论文部分内容阅读
Properties of wet-mixed fiber reinforced shotcrete and fiber reinforced concrete with similar
Abstract 摘要
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.
纖维加固喷浆(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 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 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, 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.
在許多施工工序中，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/(Wr +Ws). 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:
详情是每个纤维表面牙槽喷浆标本，所有成分均先混合在一个大的门户搅拌机进行组合，然后通过抽水管道使喷涂通过喷嘴上的木制的约 1.2X1.2毫米大小的喷嘴喷出。喷浆过程控制的机器人手臂，可使喷头沿不同的方向旋转移动。在横向喷板处，在达到60焦耳时 ,喷嘴举高了约1米，由喷嘴与喷射方向垂直于地面部分。控制与扫描运动的喷嘴, 喷浆采用逐层走上，从喷雾持续到小组厚度略高于厚度的模板。额外仔细添加石灰的喷浆，被用来生成光滑的表面。为了减少过度反弹，使用湿喷混凝土与硅粉。硅粉可以改善混凝土的粘着性能，使水泥基质坚持更好的走上倾斜和垂直表面，是另类加速器，因为它除了能喷较弱的[8]，量化反弹，单独小组( 100mm的深度)是由喷浆，以同样的方式如上所述形成的。在喷射时像一张塑料布放在周围的地面，因此任何反弹材料都可收集和权衡。明知重量材料内部组织及体重反弹材料(铁) 总反弹的计算是比西/ (西+是)。此值占总数的分数材料喷射范围内，进入反弹。样本约20公斤的重量，然后服从喷射原则。根据实测重量，密度，体积获得水，然后洗出粒子样本，而对纤维进行精心收集和权衡。光纤输出反弹( % )的計算采用下列公式计算:
For the various mixes, the total rebound ranged from 6.1% to 7.3% while the fiber rebound (Rfv) was 9.0%, 8.0%,7.8% and 7.2%, for steel, PP, PVA and hybrid fibers,respectively.For each mix, FRC specimens of the required size were also prepared by casting into steel moulds. Compaction was performed with a hand-held vibrator. To avoid disturbance of the fiber distribution, the vibrator was not inserted inside the concrete but simply held in touch with the side of the mould and the surface of the concrete.After the shotcrete panels and cast concrete specimens were made, they were kept wet for 1 day on the site before transporting (wet) back to our laboratory. Then, FRS specimens were cut or cored from the panels, and FRC specimens were removed from the moulds. All specimens for compressive,flexural and permeability tests were then kept in a 100% relative humidity curing room for 28 days. For the shrinkage tests, the specimens were instrumented with Demec gauges and placed in an environmental room at 50% relative humidity and 28 jC.
各组合的总反弹，介于6.1%至7.3%之间，而钢材，聚丙烯，聚乙烯醇和混合纤维的纤维回弹(输出)为9.0% , 8.0% , 7.8%和7.2%。每一个组合，FRC标本所需规模，还准备通过浇铸到模具钢。压实是用一台手提式振动器。为了避免干扰的纤维分布, 振动不深入混凝土内部，而只是表面接触，以压实模具表面上的混凝土。后喷板和现浇混凝土制作标本, 他们被蒙湿1天的地方，然后运送(湿)回我们的实验室。当时，对从模具小组削减芯切削的FRS标本进行测量，并汇报标本。对所有标本组件进行压敏胶, 弯曲和渗透性测试，然后分别存放在100%的相对湿度养护室28天。为缩短试验时间, 在50%相对湿度情况下，标本装有放置在一个环境空间演示仪表。
3. Experimental results实验结果
3.1. Compressive strength 抗压强度
Shotcrete is seldom required to carry compressive load.However, because the compressive strength of concrete is the most commonly reported material parameter, and concrete design is often based on this particular property, it is of interest to see how the compressive strength of FRS and FRC compares. To perform compressive strength testing,cylindrical specimens of /100_200 mm were employed.Shotcrete specimens were cored from the 200-mm-thick panels while concrete specimens were cast directly into steel molds. Testing was carried out after 28 days of curing.Three specimens were tested for each mix to obtain the average value. Test results for various compositions areshown in Table 3.
喷射是很少需要进行压缩指导，然而因为混凝土的抗压强度是最常见的申报材料参数, 而具体的设计往往是基于这一特定因素, 有意思的是看看比较FRS和FRC抗压强度。进行抗压强度测试, 圆柱标本/ 100 X 200毫米,分别使用喷浆标本芯由200毫米厚的板，而混凝土试用铸件直接进入钢模具。对试样进行了28天的测试，每个组合以取得平均值。测试结果的各种成分见表3。
From Table 3, the compressive strength for FRC specimens is higher than that for FRS specimens in all cases.Concrete specimens were compacted with conventional means, with the use of the vibrator. This appears to be more effective in removing trapped air than the shotcreting process was, where shotcreting compacts the concrete with pressure when it is shot onto the form. In most cases, the compressive strength of FRS specimens is below 75% of the value for FRC specimens. The results are in agreement with the findings of Banthia et al. [7] that FRS specimens generally exhibit significantly lower compressive strength than FRC specimens of the same composition do. Although our major interest is to compare FRC and FRS specimens of the same composition, it is also informative to look at the difference in strength between plain and fiber reinforced specimens. For specimens with 0.5% PP and 0.5% PVA fibers, the compressive strength for both FRC and FRS specimens is lower than that for plain concrete. Specifically, for FRC, the increase is over 30%, which is very high when compared with reported results [2]. In the specimen preparation process, the amount of material required for making all the specimens far exceeds the capacity of the portal mixer. As a result, many different batches (that should have had the same composition) had to be used. The exceptionally high strength of the steel fiber FRC specimen leads us to suspect that the particular batch for making these specimens had a different composition to the other batches. The compressive strength is hence different. For the case with hybrid fibers (0.5% PP + 0.3% PVA), the strength for FRC is slightly higher than in the plain concrete, while that for FRS is lower. The slight strength improvement for FRC may be due to the better control of cracks when more fibers are added. In the FRS specimens, however, this effect does not appear to be strong enough to compensate for the increased porosity due to insufficient compaction.
