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Showing 1-5 of 85 Abstracts search results

Document: 

SP345

Date: 

February 19, 2021

Author(s):

ACI Committee 549

Publication:

Symposium Papers

Volume:

345

Abstract:

Sponsors: ACI Committee 549, Rilem-MCC Editors: Barzin Mobasher and Flávio de Andrade Silva Several state-of-the-art sessions on textile-reinforced concrete/fabric-reinforced cementitious matrix (TRC/FRCM) were organized by ACI Committee 549 in collaboration with RILEM TC MCC during the ACI Fall 2019 Convention in Cincinnati, OH, and the ACI Virtual Technical Presentations in June 2020. The forum provided a unique opportunity to collect information and present knowledge in the field of TRC and FRCM as sustainable construction materials. The term TRC is typically used for new construction applications whereas the term FRCM refers to the repair applications of existing concrete and masonry. Both methods use a textile mesh as reinforcement and a cementitious-based matrix component and, due to high tensile and flexural strength and ductility, can be used to support structural loads. The technical sessions aimed to promote the technology, and document and develop recommendations for testing, design, and analysis, as well as to showcase the key features of these ductile and strong cement composite systems. New methods for characterization of key parameters were presented, and the results were collected towards the development of technical and state-of-the-art papers. Textile types include polymer-based (low and high stiffness), glass, natural, basalt, carbon, steel, and hybrid, whereas the matrix can include cementitious, geopolymers, and lightweight matrix (aggregates). Additives such as short fibers, fillers, and nanomaterials were also considered. The sessions were attended by researchers, designers, students, and participants from the construction and fiber industries. The presence of people with different expertise and from different regions of the world provided a unique opportunity to share knowledge and promote collaborative efforts. The experience of an online technical forum was a success and may be used for future opportunities. The workshop technical sessions chairs sincerely thank the ACI staff for doing a wonderful job in organizing the virtual sessions and ACI TC 549 and Rilem TC MCC for the collaboration.


Document: 

SP-343_07

Date: 

October 1, 2020

Author(s):

Javadian, A.; Mahdavi, A.; Benamrane, O. ;Majeed, M.; Aoude, H.

Publication:

Symposium Papers

Volume:

343

Abstract:

This study examines the effect of fiber properties, single fiber type and hybrid fibers on the fresh-state and hardened-state properties of self-consolidating fiber-reinforced concrete (SCFRC). As part of the study, 16 mixtures are examined with variables including the effect of fiber type, length, aspect ratio, and hybrid use of fibers (short and long fibers). Properties in the fresh state are studied using standard SCC tests including: slump flow, V-funnel and visual stability index (VSI) tests. Mechanical properties are studied by testing prisms under four-point flexural loading in accordance with the ASTM C1609 standard. The results demonstrate that self-consolidating FRC mixtures are possible at moderate fiber contents, however, once the limiting fiber contents are exceeded workability and mix uniformity are lost. The results also show the effects of fiber content, fiber type, fiber properties and hybrid fibers on the flexural toughness of SCFRC.


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_18

Date: 

October 1, 2020

Author(s):

Yao, Y.; Bakhshi, M.; Nasri, V.; Mobasher, B.

Publication:

Symposium Papers

Volume:

343

Abstract:

Precast concrete segments are the predominant support method used in tunnels dug by Tunnel Boring Machines (TBM) in soft ground and weak fractured rock, providing the initial and final ground support. Conventionally, steel bars are used in concrete segments to resist tensile stresses due to all loading cases from the time of casting through service condition. With traditional reinforcement, a significant amount of time and labor are needed to assemble the cages and place the reinforcing bars. Fiber reinforced concrete (FRC) has become more attractive for its use in tunnel lining construction as a result of improved post-cracking performance, crack control characteristics and capability of partial replacement of steel bars. Due to the strength requirements in large-diameter tunnels, which are subjected to embedment loads and TBM thrust jack forces, the use of FRC is not adequate as the sole reinforcing mechanism. Therefore, the hybrid fiber-reinforced concrete (HRC) combining both rebars and steel fibers is frequently used in practice. Tunnel segmental linings are designed for load cases that occur during manufacturing, transportation, installation, and service conditions. With the exception of two load cases of TBM thrust jack forces and longitudinal joint bursting load, segments are subjected to combined axial force and bending moment. Therefore, P-M interaction diagrams have been used as the main design tool for tunnel engineers. Standard FRC constitutive laws recently allow for a significant residual strength in tension zone below the neutral axis. However, design capacity of HRC segment is significantly underestimated using conventional Whitney’s rectangular stress block method, especially for tension-controlled failure, since the contribution of fibers in tension zone is ignored. Methods that currently incorporate contribution of fibers on P-M diagrams are based on numerical and finite-element analyses, which are normally more complicated and not readily to be implemented for practical design tools. Closed-form solutions of full-range P-M interaction diagram considering both rebar and fiber contributions are presented in this paper for HRC segments. The proposed model is verified with experimental data of compression tests with eccentricity as well as other numerical models for various cases of HRC sections. Results show that using appropriate material models for fiber and reinforcing bar, engineers can use the proposed methodology to obtain P-M interaction diagrams for HRC tunnel segments.


Document: 

SP-343_21

Date: 

October 1, 2020

Author(s):

Pourzarabi, A.; Colombo, M.; Martinelli, P.; di Prisco, M.

Publication:

Symposium Papers

Volume:

343

Abstract:

Fibre reinforced concrete (FRC) material is characterized by a high intrinsic scatter in the results when tested according to standard notched beams. However, it is observed that structures affected by a high stress redistribution show a significantly reduced scatter in their structural behaviour. Therefore, the use of the characteristic material constitutive parameters from a standard test leads to overly conservative design. The Model Code 2010 has introduced a coefficient, named structural redistribution factor, that is able to take into account a reduced variability of the structural response, when compared to that identified from a standard material test. The paper investigates the behaviour of FRC slabs to highlight the difference in structural response of FRC elements with respect to the expected response computed according to the standard specimens used for material characterization. To this aim, FRC slabs of 2×2 m, 15 cm thick, supported on four points at the mid-span of each side, are tested under a point load. Different slab solutions (R/C, FRC only and a Hybrid solution with FRC and steel rebars) are compared and discussed. The material considered can be classified as 5b according to Model Code 2010. A yield line approach is also adopted to validate the formulation proposed by Model Code 2010 for the structural redistribution factor in the cases investigated.


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