För att bibehålla elnätet stabilt är det viktigt för elproducenterna attkunna möta samhällets behov av elkraft. Detta behov varierar beroendepå tid på dygnet och även av årstid. Att kunna samla energi då behovetär lågt, för att sedan utvinna och distribuera energi då behovet ökar ärdärför viktigt. Vattenkraft är en av de energikällor som är enklast attreglera. Denna energi är dessutom relativt miljövänlig. Att ha en stabiloch säker vattenkraft är därför viktigt för samhället.I detta examensarbete har vissa problem som kan uppstå i ettvattenkraftverkets studerats, närmare bestämt alkali-silikatreaktion ibetong. Denna reaktion framträder genom att betongen sväller. Tillföljd av detta kan konstruktionen spricka. Detta beror på att en gelbildas när alkalier och kisel reagerar med varandra. Denna gel kan taupp vatten och då svälla.En specifik vattenkraftstation har i detta examensarbete studeratsnärmare, nämligen Malgomaj kraftverk. Detta är en anläggning somligger i ett område där, till skillnad från övriga Sverige, det finnsbergarter som har en medelsnabb reaktion med avseende på alkalikiselreaktion.Att denna geografiska placering blir ett problem beror påatt det stenmaterial som finns att tillgå i vattenkraftstationens närhethar använts som ballast i anläggningens betongkonstruktion.I den vattenkraftstation som studeras har problem iakttagits på grundav svällningar av betongkonstruktionen kring turbinen. För att få enuppskattning om hur vattenkraftstationens deformationer i framtidenkommer att utbildas har en modell av problemområdet byggts uppmed hjälp av finita elementmetoden, en så kallad FEM-modell. Dennamodell kalibreras mot mätdata och ska sedan ligga till grund för enuppskattning av vattenkraftstationens livslängd.Resultatet från undersökningen i detta examensarbete visar attdeformationerna är små men betydande för vattenkraftstationensmöjlighet till att fortsätta sin energiproduktion. / To maintain a stable power grid, it is important for electricity producers to meetsociety's need for electricity. This need will vary depending on time of day and eventhe season. Being able to accumulate energy when demand is low, and regain energywhen demand increases, is therefore important. Hydropower is one of the energysources that are easiest to regulate. Having a stable and secure hydropower istherefore important for society.In this thesis one problem that can occur in a hydroelectric plant has been studied,namely alkali-silica reaction (ASR) in concrete. This reaction causes the concrete toswell, due to a formation of gel when alkali and silicon react together.A specific hydropower station has been studied in detail, namely Malgomajhydropower plant. This is a facility that is located in an area where, unlike the rest ofSweden, there are stone materials that have a moderately rapid reaction with respectto the ASR.Problems for this hydroelectric power station have been observed because of swellingof the concrete structure surrounding the turbine. To get an estimate prognosis ofhow the hydropower plant will deform in the future, a finite element method-model(FEM-model) has be created of the problem area. This model is calibrated againstmeasured data and will then form the basis for an appreciation of the hydropowerstation's remaining lifetime.The results in this thesis show that the deformations are small but significant for thehydropower station's opportunity to continue its energy production.

