再生混合混凝土早龄期抗压性能及微观结构试验研究

发布时间：2018-04-18 16:29

本文选题：再生混合混凝土 + 废弃混凝土块体　；参考：《广州大学》2017年硕士论文

【摘要】：随着社会经济的飞速发展,大量房屋建筑不断兴建耗费了巨量的新混凝土,同时大量旧有建筑物的拆除也产生了巨量的废弃混凝土。为了保护自然环境,实现建筑业的可持续发展,回收废弃混凝土以减少新混凝土的生产势在必行。再生混合混凝土是一种新的废弃混凝土回收利用形式,其由大尺度废弃混凝土块体和新混凝土混合浇筑而成,将废弃混凝土的回收利用从骨料层次上升为块体层次,更加简化、高效、节能。本文在已有研究的基础上,开展了龄期和废弃混凝土块体取代率对再生混合混凝土抗压性能的影响研究,利用扫描电镜对再生混合混凝土的微观结构进行了观察分析,主要包括以下工作:分别对60个再生混合混凝土立方体试件和60个再生混合混凝土圆柱体试件进行了单轴抗压试验,研究了废弃混凝土块体取代率(0、10%、20%、30%)和龄期(1d、3d、7d、14d、28d)等因素对再生混合混凝土抗压性能(抗压强度、弹性模量、峰值应变)的影响。对试验数据进行了拟合分析,建立了龄期与再生混合混凝土抗压强度、弹性模量等因素的关系式,得到了再生混合混凝土圆柱体试件抗压强度与立方体试件抗压强度之间的转换系数。研究结果表明:(1)在废弃混凝土块体抗压强度高于新混凝土抗压强度情况下,随着废弃混凝土块体取代率的增大,再生混合混凝土的抗压强度不断增大,弹性模量先增大后减小,峰值应变先减小后增大;(2)当废弃混凝土块体取代率保持不变时,随着龄期的不断增加,再生混合混凝土的抗压强度和弹性模量不断增大,而峰值应变不断减小;(3)废弃混凝土块体的取代率对再生混合混凝土圆柱体试件抗压性能的影响小于立方体试件,再生混合混凝土圆柱体试件抗压强度与立方体试件抗压强度之间的转换系数较普通混凝土小;(4)基于拟合公式的计算结果与试验数据吻合较好。利用扫描电镜等仪器设备,对再生混合混凝土的微观形貌进行了观察,研究了再生混合混凝土微观结构随龄期的变化,揭示了龄期对抗压性能影响的微观本质。对比分析了新、旧水泥石基体的形貌特征及其水化产物,观察了新—旧水泥石界面过渡区、新水泥石—新骨料界面过渡区与旧水泥石—旧骨料界面过渡区等的微观结构,对新、旧水泥石基体以及新—旧水泥石界面过渡区进行了定量分析。与抗压试验结果相联系,初步分析研究了龄期影响再生混合混凝土宏观抗压性能的微观机理。试验结果表明:(1)新混凝土与废弃混凝土块体能够良好结合,新—旧水泥石基体界面过渡区较为致密,而废弃混凝土块体内部在使用前已存在部分缺陷,旧水泥石—旧骨料为再生混合混凝土最薄弱的环节;(2)随着龄期的不断增长,水化产物C-S-H凝胶、Ca(OH)2和AFt晶体等不断生长及相互搭接使得基体结构不断致密,填充了部分裂纹,宏观上表现为再生混合混凝土抗压性能的增强。
[Abstract]:With the rapid development of social economy, a large number of housing buildings continue to build a huge amount of new concrete, at the same time, a large number of old buildings demolition also produced a huge amount of abandoned concrete.In order to protect the natural environment and realize the sustainable development of the construction industry, it is imperative to recycle the waste concrete to reduce the production of new concrete.Recycled mixed concrete is a new form of recycling waste concrete, which is made of large scale waste concrete block and new concrete mixed pouring. The recycling and utilization of recycled concrete is increased from aggregate level to block level, which is more simplified.High efficiency and energy saving.On the basis of the existing research, the influence of age and the replacement ratio of abandoned concrete blocks on the compressive performance of recycled mixed concrete is studied, and the microstructure of recycled mixed concrete is observed and analyzed by scanning electron microscope (SEM).The main contents are as follows: 60 recycled concrete cube specimens and 60 recycled mixed concrete cylindrical specimens are tested under uniaxial compression.The influence of the replacement rate of abandoned concrete blocks (0 / 10) and the age of 1 day / 3 d / 7 d / 14 d / 28d on the compressive strength, elastic modulus and peak strain of recycled concrete are studied.The fitting analysis of test data was carried out, and the relationship between age and compressive strength and elastic modulus of recycled mixed concrete was established.The conversion coefficient between the compressive strength of recycled concrete cylindrical specimens and the compressive strength of cubic specimens is obtained.The results show that when the compressive strength of abandoned concrete blocks is higher than that of new concrete blocks, the compressive strength of recycled mixed concrete increases with the increase of the replacement ratio of abandoned concrete blocks, and the elastic modulus increases first and then decreases.When the replacement rate of abandoned concrete blocks remains constant, the compressive strength and elastic modulus of recycled mixed concrete increase with the increase of age.The effect of replacement rate of abandoned concrete blocks on the compressive performance of recycled concrete cylindrical specimens is smaller than that of cubic specimens.The conversion coefficient between the compressive strength of recycled concrete cylindrical specimens and the compressive strength of cubic specimens is better than that of ordinary concrete. The calculated results based on the fitting formula are in good agreement with the experimental data.The microscopic morphology of recycled mixed concrete was observed by means of scanning electron microscope and other instruments. The change of microstructure of recycled mixed concrete with age was studied, and the microscopic essence of the influence of age on compressive resistance of recycled mixed concrete was revealed.The morphology and hydration products of the new and old cement-stone matrix were compared and analyzed. The microstructure of the new and old cement-stone interface transition zone, the new cement-new aggregate interface transition zone and the old cement-old aggregate interface transition zone were observed.The interfacial transition zone of old cement matrix and new-old cement stone was quantitatively analyzed.In connection with the results of compressive tests, the microscopic mechanism of age affecting the macroscopic compressive properties of recycled mixed concrete was analyzed and studied.The experimental results show that the new concrete and the abandoned concrete block can be well combined, the interface transition zone between the new and the old cement stone matrix is relatively compact, but there are some defects in the waste concrete block before the use of the new concrete block.Old cement stone and old aggregate are the weakest link of recycled mixed concrete. With the increasing of age, the hydration products, such as C-S-H gel, CaOHH2 and AFt crystals, grow and overlap with each other so that the matrix structure becomes compact and some cracks are filled.Macroscopically, the compressive performance of recycled mixed concrete is enhanced.
【学位授予单位】：广州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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