Yes / This study investigates the interfacial characteristics between aggregates and cement paste matrix in nanofillers modified concrete. A three-point bend test on the specimens composed of two pieces of aggregates bonded with a thin layer of cement pastes with/without nanofillers was carried out to characterize the interfacial bond strength of the composites. The scanning electron microscope observations and energy dispersive x-ray spectrometry analysis were also performed to characterize the interfacial microstructures and compositions of the composites. The experimental results indicated that the nanocomposites have higher interfacial bond strength and narrower interfacial transition zone thickness as well as more optimized intrinsic compositions and microstructures than that of composites without nanofillers. Specifically, the interfacial bond strength of nanocomposites can reach 7.67 MPa, which is 3.03 MPa/65.3% higher than that of composites without nanofillers. The interfacial transition zone thickness of nanocomposites ranges from 9 μm to 12 μm, while that of composites without nanofillers is about 18 μm. The ratio of CaO to SiO2 in the interface of composites without nanofillers is 0.69, and that of nanocomposites increases to 0.75–1.12. Meanwhile, the nanofiller content in nanocomposite interface is 1.65–1.98 times more than that in the bulk matrix. The interfacial microstructures of nanocomposites are more compact and the content and crystal size of calcium hydroxide were significantly reduced compared with that of composites without nanofillers. / The National Science Foundation of China (51978127 and 51908103), and the China Postdoctoral Science Foundation (2019M651116).

No / This study investigates the interfacial characteristics between aggregates and cement paste matrix in nanofillers modified concrete. A three-point bend test on the specimens composed of two pieces of aggregates bonded with a thin layer of cement pastes with/without nanofillers was carried out to characterize the interfacial bond strength of the composites. The scanning electron microscope observations and energy dispersive x-ray spectrometry analysis were also performed to characterize the interfacial microstructures and compositions of the composites. The experimental results indicated that the nanocomposites have higher interfacial bond strength and narrower interfacial transition zone thickness as well as more optimized intrinsic compositions and microstructures than that of composites without nanofillers. Specifically, the interfacial bond strength of nanocomposites can reach 7.67 MPa, which is 3.03 MPa/65.3% higher than that of composites without nanofillers. The interfacial transition zone thickness of nanocomposites ranges from 9 μm to 12 μm, while that of composites without nanofillers is about 18 μm. The ratio of CaO to SiO2 in the interface of composites without nanofillers is 0.69, and that of nanocomposites increases to 0.75–1.12. Meanwhile, the nanofiller content in nanocomposite interface is 1.65–1.98 times more than that in the bulk matrix. The interfacial microstructures of nanocomposites are more compact and the content and crystal size of calcium hydroxide were significantly reduced compared with that of composites without nanofillers. / National Science Foundation of China (51978127 and 51908103), and the China Postdoctoral Science Foundation (2019M651116).

Yes / Developing a fast, cost-effective, eco-friendly solution to recycle large amounts of construction and demolition waste (CDW) generated from construction industry-related activities and natural disasters is crucial. The present investigation aims to offer a solution for repurposing CDW into building materials suitable for accelerated construction and housing in developing countries and disaster-prone areas. Feasibility of recycled concrete aggregate (RCA) inclusion in geopolymer mortars constituted entirely from CDW (masonry elements) was investigated via an environmental impact-oriented approach by addressing the composition related key parameters. Mechanical performance was evaluated through compressive strength tests, and scanning electron microscope (SEM) imaging with line mapping analyses were carried out to monitor the interfacial transition zone (ITZ) properties. To investigate the environmental impacts of the geopolymer mortars and highlight the advantages over Portland cement-based mortars, a cradle-to-gate life cycle assessment (LCA) was performed. Findings revealed that roof tile (RT)-based geopolymer mortars mainly exhibited better strength performance due to their finer particle size. Mixtures activated with 15 M NaOH solution and cured at 105 °C achieved an average compressive strength above 55 MPa. RCA size was the most influential parameter on compressive strength, and a smaller maximum RCA size significantly increased the compressive strength. Microstructural analyses showed that the ITZ around smaller RCAs was relatively thinner, resulting in better compressive strength results. LCA proved that CDW-based geopolymer mortars provide the same compressive strength with around 60% less CO2 emissions and similar energy consumption compared to Portland cement-based mortars. / This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100. The authors also wish to acknowledge the support of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under project: 117M447

