keeping mixture speimens at very low temperatures for extended periods of time [i.e., lowtemperature physial hardening (9)], extended deepfreeze periods were avoided. TEST RESULTS AND ANALYSIS Test results were ompared in order to evaluate hanges in fundamental lowtemperature properties between dry and wetted mixtures. The effet of moisture on mixture properties is summarized in Table 1. 16

3 84 TRANSPORTATION RESEARCH RECORD 144 TABLE 1 Effet of Wetting on Mixture Properties Se No Effet of Wetting on Mixture Properties En vi Strength@ Stiffness* ron Loation Shift 1 C (kpa) ment (l/at) Dry Wet time 1 Chikasha, OK Same De De In Dry Hakberry,AZ Same Same Mild De Same Freeze Thaw Oasis, NV Same De Mild De In Ottawa, KS Mild In De Same In Idaho Falls,ID In De De In Coeur d'alene,id Same De Mild De In Dry Edison, NE Same Same Mild De Same Hard 16 Freeze Marysvale, UT Mild De De De In Cody, WY Mild In Mild De Mild In Same Rangely,CO De De Mild In Same Glasgow,KY In Same In Same Pona City,OK Same De Mild De In Wet Berlin, MD In In In Same Freeze 26 Thaw Salem, SC Same De Same In Trenton, NJ In Mild In Same In Waynesville,MO Same De De Same Lawreneville,P A Same De De In Huntington, IN Mild In De De In Wet Farmington, ME In Same Same Same Hard 36 Freeze Bonnville,IN In In In Same , 37 Farmington, MN In Mild De Mild De In Frazee, MN In Mild De Mild De In *Same = no hange; De = derease; In = inrease in property indued by moisture Compliane Comparisons of master stiffness (inverse of ompliane) urves for dry and wetted speimens learly indiated that the introdution of moisture had a signifiant effet on the lowtemperature stiffness of the mixtures. Figures 2 through 7 show omparisons of master stiffness urves and shiftfator temperature relationships at a referene temperature of 1 C for three mixtures that haraterize the types of hanges observed to be indued by moisture. Atual measured data were plotted within the measured redued time range. Outside the measured redued time range, wetted stiffness was extrapolated using a hyperboli model to over the entire redued time range orresponding to speimens tested in the dry ondition. Compared with dry stiffness urves, the stiffness of wetted mixtures hanged very signifiantly for most mixtures (see Table 1). However, the effet of moisture appeared to be different for different mixtures; it was diffiult to find trends among these data. In general, but not always, wettedmixture stiffness at shorter redued time (around 1 se) was the same or greater than drymixture stiffness. On the other hand, wettedmixture stiffness at longer redued times (1 3 se or greater) either was generally less than drymixtures stiffness or was dereasing more rapidly than dry mixture stiffness. As indiated in Figures 3,, and 7, shift fator/temperature relationships also hanged as a result of hanges in moisture ontent in the mixture. Among more than half of the test setions, wetting redued the shift fators, indiating that wetted rheologial property was less temperaturedependent than dry. It is nearly impossible to determine the effet of hanges in the master ompliane urve on thermalstress development without atually performing thermalstress omputations. Thermalstress development not only depends on the magnitude and shape of the ompliane urve at a referene temperature but also on the harateristis of the shift fator/temperature relationship. For example,

4 Kim et al. 8 o 1.E+7 a... Q) : :E U 1. OOE+6 o 1. OOE+7 a... Q) : :i:: m l.ooe+6 1.E+OS 1.E3 1.E1 1.E+Ol l.ooe+3 l.ooe+os 1.E+7 l.ooe2 1.E+OO l.ooe+2 1.E+4 l.ooe+6 Redued Time (SEC) l.ooe+os 1.E3 1.E1 1.E+Ol 1.E+3 1.E+OS 1.E+7 1.E2 1.E+OO 1.E+2 1.E+4 1.E+6 Redued Time (SEC) DRY D WETI'ED Hyperboli Model FIGURE 2 Comparison of dry and wetted master stiffness urves (Setion 2). DRY o WETI'ED Hyperboli Model FIGURE 4 Comparison of dry and wetted master stiffness urves (Setion 6). le1 le1... t> u i:.t.... :. ti) le le6 le2 le3 t> i:.t.... :. ti) le4 le le6 le Temperature (C) Temperature (C) 1Dry a Wetted 1 Dry a Wetted FIGURE 3 (Setion 2). Comparison of dry and wetted shift fators FIGURE (Setion 6). Coffiparison