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Research Article

Mechanical Properties of Fiber Reinforced Lightweight Concrete Containing Surfactant

Y oo-Jae Kim, Jiong Hu, Soon-Jae Lee, and Byung-Hee Y ou

Department of Engineering Technology, Texas State University, San Marcos, TX 78666, USA Correspondence should be addressed to Y oo-Jae Kim, yk10@https://www.sodocs.net/doc/1b7202404.html,

Received 21 June 2010; Accepted 24 November 2010

Academic Editor: Tarun Kant Copyright ? 2010 Y oo-Jae Kim et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Fiber reinforced aerated lightweight concrete (FALC) was developed to reduce concrete’s density and to improve its fire resistance, thermal conductivity, and energy absorption. Compression tests were performed to determine basic properties of FALC. The primary independent variables were the types and volume fraction of fibers, and the amount of air in the concrete. Polypropylene and carbon fibers were investigated at 0, 1, 2, 3, and 4% volume ratios. The lightweight aggregate used was made of expanded clay. A self-compaction agent was used to reduce the water-cement ratio and keep good workability. A surfactant was also added to introduce air into the concrete. This study provides basic information regarding the mechanical properties of FALC and compares FALC with fiber reinforced lightweight concrete. The properties investigated include the unit weight, uniaxial compressive strength, modulus of elasticity, and toughness index. Based on the properties, a stress-strain prediction model was proposed. It was demonstrated that the proposed model accurately predicts the stress-strain behavior of FALC.

1. Introduction

In the last three decades, prefabrication has been applied to small housing and tall building construction, and precast concrete panels have become one of the widely used materials in construction system. Recently, much attention has been directed toward the use of lightweight concrete for precast concrete to improve the performances, such as dead load reduction, fire resistance, and thermal conductivity, of the buildings. Additionally, the structure of a precast building should be able to resist impact loading cases, particularly earthquakes, since resisting earthquakes of these buildings under the performances is becoming an important consideration [1, 2].Many efforts have been applied toward developing high performance concrete for building structures with enhanced performance and safety. V arious types of precast concrete products, such as autoclaved aerated lightweight concrete (AALC), fiber reinforced concrete (FRC), and lightweight concrete, have been developed and experimentally verified.

A number of them have been applied in full-scale build-ing structures. AALC is well known and widely accepted, but its small size and weak strength limit its use instructural elements [3]. Lightweight aggregate concretes offer strength, deadload reduction, and thermal conductivity,

but their limited ability to absorb earthquake energy raises concerns. In contrast, FRC has greater energy-absorbing ability, which is called “ductility or inelastic deformation capacity,” than normal concrete, but its weight poses problems. Fiber aerated lightweight concrete (FALC) has a promising future for precast concrete panels that can be used in both small and tall building structures because it combines the comfort of AALC, the adaptability of lightweight aggregate concrete, and the reliability of FRC [4-6]. The purpose of this study is to investigate the material properties of FALC, including the compressive strength, modulus of elasticity and toughness index, with different densities, fibers, and volume fractions of fiber. Also, a new modulus of elasticity equation is presented, and the effects of fibers on strength and toughness are evaluated. Based on these properties, a stress-strain prediction model is proposed.

2. Experimental Programs

To perform this experiment, lightweight concrete mix designs with various densities, air volume, chopped fiber volume and types were used. To improve compressive strength and ductility, as well as the performances for wall panel, expanded clay coarse, fine aggregate, and surfactant to control the density, two different kinds of chopped fibers and self-compaction admixture were used for laboratory experiment. Also, preliminary test results included not only a complete stress-strain curve, but also a measure of ductility, such as energy to failure per unit strength, or ratio of failure strain to yield strain to find constitutive model. In this work, the surfactant contents were 0 and 0.1%, and the fiber volume fractions were 0, 1, 2, 3, and 4%.

