scholarly journals Numerical Modelling of Concrete-to-UHPC Bond Strength

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1379 ◽  
Author(s):  
Alireza Valikhani ◽  
Azadeh Jaberi Jahromi ◽  
Islam M. Mantawy ◽  
Atorod Azizinamini
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
High Performance Concrete ◽  
Experimental Studies ◽  
Structural Behaviour ◽  
Ultra High Performance Concrete ◽  
Direct Tension ◽  
Element Analysis ◽  
Additional Material ◽  
Volume Model

Ultra-High Performance Concrete (UHPC) has been a material of interest for retrofitting reinforced concrete elements because of its pioneer mechanical and material properties. Numerous experimental studies for retrofitting concrete structures have shown an improvement in durability performance and structural behaviour. However, conservative and sometimes erroneous estimates for bond strength are used for numerically calculating the strength of the composite members. In addition, different roughening methods have been used to improve the bond mechanism; however, there is a lack of numerical simulation for the force transfer mechanism between the concrete substrate and UHPC as a repair material. This paper presents an experimental and numerical programme designed to characterize the interfacial properties of concrete substrate and its effect on the bond strength between the two materials. The experimental programme evaluates the bond strength between the concrete substrates and UHPC with two different surface preparations while using bi-surface test and additional material tests, including cylinder and cube tests for compression property, direct tension test, and flexural test to complement UHPC tensile properties. Non-linear finite element analysis was conducted, which uses a numerical zero thickness volume model to define the interface bond instead of a traditional fixed contact model. The numerical results from the zero thickness volume model show good agreement with the experimental results with a reduction in error by 181% and 24% for smooth and rough interface surfaces if compared to the results from the model with a fixed contact.

scholarly journals Effect of Elevated Temperature on the Bond Strength of Prestressing Reinforcement in UHPC

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4990
Author(s):  
Petr Pokorný ◽  
Jiří Kolísko ◽  
David Čítek ◽  
Michaela Kostelecká
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Future Research ◽  
Ultra High Performance Concrete ◽  
Negative Effect ◽  
Laboratory Investigations ◽  
Increasing Temperature ◽  
Positive Effect

The study explores the effect of elevated temperatures on the bond strength between prestressing reinforcement and ultra-high performance concrete (UHPC). Laboratory investigations reveal that the changes in bond strength correspond well with the changes in compressive strength of UHPC and their correlation can be mathematically described. Exposition of specimens to temperatures up to 200 °C does not reduce bond strength as a negative effect of increasing temperature is outweighed by the positive effect of thermal increase on the reactivity of silica fume in UHPC mixture. Above 200 °C, bond strength significantly reduces; for instance, a decrease by about 70% is observed at 800 °C. The decreases in compressive and bond strengths for temperatures above 400 °C are related to the changes of phase composition of UHPC matrix (as revealed by X-ray powder diffraction) and the changes in microstructure including the increase of porosity (verified by mercury intrusion porosimetry and observation of confocal microscopy) and development cracks detected by scanning electron microscopy. Future research should investigate the effect of relaxation of prestressing reinforcement with increasing temperature on bond strength reduction by numerical modelling.

Study on the transfer and anchorage length of steel strand in ultra high performance concrete material

2020 ◽  
Vol 10 (2) ◽  
pp. 153-164
Author(s):  
Hui Zheng ◽  
Dongdong Zhou ◽  
Xinfeng Yin ◽  
Lei Wang
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Failure Modes ◽  
High Performance Concrete ◽  
Protective Layer ◽  
Experimental Results ◽  
Ultra High Performance Concrete ◽  
Anchorage Length ◽  
Pull Out ◽  
Steel Strand

Ultra-high-performance concrete (UHPC) material, a new type of cement-based composite material, is usually employed in the bridge engineering. The transfer and anchorage length of steel strand in UHPC material is different from that in ordinary concrete; nevertheless, few design standards are found that how to anchor the transfer and anchoring length of steel strand in UHPC material under normal curing. Through central pull-out test under the different conditions of protective layer thickness and embedded length, the load-slip curves, failure modes, and bond strength of 36 UHPC material specimens under normal curing were studied. The experimental results showed that the ultimate bond stress between UHPC material and steel strand under natural curing conditions is 7.01∼11.68 MPa. When the compressive strength of cube was 157 MPa; the bond strength under natural curing was smaller than that under thermal curing; when the thickness of the protective layer of steel strand with a diameter of 15.2 mm is greater than 30 mm, it had a little influence on bond strength. The regression analysis of the test results based on the experimental results proves that the recommended formulas for the design of transfer length and anchorage length of steel strand in UHPC material were in great agreement with the results of published studies.