of dry and wetted shift fators two materials may have idential ompliane urves at a speified referene temperature, but their ompliane at another temperature may be signifiantly different if their shift fator/temperature relationships are different. These omplexities make it extremely diffiult to assess the effet of moisture hanges simply by looking at how the master ompliane urve hanged. Therefore, the effet of these hanges was evaluated by prediting pavement performane using dry and wetted rheologial properties. The results of this evaluation are presented later in this paper. More detailed researh is under way that should provide explanations to the observed hanges in rheologial properties indued by moisture. Failure Limits Comparisons of strengths and mvalues between dry and wetted speimens indiated that the introdution of moisture also had a sig nifiant effet on the frature properties of the mixtures. Figure 8 through 1 indiates omparisons of strengths at different temperatures, whereas Figure 11 provides omparisons of mvalues for the three setions presented earlier. Again, themvalue is defined as the slope of the linear portion of the master reep ompliane urve on a loglog plot. It has been found to be an important frature parameter in distinguishing between the thermalraking performane of different materials. One again, the effet was different for different mixtures, and it was diffiult to draw onlusions or trends from the data. In general, the strengths of wetted speimens were either lower or about the same as the dry speimens, while the mvalues of wetted speimens were either higher or about the same as the mvalues of dry speimens. Lower strengths result in less resistane to thermal raking, whereas higher mvalues result in better resistane to thermal raking. As for ompliane, it is nearly impossible to tell what the ombined effet of these differenes in properties might be on thermalraking performane simply by

5 86 TRANSPORTATION RESEARCH RECORD 144 4QQ...6Q..., 6Q Q... ro 1. OOE+7 a.. 6 I/) I/) Q) :i:: Zi 1.E+6 1.E+ l.ooe3 1.E1 1.E+Ol 1.E+OJ 1.E+ l.ooe+o 1.E2 1.E+OO 1.E+2 1.E+4 1.E+6 Redued Time (SEC) C... 4Q Q... 3 e::.. 2Q Q ==;<=="'m!::ul!:=f==g==i=:lllli'========t'q QC 1 Q DRY o WETIED Hyperboli Model FIGURE 6 Comparison of dry and wetted'master stiffness urves (Setion 27).,_DRY WETTED Interpolated Wetted FIGURE 8 Comparison of dry and wetted strengths (Setion 2). s le+qq le1 le2 le3 ti i;... le4... :a en le le6 le7 2 1 lq Q Temperature (C) 1 Dry e Wetted FIGURE 7 Comparison of dry and wetted shift fators (Setion 27). omparing the values. Again, performane preditions were made to evaluate the effets indued by moisture. Stripping Observations After the ITLT test at C was onduted pitures were 'taken to monitor the stripping on split faes of test oresfor both dry and wetted oresto monitor and ompare the hanges in stripping indued by moisture. In most ases, no hanges in stripping or disintegration by wetting were observed whih may imply that the wetting proedure used in this researh was not severe enough to indue any moisture damage, as that was the intent of the study. As mentioned earlier, the basi idea was to introdue moisture into mixtures without ausing signifiant breakdown of the mixtures. Effet of Wetting on ThermalCraking Performane Generally, but not always, moisture makes asphalt mixture less stiff and weaker in strength. As far as the thermalraking performane of pavement is onerned, an inrease in mixture ompliane (redution in stiffness) redues thermal stress, thereby reduing its thermalraking potential. On the other hand, a omparable derease in strength inreases thermalraking potential. A derease in 1/aT (shift fator/temperature relationship) results in higher stiffness at temperatures above the referene temperature, whih onsequently inreases thermalraking potential for mixtures with idential ompliane urves at a speifi referene temperature. Moisture in a mixture generally inreases themvalue, whih results in better resistane to thermal raking. Thus, as mentioned earlier, it is nearly. impossible to tell what effet these hanges will have on thermalraking performane without atually performing thermalstress omputations and performane preditions. 4QQ...r,..,..,.,..6Q 4Qii ;... ;......, QQH ' i i en 3 ii, i...,... 4Q en 4 'i.l... 3Q 'i.l :i 1QQ 1 QQ 6QQ 2Q Q Q!1====11===F=:CL.l!o===F=mi,'=F==:1C.&,==.1=11===='Q 2C 1C loc SC QC TEMPERATURE (C),_DRY WETTED Interpolated Wetted FIGURE 9 Comparison of dry and wetted strengths (Setion 6). 1 Q

