纳/微米多孔内养护材料对高性能混凝土自收缩的影响及作用机理

Internal curing technique is one most effective mitigation strategy of autogenous shrinkage of high performance concrete (HPC). However, due to the difficulty in dispersion of two most commonly used internal curing agents (LWAs and SAPs) in the cement matrix and their negative effect on the early-age mechanical properties of HPC, it is necessary to seek alternative internal curing agent, which shows no/minor negative effect on the mechanical property with high dispersion property. The study on the influence of above-mentioned alternative internal curing agents on the autogenous shrinkage of HPC and its mitigation mechanism is of crucial for improving the durability of modern concrete..Based on the high pozzolanic activity and porous nature of biomass ash, this project plans to study the effect of combustion process on the physico-chemical properties and pore structure of biomass ash, aiming to propose one preparation method for porous biomass material. By applying hierarchical compounding and compatibility approach, a nano/micro hierarchical porous material that suitable for internal curing is produced. Furthermore, the effect of nano/micron porous material on the mechanical property, hydration mechanism, microstructure evolution, and volume deformation of HPC is investigated to reveal the mitigation mechanism of self-desiccation and autogenous shrinkage in HPC by applying nano/micro porous material for internal curing..The results will not only propose new ideas for the preparation of internal curing agent suitable for HPC, but also provide theoretical basis for advancing solution strategy involved in the autogenous shrinkage cracking and durability issues of HPC. Meanwhile, it can realize the recycling and functional utilization of biomass ash, supplying theoretical and technical support for the environment-friendly and sustainable development of cement-based materials.

内养护技术是抑制高性能混凝土自收缩的最有效方法之一，针对轻集料和超吸水树脂等存在的难分散和不利于混凝土早期强度的技术瓶颈，开展高分散、对早期强度无或较小不利影响的内养护材料制备方法、及其对高性能混凝土自收缩的影响及抑制机理等的研究对于提升现代混凝土耐久性至关重要。.基于生物质焚烧灰的高火山灰活性和多孔特性，本研究旨在探明燃烧工艺参数对生物质焚烧灰的理化特性及孔结构的影响，提出基于孔的分级复合与配伍的纳/微米多孔内养护材料的制备方法。同时，研究纳/微米多孔内养护材料对高性能混凝土的水化过程与微观结构演变规律以及早期体积变形等的影响，揭示其对高性能混凝土内部自干燥及自收缩的抑制机制。.研究成果不仅为制备高性能混凝土内养护材料提供新思路，为解决高性能混凝土自收缩开裂及耐久性问题提供理论基础与技术支撑；同时还能实现生物质焚烧灰的资源化和功能化利用。

内养护技术是抑制高性能混凝土自收缩的最有效方法之一。针对轻集料和超吸水树脂等存在的难分散和不利于混凝土早期强度的技术瓶颈，基于生物质焚烧灰的高火山灰活性和多孔特性以及孔的分级复合配伍理念，开展了面向高性能水泥基材料的纳/微米多孔内养护材料开发与性能研究。主要研究了燃烧工艺对生物质稻壳焚烧灰的理化特性及孔结构的影响规律，形成了适宜于高性能水泥基材料内养护用高火山灰活性稻壳灰孔结构调控方法。最佳制备工艺为：燃烧温度为600℃，升温速率10℃/min，保温时间1h即可得到SiO2含量达到94%、比表面积为105m2/g的高火山灰活性与多孔结构稻壳灰。制得的稻壳灰经粉磨30min后以10%掺量加入水泥基材料能细化硬化水泥石孔径尺寸，降低孔隙率，有利于力学性能发展。进一步研究了纳米级多孔生物质灰与微米级SAPs复合内养护材料在水泥浆体中的吸水、释水过程，探讨了其对高性能水泥基材料水化特性、力学性能、微观结构及收缩性能的影响规律。研究发现当SAP/RHA为1:1时，纳/微米多孔内养护材料不仅能有效抑制自收缩的发展，同时对力学性能发展影响减小。.通过上述研究，本项目提出了易于分散且利于力学性能发展的纳/微米多孔内养护材料的制备方法，并探明了其内养护机制。研究成果将为制备高性能混凝土内养护材料提供新思路，并为解决高性能混凝土自收缩开裂及耐久性问题提供理论基础与技术支撑，对于提升现代混凝土耐久性至关重要。