1,720,988 research outputs found
A study of some factors affecting bond in cementitious fiber reinforced repairs
No full textConcrete infrastructure repair remains a formidable challenge. We need to understand the repair performance and develop innovative materials and placement processes that lead to durable, cost-effective and esthetically pleasing repairs. In this context, fiber reinforced concrete is considered promising. The influence of fibers on the properties of the interface between old concrete and fiber reinforced repair remains poorly understood. This paper describes an experimental study on the influence of fibers on the mechanical properties of the interface. Bond strength was assessed by means of slant shear tests with different slants. Shear-normal stress interaction diagrams, adhesion strength and internal friction were obtained. Repair mortars with different contents of Polyvinyl Alcohol (PVA) fibers and the influence of wet-dry cycles were investigated. Results show that PVA fibers added to the repair can significantly enhance interfacial adhesion. Once the repair interface is fully developed, fibers, however, do not mitigate damage from wetting and drying
Enhancing concrete sewer lifespan : development of sustainable multilayed graphite-doped cementitious coatings to mitigate microbially induced corrosion
No full textCorrosion in concrete sewers results from both biotic and abiotic processes. Microbially induced concrete corrosion (MICC) is a multifaceted phenomenon driven by the metabolization of sulfate-rich wastewater by sulfate-reducing bacteria in anaerobic conditions, producing hydrogen sulfide as a byproduct. This hydrogen sulfide undergoes chemical or biological oxidation and reacts with the alkaline and porous concrete surfaces of the sewer. Consequently, the reaction-transport mechanisms between the hydrogen sulfide and substrate causes the pH of the concrete surface to decrease, creating an environment conducive to the growth of sulfur-oxidizing bacteria. These bacteria further metabolize hydrogen sulfide, converting it into sulfuric acid, thus perpetuating the cycle of Microbially Induced Corrosion (MIC).
Approximately 6% of the global GDP is utilized in repairing and maintaining pipes damaged by biocorrosion, highlighting its significant economic impact. However, current mitigation strategies have demonstrated inherent limitations. To combat MIC, cement-based/polymer coating methods have emerged as popular solutions due to their effectiveness, easy application, and cost-efficiency. However, effective coatings for MIC prevention require both antibacterial and anticorrosive properties. Unfortunately, traditional coatings which utilize heavy metals like tin, copper, and zinc as anti-microbial agents pose environmental hazards, thereby limiting their widespread use. Consequently, there is an increasing focus on the development of coatings that not only provide low cytotoxicity and genotoxicity but also possess antibacterial and anticorrosive properties, while maintaining compatibility with deteriorated substrate.
In this study, the focus lies on exploring the potential of graphite, known for its reduced toxicity, corrosion resistant, and cost-effectiveness, as a biocide when encapsulated within calcium aluminate and geopolymer coating matrices. This research evaluates the mechanical properties and chemical stability of these newly developed coating materials. Additionally, the performance of these coating materials is tested under accelerated MIC conditions, and the antibacterial effectiveness is also assessed. Research findings from this study indicate promising results: graphite-doped composites demonstrate superior strength, durability, and bonding performance. Moreover, the graphite-incorporated coatings exhibit excellent resistance against biogenic acid attack, while both graphite and calcium aluminate-based coatings display antibacterial properties. Consequently, the developed coatings demonstrate potential in mitigating MICC.Applied Science, Faculty ofCivil Engineering, Department ofGraduat
CONCRETE-ICE ABRASION: SURFACE ROUGHNESS AND MEASUREMENT METHOD
No full textThe wearing of concrete material due to ice movement is a cutting edge problem for offshore and coastal engineering. The phenomenon is often referred to as concrete-ice abrasion, but the physics of this process is not clearly understood yet. A possible mechanism to explain concrete-ice abrasion is the formation of cracks on the concrete surface, due to excessive tensile stresses induced by sliding of ice asperities. Concrete surfaces exposed to moving ice are subjected to wear at various rates depending on concrete and ice properties.