2.1. Materials.

The materials used consisted of early high strength Type I cement satisfying ASTM C150, coarse lightweight aggregate, and fine lightweight aggregate. A self-compaction agent ( Sika V iscoCrete 6000) was used to reduce water and maintain good workability. Surfactant was used to control the density of concrete. Fibers currently being used in concrete can broadly be classified into two types. Low modulus, high elongation fibers, such as nylon, polypropylene, and polyethylene, are capable of large energy absorption characteristics. They do not improve strength; however, they impart toughness and resistance to impact and explosive loading. On the other hand, high strength, high modulus fibers such as steel, glass, asbestos, and carbon produce strong composites. They impart strength and stiffness to the composite and, to varying degrees, dynamic properties. Polypropylene and carbon fiber were used in this test. Table 1 presents the properties of these fibers. Tables 2 show properties of aggregates and admixtures, respectively.

2.2. Mixture Proportions.

All the mixtures had a cement content of 560 kg/m3 and a fiber content of 5.6, 11.2, 16.8, or 22.4 kg/m3 . This cement content was chosen from the previous tests to provide a compressive strength of about 38 MPa. The water cement ratio was fixed at 0.45. The self-compaction agent provided maximum water reduction ( 10% ～45% of ordinary water cement ratio), increased early strength, and provided excellent plasticity while maintaining slump for up to two hours. To prevent tangling or balling of the fibers with consequent non uniform fiber distribution, the self-compaction agent and a low shear mixer were used. Table 4 presents detailed mixing proportions .Except for batches without surfactant, the same mixing procedure was followed for all batches. First, fine aggregate and water were mixed for 2 minutes to allow for absorption, since the fine lightweight aggregates were not presoaked. Then, cement was added with surfactant for 5 minutes to make air bubbles. Following that, coarse aggregate, fibers, and a self-compacting agent were mixed for 3 minutes. No tangling or balling of the fibers was observed during the mixing. Occasionally, the mixing time was longer than as described due to surfactant contingency.

2.3. Test Specimens.

All the fiber aerated lightweight concrete cylinders for compression testing were 100 × 200 mm. The specimens were cast in plastic molds and were compacted by hand and vibrator. After casting, the specimens were covered with wet towels for 24 hours. They were then cured in a saturated water bath maintained at 23 ± 2?C for seven days. After four days of drying in the laboratory environment at 21 ± 2?C and 50 ± 15% humidity, they were tested.

All the specimens were tested in uniaxial compression using rigid steel plates on an MTS 100 ton test frame. Load and displacements were measured using the load cell and LVDT of the load frame. Axial strain was measured using extensometers located on opposite sides of the cylinder. The average of these extensometer readings was taken as the axial strain value. All the measurements were stored in the computer which runs the MTS test frame.

3. T est Results

3.1. Compressive Strength.

According to the test results (Tables 5 and 6) for polypropylene fiber lightweight concrete with no surfactant, axial stresses ranged from 31.5 to38.3 MPa, with axial strain at peak stress varying from 0.0034 to 0.0044 mm/mm. For carbon fiber lightweight concrete with no surfactant, axial stresses ranged from 29.9 to 39.4 MPa, with axial strain at peak stress varying from 0.0037 to 0.0046 mm/mm. Transversely, when 0.1% surfactant was used with polypropylene fiber lightweight concrete, axial stresses ranged from 12.1 to 17.0 MPa, with axial strain at peak stress varying from 0.0021 to 0.0028 mm/mm. For carbon fiber lightweight concrete with 0.1% surfactant, axial stresses ranged from 12.6 to 17.5 MPa, with axial strain at peak stress varying from 0.0023 to 0.0031 mm/mm. As shown in Table 6,when 0.1% of surfactant was added, compressive strength decreased by 50～58%. In polypropylene and carbon fiber lightweight concrete with no surfactant, the addition of fibers further increased the strength up to 3% of fiber volume fraction. In both polypropylene and carbon fiber lightweight concrete with 0.1% surfactant, the increase of fiber resulted in gradual decrease of compressive strength. Thus, two main factors that decrease the compressive strength are observed to be fiber volume fraction and the amount of surfactant (Figure 1).

3.2. Modulus of Elasticity . Modulus of elasticity is a primary concern in concrete strength. In the case of fiber lightweight concrete without surfactant, the increase in the modulus of elasticity appears to be affected slightly by fiber volume fraction. Moreover, the decrease in the modulus of elasticity provided by fibers with 0.1% surfactant was significant. For polypropylene and carbon fiber lightweight concrete with no surfactant, the modulus of elasticity ranged from 6.6 to 12.0 GPa, and 8.2 to 10.4 GPa, respectively. On the other hand, for polypropylene and carbon fiber lightweight concrete with 0.1% surfactant, the modulus of elasticity ranged from 5.3 to 7.3 GPa, and 6.0 to 8.3 GPa, respectively (see Table 5 and 6). According to Figure 2, the best fiber volume fraction for modulus of elasticity is between 2% and 3% in all cases.