Study on Interfacial Properties of Ultra-High Performance Concrete Containing Steel Slag Powder and Fly Ash

2011 ◽  
Vol 194-196 ◽  
pp. 956-960 ◽  
Author(s):  
Yan Zhou Peng ◽  
Kai Chen ◽  
Shu Guang Hu
Keyword(s):  
Fly Ash ◽  
Bond Strength ◽  
High Performance ◽  
Steel Fiber ◽  
High Performance Concrete ◽  
Steel Slag ◽  
Interfacial Zone ◽  
Ultra High Performance Concrete ◽  
Slag Powder ◽  
Steel Slag Powder

The interfacial properties of reactive powder concretes (RPCs), other known as ultra-high performance concrete (UHPC), containing steel slag powder and ultra fine fly ash are studied in this paper. The microstrctural characterization of interfacial transition zones (ITZs), including the aggregate-cement paste interfacial zone and the steel fiber-paste interfacial zone, is investigated by SEM. The microhardness of the aggregate-paste ITZ and the steel slag-paste ITZ is studied and the bond strength of steel fiber in matrix is tested through fiber pullout tests. The results indicate that the microhardness of the steel slag-paste ITZ is slightly higher than that of the aggregate-paste ITZ, which implies the advantage of the substitution of quartz powder with steel slag powder in preparation of RPCs to some degrees. Moreover, the hardness of these two ITZs is higher than that of the hardened paste. A certain amount of hydration products has been observed exsiting on the surface of steel fiber by SEM and the bond strength of steel fiber-martix is up to 9.3MPa. These interfical properties are definitely critical to obtain high performance of UHPCs containing steel slag powder and fly ash.

scholarly journals Ultra high performance concrete shear walls

2021 ◽  
Vol 294 ◽  
pp. 04004
Author(s):  
YiChen Fang
Keyword(s):  
Finite Element ◽  
High Performance ◽  
High Performance Concrete ◽  
Shear Walls ◽  
Element Model ◽  
Current Status ◽  
Ultra High Performance Concrete ◽  
Element Analysis ◽  
Shear Bearing Capacity ◽  
Load Displacement

The history of the development of Ultra-High Performance Concrete (UHPC) shear walls and the current status of today’s research as well as the future development prospects are comprehensively collated. The analysis process and conclusive results of the present-day domestic and international research on UHPC shear walls are highlighted. The load displacement curves, hysteresis curves and skeleton lines of ultra-high performance concrete shear walls under different experimental loads are collated and compared. Integrate the corresponding equations for shear bearing capacity and equations for the overall specimen load displacement curves. A finite element model of the ultra-high performance concrete shear wall is established to simulate and perform non-linear finite element analysis of its force process under unidirectional horizontal loading.

Enhancing Resiliency and Delivery of Bridge Elements using Ultra-High Performance Concrete as Formwork

2019 ◽  
Vol 2673 (5) ◽  
pp. 443-453 ◽  
Author(s):  
Atorod Azizinamini ◽  
Sheharyar Rehmat ◽  
Amir Sadeghnejad
Keyword(s):  
Test Specimen ◽  
High Performance ◽  
High Performance Concrete ◽  
Numerical Study ◽  
Concrete Specimen ◽  
Point Load ◽  
Ultra High Performance Concrete ◽  
Normal Concrete ◽  
Element Analysis ◽  
Normal Strength

A feasibility study of the use of ultra-high performance concrete (UHPC) shell as a formwork is presented. The core concept of the research, developed by the first author, is prefabrication of UHPC shell which acts as a stay-in-place formwork. In the proposed approach, after transporting the UHPC shell to site, the construction of structural elements is completed by placing reinforcing cage inside the UHPC shell and post-pouring with normal concrete. The superior properties of UHPC provide excellent means to enhance the service life of bridge elements, while eliminating the need for assembling or stripping of formwork. As a proof of concept, a combination of experimental and numerical studies was conducted, results of which are reported here. Before conducting experimental work, numerical study in the form of finite element analysis was carried out to investigate performance of shell during placement of the normal concrete. To provide a baseline comparison between UHPC shell formwork and conventional methods, two test specimens were constructed and tested under three-point load setup. The shell test specimen demonstrated flexural strength, 14% greater than an equivalent normal strength concrete specimen. The UHPC shell test specimen failure occurred by debonding of shell at the interface and development of a large crack in the shell. The shell test specimen exhibited improved levels of ductility before failure. The preliminary analysis demonstrated that the idea is feasible and useful for accelerated bridge construction applications.

