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Concrete is the most widely used construction material in the world. Given its relative availability, strength, economy, and versatility to fit various applications, the material has been incorporated in roadways, bridges, buildings, and a host of other infrastructure projects. Oftentimes, concrete will be exposed to several environmental conditions that ultimately affect its durability and lifespan. These conditions include repeated freezing and thawing, chloride intrusion, sulfate attack, alkali-silica reaction, and many others. Given the age and condition of American infrastructure, concrete structures throughout the country need repair or rehabilitation. Often this repair includes the removal of degraded or damaged concrete and the application of an overlay material. There are several factors affecting the bond performance of the newly formed substrate-repair concrete, such as surface roughness, overlay material, and substrate moisture condition. The work presented in this thesis is dedicated to understanding the effect of substrate moisture condition on the overlay transition zone (OTZ) of the substrate-repair concrete. The substrate moisture condition can significantly impact the microstructure characterization of the OTZ. If the substrate is too dry, then it may absorb water from the repair material, reducing the local water-to-cement (w/c) ratio in the OTZ. Conversely, if the substrate is too wet, then the w/c ratio of the OTZ will be locally increased. In both scenarios, the interfacial bond strength is expected to be modified due to the change in the local w/c ratio. To understand this effect, various test methods and degradation mechanisms were explored. Initially, substrate-repair concrete specimens were prepared utilizing three separate substrate moisture conditions: saturated surfaced dry (SSD), sub-saturated surface dry (Sub-SSD), and oven dry (OD). After allowing these samples to cure, the strength and ion penetration risk were evaluated. The bond strength of the samples was evaluated through flexural strength testing and fracture energy determined through the RILEM draft tests. The OTZ ion penetration risk was evaluated by conducting rapid chloride penetration test (RCPT) on samples prepared with the three substrate moisture conditions. Furthermore, to determine the effect of repeated freezing and thawing on the OTZ and flexural strength, additional samples were created with the three moisture conditions. After allowing these samples to cure, they were subjected to ASTM C666 and were tested to observe their flexural strength. Another important performance indicator of concrete elements is its resistance to chloride ion penetration and corrosion. Since many structural elements are designed with steel reinforcement, chloride ion penetration represents a critical parameter in projecting material performance, since chloride ions will accelerate the rate of steel corrosion. Oftentimes, a key element in projecting this performance is identifying the rate at which ions diffuse through the material. There remain many established techniques to identify this rate of diffusion and derive a chloride diffusion coefficient; however, many of them are either destructive or qualitative in nature. In recent years, transmission X-ray microscopy (TXM) has been employed to non-destructively track diffusion and develop diffusion coefficients. The work presented in this thesis surrounds the efforts of incorporating TXM experiments at Virginia Tech. This work initially utilized a SkyScan 1174 μCT, and additional work in this thesis presents the design and construction of a dental X-ray system based on the checking ion penetration (CHIP) design. This system can conduct TXM experiments utilizing a dental X-ray as the source. The research, design, and construction of the CHIP system is discussed in this thesis. Ultimately, the research in this thesis has not observed any significant relationship between substrate moisture condition and overlay bond strength. There does appear to be an increase in chloride ion resistance for drier substrates, suggesting that pre-wetting the surface increases penetrability of the interface. / Master of Science / Concrete is the most widely used construction material in the world. Given its relative availability, strength, economy, and versatility to fit various applications, the material has been incorporated in roadways, bridges, buildings, and a host of other infrastructure projects. Oftentimes, concrete will be exposed to several environmental conditions that ultimately affect its durability and lifespan. These conditions include repeated freezing and thawing, chloride intrusion, sulfate attack, alkali-silica reaction, and many others. These environmental conditions ultimately degrade the material by inducing cracks, exposing steel reinforcement, and spalling. When the concrete has experienced significant deterioration, repair and rehabilitation of the damaged section must be performed. Most often, this repair consists of the removal of damaged concrete and the application of an overlay material to prevent further deterioration. The topics discussed in this thesis evaluate the optimum substrate conditions prior to an overlay application and the implementation of techniques to evaluate deterioration mechanisms. There are several substrate conditions that will affect bonding with the overlay material, including surface roughness, moisture conditions, and overlay type. This paper focused on the moisture condition and what effect this had on bond strength and resistance to chloride intrusion. This effect was studied in laboratory conditions and under environmental conditions such as rapid freezing and thawing. Several different deterioration mechanisms may contribute to concrete degradation. The research presented in this thesis also aimed to evaluate chloride ion diffusion. To evaluate this mechanism, two systems were explored with the intent of conducting transmission X-ray microscopy (TXM). With TXM, chloride ion diffusion can be tracked to determine the rate at which ions diffuse through the concrete. The two systems explored were an X-ray computed tomography scanner and a dental X-ray system. Both systems can conduct TXM, and this paper presents the efforts dedicated to developing them for this technique at Virginia Tech. Ultimately, the research in this thesis has not observed any significant relationship between substrate moisture condition and overlay bond strength. There does appear to be an increase in chloride ion resistance for drier substrates, suggesting that pre-wetting the surface increases penetrability of the interface.