According to ACI 318-05 [1], the modulus of elasticity of concrete depends on its compressive strength and density. However, there is not a specific equation for modulus of elasticity with unit weights between 1120 and 1440 kg/m3 . Figures 3 and 4 show the comparison of the modulus of elasticity of ACI equation with experimental data from both polypropylene fiber and carbon fiber. Comparison of the modulus of elasticity from experimental data to ACI 318-05 equation shows that in unit weight between 1425.6

and 1489.7 kg/m3 with both fibers, ACI 318-05 equation overesti-lightweight concrete with 0.1% surfactant and unit weights mates about 16～104% of experimental data. Comparatively, in unit weight between 1137.3 and 1297.5 kg/m3 , the values of the modulus of elasticity with ACI Code 8.5 equation ranges from -21% to 19% with both fibers. The influences of fiber volume fraction and unit weight on the modulus of elasticity are presented in Tables 5 and 6. Equation (1) relates these results to values calculated by means of the modulus of elasticity given in ACI 318-05

（Ef c = 1.259192 1 ? e?0.8134Ec r2 = 0.94), (1)

Where Ef c = modulus of elasticity of fiber aerated lightweight concrete, and Ec = modulus of elasticity calculated by ACI 318-05 equation (GPa).

3.3. Unit Weight.

The unit weight of the concrete was measured at 7 days curing, and again after 4 days of drying in the laboratory environment at 21 ± 2?C and 50 ± 15% humidity. The results are presented in Tables 5 and 6. The unit weight of polypropylene fiber reinforced lightweight concrete ranged from 1467.7 to 1489.7 kg/m3, with compressive strengths from 31.5 to 38.3 MPa. For carbon fiber reinforced lightweight concrete, unit weight varied from 1425.6 to 1505.7kg/m3 , and compressive strengths varied from 29.9 to 39.4 MPa. For polypropylene fiber reinforced varying from 1201.4 to 1297.5 kg/m3 compressive strengths ranged from 12.1 to 17.0 MPa. For carbon fiber reinforced lightweight concrete with 0.1% surfactant and unit weights varying from 1137.3 to 1297.5 kg/m3 , compressive strengths ranged from 12.6 to 17.5 MPa. It was found that there is no trend with respect to either fiber volume fraction or types of fiber.

3.4. Toughness Index

One of the main objectives of adding fibers to a concrete matrix is to increase its toughness, its energy-absorbing capability, and make it more suitable for use in structures subjected to impact and earthquake loads. The normalized stress-strain curves (Figure 5) show that the slope of the

ascending portion of the curves in fiber reinforced lightweight concrete is the same as

for normal lightweight concrete. However, in the post-peak portion of the stress-strain curve, the curves gradually drop, then increase in strain capacity. Figure 6 indicates that the addition of fibers improved ductility to a limited extent. The increase of toughness with fiber volume fraction is more significant for carbon fiber than for polypropylene fiber .

The toughness index is defined here as the area under the stress-strain curve of fiber concrete up to a strain of 0.015, divided by the area of no fiber lightweight concrete with

normalized stress up to a strain of 0.015. The toughness of polypropylene and carbon fiber reinforced lightweight concrete with no surfactant ranged from 1.05 to 1.33, and from 1.05 to 1.74, respectively. However, with 0.1 % surfactant, toughness ranged from 2.11 to 2.75 for polypropylene, and from 1.97 to 2.64 for carbon fiber where RI is the reinforcing index (Vf ? l/φ). TI = 1.338 + 0.221 ? RI(r2 = 0.92) for polypropylene fiber,

TI = 1.354 + 0.023 ? RI(r2 = 0.89) for carbon fiber,(2)

An increase in the volume fraction and modulus of elasticity of fibers generally led to a decrease in the slope of the descending portion of the stress-strain curve. For both fibers, an increase in fiber volume fraction led to similar results. The aspect ratio (l/φ) and the fiber volume fraction seemed to play an important role in improving the peak strain and the toughness of the composite. Improvements of the toughness index due to adding more fiber were relatively significant in lower unit weight concretes.

