高寒灌区风沙吹蚀对农业水利工程混凝土抗冻耐久性的影响

Effect of wind-sand erosion on frost resistance durability of hydraulic engineering concrete in cold irrigation area

针对内蒙古引黄灌区农业水利工程混凝土实际服役环境,同时加大风积沙资源化利用效率,配制满足农业水利工程设计要求的风积沙混凝土,并研究风沙吹蚀作用对风积沙混凝土抗冻耐久性的影响。结果表明:相对动弹性模量可准确表征风积沙混凝土受风沙吹蚀影响下的冻融破坏,且风沙吹蚀影响下混凝土冻融循环后的内部损伤是未受风沙吹蚀影响下混凝土冻融循环后的2倍;在风沙吹蚀影响下的冻融过程中,风积沙混凝土水泥浆体在冻融过程发生"酥化",同时在风沙流的持续撞击、削切下,"酥化"的水泥浆体进一步剥落,迫使破坏表面水泥浆体与骨料连接处的界面过渡区较光滑;风积沙替代率为40%可以配制满足抗冻性要求的风积沙混凝土,但风积沙混凝土气泡间距系数不能准确评价其抗冻性,气泡盒维数与细骨料细度模数可反映气泡结构特征和细骨料颗粒级配,且二者呈负相关趋势,二者结合可对风积沙混凝土抗冻耐久性优劣进行初步判定。

In view of the actual situation of the concrete service environment of agricultural hydraulic engineering in the Yellow River irrigation of Inner Mongolia, due to the natural river sand becoming scarce, increasing the utilization efficiency of the local aeolian sand resources and using aeolian sand to form aeolian sand concrete meet the requirements of concrete in agricultural engineering and hydraulic engineering. The effect of wind-sand erosion on the frost resistance of aeolian sand concrete in cold irrigation area was studied. The replacement of natural river sand with the aeolian sand of quality substitution rates of 20%, 40% and 60% can be used to compose the aeolian sand concrete, the 28-day cube compressive strength of the aeolian sand concrete meets the C40 requirements. Using self-made sand-carrying flow erosion test device, the actual wind-sand environment in cold irrigation was simulated, including wind speed of 31 m/s, sand carrying capacity of 30 g/min,attack angle of 90° and erosion time of 10 min, and under these wind erosion parameters, the wind-sand erosion test of concrete was carried out. Two different test conditions were designed, i.e. the concrete frost resistance test and the concrete frost resistance test under the influence of wind-sand erosion. The mass loss rate and the relative dynamic modulus were used to evaluate the pros and cons of frost resistance test and the frost resistance test under the influence of wind-sand erosion, the super-depth three-dimensional topography of microscope was used to observe the concrete surface morphology under 2different test conditions, and the bubble spacing device was used to test the bubble characteristic parameter of hardened aeolian sand concrete under 3 different substitution rates of aeolian sand. The results show that the quality loss rate can not accurately judge the effect of the freeze-thaw damage of aeolian sand concrete under the influence of wind-sand erosion, but the relative dynamic elastic modulus can accurately characterize the freeze-thaw damage of aeolian sand concrete under the influence of wind-sand erosion. Through the relative dynamic elastic modulus, it can be seen that the internal damage of aeolian sand concrete after freeze-thaw cycles under the influence of wind-sand erosion is 2 times that after freeze-thaw cycles without wind-sand erosion. Under the influence of wind-sand erosion, the aeolian sand concrete paste is crisped in the process of freeze-thaw cycles. At the same time, under the continuous impact of the wind-sand flow, the crisped cement paste peels off,and hence eventually the interface transition zone between cement paste and aggregate of destruction surface is more smooth.The aeolian sand with the quality substitution rate of 40% can be prepared to meet the requirement of frost resistance of aeolian sand concrete in cold irrigation area. The bubble spacing factor of hardened aeolian sand concrete can not accurately evaluate the frost resistance. The bubble box dimension and fine aggregate fineness modulus can reflect the bubble structure and fine aggregate grain gradation, and the two are associated and the combination of the two can be used to determine the durability of aeolian sand concrete.