基于刚性骨架结构的SAP内养护材料多重释水调控及作用机制研究

High early self-desiccation and autogenous shrinkage are the main engineering problems of concrete with low water to cement ratio (w/c). Superabsorbent polymer (SAP) has a strong potential for these problems. However, the difficulty of early desorption regulation of SAP and the negative effect of released pores greatly limits the actual effect of internal curing, and has been the common challenges for internal curing. In present project, a novel PM/SAP composite with rigid skeleton structure (PM) would be designed. The composite structure with SAP gels filled and assembled in the PM skeleton would be built. Desorption environment of SAP would be changed and the contact proportion of SAP with cement matrix would be controlled. The chemically controlled water release of SAP and the graded desorption of porous PM framework would be used to multiply control the desorption behavior of PM/SAP composite and improving the internal curing efficiency; Based on the strengthening effect of interfacial transition zone (ITZ) around PM/SAP, coupling the mechanical bearing capacity of in-situ PM skeleton, the negative effect of macro pores left by SAP and diffusion pores by rapid desorption on mechanical performance and permeability could be effectively eliminated; On this basis, the internal curing designing and controlling method based on PM/SAP composite would be obtained. The present project aims to establish a new design theory and method for desorption regulation of PM/SAP composite, and propose a new idea to fulfill the basic theory for internal curing of concrete.

自干燥程度高、易收缩开裂是低水胶比混凝土材料面临的重要工程问题。高吸水树脂（SAP）内养护在补缩抗裂方面潜力巨大。然而，SAP存在早期释水行为难调控及释水孔负面效应的共性难题，极大限制了内养护的实际效果。本项目拟设计一种无机刚性骨架（PM）组装SAP的复合材料（PM/SAP），构建SAP凝胶与分级多孔PM骨架的穿插组装结构，调控SAP与水泥基体的接触比例，利用SAP的化学调控释水及分级多孔PM骨架的梯度物理释水，实现PM/SAP复合结构的多重释水调控及内养护水的高效率利用；基于PM/SAP释水界面区强化效应，协同PM骨架的原位承载作用，有效控制SAP释水宏观孔及扩散孔对水泥基材料力学及渗透传输的负面效应；在此基础上，形成基于PM/SAP复合材料的内养护设计与调控方法。项目旨在建立基于骨架结构的PM/SAP释水调控理论与方法，为丰富内养护混凝土基础理论提供新思路。

项目聚焦高吸水树脂（SAP）在水泥基材料内部存在早期释水行为难调控及释水孔负面效应的共性问题，构建一种无机刚性骨架（PM）组装SAP的复合材料（PM/SAP），围绕PM/SAP材料的微结构设计制备及表征、PM/SAP的水分迁移调控机理及内养护效率研究、PM/SAP界面区结构形成机理及其强化机制开展研究。明确了PM骨架对液态SAP凝胶的负载组装机理，建立了PM/SAP互穿骨架结构设计及制备方法，通过常压吸附及负压吸附两种手段，将SAP凝胶负载进入PM骨架孔隙中“原位聚合”，合成了基于刚性骨架的SAP有机无机复合材料；探明了PM/SAP在水泥基材料中的水分自调控机理及水分传输模型，发现PM骨架减小了SAP与水泥基材料的接触面积，从而有效延缓了SAP的释水速率，提高SAP在水泥基体中的内养护水有效利用率；PM/SAP通过其中SAP释水后留下的刚性骨架，有效保证了后期力学性能，同时通过改善SAP的释水过程对其早期快速释水进行了有效调节，不仅提升了补偿收缩的能力，而且使得早期的扩散孔减少，显著提升了抗氯离子渗透能力；研究了PM/SAP界面区结构及性质的强化机制，发现PM/SAP界面区具有更高的自由水含量、水化程度、显微硬度值，及更低的毛细孔含量；建立了PM/SAP的全过程释水模型，分别为在塑性阶段SAP与水泥基体少量接触时有离子渗透压控制的自由水释放；在水泥水化湿度降低毛细管压力增加时，由毛细管压力及湿度共同控制的SAP水蒸气散发阶段；在水泥水化的后期随着湿度的进一步降低，毛细管压力逐渐稳定此时主要是由湿度变化控制的内部SAP以水蒸气的形式扩散阶段。