Research On Crack Resistance Of Asphalt Mastic At Medium Temperature Based On Filler Propertieses

Asphalt mastic composed of filler and asphalt is the actual binder in asphalt concrete and the main component that determines the cracking resistance of asphalt concrete.In order to enhance the cracking resistance of asphalt concrete,this paper will investigate the effect of filler on the cracking resistance of asphalt mastic under medium temperature conditions from the filler perspective with the help of fracture energy test as well as molecular dynamics simulation techniques.Firstly,the raw material properties were tested.Five types of fillers（cement,diatomite,fly ash,hydrated lime and limestone）and matrix asphalt were used to make asphalt mastics by mixing five fillers with 70#matrix asphalt at five volume fractions（15%,20%,25%,30%and 35%）.The basic properties of the raw materials were characterized using various technical means such as scanning electron microscopy,X-ray diffraction analysis,and specific surface area analysis.The results showed that diatomite and hydrated lime were rich in surface structure and the specific surface area was significantly higher than the remaining three fillers.Secondly,the surface energy components of asphalt and filler were determined by using the lying drop method and column wick method,respectively.The adhesion work and specific adhesion work of asphalt-filler system were calculated.The order of the adhesion work of the five asphalt slurries from largest to smallest is:diatomaceous earth>hydrated lime>cement>fly ash>limestone.The modified DT test,Double Edge Notched Tension（DENT）test and Binder Fracture Energy（BFE）test were conducted to analyze the changes of cracking resistance of asphalt mastic containing different filler types and powder to cement ratios under medium temperature conditions（20°C）.The results showed that the cracking resistance of asphalt mastics showed an increasing trend with the increase of powder-to-asphalt ratio,and the optimum filler concentration varied with the filler type.The enhancement effect of fillers on the cracking resistance of asphalt mortar is ranked as follows:hydrated lime>diatomite>limestone>cement>fly ash.After that,the molecular dynamics simulation technique was used to simulate the direct tensile test of asphalt mastic.Asphalt was modeled with four components（twelve molecules）,and two fillers were modeled with nanoclusters of Si O₂ and Al₂O₃ with powder to asphalt ratio of 0%,5%and 10%,respectively.The results showed that the peak stress of asphalt mastic simulated tensile test gradually increased,while the strain corresponding to the peak stress as well as the fracture energy gradually decreased.Finally,three representative fillers（cement,diatomite and fly ash）were selected to mix asphalt mixes and perform asphalt mix splitting tests according to three powder-to-mastic ratios（0.7,0.9 and 1.1）to verify the correlation between the effect of fillers on the cracking resistance of asphalt mastic and the cracking resistance of the mixutres.The splitting strength ranking of the three asphalt mixes was:diatomite>cement>fly ash,which was consistent with the adhesion work ranking of the asphalt mastic and the direct tensile fracture performance ranking.This indicates that the cracking resistance of asphalt binders can predict the splitting strength of asphalt mixes to some extent.