从表3看出，在所有测试中，FRC标本比FRS标本抗压强度高。具体标为本板结与常规手段所用的振动器。这似乎在困比喷浆过程中可以更有效地去除空气。在调节喷射混凝土压力时，它采用的是镜头上的形式。在大多数情况下, 虽然结果是一致的，但FRS标本抗压强度低于FRC标本的75%，也就是说，与相同的成分的FRC标本相比，FRS标本一般呈现明显低于FRC标本的抗压强度。虽然我们的主要兴趣是比较FRC及FRS标本的同成分, 这也是证明，看看不同力量之间的平原和纤维标本。0.5% PP和0.5%聚乙烯醇纤维标本抗压强度及FRC及FRS标本均低于普通混凝土。一个可能的解释是，将小直径纤维混合压实，从而强度增加。因此，已然停留的最后标本，为组合钢纤维。FRC及FRS标本的抗压强度均高于普通混凝土。具体来说，增幅超过30% ,这是非常高比例的报告结果[2]。在样品制备过程中, 材料的数量也需要给出的所有标本，远远超过了门户搅拌机的容量。由于许多所使用的批次不同 (即应该有相同的成分)，使我们怀疑，特高强度钢纤维的FRC标本, 特别是批量制造这些标本进行了不同成分的其他批次，因此抗压强度不同。为此FRC混杂纤维( 0.5%聚丙烯+ 0.3%聚乙烯醇) 实力略高于平原混凝土，而FRS则较低。在FRS标本，稍有实力的改善型FRS可能是由于在控制裂缝时有较好的多纤维的补充。但这种效果似乎并不很明显，也并不足以弥补因压实不够而增加的孔隙。
3.2. Flexural strength, toughness indices and residual load抗折强度，韧度指数和剩余负荷
The ASTM C1018 test method [10] was employed to study the flexural behavior of fiber reinforced matrices. Beam specimens of approximately 350_100_100 mm in size were tested over a span of 300 mm to obtain the flexural strength and toughness indices. Note that the above member size is exact for cast FRC specimens, but ‘approximate’ for FRS specimens cut from the shotcrete panel, as the panel thickness varies slightly over its area. To ensure proper calculation of the various parameters, the actual size of each FRS specimen was measured. For each composition, three FRC and three FRS specimens were tested. To show the trend of the load versus deflection behavior, the averaged load versus deflection curves for various compositions of FRC and FRS are given in Fig. 1a to d.
ASTM c1018測试方法用于研究纤维钢筋的抗弯性能矩阵。约束标本为350 X 100 X 100毫米大小，分别试验了跨度300毫米的索取材料的抗弯强度和韧性指数。注意到以上是精确铸造FRC标本。因为小组厚度略高于它的面积，所以要将近似FRS标本剪成喷浆小组， 确保计算中的各种适当参数，对标本进行实际的测量。对每一篇作文,三个小组和三个FRS标本进行化验，显示负荷与变形的趋势, 各种成分的FRS及FRC标本的平均负荷与挠度。
To analyse the results, the flexural strength, as well as the toughness indices I5, I10 and I20,are obtained according to the current version of ASTM C1018. Specifically, the toughness indices were calculated from the ratio between (i) the area under the load deflection curve up to 3, 5.5 and 10.5 times the first crack deflection and (ii) the area up to the first crack deflection. The results for flexural strength and toughness indices are summarized in Table 4.
分析结果表明,材料的抗弯强度,以及韧性指数，获得按现行版美国ASTM c1018测试方法的认可。具体来说, 韧性指标计算出来的比例(一)面积荷载作用下挠度曲线上升至第3 , 为5.5和10.5倍,首次裂纹偏转和(二)区显示首次裂纹偏转。抗弯强度和韧性指数的结果列于表4。
In calculating the toughness indices, the point corresponding to ‘first crack’ on the load deflection curve is subjectively determined. The accuracy of its determination has always been a concern. Moreover, as pointed out by Morgan et al. [11], I5 and I10 are not very useful indicators of the postpeak load carrying capacity because they may fall within the zone of instability of the load versus deflection curve. Indeed, in the latest draft version of ASTM C1018, to eliminate these concerns, reporting of the residual loads at L/600 and L/150 (where L is the loading span) are recommended. Following this recommendation, the residual loads at L/600 (i.e., 0.5 mm) and L/150 (i.e., 2 mm) are shown in Table 5.
在計算韧性指数时，点的相应的荷载挠度曲线是由主观决定的，它的准确测定一直受到关注。此外,数据指出摩根和加载跨距没有很有效的过载承载能力，因为他们在可能范围内带有不稳定的荷载与挠度曲线。事实上，在最新的草案版本ASTM c1018标准中,以消除这些疑虑，提出消除报告中的剩余载荷l/600和l/150 ( L为加载跨距)的建议。按照这项建议,剩余载荷l/600 (即0.5毫米) , l/150 (即 2毫米) ,见表5 。
As a reference, the peak load for each composition is also provided. In both Tables 4 and 5, each result represents the average from three specimens. Results in Table 4 indicate that the flexural strengths for FRC and FRS specimens are within 20% of one another. In three out of five cases, they are within 10%. Moreover, for all cases, except the hybrid fiber composite, the FRS specimens exhibit a higher strength than the corresponding FRC. This trend, which is opposite to that for compressive strength, is again in agreement with the observations in Banthia et al. [7]. A possible explanation is as follows. The addition of fibers has two effects on the specimens. First, it makes compaction more difficult and hence increases the porosity of the specimen. Second, the presence of fibers provides bridging stresses to control the propagation of cracks. 1. (a) Averaged load/deflection curve of PVA fiber specimens. (b) Averaged load/deflection curve of steel fiber specimens. (c) Averaged load/ deflection curve of PP fiber specimens. (d). Averaged load/deflection curve of hybrid fiber specimens. It appears that in the cases studied, the bridging stress provided by fibers is not sufficient to compensate for the increased crack density. As a result, the compressive strength is dominated by the porosity, and the FRC specimens that have lower porosity exhibit higher compressive strength. In bending, failure is caused by tension and is governed by the largest crack in the specimen. With increased porosity, the maximum crack size is also likely to increase. However, for the propagation of a single crack, bridging stress provided by fibers is effective in delaying ultimate failure. While the overall compaction of FRS specimens is not as good as that for FRC specimens, ‘squeezing’ of the mix at the nozzle of the shotcreting gun may densify the fiber/matrix interface. Moreover, in the shotcreting process, preferential alignment of fibers may occur [6]. With a better interfacial bond and better alignment, the fibers in FRS are more effective in controlling crack propagation. As a result, a higher flexural strength is obtained for FRS specimens in most cases. The exception is the hybrid fiber composite, where the FRC specimens exhibit higher flexural strength. In this case, the high fiber volume may have led to the formation of large pores in the FRS, causing a significant strength reduction that cannot be compensated for by the increased bridging effect. This argument is supported by the lower compressive strength of the hybrid (PP + PVA) FRS relative to FRC (Table 3), indicating a higher porosity of the shotcrete specimens. From Table 4, the toughness indices (I5, I10 and I20) for FRS is always lower than that for FRC of the same composition. This differs from the findings in Banthia et al. [7] that some FRS specimens give higher toughness indices than corresponding FRC specimens do. When the toughness indices (I5, I10 and I20) for FRS and FRC of similar compositions are compared, they are normally within 20% and 25%, although a larger difference of over 30% is obtained for the 0.5% PP composite. However, if one looks at the results in Table 5, the residual loads of FRS at L/600 and L/150 are 11–43% and 18–56%, respectively, lower than in FRC. An improved bond, however, also makes it easier for fiber rupture to occur. After the peak load is reached, there are then less fibers bridging the crack. In addition, for fibers that are inclined to the crack, higher stress carried by the fiber will introduce higher stresses on the matrix around the fiber exit point, which increases the likelihood of local matrix spalling (Fig. 2) [12,13].