As mentioned above, the post-peak portion of the stress-strain curve for FALC is significantly related to the fiber aspect ratio and volume fraction. Therefore, an inflection poin t (εi ) based on the reinforcing index is selected for the descending portion of the curve for FALC. In the proposed equation by Ezeldin and Balaguru [4], the equation is derived from the inflection point modulus of elasticity from reinforcing index for high strength reinforced concrete, however, as indicated, the post peak portion of stress-strain curve was different between high strength and lightweight concrete. In FALC, inflection point modulus of elasticity must be

derived from modulus of elasticity of each fiber other than reinforcing index, then pick an inflection point based on toughness index is selected.

The following equation was derived:

where TI = toughness index, εi = strain at inflection point,and ε0 = strain at maximum stress.

4. Conclusions

The experimental work reported here sought to characterize the mechanical properties and stress-strain behavior of fiber aerated lightweight concrete. The following conclusions were drawn.

(1) Using conventional lightweight aggregate, FALC air dry densities as low as 1137 kg/m3can be achieved by adding 0.1% of surfactant and additives.

(2) Both compressive strength and elastic modulus are strongly dependent on the amount of air in the concrete. The increase in surfactant content results in a less compressive strength and elastic modulus compared to non surfactant concrete.

(3) Both the compressive strength and elastic modulus are weakly dependent on the amount of

fiber in the concrete.

(4) The toughness index is strongly dependent on the amount of fiber in the aerated concrete. While an increased polypropylene fiber volume fraction improves the toughness index of the concrete, carbon fiber improves this index to a greater degree.

(5) The stress-strain curve was represented by using a fractional equation based on the reinforcing index. A fair correlation was achieved in predicting the stress-strain curve.

References

[1] ACI Committee 318, Building Code Requirements for Reinforced Concrete (ACI 318-05) and Commentary, American Concrete Institute, Detroit, Mich, USA, 2005.

[2] Building Research Establishment, “Autoclaved aerated con-crete,” Building Research Establishment Digest 342, pp. 1-8, March 1989.

[3] F. C. Mc Cormick, “Rational proportioning of preformed foam cellular concrete,” ACI Journal, vol. 64, pp. 104-110, 1967.

[4] A. S. Ezeldin and P. N. Balaguru, “Normal- and high-strength fiber-reinforced concrete under compress ion,” Journal of Mate-rials in Civil Engineering, vol. 4, no. 4, pp. 415-429, 1992.

[5] C. H. Henager, “Steel fibrous concrete—a review of testing procedures,” in Proceedings of the Symposium on Fiber Concrete, pp. 16-28, London, UK, 1980.

6] C. D. Johnston, Fiber Reinforced Cements and Concretes, Gordon and Breach Science, Amsterdam, The Netherlands, 2001. [7] R. N. Swamy, P. S. Mangat, and C. V. S. K. Rao, The Mechanics of Fiber Reinforcement of Cement Matrices, Fiber Reinforced Concrete, SP44, American Concrete Institute, Detroit, Mich, USA, 1973.

研究文章

含表面活性剂的纤维增强轻质混凝土的力学性能

工程技术部，美国德克萨斯州州立大学圣马科斯，德克萨斯州78666

2010年6月21日，2010年11月24日

纤维增强加气轻质混凝土（FALC）的开发，是用来减少混凝土的密度，并提高其耐火性能，导热系数以及能量的吸收能力。通过做压缩试验，以确定FALC 的基本属性。其研究的主要的独立变量有混凝土的的类型、纤维体积分数还有在混凝土中的空气量。同时也对聚丙烯，碳纤维的影响进行了调查，大约在0到4％的体积比。

这种轻质混凝土是使用轻骨料膨胀粘土制成的。自我压实剂用来降低水灰比，并使之保持良好的和易性。表面活性剂也常常被加入到空气并引入到混凝土中。这项研究提供了有关的FALC的力学性能基本的信息，并且进行FAL与纤维增强轻质混凝土的比较。调查的性质，包括单位重量、单轴抗压强度、弹性模量、韧性指标。在应力-应变特性的基础上提出了预测模型。结果表明，该模型准确地预测了FALC的应力—应变行为。

