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Advances in Materials Science and Engineering
Volume 2012 (2012), Article ID 537432, 5 pages
http://dx.doi.org/10.1155/2012/537432
Research Article

Research on Fracture Toughness of C120 Ultra-High-Performance Concrete in Kingkey Financial Center Project

1Technology Department, China Construction Fourth Engineering Division Corp. Ltd., Guangzhou 510665, China
2Senior Scientists Association, Tsinghua University, Beijing 100084, China

Received 13 December 2011; Accepted 18 February 2012

Academic Editor: Jin Ping Lu

Copyright © 2012 Hao-Wen Ye 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.

Abstract

By adding polypropylene fiber, fracture toughness of C120 ultra-high-performance concrete in Kingkey Financial Center project has been enhanced. The tests conducted by the Building Material Lab of the Civil and Water Conservancy Institute of Tsinghua University provided satisfactory results of mechanical property and fracture toughness of C120 ultra-high-performance concrete.

1. Preface

In order to understand the mechanical property of C120 ultra-high-performance concrete under static modulus of elasticity and anticracking properties, including fracture toughness, the research group of C120 ultra-high-performance concrete conducted a series of tests in the Building Material Lab of the Civil Water Conservancy Institute of Tsinghua University.

2. Experimental Details

2.1. Raw Materials

Following raw materials are used in this research: (1) cement (Nanjing Xiaoyetian PII52.5), (2) microballoon (Made in Kunming), (3) ganister sand (from Zhunyi, Guizhou), (4) Fine aggregate (sea sand, desalted, FM2.6~2.8), (5) coarse aggregate (macadam, 5–10, 10–20 mm in diameter), (6)   Water reducer (BASF poly carboxylic acid, solid content: 40%, made in Guangdong), (7) water (Shenzhen tap water), and (8) polypropylene fiber (Grace 19 mm long fiber and short fiber provided by Shenzhen Lijian Concrete Company).

2.2. Mix Proportions

Please refer to Figure 1. This test aims to see what the difference is in concrete with long fibers and short fibers, so the compositions of every group of test pieces are the same, except fiber types and quantities.

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Figure 1: Damaged C120 concrete.
2.3. Mixing Process

Get certain amount of raw materials ready. At first, put gelatinizer and sand into a mixer and run for 1 minute; then add water and additive, mix for 2 minutes; lastly, put in coarse aggregate, mix for 1 minute. For materials that are too sticky, mix 1 more minute after adding coarse aggregate. Find Mix Proportions in Table 1.

tab1
Table 1: Mix proportions.
2.4. Specimens

Below specimens are used in the research:100 mm × 100 mm × 400 mm prisms (3),100 mm × 100 mm × 300 mm prisms (6),100 mm × 100 mm × 100 mm cubes (3).

2.5. Curing

Upon being demoulded, specimens were transferred to the caring unit and soaked into calcarea hydrica solution (lime water) for 28 days. Finished specimens were immediately sent to the Building Material Lab of the Civil Water Conservancy Institute of Tsinghua University.

3. Main Mechanical Property Tests

Results of cube compression test, prismoid compression test, and static modulus of elasticity test have been listed in Figures 1 and 2. Equipment used in the tests included YE-200A hydraulic pressure test machine, YJR-5 static digital strain gauging unit, and YEW-200A dropping electrode compression-testing machine (Tables 2 and 3).

tab2
Table 2: Compressive strength test results of cube specimens.
tab3
Table 3: Results of compressive strength and static modulus of elasticity of prism specimens.
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Figure 2: C120 high-performance concrete fracture parameter test.

4. C120 Concrete Fracture Toughness Test

4.1. Equipment

Toni2071 Pressure Flexure Compression Testing Machine was made in Germany, Maximum Capacity 200 KN, for flexure and crack opening displacement tests under constant rate of loading or rate of displacement.

4.2. C120 Concrete Fracture Parameter Test

See Figures 2 and 3.

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Figure 3: Crack opening displacement test.
4.3. P-CMOD and σ-w Curve Charts for 4 Types of Concrete

Through tests, we got the P-CMOD (loading—crack opening displacement) curve charts for basic concrete, concrete with 1 kg long fiber, concrete with 2 kg long fiber, and concrete with 2 kg short fiber, on which we came up with the O-W (softening relation) curve charts (Table 4).

tab4
Table 4: Concrete fracture parameter test results.

5. Analysis

(1)From Figures 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15, we could tell that P-CMOD and O-W curves were similar for the same type of concrete, which meant test piece’s dispersion was not large.(2)4 types of concrete were almost the same, except fiber content, which only presented difference after cracking. Therefore, the cracking load for all 4 types of concrete was similar. (3)As fiber content increased, concrete’s tensile strength almost remained the same. (4)As fiber content increased, concrete’s cracking energy mounted too. When the fiber content remained the same, fiber type played a role in cracking difference. Test results suggested that cracking energy rose in order of basic concrete < concrete with 1 kg long fiber < concrete with 2 kg long fiber < concrete with 2 kg short fiber. (5)Characteristic length of brittleness “ ” notates the brittleness of concrete. The smaller the number is, the more brittle the concrete is. From the test results, we learnt that as fiber content increased, concrete’s toughness enhanced too. Characteristic length of brittleness varies in order: basic concrete < concrete with 1 kg long fiber < concrete with 2 kg short fiber < concrete with 2 kg long fiber, and toughness varies in order:basic concrete < concrete with 1 kg long fiber < concrete with 2 kg short fiber < concrete with 2 kg long fiber.
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Figure 4: P-CMOD for basic concrete.
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Figure 5: σ-w for basic concrete.
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Figure 6: P-CMOD for concrete with 1 kg long fiber.
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Figure 7: σ-w for concrete with 1 kg long fiber.
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Figure 8: P-CMOD for concrete with 2 kg long fiber.
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Figure 9: σ-w for concrete with 2 kg long fiber.
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Figure 10: P-CMOD for concrete with 2 kg short fiber.
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Figure 11: σ-w for concrete with 2 kg short fiber.
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Figure 12: Cracking strength comparison.
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Figure 13: Tensile strength comparison.
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Figure 14: Cracking energy comparison.
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Figure 15: Characteristic length comparison.

6. Conclusions

(1)C120 ultra-high-performance concrete’s fracture toughness can be enhanced by adding fiber, and as fiber content increases, cracking energy mounts too. When fiber content stays the same, fiber type makes difference too. (2)Characteristic length of brittleness notates the brittleness of concrete. The smaller the number is, the more brittle the concrete is. As fiber content increases, concrete’s toughness enhances too.

References

  1. N.-Q. Feng, High-Performance Concrete Structure, Mechanical Industry Publishing House, 2004.
  2. Y.-L. Sun, N. Xu, et al., “Research on polypropylene fiber’s impact on concrete toughness,” Engineering Technology, no. 32: 53, 2007.