冻融循环条件下地聚合物混凝土劣化规律及机理研究

Geopolymer, the product of aluminium-silicon material reacting with high alkalinity solutions, is a new type of cementitious materials. Compared to Portland cement, geopolymer exhibits more excellent performance, and it is also an environmental-friendly material with a low carbon emission during preparation and utilization. Consequently, the prospect of application should be highlighted. It is important to further understand and improve the durability of the geopolymer concrete if the mechanism and process of structural damage under freeze-thaw cycles are systematically studied. This project aims to investigate the deterioration principles and damage mechanism of geopolymer concrete under freeze-thaw cycles based on two key parameters, pore structures and water saturation, which greatly affect the resistance ability of freeze-thaw cycles of the concrete. Thermoporometry based on capillary condensation is supposed to be used to measure the real size of pores and pore size distribution (1nm-100nm). COMSOL can be applied to simulate the moisture transport in the pores as well as.the damage process of concrete due to freezing and thawing actions, thereby to analyse the deterioration mechanism. Through a reasonably comprehensive research on the geopolymer concrete under freeze-thaw cycles, therefore, the multiscale characterization of structure and properties will be conducted from macro-mesoscopic-micro aspects.To set up a bridge between the microscopic structures and macroscopic properties,a model will be established to describe the deterioration regularity based on the study of influence of synergetic factors on the frost resistance of the concrete. The results of the project will give scientific supports to the application of geopolymer concretes in the engineering.

地聚合物是一种利用硅铝质原料和高碱溶液反应制备的新型无机胶凝材料，与硅酸盐水泥相比，其性能优异，制备和使用过程环保、低碳，应用前景广阔。系统地研究地聚合物混凝土的冻融破坏过程及机理，对于加深理解和改善其耐久性有重要意义。本项目围绕冻融循环条件下地聚合物混凝土劣化规律和破坏机理这一科学问题，从孔结构和水饱和度这两个影响混凝土抗冻融破坏能力的关键参数入手，采用Thermoporometry方法分析混凝土孔结构分布，利用COMSOL软件模拟水分在混凝土中的迁移及混凝土的冻融破坏过程，分析冻融破坏机理，对其结构与性能进行宏观-细观-微观多尺度综合表征，建立其劣化规律与各影响因素间的函数关系及地聚合物混凝土劣化模型，搭建起描述微观结构与宏观性能之间量化关系的桥梁，揭示其冻融破坏机理。为地聚合物混凝土的工程应用提供理论基础和科学依据。

地聚合物是一种利用硅铝质原料和高碱溶液反应制备的新型无机胶凝材料，系统地研究地聚合物混凝土的冻融破坏过程及机理，对于改善其耐久性及推广应用有重要意义。本项目通过对冻融循环条件下地聚合物混凝土劣化规律和破坏机理的研究，从地聚合物混凝土的配合比，体系组成及养护制度等影响因素入手，对其孔结构及水饱和度进行多尺度综合表征，建立了地聚合物混凝土结构与性能的损伤规律与各影响因素间的函数关系及抗冻性预测模型。.实验结果表明：地聚合物混凝土的孔结构及水饱和系数与普通硅酸盐水泥混凝土有较大差异，地聚合物混凝土的小尺寸孔主要分布在10nm-100nm之间，通常其水饱和系数大于0.8，临界水饱和系数为0.6左右；冻融过程中，地聚合物混凝土水分逐渐向内部迁移导致水饱和系数增大。硅铝比，钠铝比会影响地聚合物的密实程度及反应程度，进而影响地聚合物混凝土的抗冻性，在冻融过程中，地聚合物混凝土的质量损失率与相对动弹性模量的降低是不同步的，当质量损失率达到5%时，其相对动弹性模量还保持在60%以上；通过研究地聚合物混凝土微观结构与宏观性能之间的量化关系，发现偏高岭土基地聚合物混凝土冻融破坏机理主要是水结冰压力引起裂缝扩展导致结构由表及里的破坏，含钙矿物掺合料可以改善其抗冻性，钙基地聚合物混凝土冻融破坏机理是水结冰压力与温度疲劳应力共同作用下引起裂缝扩展导致结构由表及里的破坏；以地聚合物混凝土的质量损失率和水饱和系数作为衡量破坏的指标，建立了以质量损失为参数的双段损伤模型，及水饱和系数变化为参数的单段损伤模型，并根据损伤模型对地聚合物混凝土的极限冻融循环次数及使用寿命进行理论预测，搭建起地聚合物混凝土冻融破坏的微观结构与宏观性能之间量化关系的桥梁。.在上述研究的基础上，对地聚合物混凝土在盐冻环境中的破坏机理进行了拓展研究。研究结果发现，氯盐环境加速了地聚合物混凝土的冻融破坏过程，钢渣、矿渣等含钙矿物掺合料提高了地聚合物混凝土极限冻融循环次数。