摘要
LDHs耐老化路用沥青是通过加入具有紫外阻隔性能的超分子结构层状双羟基复合金属氢氧化物(layer double hydroxides,简称(LDHs),以提高路用沥青的抗紫外老化性能的复合道路材料。LDHs紫外阻隔材料的吸收、屏蔽、阻隔和散射作用,降低了紫外线对超分子结构LDHs材料耐老化沥青的不可逆老化作用,缓解沥青使用过程中的硬化开裂现象,优化路用沥青路面的服役性能,延长使用寿命。本文在实验室前期工作的基础上,通过室内加速紫外老化模拟试验、耐老化试验段现场取样等手段,深入开展耐老化路用沥青的老化性能、流变特性、路用性能和粘弹特性的研究,对LDHs耐老化沥青的推广应用提供理论基础和技术支持。
首先根据太阳辐射的规律,本文分析了人工加速老化与自然老化的相关性,提出了模拟路面紫外辐射的人工加速紫外老化环境技术参数。通过蓝色羊毛标准对比不同光源对沥青老化的影响,结果表明氙灯与实际太阳辐射的相关性较好,高压汞灯可以加速沥青老化现象,且沥青老化试验是依赖于紫外线辐照量的。通过热重分析及差示扫描量热分析制备的LDHs耐老化沥青,实验结果表明LDHs材料的加入改善了沥青的热稳定性。采用常规物理性能分析LDHs材料对沥青老化前后的常规路用性能的影响,结果表明：紫外老化使得沥青软化点升高、针入度降低、延度减小,而LDHs材料的加入降低了老化沥青软化点增量,残留针入度比和延度保留率都有所增大,实验结果表明LDHs材料明显提高了耐老化路用沥青的抗紫外老化性能。
第二,采用扫描电子显微镜(SEM)、傅立叶红外光谱(FTIR)及X射线衍射仪(XRD)分析测试超分子结构LDHs材料耐老化路用沥青的微观形貌、组成结构,并根据Mie理论对沥青中LDHs颗粒对光的吸收和散射特性进行理论分析,研究LDHs材料与沥青的适配性,为制备高性能耐紫外光老化沥青提供理论依据。研究结果表明：LDHs材料颗粒成球状,晶粒尺寸为50-150nm,粒径小于紫外线波长,且超分子结构LDHs材料耐老化路用沥青是一种均匀分散的复合结构,Mie散射理论分析提出了优选沥青材料和LDHs材料的方法。
第三,根据应用流变学相关理论和方法,采用动态剪切流变仪(DSR)研究超分子结构LDHs材料对路用沥青老化前后的流变性能影响规律。研究结果表明,超分子结构LDHs材料改变了沥青的流变性能,使得沥青的复合剪切模量升高,相位角减小；同时LDHs材料提高了沥青抗老化和抗低温开裂性能；使用真空旋转回收仪回收沥青的方法,对比了PJ90沥青及其掺量为3%的LDHs耐老化沥青在室内模拟老化和在内蒙古试验段通车1年后的粘度值以及高温车辙因子G*/sinδ,结果发现LDHs使得沥青的粘度老化指数VAI变小,老化后车辙因子减小,LDHs有效的延缓了沥青老化。
最后,采用蠕变试验研究了LDHs耐老化沥青胶浆粘弹特性,并采用合适的流变模型对其粘弹特性进行描述。研究结果表明,LDHs材料的掺入能改变沥青胶浆的粘弹性质,LDHs一方面能降低了沥青胶浆加载过程的总蠕变变形,同时又能提高沥青胶浆总变形中的弹性变形,使沥青胶浆承受外加荷载时产生的永久变形降低；老化后沥青的蠕变劲度模量随LDHs的加入而减小,说明LDHs的加入减轻了沥青的老化程度。Burgers模型能较好的描述LDHs沥青胶浆的粘弹特性,该模型拟合的结果表明,LDHs材料能较大程度影响沥青胶浆的弹性和粘性部分。
Anti-aging asphalt, which is modified by supramolecular UV resistant material-LDHs, is a kind of composite material. In order to improve the anti-UV-aging performace of the asphalt, the base asphalt is mixed by LDHs materials with supramolecular structure. LDHs can absorb, shield, prevent and scatter the ultraviolet, which can reduce the irreversible aging effects on asphalts. It can also alleviate hardening and cracking of the asphalt in the service process and enhance the service performance, which can prolong service life of the road. This paper carried forward the outcomes of work in the laboratory, by means of artificial accelerated UV aging test and field sampling.The systematic research on the asphalt modified by the LDHs was also done in this paper, which included the ageing performance, the rheological properties, and the basic pavement performance and the viscoelastic properties of the asphalt. In order to guide the application of the LDHs asphalt in practice project, a theoretical basis and technical support for the promotion and application in practice pavement was also provided in the paper.
