纤维素纤维混凝土耐久性、高温抗爆裂及徐变特性

发布时间：2018-06-29 14:04

本文选题：纤维素纤维混凝土(CFRC) + 内养护　；参考：《东南大学》2015年硕士论文

【摘要】：纤维素纤维是继化学合成纤维之后发展起来的第三代混凝土工程专用植物纤维,原料取自于高寒地区的某种特殊植物,有非常高的强度/质量比,亲水性好在混凝土拌合物中易分散。纤维素纤维混凝土(Cellulose fiber reinforced concrete,简称CFRC)具有抗裂性好、耐久性优异的特性。然而,要推广CFRC在工程中的应用,需要对其性能开展系统研究。本文针对隧道衬砌结构的服役环境,通过原材料优选、配合比设计及成型工艺的优化,制备了满足隧道衬砌结构承载力要求和耐久性能要求的CFRC,对CFRC在弯拉荷载与环境因素共同作用下的耐久性、抗高温爆裂和受压徐变性能进行了试验研究。首先,探索了纤维素纤维作为混凝土内养护纤维与混凝土耐久性提升措施的可行性与可靠性。采用激光共聚焦显微镜与SEM研究了纤维素纤维的空腔结构,测试了纤维片的饱和吸水率、纤维素纤维单丝的力学性能(主要包括拉伸强度和初始弹性模量)、纤维素纤维的吸水特性对水化进程的影响,定量评价了纤维在基体中的分散程度,并观测了纤维在硬化浆体中的形貌。结果表明,纤维素纤维具有独特的空腔结构和良好的吸水性,可以在混凝土中均匀分散,纤维空腔所吸收的自由水对混凝土的水化进程不产生影响,可以作为混凝土的内养护纤维。采用应力水平为40%的弯拉荷载与单一环境因素共同作用,研究了CFRC的抗氯离子渗透性、抗冻性、抗碳化和抗硫酸盐侵蚀等关键耐久性能。结果表明：弯拉荷载与单一环境因素共同作用下CFRC的耐久性均优于未加荷载同环境因素作用下的基准素混凝土的耐久性。而荷载作用在试件内部引入了微结构损伤,使得荷载作用下的耐久性相比于未加荷载的耐久性指标均有不同程度的削弱,冻融循环300次后相对动弹性模量下降了8.4%；电通量增加了17%；3d、7d、14d和28d时的碳化深度分别增加了0.2mm、0.7mm、0.6mm和n1.3mm。其次,研究了CFRC在300℃、600℃、800℃和1050℃下分别恒温2.5h、4h和5.5h后的高温抗爆裂性能,并通过SEM、MIP、热分析和XRD物相分析等微观测试技术分析了高温作用后混凝土的微观结构劣化规律与宏观性能衰减的对应关系及高温抗爆裂机理。结果表明：纤维素纤维可以显著提高CFRC的高温抗爆裂性能。300℃时温度接近纤维熔点,纤维已经出现软化体积减小,使基体孔隙率增加,此时恒温时间对CFRC的力学性能影响最显著,恒温时间越久,纤维软化留下的孔隙体积越大,混凝土力学性下降越显著。此时,基准素混凝土的力学性能损失率为2.3%～33.7%,纤维素纤维混凝土的力学性能损失率为3.0%～29.2%。温度超过800℃后,恒温时间的影响不再明显。微观测试结果表明：随着温度的升高,混凝土中水化产物不断脱水分解,基体由致密粘结逐渐分散变得疏松,骨料与基体界面出现裂缝,逐渐发展,最后贯穿。这个过程在宏观上表现为物理力学性能的不断损失,直至丧失承载能力。温度达到纤维素纤维熔点后,纤维熔化,在基体中留下很多孔道,虽然在一定程度上降低了混凝土试件的强度,但减轻了CFRC内部的蒸汽压力,提高混凝土的高温抗爆裂性能。最后,研究了纤维素纤维掺量为0、0.9kg/m3、1.1kg/m3、1.3kg/m3的混凝土在40%应力水平下的受压徐变,并对CEB-FIP(2010)的徐变模型进行修正,引入纤维的影响变量,对四个系列混凝土的长期徐变变形性能进行了预测。试验与预测结果表明：纤维素纤维可以减小混凝土的受压徐变变形,用于徐变试验的试件养护龄期越长,纤维越能有效减小混凝土的徐变变形。纤维对混凝土徐变性能的影响主要受纤维在混凝土中的分散、纤维与基体之间的界面层缺陷和纤维释放内部水分促进周围基体水化的内养护效用共同影响,与纤维掺量和养护龄期密切相关。通过引入纤维影响参量对CEB-FIP(2010)的徐变模型进行修正,采用修正后的模型对纤维素纤维混凝土长龄期的徐变应变进行了预测。本文创新点在于：提出了纤维素纤维在混凝土中的分散程度定量测试与评价技术、揭示了纤维素纤维作为混凝土内养护纤维的可行性,探明了CFRC在弯拉荷载与环境因素共同作用下的耐久性以及高温抗爆裂性能与受压徐变性能,建立了纤维素纤维混凝土受压徐变模型。试验与理论研究结果可以为纤维素纤维混凝土在复杂服役环境下的工程应用提供技术支撑。
[Abstract]:Cellulose fiber is the third generation of concrete plant fiber developed after the chemical synthetic fiber. The raw material is taken from some special plant in the alpine region. It has a very high strength / mass ratio, and the hydrophilicity is easy to disperse in the concrete mixture. Cellulose fiber reinforced concrete, abbreviated as CF RC) has the characteristics of good crack resistance and excellent durability. However, in order to promote the application of CFRC in engineering, it is necessary to carry out a systematic study of its performance. In this paper, according to the service environment of the tunnel lining structure, the bearing capacity and durability of the tunnel lining structure are prepared through the optimization of the raw materials, the mix proportion design and the molding process. The required CFRC is tested on the durability of CFRC under the joint action of bending load and environmental factors, high temperature cracking and compression creep. First, the feasibility and dependability of cellulose fiber as a curing fiber and concrete durability are explored. The laser confocal microscope and SEM are used to study the durability of the concrete. The cavity structure of cellulose fiber was used to test the saturated water absorption of the fiber, the mechanical properties of the cellulose fiber monofilament (mainly including tensile strength and initial modulus of elasticity), the influence of the water absorption properties of cellulose fiber on the hydration process, quantitatively evaluated the dispersion of the fiber in the matrix, and observed the fiber in the hardened pulp. The results show that the cellulose fiber has a unique cavity structure and good water absorption, which can be dispersed uniformly in concrete. The free water absorbed by the fiber cavity has no effect on the hydration process of concrete. It can be used as the internal curing fiber of concrete. The flexural tensile load of 40% stress level is combined with a single environmental factor. In the same effect, the key durability of CFRC is studied, such as resistance to chloride ion permeability, frost resistance, carbonation resistance and sulphate resistance. The results show that the durability of CFRC under the combined action of bending