Byggindustrin har i dagsläget en negativ klimatpåverkan och infrastrukturen likaså. Många länder har därför försökt undersöka möjligheten att hitta ett långsiktigt och hållbart alternativ till det konventionella reparationsmaterialet. Olika material undersöks, olika optimerade betongrecept testas för att förstå hur miljöpåverkan har minimeras för att förlänga livslängden hos betongkonstruktioner. Vid reparation av en bro är det viktigt att ta hänsyn till både kostnader och miljöpåverkan under hela dess livscykel. Kostnader som uppstår är investeringskostnader samt drift- och underhållskostnader. Miljöpåverkan från betongkonstruktioner i produkt skedet består av materialframställning, byggtransporter och produktion på byggarbetsplatserna. totala växthusgasutsläppet summeras och beräknas i kg CO2-ekv. Syftet med detta examensarbete är att studera den långsiktiga hållbarheten hos UHPC med hjälp av beräkningsmodeller såsom livscykelanalys och livscykelkostnadsanalys med avsikt att applicera reparationstekniken. Flera UHPC recept ställs mot det konventionella reparationsmaterialet detta för att kunna bedöma miljöpåverkan och kostnadseffektiviteten hos materialen. Dvs om det går det att minska klimatutsläppet och kostnaderna. De jämförda recepten är olika UHPC-recept samt traditionell betong. Recepten appliceras slutligen på en befintlig bropelare för att undersöka de olika receptens tillämpbarhet som reparationsmaterial ur ett hållbarhetsperspektiv. Det saknas tillräckligt med kunskap om UHPC:s långtidseffekter, speciellt om reparationsintervall. Med åtanke på materialets höga draghållfasthet och beständighet tillsammans med UHPC:s strukturella egenskaper har antaganden gjorts att materialet är reparationsfri under konstruktionens livslängd. Det vill säga att bropelaren som undersökts med UHPC i studien inte behövt repareras under sin livslängd. Resultatet från livscykelkostnadsanalysen visar att UHPC är dyrare i både kubikmeter (m3) och kvadratmeter (m2) med tanke på täckskiktets tjocklek än traditionell betong i materialpriset. Men med tanke på att UHPC är underhållsfritt har den en mindre livscykelkostnad. Resultatet från livscykelanalysen visar att UHPC blandningarna har större miljöpåverkan per kubikmeter. Då de olika täckskiktetstjocklek relateras till pelarens längd erhålls resultat där UHPC medför slankare konstruktioner och besparingar upp emot 50% mindre betongvolym (för den 6 m långa pelaren i fallstudien). Med UHPC som reparationsmaterial medför det till att bron inte behöver repareras under dess livslängd. Bropelaren som repareras med UHPC kommer därför ha en mindre miljöpåverkan än den traditionella betongen. Långsiktig hållbarhet och mindre totala växthusgasutsläpp (som är i riktlinje med EU:s och regeringens klimatkrav) erhålls för anläggningskonstruktioner med UHPC. / The construction industry has a negative climate impact and so does the infrastructure. Which is due to frequent repairs that are not sustainable. Many countries have therefore tried to explore the possibility of finding a long-term and sustainable alternative to conventional repair materials. Different materials are examined, different optimized concrete recipes are tested to understand how the environmental impact can be minimized and the service life of concrete structures extended. When repairing a bridge, it is important to take into account both costs and environmental impact throughout its life cycle. Costs that arise are investment costs as well as operating and maintenance costs. The environmental impact from concrete structures in the product phase consists of material production, construction transports and production at construction sites. The total greenhouse gas emissions are summed up and calculated in kg CO2 eq. The purpose of this thesis is to study the long-term sustainability of UHPC using calculation models such as life cycle analysis and life cycle cost analysis with the intention of applying the repair technique. Several UHPC prescriptions are set against the conventional repair material in order to be able to assess the environmental impact and cost-effectiveness of the materials. That is, if it is possible to reduce climate emissions and costs. The compared recipes are different UHPC recipes and traditional concrete. The recipes are finally applied to an existing bridge pillar to investigate the applicability of the various recipes as repair materials from a sustainability perspective. There is a lack of knowledge about the long-term effects of UHPC, especially about repair intervals. Given the high tensile strength and durability of the material together with the structural properties of the UHPC, it has been assumed that the material is repair-free for the life of the structure. That is, the bridge pillar examined with UHPC in the study did not need to be repaired during its lifetime. The results from the life cycle cost analysis show that UHPC is more expensive in both cubicmeters (m3) and square meters (m2) given the thickness of the cover layer than traditional concrete in the material price. However, given that UHPC is maintenance free, it has a lower lifecycle cost. The results from the life cycle analysis show that the UHPC mixtures have a greater environmental impact per cubic meter when the cover layer varies. As the thickness of the different cover layers is related to the length of the pillar, results are obtained where UHPC leads to slimmer constructions and savings of up to 50% less concrete volume (for the 6 m long pillar in the case study). With UHPC as repair material, this means that the bridge does not need to be repaired during its service life. The bridge pillar that is repaired with UHPC will therefore have a smaller environmental impact than the traditional concrete. Long-term sustainability and smaller total greenhouse gas emissions (which are in line with EU and government climate requirements) are obtained for plant constructions with UHPC.

The task of this diploma’s thesis was processing construction-technology project to revitalization the mining towers because of its current worsened state and subsequent adjustments for cultural activities.