Research On Road Performance And Rheological Properties Of Basalt Fiber Reinforced Asphalt Mixtures

Asphalt concrete(AC)is one of the most widely used pavement materials.Its mechanical behaviour exhibits obvious stress dependency,temperature dependency and load frequency dependency,which makes the pavement prone to rutting,cracking,surface peeling,pits and other diseases,seriously affecting the performance of the pavement.Basalt fiber is a kind of natural mineral fiber with the advantages of high strength,stable chemical properties,low water absorption,high temperature resistance and environmental friendliness.It has been reported that adding short basalt fibers into AC plays the role of asphalt absorbing,toughening,crack preventing and modulus reinforcement,so as to improve the road performance of the mixtures.There has been a variaty of engineering applications of the basalt fiber reinforced AC mixtures reported in the literatures,however,comprehensive and in-depth studies on the viscoelastic properties of basalt fiber AC mixture and the mechanism of the fiber reinforcement and toughening are rare.In this paper,the aggregate gradation and optimal asphalt-aggregate mass ratios of the basalt fiber AC mixtures are designed based on the Marshall tests;the influence of basalt fiber on the road performance of AC mixtures is investigated by splitting failure test,high temperature stability tests and water stability tests;Through dynamic modulus tests,creep tests and repeated loading tests,the viscoelastic properties of basalt fiber AC mixtures are evaluated,and the linear and nonlinear fractional viscoelastic(plastic)models are discussed;Based on a variety of indicators to evaluate the high-temperature anti-rutting performance,the correlation between different evaluation methods is established.The main research contents and conclusions are listed below.(1)Aggregate degradation and asphalt-aggregate ratio design of basalt fiber reinforced AC mixtures.Marshall tests are carried out on AC-13C graded basalt fiber reinforced SBS modified AC mixtures.The results show that the optimum asphalt-aggregate ratios of AC mixtures with basalt fiber contents of 0.2%,0.3%,0.4%,0.5%and without fiber(control mixture)are 4.90%,4.96%,5.03%,5.10%and4.84%respectively.It is shown that the addition of basalt fiber increases the optimum asphalt quantity of the AC mixtures.For the basalt fiber reinforced AC mixtures with optimal asphalt-aggregate ratios,the Marshall stability and gross volume relative density of the mixtures first increase and then decrease with the increase of fiber content,and the porosity first decrease and then increase with the increase of fiber content.When the fiber content is 0.4%,the Marshall stability reaches its maximum,and when the fiber content is 0.3%,the gross volume relative density and porosity reach the maximum and minimum respectively.According to the results of Marshall tests,the best content of basalt fiber is 0.3%?0.4%.(2)Road performance evaluation of basalt fiber reinforced AC mixtures.The influence of basalt fiber on the pavement performance of basalt fiber reinforced AC mixtures is evaluated by splitting failure tests,high temperature stability tests and water stability tests.Compared with the control mixture,the mechanical properties such as the splitting strength,failure tensile strain,splitting strain energy density,dynamic stability,dynamic modulus,freeze-thaw splitting strength ratio and residual stability of the basalt fiber reinforced AC mixtures are improved,and the permanent deformation under repeated loading is reduced,which indicates that basalt fibers improve the cracking resistance,high temperature stability and water stability of the AC mixtures.When the fiber content is 0.3%,the AC mixtures have the best high temperature stability and good water stability;When the fiber content is 0.4%,the AC mixtures have the best crack resistance,freeze-thaw water damage resistance and high temperature stability.