La détérioration des infrastructures au Canada due à la corrosion des armatures est l'un des défis majeurs de l'industrie de la construction. Les progrès récents dans la technologie des polymères ont conduit au développement d'une nouvelle génération de barres d'armature à base de fibres renforcées de polymères (PRF), (en particulier les fibres de verre). Ces barres, résistant à la corrosion, ont montré un grand potentiel d'utilisation pour mieux protéger les infrastructures en béton armé contre les effets dévastateurs de la corrosion. Avec la publication du nouveau code S807-10 "Spécifications pour les polymères renforcés de fibres" et la production de barres en PRF de très haute qualité, celles-ci représentent une alternative réaliste et rentable par rapport à l'armature en acier pour les structures en béton soumises à de sévères conditions environnementales. La conception des éléments en béton armé de barres en PRF est généralement gouvernée par l'état de service plutôt que l'état ultime. Par conséquent, il est nécessaire d'analyser les performances en flexion et le comportement en service en termes de déflexion et de largeur de fissures des éléments en PRF sous charges de service et de vérifier que ces éléments rencontrent les limites des codes. Aussi, de récents développements dans l'industrie des PRF ont conduit à l'introduction des barres en PRF avec des configurations de surface et des propriétés mécaniques différentes. Ces développements sont susceptibles d'affecter leur performance d'adhérence et, par conséquent, la largeur des fissures dans les éléments en PRF. Cependant, les codes de conception et les guidelines de calcul fournissent une valeur unique pour le coefficient d'adhérence (k[indice inférieur b]) en tenant compte des configurations de surface et en négligeant le type de barre en PRF, le diamètre de la barre, et le type de béton et de sa résistance. En outre, le code canadien S807-10 "Spécifications pour les polymères renforcés de fibres" fournit une étape en classant les barres en PRF par rapport à leur module d'élasticité (E[indices inférieurs frp]). Ces classifications ont été divisées en trois classes : Classe I (E[indices inférieurs frp]<50 GPa), Classe II (50 GPa [plus petit ou égal] E[indices inférieurs frp]< 60 GPa) et Classe III (E[indices inférieurs frp] [plus grand ou égal] 60 GPa). Ce programme de recherche vise à étudier expérimentalement le comportement en flexion des éléments en béton en service armé avec différents paramètres sous charges statiques. Le programme expérimental est basé sous plusieurs paramètres, dont les différents ratios de renforcement, différents types de barres (différentes classes comme classifiées par le CAN/CSA S807-10), le diamètre et la surface de la barre, la configuration ainsi que la résistance du béton. De plus, les recommandations actuelles de design pour les valeurs de k[indice inférieur b] et la vérification de la dépendance des valeurs de k[indice inférieur b] sur le type de barres (verre ou carbone), le diamètre des barres et le type de béton et sa résistance ont été étudiées. Le programme expérimental comprenait la fabrication et les essais sur 33 poutres à grande échelle, simplement appuyées et mesurant 4250 mm de long, 200 mm de large et 400 mm de hauteur. Vingt et sept poutres en béton ont été renforcées avec des barres en PRF à base de verre, quatre poutres en béton ont été renforcées avec des barres de PRF à base de carbone, et deux poutres ont été renforcées avec des barres en acier. Toutes les poutres ont été testées en flexion quatre points sur une portée libre de 3750 mm. Les paramètres d'essai étaient: le type de renforcement, le pourcentage d'armature, le diamètre des barres, configurations de surface et la résistance du béton. Les résultats de ces essais ont été présentés et discutés en termes de résistance du béton, de déflection, de la largeur des fissures, de déformations dans le béton et l'armature, de résistance en flexion et de mode de rupture. Dans les trois articles présentés dans cette thèse, le comportement en flexion et la performance des poutres renforcées de barres en PRFV et fabriquées avec un béton normal et un béton à haute performance ont été investigués, ainsi que les différentes classes de barres en PRFV et leurs configurations de surface. Les conclusions des investigations expérimentales et analytiques contribuent à l'évaluation des équations de prédiction de la déflection et des largeurs de fissures dans les codes de béton armé de PRF, pour prédire l'état de service des éléments en béton renforcés de PRF (déflection et largeur de fissures). En outre, à la lumière des résultats expérimentaux de cette étude, les équations de service (déflection et largeur des fissures) incorporées dans les codes et guidelines de design [ACI 440.1R-06, 2006; ISIS Manual No.3, 2007; CAN/CSA-S6.1S1, 2010; CAN/CSA-S806, 2012] ont été optimisées. En outre, les largeurs de fissures mesurées et les déformations ont été utilisées pour évaluer les valeurs courantes de k[indice inférieur b] fournies par les codes et les guidelines de calcul des PRF. En outre, les conclusions ne prennent pas en charge la valeur unique de k[indice inférieur b] pour les barres en PRF de types différents (carbone et verre) avec des configurations de surface similaires et s'est avéré être dépendant du diamètre de la barre.

