【作者】 李扬；

【导师】 李可；

【作者基本信息】 郑州大学 ， 防灾减灾工程及防护工程， 2024， 硕士

【摘要】 传统混凝土结构所用的硅酸盐水泥能耗大,碳排放量高,不利于土木工程行业的绿色与可持续发展。超高韧性地聚合物复合材料(Engineered Geopolymer Composites,EGC)是一种利用工业固体废弃物制备的绿色高性能建筑复合材料,具有低能耗的特征以及优良的延性、韧性与控裂性能。特别地,EGC细密的裂缝特性有利于材料的自愈合,从而提高结构的耐久性,极大降低维护成本。然而,EGC在外部碱性环境下的自愈合行为尚不明确,这阻碍了 EGC在碱性环境下(例如大量化工建筑,盐碱地区基础设施等)的应用和维护。因此,本文探究EGC在碱性环境下的自愈合行为,旨在发现新型绿色的EGC损伤修复方法。考虑不同预损伤程度、不同碱性环境、不同自愈合龄期,分析EGC自愈合过程中裂缝数量与宽度、抗拉强度、延性以及损伤因子等自愈合指标的变化情况;同时采用晶相分析等微观检测技术,研究裂缝愈合后的微观形貌及愈合产物的演变规律,揭示不同碱性环境下EGC的自愈合机理。本文主要研究内容及结论如下:(1)与无损伤EGC相同,损伤EGC在碱性环境自愈合后也表现出应变硬化与多缝开裂行为,其单轴拉伸应力-应变关系曲线可分为三个阶段:弹性阶段、应变硬化与多缝开裂阶段、应变软化阶段。(2)考虑不同的预损伤程度、碱性环境、自愈合龄期影响,进行了预损伤EGC自愈合性能试验。结果表明:在饱和Ca(OH)2溶液中EGC的自愈合性能最佳,7%及以下浓度的NaOH溶液次之,但7%以上浓度NaOH与空气环境下自愈合性能较差。EGC试件裂缝的愈合主要发生在前7d,之后愈合速率变缓;延性也在7d时达到最大值,之后略有降低。预损伤应变在3%及以下的EGC在Ca(OH)2溶液中愈合28d后的延性可超过无损标准养护试件,抗拉强度恢复率达到87.0%以上,裂缝数量减少72.7%以上,最大裂缝宽度下降40.0%以上;在7%及以下浓度NaOH溶液中,EGC的裂缝、强度与延性的恢复率随着NaOH浓度的增加有略微提升,随着自愈合龄期的增加而上升;浓度过高(7%以上)的NaOH溶液不利于EGC的自愈合,会使得EGC在7d之后裂缝数量随着愈合时间增加而上升,延性恢复率随愈合龄期增长而降低,且预损伤应变较大的试件延性恢复较差;在空气环境中,EGC裂缝愈合效果、强度与应变的恢复效果均较差。(3)提出了一种基于共振频率的损伤因子计算方法,用于评价EGC的损伤程度。EGC在饱和Ca(OH)2溶液中的损伤因子降幅最大(即损伤恢复效果最佳),在7%及以下浓度的NaOH溶液次之,在7%以上浓度NaOH与空气环境下最小。随着时间增长,EGC的损伤因子随时间的降低速率(即损伤随时间的恢复速率)不断减小,EGC损伤恢复主要发生在前7d;EGC损伤恢复率随着EGC预损伤程度的提高而略有增加。另外,基于连续因子建立了 EGC修正指数型自愈合演化本构方程。(4)揭示了EGC在碱性环境下的自愈合机制。EGC的自愈合产物主要包括水化硅铝酸钠(N-A-S-H)、水化硅铝酸钙(C-A-S-H)凝胶及部分CaCO3,基质中未反应的前驱体是形成愈合产物的主要物质来源。空气、不同浓度的NaOH溶液与Ca(OH)2溶液中EGC愈合产物的种类没有明显差异。然而,7%及以下浓度的NaOH溶液和Ca(OH)2溶液更有利于愈合产物中N-A-S-H和C-A-S-H凝胶的形成;14%及以上浓度的NaOH溶液则不利于这些凝胶的形成。更多还原

