完全浸泡再生混凝土Mg^(2+)-SO_(4)^(2-)-Cl^(-)侵蚀耐久性损伤规律与机理

Durability Degradation Laws and Mechanism of Recycled Aggregate Concrete Subjected to Mg^(2+)-SO_(4)^(2-)-Cl^(-)by Full Immersion

我国西北地区的土壤与地下水中含有高浓度Mg^(2+)、SO_(4)^(2-)、Cl^(-),这些离子导致长期掩埋于地下的再生混凝土(RAC)结构耐久性严重退化。为了揭示Mg^(2+)-SO_(4)^(2-)-Cl^(-)侵蚀RAC耐久性损伤规律与机理,采用长期浸泡的方式,系统开展复掺辅助胶凝材料RAC耐久性试验,研究复掺辅助胶凝材料方式与取代率对RAC耐久性退化规律的影响。采用X射线衍射、红外光谱及热重等分析手段,表征RAC侵蚀产物物相组成与相对含量,揭示复合盐侵蚀RAC耐久性损伤机理。结果表明,10%粉煤灰(质量分数)+20%(质量分数)矿渣复掺RAC耐久性较高,硅灰或偏高岭土取代率高于10%时RAC的耐久性较差。侵蚀离子与RAC水化产物产生化学反应并形成晶粒极大的侵蚀产物,加速C-S-H分解向M-S-H转变;高浓度离子间相互作用形成物理盐结晶,促进裂缝的萌生扩展。化学/物理双重作用破坏RAC微观结构,加速离子扩散传输,形成化学侵蚀-结构损伤-离子传输过程。RAC界面过渡区及砂浆中遍布裂缝与孔隙,再生混凝土物理力学性能急速退化。

The soil and groundwater in Northwest China contain high concentrations of aggressive ions such as magnesium,sulfate,and chloride,which lead to serious degradation of the durability of recycled aggregate concrete(RAC)structures buried underground.In order to reveal the durability’s regularity and mechanism,the experiment of RAC with supplementary cementitious materials(SCMs)immersed in Mg^(2+)-SO_(4)^(2-)-Cl^(-)solution was carried out.The influence of the collocation and replacement ratio about the SCMs on the durability degradation laws of RAC was studied.Afterwards,the mineral composition and its relative content were characterized by X-ray diffraction,infrared spectroscopy,and thermogravimetry methods.The results show that the RAC with 10%fly ash+20%slag had better durability,while the RAC with more than 10%silica fume or 10%metakaolin had worse durability.Aggressive ions reacted with hydration products to form corrosion products with large grain sizes,which accelerated C-S-H transforming to M-S-H.Otherwise,crystalline salt was formed under the interaction between aggressive ions and original ions in pore solution,promoting the initiation and expansion of cracks.The combined action of chemical corrosion and physical damage destroyed the microstructure and accelerated aggressive ions diffusion,leading to chemical corrosion-microstructure damage-ions transportation.Micro-cracks and capillary pores were appeared in the interface transform zones and mortars,resulting seriously degradation of RAC’s physical and mechanical properties.