Name: preparation of aligned steel fiber reinforced cementitious composite and its flexural behavior
Uploaded: 2018-06-27T12:30:00
Description: Watch this Scientific Journal Video about Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior at JoVE.com

The authors gratefully acknowledge financial supports from the National Nature Science Foundation of China (Grant No. 51578208), Hebei Provincial Nature Science Foundation (Grant No. E2017202030 and E2014202178), and Key Project of University Science and Technology Research of Hebei Province (Grant No. ZD2015028).

1. Solenoid Magnetic Field Setup
NOTE: The magnetic field is generated by a solenoid with a hollow chamber. The setup is a polybutylene terephthalate (PBT) board solenoid skeleton coiled with 4-6 layers of enamel insulated copper wire and wrapped with a plastic insulating layer for protection (Figure 1). After connecting the coil to DC, the current in the coil creates a uniform electromagnetic field within the solenoid chamber with a fixed direction and constant mag...

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The electromagnetic solenoid developed in this study has a chamber measuring 250&#215;250&#215;750 mm and cannot accommodate the full size structural elements. Although the size of the chamber limits the application of the setup, the concept and protocol proposed in this paper will inspire the further development of a full size setup for manufacturing ASFRC elements, particularly precast elements.
Achieving an appropriate viscosity of fresh mortar is essential factor for controlling the qualit...

Incorporating steel fibers into concrete is an effective way to overcome the inherent weakness of brittleness and to improve the tensile strength of concrete1. During the past decades, steel fiber reinforced concrete has been extensively investigated and widely used in the field. Steel fiber reinforced concrete is superior to concrete in terms of cracking resistance, tensile strength, fracture toughness, fracture energy, etc.2 In steel fiber reinforced concrete, steel fibers are randomly dispersed, thereby uniformly dispersing the reinforcing efficiency of the fibers in every direction. However, under certain loading conditions, only some of the steel fibers in concrete contribute to the performance of the structural elements because the reinforcing efficiency of the fibers requires that they be aligned with the principle tensile stresses in the structure. For instance, when using steel fiber reinforced concrete containing randomly distributed steel fibers to prepare a beam, some of the steel fibers, especially those parallel to the direction of the principal tensile stress, will make major contribution to reinforcing efficiency, while those perpendicular to the direction of the principal tensile stress will make no contribution to reinforcing efficiency. Consequently, finding an approach to align the steel fibers with the direction of the principal tensile stress in concrete is necessary to achieve the highest reinforcing efficiency of the steel fibers.
The orientation efficiency factor, defined as the ratio of the projected length along the direction of the tensile stress to the actual length of fibers, is usually used to indicate the efficiency of the reinforcement of steel fibers3,4. According to this definition, the orientation efficiency factor of the fibers aligned with the direction of the tensile stress is 1.0; that of the fibers that are perpendicular to the tensile stress is 0. Inclined fibers have an orientation efficiency factor between 0 and 1.0. The analytical results show that the orientation efficiency factor of randomly distributed steel fibers in concrete is 0.4054, while that from tests of ordinary steel fiber reinforced concrete is in the range of 0.167 to 0.5005,6. Evidently, if all the short steel fibers in concrete are aligned and have the same orientation as the tensile stress, the steel fibers will have the highest reinforcing efficiency and the specimens will have the optimum tensile behavior.
Some successful attempts to prepare aligned steel fiber reinforced concrete have been conducted since 1980s. In 1984, Shen7 applied an electromagnetic field to the bottom layer of steel fiber reinforced cementitious composite (SFRC) beams during casting, and X-ray detection analysis revealed that steel fibers were well aligned. In 1995, Bayer8 and Arman9 patented the approach for preparing aligned steel fiber reinforced concrete using a magnetic field. Yamamoto et al.10 considered the orientation of steel fibers in concrete to be mainly influenced by the casting approach and attempted to obtain aligned steel fiber reinforced concrete by keeping fresh concrete flowing into the formwork from a constant direction. Xu11 attempted to align steel fibers in shotcrete by spraying steel fibers from a constant direction. Rotondo and Wiener12 sought to make concrete poles with aligned long steel fibers by centrifugal casting. These experimental studies reveal that aligned steel fiber reinforced concrete has significant advantages over randomly distributed steel fiber reinforced concrete.
Recently, Michels et al.13 and Mu et al.14 have successfully developed a group of aligned steel fiber reinforced cementitious composites (ASFRCs) using electromagnetic fields. In these studies, various solenoids were made to provide a uniform magnetic field for aligning steel fibers in mortar specimens of different sizes. The solenoid has a hollow cuboid chamber, which can accommodate specimens of predefined sizes. When the solenoid is connected to direct current (DC), a uniform magnetic field is created in the chamber with a fixed orientation, which aligns with the axis of the solenoid. According to the principle of electromagnetics15, magnetic fields can drive ferromagnetic fibers to rotate and align in fresh mortar. Appropriate workability of the mortar is critical for allowing steel fibers to rotate in fresh mortar. A high viscosity may cause difficulty in the alignment of the steel fibers in the mortar, while low viscosity may lead to the segregation of fibers.
This paper describes the details of the preparation of ASFRC specimens and tests the flexural properties of ASFRC and SFRC. It is expected that ASFRC has a higher flexural strength and toughness than SFRC. Thus, ASFRC potentially has advantages over SFRC in withstanding tensile stress and resisting cracking if used as cover concrete, pavement, etc.
Using the fractured specimens after flexural tests, the orientation of the steel fibers in the specimens is investigated by observing the fractured cross sections and utilizing X-ray scanning computed tomography analysis16,17,18. The mechanical properties of ASFRCs, including their flexural strength and toughness, are reported and compared with those of non-electromagnetically treated SFRCs.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr >
			<td >Cement</td>
			<td >Tangshan Jidong Cement Co., Ltd.</td>
			<td >P&#215;O 42.5</td>
			<td >Oridnary Portland Cement</td>
		</tr>
		<tr >
			<td >Sand</td>
			<td ></td>
			<td >River sand</td>
			<td>Fineness modulus is 2.4</td>
		</tr>
		<tr >
			<td >Superplasticizer</td>
			<td >Subote New Materials Co., Ltd.</td>
			<td >PCA-III</td>
			<td>Polycarboxylated type, water reducing ratio is 35%</td>
		</tr>
		<tr >
			<td >Steel fiber</td>
			<td >Tianjin Hengfeng Xuxiang New Metal Materials Co., Ltd.</td>
			<td >Round straight</td>
			<td>Diameter 0.5mm, length 25mm</td>
		</tr>
	</tbody>
</table>