load and single environmental factor is better than that of standard plain concrete under the action of unloaded and environmental factors. The microstructural damage was introduced, which made the durability of the load weakened to some extent compared to the durability index of the non load. The relative dynamic modulus of elasticity decreased by 8.4% after 300 times of freezing and thawing cycle, and the electrical flux increased by 17%; the carbonization depth of 3D, 7d, 14d and 28d increased respectively by 0.2mm, 0.7mm, 0.6mm and n1.3mm., respectively, and studied C The cracking properties of FRC at 300, 600, 800, and 1050, respectively, at 2.5h, 4H and 5.5h, respectively. The corresponding micro testing techniques such as SEM, MIP, thermal analysis and XRD phase analysis were used to analyze the relationship between the microstructure deterioration and the high temperature resistance of concrete after high temperature action and the mechanism of high temperature resistance. Vitamin fiber can significantly improve the high temperature resistance of CFRC at.300 C, the temperature is close to the melting point of fiber. The softening volume decreases and the porosity of the matrix increases. At this time, the constant temperature time has the most significant influence on the mechanical properties of CFRC. The longer the constant temperature time is, the larger the pore volume is, the more the mechanical property of the concrete decreases. At this time, the loss rate of the mechanical properties of the reference concrete is 2.3% ~ 33.7%, the loss rate of the mechanical properties of cellulose fiber concrete is 3% ~ 29.2%. over 800 degrees C, and the effect of the constant temperature time is no longer obvious. The bond gradually dispersed and loose. The interface between the aggregate and the matrix appears crack, gradually developing, and running through. This process shows the loss of physical and mechanical properties at the macroscopic level, until the melting point of cellulose fiber is reached. The fiber melts and leaves a lot of channels in the matrix, although it is reduced to a certain extent. The strength of the concrete specimen is reduced, but the steam pressure inside CFRC is relieved and the high temperature resistance of concrete is improved. Finally, the compressive creep of the concrete with cellulose fiber content of 0,0.9kg/m3,1.1kg/m3,1.3kg/m3 under the 40% stress level is studied, and the creep model of CEB-FIP (2010) is corrected, and the influence variables of the fiber are introduced. The long-term creep deformation performance of four series of concrete is predicted. Experimental and prediction results show that cellulose fiber can reduce the compressive creep deformation of concrete. The longer the curing age of the specimen is used in the creep test, the more the fiber can effectively reduce the creep deformation of concrete, the effect of fiber on the creep properties of concrete is mainly fiber. The dispersion in the concrete, the interfacial layer defects between the fiber and the matrix and the internal moisture content of the fiber released to promote the internal curing effect of the hydration of the surrounding matrix are closely related to the fiber content and curing age. The modified model is used to modify the CEB-FIP (2010) model by introducing the fiber influence parameters. The creep strain of fibrous concrete for long period of age is predicted. The innovation point of this paper is that the quantitative measurement and evaluation technology of the dispersion degree of cellulose fiber in concrete is put forward, and the feasibility of cellulose fiber as the curing fiber in concrete is revealed, and the durability of CFRC under the joint action of the bending load and the environmental factors is explored. The compressive creep model of cellulose fiber reinforced concrete is established, and the experimental and theoretical results can provide technical support for the engineering application of cellulose fiber concrete in complex service environment.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528.572

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