基于纳米材料的活性粉末混凝土及其基本力学性能研究

发布时间：2018-06-07 08:19

本文选题：活性粉末混凝土 + 碳纳米管　；参考：《浙江大学》2016年博士论文

【摘要】：活性粉末混凝土(Reactive Powder Concrete,简称RPC)是根据最紧密堆积原理,采用高致密水泥基均匀体系模型,将直径为400～600微米的石英砂作为骨料,同时掺入适量短纤维和活性矿物制备出的具有超高强度、高耐久性、高韧性的水泥基材料。RPC材料以其优异的力学性能在土木建筑、水利、矿山、桥梁以及军事工程等领域有着广阔的应用前景。本文首先对国内外RPC材料基本力学研究进行综述,发现工程中常用的RPC材料的强度仍然较低且韧性不足,不能充分发挥RPC材料的优势。因此,探索一种兼具高强度和高韧性的RPC对有效减轻混凝土结构物的自重、提高结构物的耐久性、降低工程造价以及推广RPC材料应用具有重要的工程意义。首先,本研究采用表面活性剂、超声波和离心机处理可以得到稳定达到1个月以上的纳米材料预分散液,并将其分散至水泥净浆中。试验结果表明水泥基复合材料的抗压强度、抗弯强度与纳米材料掺量(0.025 wt%～0.2wP/%)有关,0.1 wt%掺量的碳纳米管可将水泥基材料的7天和28天抗压强度提升22%和15%。纳米材料掺量较低时,水泥基复合材料的强度随着其掺量的提高而提升,且对水泥基材料早期强度提升明显,而高掺量的纳米材料会降低水泥基材料的性能。断裂实验表明石墨烯和碳纳米管的加入可以大幅度提高水泥基材料的断裂能和断裂韧度。微观分析表明碳纳米管、石墨烯/氧化石墨烯材料可以将水化产物连接在一起,有效减少有害孔隙的数量,其增强与增韧的机理主要是晶核效应、桥联、拔出与填充效应。其次,由于RPC材料是由多种胶凝材料组成,本研究根据国内常用普通水泥及其辅助胶凝材料,同时配合以不同的投料顺序和高、低速搅拌方法,得到具有高流动度的RPC浆料。本研究同时探索出高温干热养护增强RPC材料的合理工艺方法,并对比分析了常温养护、湿热养护和高温干热养护条件下RPC力学性能发展规律的影响,并对RPC水泥水化产物的种类和形态、材料收缩进行了分析,得到了高温养护下的增强机理。再次,以往研究大多通过提高纤维的用量来提升RPC的韧性,但是相比于超高的抗压强度,RPC材料直接拉伸强度仍然不足10 MPa。过多的增加钢纤维的用量并不会提高基体开裂强度和峰值强度,还会造成RPC材料流动性变差等问题。本研究在钢纤维增强RPC材料的基础上,利用碳纳米管对RPC基体进行改性,研究不同种类、掺量的钢纤维和碳纳米管对RPC抗压、抗折、直接拉伸和四点弯曲等力学性能的影响,探索二者对水泥基复合材料的增强增韧机理。结果表明碳纳米管的加入可以有效提高RPC材料的强度指标,掺有0.025wPt%碳纳米管的RPC材料的抗压强度和弯曲开裂强度较对照组分别提高了 7.2%和36%,直接拉伸试件的开裂强度和极限强度均提高8%以上。微观分析表明碳纳米管可以有效的在微观尺度上延缓初始裂纹的产生和发展,多壁碳纳米管在裂缝扩张为宏观裂缝时逐渐失去作用,转而由横跨于裂缝之间的钢纤维来承担荷载作用,这两种纤维可以在材料破坏的不同阶段发挥各自的作用,起到优势互补的阻裂效果。通过合理的配合比和搅拌工艺,RPC材料的抗压强度和抗折强度可以达到208 MPa和45 MPa,单轴直接抗拉强度达到10 MPa以上,采用异形钢纤维RPC材料的峰值拉伸应变可以达到0.4%以上。最后,研究通过采用SHPB(Split Hopkinson Pressure Bar,霍普金森压杆)试验装置对RPC材料进行了冲击动力学试验,利用高速相机与数据同步采集系统得到了试样动态劈裂应力时程曲线和破坏形貌,并分析了碳纳米管的掺量和不同种类的钢纤维对RPC基体的增强增韧效果。试验表明碳纳米管的加入可以提升RPC试件的动态劈裂强度和耗能效果,在较低打击气压下碳纳米管的增强效果显著。随着碳纳米管掺量的增多,其增强效果逐渐减弱。RPC中的钢纤维在冲击劈裂荷载作用下存在明显的桥联阻裂作用,可有效提高基体高速变形下的抗拉伸损伤能力。长直钢纤维RPC动态劈拉强度可以达到35 MPa以上,较基体提高了 26.1%,且试件冲击荷载作用下基本能够保持完整。基体与钢纤维之间的粘结性状和剪切强度是控制劈裂破坏的主要因素,而非钢纤维本身抗拉强度。试验并采用DIC方法计算得到了动态变形场并验证了巴西圆盘试验的有效性,结果表明裂缝的开裂时间约为峰值荷载前40μs,动态加载下Y方向峰值应变达到1%以上,碳纳米管的加入可以提高材料的强度和耗能能力。
[Abstract]:Reactive Powder Concrete (RPC) is a cement-based material with high strength, high durability and high toughness by adding a high compact cementitious homogeneous system model and using quartz sand with a diameter of 400~600 microns as aggregate, and adding a proper amount of short fiber and active minerals to the aggregate, according to the most compact packing principle. With its excellent mechanical properties, C has a broad application prospect in the fields of civil engineering, water conservancy, mine, bridge and military engineering. This paper first summarizes the basic mechanics research of RPC materials at home and abroad, and finds that the strength of the commonly used RPC materials in the engineering is still low and the toughness is insufficient, and the advantages of the RPC materials can not be fully exploited. Therefore, it is important to explore a kind of RPC with high strength and high toughness, which can effectively reduce the weight of the concrete structure, improve the durability of the structure, reduce the cost of the project and popularize the application of RPC material. First, this study can achieve more than 1 months by using surfactants, ultrasonic and centrifuge treatment. The experimental results show that the compressive strength of the cement-based composites is related to the nano material content (0.025 wt% ~ 0.2wP/%), and the 0.1 wt% content of carbon nanotubes can increase the compressive strength of the cement based materials at 7 and 28 days by 22% and lower the content of the 15%. nanomaterials. The strength of the clay based composites is enhanced with the increase of its content, and the early strength of the cement-based material is enhanced obviously. The nano materials with high content will reduce the properties of the cement-based materials. The fracture experiments show that the addition of graphene and carbon nanotubes can greatly improve the fracture energy and fracture toughness of the cement-based materials. Carbon nanotubes, graphene / graphene oxide materials can connect the hydrated products together and effectively reduce the number of harmful pores. The mechanism of strengthening and toughening is mainly the effect of nucleation, bridging, pulling and filling. Secondly, the RPC material is made up of a variety of