1,721,032 research outputs found
Improved Corrosion Inspection Procedures for Reinforced Concrete Bridges: Electrical Resistivity of Concrete
No full textThe effects of steel reinforcement and chloride-induced corrosion initiation on the electrical resistivity measurements using the Wenner probe technique were studied experimentally on custom-designed reinforced concrete slabs. Investigation parameters included (1) probe configurations with respect to rebar mesh, (2) rebar density, (3) epoxy coating on the rebar, (4) concrete cover thickness over embedded reinforcement, (5) chloride ingress, and (6) corrosion of rebar. The concrete moisture condition and cover thickness influenced the effect of rebar mesh. It was theorized that bound chlorides increased electrical resistivity measurements and counteracted the effect of free chlorides. It was observed that epoxy coated rebar did not significantly affect measurements. Uncoated rebar affected resistivity measurements, particularly for saturated and semi-saturated concrete. Corrosion initiation was observed to have no significant effect on measurements. Larger concrete cover thicknesses provided for more discrepancy between half-cell potential and electrical resistivity measurements. Recommendations to increase electrical resistivity measurement accuracy on reinforced concrete slab surfaces are made.Pacific Northwest Transportation Consortium
Oregon State Universit
Recommended from our members
Selective Laser Melting of Duplex Stainless Steel 2205: Microstructure, Mechanical Properties, and Corrosion Performance
No full textThe aim of this work was to assess the viability of duplex stainless steel 2205 components built via selective laser melting for seawater applications. First, a comprehensive additive manufacturing assessment was done. The duplex stainless steel 2205 components were selectively laser melted from gas atomized powder (D90 5μm Ra). Finally, a study on corrosion performance was done. Two build orientations (parallel and perpendicular to build direction) and as-built (no heat treatment) and annealed conditions were studied. Parts manufactured by SLM were characterized for corrosion properties in a 3.5% NaCl electrolyte and compared to results obtained for wrought DSS 2205. The measured corrosion rates from linear polarization resistance were < 1 μm/year for all conditions. The as-built conditions showed anisotropic corrosion rates due to the preferred crystallographic orientation of the different build orientations. The anisotropy was not replicated on the annealed conditions, possibly due to elemental segregation of Si and Mn, or porosities. A novel finding was that the as-built parallel condition showed superior performance to wrought (0.33±0.10 μm/year vs 0.59±0.10 μm/year corrosion rate). No steady state pitting behavior occurred during the cyclic polarization (CP) test for any conditions tested, although certain SLM conditions showed metastable pitting (up to 10-5 A/cm2 measured during CP), likely due to open surface pores. The exception was as-built, parallel to build direction, which showed no metastable pitting due to the strongly resistant [110] ferrite texture
Recommended from our members
Investigation of x-ray computed tomography for Portland cement phase quantification
Get PDFCementitious materials are often characterized through the use of advanced analytical techniques to understand the macro-, micro-, and nano-scale properties, including phase formation during hydration, and subsequent potential deterioration mechanisms which can affect service life. A major limitation with using such analytical techniques to quantify solid phases in cementitious systems is that many techniques are destructive in nature. If one wants to monitor changes over time, samples must be extracted from different locations of the same sample, or from a different sample, at different times. This limitation can hinder the ability continually monitor the desired property. One method to extract quantifiable information non-destructively is x-ray computed tomography (x-ray CT). X-ray CT is a non-destructive, non-contact technique that uses computer-processed x-rays to produce three-dimensional tomographic images of specific zones of a sample. This technique has been successfully used in many different aspects of research, including medicine, geo-sciences, and materials science. The use of x-ray CT has been applied to cementitious systems but has been predominately limited to qualitative or semi-quantitative analysis. Quantification of cementitious properties has been hindered through two means, spatial resolution and low contrast between solid phases, including the unhydrated and hydrated phases. This low contrast has often led to quantification of void space within the cementitious sample. The work presented in this dissertation addresses methods to resolve the expected low contrast in x-ray CT images on cementitious and the potential for segmentation of the four main hydration products found in portland cement. This was achieved through an investigation of different image segmentation algorithms and a creative use of contrast agents to be bound into specific hydration products using a synchrotron x-ray CT. Advancements in x-ray CT optics and data collection are continually improving image resolution, therefore it is not discussed in this dissertation.
