Research On Asphalt Mixture Stability Based On Density Curve And Meso-Structure

At present,the Marshall design method is commonly used in the design of asphalt mixtures in China.This method adpots a unified compaction times?75 or 50 double-sided?for different types of asphalt mixture,which is equivalent to a unified compaction energy.Engineering practices have proved that,under the construction of compacting,different types of asphalt mixture shows different compction characteristics,which cannot match the uniform compaction energy.The US Superpave design method proposes a compactness of 96%as the volume control index,this allows the compaction energy can be adjusted according to the traffic.However,there still exists common defects such as rutting in the test pavement sections built under this design method,which means the traditional problem has not yet resolved.The essences of the above two design methods follow the idea of"volume design,performance verification",but neglect an important issue:whether the designed asphalt mixture has reached its most stable state.In response to the above issue,five typical mixture types?GAC,SUPERPAVE,SAC,SMA,OGFC?were selected for this study.First,adopt the Marshall design method to determine the optimal asphalt content,and then obtain the density curve of the whole process of compaction through the gyratory compaction,finally,analyze the changing trend of macro volume parameter and mesostructure information in the whole process of compaction by digital image processing technology,and the conclusions are found as below:1.Based on the density curve and the VCA_mix curve,it is evaluated whether the mixture is in a stable state when it reaches Marshall design density.Results showed:except SMA mixture,the remaining four mixtures are not in the most stable state when they reached their Marshall design density;except SUPERPAVE mixture,the remaining four mixtures VCA_mix have been reached the VCA_DRC index at the initial stage of compaction,which means coarse aggregate formation criterion VCA_mix?VCA_DRC is not a good evaluation of whether the mixture reaches a stable state.2.Based on the concept of energy index,the compaction characteristics of the mi xtures are compared.The results showed:mixtures construction stage compressibility O GFC>GAC>SUPERPAVE>SAC>SMA,traffic stage durability SMA>SUPERPAVE>SA C>GAC.The unified design of compaction energy cannot match the compaction chara cteristics of the mixtures,and the design compaction energy should be adjusted for dif ferent types of mixtures.3.Based on the digital image processing technology,the contact points curve was calculated by using different calculation parameters,and the correlation with the density curve was compared.The results showed:the contact points curve and the density curve were in good correlation,when the minimum calculated particle size was 2.36mm and the contact threshold was 0.5428mm,it achieved the best correlation.It is recommended to use these calculation parameters when calculating aggregate contact information.4.Based on the digital image processing technology,the trend of meso-structure information in the whole compaction process was compared,and the main characteristics of the mixture to reach a stable state were proposed.The results showed:the contact points curve can be divided into three phases?rapid growth phase,stable phase,and re-growth phase?,the number of contact points in the stable stage of GAC,SAC,and SMA mixtures were numerically correlated with the numbers of their dry rod condition;Aggregate inclination angle has reached a stable state in the initial stage of compaction,the types of aggregates and compaction methods were the main factors affecting the inclination of aggregates;The density and the number of contact points can be combined as a control parameter for stable state of alphalt mixture.