Evaluation of Tests To Assess Stripping Potential of Asphalt Concrete Mixtures

Transcription

1 18 TRASPORTATIO RESEARCH RECORD 1171 Evaluation of Tet To Ae Stripping Potential of Aphalt Concrete Mixture FRAZIER PARKER JR., AD FouAD A. GHARAYBEH Stre pedetal, boll, and Indirect tenile tet were evaluated for aeing the tripping potential of aphalt concrete mixture. The tet were applied to urface and bae-binder mixture that included five aggregate combination, aphalt cement from two ource, and three antitripplng agent. The field performance of mixe with the five aggregate combination ranged from good to poor, and the aphalt cement and antitripping agent are repreentative of thoe ued in Alabama. The boil and indirect tenile tet were mot promiing, although neither they nor the tre pedetal tet accurately predicted the expected performance of all mixe. They did, however, produce conitent, although at time apparently incorrect, prediction. There wa alo reaonably good correlation between boil tet and indirect tenile tet value, which improve their credibility a predictor of tripping when applied to pecific mixe. Ue of the tet for general evaluation of material ource i not recommended; they mut be applied to pecific material combination. Variability in aggregate drying, gradation, and aphalt content may be an important factor affecting tripping potential. Additional teting to etablih the influence of thee factor i recommended. The detructive influence of moiture in aphalt concrete ha been extenively invetigated. umerou tet procedure have been developed and are continually evolving to evaluate aphalt concrete mixture and poible remedie that could reduce tripping. Material alone preent thouand of variable that may influence tripping (1). Kennedy et al. (2) in 1983 invetigated the tripping potential of elected material from Texa uing three different tet. Stuart (3) in 1986 invetigated the tripping potential of material elected from everal tate with everal technique. Thee two independent tudie, and many more, have concluded that there 1 no generally applicable way to reliably evaluate the water uceptibility of propoed aggregate-aphalt combination. The quantification of tripping potential during material election and mixture deign ha remained difficult. Conventional pecification for aphalt mixture do not totally evaluate the aphalt-aggregate bond (4). A poible approach that would conider tripping with other mixture requirement could be achieved by following the conventional deign method firt, then evaluating the propoed mixture by conducting moiture uceptibility tet. Becaue of thi problem, thi tudy wa initiated in 1984 to develop or recommend, or both, a tet procedure to ae the tripping potential of Alabama aphalt concrete mixture and to F. Parker, Jr., Highway Reearch Center, Auburn Univerity, Auburn, Ala F. A. Gharaybeh, Mu'tah Univerity, Mu'tah-Karak, Jordan. tudy the effectivene of antitripping additive. The tudy incorporated five aggregate combination (two limetone and three gravel), aphalt cement from two ource, and three antitripping agent repreentative of material ued in Alabama. The tripping potential of mixture deigned with the Marhall method wa evaluated with boil tet, tre pedetal tet, and indirect tenile tet. DEVELOPMET OF TEST PROGRAM The teting program wa initiated by evaluating the boiling and tre pedetal tet on urface coure mixe with the five aggregate combination and aphalt cement from two ource. The reult of thee tet were generally better than expected and howed lack of trong correlation with field performance. Indirect tenile tet were then run on aphalt cement from one ource. Thee tet reult howed imilar correlation with field performance. Further review revealed that coarer and leaner bae-binder mixture may be more vulnerable to tripping than are finer and richer urface mixture. Field experience reinforced thi belief. Core taken from pavement contructed with ome of the aggregate under tudy howed that tripping generally began and wa concentrated in bottom layer of pavement. A ignificant exception to thi ha been tripping in urface mixe that have been overlaid. At thi tage, the deciion wa made to evaluate bae-binder mixture and to eliminate the tre pedetal tet. The remaining tet were performed with all five aggregate combination and aphalt cement from two ource. The effectivene of antitripping agent wa tudied at all tage of the teting program. MATERIALS Propertie of the component material and mixe have been previouly decribed (5) and will only be ummarized here. Aphalt Cement Aphalt cement were obtained from two ource and were labeled ACl and AC2. Both were vicoity grade AC-2 meeting Alabama Highway Department pecification. The manufacturer mix crude from variou ource, but at the time of ampling the majority of the crude oil wa from the Gulf of Mexico.