It is well-known that concrete permeability is a good indicator of its expected durability until it remains uncracked. However, in various stages of its service life, different types of cracking in concrete can be developed due to exposure to different deterioration processes such as early plastic shrinkage or chloride-induced reinforcement corrosion. Although these cracks may not endanger concrete’s structural performance from the mechanical point of view, they create a pathway for aggressive ions that can initiate degradation processes, lead to increase in concrete permeability and thus reduce its durability. Cracking in concrete might not be preventable, but its capability to naturally seal small cracks, named autogenous self-healing (SH), provides an additional feature to manufacture more durable concrete structures. However, natural self-healing capability of concrete is limited and therefore it is typically omitted in the design of concrete structures. Hence, more attention has been recently paid to Engineered Self-healing Concrete (EShC) which is associated with artificially triggered healing mechanisms into the cementitious matrix by incorporating various substances such as crystalline products. EShC helps in reducing concrete permeability; thus, increasing its service-life and durability. Due to formation of needle-shaped pore-blocking crystals, Crystalline Admixtures (CA), as a candidate from the Permeability-Reducing Admixtures (PRA) category, can be implemented into concrete mixtures to fabricate EShC concretes. Crystalline waterproofing technology is not new, but still is unknown to many researchers, engineers, and construction industry professionals. The lack of knowledge of its microstructure and self-healing properties limits CA’s proper usage in the construction industry. The techniques to assess the self-healing capability of mortar and concrete are not well-standardized yet. No research work has been done to address certain durability characteristics of this material (i.e. electrical resistivity (ER) or chloride diffusivity) especially when combined with Supplementary Cementitious Materials (SCM) and Portland Limestone Cement (PLC). Since the resistance of concrete against ions’ penetration is a function of its permeability, it might be a straightforward and reliable parameter to rapidly evaluate concrete’s durability during its intended service life. Hence, electrical resistivity measurement is considered as an indirect and alternative tool for other time-consuming permeability testing techniques to examine the CA’s efficiency as it modifies the concrete’s microstructure by crystals’ deposition; thus, leads to permeability improvement. In comparison to previous studies, on a larger scale, this thesis aims to systematically study the effects of CA on the microstructural features, self-healing properties and long-term durability and resistivity of cement-based materials and in addition, draw some comprehensive conclusions on the use of CA in new and repair applications. This study is divided into three major phases to propose all-inclusive work on using CA in construction industry. To satisfy the goals of each individual phase, a test matrix consisting of a series of four mixes with variables such as use of PLC or presence of CA in powder form is considered. In order to address to the lack of research and industry knowledge discussed above, this PhD thesis includes the following phases: Phase (I) In this phase, the main focus is on the microstructural properties and the changes in the pore structure and chemical compositions of the cement phase of mortar mixes when treated with CA. These microstructural features are studied using Scanning Electron Microscope (SEM) and Scanning Transmission Electron Holography Microscope (STEHM). Moreover, physical and chemical characteristics of the hydration products are determined using image analysis and Energy Dispersive X-ray (EDX) Spectroscopy, respectively. Phase (II) This phase is allocated to macro-level investigation of durability characteristics such as chloride/water permeability and electrical resistivity of concrete structures containing CA and PLC cement. To non-destructively measure the chloride ion concentration in the field conditions, both changes in corrosion potential of rebars and concrete electrical resistivity in treated circular hollow-section steel reinforced columns exposed to simulated marine environment is monitored and compared over a 2-year period with control samples. In addition, laboratory-size concrete samples are studied to investigate the effects of CA presence on long-term resistivity, rapid chloride permeability, water permeability and chloride diffusivity of concrete. Later, a resistivity-based model is developed to predict long-term performance of concretes incorporating slag or metakaolin, studied in various environmental conditions. The long-term goal of this phase is to develop a standard design guideline and durability-based model. Phase (III) Using an innovative self-healing testing method [1], quantitative analysis of crack closure ability and self-healing potential of CA treated and control concretes with OPC or PLC cement is accomplished during this phase. The obtained results from first phase showed that hydrated CA particle revealed fine, compact, homogenous morphology examined by STEHM and its diffraction pattern after water-activation indicated nearly amorphous structure, however, diffuse rings, an evidence for short-range structural order and sub-crystalline region, were observed which requires further investigation. The SEM micrographs taken from specimen’s fractured surface showed formation of pore-blocking crystals for all treated mixes while similar spots in un-treated sections were left uncovered. Although needle-shaped crystals were observed in the treated mortar specimens, but not all of them had shapes and chemical compositions other than ettringite (well-known to form needle-like crystals). Using backscatter SEM images and EDX spectrums, examination of polished mortar sections with and without CA also showed typical hydration phases, forming in the control system. Results from phase II showed that concretes treated with CA had almost 50% lower water penetration depth and thus smaller permeability coefficient when compared with the virgin OPC or PLC concretes. According to salt ponding test results, the use of CA helped in enhancing the resistance to chloride penetration compared to control concrete. This improvement increases with increasing in concrete age. Strong linear relationship between Surface Resistivity (SR) and Bulk Resistivity (BR) data was observed which indicates that these test methods can be used interchangeably. The presence of SCM in concrete indicated considerable increase in both SR and BR compared to control concrete. Concretes incorporating slag or metakaolin have tendency to react more slowly (or rapidly in MK case), consume calcium hydroxide over time, form more Calcium Silicate Hydrate (C-S-H) gel, densify internal matrix, and also reduce OH- in the pores’ solution; thus, increase concrete electrical resistivity. For laboratory specimens, environmental conditions such as temperature variation and degree of water saturation indicated considerable effects on electrical resistivity measurements. As temperature or water content of concrete decreases, its electrical resistivity greatly increases by more than 2-3 times from reference environmental condition. This is mostly because of variation or accessibility in electron mobility. Experimental results from field investigation showed that electrical resistivity readings were highly influenced by the presence of rebar and concrete moisture conditions. In addition, concrete cover thickness and CA addition into cementitious matrix had a negligible effect on its resistivity. In the last phase, an optical microscope was used to measure the average crack width. OPC samples had an average measured crack width of 0.244 mm as compared to 0.245 mm for OPC-CA, 0.251 mm for PLC, and 0.247 mm for PLC-CA. Self-healing test results also showed 90% self-healing ratio for CA modified mix within few days after starting experiment. Addition of CA into the mix led to higher rates of healing and full crack closure (width up to 250 µm) when compared to reference concrete. An empirical equation that relates water initial flow rate to the crack width (Q∝〖CW〗^3) was also proposed in this phase. Presence of PLC and CA in the mixture resulted in positive improvement in crack-closing capability and self-healing ratio. / Graduate / 2019-09-11

The dissertation thesis deals with the study of non-destructive acoustic methods as instruments for monitoring and analysing corrosion of reinforcing steel in reinforced concrete elements. Four acoustic methods were selected for this task - the impact-echo method, the nonlinear acoustic spectroscopy method, the acoustic emission method, and the ultrasonic pulse velocity method. To verify the functionality of these methods, testing was carried out on three sets of reinforced concrete samples that had been exposed to the effects of sodium chloride, which corroded the embedded steel reinforcement in these samples. Suitable parameters were proposed for individual acoustic methods to monitor corrosion of the reinforcements. In addition, experiments were designed to demonstrate the ability of the selected acoustic methods to reveal the corrosion of steel reinforcement and its influence on the concrete matrix and to assess the condition of the degraded elements and structures. The analysis of the measurement results based on their comparison shows the advantages and disadvantages of the individual methods and of their practical applications. To verify the results, correlation with common methods that are currently used for the study of corrosion was carried out and included for example the electrical resistivity measurement of the reinforcement and simultaneous monitoring of the sample surface using a confocal microscope to record the development of microcracks during the degradation.