Over the last decades, researchers have proposed a number of tools for the condition assessment of concrete infrastructure affected by alkali-silica reaction (ASR). Amongst those, increasing attention has been given to the Stiffness Damage Test (SDT), Damage Rating Index (DRI), and Residual Expansion (RE) laboratory test procedures that aim to determine the cause and extent (i.e., diagnosis) of damage along with the potential of further deterioration (i.e., prognosis) of affected concrete. Yet, most of the data gathered so far while using the aforementioned tools has been obtained on laboratory test specimens presenting distinct conditions from affected structural members in the field, especially regarding restraint effects. This work aims to understand the impact of restraint on ASR-induced expansion and damage. Thirty-two 450 mm by 450 mm by 675 mm concrete blocks with various reinforcement configurations (i.e., unreinforced, 1D and 2D reinforcement) and incorporating highly reactive coarse and fine aggregates (i.e., Springhill coarse and Texas sand) were manufactured and stored in conditions enabling ASR-induced development (i.e., 38°C and 100 R.H). Two expansion levels were selected for analysis (i.e., 0.08% and 0.15%); once reached, cores were extracted from three different directions (i.e., longitudinal, transversal and vertical) of all blocks and mechanical (i.e., SDT and compressive strength), microscopic (i.e., DRI, scanning electron microscope, etc.) and expansion (i.e., RE) test procedures were conducted on the concrete cores. Results suggest that the presence of restraint influences the induced expansion, resulting in an anisotropic response of the specimens. Furthermore, similar to the expansion behavior, an anisotropic distribution of induced damage and mechanical properties reduction are observed for the restrained concrete blocks in which the restraint configuration seems to significantly affect ASR-induced damage development and features. This led to the observation of a higher number of damage features, ASR development and mechanical properties reduction in cores obtained from unrestrained directions. Yet, some anticipated results from the current research will be studied in detail in the near future where the reliability of the existing techniques (i.e., residual expansion and soluble alkalis) for appraising ASR potential for further induced development and distress (i.e., prognosis) in affected concrete presenting distinct restraint scenarios will be evaluated.

Pressure is mounting in the concrete industry to adopt eco-efficient methods to reduce CO₂ emissions. Portland cement (PC), an essential concrete ingredient, is responsible for over two-thirds of the embodied energy of the concrete, generating about 8% of global greenhouse gas emissions. Extraction and transportation of aggregates and raw materials that comprise concrete mixes are also directly linked to their embodied energy; thus, recycled concrete aggregates (RCA) have been proposed as a promising alternative to increase sustainability in new construction. In this context, many studies have been conducted over the past decades on the properties of RCA concrete. Recent studies have shown that suitable fresh (i.e., flowability) and short-term hardened (i.e., compressive strength) properties might be achieved when the unique microstructural features of RCA are accounted for in the mix-design process of the recycled concrete. However, manufacturing RCA from construction demolition waste (CDW) or returned concrete (RC) presents its unique challenges. Amongst others, the variation in the source of RCA and the presence of damage due to several deterioration mechanisms causes major concern. Due to the presence of reactive aggregates in many quarries in Canada, alkali-silica reaction (ASR) is one of the most common deterioration mechanisms. The durability and long-term performance of RCA concrete are not fully understood and should be further investigated, especially in regards to a) the potential of further (secondary) deterioration of recycled concrete bearing coarse and fine alkali-silica reactive aggregates b) the impact of the severity of the initial reaction on mechanical properties and kinetics of expansion in recycled concrete and c) the impact of using sound and alkali-silica reaction (ASR) affected RCA on the chloride diffusivity (and thus corrosion initiation) of concrete. This work aims to appraise the durability performance of RCA concrete made of 100% coarse RCA, particularly two families of RCA selected (i.e., returned concrete RCA, demolished concrete RCA) to represent waste currently being generated. Furthermore, two types of reactive aggregates are selected to investigate the impact of the source of the reaction (i.e. reactive coarse aggregate as original virgin aggregate - OVA and reactive sand within the residual mortar - RM) within the RCA. ASR is the distress mechanism used to introduce damage to the manufactured RCA. A new mix design technique was used to produce recycled concrete mixtures to increase eco-efficiency, improve fresh-state properties, and reduce cement use in RCA concrete. In conclusion, the initial reaction's location and severity significantly impact the compressive strength, SDT parameters, chloride diffusion rate, and shear strength of concrete specimens. Specifically, the location of the initial reaction can influence the distribution and extension of damage within the various parts of recycled concrete, while the severity of the initial reaction can affect the overall integrity of the aggregates as well as the availability of silica and alkalis for secondary reaction. These results demonstrate the importance of assessing the severity of the initial reaction and its source in order to ensure the durability and long-term performance of recycled concrete made with reactive RCA.

