Study On The Influence Mechanism Of Basalt Fiber On Asphalt Mixture Property

In our country, overhaul period of asphalt pavement is frequently short, thus the improvement of service quality and usable life of the asphalt surface is the focus of the research at present. Researchers have done a lot of work to improve the basic properties of material, and now it is widely accepted that adding fiber can improve the performance of asphalt mixture for its effectivity and convenience.Basalt fiber is a new mineral fiber type that not for prolonged use in asphalt mixture. With high strength, big modulus, high-temperature tolerance, anti-aging and chemical stability, basalt fiber has great development potential and wide engineering application prospect. In the thesis, effect and mechanism of basalt fiber in improving the performance of asphalt mixture was analyzed by basalt fiber properties, fiber-asphalt mortar performance, fiber-asphalt mixture performance, macroscopic and microscopic fracture morphology characteristics and low-temperature viscoelasticity of basalt fiber asphalt mixture.This thesis comprises the following sections:1. Basalt fiber performance research A systematic experimental study was conducted to investigate the performance of basalt fiber which included high temperature resistance, hygroscopicity, adhesion properties to asphalt, acid and alkaline resistance, ash content, oil absorption rate and microscopic morphology analysis by scanning electron microscopy (SEM). The results provided a comprehensive evaluation on performance of the fiber adding to asphalt mixture. Based on the generalized mixture rule theory of composite material, we studied the influence of basalt fiber mass fraction to asphalt mortar viscosity, proved the applicability of the viscosity theory of weak phase support, clarified that the basalt fiber had reinforced adhesion effect.2. Effect of basalt fiber on asphalt mixture performanceBased on the laboratory tests of high temperature stability, low temperature crack resistance, water stability, fatigue and creep properties and so on, a quantitative evaluation of the performance improvement of two different basalt fiber forms in AC-16c asphalt mixture had been done and the improving mechanism of basalt fiber to the asphalt mixture was analyzed. The results proved that the cotton basalt fiber (CBF fiber) was able to improve the pavement performance significantly; short-cut basalt fiber (SCBF fiber) showed remarkable enhancement effect on all asphalt mixture properties excepting water stability. Combined with the analysis of fiber asphalt mixture performance and mechanism, we confirmed that PH value and asphalt adhesiveness of basalt fiber had an important effect on improving the performance of asphalt mixture. Therefore, we suggest that the corresponding technical index requirements should be added to the specification.3. Basalt fiber asphalt mixture fracture morphology analysisBy fractography analysis method, the appearance characteristics of asphalt mixture fracture were analyzed. We also discussed the relationship of mechanical properties and fracture morphology and analyzed the improvement mechanism of the basalt fiber on reinforcing asphalt mixture mechanical property further more.The study of macroscopic fractography showed that the inner cavity of asphalt mixture reduced while the aggregate fracture proportion and interface deboning fracture both increased after adding basalt fiber. Therefore, we can conclude that basalt fiber improves the crack resistance of asphalt mixture. The research of microscopic fractography showed that basalt fiber was lipophilic material. Fiber linking the micro crack restricted local defects and enhanced the integrity. SCBF fiber dispersed unevenly in the mixture, observed as parts-clustering phenomenon, which might become the weak point of the specimen due to the insufficient of asphalt coating, and then affected the overall strength and mixture stability.The conception of "mechanical weakness region" was proposed in this thesis by the analysis of the morphology features of basalt fiber in the asphalt mixture fracture. We considered that there was an unstable asphalt interlayer between the fiber-asphalt interface and free asphalt. Fiber would be pulled out from this region when the direction of stress generated by force and the fiber orientation were the same4. Basalt fiber asphalt mixture viscoelasticity and numerical simulation analysisBased on flexure creep test of asphalt mixture at both room temperature and low temperature conditions, the creep model parameters that suited fiber asphalt mixture were obtained by data fitting. It proved the applicability of the model, while it also indicated the mechanism how basalt fiber improve anti-cracking performance of asphalt mixture at low temperature. With time hardening model, we obtained the numerical simulation analysis of beam bending creep test on ABAQUS software.