The Research On The Erosion Damage Mechanism Of The Acid Rain On The Asphalt And Asphalt Mixture

With the increase in consumption of fossil fuel energy such as coal and oil, acid rain has become a global environmental problem nowadays, which has directly resulted in asphalt pavement diseases such as mineral aggregates softening, burnishing, and asphalt mixtures flushing oil, loose, and potholed. The diseases have become increasing serious, which leads to the durability of asphalt pavement decline. However, the studies on the corrosion mechanism of asphalt pavement under acid rain are extremely limited at home and abroad. Based on current research level, the corrosion mechanism and performance deterioration rate of asphalt under acid rain will be studied by setting up a chemical thermodynamics model and a dynamic parameter model. The performance deterioration laws and corrosion mechanism of mineral aggregates under acid rain in dry-wet cycles will be studied by microscopic methods, macroscopic methods and chemical reaction inference method. A simple and efficient evaluation method and a new technical index to performance deterioration of asphalt mixtures under acid rain will be presented. Based on the studies on asphalt and mineral aggregates corroded by acid rain, the corrosion process of asphalt mixtures under acid rain in short-term, mid-term and long-term dry-wet cycles, and a corrosion model will be presented. The research results will provide important theoretical guidance to prevent and control the corrosion as well as develop new asphalt pavement materials.(1)Effects of PH value and corroding period of simulated acid rain on the technical performance and microstructure of asphalt were investigated through the dry-wet cycle soak tests. The results showed that the penetration of asphalt increased, the viscosity and softening point and ductility were decreased, which making asphalt high temperature stability and low temperature anti-crack performance decreased under the condition of the acid rain. Esterifying reaction and alkylation reaction took place between sulfuric of the acid rain and asphalt, and during the course of reactions, is oparaffin with the longer chain were produced in asphalt. The asphalt components of carboxylic acid and phenolic compounds dissolved with the acid rain and ionizing occurred, causing content of bitumen resin reduced.Oxidative dimerization took place between the acid rain and sulfoether compounds or sulfur alcohol compounds of asphalt and during the course ofreactions, sulfoxides compounds and disulfides was produced in asphalt, causing the content of asphaltene increased.(2)Erosion effects of simulated acid rain on the technical performance of three types of aggregate (limestone, basalt and granite) were investigated through the laboratory tests. The results showed that the mass of aggregates was decreased, crushed stone value, abrasion loss of the aggregates and adhesion between the aggregates and asphalt were decreased. Corrosion mechanism of simulated acid rain on the aggregates was revealed through scanning electron microscopy and X-ray diffraction experiment. The results showed the chemical reactions between sulfuric and nitric acid of the acid rain and calcium carbonate, alkaline oxide of the aggregates can produce water-soluble calcium sulfate, calcium nitrate, potassium sulfate and other salts. These salts dissolved and loss with the acid rain, causing mineral aggregate composition changes, reducing quality, porosity increases and the decline in physical and mechanical properties.(3)Through macroeconomic performance tests of three types of asphalt mixture corroded by different PH value acid rain at different corroding period, the decay law of asphalt mixture performance was summarized. We developed a direct shear test machine and a test method for asphalt mixture, and firstly brought forward to a new index-attenuation coefficient § to evaluate erosion effects of asphalt mixture performance by acid rain.The components analysis test, infrared spectroscopy test and thermo gravimetric analysis test of the asphalt recovered from asphalt mixture soaked by the acid rain were carried. The results showed that the acid rain destroyed the organic acid salt compounds produced by reaction between asphalt and the aggregates. The acid rain can react with divalent salts of organic acids and generate new asphalt acids. These acids can respond with low alkali metal compounds and in turn aggravate solubilization, causing serious water damage of asphalt pavement.