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International Concrete Abstracts Portal

Showing 1-5 of 483 Abstracts search results

Document: 

SP343

Date: 

November 3, 2020

Author(s):

fib and ACI

Publication:

Symposium Papers

Volume:

343

Abstract:

The first international FRC workshop supported by RILEM and ACI was held in Bergamo (Italy) in 2004. At that time, a lack of specific building codes and standards was identified as the main inhibitor to the application of this technology in engineering practice. The workshop aim was placed on the identification of applications, guidelines, and research needs in order for this advanced technology to be transferred to professional practice. The second international FRC workshop, held in Montreal (Canada) in 2014, was the first ACI-fib joint technical event. Many of the objectives identified in 2004 had been achieved by various groups of researchers who shared a common interest in extending the application of FRC materials into the realm of structural engineering and design. The aim of the workshop was to provide the State-of-the-Art on the recent progress that had been made in term of specifications and actual applications for buildings, underground structures, and bridge projects worldwide. The rapid development of codes, the introduction of new materials and the growing interest of the construction industry suggested presenting this forum at closer intervals. In this context, the third international FRC workshop was held in Desenzano (Italy), four years after Montreal. In this first ACI-fib-RILEM joint technical event, the maturity gained through the recent technological developments and large-scale applications were used to show the acceptability of the concrete design using various fibre compositions. The growing interests of civil infrastructure owners in ultra-high-performance fibre-reinforced concrete (UHPFRC) and synthetic fibres in structural applications bring new challenges in terms of concrete technology and design recommendations. In such a short period of time, we have witnessed the proliferation of the use of fibres as structural reinforcement in various applications such as industrial floors, elevated slabs, precast tunnel lining sections, foundations, as well as bridge decks. We are now moving towards addressing many durability-based design requirements by the use of fibres, as well as the general serviceability-based design. However, the possibility of having a residual tensile strength after cracking of the concrete matrix requires a new conceptual approach for a proper design of FRC structural elements. With such a perspective in mind, the aim of FRC2018 workshop was to provide the State-of-the-Art on the recent progress in terms of specifications development, actual applications, and to expose users and researchers to the challenges in the design and construction of a wide variety of structural applications. Considering that at the time of the first workshop, in 2004, no structural codes were available on FRC, we have to recognize the enormous work done by researchers all over the world, who have presented at many FRC events, and convinced code bodies to include FRC among the reliable alternatives for structural applications. This will allow engineers to increasingly utilize FRC with confidence for designing safe and durable structures. Many presentations also clearly showed that FRC is a promising material for efficient rehabilitation of existing infrastructure in a broad spectrum of repair applications. These cases range from sustained gravity loads to harsh environmental conditions and seismic applications, which are some of the broadest ranges of applications in Civil Engineering. The workshop was attended by researchers, designers, owner and government representatives as well as participants from the construction and fibre industries. The presence of people with different expertise provided a unique opportunity to share knowledge and promote collaborative efforts. These interactions are essential for the common goal of making better and sustainable constructions in the near future. The workshop was attended by about 150 participants coming from 30 countries. Researchers from all the continents participated in the workshop, including 24 Ph.D. students, who brought their enthusiasm in FRC structural applications. For this reason, the workshop Co-chairs sincerely thank all the enterprises that sponsored this event. They also extend their appreciation for the support provided by the industry over the last 30 years which allowed research centers to study FRC materials and their properties, and develop applications to making its use more routine and accepted throughout the world. Their important contribution has been essential for moving the knowledge base forward. Finally, we appreciate the enormous support received from all three sponsoring organizations of ACI, fib and Rilem and look forward to paving the path for future collaborations in various areas of common interest so that the developmental work and implementation of new specifications and design procedures can be expedited internationally. June 2018 Bruno Massicotte, Fausto Minelli, Barzin Mobasher, Giovanni Plizzari


Document: 

SP-343_26

Date: 

October 1, 2020

Author(s):

Fantilli, A.P.; Tondolo, F.

Publication:

Symposium Papers

Volume:

343

Abstract:

Durability of reinforced concrete (RC) structure is mostly related to the ability of concrete cover to protect the embedded rebar from corrosion initiation and propagation. As cracks due to loads or rheological phenomena are almost inevitable, the geometry of crack pattern in service is a key parameter that needs to be evaluated in plain and fiber-reinforced R/FRC members. In fact, not only the direct ingress of aggressive agents, such as oxygen and water, is a function of crack width, but also concrete carbonation and the chloride ion ingress are accelerated by the presence of wide cracks. Furthermore, the use of fiber reinforced concrete requires detailed investigations, in order to define the relationship between durability and crack width even in presence of cyclic loads. Accordingly, in this research project, crack width is measured by using traditional mechanical strain gauges and a new device based on the optical conoscopic holography. The latter allows the non-contact measure of crack profile, at the end of each loading cycle, both in plain and fiber-reinforced ties subjected to sets of repeated loads. As a result, contrarily to crack width at the peak of load, the width of residual cracks is not always reduced by the presence of fiber, and this could affect the durability of RC and R/FRC structures.


