【作者】 李阳；

【导师】 李守义； 王瑞骏；

【作者基本信息】 西安理工大学 ， 水工结构工程， 2018， 博士

【摘要】 将废旧混凝土循环再生作为骨料制备再生混凝土既可解决其堆置与环境污染问题,又可弥补天然骨料日益短缺的不足。然而,在多种环境侵蚀因素复合作用下再生混凝土的耐久性研究成果十分欠缺,直接影响再生混凝土在实际工程中的应用。因此,对其进行深入系统研究非常必要,这与我国可持续发展的基本国策和建设绿色节约型社会是相一致的。本文运用室内试验和理论分析相结合的方法,选取自然环境下影响再生混凝土结构耐久性的主要环境因素(冻融循环、硫酸盐及二氧化碳),开展了再生混凝土冻融循环试验、冻融循环与硫酸盐侵蚀双重作用试验、冻融循环与碳化双重作用试验,并采用电镜扫描、X射线衍射及核磁共振技术等新型检测手段,对再生混凝土复合侵蚀前后的微观结构特征进行了深入系统地分析。在此基础上,以提高再生混凝土的耐久性能为目标,进行了再生骨料最优取代率及粉煤灰最优掺量等问题的研究。本文的主要研究内容包括:(1)针对不同再生骨料取代率及不同粉煤灰掺量的再生混凝土试件,运用试验方法,进行了其力学性能和流动性能的研究,探讨了再生混凝土宏观力学性能变化的内在原因,分析并揭示了其与普通混凝土在材料性能上的差异机理。(2)采用试验研究的方法,对不同再生骨料取代率以及不同粉煤灰掺量下再生混凝土抗冻性能进行测试,分析了冻融循环作用下再生混凝土质量损失率、相对动弹模量以及抗压强度的变化规律,揭示了再生骨料取代率以及粉煤灰掺量对于再生混凝土抗冻性的影响机理,建立了综合考虑再生混凝土材料参数、冻融循环作用影响的耐久性损伤模型。(3)针对不同再生骨料取代率及不同粉煤灰掺量的再生混凝土试件,设计并开展冻融循环和硫酸盐侵蚀双重作用下再生混凝土耐久性试验,研究了冻融循环和硫酸盐侵蚀双重作用下混凝土质量损失率、相对动弹模量及抗压强度的变化规律,分析了冻融循环和硫酸盐侵蚀双重作用下再生混凝土损伤机理。采用紫外分光测试法,研究了冻融循环和硫酸盐侵蚀双重作用下再生混凝土硫酸盐传输性能的变化规律。通过引入再生混凝土复合损伤影响系数λ,分析了硫酸盐侵蚀对再生混凝土抗冻性能的影响机理;建立了综合考虑再生混凝土材料参数、冻融循环和硫酸盐侵蚀双重作用影响的耐久性损伤模型。(4)针对不同再生骨料取代率及不同粉煤灰掺量的再生混凝土试件,设计并开展冻融循环和碳化双重作用下再生混凝土耐久性试验,研究了冻融循环和碳化双重作用下再生混凝土碳化深度、质量损失率、相对动弹模量及抗压强度的变化规律,定量揭示了再生混凝土在冻融环境中碳化作用速率与混凝土抗压强度之间的关系,探讨了冻融循环和碳化双重作用下再生混凝土损伤机理。引入再生混凝土复合损伤影响系数λc,分析了碳化作用对再生混凝土抗冻性能的影响;引入再生混凝土复合损伤影响系数λF,分析了冻融循环对混凝土碳化性能的影响;建立了综合考虑再生混凝土材料参数、冻融循环和碳化双重作用影响的耐久性损伤模型。(5)采用核磁共振技术,考虑再生骨料取代率与粉煤灰掺量的影响,对复合侵蚀作用前后的再生混凝土孔隙结构进行分析,探索了复合侵蚀作用下再生混凝土的孔隙率与孔隙分布的演变规律,揭示了复合侵蚀作用下再生混凝土的孔隙微观损伤特性,为复合侵蚀作用下再生混凝土耐久性的研究提供了一种新的方法和思路。(6)采用电镜扫描、X射线衍射与X射线能谱仪等微观测试技术手段,分析了复合侵蚀作用下再生混凝土微观结构裂缝的发展过程、内部界面过渡区的结构演化、主要侵蚀产物生长的发展过程、主要侵蚀生成物的结构形态和特征,并对反应的生成物进行定量化的分析,从微观角度揭示了复合侵蚀作用下再生混凝土损伤劣化机理。本文的研究工作可弥补再生混凝土耐久性劣化机理解释及模型构建方面的不足,可以为再生混凝土在复合侵蚀作用下耐久性劣化特性研究及服役寿命预测提供理论基础与技术支撑,对完善再生混凝土耐久性理论研究体系具有一定意义。更多还原