Published literature on the use of x-ray CT in cementitious materials often does not include a thorough description of the image processing procedures used for analysis. The use of arbitrary, histogram-based threshold values can lead to biased segmentation and misclassification of the voxels in the image volume. Presented in this dissertation is a method to deconstruct the greyscale values of a histogram into individual Gaussian curves in an unbiased manner. The greyscale values of laboratory synthesized calcium-silicate-hydrate (C-S-H), calcium hydroxide (CH), monosulfate (AFm), and ettringite (AFt) were determined to provide a baseline for threshold values. Pure phase, binary, and quaternary mixture samples of the four aforementioned phases were studied. A Gaussian probability density function was applied to each phase and proportioned to the known mass of each phase in the binary and quaternary mixtures. Intersections of the Gaussian curves was determined as the threshold value. Quantification of binary mixtures was successfully done with exception to C-S-H and AFm mixtures. Low contrast between the phases was observed leading to difficulties accurately quantifying such mixtures. Similar success was observed in quaternary mixtures of phases. However, difficulties in segmentation were compounded segmenting AFm, C-S-H, and CH in these mixtures.
One method to resolve low contrast is to incorporate the use of contrast agents. Success in the medical field, and other limited successes in geo-sciences, provided the motivation to determine methods to incorporate contrast agents into portland cement hydrates. Literature reports a myriad of ions which can be incorporated into the structure of C-S-H, AFm, and AFt through various mechanisms, including substitution and absorption. Due to the limitations in segmenting AFm and C-S-H in their pure form, investigations for incorporating contrast agents to improve segmentation was done. Iodine was selected as the contrast agent to be substituted for the sulfate ion in AFm. Dual energy scans above and below the absorption edge of iodine was done, and the use of image subtraction allowed for quick and accurate segmentation of the C-S-H and modified AFm phases. However, difficulties segmenting C-S-H and CH were observed in quaternary mixtures of AFt, CH, C-S-H, and a modified AFm using the Gaussian deconstruction method to determine threshold values for segmentation.
Lastly, due to the difficulties achieving consistent results during segmentation when using histogram-based threshold values, a study determining the feasibility of local segmentation algorithms was done on binary and quaternary mixtures of the four phases. These algorithms often result in more desirable results by accounting for the spatial arrangement of the greyscale values throughout the image volume. Two local segmentation algorithms, watershed and Bayesian Markov random fields, were compared to the Gaussian deconstruction method. Results indicated both local segmentation algorithms resulted in more accurate quantification of the four phases, thus providing promise for future applications to hydrating portland cement
Recommended from our members
Surface Modification to Enhance Corrosion Resistance of Carbon Steels using Additive Manufacturing
Get PDFLow carbon steels (LCS) due to their high strength-to-cost ratio are one of the most ubiquitous materials used for a wide range of applications, including but not limited to automotive, construction, and transportation. However, the low corrosion resistance of LCS in neutral, acidic, or saline environments limits its utilization and service life. Corrosion resistant alloys, such as stainless steels (316-L and UNS32750 super duplex stainless steels), provide superior corrosion resistance than LCS for such applications, albeit with a significantly higher material cost. The surface modification cladding is one of the viable methods to manufacture a composite with wear and corrosion resistant surface layer on a low-cost substrate with desired mechanical and corrosion properties, as in the case of stainless steel clad on LCS substrate.
