scholarly journals High-Power Fiber Laser Cutting for 50-mm-Thick Cement-Based Materials

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1113 ◽  
Author(s):  
Youngjin Seo ◽  
Dongkyoung Lee ◽  
Sukhoon Pyo
Keyword(s):  
Fiber Laser ◽  
Laser Cutting ◽  
High Performance ◽  
High Performance Concrete ◽  
Interaction Mechanism ◽  
Multimode Fiber ◽  
Ultra High Performance Concrete ◽  
Cross Sectional ◽  
Water To Cement Ratio ◽  
Cement Based Materials

This experimental research highlights the applicability of laser cutting to cement-based materials using multimode fiber lasers. A 9 kW multimode fiber laser is used, and the experimental variables are the water-to-cement ratio, laser speed, and material compositions such as cement paste, cement mortar and ultra high performance concrete (UHPC). The laser cutting performance on the cement-based materials is investigated in the downward laser direction. The kerf width and penetration depth of the cement-based materials are quantitatively evaluated with the parameters in the surface and cross section of the specimens after the laser cutting. Moreover, the material removal zone of each specimen is compared in terms of the penetration shapes in the cross-sectional view. Based on experimental observations, the interaction mechanism between the laser and cement-based materials is proposed.

scholarly journals Experimental Study on Bond Stress between Ultra High Performance Concrete and Steel Reinforcement

2018 ◽  
Vol 3 (12) ◽  
pp. 1235 ◽  
Author(s):  
Ahad Amini Pishro ◽  
Xiong Feng
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
High Performance ◽  
High Performance Concrete ◽  
Longitudinal Shear ◽  
Steel Reinforcement ◽  
Bond Stress ◽  
Axial Deformation ◽  
Ultra High Performance Concrete ◽  
Cement Based Materials

Due to axial deformations generally caused by flexure, shear stress will be generated across the interface between reinforcement and surrounding concrete. This longitudinal shear stress is called bond stress and coordinates deformation between concrete and reinforcement. With increasing a member's axial deformation, bond stress finally reaches its ultimate value, bond strength, after which deformation of reinforcement and surrounding concrete will be not coordinated any more. Studies have shown that addition of nanosilica into cement-based materials improves their mechanical properties. Considering the unique characteristics of nanosilica, it seems that this material can be used in ultra-high performance concrete. Therefore, further research is needed on how to use it in concrete mixes. Due to the importance of examining bond stress and the lack of exact equations for bond stress of ultra-high performance concrete and steel reinforcement, the present study aimed to assess the bond stress between concrete and steel reinforcement.

Full-scale bending test and parametric study on a 30-m span prestressed ultra-high performance concrete box girder

2019 ◽  
Vol 23 (7) ◽  
pp. 1276-1289 ◽  
Author(s):  
Jia-zhan Su ◽  
Xi-lun Ma ◽  
Bao-chun Chen ◽  
Khaled Sennah
Keyword(s):  
Parametric Study ◽  
High Performance ◽  
High Performance Concrete ◽  
Full Scale ◽  
Bending Test ◽  
Ultra High Performance Concrete ◽  
Original Design ◽  
Cross Sectional ◽  
Box Girder ◽  
Concrete Box Girder

Due to its structural efficiency, durability, and cost-effectiveness, ultra-high performance concrete was utilized to build the first highway overpass bridge in China. The bridge was made of prestressed ultra-high performance concrete box girders of four continuous spans of 30 m each. As the original design of such bridge was observed to be somewhat conservative, its cross-sectional dimensions, in the form of the box girder wall thicknesses were optimized in this research to lower the material cost in future bridge construction. Then, a full-scale simply supported ultra-high performance concrete box girder of 30 m span, incorporating the new box girder wall thicknesses, was fabricated and then tested under static loading to obtain research data to justify the revised design. The loading system was designed to examine the flexural behavior of the girder using two concentrated loads symmetrically located at the mid-span. Experimental results show that the optimized girder has a favorable ductile behavior and excellent flexural strength, which can meet the design requirements for serviceability and ultimate limit states. A finite element model of the tested girder was developed, using ABAQUS software, and then was verified using the experimental findings. A parametric study was then conducted to investigate the influence of key parameters on the structural response, namely, the reinforcement ratio, the number of the prestressing wires, and the web thickness. Recommendations on minimum and maximum compressive strength and tensile property of ultra-high performance concrete were proposed. Also, a simplified calculation method of prestressed ultra-high performance concrete box girder was developed based on a verified strain and stress diagrams for cross-sectional analysis. The proposed methodology can be used in future practice with confidence.

Flexural design of precast, prestressed ultra-high-performance concrete members

PCI Journal ◽  
2020 ◽  
Vol 65 (6) ◽  
pp. 35-61
Author(s):  
Chungwook Sim ◽  
Maher Tadros ◽  
David Gee ◽  
Micheal Asaad
Keyword(s):  
Prestressed Concrete ◽  
High Performance ◽  
High Performance Concrete ◽  
Limit State ◽  
Design Guidelines ◽  
Design Tool ◽  
Supplementary Cementitious Materials ◽  
Ultra High Performance Concrete ◽  
Concrete Members ◽  
Cylinder Strength

Ultra-high-performance concrete (UHPC) is a special concrete mixture with outstanding mechanical and durability characteristics. It is a mixture of portland cement, supplementary cementitious materials, sand, and high-strength, high-aspect-ratio microfibers. In this paper, the authors propose flexural design guidelines for precast, prestressed concrete members made with concrete mixtures developed by precasters to meet minimum specific characteristics qualifying it to be called PCI-UHPC. Minimum specified cylinder strength is 10 ksi (69 MPa) at prestress release and 18 ksi (124 MPa) at the time the member is placed in service, typically 28 days. Minimum flexural cracking and tensile strengths of 1.5 and 2 ksi (10 and 14 MPa), respectively, according to ASTM C1609 testing specifications are required. In addition, strain-hardening and ductility requirements are specified. Tensile properties are shown to be more important for structural optimization than cylinder strength. Both building and bridge products are considered because the paper is focused on capacity rather than demand. Both service limit state and strength limit state are covered. When the contribution of fibers to capacity should be included and when they may be ignored is shown. It is further shown that the traditional equivalent rectangular stress block in compression can still be used to produce satisfactory results in prestressed concrete members. A spreadsheet workbook is offered online as a design tool. It is valid for multilayers of concrete of different strengths, rows of reinforcing bars of different grades, and prestressing strands. It produces moment-curvature diagrams and flexural capacity at ultimate strain. A fully worked-out example of a 250 ft (76.2 m) span decked I-beam of optimized shape is given.

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