Ultra-High-Performance Concrete Shear Keys in Concrete Bridge Superstructures

2020 ◽  
pp. 036119812096472
Author(s):  
Elsy Y. Flores ◽  
Jordan Varbel ◽  
William K. Toledo ◽  
Craig M. Newtson ◽  
Brad D. Weldon
Keyword(s):  
High Performance ◽  
Load Transfer ◽  
Mechanical Performance ◽  
High Performance Concrete ◽  
Surface Preparation ◽  
Ultra High Performance Concrete ◽  
Direct Tension ◽  
Girder Bridges ◽  
Grouting Material ◽  
Shear Keys

This research investigated the use of locally produced, non-proprietary ultra-high-performance concrete (UHPC) as a grouting material to repair deteriorated shear keys. Shear keys are used in adjacent girder superstructures to produce monolithic behavior and load transfer across the structure. Shear key degradation can jeopardize the integrity of the structure. Transportation agencies have reported that 75% of distress in adjacent girder bridges is because of cracking and de-bonding along shear keys. Previous research has shown that locally produced UHPC has excellent mechanical and durability properties. UHPC has also been shown to have good bonding characteristics that are desirable in a potential grouting material. Bond strength between UHPC grout and substrate concrete was evaluated using slant-shear and direct tension tests. Results showed that adequate bond was achieved at 7 days. Low strengths at 28 days were observed because of low strength of the substrate concrete. Shrinkage of UHPC grout was also investigated. Shrinkage at 28 days was less than 600 µstrain which is acceptable for repair practices. Full-scale testing was used to evaluate load-deflection behavior of channel girder assemblages with grouted shear keys. Results showed that UHPC grout and non-shrink grout had similar mechanical performance. Excellent bond was achieved with all grouts, even with minimal surface preparation. The similar performances of the non-shrink grout and the UHPC grout indicates that UHPC grout does not provide a mechanical benefit over the non-shrink grout.

New Connection Detail to Connect Precast Column to Cap Beam using Ultra-High-Performance Concrete in Accelerated Bridge Construction Applications

2018 ◽  
Vol 2672 (41) ◽  
pp. 207-220 ◽  
Author(s):  
Mohamadreza Shafieifar ◽  
Mahsa Farzad ◽  
Atorod Azizinamini
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Precast Concrete ◽  
Experimental Program ◽  
Accelerated Bridge Construction ◽  
Ultra High Performance Concrete ◽  
Bridge Construction ◽  
Construction Time ◽  
Element Analysis ◽  
Displacement Ductility

Accelerated bridge construction (ABC) is a paradigm change in delivery of bridges. ABC minimizes the traffic interruption, enhances safety to public and workers by significantly reducing on-site construction activities, and results in longer-lasting bridges. The use of precast elements is gaining attention owing to inherent benefits of accelerated construction. Designing an economical connection is one of the main concerns for these structures. New improved materials such as ultra-high-performance concrete (UHPC) with superior characteristics can provide solutions for joining precast concrete elements. In this paper two types of column to cap beam connection using UHPC are proposed for seismic and non-seismic regions. Among the merits of the proposed details, large tolerances in construction and simplicity of the connection can be highlighted which facilitates and accelerates the on-site construction time. The experimental program was carried out to evaluate the performance and structural behavior of the proposed connections. Four specimens were subjected to constant axial compressive loads and cyclic lateral loading. Results of the experiment showed that the displacement ductility of the specimens, incorporating suggested details, demonstrated adequate levels of displacement ductility. More importantly, the proposed connections prevented the damage into capacity protected element—in this case the cap beam. Analytical and nonlinear finite element analysis on the specimens was carried out to better comprehend the behavior of the proposed connections.

scholarly journals A Numerical Study on Structural Performance of Railway Sleepers Using Ultra High-Performance Concrete (UHPC)

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2979
Author(s):  
Moochul Shin ◽  
Younghoon Bae ◽  
Sukhoon Pyo
Keyword(s):  
Cross Section ◽  
High Performance ◽  
High Performance Concrete ◽  
Numerical Study ◽  
Structural Performance ◽  
Geometrical Parameters ◽  
Ultra High Performance Concrete ◽  
Direct Tension ◽  
Design Factor ◽  
The Cross

This numerical study investigates the structural performance of railway sleepers made of ultra high-performance concrete (UHPC). First, numerical concrete sleepers are developed, and the tensile stress-strain relationship obtained from the direct tension test on the UHPC coupons is used for the tensile constitutive model after applying a fiber orientation reduction factor. The numerical sleeper models are validated with the experimental data in terms of the force and crack-width relationship. Second, using the developed models, a parametric study is performed to investigate the performance of the UHPC sleepers while considering various design/mechanical/geometrical parameters: steel fiber contents, size of the cross-section, and diameter and strength of prestressing (PS) tendons. The simulation results indicate that the size of the cross-section has the most impacts on the performance, while the effect of yielding strengths of PS tendons is minimal among all the parameters. Engineers need to pay attention to efficiency and an economical factor when using a larger cross-section, since sleepers with larger cross-sections can be an over-designed sleeper. This study suggests an economical design factor for engineers to evaluate what combination of parameters would be economical designs.

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