2 Parker and Gharaybeh combination were elected, after conultation with Alabama Highway Department central laboratory and diviion peronnel, to provide a range of field performance from good to poor. The characterization of an aggregate combination i ubjective and baed on experience of field peronnel with aphalt-aggregate mixe containing the aggregate. The characterization i, therefore, general in nature rather than pecific and relate to the potential for tripping rather than to the performance of a particular mix. A reaonable characterization would be that a mix of "A" material would be le likely to trip than a mix of "B" material. A reult preented later will verify, factor other than aggregate compoition (gradation and aphalt content) influence tet reult. Five typical aggregate combination of from three to five individual aggregate each were elected and arbitrarily labeled A through E. were combined to produce mixe that met either urface or bae-binder coure pecification. Therefore, for each aggregate combination, there will be a urface mix and a bae-binder mix. The gradation and deign aphalt content were thoe obtained by the Marhall mix deign procedure. Combination A Thee are baically limetone mixe that have good reported performance with few ign of pavement ditre attributable to tripping. Mix A contain 85 percent cruhed limetone and 15 percent natural and and ha an aphalt content of 5.5 percent. It ha been ued primarily for houlder paving and leveling. Bae-Binder Mix A contain 1 percent cruhed limetone and ha an aphalt content of 4.25 percent. The limetone i dene (pecific gravity "" 2.8) dolomitic material with an aborption of about 1 percent. Combination B Thee are baically gravel mixe with variable reported performance. Before the ue of antitripping additive, tripping damage wa evere. Antitripping additive have improved performance; however, ome tripping problem are till reported. Both urface and bae-binder mixe contain 1 percent limetone creening and 9 percent iliceou and and gravel. The urface mix ha an aphalt content of 7.5 percent and the bae-binder mix 4.5 percent. The gravel and and are from the ame ource and are decribed a "cherty" material (pecific gravity "" 2.5) with relatively high aborption (3 percent). The urface mix contain cruhed gravel and the bae-binder mix contain uncruhed gravel. Combination C Thee are iliceou gravel mixe with moderate reported performance. Even before the ue of antitripping additive, only minor tripping problem were reported. Both the urface and the bae-binder mixe contain 15 percent fine and and 85 percent coare and and gravel from a primary ource. Aphalt content are 6.25 and 4.55 percent for the urface and baebinder mixe, repectively. The coare and and gravel are predominantly ound quartz and quartzite material (pecific gravity "" 2.6) with relatively low aborption (1 percent). Combination D Thee are iliceou gravel mixe with poor reported tripping performance. The ue of antitripping additive ha improved performance, but gravel from thi region of the tate continue to be regarded a particularly uceptible to water damage. The mixe contain 1 and 15 percent fine and and 9 and 85 percent wahed and and gravel from a primary ource. Aphalt content are 6.25 and 4.9 percent for the urface and baebinder mixe, repectively. The wahed and i primarily ound quartz, but the coarer particle tend to be imilar to the gravel. The gravel i a highly variable cherty material (pecific gravity "" 2.5) including light and porou particle. Aborption i relatively high at about 2.7 percent. Combination E Thee are baically limetone mixe with good reported tripping performance. Both the urface and the bae-binder mixe contain 1 percent natural and and 9 percent cruhed limetone from a primary ource. Aphalt content are 5.5 and 4.15 percent for the urface and bae-binder mixe, repectively. The limetone ha a relatively high calcium carbonate content (approximately 9 percent), a pecific gravity of about 2.6, and aborption of about 1 percent. Antltrlpping Additive Three antitripping additive were ued: hydrated lime and two proprietary chemical agent. The hydrated lime (HL) i high calcium and wa applied at a rate of 1 percent by weight of aggregate. One proprietary liquid agent, labeled BA, i a metalloamine (or polyamine) with a recommended doage rate of.5 percent by weight of aphalt cement. The econd proprietary liquid agent, labeled KB, i an amidoamine with a recommended doage rate of.5 to 1 percent by weight of aphalt cement. TEST PROCEDURES were combined according to the job mix formula, and ieved on eight ieve to produce portion with particle ize ranging from paing 1 1 /2 in. to o. 2. Required aggregate from each portion wa then combined to meet required gradation. After thi tage, ample preparation and teting were dependent on the type of tet. Indirect Tenile Tet Sample were prepared in accordance with ASTM D Mixing and compaction temperature were elected on the bai of aphalt cement vicoity. Compaction level were varied to meet the 6 to 8 percent void requirement. Two teting procedure were ued (Table 1). Boil Tet Sample for boil tet were prepared and teted in accordance with ASTM D 3675 except for the following variation: 19

