【作者】 杨礼明；

【导师】 余红发；

【作者基本信息】 南京航空航天大学 ， 道路与铁道工程， 2013， 博士

【摘要】 混凝土耐久性问题十分复杂，既是实际土木工程中不可忽视的重大技术问题，又是当今国内外混凝土学术界重点关注的重大科技问题。硫酸盐、氯盐和镁盐等化学腐蚀问题，干湿循环引起的盐结晶问题和外部荷载引起的应力腐蚀问题，以及盐结晶与应力腐蚀等耦合作用，都是影响混凝土耐久性的重要因素。本文在参考了大量文献的基础上，优化配合比设计，综合运用矿物掺合料的复合效应、高效外加剂的减水和引气作用、膨胀剂补偿收缩作用和纤维增强作用等技术，制备了粉煤灰混凝土（Fly ash concrete，FAC）、高性能混凝土（High performanceconcrete，HPC）和绿色高耐久性混凝土（Green high durable concrete，GHDC），研究了不同混凝土在化学腐蚀、盐结晶、应力腐蚀以及盐结晶和应力腐蚀耦合作用下的相对动弹性模量和质量变化规律、表面剥蚀形态、腐蚀产物和显微结构变化，建立了混凝土的表面剥蚀等级变化规律、腐蚀损伤演化方程、腐蚀裂纹密度模型以及基于裂纹密度时空演变的快速寿命预测方法，为混凝土材料耐久性评估与设计提供理论参考。本文的主要研究内容和结果如下：第一章综述了混凝土在化学腐蚀、盐结晶、应力腐蚀以及盐结晶和弯曲应力腐蚀耦合作用下耐久性问题和寿命预测方法研究的意义和最新进展，指出当前存在的问题，在此基础上提出本文的主要研究内容和方向。第二章详细介绍了混凝土原材料、配合比设计、混凝土制备、试验主要仪器和试验方法，设计了施加混凝土试件轴拉与轴压应力的耐久性实验装置。设计了4种C50混凝土：粉煤灰（Fly ash，FA）掺量20%的FAC，复合掺加40%FA、10%磨细矿渣（Slag，SG）和5%硅灰（SilicaFume，SF）的HPC，在HPC基础上综合采用混杂纤维、膨胀剂和引气剂的GHDC，其中，GHDC1采用（聚丙烯＋钢纤维）二元混杂纤维，GHDC2采用（聚丙烯＋聚酯纤维＋钢纤维）三元混杂纤维。第三章主要研究了混凝土在氯盐、硫酸盐-镁盐和硫酸盐-镁盐-氯盐环境下的化学腐蚀作用。结果表明：氯盐对混凝土不存在化学腐蚀作用；硫酸盐-镁盐对混凝土产生明显的化学腐蚀作用；硫酸盐-镁盐-氯盐对混凝土产生的化学腐蚀作用比硫酸盐-镁盐环境下严重；氯盐加速硫酸盐-镁盐对混凝土的化学腐蚀作用。GHDC2具有较好的抗硫酸盐-镁盐腐蚀和硫酸盐-镁盐-氯盐腐蚀能力。第四章主要研究了混凝土在氯盐、硫酸盐-镁盐和硫酸盐-镁盐-氯盐环境下的盐结晶腐蚀作用。结果表明：氯盐对混凝土不存在明显的盐结晶腐蚀作用；硫酸盐-镁盐对混凝土产生明显的盐结晶腐蚀作用；硫酸盐-镁盐-氯盐对混凝土产生的盐结晶腐蚀作用比硫酸盐-镁盐环境下严重；盐结晶加速硫酸盐-镁盐对混凝土的化学腐蚀作用，氯盐加速硫酸盐-镁盐环境下混凝土的盐结晶腐蚀作用，HPC具有较好的抗硫酸盐-镁盐和硫酸盐-镁盐-氯盐盐结晶腐蚀能力。第五章主要研究了混凝土在氯盐、硫酸盐-镁盐和硫酸盐-镁盐-氯盐环境下的应力腐蚀作用。结果表明：氯盐对混凝土不存在应力腐蚀作用；硫酸盐-镁盐对混凝土产生明显的应力腐蚀作用，应力状态对混凝土的应力腐蚀破坏作用有重要影响。混凝土在相同应力水平、不同应力状态下的硫酸盐-镁盐腐蚀损伤速度大小为：拉应力腐蚀>压应力腐蚀>弯曲应力腐蚀>化学腐蚀。硫酸盐-镁盐-氯盐对混凝土产生的弯曲应力腐蚀作用比硫酸盐-镁盐环境下严重；弯曲应力加速硫酸盐-镁盐对混凝土的化学腐蚀作用，氯盐加速硫酸盐-镁盐环境下混凝土的应力腐蚀作用。HPC具有较好的抗硫酸盐-镁盐拉/压应力腐蚀能力和抗硫酸盐-镁盐-氯盐弯曲应力腐蚀能力，GHDC2的抗硫酸盐-镁盐弯曲应力腐蚀能力较强。第六章研究了混凝土在氯盐、硫酸盐-镁盐和硫酸盐-镁盐-氯盐环境下的盐结晶和应力腐蚀耦合作用。结果表明：氯盐对混凝土不存在盐结晶和应力腐蚀耦合作用；硫酸盐-镁盐对混凝土产生明显的盐结晶和应力腐蚀耦合作用；硫酸盐-镁盐-氯盐对混凝土产生的盐结晶与弯曲应力腐蚀的耦合破坏作用比硫酸盐-镁盐环境下严重；硫酸盐-镁盐和硫酸盐-镁盐-氯盐环境下，盐结晶和弯曲应力腐蚀的耦合产生叠加效果，盐结晶与弯曲应力腐蚀两者相互促进；氯盐加速硫酸盐-镁盐和硫酸盐-镁盐-氯盐环境下混凝土的盐结晶和弯曲应力腐蚀耦合作用。GHDC2具有较好的抗硫酸盐-镁盐盐结晶和弯曲应力腐蚀耦合破坏能力，FAC和HPC具有较好的抗硫酸盐-镁盐-氯盐盐结晶与弯曲应力腐蚀耦合破坏能力。第七章采用XRD和SEM-EDAX方法研究了混凝土的腐蚀产物和显微结构变化。结果发现：混凝土内部的腐蚀产物主要是石膏、AFt、AFm、C3A·CaCl2·10H2O和氢氧化镁；根据不同混凝土在多种腐蚀条件下的SEM图，提出导致混凝土内部微裂纹产生和扩展的“起裂元”新概念，微裂纹沿着起裂元周围呈星形辐射状引发、扩展、连生、贯通成裂纹网络；矿物掺合料发生了火山灰反应，导致混凝土结构更加致密，提高了混凝土的抗腐蚀能力；掺加引气剂形成的球形气孔能够大量地释放气孔附近区域腐蚀微裂纹的扩展表面能，降低腐蚀微裂纹尖端的应力集中程度，减少混凝土腐蚀过程中的膨胀应力和结晶应力，有助于混凝土抗腐蚀能力的进一步提升。第八章总结大量试验结果和数据分析的基础上，建立混凝土腐蚀过程中的内部损伤演化方程，并在损伤演化方程的基础上进一步推导，获得混凝土内部裂纹密度模型，得到混凝土在多种腐蚀条件下损伤过程中内部微裂纹的时空演变规律和特征；建立了运用损伤演化方程和裂纹密度演化方程预测腐蚀环境下混凝土寿命的方法，与实测值比较发现：运用混凝土损伤演化方程和裂纹密度损伤演化方程快速预测混凝土的腐蚀寿命，是切实可行的，其中裂纹密度损伤演化方程的预测效果会更好。第九章总结全文结论和创新点，提出了本文研究的不足之处和改进的建议。更多还原

【Abstract】 Durability of concrete is a complicated, important and major scientific issue concerned at homeand abroad. Effect of chemical attack caused by sulfate, chloride, magnesium etc, salt crystallizationattack caused by dry-wet cycles, stress attack caused by applied loading, and combined action of saltcrystallization attack and stress attack on concrete durability is very important. In this study, based on anumber of reference, optimization proportion design and incorporating with synergistic effect ofmineral admixture, water reducing and air-entraining properties of concrete admixture, shrinkagecompensation functions of expansion agent and reinforcing effects of fibers, fly ash concrete (FAC),high performance concrete (HPC) and green high durability concrete (GHDC) were prepared. The lawsof the changes of relative dynamic modulus of elasticity (Erd) and surface spalling, corrosion productsand evolution of microstructure under the chemical attack, slat crystallization, stress attack and thecoupling effect of slat crystallization and stress attack were investigated. Changes of visual rating of thedeterioration, damage evolution equation, a theoretical model of density of cracks and a method forservice life of concretes based on density of cracks were established. The main contents and results ofthis paper are as follows:In Chapter1, the research significance and latest development of durability of concretes exposedto chemical attack, slat crystallization attack, stress attack and the coupling effect of slat crystallizationattack and stress attack and service life predicting methods were summarized. Problems remaining tobe investigated were also proposed, and outline of this contribution was sketched.In Chapter2, raw materials, mix design, major experimental equipment and method ofexperiment were described in detail and equipments on durability experiment for applying tensilestress and compressive stress were designed. Four types of C50concrete were prepared. They areFAC incorporated with20%FA by mass of cement, HPC incorporated with fly ash (FA), slag (SG)and silica fume (SF), in which dosage of supplementary binder is10%FA+20%SG+20%SF by massof cement, and GHDC based on HPC and then incorporated fibers, expansion agent and Air-entrainedagent. For different fibers added in, GHDC was denoted as GHDC1that was incorporated steel fiberand polypropylene fiber and GHDC2that was incorporated steel fiber, polypropylene fiber andpolyester fiber.In Chapter3, the chemical attack to concrete exposed to chloride, magnesium sulfate andsulfate-magnesium-chloride was investigated. There is no chemical attack to concrete exposed tochloride. Chemical attack is severe to concrete exposed to magnesium sulfate and that is more severe toconcrete exposed to sulfate-magnesium-chloride. Chemical attack to concrete exposed to magnesiumsulfate is accelerated by chloride. GHDC2shows good durability tunder chemical attack caused bymagnesium sulfate and sulfate-magnesium-chloride.In Chapter4, the salt crystallization attack to concrete exposed to chloride, magnesium sulfate andsulfate-magnesium-chloride was investigated. There is no salt crystallization attack to concrete exposedto chloride. Salt crystallization attack is severe to concrete exposed to magnesium sulfate and that ismore severe to concrete exposed to sulfate-magnesium-chloride.. Chemical attack to concrete is accelerated by salt crystallization and salt crystallization attack to concrete exposed to magnesiumsulfate is accelerated by chloride. HPC shows good durability under salt crystallization attack causedby magnesium sulfate and sulfate-magnesium-chloride.In Chapter5, the stress attack to concrete exposed to chloride, magnesium sulfate andsulfate-magnesium-chloride was investigated. There is no stress attack to concrete exposed to chloride.Stress attack is severe to concrete exposed to magnesium sulfate. The effect of stress state is veryimportant to stress attack. When in the same stress level but different stress state, the value of thedamage velocity to concrete is tensile stress> compressive stress> bending stress. Stress attack is moresevere to concrete exposed to