Study On Property Of Basalt Fiber And Basalt Fiber Modified Asphalt

The heavier vehicle loads, higher traffic volumes and worse serving environment have accelerated deterioration and eventual failure of asphalt concrete. The asphalt concrete has an obvious tendency to become brittle at low temperatures and soft at high temperatures (so called "temperature susceptibility"). To improve the pavement performance of asphalt, various types of fibers such as cellulose fiber, asbestos, glass fiber, polymer fiber and basalt fiber were used as modifiers in asphalt concrete. Recently, researchers draw more attention to basalt fiber due to its excellent mechanical properties, good thermal stability, and relatively low cost. Some papers dealt with the introduction of basalt fiber for improving asphalt, while the microstructure and property of basalt fiber and the detailed rheological properties of asphalt mortar are still poorly understood. The microstructure, chemical stability and thermal stability of basalt fiber are the basic premise for playing its role of reinforcement, are the key technique to reveal the interaction mechanism of between fiber and asphalt in the asphalt mortar.In this paper, SEM, EDS, FTIR and Raman spectra were used to characterize the morphology, components and molecular structure of basalt fiber. The phase of basalt fiber was characterized by X-Ray diffractometer, and the order in the short range was calculated by the quasi Scherrer formula and Gaussian fitting. In addition, the random network parameters were obtained by components results of basalt fibers. For the study of chemical stability, SEM, EDS, XRD and FTIR were were used to characterize the morphology, components, phase, order in the short range and molecular structure of acid-treated and alkali-treated basalt fibers. Also, weight loss experiment and tensile test were used to study the damage rule of mass and mechanical properties of acid-treated and alkali-treated basalt fibers. For the study of thermal stability, TG-DSC curves in different atmosphere were used to study the physical and chemical reactions of basalt fibers during the whole process of heat treatment. Then, metallographic microscope, FTIR spectrum and tensile testing were used to study effect of heat treatment on the morphology, molecular structure and mechanical properties of acid-treated and alkali-treated basalt fibers. X-Ray diffractometer was used to study the phase changes of heat-treated fibers, and then obtain the crystallization rules. For the study of combination state of basalt fiber and asphalt, rotational viscometer, Vicat apparatus, mesh-basket draindown experiment, softening point testing and FTIR spectra were used to evaluate the effect of fibers on viscosity, penetration, absorption, and softening point of asphalt mortar. Dynamic shear rheometer test was used to study the rheological property of fiber modified asphalt mortar. And then we research the effect of fiber’s mixing amount, tesing temperature, fiber species, load frequency and aspect ratio of fibers on the rheological property of fiber modified asphalt mortar. At last, we give a regression relation between the rutting parameters of asphalt mortar and tesing temperature. The fitting parameters in the fitting equation were endued with some meanings.The main conclusions in this paper are summarized as follows:1. Basalt fiber has a regular cylindrical geometry with a relatively smooth surface except for some protuberances. The similar morphology may form in the fiber spinning process because the surface area of the molten would shrink into minimum cylindrical shape due to surface tension effects. Major portion of basalt fiber remains glassy and the order in the short range is4.12A, that is to say, basalt fiber is of an ordered structure in the short range and of a disordered structure in the long range. In the FTIR spectrum, the strongest absorption band at1001cm-1is attributed to the anti-symmetric stretching of Si—O—Si (Al). The corresponding symmetric stretching vibration and the bending vibration of Si—O—Si (Al) appear at725and450cm-1respectively. Based on the Random Network Models, the random network parameters of basalt fiber were obtained, and those parameters were similar to the random network parameters of Na2O·0.5Al2O3·2SiO2. That is to say, basalt fibers almost all have the framework structure.2. The acid-treated basalt fiber has cylinder-like shape, and its components are nearly Si and O. This fiber still keeps glassy, and the order in the short range becomes higher. And in FTIR finger region the peaks become sharper and move to high frequency region. In addition, the Si—OH also appears in this FTIR spectrum. The values of tensile strength retention and modulus retention of basalt fiber decline and gradually reach a steady value with different etching time. This suggests that at the beginning stage, Al3+and other cations react with acid medium, and then enter into the acid solution. At last, the random network of basalt fiber turn into the random network composed of high content of Si and O. The alkali-treated basalt fiber had skin-core structure, and its surface became very rough. There were some exfoliated materials on the surfaces of fibers. The alkali-treated fiber still keeps