3 2 TABLE 1 IDIRECT TESILE TEST PROCEDURES Treatment Procedure 1 Procedure 2 Mix aging o aging 15 hr at 14 F Compacted pecimen o curing 24 hr at room curing temperature Initial aturation Freezing o freezing 15 hr at ± 4 F Soaking 24 hr at 14 F 24 hr at 14 F 3 hr at 77 F 3 hr at 77 F Age of pecimen at teting (day) 2 4 Void range Loading trip (width in in.) l/2 lfl Rate of loading (in./min) 2 2 Teting temperature (of) Similar procedure Tunnicliff and Modified Lottman Root (1) (6) 1. Boiling time wa 1 min, 2. Sample were tirred three time during boiling, and 3. Specimen were cooled to room temperature before the water wa drained. Detail of the tet procedure are given elewhere (7). Stre Pedetal Tet The tet procedure i an adaptation of a tet propoed by the Laramie Energy Technology Center (8). The tet wa performed according to procedure recommended by Kennedy et al. (9). DISCUSSIO OF TEST RESULTS Indirect Tenile Tet Reult from indirect tenile tet are ummarized in Table 2 and plotted in Figure 1 and 2. The following can be inferred from thee data: 1. Tet Procedure 2 i more evere than Procedure 1 (except for Combination B). Thi may be the reult of difference in aging of the mixture, curing of the compacted pecimen, and pecimen conditioning. The aging and curing for Procedure 2 may enhance adheion and reult in a higher mechanical trength. The cycle of freezing for Procedure 2 may reult in larger lo of trength than doe only oaking in Procedure 1. In general, the larger trength lo more than compenate for the trength increae due to aging and curing. However, Combination B ha porou cherty gravel of high aborption. The aging and curing may have increaed aphalt aborption and adheion enough to offet the more detrimental effect of freezing. The net reult i that Procedure 2 gave higher trength ratio for thi particular aggregate combination. 2. From Figure 2 it appear that mixture with AC2 are omewhat le uceptible to water damage than are thoe with ACl, although the difference are not large. Standard phyical tet indicate no dramatic difference in aphalt cement propertie, and retained trength difference are thought to be the reult of aphalt-aggregate interaction. ole Reull ACI. TRASPORTATIO RESEARCH RECORD 1171, I.a AGGR EGA TE CO MBIATIO ----r ei SURF.,PROC.I!<J $' & SURF.,PROC.2 c ' )..._ "!" FIGURE l Effect of tet procedure and type of mixture on TSR. A GGREGATE COMBIATIO a:: U) 4 I PROC.I 8. AC2 Q"l" <!' "!" PROC.2 8. ACI PROC.2 8. AC2, 'l tj ff (j FIGURE 2 Effect of tet procedure and ource of aphalt cement on TSR.,.., ff 3. Figure 1 how that bae-binder mixture are more vulnerable to water damage than are urface mixture. Speculation i that the difference in tenile trength ratio (TSR) are due to the coarer gradation and lower aphalt content of the baebinder mixture. Aphalt content of bae-binder mixture i compenated for omewhat by coarer gradation, but generally thee mixture are "leaner" than urface mixture. Gradation will alo affect the nature of the void in a mix. Although void content wa controlled at 6 to 8 percent, coarer gradation will produce fewer but larger void. Thee larger void will permit eaier acce to water and, thu, increae the potential for tripping. Thi phenomenon wa apparent during vacuum aturation. During the trial-and-error attempt to achieve 6 to

4 Parker and Gharaybeh 21 TABLE 2 IDIRECT TESILE TEST RESULTS, O ADDITIVES Procedure 1 a Procedure 2a Combination Aphalt Cement 1 Aphalt Content Initial Void Final Saturation TSR SMR Initial Void Final Saturation TSR SMR A E c B D Aphalt Cement 2 A, E, C, B, D, ote: = bae-binder. aaverage of at leat three pecimen. 