Determination of Creep Compliance and Tensile Strength of Hot-Mix ...

voids generally describes the average level of compaction immediately postconstruction.MoDOT’s specifications require in-place (as-constructed) densities of94 ± 2% of theoretical maximum specific gravity (G mm ) for Superpave (SP) mixes(i.e. 4 – 8% voids), ≥94% of G mm for Stone Matrix Asphalt (SMA) mixes (maximum of6% voids), and ≥92% of G mm for Bituminous Pavement (BP) mixes (maximum of 8%voids). Thus, 6.5% air voids fits nicely within the specifications for all three mixtypes. Additional testing at 4 and 9% air voids allows for the development ofrelationships between material properties determined through testing and the level ofair voids. Therefore the prediction of material properties can be made at differentlevels of voids other than those actually used during testing.Specimen FabricationHaving obtained the plant-produced mixes, MoDOT Central Lab staff firstdetermined the maximum specific gravity of each mix (G mm ) according to testmethod AASHTO T 209 (5). Having the G mm of each mix and using well establishedalgorithms, the mix weight was determined that would produce a gyratorycompactedspecimen 150 mm in diameter, 115 mm in height, and with a voidcontent approximating the target. After the specimens were compacted and hadbeen stored at room temperature overnight, a water-cooled masonry saw was usedto first trim off at least 6 mm of height from the top and bottom of the specimen, andthen saw the remainder of the specimen in half producing two IDT specimens (eachwith two parallel sawn faces) 150 mm in diameter and about 50 mm in height (inmost cases; there was an exception for one mix). Each IDT specimen was thendried using the CoreDry® device. Bulk specific gravities (G mb ) and the actual % airvoids of each were then determined using ASTM D 6752 (6) (NOTE: ASTM D 6752,essentially the CoreLok® method, is a deviation from T 322-07 which specifiesAASHTO T 166 (7) for G mb determination). Finally, each IDT specimen wasmeasured (4 thickness and 2 diameter measurements taken and then averaged),marked, wrapped in cling wrap, and boxed for delivery to Missouri S&T. Table 2gives more detailed information about the mixes.Table 2: Additional Mix PropertiesMix ID % Virgin Binder % Binder in RAP Total % Binder % Fibers G mm06-101 5.7 NA 5.7 0 2.51506-150 5.0 4.8 5.5 0 2.46706-125 6.5 NA 6.5 0 2.41206-105 5.1 4.8 5.6 0 2.45506-84 6.3 NA 6.3 0.3 2.43607-123 4.2 5.7 5.3 0 2.5014