Experimental Study On The Durability Of Asphalt Concrete Structures With Large Voids

The large void asphalt concrete structure,as a functional road surface layer,not only improves driving safety and reduces road noise but also facilitates rapid drainage,alleviating the burden on urban drainage systems and mitigating the urban heat island effect.It is a primary measure in the construction of sponge cities in the field of road engineering,thus possessing vast development prospects.However,the characteristics of large voids make it more susceptible to natural environmental damage,such as water and temperature,significantly reducing its service life.Therefore,this study takes into full consideration the actual environmental conditions during the service life of the large void asphalt concrete structure and focuses on targeted research to enhance its durability,including high-viscosity asphalt development,gradation optimization,evaluation of water and temperature damage characteristics,and other aspects,providing a necessary research foundation for the promotion and application of large void asphalt pavements in the development process of sponge cities.Firstly,based on orthogonal experimental design,the matrix asphalt is subjected to composite modification,with styrene-butadiene-styrene(SBS)used as the main modifier to ensure that the modified asphalt exhibits good high and low-temperature performance.Additionally,a tackifying resin is used as an auxiliary agent to further increase the viscosity of the asphalt.Plasticizers are also added to improve the compatibility and stability of the modification process while reducing the asphalt’s viscosity to meet construction and workability requirements.Based on the results of the orthogonal experiment,key performance indicators such as 60°C dynamic viscosity,softening point,and 135°C Brookfield viscosity are analyzed.Taking into account performance and cost considerations,the optimal proportioning scheme for highviscosity modified asphalt is determined.The research shows that the independently developed high-viscosity asphalt meets all the basic performance requirements specified by the standards.The key performance indicator for 60°C dynamic viscosity exceeds 60000 Pa·s,and the 135°C Brookfield viscosity is less than 3 Pa·s.It possesses high viscosity while meeting the requirements for construction and workability.It also exhibits good performance in subsequent tests for mixture performance.Furthermore,compared to the more commonly used dry highviscosity asphalt(with high-viscosity additives),the use of the formulated high-viscosity asphalt in this study can save nearly 30% of material costs.Secondly,based on the theory of gradual filling,experiments are conducted on the compacted density of coarse aggregates.The coarse aggregate proportion is optimized through the compactness coefficient,and the optimal proportion of coarse and fine aggregates is determined using the main skeleton filling design method,thereby establishing the basic gradation of the large void asphalt concrete.By changing the key sieve passage of the basic gradation,different mixture gradations are obtained.The compaction state of different composition gradations is evaluated through penetration tests,and the influence of coarse,medium,and fine gradations,as well as reclaimed powder and polyester fibers,on the mixture’s performance is analyzed.The results show that among the coarse,medium,and fine gradations,the medium-grade basic large void asphalt mixture exhibits the best high-temperature performance,with a dynamic stability of 6849 times/mm and a permeability coefficient of 4277ml/min.Therefore,the proposed gradation design scheme for large void asphalt concrete can meet drainage functionality while having optimal skeleton compaction ability.Additionally,substituting reclaimed powder for equal-quality mineral powder does not affect the permeability performance of the mixture but negatively impacts water stability and high-temperature performance.On the other hand,the addition of polyester fibers can enhance the performance of large void asphalt concrete for road applications.Finally,based on indoor water-temperature damage conditions,fly-off tests were conducted on mixture specimens subjected to 60°C hot water baths,plain water freeze-thaw cycles,and 5%melting salt freeze-thaw cycles.The impact of gradation composition and additives on the durability degradation of the large void asphalt concrete structure was analyzed.The results indicate that freeze-thaw cycles have a more severe adverse effect on the peel resistance of the mixture compared to hot water baths,and the use of deicing salt exacerbates the flying loss of the mixture under freeze-thaw cycles.The extent of water damage to the mixture is closely related to the gradation composition,where a higher proportion of coarse aggregates leads to poorer resistance to looseness,and vice versa.The addition of reclaimed powder accelerates the process of water damage to the mixture.Therefore,the use of reclaimed powder should be prohibited during the composition design of large void asphalt concrete,and the clay content in the aggregates should be strictly controlled.On the other hand,the appropriate addition of polyester fibers improves the resistance to looseness,water stability,and high-temperature performance of the large void asphalt concrete structure.It is recommended to use 0.1% polyester fibers in large void asphalt concrete.