Experimental Study On Concrete Under Wind-Blown Sand Environment After Mixed And Single Salt Freezing And Thawing Cycles

In northwest China, the severe cold, saline, blown sand and other special natural environment had a seriously influence on concrete structure durability and security, especially the pavement concrete, the service life and people’s daily lives were also seriously influenced.In this paper, the saline soil and the desert area were selected as the research region, which has many highways crossing here, such as G6、G7 highways, the selected regions had the practical significance and engineering background. On the basis of environment characteristics of saline and severe cold of northwest Inner Mongolia salt freeze-thaw cycles, the sediment-air injection method was utilized to study the relationship between the concrete erosion rate or loss and salt-frozen and wind-blown sand environment, the erosion wear rules and erosion mechanism were also studied, with the combination of Taguchi orthogonal test method, the various environmental factors were assessed concretely, which made the test results more reliably.This project is supported by the National Natural Science Foundation of China(Study on the damage mechanism of concrete under the wind-blown sand in the West saline soil area under severe cold conditions)(Project approval number: 51468049), the specific research contents are as follows:1. The saline soil samples obtained from Erdos of Central and western regions of Inner Mongolia are analyzed to define the composition of soluble salt in order to make single(sulfate or chloride) and multi-salt erosion solution(sulfate and chloride), and the concrete specimens are used to conduct salt erosion and freeze-thaw cycling. The contrast tests are made as well under the condition of single salt environment on the basis of evaluation norms of the mass and compressive strength; the micro topography of concrete after the freezing-thaw cycles was observed by the field emission scanning electron microscope(FESEM), and the internal corrosion degree of concrete was comparatively analyzed by the energy spectrum analysis and chemical element analysis. The tests results show that,(1) at the early stage of freezing-thaw cycles, the mass and compressive strength of concrete all increased, but when the times of cycle exceed 10 times, the mass and compressive strength decreased;(2) the chemical elements were observed after the multi/single salt freezing and thawing cycles.2. Based on the climatic characteristics of sand and dust weather in the central and western Inner Mongolia, the selection of erosion parameters was carried out. Five different conditions of the sand erosion test were designed; concrete in different solution environment after freeze-thaw cycles of wind erosion test was conducted.3. The erosion simulation system of wind-blow sand environment was utilized to study the concrete erosion, and the research results of different conditions were calculated and analyzed. Combined with the microscope(DSX 500), the erosion morphology of concrete was observed, the damage mechanism of erosion wear was analyzed. The results showed that:(1) under the five working conditions, the erosion rate of concrete increase with the increasing erosion velocity under the same conditions, and the two has an empirical power law relationship;(2) the concrete erosion rate increases with the increase of the erosion angle under the same freeze-thaw cycles;(3) the concrete erosion rate decreases with the increase of the sand flow rate under the same freeze-thaw cycles;(4) Through the erosion wear comparison of Hobq and Tengger Desert sand, it is concluded that at low erosion angle, concrete erosion rate impacted by Hobq sand is higher than Tengger sand, but when the erosion angle increased, the concrete erosion rate impacted by Tengger sand is higher than Hobq sand.4. Experimental study into erosion wear of concrete after the freeze-thaw cycle of sulfate solution was conducted with the application of Taguchi orthogonal test method, the results show that the influence of erosion angle on concrete is the most severe factor, followed by the erosion velocity, sand flow rate and sodium sulfate solution freeze-thaw cycles(45 times of freeze-thaw cycles).