【Abstract】 Silicate cement used in traditional concrete structures has high energy consumption and carbon emissions,which is not conducive to the green and sustainable development of the civil engineering industry.Engineered Geopolymer Composites(EGC)is a kind of green high-performance building composites prepared by utilizing industrial solid waste,which has the characteristics of low energy consumption as well as excellent ductility,toughness and crack control properties.In particular,the fine cracking characteristics of EGC facilitate the self-healing of the material,which improves the durability of the structure and greatly reduces the maintenance cost.However,the self-healing behaviour of EGC in external alkaline environments is unclear,which hinders the application and maintenance of EGC in alkaline environments(e.g.,a large number of chemical buildings,infrastructures in saline areas,etc.).Therefore,the self-healing behaviour of EGC in alkaline environments with the aim of discovering novel and green methods for EGC damage repair were explored in this paper.Considering different pre-damage degrees,different alkaline environments,and different self-healing ages,the changes of self-healing indexes,such as the number and width of cracks,tensile strength,ductility,and damage factor in the self-healing process of EGC were analyzed.The microscopic morphology of cracks after healing and the evolution of healing products were studied by crystal phase analysis and other microscopic detection techniques.Therefore,the self-healing mechanism of EGC under different alkaline environments was revealed.The main research contents and conclusions of this paper are as follows:(1)Similar to nondamaged EGC,damaged EGC also exhibited strain hardening and multi-seam cracking behaviour after self-healing in alkaline environment,and their uniaxial tensile stress-strain relationship curves could be divided into three stages:elastic stage,strain hardening and multi-seam cracking stage,and strain softening stage.(2)Considering the effects of different pre-damage degree,alkaline environment,and self-healing age,a pre-damaged EGC self-healing performance test was conducted.The results showed that the best self-healing performance of EGC was achieved in saturated Ca(OH)2 solution,followed by NaOH solution of 7%and below,but the selfhealing performance was poorer in the environment of more than 7%NaOH and air,and the healing of cracks in EGC specimens mainly occurred in the first 7d,and then the healing rate slowed down,and the ductility reached its maximum value in 7d.and then slightly decreased.The ductility of EGC with pre-damage strains of 3%and below healed in Ca(OH)2 solution after 28d could exceed that of the nondamaged standardconditioned specimens,and the recovery rate of tensile strength reached more than 87.0%,the number of cracks was reduced by more than 72.7%,and the maximum width of the cracks was decreased by more than 40.0%;the recovery rates of the cracks,strengths,and ductility of EGC in NaOH solutions with concentrations of 7%and below increased slightly with the increase of the NaOH concentration,and rose with the increase of self-healing age:excessive concentration(above 7%)of NaOH solution was not conducive to the self-healing of EGC.which would make the number of cracks in EGC rise with the increase of the healing time after 7d.and the recovery rate of the ductility decreased with the increase of the healing age,and the recovery rate of the ductility of the specimen with a large pre-damage strain was poorer;in air environment,the cracks of EGC healing effect,strength and strain recovery were poor.(3)A resonance frequency-based damage factor calculation method was proposed for evaluating the damage degree of EGC.The rate of decrease of damage factor of EGC was greatest(i.e.,the best damage recovery)in saturated Ca(OH)2 solution,followed by NaOH solution at 7%and lower concentrations,and was smallest in the environment of more than 7%concentration of NaOH with air.The rate of decrease of damage factor with time(i.e.,the rate of damage recovery with time)of EGC decreased with time,and the EGC damage recovery mainly occurred in the first 7d;the EGC damage recovery rate increased slightly with the increase of the degree of EGC predamage.In addition,the EGC modified exponential self-healing evolutionary ontological equation was established based on the continuum factor.(4)The self-healing mechanism of EGC in alkaline environment was revealed.The self-healing products of EGC mainly include hydrated sodium silica-aluminate(NA-S-H),hydrated calcium silica-aluminate(C-A-S-H)gel and part of CaCO3,and the unreacted precursors in the matrix are the main source of substances for the formation of healing products.There was no significant difference in the types of EGC healing products in air,NaOH solutions of different concentrations and Ca(OH)2 solutions.However,NaOH solutions with concentrations of 7%and below and Ca(OH)2 solutions were more favorable for the formation of N-A-S-H and C-A-S-H gels in the healing products;NaOH solutions with concentrations of 14%and above were unfavorable for the formation of these gels.更多还原