在表4和表5，中作为参考, 还为每一篇作文提供每项成果的平均3个标本的高峰负荷。表4结果表明，FRC及FRS标本材料的抗弯强度均在20%以内的一环。在三到五个案例中，他们都在10%以内。此外,对所有混杂纤维复合材料的案件中, FRS标本显示出一种大于相应FRC标本的高强度趋势。而相反,抗压强度又显示出是一致的。一个可能的解释是，有两对标本进行纤维添加。首先,它使得压实更加困难,从而增加了标本的孔隙；第二,纤维的提供控制了裂缝再生，受压时,发生故障,通过贯通裂缝蔓延，较高的孔隙率意味着有较多薄弱地带裂缝的形成。虽然整体压实FRS标本不如FRC标本，但混合喷嘴的喷枪具有致密纤维与基体界面，此外,在喷浆过程中, 可能发生混凝土纤维的流失。一种更好的界面结合,可以更好地调整纤维在FRS标本中的作用，更有效地控制裂纹。这就导致了在大多数情况下FRS标本得到了较高的抗弯强度。在FRC标本显示出较高的抗弯强度时，唯一的例外是混杂纤维复合材料。在这种情况下, FRS的高纤维体积可能导致形成大孔隙，使强度大大降低,不能补偿的效果日益缩小。在这一论点的支持下孔隙喷浆标本的混合(聚丙烯+ PVA )与FRS相对于FRC(见表3 ) 显示出较高的抗压强度。从表4看出，在韧性指数方面，FRS总是低于同一成分的FRC。这与测试结果不同。一些FRS标本比相应的FRC标本给予了更高的韧性指数。当FRS和FRC韧性指数在类似情况下进行成分相比, 他们通常在20%至25%之间, 虽然有较大的差异，但没有超过30% ,获得了0.5%的聚丙烯复合材料。但是,如果我们看一下结果,在表5 FRS的剩余载荷在l/600与l/150之间 ,在1911年至1943年为18%-56 % ,低于FRC。换句话说, 更大的差别表现在FRC和FRS所反映的剩余载荷比和韧性指数之间。从现实的角度来看, 以防止裂缝，我们对此很有兴趣。从这个意义上讲, 韧性指标的剩余载荷值是较有意义的指标比。首先裂缝是如何形成的. 正如前述, 在FRS标本中，由于较高的抗弯强度可能是对准优惠光纤和纤维和基质更好的纽带。虽然经过改进,但也能使纤维发生断裂，后是用电负荷达到的，有那么少纤维弥合裂缝。此外,对倾向于裂纹的纤维应力通过光纤将提出更高的矩阵，要求周围纤维有高出境点, 其中增大局部矩阵的可能性减小。如图2。
Either of these mechanisms can lead to a reduction in postpeak load. For the hybrid composite, the high porosity in the FRS specimen may affect both the peak load and the postpeak behavior, thus, the toughness indices and residual loads of FRS are also lower than those for the FRC specimens.
上述两种机制可以导致减少过载负荷。可能增强的复合材料FRS标本的高孔隙率会影响双方的高峰负荷和过载能力。因此, FRS的韧度指数和剩余载荷也是欧盟的标准。
3.3. Permeability渗透性
To perform the permeability test, a novel approach developed at HKUST was employed [14]. Both cast FRC cylinders and cored FRS specimens with 100-mm diameter were cut into specimens 80 mm in length. A waterproofing primer was applied to the sides of the specimen, and its top and bottom were ground flat and smooth. The specimen was then put into the permeability cell, as shown inFig. 3.
进行渗透试验,一种新型的发展方式。在斜坡的支护问题上，无论是FRS和还是FRC标本，标本被切割成直径100毫米，长度80毫米。 详明的证明了底漆适用于的标本，其顶部和底部的地面平整，光滑。标本具有细胞通透性。如图.3。
In the cell, deionized water was added into a water reservoir above the specimen. Then, the permeability cell was placed inside an autoclave, where a pressure ranging from 0.67 to 1 MPa was applied at room temperature for 24 h to accelerate the penetration of deionized water into the specimen. From each half, the depth of water penetration was identified from the boundary between wet and dry concrete (which shows different colors). The penetration depth was measured at 10 locations across each section to obtain an average Fig. 2. Matrix spalling leading to reduction in fiber bridging force. value. The permeability coefficient (k) was then calculated from Refs. [15,16]:
在細胞内，纯水中加入了水库中以上的标本。然后，渗透细胞被放在一个容器中，压力从0.67至1兆帕斯卡，应用在室温下24小时，以加速渗透纯水成标本。压力范围由经验确定出，以确保水质深埋构成标本，可靠此测量其深度。但是，它不穿透整个深度，否则，只有一个下界值为渗透性。最后检测取出的标本的细胞通透性，首次测定为了提高质量。然后加载，再在把在巴西试验的分裂标本撕成两半。一半深度透水，另一半边界有干湿混凝土(显示不同颜色)。经过深度测量，在10个横跨点每一节点获得平均值为渗透系数( K ) ,然后计算出参数值。
The permeability results for all tested specimens are shown in Table 6.
通透性结果的所有测试样本见表6 。
The results indicate high variability of the permeability coefficient among the same types of specimens, which is quite common for permeability measurements. However, the difference between FRC and FRS specimens of the same composition is significantly greater than the variation among the FRC or FRS specimens themselves. For all mixes, shotcrete specimens exhibit higher permeability coefficients than do concrete specimens of the same composition, and are hence more permeable. we pointed out that the porosity in the fiber reinforced specimens may be higher than that in the plain specimens. If so, the permeability for the plain FRC or FRS should also be the lowest. From Table 6, this is not the case, in general. The lower permeability for some fiber reinforced specimens may be due to the presence of fibers that reduce internal microcracking (e.g., due to shrinkage) in the cementitious matrix and hence improve the resistance to water penetration.
