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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.
Trabucchi, I.; Conforti, A.; Tiberti, G.; Plizzari, G.A.; Winterberg, R.
The use of fiber reinforced concrete in tunnel linings, with or without conventional rebars,
has increased in the two last decades, especially in segmental linings. In the meanwhile, in the
scientific community there was a growing interest on macro-synthetic fibers for use in
underground structures. Within this framework, the present study investigates the possibility
of using macro-synthetic fiber reinforcement in precast tunnel segments by means of a
Firstly, an experimental program based on three point bending tests was carried out on
polypropylene fiber reinforced concretes (PFRCs) characterized by different fiber contents in
order to assess their post-cracking residual strength. Secondly, the corresponding stress vs.
crack opening laws, representative of the PFRCs investigated, were calculated through
inverse analysis procedure. Then, a segment of a typical tunnel lining having small diameter
was adopted as reference to optimize the reinforcement solution (macro-synthetic fibers and
conventional rebars, i.e. hybrid solution) and to study its structural behavior by numerical
analyses. Particular attention was devoted to the Tunnel Boring Machine (TBM) thrust jack
phase, in which the TBM moves forward by pushing the thrust jacks on the bearing pads of
the latest assembled ring, introducing high-concentrated forces in the lining.
Yao, Y.; Bakhshi, M.; Nasri, V.; Mobasher, B.
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.
Meda, A.; Rinaldi, Z.; Spagnuolo, S.; De Rivaz, B.; Giamundo, N.
The interest in using fiber reinforced concrete (FRC) for the production of precast
segments in tunnel lining, installed with Tunnel Boring Machines (TBMs), is continuously
growing, as witnessed by the studies available in literature and by the actual applications. The
possibility of adopting a hybrid solution of FRC tunnel segments with Glass Fiber Reinforced
Polymer (GFRP) reinforcement is investigated herein. Full-scale tests were carried out on
FRC segments with and without GFRP cage, with a typical geometry of metro tunnels. In
particular, both flexural and point load full-scale tests were carried out, for the evaluation of
the structural performances (both in terms of structural capacity and crack pattern evolution)
under bending, and under the TBM thrust. Finally, the obtained results are compared, in order
to judge the effectiveness of the proposed technical solution.
Plückelmann, S.; Breitenbücher, R.
In special cases, concrete members are exposed to high locally concentrated loadings. Such
concentrated loadings lead to a multi-dimensional stress state beneath the loaded area. Due to
the load diffusion, large splitting tensile stresses are generated in the upper regions of the
concrete member (i.e. St. Venant disturbance zone) and spread along directions perpendicular
to the load. In order to resist these splitting tensile stresses, the state of the art is to reinforce
concrete members with transverse steel reinforcement. An alternative approach is to add steel
fibers to the concrete matrix. However, regarding economic concerns it may not appropriate
to reinforce the entire concrete member with an adequate high amount of steel fibers, rather
only those zones where high splitting stresses are expected.
The main objective of the presented experimental study was to investigate the load-bearing
and fracture behavior of hybrid concrete elements with splitting fiber reinforcement under
concentrated load. For this purpose, in a first step, hybrid specimens were produced
containing both plain and fiber concretes. The reference specimens consisted exclusively of
plain concrete, while the hybrid specimens were partially strengthened with various types of
steel fibers only in the St. Venant disturbance zone, instead of a full range fiber
reinforcement. The thickness of the reinforcement layer was varied in order to determine the
optimal configuration of fiber reinforcement. Taking into account the influence of the casting
direction on the fiber orientation and consequently on the bearing and fracture behavior, the
hybrid specimens were cast either in standing or in lying molds by means of a “wet-on-wet”
casting technique. These hybrid elements were then tested under concentrated load.
The test results showed that under concentric loads the maximum bearing capacity of the
hybrid specimens increased progressively with growing thickness of the fiber reinforced
concrete layer. In contrast to the plain concrete specimens, the fiber reinforcement led to a
remarkable improvement in the post-cracking ductility. Compared to the fully reinforced
specimens, the hybrid specimens that were only reinforced in the St. Venant disturbance zone
exhibited - besides an almost identical bearing capacity - a similar local behavior in the postcracking
zone. Furthermore, a significant impact of the casting direction on the bearing as
well as fracture behavior could be proved.