At NTNU, Department of Structural Engineering, we are studying ice abrasion phenomena both theoretically and experimentally. This paper analyses the wear rate of concrete; concrete surface roughness and its relevance for the abrasion mechanism. The results indicate that increasing concrete-ice abrasion relates to increasing surface roughness. Furthermore, measurement of abrasion mechanically and with an optical scanner gave similar average abrasion
Sprayable geopolymer for underground wastewater infrastructure
No full textUnderground concrete infrastructure used to transport wastewater is deteriorating faster than its expected design life in many parts of the world due to microbial-induced concrete corrosion (MICC). This accelerated degradation is costing governments and municipalities billions of dollars in repairs, in addition to the significant environmental consequences associated with repairing or replacing damaged structures.
Current industry solutions fail to provide long-term durability, are difficult to implement, and often release toxic chemicals into the environment. Additionally, these solutions typically have a high embodied carbon, raising critical sustainability concerns. Geopolymers (GP), in contrast, offer a promising alternative due to their improved sustainability, reduced toxicity, and enhanced performance compared to traditional rehabilitation techniques. This thesis details development of a novel sprayable geopolymer to apply as a repair material to deteriorated wastewater infrastructure. The work also investigates this goal by exploring performance of the novel geopolymers in field conditions to gain an understanding of how mixes can be optimised for Microbial Induced Corrosion (MIC) resilience, which has only been completed to a rudimentary degree prior to this study. Additives including heavy metals, and fibres alongside variations in calcium content are explored to understand what factors impact GP performance. Assessment is completed with physical, mechanical, and chemical analysis to provide holistic conclusions on GP performance. This is complimented with a rheological study, to facilitate the sprayability of geopolymer mixes. Sprayability is vital to allow practical application of such a material, however, exploration of sprayed geopolymers has been limited until this point.
The results of these studies are combined to present an optimised mix of MIC resilient GP that can be sprayed to meet the original goal of the study: to develop a sustainable material that can be adopted by industry to repair existing underground infrastructure.Applied Science, Faculty ofCivil Engineering, Department ofGraduat
Robust IoT-enabled sensors for bridge scour monitoring : laboratory and field studies
No full textThis thesis evaluates industrially-available sensors for their effectiveness in real-time monitoring of foundation soil level and bridge scour. Two types of photoelectric sensors, namely diffusive-reflective and through-beam, and two types of dielectric (capacitance) sensors, namely low frequency printer-circuit board type, and higher frequency stainless steel type, were independently investigated.
Laboratory investigations carried out in a hydraulic flume used a simulated bridge pier comprising of an array of sensors mounted vertically and interfaced via Arduino. The state of “burial” in foundation soil or the state of “exposure” to water was determined from the sensor output. On scouring, the sensors provided an instantaneous shift in signal from the state of “buried” to “exposed”, and vice versa. The results indicate that all the four sensors could be monitor sediment level, scour, scour-hole refill, and scouring rate.
The dielectric sensors were susceptible to misinterpretation at high concentrations of NaCl in water. Improvements on isolating the effects of NaCl were made using lab-made steel electrodes excited using an external electrical waveform ranging from 1 Hz to 70 MHz. The results indicate that low frequencies were influenced by NaCl content, whereas at high frequencies (35-50 MHz), the sensors performed well. Although a single signal frequency worked well for the range of NaCl content from 0% to 3.5%, the use of two or more frequencies is recommended for higher reliability.
Passive thermometry using a vertical array of DS18B20 digital temperature sensors buried at different depths in sediment and water studied the diurnal thermal variations in the media. Although the technique required historic data (few diurnal cycles), a clear distinction could be noticed in the buried and the exposed temperature waveforms.