结果表明，标本在同一类型的渗透系数变异性高，这是很普遍的渗透性测量。然而， FRC标本及FRS标本的区别是，对同一成分FRC标本的变异明显大于FRS标本。因此更容易接受所有混合噴浆标本比同成分混凝土做标本展示的渗透系数更高。这也再次说明了，在喷浆标本产生有效减少土壤板结时有较高的孔隙率。在样品制备程序中，我们观察到PVA纤维有增加的趋势。结果表明，FRS相对FRC的渗透系数，有一个特别大的影响。根据调查结果，对混凝土的试验，我们已指出，标本孔隙的纤维可能会比在平面标本的抗压强度低。所以，平面FRS和FRC的渗透性也应该是最低的。而从表6中可以看出，在一般情况事实并非如此。一些样本纤维具有低渗透，可能是由于存在纤维,减少内部孔隙(例如,由于收缩)，以及胶凝基质，从而改善了抗水渗透。
3.4. Shrinkage 收缩
To study the shrinkage of FRC, 500_100_100 mm concrete prisms were cast directly in steel moulds. FRS specimens of similar size were cut from shotcrete panels. After 1 day of curing, Demec gauges (with gauge length of 200 mm) were glued onto four surfaces of each specimen, as shown in Fig. 4.
研究直接在钢模具收缩的FRC500 X 100 X 100毫米棱镜混凝土预制块。在混凝土板上，FRS标本类似规模裁员。经过1天的腌制，限界(长度200毫米)分别粘到四个面的每一个标本，如图. 4。
The specimens were then placed in an environmental room with a relative humidity of 50% and temperature of 28 jC. To measure shrinkage as a function of time, the strains recorded on four surfaces of each specimen were averaged. For each composition, and for each of the concrete and shotcrete mixes, three specimens were employed for shrinkage testing. Typical results are shown in Fig. 5a to c. Each line was obtained as the average reading for the four surfaces of a particular specimen. For all the compositions studied, the shrinkage behaviors of FRC and FRS were found to be very similar. In some cases, the Fig. 3. Cell and specimen for the permeability test. FRC specimens were found to shrink more. For other cases, FRS specimens showed higher shrinkage. From a practical point of view, the difference in the shrinkage behavior of FRC and FRS specimens is considered not significant [8].
采集完标本,然后放在一个相对湿度50%，温度为28度的环境空间，设定时间。对每一个品种，记录四个面每个标本的平均值。而每次的混凝土及混凝土搅拌，三个标本采用收缩测试。典型结果列于图. 5中A至C 。每条生产线获得四个表面某一标本的平均值。对所有成分的研究发现，在某些情况下发现FRC及FRS有很相似的收缩性能。
4. Discussions and implications to design讨论并设计
In the discussion above, various properties have been measured for FRS and FRC with the same composition. From the results, we would like to see if it is possible to carry out preliminary mix design of FRS based on data on FRC. In the following discussions, we focus on two common applications of FRS, namely, repair of structures and waterproofing of soil slopes. In these applications, FRS is placed over a large area as a relatively thin layer. Shrinkage is therefore a major concern. In addition, differential and constrained shrinkage may result in high tensile stresses and cracking. The flexural strength is hence of interest, but the residual loads (at deflections of L/600 and L/150) are also important because they control the crack opening after cracking occurs. As FRS is not intended to carry compression, the compressive strength is not needed for design. However, because it is the most commonly measured parameter for cementitious materials, it is of interest to see if it correlates with the other FRS properties. As shown in Fig. 5, the shrinkage behavior of FRS and FRC is very similar. Under similar conditions, the FRS and FRC specimens will shrink to similar extents. The flexural strength for FRS and FRC are similar, with FRS showing a higher value in most cases (four out of the five mixes studied). On the other hand, the residual loads of FRS at L/600 and L/150 are, respectively, 11–43% and 18–56% lower than the corresponding values for FRC. In certain special applications, such as the repair of internal surfaces of a water or sewage pipe, the high humidity of the environment may limit the shrinkage to small values. For such cases, as long as the stress produced by restrained shrinkage does not exceed the flexural strength, no cracking will occur. Because the flexural strength of FRS is comparable to that of FRC, and higher in most cases, one can select preliminary FRS mixes directly from results on FRC, obtained either from the literature or from new tests conducted in the laboratory. (Note: when FRS mixes are designed based on FRC results, the FRC should have a composition suitable for shooting.) In summary, because most laboratories do not have proper shotcreting facilities, and shotcrete specimens are far more time consuming to prepare than concrete members is, it is advisable to perform preliminary tests on FRC specimens first. Based on the understanding that the flexural strength for FRS and FRC are similar, while the residual loads can be up to 50% lower for FRS, appropriate FRC mixes can be identified to prepare corresponding FRS specimens for further experiments. When waterproofing is a concern, permeability is an important parameter to be considered. From Table 6, it is clear that the permeability of FRS can be one to two orders of magnitude higher than that for FRC of similar composition. To come up with a trial mix of FRS to fulfil permeability requirements, the composition for an FRC with much lower permeability should be employed. Fig. 5. (a) Shrinkage strain vs. time for plain concrete specimens. (b) Shrinkage strain vs. time for 0.5% polypropylene fiber specimens. (c) Shrinkage strain vs. time for 0.5% steel fiber specimens. It should also be pointed out that the compressive strength differences between FRS and FRC do not correlate well with the flexural strength and shrinkage behavior.From Table 3, the compressive strength of FRS is consistently below that of FRC, by up to 30–40% in three out of the four compositions of FRS. However, the shrinkage behavior of FRS and FRC is essentially the same, and the flexural strength of FRS (Table 4) is higher than that of FRC for most cases (except the case with hybrid fiber reinforcement, where there may be high porosity). Therefore, it is not possible to predict the postcracking behavior from the compressive strength. If shrinkage cracking is an important concern, trial mixes for FRS should not be selected based on the compressive strength of FRC. For permeability, except for the steel fiber composite, a larger relative difference in compressive strength does indicate a higher increase in the permeability of the FRS specimen. However, we do not have sufficient data to obtain a quantitative correlation between the compressive strength and the permeability of FRS. If waterproofing is important, the permeability test should be carried out.