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-10-28T11:36:30Z No. of bitstreams: 1 Daniel Gustavo Brusius Wilbert_.pdf: 4731645 bytes, checksum: 08c801a9545a481516dfe01632256d9c (MD5) / Made available in DSpace on 2015-10-28T11:36:30Z (GMT). No. of bitstreams: 1 Daniel Gustavo Brusius Wilbert_.pdf: 4731645 bytes, checksum: 08c801a9545a481516dfe01632256d9c (MD5) Previous issue date: 2015-07-22 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / FAPERGS - Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul / O setor da construção civil é responsável por um grande impacto ambiental, destacando-se dois principais fatores, a quantidade de matéria-prima consumida e de resíduos gerados. Estes resíduos, em grande parte apresentam um grande potencial de reciclagem. Dentre estes resíduos, os de concreto apresentam um excelente potencial de utilização. Inúmeras pesquisas já comprovaram a viabilidade de utilização do Agregado Reciclado de Concreto (ARC). Porém, a menor qualidade do ARC em comparação aos agregados naturais, resultada em queda no desempenho destes concretos, principalmente nas propriedades de durabilidade. Como consequência ocorre um enfraquecimento da zona de transição entre a argamassa velha e a nova. Em função desta queda de desempenho ao se utilizar ARC, a presente pesquisa teve por objetivo a análise desta zona de transição, através do estudo da interface entre duas argamassas de concreto por meio da técnica de nanoindentação. Para esta análise foram moldados agregados reciclados de concretos modificados, todos no traço referência (sem adição), e posteriormente aplicada uma nova camada de argamassas com diferentes traços. Os traços variaram entre dois tipos de adição (Finos Basálticos – FB e Cinza da Casca de Arroz – CCA), em diferentes teores de adição ao cimento, 0, 5, 10 e 15% para os finos e 0, 5 7,5 e 10% para a CCA. Após cura de 63 dias, as amostras foram preparadas para a realização dos ensaios. Para a análise das medidas de nanoindentação na interface, foram propostos três métodos de análise. As propriedades macroestruturais foram avaliadas aos 28 dias, como módulo de elasticidade dinâmico, resistência à compressão, resistência à tração por compressão diametral e absorção de água por capilaridade. Os resultados demonstraram a melhora das propriedades macroestruturais das argamassas com 15% de FB e CCA em relação à referência. Foram identificadas alterações na região de interface entre as argamassas no traço com 15% de finos de basalto e em todos os traços com CCA, que apresentaram os melhores resultados. A comparação entre a região mais próxima à zona de transição resultou, para todos os traços, em valores semelhantes aos obtidos em regiões de pastas mais distantes à zona de transição, demonstrando que o uso de uma argamassa antiga na condição seca (simulando um agregado reciclado seco) melhorou as condições da zona de transição com a argamassa nova. / Construction is responsible for a large environmental impact, highlighting two main factors: consume of raw materials and generation of waste materials. By other hand, construction and demolition waste has a good potential of recycling. Many studies have demonstrated the viability of using recycled concrete coarse aggregate (RCA) in new concrete. However, due to the RCA’s properties, most results point to a lower durability of the concrete. It is also consensus that the main reasons for the lower quality of the new concrete are the mortar layer adhered to the natural aggregate and the weakening in the new Interfacial Transition Zone (ITZ) between the old and the new mortar. This study analyze the new interfacial transition zone in these concretes through nanoindentation. There were produced recycled concrete aggregates without addition of filler, and over these aggregates there were produced a new mortar layer with different mix compositions. There were used basaltic filler and rice husk ash-RHA in different levels of addition: 0, 5, 10 and 15% for the filler, and 0, 5, 7,5 and 10% for the ash. Their interfaces were evaluated using different methodologies. Modulus of elasticity, compressive strength, tensile strength and capillarity were determined. The use of fines improved the mortar properties in relation to the reference, especially those with 15% filler and the samples with RHA. The region near to the ITZ shows similar elastic moduli values to those obtained in the paste, in all mortars, proving that using dry recycled aggregates the new mortar loose water to the aggregates and increase their mechanical properties.