Various traditional manufacturing techniques such as welding, hot rolling, powder roll bonding, cold/thermal spraying have been used to produce the said clads, however, with limited success. Failure at the clad-substrate interface has been the drawback of the cladded composites produced with the said traditional processes. Recent developments in additive manufacturing (AM) technologies make them an excellent candidate to produce cladded systems with desired properties. Traditionally, the AM techniques have employed to produce three-dimensional (3D) components. However, one of the AM techniques, laser powder bed fusion (LPBF), is a promising method for cladding operations because of its higher resolution and dimensional accuracy than the other AM technologies. Furthermore, the LPBF technique results in lower surface roughness of the components produced with higher material savings per unit volume of print. Therefore, this research makes novel use of the LPBF technique for 2D cladding applications to enhance the corrosion resistance of LCS.
This research aims to improve the corrosion resistance of the LCS by cladding it with 316L SS and super duplex stainless steel (SDSS) using the LPBF process. Critical process parameters such as laser power, laser scan speed, hatch spacing, and powder layer thickness were optimized to achieve the best possible metallurgical bonding between the clad and the substrate.
Due to high local melt pool temperatures during laser melting, the evaporative losses of the elements resulted in clad layers with lower Cr, Ni content as compared to the feedstock powder. The LPBF process, due to the high cooling rates, is associated with high residual and thermal stresses and as printed parts are characterized by defect density and non-equilibrium microstructures; consequently, additively manufactured clads were subjected to post-printing heat treatment procedures for stress relief and to restore metallurgical, mechanical properties of the as printed clads. The metallurgical and corrosion response of the clads before and after heat treatments were compared. For super duplex stainless steel clads, the as printed (AP) clads showed predominantly δ-ferrite matrix, with allotriomorphic austenite precipitating at the ferrite grain boundaries. Increasing laser scan speeds resulted in decreasing austenite phase fraction, with dominant widmannstatten morphology at higher scan speeds. The heat treatment restored the δ-γ phase balance, thereby increasing the corrosion resistance of the heat-treated (HT) clads as compared to AP clads. Increasing scan speed had a negative impact on the corrosion resistance, and the pitting potential of the AP and HT clads exposed to 3.5 wt. % NaCl aqueous solution. In general, increasing laser scan speeds resulted in decreasing corrosion resistance for the AP and HT clads, as indicated by OCP, EIS, and LPR and CP results. Clads produced at the lowest scan speeds showed comparable corrosion resistance to the as-cast or wrought 316L/SDSS counterparts.
Subjecting the cladded composite to tensile stresses (yield and ultimate tensile stress) increased the corrosion rates; however, these stress effects were eliminated by post stressing heat treatments. The SDSS clads showed a superior metallurgical bonding with the LCS substrate did not delaminate even at failure strains at all laser scan speeds.
Furthermore, the passivation behavior and the critical chloride thresholds of the additively manufactured super duplex stainless steel clads (SDSS) on carbon steels were also studied in simulated concrete pore solution. The effects of LPBF laser scan speed on the early passivation, full passivation, and critical chloride threshold of the SDSS clads were investigated. Increasing δ-ferrite phase fraction with scan speeds resulted in fast film formation kinetics for early passivation but showed low critical chloride thresholds for the clads. The SDSS clads produced at 100 mm/s, 600 mm/s and 1000 mm/s showed critical chloride threshold values of 4 M, 2.5 M and 1.5 M. The as-cast SDSS alloy did not show any signs of depassivation until 5M Cl- concentration, whereas LCS substrates depassivated at 0.75 M Cl-. Therefore, additively manufactured SDSS clads showed significant enhancement in chloride threshold values over LCS substrates.
