严寒区天然浮石混凝土服役期内孔结构动态演变规律的研究

Aiming at the cold environment faced by the hydraulic structures in Inner Mongolia area, closely combined with the characteristics of natural pumice concrete, continuous, tracking and dynamic analysis the law of pore structure parameters of natural pumice concrete within the period of service. The porosity testing, pore size distribution, air-void spacing factor, the shape of the pore and other characteristic parameters during the growth stage of natural pumice concrete and the damage stage of freeze-thaw process were tested continuously, which were concluded by using Nuclear Magnetic Resonance (NMR) technology, Instrument for measuring spacing coefficient of foam concrete, environmental scanning electron microscope, electronic computer X-ray computed tomography (CT) and Laser scanning con-focal microscopy. Thus, the dynamic variation law and the partition interval of pore structure of natural pumice concrete during the service period were measured. Combined with the macro-mechanical properties and microstructure damage situation of natural pumice concrete, to quantitatively describe the whole process of freezing damage to natural pumice concrete and establish the prediction model of frost resistance durability of lightweight aggregate concrete, expand the natural pumice concrete in new ways of application in cold regions.

针对内蒙古地区水工建筑物所面临的严寒环境，密切结合天然浮石混凝土的特征，连续追踪、动态地剖析天然浮石混凝土服役期内孔结构特征参数变化规律。利用核磁共振仪、气泡间距系数测定仪、环境扫描电镜、CT断层扫描仪、激光扫描共聚焦显微仪等测试手段，分析天然浮石混凝土发育成长和冻融循环损伤阶段的孔隙率、孔径分布、气泡间距系数、孔结构形态等特征参数，掌握天然浮石混凝土服役期间孔结构动态时变规律及孔结构的划分区间。结合天然浮石混凝土的宏观力学性能和微观结构损伤破坏规律，对天然浮石混凝土冻害的全过程进行定量描述，建立天然浮石混凝土抗冻耐久性预测模型，拓展天然浮石混凝土在寒冷地区的研究新途径。

本项目以内蒙古天然浮石混凝土为研究对象，制作3种不同强度的天然浮石混凝土试件，连续追踪天然浮石混凝土在发育阶段（3d、7d、14d、21d、28d、90d）孔结构特征参数的变化规律，分析了孔结构与宏观性能的关系；并连续测试天然浮石混凝土冻融损伤阶段孔隙率、孔径分布、孔结构形态等特征参数，阐明了孔结构内部液体介质的变迁规律，得到天然浮石混凝土冻融循环过程中的孔结构损伤动态时变规律。结合天然浮石混凝土的孔结构、宏观力学性能和冻融损伤破坏情况，应用疲劳损失力学的理论，建立了天然浮石混凝土抗冻耐久性预测模型，对天然浮石混凝土冻害的全过程进行了定量描述。结果表明：天然浮石混凝土孔径范围在0.0001～130μm。浮石骨料的多孔性，减小了混凝土气泡间距系数，从而降低了静水压力，提高了抗冻性。天然浮石混凝土的冻害温度范围为0℃～-15℃之间，冻结过程中孔溶液的结冰比较滞后，融化过程的含冰量则变化不大，利用冷冻过程的结冰量估算静水压值比较符合实际现象。通过损伤变量，将冻结过程产生的内应力与天然浮石混凝土宏观力学性能的降低联系起来，推导出天然浮石混凝土冻融损伤模型，计算值与试验值吻合较好。本项目相关研究成果可为天然浮石混凝土在寒冷地区水利工程建设提供必要的研究背景和理论基础。