| Semi-flexible pavement(SFP)as a typical organic-inorganic composite material,is formed by injecting special cementitious grout into a porous asphalt mixture(PAM),with the porous asphalt mixture serving as the matrix,typically having a void content between 20% and 30%.SFP material combines the advantages of asphalt pavement rigidity and cement pavement flexibility and is widely used in road engineering due to its excellent resistance to rutting.However,in pavement engineering,SFP materials also suffer from distress such as cracking at the interface transition zone(ITZ)between asphalt and cementitious grout.This paper focuses on the asphalt-cementitious grout composite interface of SFP and investigates its influence on the macroscopic mechanical properties,microstructure,and damage process of the overall SFP at macro,micro,and meso levels,respectively.The main research contents and results are as follows:(1)The semi-flexible pavement(SFP)material comprises numerous organicinorganic composite interfaces,among which the interface between asphalt and cementitious grout is the primary interface in SFP composite materials.This interface significantly affects the overall mechanical properties of SFP materials.Silane coupling agents are commonly employed in inorganic cementitious composite materials to enhance their overall mechanical properties.To address the influence of the asphaltcementitious grout composite interface on the overall SFP composite material,this study conducted a series of material property tests and calculations,including compressive strength,flexural strength,shear strength,and elastic modulus,using three different compressive strength cementitious grouts: Sobute(GM-40),Sino(GM-60),and Unikrete(GM-70).Granite and diabase aggregates,representing acidic and alkaline aggregates,were prepared as specimens.These aggregates were pre-coated with surface asphalt,immersed in KH-570 silane coupling agent solution,and then cast with the three types of cementitious grouts to form pull-out specimens,which were cured for 28 days.Finally,pull-out tests were conducted to evaluate the tensile strength of the acidic and alkaline aggregates with surface pre-coated asphalt and different compressive strength cementitious grouts,considering the enhancement of the interface with silane coupling agent immersion.The research results demonstrate the feasibility of using silane coupling agent solution to enhance the bonding performance of the asphaltcementitious grout composite interface in SFP materials.(2)The immersion of aggregate specimens pre-coated with asphalt in silane coupling agent solution and then casting into pull-out specimens enhanced the bond strength of the asphalt-cementitious grout composite interface.Considering two types of matrix asphalt mixtures surface conditions,i.e.,enhanced by immersion in silane coupling agent solution,ordinary interface,and different strength cementitious grouts,i.e.,GM-40,GM-60,GM-70,in SFP materials,the effect of bond strength of asphaltcementitious grout composite interface on the performance of overall semi-flexible pavement composite materials was studied through multiple strength tests,stiffness tests(dynamic modulus test),and fatigue tests.The results show that the strength of grouting materials affects the crack resistance and fatigue life of SFP composite materials,and the overall uniaxial compressive strength of formed SFP composite materials increases with the increase of compressive strength of grouting materials.Enhancing the bond strength of asphalt-cementitious grout composite interface with silane coupling agent solution significantly improves the overall mechanical properties of SFP materials formed with low strength grouting materials.Furthermore,SFP materials formed after interface modification exhibit higher dynamic modulus and fatigue resistance.(3)The asphalt-cementitious grout composite interface of SFP was characterized from three aspects: interface performance,microstructure,and chemical composition,using atomic force microscope(AFM),scanning electron microscope(SEM),and energy dispersive spectrometer(EDS)techniques,respectively.The microscopic properties of asphalt and three types of cementitious grouts forming composite interfaces before and after immersion in interface modifiers were compared and analyzed,and based on this,the influence mechanism of composite interfaces on macroscopic mechanical properties was studied.The results show that the asphaltcementitious grout interface is a double-layer interface structure,and the transition of the asphalt-cementitious grout interface becomes smoother after immersion in interface modifiers.A large amount of calcium hydroxide aggregates appears near the SFP composite interface,with crystals having a larger volume and prone to cracking,which is the weak position of the overall SFP material.After interface enhancement,the distribution of all elements at the asphalt-cementitious grout interface becomes more continuous without the occurrence of fractures,but the synchronous enrichment of elements is significant,with two groups of element enrichment regions,indirectly confirming the double-layer interface structure of SFP composite interfaces.(4)A refined numerical model reflecting the distribution of internal components of SFP micro-materials was established based on digital image technology and finite element method.Using the concrete damaged plasticity(CDP)model,the influence of asphalt-cementitious grout composite interface strength on the uniaxial compression mechanical properties and failure modes of SFP materials was studied.The results show that adding an interface layer can significantly improve the accuracy of stress characteristic analysis when simulating SFP materials.For SFP materials formed with low strength grouting materials,enhancing the strength of the asphalt-cementitious grout composite interface can increase the overall peak compressive strength of semiflexible pavement materials.The asphalt-cementitious grout interface inside SFP is a weak point in the structure,prone to cracking and rapid propagation,leading to gradual delamination of grouting materials from matrix asphalt mixtures.Numerical simulation methods based on digital image modeling can accurately simulate the real failure process and crack propagation of SFP materials,providing references for the performance optimization of SFP materials. |
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