Performance Activation Technique Of Reclaimed Asphalt Pavement For Cold Recycling Asphalt Mixture

Under the strategy of“carbon peaking and carbon neutrality”,the research on the utilization of reclaimed asphalt pavement with large dosage,low energy consumption,large scale and high value has attracted wide attention.Emulsified asphalt cold recycling technology can meet the needs of efficient utilization of reclaimed asphalt pavement with low carbon and environmental protection.It has great potential for development,but it cannot give full play to the performance of old asphalt as binder.The high and low temperature performance,water damage resistance and fatigue resistance of emulsified asphalt cold recycling mixture need to be improved.According to the characteristics of cold recycling process and the strength formation mechanism of emulsified asphalt cold recycling mixture,a performance activator used in cold recycling asphalt mixture（hereinafter referred to as the activator）was developed,which can activate the performance of old asphalt at room temperature and improve the road performance of emulsified asphalt cold recycling mixture.The effect of the activator in Emulsified asphalt cold recycling mixture was verified.Firstly,the reclaimed asphalt pavement from different sections in Beijing was collected and 6 kinds of old asphalt was obtained.Basic performance,dynamic viscosity and rheological properties can be tested to understand the characteristics of old asphalt in reclaimed asphalt pavement.It was found that the average softening point of the old asphalt is 61.4℃,and the average penetration degree is 23.6（0.1mm,25℃）,which is slightly lower than that of the 30#matrix asphalt,but the average elongation at 15℃is only 7.7cm,and the low temperature performance is obviously insufficient.The dynamic viscosity at 60℃becomes 10-20 times that of 70#matrix asphalt,and the non-recoverable creep compliance at 64℃is about 1/5-1/10 that of 70#matrix asphalt.By comparing the performance parameters of old asphalt,the preparation method of artificial old asphalt with similar properties to old asphalt was determined.Secondly,with the existing cold recycling technology at normal temperature,the old asphalt is difficult to play the role of cementing material.To solve the problem,the concept of“old asphalt activation”is proposed based on diffusion theory,and the activator is developed.According to the performance characteristics of the old asphalt,the activator is divided into the core component by the diffusion group,SBS as the main functional component.The key technological path is to open the diffusion channel of the old asphalt and the collaborative diffusion of the functional components into the old asphalt,so as to realize the activation of the old asphalt at room temperature and play the role of the asphalt binder.Based on contact angle theory and cohesion theory,the diffusion effect evaluation method is designed independently.This method can effectively evaluate the diffusion effect of the diffusion components at room temperature,and fill a gap in existing technology.The diffusion behavior of activator to old asphalt was observed using Frozen Section and FTIR.The results show that the average diffusion rate of the activator is greater than 12.5μm/h at room temperature,and the activator can be diffused into the old asphalt within 1 hour.Additionally,the performance of activated asphalt was evaluated by basic properties,dynamic viscosity,rheological properties,fatigue properties and adhesion to aggregates,and the properties of emulsified asphalt mortar were evaluated by SEM,drawing test and time scanning test.With the increase of the dosage of activator,the degree of penetration and elongation of activated asphalt increased,and the softening point decreased.For the activated asphalt containing emulsified asphalt,the penetration and elongation increased obviously,while the softening point decreased gently.Without emulsified asphalt,the dynamic viscosity of activated asphalt decreased from 4723.2Pa·s to 1522.1Pa·s at 60℃with 0.3%activator,and the non-recoverable creep compliance₉)increased from 0.32 k Pa^-1 to 0.82 k Pa^-1.Under the synergic action of emulsified asphalt,the dynamic viscosity of activated asphalt decreases more obviously at 60℃,and the dynamic viscosity decreases to 780.3 Pa·s.Non-recoverable creep compliance₉)increased from 1.29 k Pa^-1 to 2.59 k Pa^-1,and the creep stiffness decreases by18.1%at-12℃.The time scanning test shows that the fatigue resistance of activated asphalt is5.85 times that of old asphalt.Compared with the old asphalt,the spalling rate of activated asphalt on aggregate surface decreased by 28.1%after water leaching,and the drawing strength increased by 13.6%at 15℃.By SEM,the structure and the microscopic pore morphology of emulsified asphalt mortar were observed.It was found that the porosity of activated emulsified asphalt mortar decreased by 70.83%,and the strengthening components in the activator were separated out,forming a strengthened and toughened polymer net.Drawing test and time scanning test show that compared with ordinary emulsified asphalt mortar,activated emulsified asphalt mortar has a higher drawing strength of 61.9%and a higher fatigue life of 104.1%.After activation,the emulsified asphalt mortar has a denser structure and stronger mechanical properties.Finally,the mechanical properties,high and low temperature properties,water stability and fatigue resistance of the emulsified asphalt cold recycling mixture with three activators（0.3%,0.5%and 0.8%）were compared with those of the emulsified asphalt cold recycling mixture without activator and the emulsified asphalt cold recycling mixture with only regenerator.The results show that the performance of the emulsified asphalt cold regeneration mixture with the activator content of 0.3%is improved.Compared with the emulsified asphalt cold recycling mixture without the activator,the splitting strength increases from 0.89 MPa to0.92 MPa at 15℃,the dynamic stability increases by 51.6%,and the maximum flexural tensile strain increases by 28.7%in the low temperature bend test.The mass loss of Cantabro test is reduced by 27.2%,and the anti-fatigue performance of four-point bending fatigue test is improved by 16 times.By further comparing the effect of activator and rejuvenation agent on the performance of emulsified asphalt cold recycling mixture,it was found that the splitting strength and high temperature performance of emulsified asphalt cold recycling mixture decreased after the addition of rejuvenation agent.The performance of emulsified asphalt cold recycling mixture mixed with 0.3%activator improved in a comprehensive way.Compared with the cold recycling mixture mixed with 0.3%activator,the splitting strength was 15.2%higher,the dynamic stability was 55.4%higher,the freeze-thaw splitting strength was 3.3%higher,and the standard flying mass loss was 19.1%lower,which verified the superiority of the cold recycling mixture performance activation technology.