8 percent aturation, le intene partial vacuwn and much maller time were required with bae-binder mixture. Table 3 give a ummary of a three-way analyi of variance to determine the overall effect of tet parameter on tenile trength and TSR for different mixture. In thi table, the aggregate combination are grouped into three ubgroup in relation to reported field performance a follow: ontripping mixture: Combination A and E, Stripping mixture: Combination B and D, and Variable mixture: Combination C. Analyi of variance wa conducted on all mixture a well a on tripping and nontripping ubgroup at the 5 percent level of ignificance. Table 3 can be interpreted a follow: 1. mineralogy i the dominant factor affecting tenile trength and TSR. 2. Tet procedure and ource of aphalt cement affect both conditioned and unconditioned trength with a reulting inignificant effect on TSR. 3. There i no relationhip between the combined effect of tet parameter and the individual effect of each parameter. For example, if the ource of aphalt produce a ignificant effect and the type of aggregate alo produce a ignificant effect, the combined effect may or may not be ignificant. The effectivene of antitripping agent wa tudied by uing them to improve mixture that had low TSR. In accordance with thi criterion, antitripping agent were ued in bae-binder mixture for Combination A and B only. Figure 3 how the enitivity of the teted mixture to antitripping agent. It can be een from the figure that the agent increaed TSR value above the 7 to 8 percent range only for Combination B. A poible reaon i that the agent were formulated for iliceou material not limetone. However, an extenuating circumtance i the lower TSR value for Combination A without additive. The percentage increae in TSR are imilar for both combination. FIGURE 3 Effect of additive on TSR for Combination A and B a: en 4 f

5 22 TRASPORTATIO RESEARCH RECORD 1171 TABLE 3 EFFECT OF TEST PARAMETERS (ignificance table) Tet Parameter Tet Type of Source Procedure Type Variable Mixture (A) (T) (M) TSR All ontrip Strip Unconditioned trength All ontrip Strip Conditioned trength All ontrip Strip Aphalt Cement Tet Combination of Tet Parameter orn: S = ignificant at 5 percent level (a. =.5), =not ignificant at 5 percent level (a. =.5), and dahe =not teted. AT AM TM ATM The Duncan multiple range tet, at the 5 percent ignificance level, wa ued to rank the additive according to their improvement of TSR. For Limetone Mix A, all of the additive fell at the ame rank. For Gravel Mix B, at the 5 percent level of ignificance, antitripping agent BA and KB at 1 percent doage were the firt ranked, KB at.5 percent doage wa the econd, and the hydrated lime wa third. Boil Tet Boil tet reult are tabulated in Table 4. Value without antitripping additive are plotted in Figure 4. Comparion of coating retention for ACl and AC2 indicate little difference. Coating retention difference for urface and bae-binder mixture can be noted in Figure 4. Bae-binder Mixture A and B retain much le aphalt after boiling than do urface mixture. The difference are much le pronounced for Combination C, D, and E, which i conitent with indirect tenile tet reult. The effect of additive on coating retention wa alo invetigated for Combination A and B. The data in Table 4 indicate greater improvement in coating retention for liquid agent than for hydrated lime. When lime i ued, a white powdery coating (aumed to be due to unbound lime) often reult. Thi tend to reduce the luter and intenity of the black coating, which in turn reduce perceived coating retention and, therefore, the rating. Thi obervation ugget that the boiling tet may not adequately judge the effectivene of lime a an antitripping agent. Hazlett (6) ha alo uggeted that the boil tet more favorably evaluate liquid antitripping agent. The data in Table 4 alo indicate that the antitripping agent improved coating retention more for Combination B than for Combination A. Thi i conitent with the indirect tenile tet reult. Stre Pedetal Tet A limited tudy wa performed with urface mix aggregate proportion only. Aphalt cement from both ource and three antitripping agent were ued in teting the five aggregate combination. Tet reult are given in Table 5. o ignificant difference between ACl and AC2 could be detected. Lime increaed cycle for cracking above 25 [uggeted limit in Kennedy et al. (9)] for Combination A, B, and C. With the exception of Agent BA at.5 percent doage, liquid antitripping agent did not increae cycle to cracking. Unlike the boil tet, the tre pedetal tet favorably evaluate lime. TABLE 4 BOIL TEST RESULTS WITH AD WlTHOUT ADDITIVES Percentage of Aphalt Coating Retained Aphalt Cement 1 with Antitripping Agent Aphalt Cement 2 with Antitripping Agent Mix Combination Type one HLa BAb KBb KBC one HLa BAb KBb KBC A Bae E 95 9 Bae 9 9 c Bae 8 85 B Bae D Bae 9 95 a 1 perccr>l hydrnted lime (baed on aggregalc weight). bo.5 percenl amitripping agent (baed on apha.il weight). CI percent antitripping agent (baed on aphalt weight).