【Abstract】 Recycling waste concrete to prepare recycled aggregate concrete(RAC)can not only solve the problems of construction waste stacking and environmental pollution,but also make up for the shortage of natural aggregate resources.However,the research results of durability of RAC under the combined action of various environmental erosion factors are very little,which directly affect the application of RAC in practical engineering.Therefore,it is necessary to study it systematically,which is consistent with the basic national policy of sustainable development and the construction of a green conservation-oriented society.In this paper,the main environmental factors(freeze-thaw cycle,sulfate attack and carbon dioxide)affecting the durability of RA C structure were selected by using the method of laboratory test and theoretical analysis.The freeze-thaw cycle test,combined action of freeze-thaw cycle and sulfate attack test,combined action of freeze-thaw cycle and carbonization test were carried out.The microstructure characteristics of RAC before and after composite erosion were analyzed systematically by using scanning electron microscope(SEM),X-ray diffraction(XRD)and nuclear magnetic resonance(NMR)technology.On this basis,in order to improve the durability of RAC,the optimal replacement ratio of RAC aggregate(RCA)and optimal content of fly ash were studied.The main contents of this paper include:(1)According to the RAC specimens with different replacement ratio of RCA and different fly ash content,the mechanical properties and flow properties of RAC were studied by using the test method.The internal reasons for the change of macroscopic mechanical properties of RAC were discussed,and the difference mechanism between RAC and ordinary concrete in material properties was analyzed and revealed.(2)The frost resistance was studied on RAC with different replacement ratio of RCA and different fly ash content.The change law of mass loss,relative dynamic modulus of elasticity(RDME)and compressive strength of RAC under freeze-thaw cycle was analyzed.The influence mechanism of replacement ratio of RCA and fly ash content on frost resistance of RAC was revealed.The durability damage model was established considering the influence of RAC material parameters and freeze-thaw cycle.(3)According to the RAC specimens with different replacement ratio of RCA and different fly ash content,the durability test of RAC subjected to the combined action of freeze-thaw cycle and sulfate attack was designed and carried out.The change laws of mass loss,RDME and compressive strength of concrete were studied,and the damage mechanism of RAC was analyzed.The variation of sulfate transport performance of RAC under combined action of freeze-thaw cycle and sulfate attack was studied by ultraviolet spectrophotometer.The influence mechanism of sulfate solution on frost resistance of RAC was analyzed by introducing the coefficient of λ.A durability damage model considering the effects of RAC material parameters,combined action of freeze-thaw cycle and sulfate attack was established.(4)According to the RAC specimens with different replacement ratio of RCA and different fly ash content,the durability test of RAC under the combined action of freeze-thaw cycle and carbonization was designed and carried out.The carbonation depth,mass loss rate,RDME and compressive strength of RAC were studied.The relationship between carbonation rate and compressive strength of RAC under freeze-thaw environment was quantitatively revealed.The damage mechanism of RAC was discussed.The influence coefficient λC of composite damage of RAC was introduced,and the influence of carbonization on frost resistance of RAC was analyzed.The influence coefficient λF of composite damage of RAC was introduced,and the influence of freeze-thaw cycle on carbonation performance of concrete was analyzed.A durability damage model considering the effects of RAC material parameters,combined action of freeze-thaw cycle and carbonization was established.(5)By using NMR,considering the influence of RCA replacement ratio and fly ash content,the pore structure of RAC before and after composite erosion was analyzed.The evolution of porosity and pore distribution of RAC under composite erosion was explored.The pore micro-damage characteristics of RAC under composite erosion were revealed,which provided a new method and idea for the study of the durability of RAC under composite erosion.(6)By means of SEM,XRD and EDS,the development process of micro-structure cracks,the structure evolution of interface transition zone in concrete,the growth process of main erosion products,the structure form and characteristics of main erosion products were analyzed.The quantitative analysis of the erosion products were carried out and the damage and deterioration mechanism of RAC under composite erosion were revealed from micro-angle.The research work in this paper can make up for the defects of the mechanism explanation and model construction of the durability damage of RAC.It provides theoretical basis and technical support for the study of the durability degradation characteristics and service life prediction of RAC under the action of composite erosion,and has certain significance for perfecting the theoretical research system of the durability of RAC.更多还原