A field prototype using photoelectric sensors was installed in a small creek in UBC, and a second prototype using dielectric and temperature sensors was installed at a scour-susceptible over-water platform on Guichon Creek, Burnaby. Both the field prototypes validated laboratory results, were able to notify the onset and progression of scour around the pier over long periods of time. The detected scour events and subsequent re-deposition could be correlated to reference water level and rainfall data.Applied Science, Faculty ofCivil Engineering, Department ofGraduat
CONCRETE-ICE ABRASION: SURFACE ROUGHNESS AND MEASUREMENT METHOD
Get PDFThe wearing of concrete material due to ice movement is a cutting edge problem for offshore and coastal engineering. The phenomenon is often referred to as concrete-ice abrasion, but the physics of this process is not clearly understood yet. A possible mechanism to explain concrete-ice abrasion is the formation of cracks on the concrete surface, due to excessive tensile stresses induced by sliding of ice asperities. Concrete surfaces exposed to moving ice are subjected to wear at various rates depending on concrete and ice properties.
At NTNU, Department of Structural Engineering, we are studying ice abrasion phenomena both theoretically and experimentally. This paper analyses the wear rate of concrete; concrete surface roughness and its relevance for the abrasion mechanism. The results indicate that increasing concrete-ice abrasion relates to increasing surface roughness. Furthermore, measurement of abrasion mechanically and with an optical scanner gave similar average abrasion.Published pape
Carbon fiber-based chemiresistors for structural health monitoring
No full textWith the increasing demand for durable infrastructure in chemically aggressive environments, the development of self-sensing cement-based materials has emerged as a promising approach for real-time SHM. Traditional methods of assessing infrastructure often rely on periodic inspections, which are not only costly and time-consuming but also limited in their ability to detect early-stage deterioration. This thesis investigates the development and application of carbon fiber-reinforced cement-based chemiresistors designed to detect chemical-induced degradation in concrete infrastructure. The research addresses a critical gap in Structural Health Monitoring, where traditional piezoresistive sensors primarily focus on strain detection, overlooking the effects of chemical exposure.
The study explores the performance of these chemiresistors under exposure to 5% NaCl, 3% and 7% H₂SO₄, 10% and 20% NH₄NH₃, simulating conditions found in marine environments, wastewater systems, and agricultural settings. Cement composites incorporating two types of carbon fibers and hybrid fiber systems (carbon and steel fibers) were fabricated and subjected to cyclic wetting-drying exposure at 50ºC for 30 days to accelerate degradation and create a more realistic environment. Electrical resistivity and UPV were used to monitor degradation over time. The result of this research discusses the best type of carbon fiber, fiber content, and a range of FCR that is expected to be seen after 30 days of exposure.
The research introduces cement-based chemiresistors as a novel SHM solution for detecting chemical damage in real time. The dual assessment of resistivity and UPV provided a comprehensive understanding of both electrical and mechanical degradation mechanisms. This enhances sensor performance. The findings have significant implications for developing smart, self-sensing materials capable of improving the durability and safety of critical infrastructure exposed to harsh chemical environmentsApplied Science, Faculty ofCivil Engineering, Department ofGraduat
Development and validation of a novel 3D printed concrete material with artificial lightweight aggregate
No full textDespite recent advances in construction digitization and concrete 3D printing, engineering a printable concrete mixture for extrudability and buildability with a minimal carbon footprint still presents technical challenges.
Recent studies showed that to meet the requirements of extrudability and buildability, printable concretes are often designed with relatively smaller size aggregate and higher cement content of 3D printing concrete (3DPC) as compared to conventional concretes. The higher binder content and the relatively smaller aggregate sizes used in printable mortars make it more susceptible to thermal and shrinkage cracking. There are only a few limited studies examining the prospects of using coarse aggregates and lower cement content in printable concretes.
In the current study, fly ash based lightweight aggregate (LWA) were used as a partial substitution of natural sand in varying proportions (15%,30%,50%). After conducting aggregate characterization to ensure repeatability, both fine and coarse LWAs were utilized. This study investigated both fresh and hardened properties. The flowability was checked by conducting the slump flow test and flow table test. The effect of fine and coarse LWA inclusion on extrudability was investigated by visual inspection to determine the maximum printing distance that the filament may be extruded without any fracture, blockage, segregation, and bleeding. The extrudability of the concrete mixture was determined by measuring the yield stress using the rheometer. The influence of incorporating LWA on buildability was evaluated through visual inspection, comprising layer settlement and layer deformation tests. Moreover, stress growth, viscosity recovery, and flow curve tests were conducted. The compressive strength test, flexural test, split tensile bond test were conducted on the printed concrete specimen.