1．介绍

在过去的三十年中，预制已广泛应用于小型房屋和高层建筑的建设施工中，混凝土预制板已成为在建设系统中广泛使用的材料之一。最近，轻质混凝土预制混凝土的使用备受关注，关注的方面集中在改善建筑物的负荷减少，耐火性能，以及导热系数等。此外，一个预制建筑物的结构应该能够抵御冲击负荷的情况，特别是地震的时候，因此这些建筑物的抗震性能正在成为一个重要的考虑因素。在发展高性能混凝土与具有增强性能和安全性能的建筑结构的应用方面人们也已经做了很多的努力。各类预制混凝土产品，如蒸压加气轻质混凝土（AALC），纤维增强混凝土（FRC），轻质混凝土，都已经得到开发和实验验证。

其中一些已经应用于大规模的建设结构中。AALC是众所周知的，并且也被人们所广泛接受。但其体积小、强度弱，限制了它对结构元素的使用【3】。轻骨料混凝土有着很好的强度，负荷减少以及导热性，但其吸收地震能量的有限能力引起人们的忧虑。相比之下，FRC比普通混凝土有着更好的能量吸收能力，也就是人们所说的“塑性或弹性变形能力”，但它的重量也往往会带来问题。纤维加气轻质混凝土（FALC）有着一个广阔前途的未来，可以广泛应用于小型和高层建筑结构的预制混凝土板，因为它结合了AALC的舒适性，轻骨料混凝土的适应性以及FRC的可靠性【4-6】。本研究的目的是探讨具有不同密度，纤维，纤维体积分数的FALC材料的性能，包括抗压强度，弹性模量和韧性指数。此外，研究提出了一个新的弹性模量的弹性方程，对纤维的强度和韧性对材料性能的影响进行评估。基于以上这些特性，提出了应力—应变预测计算模型。

2．实验方案

做这个实验过程中，使用不同的密度，空气量，切碎纤维的数量和种类的轻质混凝土配合比进行设计。为了提高抗压强度和延展性，以及墙板的性能，扩大粘土粗细程度，细骨料以及表面活性剂来控制密度，并将两种不同类型的切碎纤维和自密实剂用于实验室的实验中。此外，初步测试的结果不仅包括一个完整的应力－应变曲线，也提供了一种衡量延展性的方法，在这项工作中，表面活性剂含量为0%和0.1%，纤维体积分数分别为0%，1%，2%，3%，和4%。

2.1．物料

实验所用的材料包括早期强度高，Ⅰ号型水泥ASTM C150，粗轻骨料，细质轻骨料。自压实剂（Sika ViscoCrete 6000）用来以减少水和保持良好的和易性。表面活性剂用来控制混凝土的密度。目前用在混凝土中的纤维大致可分为两类。一种低模量、高伸长率纤维，如尼龙、聚丙烯、聚乙烯，有能够大量吸收能量的特性。它们不提高强度；但是, they impart toughness and resistance to impact and explosive loading。另一方面，高强度、高模量纤维，如钢铁、玻璃、石棉

还有和碳产生强烈反应的复合材料。They impart strength and stiffness to the composite and, to varying degrees, dynamic properties。在这个测试中，采用聚丙烯，碳纤维。表1给出了这些纤维的性能。表2分别给出了骨料和外加剂的属性。

2.2．混合比例

所有的混合物有560 kg/m3的水泥含量，纤维含量分别为5.6 kg/m3、11.2

kg/m3、16.8 kg/m3或者22.4 kg/m3。这个选自以前的测试结果的水泥含量提供大约38 Mpa的抗压强度，水灰比固定在0.45。自密实剂提供最大的减水（10％?45％的普通水灰比），提高早期强度，并提供良好的可塑性，同时保持长达两个小时的衰退。为了防止混乱或纤维成球产生的非纤维均匀分布，使用了自压实剂和低剪切混合器。表4给出了详细的混合比例。除了无表面活性剂的批次，所有的批次按照相同的混合步骤进行混合。首先，细骨料和水混合2分钟，以保证水分的吸收，因为细轻质骨料是不浸的。然后，水泥加入表面活性剂5分钟以产生气泡。随后，粗骨料，纤维和自密实剂混合3分钟。在混合过程中没有No tangling or balling of the fibers was observed。偶然的，由于表面活性剂的意外情况，搅拌时间可能会长于以上所述。