Finally, the galvanic coupling of the super duplex stainless steel (SDSS) clads on low carbon steel substrate was investigated in 0.1 M NaCl aqueous solution via scanning vibrating electrode technique (SVET). It was found that the clad metallurgy and the microstructural features arising from the LPBF process had a prominent effect on the clad-substrate galvanic coupling. The galvanic coupling exponentially decreased with increasing laser scan speeds. The general corrosion resistance of the clads and the galvanic coupling were found to be proportionally linked with each other; therefore, highly corrosion resistant clads would also give rise to high galvanic coupling. The post-print heat treatment resulted in increased corrosion resistance of the clads, but at the expense of increased galvanic coupling. Since the LPBF process used in this study yielded clads with a very low number of defects and highly dense structures with strong bonding with the substrate, and the clad thickness can be increased on-demand depending on the needs, the galvanic coupling issues that might arise due to possible clad defects or failures are considered to be relatively low. Regardless, more research is needed to improve the galvanic corrosion resistance of clads, especially for cases where cathode-to-anode area ratio could be rather large
Recommended from our members
Chloride Binding of Portland Limestone Cement containing Supplementary Cementitious Materials
Get PDFChloride binding in Portland limestone cements (PLC) can be attributed to the chemical reaction between chloride ions and carboaluminate phases to form Friedel’s salt and the physical interaction between chloride ions and calcium-silicate-hydrates (C-S-H). This thesis examines the chloride binding of mortar samples containing varying amounts of limestone, fly ash, silica fume, and slag, exposed to NaCl and CaCl₂ salts mixed in simulated pore solutions at 23°C. PLC and OPC+10LS systems can be used as a direct substitute for OPC as there is no significant difference in bound chloride contents. There is variation among the amount of chlorides bound by the mixtures with different SCM contents. Fly ash, silica fume, and natural pozzolans do not affect the chloride binding capacity in the presence of limestone. Slag significantly increased the bound chloride content by up to 21% at 0.1M NaCl in a cementitious system containing up to 15% interground limestone. Based on these findings, as it relates to chloride binding, limestone should be considered part of the binder content
Recommended from our members
Assessment and Service Life Prediction of Microbial Induced Corrosion of Concrete (MICC)
No full textMicrobial-induced corrosion of concrete (MICC) is a multi-stage deterioration process caused by microbial activity in wastewater infrastructure. MICC is a worldwide issue due to the reduced service life of the wastewater infrastructure and the economic impact associated with increased maintenance and reconstruction costs. This thesis explores two critical aspect of this complex and costly problem. The first thrust of this research is related to the service life prediction of concrete used in wastewater sewers using the data from standardized benchtop biogenic acidification tests. The second thrust explores the role limestone addition in cementitious mixtures during the acidification process, with a focus on portland-limestone cement.
Microbially induced corrosion of concrete is a multi-stage deterioration process influenced by the presence and activities of bacteria in wastewater collection, storage, and treatment infrastructure. MICC reduces concrete service life significantly and is a
serious issue due to enormous cost and environmental effects. Conventional accelerated laboratory methods may not accurately represent the rate of concrete deterioration that occur in field conditions. However, recently, a biogenic benchtop method for assessing MICC has been developed and standardized (ASTM 1904-20). This new approach does not rely on H2S as the nutrient source for the sulfur oxidizing bacteria, but rather uses elemental sulfur species, therefore, it is practical, safer, and rapid. The objective of this study is to develop a service life modeling approach to study MICC to correlate the results of the ASTM 1904-20 approach to real field conditions such as whose found in sewer pipes. This correlation is based the Pomeroy model that relates the field H2S concentrations, wastewater flow conditions, geometry and the properties of the concrete. The model will be provided by using ‘correlation factors” and a demonstration study showing how the ASTM C1904 data could be used to predict the performance of different types of concrete and antimicrobial products in realistic exposure scenarios will be explained.