preparation of aligned steel fiber reinforced cementitious composite and its flexural behavior

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth&#39;s magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a uniform electromagnetic field to fresh mortar containing short steel fibers, whereby the short steel fibers were driven to rotate in alignment with the magnetic field. The degree of alignment of steel fibers in hardened ASFRC was assessed both by counting steel fibers in fractured cross-sections and by X-ray computed tomography analysis. The results from the two methods show that the steel fibers in ASFRC were highly aligned while the steel fibers in non-magnetically treated composites were randomly distributed. The aligned steel fibers had a much higher reinforcing efficiency, and the composites, therefore, exhibited significantly enhanced flexural strength and toughness. The ASFRC is thus superior to SFRC in that it can withstand greater tensile stress and more effectively resist cracking.

The flexural strengths of ASFRCs and SFRCs determined from three-point bending tests are shown in Figure 5. The flexural strengths of ASFRCs are higher than those of SFRCs for all fiber dosages. The flexural strengths of ASFRCs were 88%, 71%, and 57% higher than those of SFRCs at the fiber volume fractions of 0.8%, 1.2%, and 2.0%, respectively. These results imply&#160;that the aligned steel fiber reinforces the cementitious matrix more effectively than rando...

Watch this Scientific Journal Video about Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior at JoVE.com

Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior

This protocol describes an approach for manufacturing aligned steel fiber reinforced cementitious composite by applying a uniform electromagnetic field. Aligned steel fiber reinforced cementitious composite exhibits superior mechanical properties to ordinary fiber reinforced concrete.

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the ...

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