sulfate-magnesium-chloride than that exposed to magnesium sulfate.Chemical attack to concrete exposed to magnesium sulfate is accelerated by compressive stress andbending stress attack to concrete exposed to magnesium sulfate is accelerated by chloride. HPCexposed to sulfate magnesium shows good durability under tensile stress attack and compressive attackand GHDC2exposed to sulfate magnesium and sulfate-magnesium-chloride displays good durabilityunder bending stress attack.In Chapter6, the coupling effect of slat crystallization attack and stress attack on concrete exposedto chloride, magnesium sulfate and sulfate-magnesium-chloride was investigated. There is no couplingeffect of slat crystallization attack and stress attack on concrete exposed to chloride. The couplingeffect of slat crystallization attack and stress attack is severe to concrete exposed to magnesium sulfateand that is more severe to concrete exposed to sulfate-magnesium-chloride. The coupling effect of slatcrystallization attack and stress attack brings superposition effect that means accelerating the chemicalattack to concrete more quickly. Slat crystallization accelerates the bending attack to concrete andbending stress accelerates the salt crystallization attack to concrete. The coupling effect of slatcrystallization attack and stress attack on concrete exposed to magnesium sulfate is accelerated bychloride. Exposed to sulfate magnesium, GHDC2shows good durability under the coupling effect ofslat crystallization attack and stress attack. Exposed to sulfate-magnesium-chloride, FAC and HPCdisplay good durability under the coupling effect of slat crystallization attack and stress attack.In Chapter7, corrosion products and the evolution of microstructure were investigated by usingXRD and SEM-EDAX. Results show that the major corrosion products are gypsum, AFt, AFm,C3A·CaCl2·10H2O and magnesium hydroxide. Base on a number of SEM pictures about differentconcrete exposed to different corrosion condition, the new concept of “Microcrack Initiation” is presentand along which the microcrack grows as a star, develops and connects to form a net of cracks. Thepozzolanic reaction of mineral admixture compact the structure and improve the corrosion resistance ofconcrete. The spherical pore for addition of air-entrained agent releases surface developing energy ofmicrocracks that near the spherical pore, decreases stress concentration of tip of microcracks, reducesthe expansion stress and crystal stress during corrosion process, and improves further the corrosionresistance.In Chapter8, based on the results of concrete experiments on durability and experiment dataanalysis, a damage developing equation of Erd was established, and then, a quick service life predictingmethod based on density of cracks were established further. The laws of evolution of micro-cracksduring corrosion process under different corrosion environment. Results show that the conclusions ofdamage developing equation and service life predicting method match the experiment results and fit thepractical engineering. The service life predicting method based on density of cracks show more well results.In Chapter8，a summarization of this contribution was presented and the shortcomings of thisstudy and proposition for further researches were listed.更多还原