Abstract 摘要
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.
纖维加固喷浆(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 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 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, 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.
在許多施工工序中，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/(Wr +Ws). 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:
详情是每个纤维表面牙槽喷浆标本，所有成分均先混合在一个大的门户搅拌机进行组合，然后通过抽水管道使喷涂通过喷嘴上的木制的约 1.2X1.2毫米大小的喷嘴喷出。喷浆过程控制的机器人手臂，可使喷头沿不同的方向旋转移动。在横向喷板处，在达到60焦耳时 ,喷嘴举高了约1米，由喷嘴与喷射方向垂直于地面部分。控制与扫描运动的喷嘴, 喷浆采用逐层走上，从喷雾持续到小组厚度略高于厚度的模板。额外仔细添加石灰的喷浆，被用来生成光滑的表面。为了减少过度反弹，使用湿喷混凝土与硅粉。硅粉可以改善混凝土的粘着性能，使水泥基质坚持更好的走上倾斜和垂直表面，是另类加速器，因为它除了能喷较弱的[8]，量化反弹，单独小组( 100mm的深度)是由喷浆，以同样的方式如上所述形成的。在喷射时像一张塑料布放在周围的地面，因此任何反弹材料都可收集和权衡。明知重量材料内部组织及体重反弹材料(铁) 总反弹的计算是比西/ (西+是)。此值占总数的分数材料喷射范围内，进入反弹。样本约20公斤的重量，然后服从喷射原则。根据实测重量，密度，体积获得水，然后洗出粒子样本，而对纤维进行精心收集和权衡。光纤输出反弹( % )的計算采用下列公式计算:
For the various mixes, the total rebound ranged from 6.1% to 7.3% while the fiber rebound (Rfv) was 9.0%, 8.0%,7.8% and 7.2%, for steel, PP, PVA and hybrid fibers,respectively.For each mix, FRC specimens of the required size were also prepared by casting into steel moulds. Compaction was performed with a hand-held vibrator. To avoid disturbance of the fiber distribution, the vibrator was not inserted inside the concrete but simply held in touch with the side of the mould and the surface of the concrete.After the shotcrete panels and cast concrete specimens were made, they were kept wet for 1 day on the site before transporting (wet) back to our laboratory. Then, FRS specimens were cut or cored from the panels, and FRC specimens were removed from the moulds. All specimens for compressive,flexural and permeability tests were then kept in a 100% relative humidity curing room for 28 days. For the shrinkage tests, the specimens were instrumented with Demec gauges and placed in an environmental room at 50% relative humidity and 28 jC.
各组合的总反弹，介于6.1%至7.3%之间，而钢材，聚丙烯，聚乙烯醇和混合纤维的纤维回弹(输出)为9.0% , 8.0% , 7.8%和7.2%。每一个组合，FRC标本所需规模，还准备通过浇铸到模具钢。压实是用一台手提式振动器。为了避免干扰的纤维分布, 振动不深入混凝土内部，而只是表面接触，以压实模具表面上的混凝土。后喷板和现浇混凝土制作标本, 他们被蒙湿1天的地方，然后运送(湿)回我们的实验室。当时，对从模具小组削减芯切削的FRS标本进行测量，并汇报标本。对所有标本组件进行压敏胶, 弯曲和渗透性测试，然后分别存放在100%的相对湿度养护室28天。为缩短试验时间, 在50%相对湿度情况下，标本装有放置在一个环境空间演示仪表。
3. Experimental results实验结果
3.1. Compressive strength 抗压强度
Shotcrete is seldom required to carry compressive load.However, because the compressive strength of concrete is the most commonly reported material parameter, and concrete design is often based on this particular property, it is of interest to see how the compressive strength of FRS and FRC compares. To perform compressive strength testing,cylindrical specimens of /100_200 mm were employed.Shotcrete specimens were cored from the 200-mm-thick panels while concrete specimens were cast directly into steel molds. Testing was carried out after 28 days of curing.Three specimens were tested for each mix to obtain the average value. Test results for various compositions areshown in Table 3.
喷射是很少需要进行压缩指导，然而因为混凝土的抗压强度是最常见的申报材料参数, 而具体的设计往往是基于这一特定因素, 有意思的是看看比较FRS和FRC抗压强度。进行抗压强度测试, 圆柱标本/ 100 X 200毫米,分别使用喷浆标本芯由200毫米厚的板，而混凝土试用铸件直接进入钢模具。对试样进行了28天的测试，每个组合以取得平均值。测试结果的各种成分见表3。
From Table 3, the compressive strength for FRC specimens is higher than that for FRS specimens in all cases.Concrete specimens were compacted with conventional means, with the use of the vibrator. This appears to be more effective in removing trapped air than the shotcreting process was, where shotcreting compacts the concrete with pressure when it is shot onto the form. In most cases, the compressive strength of FRS specimens is below 75% of the value for FRC specimens. The results are in agreement with the findings of Banthia et al. [7] that FRS specimens generally exhibit significantly lower compressive strength than FRC specimens of the same composition do. Although our major interest is to compare FRC and FRS specimens of the same composition, it is also informative to look at the difference in strength between plain and fiber reinforced specimens. For specimens with 0.5% PP and 0.5% PVA fibers, the compressive strength for both FRC and FRS specimens is lower than that for plain concrete. Specifically, for FRC, the increase is over 30%, which is very high when compared with reported results [2]. In the specimen preparation process, the amount of material required for making all the specimens far exceeds the capacity of the portal mixer. As a result, many different batches (that should have had the same composition) had to be used. The exceptionally high strength of the steel fiber FRC specimen leads us to suspect that the particular batch for making these specimens had a different composition to the other batches. The compressive strength is hence different. For the case with hybrid fibers (0.5% PP + 0.3% PVA), the strength for FRC is slightly higher than in the plain concrete, while that for FRS is lower. The slight strength improvement for FRC may be due to the better control of cracks when more fibers are added. In the FRS specimens, however, this effect does not appear to be strong enough to compensate for the increased porosity due to insufficient compaction.