cementitious materials. This study is based on common cement and its auxiliary in common use in China. At the same time, the RPC slurry with high fluidity was obtained with different feeding order and high low speed stirring method. The reasonable process method of strengthening RPC material was explored at the same time, and the development law of mechanical properties of RPC under the condition of normal temperature curing, wet and hot curing and high temperature dry and hot curing was compared and analyzed. In addition, the types and forms of RPC cement hydration products and the shrinkage of the material are analyzed, and the strengthening mechanism under high temperature curing is obtained. Again, most of the previous studies have improved the toughness of RPC by increasing the amount of fiber, but the direct tensile strength of the RPC material is still less than 10 MPa. to increase the steel fiber by comparing with the ultra high compressive strength. The amount of vitamin D does not increase the crack strength and peak strength of the matrix, but also causes the poor fluidity of the RPC material. On the basis of the steel fiber reinforced RPC material, the carbon nanotube is used to modify the RPC matrix, and the different kinds of steel fiber and carbon nanometers are used to study the compression, bending, direct stretching and four point bending of RPC. The strengthening and toughening mechanism of the two kinds of cement based composites is explored by the influence of the mechanical properties. The results show that the addition of carbon nanotubes can effectively improve the strength of the RPC materials. The compressive strength and the bending cracking strength of the RPC materials with 0.025wPt% carbon nanotubes are improved by 7.2% and 36% compared with the control components. The fracture strength and ultimate strength are increased by more than 8%. Microanalysis shows that the carbon nanotubes can effectively delay the formation and development of the initial cracks at the micro scale. The multi wall carbon nanotubes gradually lose their function when the cracks expand into macro cracks, and then take the loading action of the steel fibers that cross the cracks. These two fibers can be used. The compressive strength and flexural strength of RPC material can reach 208 MPa and 45 MPa through reasonable mix ratio and stirring process, and the tensile strength of the uniaxial direct tensile strength reaches more than 10 MPa, and the peak tensile strain of the hetero steel fiber RPC material can reach to the peak tensile strain. To more than 0.4%. Finally, the impact dynamic test of RPC material was carried out by using SHPB (Split Hopkinson Pressure Bar, Hopkinson pressure bar) test device. The dynamic splitting stress time history curve and broken morphology were obtained by the high-speed camera and the data synchronous acquisition system, and the content and difference of the carbon nanotube were analyzed. The strengthening and toughening effect of the steel fiber on the RPC matrix shows that the addition of carbon nanotubes can enhance the dynamic splitting strength and energy dissipation effect of the RPC specimen. The enhancement effect of the carbon nanotubes is remarkable under the lower barometric pressure. With the increase of the amount of carbon nanotubes, the enhancement effect gradually reduces the impact splitting load of the steel fiber in the.RPC. The tensile strength of the long straight steel fiber RPC can reach more than 35 MPa and 26.1% more than that of the matrix. The bond property and shear strength between the base and the steel fiber can be maintained completely under the impact load of the specimen. It is the main factor controlling splitting failure, not the tensile strength of the steel fiber itself. The dynamic deformation field is calculated by the DIC method and the validity of the Brazil disc test is verified. The results show that the cracking time of the crack is about 40 s before the peak load, the peak strain of Y is over 1% under dynamic loading, and the addition of carbon nanotubes is added. It can improve the strength and energy dissipation of the material.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU528

【参考文献】