The low-temperature rheological properties of binders in the recycled asphalt pavement (RAP) material without the damaging effects of solvent extractions were analyzed. The developed procedure is based on testing of bitumen-RAP mortars produced by mixing the fresh (virgin) binder with RAP material smaller than # 8 sieve. Different mortars were prepared, containing RAP material passing the #8 sieve and 15% by weight of fresh binder. Low temperature properties of these mortars were investigated by using the bending beam rheometer (BBR) test procedure that is specially modified for testing of the RAP mortars. The modification involved the development of a new kind of mold and different testing parameters. The RAP material used in the experimental study were both extracted from real reclaimed pavement and prepared in the laboratory, by aging binder through repeated PAV cycles. The results indicate the new procedure can capture the effect of aged properties of bitumen in the RAP and can be used to estimate the PG low temperature grade of the blended binder. Although data is limited in size, the modification of the BBR appears to be simple and provide repeatable data.
On basis of the Burgers model, a new model consisting of modified dashpot and Van Der Poel model was derived from rheological and viscoelastic theory. Subsequently, triaxial repeated load permanent deformation tests of AC16 asphalt mixtures were conducted to validate this new developed model. Parameters of new developed model were obtained by a nonlinear regression analysis of test data, and then permanent strains and flow number of each mixture were calculated. The experimental results prove that the new developed model can well describe three phases permanent deformation of asphalt mixture under repeated load and it can be used for pavement mechanical analysis and rutting prediction.
在常用的各种力学模型中,修正Burgers模型是目前公认相对准确而又简单的模型,然而该模型只对静态荷载下混合料蠕变特性适用,且不能将延迟粘弹性变形与粘性流动变形区分出来,以此进行车辙预估必然导致预估车辙偏大。将修正Burgers模型看成是由三单元范德普(Van Der Poel)模型与修正的外置粘壶组成,就能将永久应变与弹性应变区分开来,更加合理。考虑耦合损伤的修正Burgers模型能反映混合料高温变形的三阶段,且当卸载时间为加载时间的10倍左右时,残余粘弹性变形占不到10%,可以略去不计。推导间歇加载半正矢波下混合料的本构模型,用origin7.5软件进行拟合,相关度0.99以上。最后提出基于耦合损伤力学模型的混合料高温性能评价新指标蠕变度和平均车辙深度。
A new testing procedure to estimate the low-temperature stiffness of the reclaimed asphalt pavement(RAP) binder was developed.In the testing procedure,the SuperpaveTM Bending Beam Rheometer(BBR) with special modifications and binder blending charts by Asphalt Institute were utilized.Modifications involved the development of a new kind of sample mold and different testing parameters were made to BBR testing procedure to capture the rheological properties of bitumen mortars produced by mixing fresh binder with fine RAP materials or RAP aggregate.The stiffness relationship between binder and bitumen mortar was established based on the BBR test results.The blended binder stiffness in bitumen RAP mortar was estimated from the RAP mortar stiffness based on the bindermortar relationship.And finally,the RAP binder stiffness was estimated from the blended binder and fresh binder stiffness based on the blending charts by Asphalt Institute.The results indicate that the new procedure can capture the rheological properties of bitumen mortar and can be used to estimate the low temperature stiffness of RAP binder without binder extraction and/or any chemical treatments.
The moisture aging effect and mechanism of asphalt binder during the in-service life of pavement were investigated by laboratory simulating tests.Pressure aging vessel(PAV) test simulating the long-term aging of binder during the in-service life of pavement was modified to capture the long-term moisture aging effect of binder.Penetration grade tests including penetration test,soften point test,and ductility test as well as SuperpaveTM performance grade tests including viscosity test,dynamic shear rheometer test,and bending beam rheometer test were conducted to fully evaluate the moisture aging effect of binder.Fourier transform infrared spectroscopy test and Gel-permeation chromatography test were applied to provide a fundamental understanding of the moisture aging mechanism of binder.The results indicate that moisture condition can accelerate the aging of asphalt binder and shorten the service life of asphalt binder.The modified PAV test with moisture condition can well characterize the moisture aging properties of asphalt binder.
The objective of this research was to show a way to conduct rejuvenation of aged polymer modified asphalt binder(PMB) successfully.To fully evaluate and understand the rejuvenation of aged PMB,the Penetration grade tests including penetration,soften point,ductility and elastic recovery and SuperpaveTM PG grade tests including DSR,BBR and DDT were conducted.The rejuvenation effect of aged PMB by utilizing a fluid recycling agent in common use for binder rejuvenation was evaluated.And then the compound rejuvenation effect of aged PMB by utilizing the recycling agent with a new modifying additive for binder modification was evaluated.The experimental results indicated that the recycling agent in common use currently does not apply to polymer modified asphalt binder rejuvenation.But the recycling agent together with the modifying additive can restore the characteristics of aged polymer modified binder very well.Therefore,compound rejuvenation of polymer modified asphalt binder is recommended.