从表3看出，在所有测试中，FRC标本比FRS标本抗压强度高。具体标为本板结与常规手段所用的振动器。这似乎在困比喷浆过程中可以更有效地去除空气。在调节喷射混凝土压力时，它采用的是镜头上的形式。在大多数情况下, 虽然结果是一致的，但FRS标本抗压强度低于FRC标本的75%，也就是说，与相同的成分的FRC标本相比，FRS标本一般呈现明显低于FRC标本的抗压强度。虽然我们的主要兴趣是比较FRC及FRS标本的同成分, 这也是证明，看看不同力量之间的平原和纤维标本。0.5% PP和0.5%聚乙烯醇纤维标本抗压强度及FRC及FRS标本均低于普通混凝土。一个可能的解释是，将小直径纤维混合压实，从而强度增加。因此，已然停留的最后标本，为组合钢纤维。FRC及FRS标本的抗压强度均高于普通混凝土。具体来说，增幅超过30% ,这是非常高比例的报告结果[2]。在样品制备过程中, 材料的数量也需要给出的所有标本，远远超过了门户搅拌机的容量。由于许多所使用的批次不同 (即应该有相同的成分)，使我们怀疑，特高强度钢纤维的FRC标本, 特别是批量制造这些标本进行了不同成分的其他批次，因此抗压强度不同。为此FRC混杂纤维( 0.5%聚丙烯+ 0.3%聚乙烯醇) 实力略高于平原混凝土，而FRS则较低。在FRS标本，稍有实力的改善型FRS可能是由于在控制裂缝时有较好的多纤维的补充。但这种效果似乎并不很明显，也并不足以弥补因压实不够而增加的孔隙。
3.2. Flexural strength, toughness indices and residual load抗折强度，韧度指数和剩余负荷
The ASTM C1018 test method [10] was employed to study the flexural behavior of fiber reinforced matrices. Beam specimens of approximately 350_100_100 mm in size were tested over a span of 300 mm to obtain the flexural strength and toughness indices. Note that the above member size is exact for cast FRC specimens, but ‘approximate’ for FRS specimens cut from the shotcrete panel, as the panel thickness varies slightly over its area. To ensure proper calculation of the various parameters, the actual size of each FRS specimen was measured. For each composition, three FRC and three FRS specimens were tested. To show the trend of the load versus deflection behavior, the averaged load versus deflection curves for various compositions of FRC and FRS are given in Fig. 1a to d.
ASTM c1018測试方法用于研究纤维钢筋的抗弯性能矩阵。约束标本为350 X 100 X 100毫米大小，分别试验了跨度300毫米的索取材料的抗弯强度和韧性指数。注意到以上是精确铸造FRC标本。因为小组厚度略高于它的面积，所以要将近似FRS标本剪成喷浆小组， 确保计算中的各种适当参数，对标本进行实际的测量。对每一篇作文,三个小组和三个FRS标本进行化验，显示负荷与变形的趋势, 各种成分的FRS及FRC标本的平均负荷与挠度。
To analyse the results, the flexural strength, as well as the toughness indices I5, I10 and I20,are obtained according to the current version of ASTM C1018. Specifically, the toughness indices were calculated from the ratio between (i) the area under the load deflection curve up to 3, 5.5 and 10.5 times the first crack deflection and (ii) the area up to the first crack deflection. The results for flexural strength and toughness indices are summarized in Table 4.
分析结果表明,材料的抗弯强度,以及韧性指数，获得按现行版美国ASTM c1018测试方法的认可。具体来说, 韧性指标计算出来的比例(一)面积荷载作用下挠度曲线上升至第3 , 为5.5和10.5倍,首次裂纹偏转和(二)区显示首次裂纹偏转。抗弯强度和韧性指数的结果列于表4。
In calculating the toughness indices, the point corresponding to ‘first crack’ on the load deflection curve is subjectively determined. The accuracy of its determination has always been a concern. Moreover, as pointed out by Morgan et al. [11], I5 and I10 are not very useful indicators of the postpeak load carrying capacity because they may fall within the zone of instability of the load versus deflection curve. Indeed, in the latest draft version of ASTM C1018, to eliminate these concerns, reporting of the residual loads at L/600 and L/150 (where L is the loading span) are recommended. Following this recommendation, the residual loads at L/600 (i.e., 0.5 mm) and L/150 (i.e., 2 mm) are shown in Table 5.
在計算韧性指数时，点的相应的荷载挠度曲线是由主观决定的，它的准确测定一直受到关注。此外,数据指出摩根和加载跨距没有很有效的过载承载能力，因为他们在可能范围内带有不稳定的荷载与挠度曲线。事实上，在最新的草案版本ASTM c1018标准中,以消除这些疑虑，提出消除报告中的剩余载荷l/600和l/150 ( L为加载跨距)的建议。按照这项建议,剩余载荷l/600 (即0.5毫米) , l/150 (即 2毫米) ,见表5 。
As a reference, the peak load for each composition is also provided. In both Tables 4 and 5, each result represents the average from three specimens. Results in Table 4 indicate that the flexural strengths for FRC and FRS specimens are within 20% of one another. In three out of five cases, they are within 10%. Moreover, for all cases, except the hybrid fiber composite, the FRS specimens exhibit a higher strength than the corresponding FRC. This trend, which is opposite to that for compressive strength, is again in agreement with the observations in Banthia et al. [7]. A possible explanation is as follows. The addition of fibers has two effects on the specimens. First, it makes compaction more difficult and hence increases the porosity of the specimen. Second, the presence of fibers provides bridging stresses to control the propagation of cracks. 1. (a) Averaged load/deflection curve of PVA fiber specimens. (b) Averaged load/deflection curve of steel fiber specimens. (c) Averaged load/ deflection curve of PP fiber specimens. (d). Averaged load/deflection curve of hybrid fiber specimens. It appears that in the cases studied, the bridging stress provided by fibers is not sufficient to compensate for the increased crack density. As a result, the compressive strength is dominated by the porosity, and the FRC specimens that have lower porosity exhibit higher compressive strength. In bending, failure is caused by tension and is governed by the largest crack in the specimen. With increased porosity, the maximum crack size is also likely to increase. However, for the propagation of a single crack, bridging stress provided by fibers is effective in delaying ultimate failure. While the overall compaction of FRS specimens is not as good as that for FRC specimens, ‘squeezing’ of the mix at the nozzle of the shotcreting gun may densify the fiber/matrix interface. Moreover, in the shotcreting process, preferential alignment of fibers may occur [6]. With a better interfacial bond and better alignment, the fibers in FRS are more effective in controlling crack propagation. As a result, a higher flexural strength is obtained for FRS specimens in most cases. The exception is the hybrid fiber composite, where the FRC specimens exhibit higher flexural strength. In this case, the high fiber volume may have led to the formation of large pores in the FRS, causing a significant strength reduction that cannot be compensated for by the increased bridging effect. This argument is supported by the lower compressive strength of the hybrid (PP + PVA) FRS relative to FRC (Table 3), indicating a higher porosity of the shotcrete specimens. From Table 4, the toughness indices (I5, I10 and I20) for FRS is always lower than that for FRC of the same composition. This differs from the findings in Banthia et al. [7] that some FRS specimens give higher toughness indices than corresponding FRC specimens do. When the toughness indices (I5, I10 and I20) for FRS and FRC of similar compositions are compared, they are normally within 20% and 25%, although a larger difference of over 30% is obtained for the 0.5% PP composite. However, if one looks at the results in Table 5, the residual loads of FRS at L/600 and L/150 are 11–43% and 18–56%, respectively, lower than in FRC. An improved bond, however, also makes it easier for fiber rupture to occur. After the peak load is reached, there are then less fibers bridging the crack. In addition, for fibers that are inclined to the crack, higher stress carried by the fiber will introduce higher stresses on the matrix around the fiber exit point, which increases the likelihood of local matrix spalling (Fig. 2) [12,13].