2.3．试验样品

所有的纤维轻质加气混凝土抗压试验所用的汽缸尺寸为100×200mm。这个标件铸在塑料模具中，并通过手和振动压实。铸造完成后，标件用湿毛巾捂24小时。接着他们被固化在饱和的水温保持在23±2℃的水中7天。在经过放在21±2℃和50±15%湿度的试验环境下干燥4天之后，最后对它们进行测试。

所有的标件都在使用刚性板的100吨MTS试验框架上进行单轴压缩测试。载荷和位量使用称重传感器和位移传感器的负载架进行测量。轴向应变使用引伸坐落在两侧的气缸进行测量。取这些引伸计读数的平均数作为最后的轴向应变值。所有的测量都存储在运行测试MTS框架的计算机系统上。

3．测试结果

3.1．抗压强度

根据测试结果（表5和表6）对于没有表面活性剂的聚丙烯纤维轻质混凝土，轴向应力介于31.5 到38.3Mpa，轴向应力峰值处的轴向应变在0.0034到

0.0044mm/mm之间变化。对于没有表面活性剂的碳纤维轻质混凝土，轴向应力在29.9到39.4Mpa之间变化，轴向应力峰值处的轴向应变在0.0037到

0.0046mm/mm之间不等。横向的，对于含0.1％表面活性剂的聚丙烯纤维轻质混凝土，轴向应力介于12.1到17.0Mpa之间，轴向应力峰值处的轴向应变在0.0021到0.0028mm/mm之间浮动。对于含0.1％表面活性剂的碳纤维轻质混凝土，轴向应力介于12.6到17.5Mpa之间，轴向应力峰值处的轴向应变从0.0023到0.0031mm/mm不等。如表6所示，添加表面活性剂0.1％时，抗压强度下降50％?58％。在无表面活性剂的聚丙烯、碳纤维轻质混凝土中，纤维的使用一使强度提高到纤维体积分数为3％的混凝土的强度。在聚丙烯和0.1％表面活性

剂的碳纤维轻质，纤维的增加导致了混凝土抗压强度的逐渐减少。因此，降低抗压强度的两个因素是纤维体积分数和表面活性剂的量（图1）。

3.2．弹性模量

弹性模量是混凝土强度的主要考虑因素。在纤维轻质混凝土没有表面活性剂的情况下，纤维体积分数对弹性模量的增大的影响很小。此外，含0.1％表面活性剂的纤维轻质混凝土的弹性模量下降显着。对于不含表面活性剂的聚丙烯和碳纤维轻质混凝土，弹性模量分别介于6.6到12.0 GPa之间和8.2至

10.4GPa之间。另一方面，聚丙烯和含0.1％表面活性剂的碳纤维轻质混凝土，

弹性模量分别介于5.3到7.3 GPa之间和6.0至8.3 GPa之间。（见表5和6）根据图2，在所有情况下，对于弹性模量，混凝土的最佳纤维体积分数为2％和3％之间。

根据ACI318-05[1]，混凝土的弹性模量取决于其抗压强度和密度。然而，对于单位重量介于1120 kg/m3到1440 kg/m3的混凝土的弹性模量没有具体的计算公式。图3和图4显示了聚丙烯纤维材料和碳纤维材料的实验数据的ACI方程的弹性模量的比较。通过实验的数据和ACI318-05方程计算出的弹

从实验数据的ACI318-05方程的弹性模量的比较表明，在这两种纤维的ACI318-05方程高估轻质混凝土与0.1％的表面活性剂和单位重量的队友单位，之间1425.6and1489.7 kg/m3的重量约16?104％的实验数据。相比之下，在1137.3和1297.5 kg/m3的单位重量，ACI规范8.5方程的范围从-21％到19％同时纤维的弹性模量的值。纤维体积分数和弹性模量，单位重量的影响列于表5和表6。方程（1）有关这些结果的弹性模量计算值的ACI318-05

