This research activity includes two fundamental tasks. The first is related to the improvement of FRP bars that already exist or have been recently developed during the first five-year term of the chair. The second task is related to the development of new types of FRP reinforcing bars according to the needs of the construction industry raised by the industrial partners of the chair.
A cutting edge nano-technology has emerged in polymer engineering and the polymeric nano-composite (PNC) materials have been shown to provide tremendous improvements in various properties of several different thermoplastics and thermosets. These properties include flammability resistance, and resistance against diffusion/permeation of low molecular-weight materials like gases and liquids. Among the available nano-particles, natural nano-clays are the most attractive due to their sound reinforcing characteristics and low cost. In general, the nano-clay particles have a flat, thin sheet-like crystalline structure, and the thickness of the crystalline layer is about 1 nm while the other dimensions can be up to 1000 nm or more. This can permit an extremely high aspect ratio, a very important factor in reinforcing. Due to their highly hydrophilic characteristics, the nano-clay surface must be chemically treated to become compatible with various polymer matrices, which are often highly hydrophobic. The treatment also serves to exfoliate the nano-clay particles, which are naturally self-bonded, into the polymer matrices. Given that the interaction between the polymer matrix and the nano-clays is at the atomic level, a combination of less than 5% of inexpensive natural nano-clay particles with conventional polymers can lead to a significant improvement in mechanical performance, chemical resistance, thermal stability and fire resistance as indicated in several patents and publications [Ton-That and Denault 2001]. In addition to this nano-technology, other aspects will be investigated including, but not necessarily limited to:
New types and percentage of additives and fillers used with the different types of resins to enhance the durability performance of the FRP composite bars;
Manufacturing process (fibre pulling rate during the pultrusion process, relationship between curing - time and temperature - and polymerization percentage, and sizing process).
New types of fibres such as glass fibres type E, ECR, and advantex and basalt fibres.
The development of large size (diameters more than 32 mm) carbon and glass FRP rods and FRP thread rods (bolts) and nuts systems to be used as rock/concrete bolts and cement grouted anchors.
Furthermore, laboratory testing and analytical investigations will be carried out to evaluate the bond characteristics (transfer and development length and lap splice) of these improved FRP bars to concrete. This will be carried out through a series of pull-out tests and large scale concrete beams (e.g. 250 × 400 × 4500 mm).
Stirrups used for shear reinforcement are normally located as an outer reinforcement with respect to the flexural reinforcement and, therefore, are more susceptible to severe environmental effects. Using FRP stirrups in concrete structures may achieve a durable structure and ductile failure mode by confining the concrete in the compression zones. The first generation of carbon FRP stirrups has been developed during the last two years of the first five-year term of the chair. However, the use of these stirrups in concrete elements encountered some problems during fabrication (bend radius and tail length) and structural testing around and at the bend (a tensile strength of only 400 MPa could be achieved). In the coming five-year term, the adequate shape and dimensions (bar diameter, radius of bent, and tail or anchorage length) of stirrups made of carbon FRP will be determined through testing of specially designed specimens (using two concrete prisms of 300300500 mm). Then the behaviour and validity of using these developed stirrups as shear reinforcement for concrete beams will be investigated. Large scale concrete beams, with different shapes of cross sections (rectangular, T-shaped, and I-shaped) and different types of flexural reinforcement (conventionally reinforced or prestressed with steel or FRP tendons), will be constructed and tested.
To date, the use of FRP bars as compression reinforcement has not been yet explored and non of the FRP design codes or guidelines has considered it due to a lack of research in this area. However, this FRP application is needed in many cases such as columns in parking structures especially at the bottom part (subjected to corrosion due to the use of de-icing salts). In addition, at the beam-column joints, the reinforcement of the beam should be extended inside the column to provide the required transfer length and give adequate integrity to the joint. This transfer length is usually longer than the breadth of the column at the location of the joint and is provided by bending the flexural reinforcement of the beam into the column. Hence, to reinforce that type of joints, it is required to use FRP straight bars (compression reinforcement for the column), bent bars (flexural reinforcement for the beam at the joint), and closed stirrups (as confinement for columns and as shear reinforcement for beams). Experimental research is needed to verify the applicability of FRP reinforcement for these joints under different stress conditions and particularly subjected to seismic reversed cyclic loading. The primary objective of this research task is to investigate the behaviour of FRP reinforced concrete columns and beam-column joints to develop design and detailing requirements under compression and/or seismic loading. The specimens will be T-shaped joints consisting of two columns and one beam representing half portion of first and second floor of one-bay reinforced concrete frame, or exterior joint of frames with more than one bay. The effect of the following variables will be investigated: column stirrup spacing as different confinement for column and joint, amount of the constant axial load for columns, and area of stirrups as transverse shear reinforcement at the joints.
