ncat completes hma field compactability study - Samuel Ginn ...

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ASPHALT FORUMNCAT invites your comments and questions. Questions and responses are published in eachissue of Asphalt Technology News. Some are edited for consistency and space limitations.Connecticut (Keith Lane, Connecticut Department ofTransportation)Has any other state considered minimizing the number anduse of some of the Superpave design levels and/or NMAS(nominal maximum aggregate size) classes to reduce thelarge number of mixes currently available to be specifiedby contract?National Center for Asphalt Technology (Prithvi “Ken”Kandhal, NCAT)NCAT has conducted extensive field research in the areaof HMA longitudinal joint construction over the years,which has been reported from time to time in the AsphaltTechnology News and has been published in varioustechnical journals. Many state highway agencies suchas Kentucky and Wisconsin have also conducted fieldexperiments using different techniques of longitudinaljoint construction. Various techniques such as rubberizedjoint adhesive, notched wedge joint, cutting wheel, jointmaker, and infrared joint heaters have been evaluated inthe field by NCAT and other states. We would like to knowhow severe the longitudinal joint problem is in your stateand what are you doing about it in terms of specificationsand/or research.EDITOR’S FAREWELLI have been editing the Asphalt Technology Newssince its inception in January 1989. I still rememberthat time when NCAT had just been established witha skeleton staff: Freddie Roberts as director and RayBrown and myself as two assistant directors. Besidesconducting research, I was given the responsibility ofdeveloping and editing a practical asphalt newsletter.Having worked as the state bituminous engineerfor the Pennsylvania Department of Transportationfor 17 years, I did not have any experience in thearea of editing. Fortunately, readers throughout theworld liked the Asphalt Technology News and it wasacclaimed as a useful, practical newsletter.I have enjoyed editing this newsletter for the last 19years. Now it’s time to hand over this responsibilityto younger staff. Don Watson will assume the roleof editor for the next issue. I am sure he will do anexcellent job. I take this opportunity to thank allthose who over the years contributed to the successof the Asphalt Technology News.Prithvi “Ken” KandhalEditor/Associate Director EmeritusNational Center for Asphalt TechnologyA group of 15 Chinese engineers from Liaoning Province, PRC, visited NCAT in May 2007.
ASPHALT FORUM RESPONSESThe following responses have been received to questions raised in the Spring 2007 Asphalt Forum.Several important findings have resulted from the first andsecond cycles of experiments conducted from 2000 to 2005on the test track, which has been subjected to 20 millionESALs of traffic. We would like to have your comments onthree of these findings.(Prithvi “Ken” Kandhal, NCAT)1. The amount of rutting in coarse-graded and finegradedSuperpave mixes was approximately thesame.Connecticut (Keith Lane, Connecticut DOT)With the implementation of Superpave in 1998, weobserved that the coarse-graded mixes were more difficultto compact, had a noticeably more open texture, and tookmuch longer to dry out after rain. This concerned us dueto the anticipated higher levels of oxidation, permeability,and black ice potential during the winter. In 2002-03, theConnecticut DOT requested that all Superpave mixes(Design levels 1 through 3) be designed above the primarycontrol sieve (PCS) point for the respective nominalmaximum aggregate size (NMAS). As a result, we havehad great success in producing and placing most of ourfine-graded Superpave mixes.Kansas (Cliff Hobson, Kansas DOT)In the early days of Superpave pavements in Kansas,coarse-graded mixes were often used on high-trafficvolume routes to take advantage of the potential stone-onstonecontact provided by these mixes. However, ruttingoccurred early in the life of these mixes, primarily fromstripping due to their higher permeability. In an attempt toquantify the difference in performance between the coarseandfine-graded mixes, the Kansas DOT contracted withKansas State University to test both the coarse-graded andfine-graded mixes in the Hamburg Wheel Rut Tester. Theresults of this study indicated that the fine-graded mixeshad less rutting potential than the coarse-graded mixes.In April 2003, due to the on-going permeability concernswith coarse-graded mixes, the Kansas DOT changed tofine-graded mixes for most Superpave mix designs.Kentucky (Allen Myers, Kentucky TransportationCabinet)Early in the implementation of Superpave, the KentuckyTransportation Cabinet (KYTC) held to the notion thatcoarse-graded mixes were more rut-resistant than finegraded.Therefore, we required coarser mixes on facilitieswith higher ESAL counts. Our native materials very readilyproduced coarse gradations, so this arrangement workedwell. In later years, due to permeability concerns, Kentuckyhas increasingly utilized finer gradations. Many of thesemixes have been placed on heavily-loaded facilities. Theperformance of these fine-graded mixes has been good todate. To summarize, KYTC has noted similar levels of rutresistance for both coarse- and fine-graded HMA.Ontario (Kai Tam, Ontario Ministry of Transportation)This statement is too general, it should be qualified bystating “for the same aggregates used and meeting mixrequirements for the given traffic category.”2. Although only crushed stone is recommended instone matrix asphalt (SMA), the SMA containing onlycrushed gravel aggregate gave satisfactory performancein terms of permanent deformation.Kansas (Cliff Hobson, Kansas DOT)Kansas has only two recently constructed projectsusing the current SMA design. Both of those projects usedlimestone aggregates. The Kansas DOT plans to constructsix SMA projects in 2008. At least half of those projectshave the potential of using crushed gravel as the aggregate.The NCAT test track results indicating that SMA usingcrushed gravel gave satisfactory results are encouraging.Kentucky (Allen Myers, Kentucky TransportationCabinet)In 2004, approximately 7,500 tons of an SMA mixturecontaining crushed gravel coarse aggregate was placed innortheastern Kentucky. The rut resistance of this pavementhas been good to date.Mississippi (James Williams, Mississippi Department ofTransportation)Mississippi has successfully used crushed gravelSuperpave mixes since the inception of Superpave. Wehave several SMA projects scheduled using a crushedgravel-limestone blend.Nebraska (Laird Weishahn, Nebraska Department ofRoads)I don’t recall specifics, but years ago Nebraska placedan SMA mixture with a significant percentage of crushedgravel and found it to resist permanent deformation.3. It is possible to blend some limestone aggregate withcrushed gravel aggregate in the wearing course mixwithout compromising the skid resistance.(continued on page 15)
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