Firstly, according to the law of solar radiation and the analysis of the correlation between the artificial accelerated ageing test and the wild ageing test, the paper put forward the model parameters of the artificial accelerated UV aging environment. The blue wool standard test was used to compare the effects of asphalt UV aging with different light source.The results showed that the high pressure mercury lamp light source could cause more serious damage and speed up the test and that the correlation between xenon lamp and practical solar radiation is better.Moreover, the test results did not rely on the irradiance intensity, but only depended on the total irradiation. Then, the anti-aging asphalts modified by LDHs were prepared by mass ratio3wt%under optimal conditions with agitator and shearing apparatus in Lab. TG-DSC test illustrated that the LDHs could improve the thermostabilization of asphalt. The effects on the performance of the asphalts by adding LDHs materials was studied by mean of normal tests, the results of which showed that the softening point of aged asphalts rose slightly while the penetration and the ductility were on the decline drastically as well as the moderate enhancement of viscosity. It also showed that LDHs materials could play the significant role on the UV-resistant performance of the asphalt.
Secondly, the tests on the microcosmic appearance of the LDHs material and the microstructure of the modified asphalts were carried out by SEM, FTIR and XRD. Researches on the absorption and scattering properties of LDHs particles dispersed in asphalt were based on the Mie theory, in order to study the suitability between the asphalts and the LDHs materials and provide a theoretical basis for preparing different kinds of LDHs asphalts by the excellent combination property, the results showed that the diameter of the LDHs particle was50-150nm, less than the wavelength of UV, and the modified asphalt had the composite structure in which the LDHs material could homogeneously disperse. The analysis of the absorption and scattering properties based on Mie theory could make the optimized selection for both the kinds of the asphalts and the diversity of LDHs materials.
Thirdly, the rheological charateristics of the LDHs asphalts were studied by rheology theory. Dynamic Shearing Rheomemter (DSR) was adopted to study the rheological properties of the asphalts samples before and after UV ageing and the results showed that the ability of bearing loads and elastic properties of the asphalts were improved by the LDHs materials. In addition, the complex modulus was on the increase and the phase angle decreased which illustrated that LDHs modified asphalt had the better anti-aging and anti-cracking property at low temperature in comparion with base asphalt. In order to compare the results of UV ageing test between in laboratory and in the practical pavement enviroment, the asphalt paved in NeiMeng in2011was extracted and the asphalts included PJ90and LDHs-PJ90. The viscosity test and DSR test showed that both the aging index (AI) of the LDHs asphalt and rutting factor were smaller than the base asphalt which represents that the LDHs could slower UV ageing process.
Finally, the viscoelastic characteristics of LDHs asphalt binders were investigated by the creep test, and proper rheological models were employed to describe the characteristics. Results indicated that the viscoelastic properties of asphalt binders can be altered by LDHs materials. The total deformation of LDHs asphalt binders decreased during loading period and the elastic deformations increased, leading to the reduction of permanent deformation of asphalt binder. First-order Burgers model could be used to describe the viscoelastic characteristics for LDHs asphalt binders, which reveals the elastic and viscous property of asphalt binders can be greatly affected by the LDHs materials.
引文
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