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    Properties of wet-mixed fiber reinforced shotcrete and fiber reinforced concrete with similar

    Abstract

    Fiber reinforced shotcrete (FRS) is commonly used in slope protection, tunnel linings as well as structural repair and rehabilitation. For the design of shotcrete mixes, it is of interest to see if data on fiber reinforced concrete (FRC) can be employed as an initial guideline. In this study, various properties of FRS, including its compressive strength, flexural behavior, permeability and shrinkage behavior, are compared with FRC of similar composition. The results, based on five different mixes, indicate that the fabrication process (i.e., shotcreting vs. casting) can significantly affect compressive strength and permeability, but has relatively little effect on shrinkage behavior. The flexural strength of FRS is slightly higher than that for FRC in most cases, but the residual load carrying capacity in the postcracking regime can be significantly lower. Based on the differences in the properties of FRC and shotcrete, implications to material design are discussed. D 2004 Elsevier Ltd. All rights reserved.

    纤维加固喷浆(FRS)是常用的护坡原料,用于隧道衬砌以及结构修复。 为设计混合喷浆,通过看纤维混凝土(FRC)数据, 我们可以看到有意思的是, 纤维混凝土(FRC)可用于初次指引方式。 在这项研究中,各种性能的FRS,包括其抗压强度,抗折性能,渗透性和收缩行为, 比较了FRC类似的组成。结果表明基于五种不同组合,显示了制备工艺(即 喷浆与铸造),可以大大影响组件压杆强度和透气性,但对收缩行为相对影响不大。在大多数情况下,抗折强度FRS略高于FRC,但残余的承载能力在断裂的允许范围内,可以大大降低。基于不同性能的FRC和FRS,影响着材料的设计与讨论。

    Keywords Shotcrete; Fiber reinforcement; Flexural behavior; Permeability; Shrinkage

    关键字喷射;增强纤维;弯曲的行为;浸透性;收缩

    1. Introduction 介绍

    Shotcrete finds applications in many construction processes.Common examples include the repair and rehabilitation of concrete structures, the building of tunnel linings,as well as the stabilization of rock and soil slopes. To prevent cracking of the shotcrete layer, steel mesh is often placed before the shotcreting operation. The placing of mesh is a labor-intensive and time-consuming process. Moreover,the presence of mesh may result in a ‘shadowing’ effect,leading to the formation of large voids at regions where the shotcrete has difficulty penetrating the mesh. As an alternative to using steel mesh, the incorporation of fibers can also improve the crack resistance and strength of the shotcrete layer. Indeed, in many tunneling projects, over the world,with the use of fiber reinforced shotcrete (FRS), steel mesh in the lining can be removed [1]. In Ref. [2], the application of FRS (without steel mesh) in slope stabilisation, repair and the construction of shell structures is described. Based on available information in the literature, FRS appears to be a competitive alternative to mesh reinforced shotcrete for many applications. Indeed, various institutions have developed design guidelines for the use of shotcrete in practice[3,4].Similar to concrete, the design of FRS is based on empirical information obtained from material tests [5,6].When a new type of fiber is employed or when a certain application imposes new requirements on material properties,a large number of tests may have to be performed to come up with the appropriate mix design. Because concrete specimens are much easier to prepare than shotcrete specimens,it is of practical interest to see if tests can be conducted on fiber reinforced concrete (FRC) first to provide guidelines for the preliminary mix design of FRS.It should be emphasized 万博manbetx网页版,万博manbetx官网,万博manbetx官网 that for the FRC results to be useful, the composition of the FRC must be suitable for shooting. Due to the difference in compaction processes, FRS and FRC with the same mix proportions are expected to have different properties. Banthia et al. [7] have conducted an investigation to compare the compressive and flexural properties of FRC and FRS with the same composition.In their work, deformed steel fibers with five different geometries were studied. In the present investigation,FRC and FRS specimens were prepared with different types of fibers including steel (ST), polypropylene (PP), polyvinylalchol (PVA), as well as a hybrid of PP and PVA. Thecompressive and flexural properties, shrinkage behavior and permeability of the FRC and FRS were measured. If a correlation between FRS and FRC properties exists, then,preliminary FRS 万博manbetx网页版,万博manbetx官网,万博manbetx官网 compositions for various applications can be determined based on the results of tests on FRC.FRS is commonly used in slope protection and surface repair of structures. In these applications, the surface area to volume ratio of the shotcrete layer is high. Shrinkage and restrained shrinkage cracking are therefore important concerns. The resistance to shrinkage cracking depends on the flexural behavior of the FRS, including both the flexural strength and the postpeak load-carrying capacity [2]. In some applications (e.g., protection of soil slopes), the shotcrete layer has to prevent water penetration, thus, the permeability of FRS is also important. Following the above discussions, the present study focuses on comparing the flexural properties, shrinkage and permeability of FRS and FRC. Because compressive strength is the most commonly reported parameter in concrete technology, 万博manbetx网页版,万博manbetx官网,万博manbetx官网 it was also measured for comparison. Note that the conclusions drawn from the study are only applicable to the wet-mix FRS, prepared as described in the following section. Shotcrete prepared by the dry-mix process may perform differently.

