Jean-Philippe Charron

Water Permeability of Reinforced Concrete Subjected to Cyclic Tensile Loading

A large proportion of reinforced concrete structures are cracked and subjected to cyclic loading in service. The presence of cracks enhances the ingress of aggressive agents into the concrete, resulting in faster structure deterioration. On the other hand, crack self-healing and inclusion of fibers in concrete can improve structure durability. Self-healing under constant loading is a well-known phenomenon; however, the possibility for self-healing to occur under cyclic loading has received insufficient attention. This study used an innovative permeability device to investigate the water permeability of reinforced normal-strength concrete (NSC) and fiber-reinforced concrete (FRC) simultaneously subjected to tensile cyclic loading. Complementary mechanical tests were performed under the same loading procedure to assess the crack-pattern evolution. The experimental results showed that, at an equivalent stress level in the reinforcement, the water permeability was significantly lower in the FRC than in the NSC—both under constant and cyclic loading. Moreover, two opposite phenomena occurred during cyclic loading: crack propagation and self-healing. In the NSC, the self-healing that occurred under cyclic loading, compensated for the increase of permeability resulting from the crack propagation. In the FRC, crack growth was minor; therefore, the self-healing was not affected by the cyclic loading and may have even been promoted in comparison to self-healing under constant loading. The results emphasize the benefit of using FRC in structures.

Static and Dynamic Behavior of High- and Ultrahigh-Performance Fiber-Reinforced Concrete Precast Bridge Parapets

New designs of precast bridge parapets made with fiber-reinforced concrete (FRC) were developed using nonlinear finite-element calculations. Specific properties of high- and ultrahigh-performance FRC were exploited in these designs. The conventional reinforcement required in the FRC precast parapets varied from 0 to 50% when compared with a reference built-on-site parapet. An extensive experimental program was carried out to verify the performance of the FRC precast parapets. The parapet mechanical behavior was established under quasi-static tests and under dynamic loading replicating a vehicle impact. The results of the quasi-static tests indicate that precast FRC parapets possess the required strength and have ductility comparable to reference parapets. Quasi-static tests carried out after the dynamic tests indicate that the residual strength of the parapets corresponds to 75 to 100% of their original capacity. The finite-element model adopted in the project satisfactorily reproduced the strength, stiffness, and failure mode of the parapets. Finally, the system efficiency of precast FRC parapets was established for their application in a typical urban bridge project, considering the mechanical performance, the fabrication costs, and the required installation time.

3D Nonlinear Finite-Element Modeling of Lap Splices in UHPFRC

AbstractDevelopment in ultra-high-performance fiber-reinforced concrete (UHPFRC) structural applications that has taken place over the last two decades has generated innovative concepts that could significantly impact the concrete construction practice. The transition from conventional concrete with brittle behavior to strain-hardening behavior in direct tension allows consideration of the design of innovative structural components and offers development of new techniques for rehabilitation. Building on experimental results of internally instrumented reinforcing bars, this paper investigates the impact of tensile characteristics of UHPFRC on the performance of lap splice connections using a refined three-dimensional (3D) finite-element (FE) model at rib scale and a 3D concrete constitutive model implemented in a computer program. The results show that the model reproduces with accuracy the experimental behavior of lap splice connections in UHPFRC in terms of maximum strength, splitting failure mode, crack...

Creep Behavior of Cement Paste, Mortar, and Concrete: The Role of Relative Humidity and Interface Porosity

Delayed deformations in concrete under sustained loading may depend on complex chemo-hydro-mechanical phenomena. Generally, the creep deformation of a cement paste is distinguished in the short-term and long-term. Simply speaking, the former can be associated to the diffusion of gel water in pores and cracks and it is mainly volumetric (i.e., volumetric deformation), reversible, and bounded. The latter can be associated to the sliding of the sheets of Calcium-Silicate-Hydrate (C-S-H), which is mainly deviatoric (i.e., shape deformation), irreversible and with an unbounded asymptotic deformation. From an experimental point of view, recent studies have shown that microindentation is a powerful technique to quickly characterize basic creep thanks to the reduced characteristic time of a sample size of few micrometers. The objective of this project is twofold: (1) investigating the effect of relative humidity on the creep behavior by microindentation; (2) characterize the viscous behavior of the interface transition zones (ITZ) around a rigid inclusion. In particular, the project investigated two different relative humidity, 33% and 85%, by considering both creep and relaxation microindentation tests. The presented results show the effect of the moisture content on the creep behavior of cement paste both at short and long terms. In addition, the results showed that the ITZ zone around an aggregate showed higher creep than the bulk cement paste. Those results provide new insights to understand the role of water and interface porosity on the creep mechanisms of concrete.

