超高韧性水泥基复合材料中高掺量粉煤灰活性激化机理与性能提升研究

Based on domestic cementitious materials, Ultra High Toughness Cementitious Composite (UHTCC) has been developed in China in recent years. It is a kind of new construction material with excellent crack-controlling and seismic capacity. The hardened material exhibits significant pseudo strain-hardening and multiple-cracking behaviors with tensile strain capability above 3%~6%. On the basis of micro-nano technology and double admixing technology, high-volume fly ash will be used in this project to substitute for most of cement in UHTCC. Microcosmic structure will be carefully observed during hydration and hardening process of UHTCC. Crystallite nucleation effect, heterogeneous induced activation effect, and secondary hydration and micro-aggregate effect of fly ash will be applied to improve mechanical properties and durability of UHTCC. Mechanical properties tests including direct-tension, four-point bending, prism compressive will be carried out. Also, durability performances, such as compactness, permeability resistance, freezing resistance, Chloride ion penetration resistance, anti-carbonation properties will be investigated during the project. Constitutive equations will be established to describe the multi-cracking and strain hardening process of high-volume fly ash UHTCC. Then calculation and analysis method of crack spacing, crack width and fracture strain energy density will be proposed for the development of new kinds of UHTCC materials. The purpose of this project is to realize material-structure integrated design and nano-micro-macro integrated modification. Industrial wastes will be utilized with high technology and efficiency. At the mean time, Durability and service life of structures can be improved significantly.

超高韧性水泥基复合材料(UHTCC)是我国学者近年结合国产胶凝材料自主研发的具有优异防裂防渗抗震性能的新结构材料，其极限拉应变可稳定地达到3%至6%。本项目拟采用高掺量粉煤灰大量替代水泥，运用微纳米技术和双掺技术相结合的方法，开展UHTCC材料水化硬化过程纳微观结构实验观测，利用微晶成核效应、非均相诱导激活效应、粉煤灰的二次水化特性和微集料效应改善基体和界面性能，有效提升UHTCC材料初裂强度、极限抗拉强度、抗压强度等力学性能，同时提升密实性、抗渗性、抗冻性等耐久性能。进行UHTCC材料力学性能实验，建立高掺量粉煤灰UHTCC材料的微细多缝开裂及应变硬化过程全程分析的应力应变本构方程，提出微细裂缝间距与宽度及断裂能密度计算分析方法，采用性能驱动设计新方法，研制新一代UHTCC材料。实现材料与结构研究一体化、纳-微-宏观改性一体化和工业废料的高端高效利用，大幅提高结构的耐久性和使用寿命。

超高韧性水泥基复合材料（UHTCC）是一种具有优异变形能力的乱向短纤维增韧水泥基材料，设计时常将粉煤灰作为胶凝材料替代部分水泥加入UHTCC中。但粉煤灰反应活性较低、水化速度较慢，从而一定程度影响UHTCC材料早期强度及耐久性能。本研究通过掺加纳米SiO2得到具有高强、高韧及高耐久性的高性能水泥基材料，研究成果对于工业废料的高效高端利用，大幅减少水泥用量，节约资源，减少污染，降耗减排具有十分重要的社会意义和应用价值。具体研究内容及成果如下：.1、研究了纳米SiO2对UHTCC材料工作性能、干缩性能、孔结构、力学性能的影响，通过孔结构复合体模型分析了纳米SiO2的增强机理，得到了满足工程需要的材料配合比。.2、通过纳米SiO2对UHTCC材料水化产物、微观形态的影响，研究了UHTCC的强度形成机理，发现了纳米SiO2对水泥粉煤灰的活性激化作用。与未掺纳米SiO2的UHTCC材料相比，胶凝材料的水化反应速度快、强度高、早期强度增长快；随着纳米SiO2掺量的逐渐增加，粉煤灰水化程度不断提高，Ca(OH)2含量显著降低。.3、研究了混杂纤维对纳米SiO2改性UHTCC材料的增韧机理，以单根纤维拔出性能为基础，得到了构件裂缝面混杂纤维桥连应力计算公式，通过多缝开裂下的纤维桥连模型提出了混杂纤维体积掺量的上限判断标准，为应变硬化材料配比设计提供了一种有效分析方法。.4、研究了纳米SiO2改性UHTCC材料的耐久性能，发现随着纳米SiO2掺量的增加，UHTCC材料相对渗透系数显著降低，耐久性能得到明显改善。配筋UHTCC梁的抗海水侵蚀能力远高于配筋混凝土梁，该材料在海岛建设项目中具有广阔应用前景。.5、研究了高温对于纳米SiO2改性UHTCC材料微观结构及力学性能的影响，发现该材料在高温下不发生爆裂，当温度达到600℃时材料微观结构才开始出现劣化。将纳米SiO2改性UHTCC材料作为钢筋混凝土柱的外包防火材料，能显著提升钢筋混凝土柱残余强度及抗爆能力。