SAP在超高性能混凝土中释水和内养护机理

Ultra high performance concrete (UHPC) with high amount of cementitious material and low water/binder ratio shows great self-desiccation shrinkage. Super absorbent polymer (SAP) as an internal curing agent can effectively reduce or eliminate self-desiccation shrinkage, but the water release and internal curing mechanisms of SAP are still unclear. In this proposed project, the effects of water release of SAP with different amounts and particle sizes on the strength, internal humidity and self-desiccation shrinkage of UHPC and the hydration of cementitious material will be analyzed. The internal relationships between internal humidity, self-desiccation shrinkage and amount of water release of SAP and between amount of water release of SAP, internal humidity, porosity and hydration degree are established. Moreover, the microstructural characterizations of SAP water release area are revealed by comparing the composition and micromechanics of hardened paste in the different areas. On the basis of the analysis of the above results, the mechanisms of release water and internal curing of SAP will be proposed. Those results from this study will provide some theoretical bases for the preparation and engineering applications of UHPC.

超高性能混凝土（UHPC）因胶凝材料用量多和水胶比低表现出显著的自收缩，而用高吸水树脂（SAP）做内养护剂能有效减少或消除自收缩，但其释水和内养护机理还不太清楚。本课题将研究SAP粒径和掺量对UHPC强度、自收缩、内部湿度、胶凝材料水化和SAP作用区域内硬化浆体组成与微观力学的影响规律，阐明SAP释水、混凝土内部湿度与自收缩和SAP释水量、内部湿度、毛细孔率与水化程度间内在联系，建立胶凝材料水化动力学，揭示硬化浆体的微观结构特征，从而提出SAP释水和内养护机理，为UHPC制备和工程应用提供理论依据。

高吸水树脂（SAP）是一种能有效降低超高性能混凝土（UHPC）自收缩的内养护剂，但其释水和内养护机理还不太清楚。本课题开展了SAP在低水胶比水泥浆体中的吸水行为及SAP吸水对UHPC流变性影响，SAP释水与UHPC物理性能、内部湿度梯度、水化及孔结构的关系，SAP孔与胶凝材料基体间界面区特征和SAP释水与内养护机理等研究。发现水胶比对SAP在浆体过滤液中吸水影响不大，但会影响到低水胶比浆体中吸水，使浆体的屈服应力、塑性粘度和触变性增大；SAP的蓄水改变了体系自由水含量随时间的变化，使UHPC内部保持较高的IRH，并延缓IRH变化，降低了临界毛细孔径和毛细孔力，从而使自收缩明显降低或开始时间后移；SAP释水降低了干燥深度，促进了水化，降低孔隙率，细化了孔径，改善了抗渗性，后期供水可进一步发挥SAP积极作用；SAP对强度的影响取决于SAP对水分蒸发、水化程度及SAP孔的影响，在初始加水量相同时，水分蒸发量的降低和水化程度的提高可以弥补SAP孔的不利影响；SAP失水形成SAP孔，SAP孔和水泥基体之间界面区由内、外界面区组成，外界面区与基体组成相似，但微观力学强度较高，而界面区由基体水化离子扩散到SAP孔边沿形成CSH层构成，且孔隙率在向SAP孔放向逐渐增加。SAP粒径增加会进一步提高水化程度，降低自收缩和改善抗渗性，且在干燥条件下SAP孔增加对强度不利影响减弱。当减缩剂与SAP复合使用时，自收缩进一步降低了，SAP对干缩和强度的有利影响增强。总体而言，SAP对UHPC自收缩及干缩的影响与其对自由水调控和临界毛细孔径降低有关，SAP对强度、孔结构、渗透性及SAP孔周围的界面过渡区的影响与SAP对水化的贡献有关。