In this thesis different mechanical properties for shotcrete (sprayed concrete) such as compression strength, bond strength, bending tensile strength, elastic modulus, free and restrained shrinkage as a function of its age was investigated. One of the main issues was to investigate the difference between ordinary cast concrete and shotcrete. Reliable material data for young and hardening shotcrete is scarce which in the past have made such comparisons difficult. Also, less accurate data representative for cast concrete has often been used in numerical modelling and design analyses. The focus of the project has particularly been on the properties bond strength and restrained shrinkage for which two new testing methods has been developed and evaluated. Microstructural studies have also been performed as a complement to the bond strength testing. The bond to rock is one of the most important properties for shotcrete used as rock reinforcement. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. The investigation of early age bond strength of shotcrete is of great importance both from a production perspective and a safety perspective. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting. The bond, or adhesion, depends on several factors such as texture of the rock, the type of accelerator, application technique, etc. In this work the development of the microstructure in the interfacial transition zone (ITZ) and strength of the bond was investigated. The results show that the bond strength is related to the hydration process, i.e. the strength gain of the shotcrete. The early development of the ITZ was here studied using a scanning electron microscope (SEM) making it possible to observe changes over time, before and after proper cement hydration. Restrained shrinkage cracking of shotcrete, especially in the case of shotcrete sprayed on soft drains that are parts of a tunnel lining not continuously bonded to the rock, can be detrimental for the sustainability of an infrastructure tunnel system. Maintenance and repair costs can be high over time. It is shown that the developed test method realistically captures the behaviour of shotcrete drains on hard rock in situ. The method can be used in the evaluation of different technical solutions for avoiding or minimizing shrinkage cracks in shotcreted soft drains. It can also be used to assess the performance of shotcrete fully bonded to a rock surface, with respect to the ability to prevent cracking or to distribute possible shrinkage damage into several fine cracks instead of one wide. / <p>QC 20140526</p>

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.

The microstructure of concrete contains random features over a wide range of length scales in which each length scale possess a new random composite. The influence of individual material constituents at different scales and their mutual interactions are responsible for the formation of fracture process zone (FPZ). The presence of the FPZ and the various toughening mechanism occurring in it, influences the fatigue and fracture behavior of concrete which also gets influenced by the geometry, spacial distribution and material properties of individual material constituents and their mutual interactions. Hence, in order to study the influence of interfacial transition zone, microcrack and aggregate bridging on the fracture and fatigue behavior of concrete, a multiscale analysis becomes necessary. This study aims at developing a linearized model which helps in understanding the fracture and fatigue behavior of cementitious materials by considering the predominant fracture process zone (FPZ) mechanisms such as microcracking and aggregate bridging. This is achieved by quantifying the critical microcrack length and the bridging resistance offered by the aggregates. Further, the moment carrying capacity of a cracked concrete beam is determined by considering the effect of aggregate bridging. A modified stress intensity factor (SIF) is derived based on linear elastic fracture mechanics (LEFM) approach by considering the material behavior at different scales through a multiscale approach. The model predicts the entire crack growth curve for plain concrete by considering these process zone mechanisms. Furthermore, the fracture and fatigue response of concrete is studied through the development of analytical models which include the properties of the mix constituents using the multiscale based SIF. The effect of the interfacial transition zone, microcracks and resistance offered through aggregate bridging on the resistance to crack initiation and propagation are studied. A fatigue crack growth law is proposed using the concepts of dimensional analysis and self-similarity. Through sensitivity analyses, the influence of different parameters on the overall fracture and fatigue behavior are studied. In addition, studies related to concrete-concrete bi-material interfaces are conducted in order to understand the influence of repair materials on the service life of damaged concrete structures when subjected to fatigue loading. An analytical model is proposed in this study to predict the crack growth curve using the concepts of dimensional analysis and self-similarity in conjunction with the human population growth model. It is seen that a repair done with a patch having similar elastic properties as those of the parent concrete will have a larger fatigue life.

The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.

Concrete as a building material is subject to continuous innovation and thanks to advanced technology and quantum of research, its properties are still improved. It is logical that the more concrete we produce, the more waste it arises. The volume of this waste can not be stored in landfills endlessly, nowadays most of the waste economies in the world are trying to recycle concrete rubble. The recycling is not such a problem, the technology has been long verified but the quality of the recycled concrete aggregate is unquestionably one of the primary assumption which leads to accomplish required properties of concrete. In fact, the recycling process is „crushing“ the concrete into particles with an effort to eliminate the cement paste on the surface of the aggregate. An ideal solution would be create a resistant and firm coating that would adhere perfectly to the cement matrix. This diploma thesis is focused on the properties of recycled concrete aggregate and methods of improvement and optimization of the concrete mix composition.