6 Parker and Gharaybeh 23 AGGREGATE COMBIATIO B/B-AC2 "f 4" B/B-ACI z i==.z w I- w a:: Cl z i== <( u /.._..., 'I" FIGURE 4 Effect of type of mixture and ource of aphalt on coating retention. Comparion of Boil and Indirect Tenile Tet Both the indirect tenile and the boiling tet expre the moiture damage to the mix a a ratio. A correlation of thee reult i hown in Figure 5 in which TSR for Tet Procedure 1 and 2 are conidered eparately. Both leat-quare linear regreion equation fall to the right of the line of equality, indicating that the TSR percentage i greater than the coating retention percentage. The coefficient of determination indicate a much tronger correlation with Procedure 1. The freezing in Procedure 2 may introduce additional variability. The poitive nature of the correlation, combined with the reaonably trong coefficient of determination for Procedure l, indicate that both tet are, at leat in part, meauring imilar phenomena. The tet reult are plotted in Figure 6 and 7 for urface and bae-binder mixture, repectively. If 7 percent TSR and 9 percent coating retention are ued a criteria for eparating tripping and nontripping, Figure 6 indicate that both tet correctly characterize Mixture E a a nontripper and incorrectly characterize Mixture D a a tripper. Moreover, the indirect tenile tet reult indicate that all of the urface mixture are nontripper, and the boiling tet predict only Mixture A and B a tripper z 7 E uolll Line i== z w 6 I- w a:: 5 D Cl 4 I- <( 3 u a 2 a PROC.! 1 "'PROC.2 R'=O. / oproc TSR 1%J FIGURE 5 Relationhip between indirect tenile and boil tet reult. Figure 7 how that, for bae-binder mixture, a trong correlation exit between the boiling and indirect tenile tet. Both tet correctly characterize Mixture E a a nontripper and incorrectly characterize Mixture D a a nontripper. Both tet alo incorrectly characterize Mixture A a a tripper and correctly characterize Mixture B a a tripper. The boiling tet indicate that Mix C i a tripper, and the indirect tenile tet indicate that Mix C i a nontripper. MATERIAL EVALUATIO The five aggregate combination, the aphalt cement from two ource, and the two tenile tet procedure were evaluated uing indirect tenile and boiling tet reult. Table 6 give the ranking of the five aggregate combination baed on tenile trength and tripping reitance a indicated by TSR and coating retention. Each mean value of trength, TSR, and coating retention for a pecific type of mix, ource of aphalt cement, and type of tet procedure wa aigned a number of point from one to five. For example, the lowet mean unconditioned trength value for Combination A through E for each tet procedure wa given one point, the econd lowet wa given two point, and o on until the highet value wa given five point. The number of point for each aggregate combination in each cae wa totaled. The aggregate combination that had the highet total point wa given the highet rank (i.e., one). TABLE 5 RESULTS OF STRESS PEDESTAL TEST O SURFACE MIXTURES Aphalt Cement 1 with Antitripping Agent Combination one HLa BAb KBb KBC A 15 E >25 c 15 B 16 > D >25 a1 percen t hydrated lime (baed on nggregate weight). bo. percent antitripping agent (baed on aphalt weight). CI percent antitripping agent (baed on aphalt weight). 9 Aphalt Cement 2 with Antitripping Agent one HLa BAb KBb KBC 13 >25 >25 11 >25 18 > > >25

7 24 TRASPORTATIO RESEARCH RECORD t I "", /.' )( ; + I 9 ' :.: I I f 1 'Z / u 1 o I o _/_yl I- -1;/ / I r. ' 8 l 7 5 v c 6.2 c 4 / o a; " 6 c "' U) Vi f- on lr ipp nq S rpnl) / "' 3 4 c 3 u ' r / / :io ( // ole 2 Holet.in9,.nd1to!ei l, o Bo1tio9 1 oq<cmool llh I I +Proc. t / 1 rf!pcrtied pl1rformonco XProc. 