Structural Behavior of Bridge Decks with Cast-in-Place and Precast Concrete Barriers: Numerical Modeling

AbstractNonlinear finite-element (NLFE) calculations were used to compare and optimize the load transfer and failure mode of precast and cast-in-place bridge barriers subjected to transverse loads on bridge deck overhangs. The NLFE calculations were validated by successfully simulating the behavior of concrete barriers anchored to bridge deck overhangs and submitted to static transverse loading. The behaviors of three different barrier configurations—a normal concrete cast-in-place barrier, high-performance fiber-reinforced concrete (HPFRC) precast barriers, and HPFRC precast barriers with barrier-to-barrier connections—anchored to slab overhangs were accurately simulated with NLFE models. The validated models were then used to investigate the impact of the fiber orientation in the HPFRC precast barriers, the effect of the precast barrier length, the eccentric load application, and the utilization of a HPFRC slab overhang. The fiber orientation of the HPFRC precast barriers was shown to be well oriented t...

Static and Dynamic Behavior of Hybrid Precast Bridge Parapet Made of Ultra-High Performance Fiber Reinforced Concrete

An industrial research project was launched in 2007 at Ecole Polytechnique de Montreal to develop a new generation of precast bridge parapets using nonlinear finite element calculations. The paper presents the design of a hybrid precast parapet made with ultra-high performance fiber reinforced concretes (UHPFRC) and its experimental validation. The hybrid parapet consisted of a thin shell of UHPFRC paired with a normal strength concrete core. The outstanding properties of the UHPFRC permitted the removal of all conventional reinforcement while keeping the cast-on-site parapet thickness. A new anchorage system was optimized for parapet installation on a new bridge deck. Quasi-static tests, and dynamic tests replicating 4 levels of vehicle impacts, were conducted on full-scale parapets. Test results showed that the load-carry capacity of the hybrid UHPFRC parapet exceed the PL-2 or TL-4 parapet specifications of CSA and AASHTO. Moreover it offers a strength level equivalent to standard cast-on-site constructions.

Creep Behavior of a SFRC Under Service and Ultimate Bending Loads

A research project was carried out to evaluate the flexural creep behaviour of SFRC beams under sustained service loads and the crack propagation under high sustained loads. The evolution of the deflection, the crack width and the crack propagation were measured in service conditions (CMOD ws = 0.1 mm, load level P/Ps = 60 %) and ultimate conditions (wu = 0.5 mm, P/Pu = 60–90 %). The results allowed assessing the impact of the initial CMOD and sustained load levels on creep, crack propagation, damage evolution, and the mechanisms leading to the rupture of the beams. In service conditions, the results show that the deflection and crack opening of SFRC beams under sustained loading stabilises quickly toward an asymptote and that the compliance remains constant. In ultimate conditions, the results show that crack propagation governs the failure mechanisms of SFRC beams subjected to high sustained load levels. Moreover, it was observed that the beams failure occurs when the state of damage defined by the static behaviour envelope is attained.

Precast Fiber-Reinforced Concrete Barriers with Integrated Sidewalk

Three concepts of bridge barriers with integrated sidewalk were designed, built, and tested. Two precast barriers were designed with high-performance fiber-reinforced concrete (HPFRC)—the former with a tensile strain-softening material and the latter with a tensile strain-hardening material. Use of HPFRC allowed a significant reduction of concrete sections and reinforcement of precast barriers. Moreover, a new connection method was developed to anchor barriers to the bridge slab. One high-performance concrete (HPC) cast-in-place barrier was also designed as a reference. All barriers were submitted to quasi-static transverse loading up to failure and exceeded CSA PL2 and AASHTO TL4 design load requirements. Finite element models used at the design process provided an accurate reproduction of test results in terms of stiffness, ultimate strength, cracking pattern, and displacement. A numerical parametric study was conducted with the validated models to evaluate the effect of key economical and construction characteristics of the precast barriers.