    在许多施工工序中,采用喷浆认定申请。常见的例子包括修复的混凝土结构,建设隧道衬砌,以及稳定的岩石和泥土斜坡上。为防止混凝土层的裂缝,钢丝网是经常地摆喷操作。配售网是一个劳动密集型和费时的过程。此外,残留的主要部分可能会造成一种“阴影”效果,从而形成大量气泡,在区域喷浆难以穿透的主要部分,使用钢丝网作为替代品,还可以将喷射材料的纤维抗裂度的强度提高。 的确,在许多隧道工程,在世界上使用的纤维喷浆(FRS),钢丝网在衬砌时可以消除[1],应用FRS(无钢丝网)在斜坡修理和建造壳结构的描述。根据资料显示,在文献中FRS似乎是一个在竞争替代钢筋网喷浆时有多种应用。事实上,各院校都制定设计准则在实践使用喷浆[3,4] 类似混凝土。设计FRS是基于实证资料,从材料试验中得到〔5,6〕。当一种新型纤维被用于或者当某个应用带来新的要求时,对材料的性能,,大量的测试可能要表现出适当的组合设计。因为混凝土样本,更容易得到许多准备比例喷浆标本。就现实利益看,如果进行测试,对纤维增强混凝土(FRC)首先提供指引的初步结构设计的FRS,应该强调指出的行动结果是有益的, 组成的组织必须适合拍摄.。由于差异压实过程中, FRS和FRC以相同比例混合预期有不同的属性。以比较的抗压,抗折性能FRC,并与FRS相同的成分。在工作中,变形的钢纤维,用5种不同的几何结构进行了研究。在本次调查表明,组织及FRS标本,编写不同类型的纤维包括钢(路段) ,聚丙烯( PP ) , 聚乙烯醇,以及混合PP和聚乙烯醇。抗收缩开裂取决于FRS的抗弯性能,包括材料的抗弯强度和过载承载能力[2]。在一些应用中(例如,保护土坡)的混凝土层,以防止水渗透,因此,渗透性FRS也很重要。继上述讨论后,目前的研究重点放在比较抗折性能,收缩性和通透性FRS和FRC上。因为抗压强度是最常报道的参数,在具体的技术环节,也是衡量比较的标准。注意到,研究结论只适用于湿拌的FRS。

    2. Specimen preparation样品制备

    In this paper, results from five different sets of specimens are reported. Each set consists of FRS and FRC members of the same composition. The mix proportion of the cementitious materials plus aggregate matrix is the same in all cases and is given in Table 1.

    本文结果从五个不同的标本报告方面介绍。每套由FRS和FRC组成相同的成分。混合比例的胶凝材料加总计矩阵是全部一样的情况,并给出表1。

    (Note the stone fines are crushed aggregates with size between 0.15 to 5 mm.) One set of specimens contained no fiber, i.e., plain matrix. The other four sets were prepared with 0.5% PP fiber, 0.5% PVA fiber, 0.5% ST fiber and a combination of 0.5% PP and 0.3% PVA(hybrid) fibers. Details of each fiber are shown in Table 2.

    (注 石材限制碎石大小介乎于0.15至5毫米)。一套样本不含纤维,即单纯矩阵。另外四套备0.5%丙纶,0.5%聚乙烯醇纤维,0.5%ST和光纤相结合,0.5% PP和0.3%聚乙烯醇(杂交)纤维。每个纤维的细节都显示在表2.

    For the shotcrete specimens, all the constituents were first mixed in a large portal mixer. The mix was then pumped through a pipeline and sprayed through a nozzle onto wooden forms to produce panels about 1.2_1.2 m in size.The shotcreting process was controlled by a robot arm that could rotate the nozzle and move it along different directions.During shotcreting, the panels were oriented at about 60j to horizontal. The nozzle tip was held at about 1 m from the panel, and the spraying direction was perpendicular to the panel surface. With controlled scanning motion of the nozzle, shotcrete was applied layer by layer onto the form.Spraying continued until the panel thickness was slightly higher than the thickness of the formwork. The extra shotcrete was carefully screeded off, and a float was employed to produce a smooth surface. Silica fume improves the adhesive properties of shotcrete, enabling the cementitious matrix to stick onto inclined and vertical surfaces better.Accelerator was not used, as its addition will make a weaker shotcrete [8]. To quantify rebound, a separate panel (100mm in depth) was prepared by shotcreting in the same way as described above. During shotcreting, a plastic sheet was placed on the ground around the panel so any rebound material could be collected and weighed. The panel was also weighed both before and after shotcreting. Knowing the weight of material inside the panel (Ws) and the weight of rebound material (Wr), the total rebound is calculated as the ratio Wr/(WrWs). Physically, this value represents the fraction of total material shot at the panel that goes into rebound.A sample about 20 kg in weight was then taken from the shotcrete panel. Based on the measured weight and density,the volume was obtained. Water was then applied to wash out the particles in the sample, while fibers were carefully collected and weighed. Following Banthia et al. [9], the fiber rebound Rfv (in percent) was calculated using the following equations

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