scholarly journals Modified Formula for Designing Ultra-High-Performance Concrete with Experimental Verification

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4518 ◽  
Author(s):  
Jarosław Siwiński ◽  
Anna Szcześniak ◽  
Adam Stolarski
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Experimental Studies ◽  
Ultra High Performance Concrete ◽  
Good Convergence ◽  
Fine Grained ◽  
Reinforcing Fibers ◽  
Proposed Modification ◽  
Modified Formula ◽  
Specimen Shape

The main purpose of the study was to propose a modification of Larrard’s formula for both the design and compressive-strength evaluation of ultra-high-performance concrete. The proposed modification consisted of the introduction of new parameters into the original formula that allowed it to consider the amount of binders and fine-grained aggregates, the amount of reinforcing fibers, the specimen shape and size, the curing time, and a reinterpretation of the water/cement ratio. The proposed modification was verified based on comparative analysis with the results of our own experimental studies and results taken from the literature. A very good convergence of these results was demonstrated, indicating the validity of the proposed modification.

Volumetric Changes of the UHPC Matrix and its Determination

2016 ◽  
Vol 827 ◽  
pp. 215-218 ◽  
Author(s):  
David Čítek ◽  
Milan Rydval ◽  
Jiří Kolísko
Keyword(s):  
Mechanical Properties ◽  
High Performance ◽  
High Performance Concrete ◽  
Experimental Tests ◽  
Structure Design ◽  
Ultra High Performance Concrete ◽  
Fine Grained ◽  
Durability Properties ◽  
Shrinkage And Creep

Research in the Ultra-High Performance Concrete applications field is very important. Current experiences shows that the structure design should be optimize due to relatively new fine-grained cement-based Hi-Tech material with excellent mechanical and durability properties. It is not sure if some of the volumetric changes like creep or shrinkage has or has not an impact on an advantage for the construction and for the structure design. The effect of the shrinkage and creep of common used concretes are well known and well described at publications but the effect of volumetric changes of the UHPC is mostly unknown because of the fact that some of experimental tests are long term and the development of UHPC is still in its basics. A lot of works are focused on a basic mechanical properties and durability tests.

Estimation of Shear Behavior of Ultra High Performance Concrete I Girder without Shear Stirrups

2012 ◽  
Vol 525-526 ◽  
pp. 557-560
Author(s):  
Jung Woo Lee ◽  
Chang Joh ◽  
E.S. Choi ◽  
I.J. Kwak ◽  
Byung Suk Kim
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Crack Opening ◽  
Experimental Studies ◽  
Design Procedure ◽  
High Strength ◽  
Shear Behavior ◽  
Ultra High Performance Concrete ◽  
Shear Design ◽  
Loss Of Strength

Thinner and lighter members can be designed by utilizing the high stiffness and toughness, and high compressive strength of Ultra High Performance Concrete (UHPC), which reaches up to 180MPa. This high strength and ductile tensile behavior of UHPC makes it possible to design the web of the UHPC I Girder without conventional shear stirrups, which makes the UHPC I girder slender, light and economical. However, establishing shear design procedure for UHPC I girders without stirrups requires additional theoretical and experimental studies. This paper investigated shear behavior of UHPC I girder without shear stirrups. The test results show, in spite of no shear stirrups, test specimens have high ductility due to the bridging action of steel fibers against crack opening. UHPC I girders without shear stirrups tested show gradual increase of strength after initial cracking instead of brittle loss of strength as expected from the ordinary reinforced concrete I girders without stirrups. The decrease of the shear span-depth ratio increase the shear strength of the UHPC I girder without stirrups.

Use of Textile Reinforced Concrete – Especially for Facade Panels

2014 ◽  
Vol 923 ◽  
pp. 142-145 ◽  
Author(s):  
Magdaléna Novotná ◽  
Michaela Kostelecká ◽  
Julie Hodková ◽  
Miroslav Vokáč
Keyword(s):  
Reinforced Concrete ◽  
High Performance ◽  
High Performance Concrete ◽  
Raw Materials ◽  
Textile Reinforced Concrete ◽  
Ultra High Performance Concrete ◽  
Concrete Element ◽  
Minimum Thickness ◽  
Fine Grained ◽  
Environmental Savings

In recent years, textile reinforced concrete (TRC) is at the beginning of industrial production mainly in Germany and relates especially to facade panels and concrete footbridges. The subtle panels with a minimum thickness of coverage layer can be designed due to the textile reinforcement, which is resistant to corrosion. Furthermore, a long durability is expected in case of these structures. The textile reinforcement with the fine-grained ultra-high performance concrete (UHPC) enables to produce concrete elements with a minimum thickness. Therefore, the concrete element with up to 70 % lower weight compared to element with conventional reinforcement can be produced and significant environmental savings can be achieved (reducing the consumption of non-renewable raw materials, transport energy, reduced dead load acting on the supporting structure, etc.).

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 Prediction of the Interface Shear Strength between Ultra-High-Performance Concrete and Normal Concrete Using Artificial Neural Networks

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5707
Author(s):  
Changqing Du ◽  
Xiaofan Liu ◽  
Yinying Liu ◽  
Teng Tong
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
High Performance Concrete ◽  
Ann Model ◽  
Ultra High Performance Concrete ◽  
Shear Tests ◽  
Research Papers ◽  
Artificial Neural ◽  
Modified Formula ◽  
Slant Shear

The bond strength between ultra-high-performance concrete (UHPC) and normal-strength concrete (NC) plays an important role in governing the composite specimens’ overall behaviors. Unfortunately, there are still no widely accepted formulas targeting UHPC–NC interfacial strength, either in their specifications or in research papers. To this end, this study constructs an experimental database, consisting of 563 and 338 specimens for splitting and slant shear tests, respectively. Moreover, an additional 35 specimens for “improved” slant shear tests were performed, which could circumvent concrete crushing and trigger interfacial debonding. Additionally, for the first time in our tests, the effect of casting sequence on UHPC–NC bond strength was identified. Based on the database, an artificial neural network (ANN) model is proposed with the following inputs: namely, the normal stress perpendicular to the interface, the interface roughness, and the compressive strengths of the UHPC and NC materials. Based on the ANN analyses, the explicit expression of UHPC–NC bond strength is proposed, which significantly lowers the prediction error. To be fully compatible with the specifications, the conventional shear-friction formula is modified. By splitting the total force into adhesion and friction forces, the modified formula additionally takes the casting sequence into account. Although sacrificing accuracy to some extent compared to the ANN model, the modified formula relies on a solid physical basis and its accuracy is enhanced significantly compared to the existing formulas in specifications or research papers.

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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