Marc Jolin

BRIDGE INTEGRITY ASSESSMENT BY CONTINUOUS WAVELET TRANSFORMS

The potential of continuous wavelet transforms for damage assessment of existing bridges is investigated herein. Different types of continuous wavelet transforms have been under investigation and the most effective ones have been introduced in a toolbox to automate the damage assessment procedure. In this paper, the performance of the wavelet approach and the influence of different parameters in the damage assessment procedures are studied through two examples: a simply supported beam and a three-span concrete bridge. Applying the wavelet transforms to a structures static and/or dynamic response showed promising results with regard to localization of structural modification or damage. This paper underlines the high sensitivity of the wavelet analysis to damage intensity and its ability to be applied directly to the damaged data. These key characteristics could lead to this approach becoming one of the best for structural health monitoring of existing bridges in the near future.

Experimental and Numerical Investigation of Particle Kinematics in Shotcrete

AbstractThe intent of this paper is to identify the basic physical laws governing particle kinematics in a shotcrete spray. This paper presents a governing equation based on Newton’s second law where nozzle and airflow characteristics, and particle features are used to predict impact velocity of the material exiting the nozzle. Experimental values obtained using high-speed imaging measurements on marbles and aggregate particles correlate well with the results of numerical simulations on a simplified spraying system. With the controlling parameters of particle kinematics fully understood, the analysis of the governing equations offers essential elements for nozzle optimization and new mix design investigations. This paper also addresses the necessity of broadening the investigation to the entire spray of particles exiting the nozzle for a complete understanding of the spraying process on placement mechanisms at a process scale.

Effects of Particle-Size Distribution in Dry Process Shotcrete

Dry-mix shotcrete has been successfully used for many years in construction and repair. Its unique pneumatic application yields an in-place material with low workability and relatively high stiffness well adapted to vertical and overhead applications without formwork. For some time, reduction of rebound--particles not adhering to the surface during shooting--has received attention due to its important effects on costs and in-place properties. The aim of this project is to study the effects of the particle-size distribution of the granular phase in dry-mix shotcrete. The results presented confirm the validity of what is known as ACI Gradation No. 2 for shotcrete recommended by ACI Committee 506, Shotcreting. Moreover, a fundamental approach involving optimal packing density offers a simple and interesting explanation of the observed behavior and a basis for future work.

Analysis of the representativeness and relative severity of ASTM C672 and NQ 2621-900 standard procedures in evaluating concrete scaling resistance

The aim of this study is to gain an understanding of the representativeness and relative severity of ASTM C672 and NQ 2621-900 standard test procedures in evaluating the scaling resistance of concr...

Bond Strength of Reinforcing Bars with Varying Encapsulation Qualities

The encapsulation quality of reinforcing bars represents a common concern among structural engineers when shotcrete structures are designed. Because little scientific information is available regarding the potential bond strength reduction of bars with adjacent defects along their length, ASTM A944-10 “beam-end” specimens with different encasement qualities were tested. To limit the size variability of voids when spraying, voids were created using silicone inserts, which also made it possible to control their exact size and position. Artificial voids were encased with a placed shotcrete mixture and transversal lengths of up to 30% of the bars’ perimeter were investigated. A low water-binder ratio (w/b) was employed to guarantee an insignificant bleeding capacity of the mixture as is commonly observed in shotcrete. The results support previous investigations by showing that transversal void lengths beyond 20% induce a considerable change in the slope of the stress-slip curve and an important reduction of the ultimate bond stress.

Studies on the Influence of Drying Shrinkage Test Procedure, Specimen Geometry, and Boundary Conditions on Free Shrinkage

Although considerable progress has been made in enhancing the use and interpretation of free ring shrinkage test, little is known about the impact of the test procedure, the specimen geometry, the surface area-to-volume (S/V) ratio exposed to drying, and the boundary conditions (sealing configuration) on the measured shrinkage. This paper highlights recent findings illustrating the influence of the test procedure, the S/V ratio exposed to drying, the geometry of specimen, and the boundary conditions. A series of experimental results are presented from free shrinkage on ring test specimens to illustrate that the test procedure can significantly influence the measured free shrinkage. A second series of experimental results are presented from specimens with different geometries and S/V ratio exposed to drying to illustrate that drying shrinkage is dependent on both the specimen geometry and the surface exposed to drying. Test results further show that, even for the same S/V ratio exposed to drying, shrinkage is strongly dependent on the specimen’s geometry and boundary conditions.

Robustness of Shrinkage-Compensating Repair Concretes

Drying shrinkage is one of the least desirable properties of repair concrete, because in restrained conditions, it may lead to shrinkage cracking and thus adversely affect its durability. Shrinkage compensating concretes (ShCCs) made with expansive mineral admixture represent an attractive alternative to prevent shrinkage cracking. This paper outlines a project devoted to the study of ShCC repair material robustness as a function of selected parameters. Two types of expansive agents were used, a calcium sulfoaluminate-based admixture (Type K) and a calcium oxide-based (Type G) one. The assessment of robustness addressed the influence of both the mixture design parameters (cement composition, type and dosage of expansive agent, w/cm ratio) and the curing conditions (moist curing conditions, temperature) upon the ShCC expansive behavior, the bond between ShCC repairs and concrete substrates, and ShCC frost durability. Overall, the results yielded in this study demonstrate interesting potential of ShCCs as crack-resistant and durable repair materials.