Research On Snow Melting And Solar Energy Collection For Thermal Conductive Asphalt Pavement

Asphalt solar collectors are becoming a new way of harnessing solar energy due to its excellent heating-absorption property. While in the low-temperature weather, the heat energy collected in summer can be developed for the heating and cooling of adjacent buildings as well as to melt the snow and ice on the asphalt pavement. As a result, this technology not only can solve the problems of energy sources and impove road safety, but also can effectively reduce the pavement temperature and urban heat island effect, reduce the damages of bleeding, traction, rutting and other usually happened on asphalt pavement during summer. Heat exchanger in asphalt pavement is a key component in heat collection process of solar energy and ice-snow melting process. Before realize and improve the fuction of solar collection and ice-snow melting on asphalt pavement, the fuction of roadways and pavement performance must be guaranteed.The asphalt pavement structural form is proposed, which will be applied in pavement solar collection and ice-snow melting. Pavement construction materials is designed and prepared, including the preparation of thermal conductive asphalt concrete by adding thermal conductive fillers, preparation of heat insulation asphalt concrete with expanded shale and so on. System testing and optimization study on mechnical properties of pavement construction materials are used to evaluate the effect of conductive fillers on asphalt mortar and asphalt concrete, inspect the pavement performance of asphalt concrete with expanded shale. The results show that it is better for conductive asphalt concrete to use graphite as conductive filler, but the content of graphite should be controlled.Secondly, Based on fundamentals of heat transfer theory and meteorology, analyzes principles and thermal process of asphalt pavement solar collection and ice-snow melting. Such basic concepts as pavement materials with an influence on asphalt solar collection and ice-snow melting, its structure characteristics as well as different environments and types of climate as are still explained in this paper in order to define key parameters that have effects on asphalt concrete’s heat exchang performance. The thermal parameters of asphalt mortar and asphalt concrete are measured by transient plant source method. Comparing some typical thermal conductive model with experimental data of filled thermal composites, the thermal conductive principle in filled asphalt mortar and conductive asphalt concrete are identified and the proper calculation models for predict the thermal conductivity of filled asphalt mortar and conductive asphalt concrete are proposed.Thirdly, the solar collection and ice-snow melting process will change the variation laws of pavement temperature and accelerate the impact of the coupled thermal and water on asphalt pavement.The study in the following aspects:the repeated freezing-thawing cycles test is used to evaluate the resistance capacity of the coupled impact of thermal and water; the full-depth asphalt concrete slab with thermal conductive layer is prepared to simulate the asphalt pavement structure and self-monitoring method to assess the effect of the variation of temperature on asphalt concrete properties and structure; the proper testing method and specifications for conductive asphalt concrete to evaluate the resistance capacity of the coupled impact of thermal and water.Fourthly, with reference to relative national standards and the actual situation of preparation and formation of asphalt concrete, the design of the laboratory testing system for solar energy collection and ice-snow melting, including that of the data acquisition and processing unit, the temperature\flow measure and control unit and radiation test and control system are stated in this study. An experimental system with large asphalt concrete slab for snow melting experiments is built in field and low-temperature heating fuild is used to study snow melting performance. In discussing the behavior of heat and mass transfer and evaluating snow melting performance, it is mainly involved in confirming the surface free-area ratio, temperature variation at feature locations, the snow melting time and surface temperature distribution.Despite the entire snowmelt time is longer than expected and higher fluid temperature is a positive way to improve the performance of melting system, it is acceptable for us to use asphalt solar collector for snow melting. Especially, it is feasible that low temperature water about25℃is used for snow melting. During practical design and applications, to utilize low temperature water is of significance to reduce the waste of energy and it is unnecessary to keep a too high fluid temperature. The variations of free-area ratio and temperature at lacation between pipes during snow melting process generally include four stages:the starting period, accelerated period, stable period and post-acceleration. The conductive asphalt concrete can accelerate the heat transmission and improve the snow melting efficiency. The time of snow melting decreases about30%with the thermal conductivity of asphalt concrete.Lastly, it is proved that factual solar collecting circumstance can be simulated and temperature distribution test of the asphalt concrete slab is practical through heat-extracting test. The accuracy of the test results under the laboratory situation meets the demand of evaluating sample asphalt concrete’s solar energy collecting performance. With the aid of equipment, the climatic conditions of pavement are simulated so that the temperature distribution can be measured. It can be concluded through such results as the whole changing process of the pavement temperature, the temperature vertical distributions and the temperature change rate and temperature gradient that thermal conductive asphalt concrete has a great influence on pavement temperature distribution, which helps to deduce that the optimum depth of pipe-laying is2.5cm-5cm.Solar energy collection experiments using asphalt concrete slabs are operated in laboratory and atmospheric environment. The change process of internal temperature of the collector is measured, the effects of various flows on deducing pavement temperature are evaluated and the effects of initial temperature on the temperature changes are assessed during collection. The experiments mentioned above prove that solar energy collecting of asphalt concrete pavement can considerably reduce surface temperature:with the increase in flow, pavement surface temperature witnesses a linearity decrease; the thermal energy gain per unit area and collection efficiency rises gradually as the outleting water temperature drops. Under the given indoor conditions, the collection efficiency reaches37.5%～47.7%in conductive asphalt concrete slabs, while the daily average efficiency of29.7%in conductive asphalt concrete slabs due to the pipe spacing increases to30mm and under the atmospheric radiation condition.