6 Kim etal ,... ;...,...,... 6 j Ci) C 1C loc SC QC TEMPERATURE (C),_DRY WETI'ED Interpolated Wetted FIGURElO (Setion 27) e.4.3 :2.1 Comparison of dry and wetted strengths 2 6 SECTION NO. 1DRY WETI'ED 27 6 Thus, the average depth of transverse raks within the pavement is omputed on a daily basis. A probabilisti approah is then used to determine the amount of raking in the pavement. A detailed desription of the model is presented elsewhere (7). A generalized fourelement Maxwell model was seleted to represent the visoelasti properties of the asphalti onrete mixture. Mathematially, the generalized Maxwell model is expressed aording to the following Prony series expansion: 4 E(i;) = L E;eV>; (1) i=l where E(i;) is the relaxation modulus at redued time t;, and E;, A; are Prony series parameters for master relaxation modulus urve. The Prony series was fit to the ITLT ompliane data obtained from both the dry and wetted speimens for input into the thermalraking model. Details onerning the Prony series parameter fitting are presented elsewhere (7). Thermalraking preditions then were made for eah test setion, using both dry and wetted properties, to determine the differene in predited performane. All other input data were the same for both sets of preditions. The effet of moisture on mixture properties was refleted in the predited thermalraking performane of the pavement setions. The results of thermalraking preditions for the three test setions for whih properties were presented earlier in the paper, are presented in Figures 12 through 14. As expeted, the effets of moisture on predited performane varied signifiantly from mixture to mixture: very little differene in thermalraking performane was observed for some setions (e.g., PTI Setion 2; Figure 12), whereas signifiant differenes were observed in other setions (e.g., PTI Setion 6; Figure 13). As mentioned earlier, moisture affets numerous mixture properties (i.e., ompliane, strength, shift fator, and mvalue eah of whih may ontribute to the thermalraking performane of a partiular mixture. The ombined effet of suh moistureindued property hanges determines. whether moisture has been benefiial, harmful, or has had no effet on thermalraking performane. In summary, the introdution of moisture resulted in little or no hange in the thermalraking performane of 13 test setions, FIGURE 11 Comparison of dry and wetted mvalues. A mehanisbased thermalraking model developed at Penn State, whih has been inorporated into the SHRP SUPERPA VE software, was used for this analysis. The model predits the amount (or frequeny) of thermal raking as a funtion of time. Inputs to the model inlude: fundamental properties (master relaxation modulus urve and frature parameters A and n) obtained from the ITLT, pavement struture, and sitespeifi weather data. The model predits thermal stress as a funtion of pavement depth on an hourly basis throughout the analysis period. Thermal stresses are used to predit rak propagation and the amount of transverse thermal raking as a funtion of time. Pavement temperatures used in these omputations are predited from daily air temperature data using the FHWA Environmental Effets Model (1). Thermal stresses are omputed using an algorithm based on Boltzmann's superposition priniple as it applies to visoelasti materials. Visoelasti mixture properties (i.e., the master relaxation modulus urve) as measured by the ITLT test are used for these omputations. Thermal stresses are then used to determine stress intensity fators for use in the Paris law of rak propagation [C =A (LKr] a tt 16 ::::: (,) u 1._ 8 : :::s / TIME (YEARS) 1DRY a WETI'ED FIGURE 12 Effet of moisture on thermal raking performane (Setion 2).