The findings indicated that incorporating binder material consisting of 80% fly ash and 20% cement resulted in the aggregates being classified as lightweight. This mix demonstrated satisfactory physical and mechanical properties. The fresh characteristics of 3DPC were influenced by particle size. Furthermore, it was observed that fine LWAs contributed to higher compressive strength compared to coarse LWAs, attributed to enhanced particle packing, increased density, stronger bonding, and reduced porosity. Additionally, both flexural and bond strength were influenced by LWA particle size.Applied Science, Faculty ofCivil Engineering, Department ofGraduat
Fly ash-based geopolymers for immobilization of nuclear waste containing cesium
No full textGeopolymers (GP) are a class of relatively new sustainable inorganic materials considered as an alternative to ordinary Portland cement (OPC). GP technology provides an economical solution to utilizing fly ash with a positive environmental impact. The performance advantages of GP relate to their resistance to acid/sulfate attack, thermal stability, and durability. The growing nuclear safety concerns call for better solutions than OPC-based materials to retain radionuclides. Fly ash-based geopolymers (FA-GP) are targeted in this work as a potential sub-class of GP with an ability to immobilize radionuclides, especially cesium (Cs). The work includes a series of fundamental studies and engineering process development of low-cost NaOH-activated FA-GP, exploring the effects of process parameters on non-radioactive equivalent Cs immobilization (quantified as Cs leachability index LX and effective diffusion coefficient, D), in-situ Cs-containing zeolite crystallization, and microstructural development. The applied aspect of the work was to maximize Cs immobilization in FA-GP systems. Phase analysis (XRD), microstructural (SEM), pore structure (BET), and mechanical (compressive strength) studies led to a deeper understanding of the fundamental transformations that occur during the geopolymerization and zeolite crystallization processes. The factorial design of experiments and analysis of variance enabled us to establish quantitative relationships between the degree of Cs immobilization (LX) and the processing parameters in the FA-GP systems. Enhanced immobilization of Cs (measured through LX = 14.6, De = 2.5×10⁻¹⁵ cm²/s), not reported previously, was achieved by in-situ pollucite crystallization via a one-step synthesis route at a modest temperature of 90 °C. The degree of Cs immobilization and other properties were quantified as a function of in-situ pollucite content and shown to have a linear correlation. Johnson-Mehl-Avrami-Kolmogorov kinetics model described well in-situ pollucite crystallization below 90 °C. The activation energy of pollucite formation was found to be 25 kJ/mol. In addition to the advancement of understanding of the fundamentals of Cs-FA-GP system, this work also demonstrated the significant potential of FA-GP processed at relatively low temperatures as a conditioning matrix for long-term immobilization of cesium-containing nuclear waste.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat
Investigating the self-sealing of a healing agent via a Korean permeability test and a migration test
No full textCracks in reinforced concrete are a fast entry point for aggressive substances possibly leading to reinforcement corrosion and concrete deterioration, which leads to a decreased service life and a need for repair. This paper investigates self-healing concrete, which is able to heal the formed cracks. An organic/inorganic hybrid admixture was used in a mortar mix as a healing agent and compared to a reference mortar. The sealing efficiency of the mixture with and without healing agent was compared through a Korean water permeability test on cylindrical specimen. The specimens were cracked in an indirect tensile strength test after which the two halves were tied back together with silicone spacers in order to have a crack width of 300 µm. The results showed that the organic/inorganic hybrid admixture obtained a better sealing efficiency in comparison to the reference mortar. Additionally, a chloride migration test was performed on a different set of reference specimens and specimens with the organic/inorganic hybrid admixture. After 0 and 28 days of healing, the specimens with the hybrid admixture had a significantly lower migration coefficient
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