| The embedded sensor of pavement structure is the important ways to realize active perception of pavement structure during service period.However,due to the complex working environment and multi influencing factors,the mechanical response of asphalt pavement still lacks reliable,durable,accurate and real-time monitoring means.The existing mechanical detection sensors of pavement structure layer at home and abroad are mainly scientific research technology,high cost,difficult to be applied in large-scale engineering.Therefore,the reliable technology,low cost,can be used for pavement structure long life sensing sensor and its monitoring technology has become the technical bottleneck in the industry to carry out pavement design,technical management,maintenance and maintenance decisions.In this paper,the mechanical properties monitoring sensor of road asphalt were designed and developed based on the micro-nano structure polymer composites materials with smart selfsensing properties.The parameters of material composition,mix design and preparation technology were explored.Based on the molecular dynamics model of whole atomic system combined with the microstructure characteristics,the conduction mechanism and mechanismelectric response mechanism of composite materials were analyzed.Strain-resistance response model of micro-nano polymer composite materials was optimized and constructed.The sensing properties and application technology of smart materials are systematically studied,furthermore,the engineering field verification is carried out successfully.By the study of this paper,problems such as low survival rate,poor durability and high price of the asphalt pavement monitoring technology can be solved and the real-time,accurate monitoring of mechanical properties of pavement structures can be realized.The main research contents and achievements of this paper are as follows:(1)The conductive percolation threshold of carbon nanotubes(CNTs)/epoxy resin composite smart material was around 0.8wt%.The addition of carbon black(CB)or graphene(GNP)significantly reduced the resistivity of CNTs/epoxy composites.With the increase of tensile strain,the variation of resistance shows obvious"interval".The addition of CB filler significantly improved the autogenous sensitivity of CNTs/epoxy resin composites,especially in the range of 0～200με.In this paper,the strain sensitivity of composite astute material ranges from 2.04 to 19.4,which verifies the feasibility of composite astute material in strain monitoring and the adjustable sensitivity.The optimal selection and stiffness allocation of polymer matrix can be realized by the modulator SL type polyurethane,which is suitable for monitoring mechanical properties of different layers.(2)The whole-atom system of molecular dynamics models were constructed for the micro-nano structure composite.COMPASS molecular force field was selected for model calculation.Solidified crosslinking script was written based on Perl language to realize a breakthrough in the whole atom simulation of conductive properties of micro/nano conductive filler/polymer composite smart materials.The conduction performance is characterized by conduction rate Λ.The conduction rate Λ,radial distribution function RDF,maximum cluster size Cn,total number of clusters Nc,the coordination number CN and the distribution probability PN of micro-nano composites are analyzed in static and tensile state respectively.The dispersion state of the internal conductive network of the composite is studied by the above parameters.For the micronano structure composite conductive filler,the contribution value P of the conductive filler was calculated to analyze the contribution of CB and GNP in the composite conductive network of CNTs/CB and CNTs/GNP.Interaction energy changes with the parameters of conductive filler were investigated.The correlation between interaction energy,conductive property and dispersion state was analyzed as well as the interaction between the interface behavior of micronano structure and resin and conductive behavior.Combined with the SEM microstructure of conductive network in the composite material,the factors affecting the strain resistance response sensitivity were explored from the molecular level.(3)Based on J.G.Simmons tunnel current model,the dual effects of tunnel effect and field emission effect on tunnel resistance are considered by introducing coefficients β1 and β2.Resistance Ri on the effective conductive path of No.i,the effective conductive path N,tunnel clearance d and tunnel resistance R are all functions of strain ε so as to get the ultimate strain response-resistance change rate model is derived.The model reliability is verified by comparing the theoretical calculation results with the experimental data in this paper and some literature review results.(4)The sensing characteristics and engineering application characteristics of composite smart sensor are systematically investigated.Repeatability tests and 1000,000 fatigue load cycles demonstrated the mechanical durability,fast response and low hysteresis of the composite strain sensor.The slope of the force-electric response curves of the composite materials at different temperatures has a good linear correlation with the temperature.After the integrated molding and vacuum packaging technology,the extreme value of resistance changes rate ΔR/Ro caused by humidity range of R.H.30%～R.H.80%can range from 0.12%before packaging to about 0.01%after packaging.Based on the coupling model between pavement and sensor by ABAQUS finite element numerical simulation method,the influence of embeded sensor elements on mechanical response of asphalt pavement structure was studied as well as the structure of sensors was optimized.The results show that the synergistic deformation characteristic of I-shaped sensor with asphalt concrete is better than that of bamboo-shaped sensor.(5)Finally,through the asphalt rutting plate wheel rolling test and the engineering field application,the developed strain sensor showed a good survival rate under the condition of high temperature and high-pressure compaction of asphalt mixture.The strain sensitivity and reliability of the composite strain sensor in mechanical property monitoring of asphalt pavement were verified. |
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