DEM simulation and electron microscopy analysis of the fatigue behavior of ultra-high performance concrete

2019 ◽  
pp. 1427-1432
Author(s):  
S. Rybczyński ◽  
M. Dosta ◽  
G. Schaan ◽  
M. Ritter ◽  
F. Schmidt-Döhl
Keyword(s):  
Electron Microscopy ◽  
High Performance ◽  
High Performance Concrete ◽  
Fatigue Behavior ◽  
Ultra High Performance Concrete ◽  
Dem Simulation ◽  
Electron Microscopy Analysis ◽  
Microscopy Analysis

Fatigue prediction model of ultra-high-performance concrete beams prestressed with CFRP tendons

2021 ◽  
pp. 136943322110623
Author(s):  
Rui Hu ◽  
Zhi Fang ◽  
Ruinian Jiang ◽  
Yu Xiang ◽  
Chuanle Liu
Keyword(s):  
Prediction Model ◽  
High Performance ◽  
High Performance Concrete ◽  
Fatigue Behavior ◽  
Fiber Reinforced Polymer ◽  
Test Results ◽  
Ultra High Performance Concrete ◽  
Flexural Fatigue ◽  
Reinforced Polymer ◽  
Fatigue Development

In the present paper, a comprehensive study on the flexural fatigue behavior of ultra-high-performance concrete (UHPC) beams prestressed with carbon-fiber-reinforced polymer (CFRP) tendons is reported. A total of two UHPC beams prestressed with CFRP tendons were experimentally investigated. On the basis of the fatigue constitutive model of the materials, a fatigue prediction model (FPM) was developed to simulate the flexural fatigue evolvement of the beams. The strain and stress in UHPC and CFRP tendons were calculated by the sectional stress analysis. The influence of steel fiber was considered in the formulae for the crack resistance and crack width, and the midspan deflection was calculated using the sum of deflection before cracking and increment after cracking. The obtained test results were used to verify the FPM. A parametric study was then conducted to analyze the fatigue development of such component, and a formula to predict the flexural fatigue life of UHPC beams under different fatigue loads was proposed.

scholarly journals Static and Fatigue Behavior of Rubber-Sleeved Stud Shear Connectors as Part of Field-Cast Ultra-High Performance Concrete Connections

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2269 ◽  
Author(s):  
Zhigang Zhang ◽  
Xiaoqing Xu
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Fatigue Behavior ◽  
Precast Concrete ◽  
Shear Connector ◽  
Ultra High Performance Concrete ◽  
Shear Connectors ◽  
Rubber Sleeve ◽  
Strength And Stiffness ◽  
Stud Shear Connector

Field-cast ultra-high performance concrete (UHPC) connections are an innovative and prospective solution for combining full-depth precast concrete decks and steel girders. However, previous studies show that the slip capacity of stud shear connectors embedded in UHPC cannot meet the requirements for ductile connectors by Eurocode 4, which can reduce the resistance of steel and concrete composite members. In this study, the rubber-sleeved stud shear connector, which is a composite of ordinary stud and rubber sleeve, was adopted for the field-cast UHPC connections. Push-out tests were conducted to investigate the static and fatigue behavior of the rubber-sleeved stud shear connector as part of field-cast UHPC connections. Results of static tests showed that the rubber-sleeved stud shear connector has sufficient deformation capacity and its slip capacity is 1.5 times that of the ordinary stud shear connector. Compared to ordinary stud shear connectors, UHPC with high strength and stiffness has a relatively small effect on improving the shear strength and stiffness of rubber-sleeve stud shear connectors. Results of fatigue tests showed that the rubber-sleeved stud shear connector in UHPC has similar fatigue behavior to that in normal strength concrete. Though UHPC improves the restraint to the stud deformation, the influence of rubber sleeves is still decisive in determining the fatigue behavior of rubber-sleeve stud shear connectors. In addition, based on the results of strain gauges at stud roots, it was found that the crack initiation process consumes a small proportion of the fatigue life of rubber-sleeved stud shear connectors, which is about 5%.

scholarly journals A review study on sustainable development of ultra high-performance concrete

2021 ◽  
Vol 9 (1) ◽  
pp. 9-35
Author(s):  
Ashhad Imam ◽  
◽  
Keshav K Sharma ◽  
Virendra Kumar ◽  
Neeraj Singh
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Fatigue Behavior ◽  
High Strength ◽  
Ultra High Performance Concrete ◽  
Sustainable Building ◽  
Curing Conditions ◽  
Basic Features ◽  
Hostile Environments

<abstract> <p>A systematic literature review was undertaken in this report to illustrate the development concepts and properties of ultra-high performance concrete (UHPC). UHPC's affluent development relies on its compositional content, water–binder (w/b) ratio, and design mix approach, which contributes to denser and comparatively more homogeneous packaging of particles. Numerous research studies from around the world were used to compile a database on UHPC mechanical and durability properties. Moreover, the results of this study reveal that the curing conditions, aggregates, fibre dosage and characteristics, and curing time are the most important elements in determining the mechanical and durability qualities of UHPC. Furthermore, due to its ultra-high-strength features, superior fatigue behavior, and extremely low porosity, UHPC is considered a practical and long-term alternative for improved sustainable building, resulting in increased resilience to hostile environments. Besides that, attempts are being taken to resolve existing challenges (such as high initial costs, a lack of skills, and a lack of design code) and their solutions to their widespread economic use. This study aims to help architects, builders, and other construction stakeholders better grasp UHPC's basic features and capacities, which will help to understand this durable and long-lasting building material.</p> </abstract>

scholarly journals Discrete Element Modeling and Electron Microscopy Investigation of Fatigue-Induced Microstructural Changes in Ultra-High-Performance Concrete

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6337
Author(s):  
Sebastian Rybczynski ◽  
Gunnar Schaan ◽  
Maksym Dosta ◽  
Martin Ritter ◽  
Frank Schmidt-Döhl
Keyword(s):  
Electron Microscopy ◽  
High Performance ◽  
Lightweight Concrete ◽  
High Performance Concrete ◽  
Fatigue Tests ◽  
Cement Clinker ◽  
Discrete Element Modeling ◽  
Ultra High Performance Concrete ◽  
Microstructural Changes ◽  
The Matrix

In view of the growing demand for sustainable and lightweight concrete structures, the use of ultra-high-performance concrete (UHPC) is becoming increasingly important. However, fatigue loads occur more frequently in nature than static loads. Despite the impressive mechanical properties of UHPC, a reduced tolerance for cyclic loading is known. For this reason, our paper deals with experimental and numerical investigations regarding the main causes for crack initiation on the meso, micro, and nanoscale. After mechanical fatigue tests, we use both scanning (SEM) and transmission electron microscopy (TEM) to characterize microstructural changes. A new rheological model was developed to apply those changes to the mesoscopic scale. The origins of fatigue damaging can be traced back to a transformation of nanoscale ettringite, resulting in a densification of the surrounding binder matrix. Additionally, a higher content of unhydrated cement clinker in the matrix benefits fatigue resistance. On the mesoscale, stress peaks around aggregate grains expand into the surrounding binder with increasing load cycles and lead to higher degradation.

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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