Many highway and hydraulic structures in North America have been reported to be affected by alkali aggregate reaction (ASR). It is anticipated that most of these structures will be demolished as they approach the end of their service lives. Recycling demolished concrete as aggregates in new concrete is an option that not only reduces the amount of construction demolition waste (CDW) disposed in landfills but also lessens the consumption of non-renewable resources such as natural aggregates. However, the use of recycled concrete aggregate (RCA) in new concrete requires detailed research to make sure that the durability of the recycled material is not compromised, especially if the RCA had been previously affected by ASR. In this research project, coarse recycled concrete aggregate (RCA) is reclaimed and processed from distinct members (i.e. foundation blocks, bridge deck and columns) of an ASR-affected overpass after nearly 50 years of service. RCA concrete mixtures incorporating 50 and 100% replacement are manufactured and stored in conditions enabling further ASR development. Mechanical (i.e. Stiffness Damage Test - SDT) and microscopic (Damage Rating Index - DRI) analyses are performed at a fixed “secondary” induced expansion of 0.12%. Results show that the overall performance of the ASR-affected recycled mixtures depends upon the “past” condition of the RCA particles. Moreover, the DRI was able to capture the “past” and “secondary” induced expansion and damage of affected RCA while the SDT only detected the “secondary” distress development. Lastly, an adapted version of the DRI was proposed to further evaluate the overall damage of recycled concrete along with properly displaying “past” and “secondary” induced distress.

Concrete has proven to be, by far, one of the most reliable materials for the construction of critical infrastructure. However, despite its structural capacity, concrete members are susceptible to damage mechanisms that may decrease its performance and durability throughout its service life. One such mechanism is alkali-silica reaction (ASR), which takes place when unstable siliceous phases present in coarse or fine aggregates react with the alkali hydroxides from the concrete pore solution, generating a secondary product (i.e., ASR gel); this product swells upon moisture uptake from the surrounding environment, leading to cracking and expansion of the affected concrete. In severe cases of ASR-affected infrastructure, structural safety could become a problem, and thus requiring the demolition of affected members. It is, therefore, necessary to adopt effective protocols for the diagnosis and prognosis of aging infrastructure, to ensure its performance over time along with properly planning for rehabilitation strategies, whether required. This work presents a two-stage case study of the S.I.T.E. building at the University of Ottawa for the diagnosis and prognosis of ASR-affected members (i.e., columns) after nearly 20 years in service. The diagnosis phase was conducted with the aim of evaluating the cause and extent of distress and interpreting its impact on the performance of the affected structure. First, a visual inspection was conducted to evaluate potentially damaged members, in order to select the best location for core-drilling. Once ASR was confirmed through petrographic examination, specimens were evaluated through the multi-level assessment (i.e., coupling of microscopic and mechanical assessment). A range of damage was discovered among the examined columns (i.e., 0.03%, 0.05%, and 0.08% expansion). Moreover, evidence of developing freeze and thaw (FT) damage was discovered in columns with greater levels of expansion, raising future concerns regarding the durability and serviceability of members affected by this coupling of damage (i.e., ASR+FT). For the second stage of this project (i.e., prognosis), a novel ASR semi-empirical model was developed with the aim of predicting future ASR-induced expansion and damage in the S.I.T.E. building. The above model was developed and validated (using ASR exposure site data) through the coupling of existing chemo-mechanical macro-models, which were used to predict material behaviour on the structural scale, and novel mathematical relationships for the prediction of anisotropy in the columns. Moreover, the use of the multi-level assessment to predict the mechanical implications of predicted distress was found to enhance the model’s capacity for prognosis and demonstrated important potential for the accurate prediction of multi-level damage in the S.I.T.E. columns.