2 A E c B D "' C i in the middle. Thi i conitent with reported field performance for Mixture B, C, and E but inconitent for A andd. Evaluation of tet procedure and aphalt cement ource wa baed on mean value. Table 7 give mean value for tenile trength, TSR, and coating retention. AC2 conitently produced higher trength, TSR, and coating retention than did ACl. Although the difference are not large, becaue of their conitency it may be inferred that mixe with AC2 would Combination FIGURE 6 Comparion of boil and indirect tenlle tet reult for urface mixture. It can be een from the table that, in term of unconditioned ;trength, Mix E ha the highet rank and Mix D ha the lowet. 6J'ter conditioning, the table indicate that Mix C ha the lighet trength and that Mix A ha the lowet. The data in the table indicate that the indirect tenile and the boiling tet are well correlated in ranking the material in term of tripping reitance a indicated by TSR and coating retention. The ranking indicate that Mixture D and E are more reitant to water damage than are Mixture A and B; Mixture TABLE 6 RAKIG OF AGGREGATE COMBIATIOS Point Baed on Meana Bae-Binder ACl Bae-Binder AC2 ACl Procedure Procedure Procedure Combination Total Rankb Unconditioned A trength B C c C D E Conditioned A trength B c l D E TSR A 3 2.5c B 1 2.5C 2 2.5c c 4.5C D 4.5C C E c 4.5C Coating A 2 I.SC 1.5C 5 4 retention B 1 1.5C 1.5C 4 5 c D 5 4.5C E 4 4.5C apoint = 1 (lowet mean) to 5 (highet mean). brank = 1 hi ghc.t Lotal) to 5 (lowet total). CRqual mean.

8 Parker and Gharaybeh TABLE 7 EVALUATIO OF TEST PROCEDURES AD ASPHALT CEMET FROM TWO SOURCES Mean Mean Mell!J Unconditioned Conditioned Mean Coating Strength Strength TSR Retention (pi) (pi) ACl AC Procedure Procedure have omewhat greater reitance to detrimental effect of moiture. Finally, the data in the table indicate that Tet Procedure 2 produce higher trength but lower TSR than doe Procedure 1. Thi i a expected, becaue aging of the mix and curing of the pecimen increae trength in Procedure 2. However, freezing in Procedure 2 produce larger trength reduction that more than compenate for the larger unconditioned trength. Thi reult in lower TSR for Tet Procedure 2. umerou factor including aggregate compoition, aphalt content, and gradation influence boil and indirect tenile tet reult. Thee, combined with the ubjective nature of the characterization of the tripping propenity of the mixe, reult in the not totally unexpected poor correlation with tet reult. Thi hould not be interpreted a an invalidation of the tet procedure or performance. Rather it indicate that additional refinement of tet procedure and application to pecific mixe will be neceary to improve tet reult-performance correlation. An extenion of thi reearch will provide the data for improving thee correlation. Material and mix ample will be taken during contruction and ubjected to laboratory tet to tudy the effect of incomplete drying and egregation (gradation). Difference between complete laboratory drying and incomplete field drying may be primary contributor to lack of correlation for porou gravel uch a thoe in Combination D. Core will be taken immediately after contruction and periodically thereafter to tudy the effect of compaction (void) and to develop mix-pecific performance data. COCLUSIOS Meaurement of moiture damage i a complex problem that i enitive to dicrepancie between laboratory and field condition. Ideal teting and handling of material, which can be achieved in the laboratory, can hardly be achieved in the field. On the other hand, field environmental condition can only be approximately imulated in the laboratory. Concluion include the following obervation: 1. A pa-fail criterion, according to which all reported moiture-uceptible mixture fail and all reported moiturereitant mixture pa, could not be developed for any of the tet evaluated. 