Microstructure And Performance Of Epoxy Asphalt Binders Modified By Core-shell Rubber Nanoparticles

Epoxy asphalt(EA)is one type of reactive polymer modified asphalts with excellent performances which combines the advantages of thermosetting epoxy resin with thermoplastic asphalt.Nowadays,epoxy asphalts have many applications on road pavements with special uses especially for the pavement of the orthotropic steel bridge deck.Although epoxy asphalts have good flexibility to some extent,longitudinal fatigue cracks become the most common failure of epoxy asphalt concretes after long-time service under the high deformation of OSD,especially at low temperature.To solve this problem,the toughness of epoxy asphalt binders needs to be improved.CSR nanoparticles with a thin layer of a hard glass shell and a soft rubber core is the second generation of rubber modifier for improving the toughness of epoxy resins.CSR nanoparticles can significantly improve the toughness of epoxy resin without sacrificing the glass transition temperature(T_g)of epoxy resin.In this thesis,CSR nanoparticles in the form of epoxy masterbatch were chosen to toughen epoxy asphalt.The influence of both loadings and rubber core structures on the microstructures and properties of epoxy asphalts were studied.The phase-separated microstructures of the cured pure EA and its CSR blends were investigated by laser scanning confocal microscopy(LSCM).Meanwhile,the phase separation evolutions and mechanisms of both the pure EA and CSR nanoparticles modified EAs during curing were compared.In addition,the viscosity,thermostability and dynamic mechanical properties,mechanical performance of CSR nanoparticles modified EAs were characterized by using Brookfield viscometer,thermogravimetric analysis(TGA),dynamic mechanical analysis(DMA)and universal testing machine.Firstly,a masterbatch of CSR nanoparticles pre-dispersed in the epoxy oligomers was introduced into the epoxy oligomer of the pure EA and then reacted with hardener in the existence of the base asphalt.LSCM results showed the glassy shell of CSR nanoparticles was broken and the rubbery core of CSR nanoparticles swollen in the epoxy asphalt.New micro-scale swollen polymer domains uniformly dispersed in the continuous epoxy phase of the cured epoxy asphalt.The inclusion of CSR nanoparticles with a higher loading altered the phase separation mechanism of the pure epoxy asphalt.The sea-island morphology of the pure epoxy asphalt and the epoxy asphalt blend containing 1 wt%CSR took place through the nucleation and growth(NG)mechanism,while phase-separated microstructures in the epoxy asphalt blends with 3 wt%and 5 wt%CSR formed through the spinodal decomposition(SD)mechanism.The incorporation of CSR nanoparticles significantly increased the viscosity of the pure epoxy asphalt during curing.Even with 5 wt%CSR,the epoxy asphalt blend exhibited extremely long allowable construction time(more than 2.5 h)for mixture pavements.The glass transition temperature and thermal stability of the pure epoxy asphalt were improved by the inclusion of higher CSR loadings.The incorporation of CSR nanoparticles greatly enhanced the mechanical properties of the pure epoxy asphalt.In the case of 1 wt%CSR inclusion,29%increase in the tensile strength,60%improvement in the elongation at break and 2-fold increment in the toughness were obtained.Secondly,the role of core structures of CSR nanoparticles on the microstructure and the performance of epoxy asphalt was investigated.Two kinds of CSR nanoparticles with 2 wt%loading were employed to toughen epoxy asphalt binder.The CSR nanoparticles had the same shell composition,but different core structures.The results revealed that the viscosity of CSR with styrene-butadiene copolymer(SB)core(CSR_SB)modified epoxy asphalt was higher than that of CSR with polybutadiene(PB)core(CSR_PB)modified epoxy asphalt during curing.LSCM showed the shell destruction of CSR nanoparticles resulted in the swelling of the core polymer in the micron scale.The phase separation of CSR_PB modified epoxy asphalt occurred in the spinodal decomposition mode,which was different from the nucleation and growth mode of the pure and CSR_SB modified epoxy asphalts.The swollen core polymer particles along with asphalt particles dispersed in the continuous epoxy phase of CSR modified epoxy asphalts.The area fraction of CSR_PB particles in the CSR modified epoxy asphalt was greater than that of CSR_SB particles.The inclusion of CSR nanoparticles enhanced the thermal stability of the pure epoxy asphalt.Nevertheless,the core structure had a negligible effect on the thermal stability of CSR modified epoxy asphalt.When adding CSR nanoparticles,the storage and loss moduli of the pure epoxy asphalt were improved in the rubbery stage.Furthermore,CSR_SB modified epoxy asphalt had higher storage and loss moduli than CSR_PB modified epoxy asphalt.The glass transition temperature,?transition temperature and damping ability of the pure epoxy asphalt were enhanced with the addition of CSR nanoparticles.The incorporation of CSR nanoparticles significantly improved the mechanical properties of the pure epoxy asphalt,especially for the toughness.CSR_PB modified epoxy asphalt had higher tensile strength and toughness than CSR_SB modified epoxy asphalt.However,the elongation at break of the CSR_PB modified epoxy asphalt was slightly lower than that of CSR_SB modified epoxy asphalt.With 2 wt%CSR_PB and CSR_SBnanoparticles being adding,the tensile strength of the pure epoxy asphalt was increased by 53%and 20%,respectively.The elongation at break was improved by 42%and 51%,respectively.The toughness was enhanced by 110%and 82%,respectively.