Document: 

SP-343_32

Date: 

October 1, 2020

Author(s):

Antroula, G.; Stavroula, P.

Publication:

Symposium Papers

Volume:

343

Abstract:

With the advent of strain hardening fiber reinforced cementitious composites (SHFRCC) the development of a new generation of structural systems that benefit from the inherent ductility of concrete in tension in order to reduce the amounts of transverse reinforcement (stirrups), shear strength, and tension-force development capacity to the main reinforcement is possible. In this study a number of tests are conducted to explore the behavior of SHFRCC materials under cyclic loads, simulating seismic effects. The experimental responses of two half-scale interior beam column connections subjected to reversed cyclic loading are compared; one of the connections was constructed with a cementitious matrix without fibers, and was detailed according with the Eurocode provisions for ductility class M (moderate, μ=3.5). The other connection was constructed with a SHFRCC mix; (2% by volume of PVA fibers was used to reinforce the matrix and the minimum amount of shear reinforcement allowed by Eurocode 2 for non-seismic detailing was used in the specimens). Several supporting experiments were also conducted to support analysis of the cyclic behavior (uniaxial tension, compression, splitting tests). The behavior of the members under reversed cyclic displacement is also simulated with advanced nonlinear Finite Element Analysis, with results that are correlated with the experimental observations. The SHFRCC specimen with minimum detailing showed improved performance and enormous ductility suggesting new possibilities to the seismic design of structures.


Document: 

SP-343_24

Date: 

October 1, 2020

Author(s):

Bernard, E. S.

Publication:

Symposium Papers

Volume:

343

Abstract:

Numerous investigations of the effect of fibre addition on the seismic performance of conventionally reinforced concrete members have been published. These generally show that fibres can improve robustness and survivability during reverse-cycle loading, but the dosage rate of fibre required to achieve significant improvements in performance is substantial. Recently, pure FRC members have increasingly been used in structures such as tunnel linings, including both fibre reinforced shotcrete and pre-cast FRC segments. Concerns have been raised about the absence of data on the seismic resistance of such members given that all previous research on seismic performance has essentially involved hybrid members incorporating both steel reinforcing bars and fibres. The present investigation has focused on the reverse-cycle flexural performance of FRC members in the absence of conventional steel reinforcing bars. Laboratory testing was performed on plain, bar-reinforced, and steel fibre reinforced concrete members, and their performance was compared. The tests indicate that steel fibres provide a small improvement in flexural capacity under reverse-cycle loading compared to plain concrete, but that the robustness of pure FRC members is relatively poor compared to steel bar-reinforced members incorporating steel stirrups. The data suggest that, when used at practical dosage rates, large hooked-end steel fibres cannot be relied upon to provide seismic performance in flexure comparable to steel bar reinforced concrete members.


Document: 

SP-343_02

Date: 

October 1, 2020

Author(s):

Li, L.; Cao, M.

Publication:

Symposium Papers

Volume:

343

Abstract:

Nowadays polyvinyl alcohol (PVA) and steel hybrid fibre reinforced cement-based composites (HFRCC) are studied to resist static, seismic and impact loading. In this research, calcium carbonate (CaCO3) whisker is introduced to develop a multi-scale HFRCC, with 35mm hooked end steel fibre, 6mm PVA fibre and CaCO3 whisker. The compressive and flexural behaviors of the new HyFRCC are explored. Compared to the conventional hybrid fibers (steel fibre and PVA fibre), the addition of multi-scale fibres (steel fibre, PVA fibre and CaCO3 whisker) can improve the compressive strength and toughness of cement-based composite. Multi-scale fibre usage leads to notable increase to both the flexural strength and flexural toughness values of cement-based composite. Based on these test results, we can conclude that there is a remarkable fiber synergy in multi-scale hybrid fibre reinforced cement-based composites with 35mm hooked end steel fibre, 6mm PVA fibre and CaCO3 whisker. Moreover, it seems possible that the steel fibres and PVA fibres can be partly replaced by CaCO3 whiskers, which is very beneficial in decreasing the production cost of HFRCC for potential structural applications.


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