在表4和表5，中作为参考, 还为每一篇作文提供每项成果的平均3个标本的高峰负荷。表4结果表明，FRC及FRS标本材料的抗弯强度均在20%以内的一环。在三到五个案例中，他们都在10%以内。此外,对所有混杂纤维复合材料的案件中, FRS标本显示出一种大于相应FRC标本的高强度趋势。而相反,抗压强度又显示出是一致的。一个可能的解释是，有两对标本进行纤维添加。首先,它使得压实更加困难,从而增加了标本的孔隙；第二,纤维的提供控制了裂缝再生，受压时,发生故障,通过贯通裂缝蔓延，较高的孔隙率意味着有较多薄弱地带裂缝的形成。虽然整体压实FRS标本不如FRC标本，但混合喷嘴的喷枪具有致密纤维与基体界面，此外,在喷浆过程中, 可能发生混凝土纤维的流失。一种更好的界面结合,可以更好地调整纤维在FRS标本中的作用，更有效地控制裂纹。这就导致了在大多数情况下FRS标本得到了较高的抗弯强度。在FRC标本显示出较高的抗弯强度时，唯一的例外是混杂纤维复合材料。在这种情况下, FRS的高纤维体积可能导致形成大孔隙，使强度大大降低,不能补偿的效果日益缩小。在这一论点的支持下孔隙喷浆标本的混合(聚丙烯+ PVA )与FRS相对于FRC(见表3 ) 显示出较高的抗压强度。从表4看出，在韧性指数方面，FRS总是低于同一成分的FRC。这与测试结果不同。一些FRS标本比相应的FRC标本给予了更高的韧性指数。当FRS和FRC韧性指数在类似情况下进行成分相比, 他们通常在20%至25%之间, 虽然有较大的差异，但没有超过30% ,获得了0.5%的聚丙烯复合材料。但是,如果我们看一下结果,在表5 FRS的剩余载荷在l/600与l/150之间 ,在1911年至1943年为18%-56 % ,低于FRC。换句话说, 更大的差别表现在FRC和FRS所反映的剩余载荷比和韧性指数之间。从现实的角度来看, 以防止裂缝，我们对此很有兴趣。从这个意义上讲, 韧性指标的剩余载荷值是较有意义的指标比。首先裂缝是如何形成的. 正如前述, 在FRS标本中，由于较高的抗弯强度可能是对准优惠光纤和纤维和基质更好的纽带。虽然经过改进,但也能使纤维发生断裂，后是用电负荷达到的，有那么少纤维弥合裂缝。此外,对倾向于裂纹的纤维应力通过光纤将提出更高的矩阵，要求周围纤维有高出境点, 其中增大局部矩阵的可能性减小。如图2。
Either of these mechanisms can lead to a reduction in postpeak load. For the hybrid composite, the high porosity in the FRS specimen may affect both the peak load and the postpeak behavior, thus, the toughness indices and residual loads of FRS are also lower than those for the FRC specimens.
上述两种机制可以导致减少过载负荷。可能增强的复合材料FRS标本的高孔隙率会影响双方的高峰负荷和过载能力。因此, FRS的韧度指数和剩余载荷也是欧盟的标准。
3.3. Permeability渗透性
To perform the permeability test, a novel approach developed at HKUST was employed [14]. Both cast FRC cylinders and cored FRS specimens with 100-mm diameter were cut into specimens 80 mm in length. A waterproofing primer was applied to the sides of the specimen, and its top and bottom were ground flat and smooth. The specimen was then put into the permeability cell, as shown inFig. 3.
进行渗透试验,一种新型的发展方式。在斜坡的支护问题上，无论是FRS和还是FRC标本，标本被切割成直径100毫米，长度80毫米。 详明的证明了底漆适用于的标本，其顶部和底部的地面平整，光滑。标本具有细胞通透性。如图.3。
In the cell, deionized water was added into a water reservoir above the specimen. Then, the permeability cell was placed inside an autoclave, where a pressure ranging from 0.67 to 1 MPa was applied at room temperature for 24 h to accelerate the penetration of deionized water into the specimen. From each half, the depth of water penetration was identified from the boundary between wet and dry concrete (which shows different colors). The penetration depth was measured at 10 locations across each section to obtain an average Fig. 2. Matrix spalling leading to reduction in fiber bridging force. value. The permeability coefficient (k) was then calculated from Refs. [15,16]:
在細胞内，纯水中加入了水库中以上的标本。然后，渗透细胞被放在一个容器中，压力从0.67至1兆帕斯卡，应用在室温下24小时，以加速渗透纯水成标本。压力范围由经验确定出，以确保水质深埋构成标本，可靠此测量其深度。但是，它不穿透整个深度，否则，只有一个下界值为渗透性。最后检测取出的标本的细胞通透性，首次测定为了提高质量。然后加载，再在把在巴西试验的分裂标本撕成两半。一半深度透水，另一半边界有干湿混凝土(显示不同颜色)。经过深度测量，在10个横跨点每一节点获得平均值为渗透系数( K ) ,然后计算出参数值。
The permeability results for all tested specimens are shown in Table 6.
通透性结果的所有测试样本见表6 。
The results indicate high variability of the permeability coefficient among the same types of specimens, which is quite common for permeability measurements. However, the difference between FRC and FRS specimens of the same composition is significantly greater than the variation among the FRC or FRS specimens themselves. For all mixes, shotcrete specimens exhibit higher permeability coefficients than do concrete specimens of the same composition, and are hence more permeable. we pointed out that the porosity in the fiber reinforced specimens may be higher than that in the plain specimens. If so, the permeability for the plain FRC or FRS should also be the lowest. From Table 6, this is not the case, in general. The lower permeability for some fiber reinforced specimens may be due to the presence of fibers that reduce internal microcracking (e.g., due to shrinkage) in the cementitious matrix and hence improve the resistance to water penetration.