Recycled concrete is among the rising eco-friendly construction materials which helps to reduce waste and the need for new natural resources. However, such concrete may present previous deterioration due to, for instance, alkali-silica reaction (ASR), which is an ongoing distress mechanism that may keep being developed in the recycled material. This work aims to evaluate the potential of further distress and crack development (i.e. initiation and propagation) of AAR-affected RCA concrete in recycled mixtures displaying distinct past damage degrees and reactive aggregate types. Therefore, concrete specimens incorporating two highly reactive aggregates (Springhill coarse aggregate and Texas sand) were manufactured in the laboratory and stored in conditions enabling ASR development. The specimens were continuously monitored over time and once they reached marginal (0.05%) and very high (0.30%) expansion levels, they were crushed into RCA particles and re-used to fabricate RCA concrete. The RCA specimens were then placed in the same previous conditions and the “secondary” ASR-induced development monitored over time. Results show that the overall damage in ASR-affected RCA concrete is quite different from affected conventional concrete, especially with regards to the severely damaged RCA particles, where ASR is induced by a reactive coarse aggregate, as the RCA particle itself may present several levels of damage simultaneously caused by past/ongoing ASR and newly formed ASR. Moreover, the influence of the original damage extent in such RCA concrete was captured by the slightly damaged RCA mixture eventually reaching the same damage level as the severely damaged mixture. Furthermore, the original extent of deterioration influence the “secondary” induced expansion and damage of RCA concrete since the higher the original damage level, the higher the cracks numbers and lengths observed in the RCA concrete for the same expansion level whereas wider cracks are generated by RCA having previously been subjected to slight damage thus indicating the difference in the distress mechanism as a function of original extent of damage. In addition, it has been found that distress on RCA containing a reactive sand generates and propagates from the residual mortar (RM) into the new mortar (NM) as opposed to RCA containing a reactive coarse aggregate, being generated and propagated from the original coarse aggregate (i.e. original virgin aggregate – OVA) into the NM. Likewise, RCA containing a reactive sand caused longer and higher number of cracks for the same “secondary” induced expansion than the RCA made of reactive coarse aggregate. Finally, novel qualitative and descriptive models are proposed in this research to explain ASR-induced distress generation and propagation on RCA mixtures made of reactive fine and coarse aggregates.

Afin de répondre aux questions des propriétaires de structures atteintes de réaction alcali-silice (RAS), ce travail se concentre sur une partie d'une méthodologie globale, proposée initialement par le LMDC et EDF, et dont le but est l'étude du comportement mécanique des constructions endommagées par la RAS. Pour atteindre cet objectif, l'avancement chimique de la RAS des granulats récupérés dans les structures affectées doit être évalué. Ainsi, ce travail est consacré à la quantification de la silice potentiellement réactive des granulats, par l'utilisation de deux approches : une approche indirecte par un test d'expansion et une approche directe par des méthodes chimiques. La présentation du manuscrit s'articule autour des points suivants :• Un test d'expansion pertinent et rapide sur mortiers pour relier la quantité de silice réactive à l'expansion mesurée. Les conditions expérimentales suivantes ont été choisies pour tester différentes tailles et natures de granulats, ainsi que différentes tailles d'éprouvettes : solution de NaOH à 1 mol/l et température de conservation de 60°C.• Une méthode chimique rapide de dissolution sélective pour mesurer directement la quantité de silice réactive disponible pour la RAS. La méthode HF / HF+HCl a été trouvé comme étant la plus efficace.• Un modèle chemo-mécanique pour analyser les effets de la taille des granulats et des éprouvettes, et évaluer l'avancement chimique de la réaction.Finalement, une méthodologie est proposée pour calculer la constante cinétique de la réaction dans le cadre de la requalification des structures atteintes de RAS. / In order to answer the questions of the ASR-affected structures owners, this work focused on a part of a global methodology, which is proposed originally by the LMDC and EDF, aiming to reassess the mechanical behavior of ASR-damaged constructions. To achieve this purpose, the chemical advancement of ASR in the aggregates recovered from the structure should be evaluated. Thus, this work focuses on the assessment of the potentially reactive silica content with two main methods: indirectly by expansion test and directly by chemical methods. The presentation of this manuscript is around the following points: • A relevant and rapid expansion test on mortars to link the reactive silica content to measured expansion. The experimental condition: 1 mol/l NaOH solution conserved at 60°C is chosen to test different aggregate sizes, specimen sizes and natures of aggregate. • A fast chemical method of selective dissolution to measure directly the silica available for ASR. Acid/basic methods are tested and compared; HF / HF+HCl method is found to be the most effective. • A chemo-mechanical model to analyze the effect of aggregate size and specimen size, and evaluate the chemical advancement of ASR. Finally, a methodology is proposed to calculate the kinetics constant in the framework of structural requalification. Key words: alkali-silica reaction (ASR), chemical advancement, reactive silica, expansion test, chemical test, chemo-mechanical model, kinetic constant, selective dissolution