7 88 TRANSPORTATION RESEARCH RECORD h + i.... a ,...,. +...,...,,... ; !...,...,...,,...;... ;...;...;...,; !><: 12 g u 1 'O 8t...,...,!... T...;...;...;...,...;...;...;...;...;f t...;... ;...;...;...;......,... j :::l ;...,...,...;... ;... ;...;...;.... ;... i/ ;..., 41t + ;;.. t i i + i ±7'l'.. + i.. 2 t r.,...,..., ;...,... ;... ; ; ;...! O._$ofP"F=i===fil':::::...+1t++++++i++iij TIME (YEARS) a 1.!><: u ell u... :::l E <: _...,,_..,_,._..._... l'.,_...i TIME (YEARS) 1 DRY a WETTED 1 DRY a WETTED FIGURE 13 Effet of moisture on thermal raking performane (Setion 6). FIGURE 14 Effet of moisture on thermal raking performane (Setion 27). signifiantly improved the performane of 6 test setions, and signifiantly redued the performane of 2 test setions. It should be noted that the fat that no hange in predited performane was observed for a partiular_ setion in a partiular environment does not mean that this same hange in properties would not produe a signifiant hange in performane in a different environment. It appears that the effets of moisture may be both mixture and environment dependent. At this point, it is not entirely lear why moisture had a different effet on different mixtures. It appears that these hanges may be related to the pore struture of the mixture, whether or not the pore water froze, and the effet of freezing on the struture of the mixture. More researh is being onduted to evaluate these effets. CONCLUSIONS Conlusions from this work may be summarized as follows: Changes in moisture ondition within asphalt mixtures sig_ nifiantly affet the lowtemperature properties of asphalt mixtures. Generally, but not always, the introdution of moisture into the mixture results in lower strength and higher ompliane at longer redued times. The magnitude of the moistureindued hanges in properties is highly mixture dependent. Changes in moisture ondition within asphalt mixtures may have a signifiant effet on the thermalraking performane of asphalt pavements. Changes in properties and performane our even when moisture does not damage the mixture signifiantly. These results learly indiate that great are must be exerised to bring field ores to standard moisture ondition before laboratory testing for determination of fundamental lowtemperature properties. Further researh is reommended to identify mixture harateristis that lead to mixtures whose properties and performane are signifiantly affeted by moisture hanges. ACKNOWLEDGMENT Funding for the work presented in this paper was provided by SHRP. REFERENCES 1. Graf P. E. Fators Affeting Moisture Suseptibility of Asphalt Conrete Mixes. Pro., Assoiation of Asphalt Paving Tehnologists, Vol., St. Paul, Minn. 1986, pp Bushing, W., S. N. Amirkhanian, J. L. Burati, J.M. Alewine, and M.. Flether. Effets of Seleted Asphalts and Antistrip Additives on Tensile Strength of LaboratoryCompated Marshall Speimens: A Moisture Suseptibility Study. Pro., Assoiation of Asphalt Paving Tehnologists, Vol., 1986, St. Paul, Minn., pp Coplantz, J. S. and D. E. Newomb. Water Sensitivity Test Methods for Asphalt Conrete Mixtures: A Laboratory Comparison. In Transportation Researh Reord 1171, TRB, National Researh Counil, Washington, D.C., 1988, pp Shmidt, J. and P. E. Graf. The Effet of Water on the Resilient Modulus of Asphalt Treated Mixes. Pro., Assoiation of Asphalt Paving Tehnologists, Vol. 41, 1972, St. Paul, Minn., pp Shapery, R. A. A Theory of Crak Growth in Visoelasti Media: Researh Report MM Mehanis and Materials Researh Center, Texas A&M University, College Station, Marh Roque, R. and W. Buttlar. Development of a Measurement and Analysis System to Aurately Determine Asphalt Conrete Properties Using the Indiret Tensile Mode. Pro., Assoiation of Asphalt Paving Tehnologists, Vol. 61, 1992, St. Paul, Minn., pp Lytton, R. L., R. Roque, J. Uzan, D.R. Hiltunen, E. Fernardo, and S. M. Stoffels. Performane Models and Validation of Test Results. Final Report to Strategi Highway Researh Program; Asphalt Projet A, July Lottman, R. NCHRP Report 246: Prediting MoistureIndued Damage to Asphalt ConreteField Evaluation Phase. TRB, National Researh Counil, Washington, D.C Bahia, H. Low Temperature Physial Hardening of Asphalt Cements. Ph.D. thesis. Pennsylvania State University, University Park, Lytton, R. L., D. E. Pufahl, C.H. Mihalak, H. S. Liang, and B. J. Dempsey. An Integrated Model of the Climati Effets on Pavements. Report FHWARD933. FHWA, U.S. Department of Transportation, Nov Publiation of this paper sponsored by Committee on Charateristis of Bituminous Paving Mixtures To Meet Strutural Requirements.