结果表明，标本在同一类型的渗透系数变异性高，这是很普遍的渗透性测量。然而， FRC标本及FRS标本的区别是，对同一成分FRC标本的变异明显大于FRS标本。因此更容易接受所有混合噴浆标本比同成分混凝土做标本展示的渗透系数更高。这也再次说明了，在喷浆标本产生有效减少土壤板结时有较高的孔隙率。在样品制备程序中，我们观察到PVA纤维有增加的趋势。结果表明，FRS相对FRC的渗透系数，有一个特别大的影响。根据调查结果，对混凝土的试验，我们已指出，标本孔隙的纤维可能会比在平面标本的抗压强度低。所以，平面FRS和FRC的渗透性也应该是最低的。而从表6中可以看出，在一般情况事实并非如此。一些样本纤维具有低渗透，可能是由于存在纤维,减少内部孔隙(例如,由于收缩)，以及胶凝基质，从而改善了抗水渗透。
3.4. Shrinkage 收缩
To study the shrinkage of FRC, 500_100_100 mm concrete prisms were cast directly in steel moulds. FRS specimens of similar size were cut from shotcrete panels. After 1 day of curing, Demec gauges (with gauge length of 200 mm) were glued onto four surfaces of each specimen, as shown in Fig. 4.
研究直接在钢模具收缩的FRC500 X 100 X 100毫米棱镜混凝土预制块。在混凝土板上，FRS标本类似规模裁员。经过1天的腌制，限界(长度200毫米)分别粘到四个面的每一个标本，如图. 4。
The specimens were then placed in an environmental room with a relative humidity of 50% and temperature of 28 jC. To measure shrinkage as a function of time, the strains recorded on four surfaces of each specimen were averaged. For each composition, and for each of the concrete and shotcrete mixes, three specimens were employed for shrinkage testing. Typical results are shown in Fig. 5a to c. Each line was obtained as the average reading for the four surfaces of a particular specimen. For all the compositions studied, the shrinkage behaviors of FRC and FRS were found to be very similar. In some cases, the Fig. 3. Cell and specimen for the permeability test. FRC specimens were found to shrink more. For other cases, FRS specimens showed higher shrinkage. From a practical point of view, the difference in the shrinkage behavior of FRC and FRS specimens is considered not significant [8].
采集完标本,然后放在一个相对湿度50%，温度为28度的环境空间，设定时间。对每一个品种，记录四个面每个标本的平均值。而每次的混凝土及混凝土搅拌，三个标本采用收缩测试。典型结果列于图. 5中A至C 。每条生产线获得四个表面某一标本的平均值。对所有成分的研究发现，在某些情况下发现FRC及FRS有很相似的收缩性能。
4. Discussions and implications to design讨论并设计
In the discussion above, various properties have been measured for FRS and FRC with the same composition. From the results, we would like to see if it is possible to carry out preliminary mix design of FRS based on data on FRC. In the following discussions, we focus on two common applications of FRS, namely, repair of structures and waterproofing of soil slopes. In these applications, FRS is placed over a large area as a relatively thin layer. Shrinkage is therefore a major concern. In addition, differential and constrained shrinkage may result in high tensile stresses and cracking. The flexural strength is hence of interest, but the residual loads (at deflections of L/600 and L/150) are also important because they control the crack opening after cracking occurs. As FRS is not intended to carry compression, the compressive strength is not needed for design. However, because it is the most commonly measured parameter for cementitious materials, it is of interest to see if it correlates with the other FRS properties. As shown in Fig. 5, the shrinkage behavior of FRS and FRC is very similar. Under similar conditions, the FRS and FRC specimens will shrink to similar extents. The flexural strength for FRS and FRC are similar, with FRS showing a higher value in most cases (four out of the five mixes studied). On the other hand, the residual loads of FRS at L/600 and L/150 are, respectively, 11–43% and 18–56% lower than the corresponding values for FRC. In certain special applications, such as the repair of internal surfaces of a water or sewage pipe, the high humidity of the environment may limit the shrinkage to small values. For such cases, as long as the stress produced by restrained shrinkage does not exceed the flexural strength, no cracking will occur. Because the flexural strength of FRS is comparable to that of FRC, and higher in most cases, one can select preliminary FRS mixes directly from results on FRC, obtained either from the literature or from new tests conducted in the laboratory. (Note: when FRS mixes are designed based on FRC results, the FRC should have a composition suitable for shooting.) In summary, because most laboratories do not have proper shotcreting facilities, and shotcrete specimens are far more time consuming to prepare than concrete members is, it is advisable to perform preliminary tests on FRC specimens first. Based on the understanding that the flexural strength for FRS and FRC are similar, while the residual loads can be up to 50% lower for FRS, appropriate FRC mixes can be identified to prepare corresponding FRS specimens for further experiments. When waterproofing is a concern, permeability is an important parameter to be considered. From Table 6, it is clear that the permeability of FRS can be one to two orders of magnitude higher than that for FRC of similar composition. To come up with a trial mix of FRS to fulfil permeability requirements, the composition for an FRC with much lower permeability should be employed. Fig. 5. (a) Shrinkage strain vs. time for plain concrete specimens. (b) Shrinkage strain vs. time for 0.5% polypropylene fiber specimens. (c) Shrinkage strain vs. time for 0.5% steel fiber specimens. It should also be pointed out that the compressive strength differences between FRS and FRC do not correlate well with the flexural strength and shrinkage behavior.From Table 3, the compressive strength of FRS is consistently below that of FRC, by up to 30–40% in three out of the four compositions of FRS. However, the shrinkage behavior of FRS and FRC is essentially the same, and the flexural strength of FRS (Table 4) is higher than that of FRC for most cases (except the case with hybrid fiber reinforcement, where there may be high porosity). Therefore, it is not possible to predict the postcracking behavior from the compressive strength. If shrinkage cracking is an important concern, trial mixes for FRS should not be selected based on the compressive strength of FRC. For permeability, except for the steel fiber composite, a larger relative difference in compressive strength does indicate a higher increase in the permeability of the FRS specimen. However, we do not have sufficient data to obtain a quantitative correlation between the compressive strength and the permeability of FRS. If waterproofing is important, the permeability test should be carried out.