(3)Analysis of dynamic viscoelastic properties of basalt fiber reinforced AC mixtures.The unconfined dynamic modulus tests of basalt fiber reinforced AC mixtures are carried out at five temperatures and six frequencies.The results show that adding basalt fiber can reduce the phase angle and low-temperature dynamic modulus,and improve the high-temperature dynamic modulus of the mixtures,so as to improve the low-temperature toughness and high-temperature rutting resistance of the AC mixtures.Furthermore,the influence of basalt fiber content on the dynamic viscoelastic properties(dynamic modulus and phase angle)is dependent on temperature.With the increase of basalt fiber content,the high-temperature dynamic modulus first increases and then decreases,and reaches the maximum when the fiber content is 0.3%;The low-temperature dynamic modulus decreases monotonously with the increase of fiber content;In the range of test temperatures,the phase angle first decreases and then increases with the increase of fiber content,and reaches the minimum value when the fiber content is 0.3%.Based on the time temperature superposition principle and generalized Maxwell model,the dynamic modulus master curves and phase angle master curves of the AC mixtures are constructed,and the relaxation time spectrum and retardation time spectrum are calculated.Then the relaxation modulus master curve and creep compliance master curve are constructed,which provide foundation for analyzing the dynamic mechanical properties in wide frequency domain and the long-term static mechanical properties of the basalt fiber AC mixtures.(4)Development of a nonlinear fractional viscoelastic plastic creep model for AC mixtures.Uniaxial compressive creep tests at room temperature are conducted under different stress levels to study the creep characteristics and constitutive model of the AC mixtures.The experimental results show that the low stress creep only consists of primary creep and steady creep,while the high stress creep includes teriary stage,indicating nonlinear characteristics.Based on the Nishihara model,a nonlinear fractional viscoelastic plastic creep model is proposed by replacing the Newton dashpot with Koeller springpot.The model considers instantaneous elasticity,fractional order viscoelasticity,time hardening viscoplasticity and nonlinear damage evolution concurrently.The whole creep process including primary,steady and teriary stages of the AC mixtures under different stresses can be well described by the same set of model parameters,and the model predictions are in good agreement with the experimental results.(5)Modelling of the permanent deformation of basalt fiber reinforced AC mixtures.In order to develope the constitutive model for describing the permanent deformation and evaluate the effect of basalt fibers on the permanent deformation,the repeated loading tests are accomplished on the basalt fiber reinforced AC mixtures at high temperature of 60~oC.The tests show three stages of migration-stability-acceleration of the permanent deformation behavior.Compared with pure AC mixtures,the permanent deformation of the basalt fiber reinforced AC mixtures are smaller,which indicates that basalt fibers enhance the high-temperature deformation resistance of the mixtures.With the increase of fiber content,the permanent deformation first decreases and then increases after the same number of cycles.The mixture with fiber content of 0.3%has a smallest permanent deformation,indicating the best high-temperature anti-rutting performance.Considering the viscoelasticity,fractional viscoplasticity and nonlinear damage evolution,a nonlinear fractional viscoelastoplastic constitutive model is proposed.The theoretical model for calculating permanent deformation of AC mixtures under Haversine loading with intermittent times is developed,and the permanent deformation behavior of the AC mixtures with basalt fiber contents of 0.0%,0.2%,0.3%,0.4%and 0.5%are analyzed,then based on the permanent deformation theory model,a method is proposed to directly calculate the flow number FN and FN index of asphalt mixture(6)Comparative evaluation of high-temperature rutting resistance of basalt fiber reinforced AC mixtures.The correlation between flow number FN and FN index,dynamic modulus and fractional order is established.The results show that flow number FN,FN index,dynamic modulus and fractional order can be used as evaluation indexes of high-temperature rutting resistance of AC mixtures:the larger FN is,the smaller FN index is,the larger dynamic modulus is?The smaller the temperature is,the higher the rutting resistance is.The results show that the ranking evaluation based on FN index and high temperature dynamic modulus is consistent.The AC mixtures with 0.3%basalt fiber has the best high-temperature anti-rutting performance.The ranking of high-temperature anti-rutting performance of the basalt fiber reinforced AC mixtures with different basalt fiber content from high to low is0.3%>0.4%>0.2%>0.5%>0.0%.