glassy, and the order in the short range becomes lower. Also, the values of tensile strength retention and modulus retention of basalt fiber decline slowly at first, and then decline quickly. This suggests that at the beginning stage, there are still cations changing with the alkali medium. At the later stage, the network has been destroyed by the medium and the skin-core structure appeared.3. The oxidation of the iron happened about1000℃during the crystallization process, and this process caused50%of the weight gain. This formation of magnetite is the beginning of crystal nucleation. When the temperature was above700℃, the process about crystallization is complicated. For the samples heat-treated at400℃, some irregular punctuate and warty defects were found on the surfaces of fibers. For the samples heat-treated at500℃, the bigger warty defects appear on the surfaces of fibers. For the samples heat-treated at600℃,some pits appear on the surfaces of fibers. When the temperature reaches700℃, many cracks have been found on the surface of basalt fibers. The crystallization behavior appears during the temperature region700-1050℃. And the corresponding crystal phases are the main phase diopside and the minor phase anorthite. The absorption bands of heat-treated samples in FTIR spectra become relatively sharp and split into several peaks. All the spited bands are attributed to the characteristic absorption bands of diopside and anorthite. When the temperature is below700℃, crystal nucleus appeared but crystals cannot grow. When the temperature is above1050℃, there are no crystal nucleuses formed.4. After the basalt fiber added, the viscosity of asphalt mortar increases rapidly in the temperature region of150-185℃, and the valules of viscosity keeps about8.0Pa-s. And the viscosity changes very little with the temperature. For the mineral powder modified asphlt mortar, the penetration declines with temperature, and the relationship between penetration and temperature is in accord with the Boltzmann equation. The effect of mineral powder on the asphalt mortar is more obvious at high temperature region than the one at the low temperature region. For the softening point testing, the softening point of the rock wool modified asphalt mortar increases more quickly than the one of basalt fiber modified asphalt mortar when the fiber’s mixing amount is below3.5%. However, the effect of basalt fiber on the asphalt mortar is more obvious than the effcet of rock wool. This indicates that basalt fibers can disperse uniformly in the asphalt mortar at the high fiber’s mixing amount. In the mesh-basket draindown experiment, the asphalt adsorption of basalt fiber decreases with the temperature. When the temperature is above140℃, the asphalt adsorption decreases more qucikly than the asphalt adsorption at the temperature region of100-140℃. Compared with other kinds of fibers, the asphalt adsorption of basalt fiber changes the least with the tesing time and temperature. This suggests that basalt fibers can combine with asphalt firmly, and the firm structural asphalt form at the interface of fiber and asphalt. Also, there is no new band found in the FTIR spectrum of fiber modified asphalt mortar, this may be caused by the low fiber’s mixing amount or the weak absorption peaks of fibers. In addtion, asbestos fibers have dendritic and hollow structure. The glass fiber and polymer fiber both have cylindrical structure. And the characteristic group of polymer fiber is the most complex, such as carbonyl group and ether group. All the groups are beneficial to the combination degree with asphalt mortar.5. The basalt fiber causes an increase in complex modulus, storage modulus, loss modulus and rutting parameters, while decrease in the phase angle and temperature susceptibility of asphalt mortar remarkablely, especially in the high temperature region. These suggest that the asphalt mortar becomes more viscous and has better rutting resistance. The regression relation between the rutting parameters and temperature closely fits Model ExpDec1. This improvement effect may be closely related to the microstructure of fibers such as large surface, polar groups on the surface, and the distribution state of fibers in asphalt mortar. The rutting parameters keep the highest valule when the fiber’s mixing amount is1.0%. And at the temperature region of30-50℃, the rutting papameters of polymer fiber are lower than those of basalt fiber. When the temperature is above50℃, the the rutting papameters of polymer fiber increase rapidly. This indicates that the polymer fiber can not play the reinforcment role sufficiently at the low temperature region. Under the high frequency load, the rutting papameters of basalt fiber increase with the fiber’s mixing amount. The rutting papameters of the7.5%sample decrease, and the value is near the rutting papameters of the3.5%sample. This is because the basalt fiber can not disperse uniformly in the asphalt mortar system. In addtion, the effect of aspect ratio of fibers on the rheological property of the asphalt mortar is very unconspicuous. This is possibility beause that the difference between the selected values of the aspect ratio is not big enough, so we need to add more experiments about more aspect ratio of fibers.