其中E

fc 代表纤维加气轻质混凝土的弹性模量，E

代表ACI318-05方程（GPA）

计算的弹性模量。

3.3．单位重量

单位重量的具体测量7天治疗，再经过4天晒在实验室环境中在21℃和

50±2?±15%湿度。结果在表5和表6。单位重量的聚丙烯纤维增强轻骨料混凝土的范围从1467.7到1489.7公斤/立方米，与com-pressive强度从31.5到38.3兆帕。碳纤维增强轻质混凝土，容重1425.6～1505.7公斤/立方米，与抗压强度的不同从29.9到39.4兆帕。聚丙烯纤维增强不同从1201.4到1297.5公斤/立方米抗压强度sranged从12.1到17兆帕。碳纤维增强轻质混凝土与0.1%表面活性剂和单位重量的不同从1137.3到1297.5公斤/立方米，抗压强度为12.6～17.5兆帕。结果发现，有无趋势方面的任何类型的纤维或纤维体积分数。

3.4．韧性指数

加入到混凝土基体的纤维的主要目标之一是增加其韧性，其能量吸收能力，使其更适合使用在受到冲击和地震荷载的结构。归应力- 应变曲线（图5）表明，纤维的曲线的上升部分边坡加固轻质混凝土是正常轻质混凝土相同。然而，在峰后的应力- 应变曲线的部分，曲线逐渐下降，然后提高应变能力。图6表明，除纤维改善延性在有限的范围内。更多的碳纤维，显着高于聚丙烯纤维的韧性与纤维体积分数的增加。

这里作为该地区韧性指标定义下纤维混凝土的应力- 应变曲线应变为0.015，除以面积与无纤维轻质混凝土归应力应变到0.015。

从1.05至1.33之间没有表面活性剂的韧性聚丙烯，碳纤维增强轻质混凝土，从1.05到1.74，分别。然而，用0.1％的表面活性剂，韧性介于2.11至2.75聚丙烯，RI是碳纤维增强指数（VF?L/φ）从1.97到2.64。

一般体积分数和纤维的弹性模量的增加导致的应力- 应变曲线的下降部分的斜率下降。对于这两种纤维，在纤维体积分数的增加导致了类似的结果。纵横比（L /φ）和纤维体积分数似乎发挥了重要作用，在提高峰值应变和复合材料的韧性。由于加入更多的纤维，韧性指标的改善是相对较低的单位重量的混凝土显着。如上所述，纤维长宽比和体积分数的FALC的应力- 应变曲线峰后部分显着相关。因此，加强指数为基础的一个转折点（εi）被选中的FALC曲线的下降部分。

[4]在拟议由Ezeldin和Balaguru方程，方程拐点钢筋混凝土加强高强度的指数弹性模量的派生，但是，作为表明，应力- 应变曲线postpeak部分之间的高强

度不同轻质混凝土。FALC，除了加强指数的每个纤维的弹性模量的弹性的拐点模量必须从，然后选择选择韧性指标为基础的一个转折点。

下面的公式推导出：

TI=韧性指标，εi=拐点的应变，ε0=最大应力应变。

4．结论

试点工作的报告，在这里寻求特征的力学性能和纤维加气轻质混凝土的应力应变行为。得出以下结论。

（1）利用传统轻质骨料，空气的FALC干密度低1137 kg/m3can的加入0.1％的表面活性剂和添加剂。

（2）无论是抗压强度和弹性模量，很大程度上取决于对空气中的具体数额。非表面活性剂的混凝土的表面活性剂含量结果相比，在较低的抗压强度和弹性模量的增加。

（3）抗压强度和弹性模量对纤维在混凝土中的金额是弱依赖。

（4）韧性指标是强烈的纤维量在加气混凝土的依赖。而增加的聚丙烯纤维体积分数提高了混凝土的韧性指数，碳纤维更大程度上提高了该指数。

（5）应力- 应变曲线代表用分数方程的基础上加强指标。一个公平的相关性

达到预测的应力- 应变曲线。

参考文献

[1] ACI Committee 318, Building Code Requirements for Reinforced Concrete (ACI 318-05) and Commentary, American Concrete Institute, Detroit, Mich, USA, 2005.

[2] Building Research Establishment, “Autoclaved aerated con-crete,” Building Research Establishment Digest 342, pp. 1-8, March 1989.