Carbon FRP materials have emerged as an alternative to steel tendons in prestressed concrete structures, since they are noncorroding and possess mechanical properties similar to steel. However, CFRP tendons have had very limited use in these applications due to the lack of a suitable anchorage to maintain the prestressing force in the tendon. Anchorage and deviator technology for steel tendons can not be applied to CFRP tendons because the FRP materials are orthotropic and possess low lateral strength, leading to premature failure of the tendon at the anchorage or deviator location. In addition, the currently available carbon FRP tendons are very expensive and not easily accessible in Canada or North America (manufactured in Japan). The aim of this research task is to develop a locally or nationally (Canadian) manufactured carbon FRP tendons using the currently available carbon FRP reinforcing bars (recently developed through the chair in collaboration with the industrial partner, Pultrall Inc.), which have a tensile strength of approximately 1500 MPa as a starting point. This research activity includes three phases. Phase 1 include the development and material characterisation of CFRP tendons. The targeted tensile strength of the expected carbon FRP tendon is at least 2400 MPa. This target strength can be achieved through a deep investigation of the different parameters such as fibre volume ratio, other types of carbon fibres, curing and sizing process, diameter of tendon. Then the diameter (6, 8, 10, and 12 mm) and the surface (deformed, sand-coated, and smooth surface) of the CFRP tendon will be adjusted for lowest cost and the highest possible performance (bond behaviour, development and transfer lengths). This will be carried out through a series of pullout tests (using concrete blocks and cylinders) and beam tests (large scale non-prestressed concrete beams, e.g. 150 ×250 × 3000 mm). In parallel to this, the mechanical characteristics of the developed CFRP tendons will be determined including long-term behaviour under sustained (creep) and repeated loads (fatigue) using accelerated ageing conditions as explained in research activity 2 of this proposal.
Phase 2 includes the development of a mechanical anchorage system to successfully employ CFRP tendons in new prestressed concrete structures, and as a strengthening measure in deteriorated structures. An interactive development approach is proposed, comprising mechanical modelling (finite element method) and verification testing of anchorage and deviator systems for the CFRP tendon. This work will be followed by full-scale tests of prestressed members (beams or slabs) utilizing CFRP tendon/anchorage/deviator systems. The finite element method will be used to analyze the behaviour at the interface between the tendon and anchorage under a variety of simulated loading conditions. These analyses will be used to develop anchor designs that provide the necessary structural performance while maintaining tendon integrity and minimize critical stresses that may lead to premature tendon failure. Successful anchorage and deviator systems arising from the analytical study will be fabricated and subjected to performance and acceptance testing. Static and cyclic tension tests will be conducted on tendon/anchorage and tendon/deviator subassemblies to evaluate and verify the efficiency of these systems. Following acceptance testing of the newly developed CFRP tendons and anchorage systems, CFRP prestressed concrete beams (with T or I-shaped) will be constructed and tested under static and cyclic loading conditions. Also, in collaboration with the MTQ, one third to half scale NETB concrete girders prestressed with the developed system (CFRP tendons and anchorage) and reinforced in shear with the carbon FRP stirrups (developed above) will be constructed and tested in the laboratory.
Phase 3 includes field implementation with full scale concrete elements in bridges, parking garages and other structures. In this phase, prestressed concrete double T beams will be used in the construction of the new laboratory building at the Université de Sherbrooke (See activity 8: Field implementation and structural health monitoring under subtitle: “CFI Laboratory Building,” which is located in the Department of Civil Engineering at the Université de Sherbrooke)