2. The tet correctly categorized Combination B, C, and E a reported by field performance, but they did not correctly characterize Combination A a a nontripper or D a a tripper. Thi weak correlation with field performance, coupled with the trong correlation between tet reult, led to the following concluion: 1. The tet may not be valid indicator of tripping, or the ubjective reported field performance may not be valid for pecific mixe. 2. Variability in gradation, aphalt content, drying, mixing, and compaction may ignificantly affect tripping potential. Standard laboratory tet on ample with carefully controlled gradation and aphalt content, according to mix deign, may not be ufficiently evere. Field ampling and teting hould be conducted to etablih the influence of contruction variability on tripping potential and to etablih correlation between laboratory tet and pecific mix performance. Given the aumption that the tet are valid indicator of tripping, the material teted can be decribed a follow: 1. Limetone Combination A and E have different tripping potential although they poe high tenile trength. Bae-binder mixe with Combination A have much higher tripping potential than do imilar E mixe. 2. Cherty gravel Combination B and D alo have different tripping potential; Mix D ha lower trength but a higher retained ratio than Mix B. 3. Combination C poee moderate tripping potential. 4. Bae-binder mixture are more uceptible to moiture damage than are urface mixture made up of the ame contituent. Thi i attributed to difference in aphalt content (film thickne) and the nature of the void reulting from difference in gradation. 5. AC2 i omewhat more reitant to moiture damage than i ACl. 6. The tet meaure improvement when antitripping agent are added. The tre pedetal tet aee the effect of lime favorably, but the boil tet aee it effect unfavorably. ACKOWLEDGMETS The work reported in thi paper wa ponored by the Alabama Highway Department through the Federal Highway Adminitration, U.S. Department of Tranportation. The author are grateful for the ponorhip, aitance, and cooperation of thee organization. REFERECES 1. D. G. Tunnicliff and R. E. Root. CHRP Report 274: Ue of Antilripping Additive in Aphaltic Concrete Mixture. TRB, ational Reearch Council, Wahington, D.C., T. W. Kennedy, F. L. Robert, and K. W. Lee. Evaluation of Moiture Effect on Aphalt Concrete Mixture. In Tranportation Reearch Record 911, TRB, ational Reearch Council, Wahington, D.C., 1983, pp K. D. Stuart. Evaluation of Procedure Ued lo Predict Moiture Damage in Aphalt MiX1ure. FHWA Report RD-86/91. FHWA, U.S. Department of Tranportation, M. C. Ford, P. G. Manke, and C. E. O'Bannon. Quantitative Evaluation of Stripping by the Reaction Tet. In Tranportation Reearch Record 515, TRB, ational Reearch Council, Wahington, D.C., 1974, pp

9 26 5. F. Parker and F. A. Gharaybeh. Evaluation of Indirect Tenile Tet for Aeing Stripping of Alabama Aphalt Concrete Mixture. In Tranporlation Reearch Record 1115, TRB, ational Reearch Council, Wahington, D.C., 1987, pp D. G. Hazlett. Evaluation of Moiture Suceptibility Tet for Aphaltic Concrete. Report 3-C Material and Tet Diviion, Texa State Department of Highway and Public Tranportation, Autin, T. W. Kennedy, F. L. Robert, and K. W. Lee. Evaluation of Moiture Suceptibility of Aphalt Mixture Uing the Texa Boiling Tet. In Tranporlalion Reearch Record 968, TRB, ational Reearch Council, Wahington, D.C., 1984, pp H. Plancher, G. Miyake, R. L. Venable, and J. C. Peteron. A Simple Laboratory Tet to Indicate the Suceptibility of Aphalt Mixture to Moiture Damage During Repeated Freeze Thaw Cycling. Proc., Canadian Technical Aphalt Aociation, 198. TRASPORTATIO RESEARCH RECORD T. W. Kennedy, F. L. Robert, and W. L. Lee. Evaluation of Moiture Suceptibility of Aphalt Mixture Uing the Texa Freeze Thaw Pedetal Tet. Proc., Aociation of Aphalt Paving Technologit, Vol. 51, The conlenl of thi paper rejlecl lhe view of the author who are reponible for thefacl and the accuracy of the data preented herein. The content do not necearily reflect the official view or policie of the Alabama Highway Deparlment or the Federal Highway Adminitralion. Thi paper doe not contitute a landard, pecification, or regulation. Publicalion of lhi paper ponored by Commillee on Characterilic of Biluminou Malerial.