风沙吹蚀与干湿循环作用下风积沙混凝土抗氯盐侵蚀机理

针对风蚀区盐湖及盐渍土环境下服役的混凝土,配制满足特殊环境下工程要求的风积沙混凝土.分析风沙吹蚀与干湿循环耦合作用下风积沙混凝土抗氯盐侵蚀的损伤过程,借助超景深三维显微镜、X射线衍射物相分析、核磁共振孔隙分析等手段探讨风积沙混凝土抗氯盐侵蚀耐久性机理.研究表明风沙吹蚀对混凝土表面产生破坏,干湿循环对混凝土内部造成损伤;风沙吹蚀对混凝土表面造成的“吹蚀坑”可为盐离子入侵混凝土内部提供“通道”;氯盐侵蚀后生成以Friedel盐为代表的腐蚀结晶物,可填充1～4 nm胶凝孔,消耗Ca(OH)2等有效物质,迫使4～10nm小毛细孔增多,随盐蚀损伤程度加剧,10～20 nm中毛细孔和20～100 nm大毛细孔向＞100 nm非毛细孔发展,非毛细孔彼此贯通产生裂纹,致使混凝土加速破坏.该研究可为风积沙混凝土在风蚀区氯盐环境下农业水利工程建设与应用提供依据.

Mechanism analysis of chloride resistance of aeolian sand concrete under wind-sand erosion and dry-wet circulation

Aiming at the concrete in the special environment of salt lake and saline soil in wind erosion area,the aeolian sand concrete satisfying the service requirement in the special environment is formulated.The aeolian sand concrete with the aeolian sand substitution rate of 40％ was selected as the research object.Based on the method of indoor acceleration simulation,the chloride-resistant erosion of aeolian sand concrete under the condition of wind-sand erosion and dry-wet circulation was studied.The self-made concrete wind-sand erosion testing machine was used to simulate the actual dust storm environment in the northwest of China,in which wind speed was 31 m/s,sand carrying capacity was 30 g/min,attack angle was 90° and erosion time was 10 min,and the wind-sand erosion test of concrete was carried out.Using the dry-wet circulation testing machine to test chloride dry-wet cycles,NaC1 solution with a concentration of 3％ was selected as an attack medium;a dry-wet cycle is 24 h,which contains the chloride soaking for 15 h,drainage and air drying for 1 h,high-temperature drying for 6 h,and room temperature cooling for 2 h.Experimental design includes 2 different working conditions:Condition I,aeolian sand concrete chloride-resistant corrosion test under dry-wet circulation;Condition Ⅱ,aeolian sand concrete chloride-resistant corrosion test under the coupling effect of wind-sand erosion and dry-wet circulation.The mass loss rate,the relative dynamic elastic modulus and the maximum depth of chloride ion erosion were taken as the test indicators.The damage process of concrete surface was measured by the super-depth 3D (three-dimensional) microscope,the concrete composition was analyzed by the X-ray diffraction (XRD),and the concrete pore size change was calculated by the nuclear magnetic resonance (NMR) technique.The durability mechanism of aeolian sand concrete's chloride resistance under the coupling effect of wind-sand erosion and dry-wet circulation was discussed.Results showed that under wind-sand erosion and dry-wet circulation coupling,aeolian sand concrete's surface slurry exfoliation was intensified.Wind-sand erosion exerted greater impact on the concrete mass loss rate,but little effect on the relative dynamic elastic modulus change.Wind-sand erosion accelerated the emergence of “inflection point” of the total loss rate of concrete;wind-sand erosion caused the damage on the concrete internal structure which accounted for about 8.77％ of the total damage,while the damage of concrete internal structure caused by the wet and dry cycle in the condition of chlorine salt solution accounted for about 91.23％.The concrete surface damage can provide “channel” for the intrusion of chloride ion,which increases the depth of chloride ion erosion under the coupling of wind-sand erosion and dry-wet circulation.The maximum erosion depth under the coupling of wind-sand erosion and dry-wet circulation was 1.4-1.6 times that under pure dry-wet circulation.The Friedel's salt as the representative of a variety of corrosive crystals was formed after chloride salt erosion in aeolian sand concrete,and the corrosive crystals could fill the 1-4 nm gel pores to reduce the cement stone gel pores,consume Ca(OH)2 and other components,and force 4-10 nm small capillary pores increased;with the intensification of salt corrosion,10-20 nm middle capillary pores and 20-100 nm large capillary pores developed toward ＞100 nm non-capillary pores,and non-capillary pores were connected with each other to form microcracks,which ultimately led to the acceleration of the damage to concrete.