[3] F. C. Mc Cormick, “Rational proportioning of preformed foam cellular concrete,” ACI Journal, vol. 64, pp. 104-110, 1967.

[4] A. S. Ezeldin and P. N. Balaguru, “Normal- and high-strength fiber-reinforced concrete under compression,” Journal of Mate-rials in Civil Engineering, vol. 4, no. 4, pp. 415-429, 1992.

[5] C. H. Henager, “Steel fibrous concrete—a review of testing procedures,” in Proceedings of the Symposium on Fiber Concrete, pp. 16-28, London, UK, 1980.

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中等分辨率制备分离的快速色谱技术 W. Clark Still,* Michael K a h n , and Abhijit Mitra Departm(7nt o/ Chemistry, Columbia Uniuersity,1Veu York, Neu; York 10027 ReceiLied January 26, 1978 我们希望找到一种简单的吸附色谱技术用于有机化合物的常规净化。这种技术是适于传统的有机物大规模制备分离，该技术需使用长柱色谱法。尽管这种技术得到的效果非常好，但是其需要消耗大量的时间，并且由于频带拖尾经常出现低复原率。当分离的样本剂量大于1或者2g时，这些问题显得更加突出。近年来，几种制备系统已经进行了改进，能将分离时间减少到1-3h，并允许各成分的分辨率ΔR f≥（使用薄层色谱分析进行分析）。在这些方法中，在我们的实验室中，媒介压力色谱法1和短柱色谱法2是最成功的。最近，我们发现一种可以将分离速度大幅度提升的技术，可用于反应产物的常规提纯，我们将这种技术称为急骤色谱法。虽然这种技术的分辨率只是中等（ΔR f≥），而且构建这个系统花费非常低，并且能在10-15min内分离重量在的样本。4 急骤色谱法是以空气压力驱动的混合介质压力以及短柱色谱法为基础，专门针对快速分离，介质压力以及短柱色谱已经进行了优化。优化实验是在一组标准条件5下进行的，优化实验使用苯甲醇作为样本，放在一个20mm*5in.的硅胶柱60内，使用Tracor 970紫外检测器监测圆柱的输出。分辨率通过持续时间（r）和峰宽（w,w/2）的比率进行测定的（Figure 1），结果如图2-4所示，图2-4分别放映分辨率随着硅胶颗粒大小、洗脱液流速和样本大小的变化。

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英文翻译英语原文： . Introducing Classes The only remaining feature we need to understand before solving our bookstore problem is how to write a data structure to represent our transaction data. In C++ we define our own data structure by defining a class. The class mechanism is one of the most important features in C++. In fact, a primary focus of the design of C++ is to make it possible to define class types that behave as naturally as the built-in types themselves. The library types that we've seen already, such as istream and ostream, are all defined as classesthat is,they are not strictly speaking part of the language. Complete understanding of the class mechanism requires mastering a lot of information. Fortunately, it is possible to use a class that someone else has written without knowing how to define a class ourselves. In this section, we'll describe a simple class that we canuse in solving our bookstore problem. We'll implement this class in the subsequent chapters as we learn more about types,expressions, statements, and functionsall of which are used in defining classes. To use a class we need to know three things: What is its name? Where is it defined? What operations does it support? For our bookstore problem, we'll assume that the class is named Sales_item and that it is defined in a header named Sales_item.h. The Sales_item Class The purpose of the Sales_item class is to store an ISBN and keep track of the number of copies sold, the revenue, and average sales price for that book. How these data are stored or computed is not our concern. To use a class, we need not know anything about how it is implemented. Instead, what we need to know is what operations the class provides. As we've seen, when we use library facilities such as IO, we must include the associated headers. Similarly, for our own classes, we must make the definitions associated with the class available to the compiler. We do so in much the same way. Typically, we put the class definition into a file. Any program that wants to use our class must include that file. Conventionally, class types are stored in a file with a name that, like the name of a program source file, has two parts: a file name and a file suffix. Usually the file name is the same as the class defined in the header. The suffix usually is .h, but some programmers use .H, .hpp, or .hxx. Compilers usually aren't picky about header file names, but IDEs sometimes are. We'll assume that our class is defined in a file named Sales_item.h. Operations on Sales_item Objects