The second thrust of this work analyzes chemical acidification in cement pastes made where a portion of the clinker is replaced with limestone (LS, calcium carbonate). This research addresses the question of how ASTM C595 cements (more specifically portland-limestone cement) respond to acid exposure as compared with ASTM C150 cements. To answer this question, the performance of OPC, OPC+LS systems respond when exposed to acid at a pH of 2 and 3. The degradation of the material was measured over time using thermogravimetric analysis (TGA) to assess calcium hydroxide
(Ca(OH)2) and calcium carbonate (CaCO3) changes as well as flexural strength reduction. Results indicate that there was no significant difference between the flexural strength and CH loss of different limestone mixtures during pH~3 immersion of 42 days. The flexural strength and TGA results have become more distinctive for more severe acidic conditioning at pH~2. The consumption of titration solution to keep the pH constant was correlated with the consumption of Ca(OH)2 and CaCO3 by using TGA results. When clinker is replaced with CaCO3 the sacrificial characteristic of CaCO3 offsets dilution. The use of limestone changes the hydration products and produces monocarbonate instead of monosulfate phase, which might affect the reaction of hydration products with sulfuric acid
Cathodic Protection of Reinforced concrete infrastructure using MMO-Coated Titanium Alloy Bars
No full textASTM B1009 titanium alloy bars (TiABs), which are chemically and mechanically equivalent to Grade 5 titanium, have recently gained attention as dual-purpose materials for near-surface-mounted retrofit (NSMR) of concrete. These bars offer both structural reinforcement and corrosion protection when used as anodes in impressed current cathodic protection (ICCP) systems. While TiABs without mixed metal oxide (MMO) coating provide inherent corrosion resistance as an ICCP anode, their effectiveness in ICCP applications may be limited. This study evaluates the electrochemical behavior of iridium-based MMO coatings on TiABs that are designed as ICCP anodes. Open circuit potential (OCP) measurements showed that both uncoated and coated metals stabilized at similar potentials, while uncoated bars initially exhibited more active behavior. Additionally, linear polarization resistance (LPR) results revealed that MMO-coated TiABs exhibit approximately three times higher reactivity compared to bare TiABs. Electrochemical impedance spectroscopy (EIS) further confirmed that MMO-coated TiABs possess significantly greater conductivity, making them a superior option for use as anodes in ICCP systems. Studies on long-term performance also show that MMO coated bars are better suited for the dual-purpose application
Strategies to increase the service life of existing bridge decks
No full textsubmitted by Burkan Isgor, Jason Ideker, David Trejo, Oregon State University ; for Oregon Department of Transportation, Research Unit.Title from PDF title page (viewed on April 10, 2020)."SPR 780."Covers OCLC #1149991467.This archived document is maintained by the State Library of Oregon as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Includes bibliographical references.Mode of access: Internet from the Oregon Government Publications Collection.Text in English
Recommended from our members
Measuring and Correcting the Electrical Resistivity of Concrete Pore Solution in Fresh Mixtures
Get PDFA vital aspect of concrete construction is quality assurance and control (QA/QC). Engineered structures must meet pre-determined and agreed-upon strength and durability requirements. Concrete falls into a specific category of infrastructure material because in most cases, these strength and durability requirements cannot be found until the material has at least partially cured (7-28 days). Recent research has suggested that fresh concrete electrical resistivity may be a possible indicator of critical hardened concrete properties; therefore, it can be used to supplement existing QA/QC protocols of concrete.
The electrical properties of fresh and hardened concrete have been investigated for more than 80 years. However, two key aspects of measuring fresh concrete resistivity in the field have not been extensively studied. The main goal of this thesis is to answer the following two questions: (1) how can the electrical resistivity of concrete pore solution be measured practically in the field and (2) would aggregates affect these measurements.
The first part of this thesis statistically compares techniques for fresh concrete resistivity extraction and measurement. These procedures must be cost-effective, easy to upscale for industry, and yield faster results. The centrifuge approach of extraction and conductivity probe for measuring resistivity are found to be the most practical techniques for potential field use. Additionally, it is found that pore solution extraction and measurement can be performed 30-90 minutes after mixing without significantly affecting the resistivity. Finally, a practical method is proposed to determine the resistivity from a diluted cement paste sample when the extracted pore solution volume is inadequate for accurate measurement.
The second part of this thesis examines the influence of fine aggregates on the pore solution of fresh mortars. Specifically, this chapter considers the dilution of pore solution due to the water content of aggregates, and the potential adsorption of pore solution ions on the surface of aggregates. Results indicate that aggregates may play a significant role in the chemistry of a fresh mortar system. A test method is proposed to identify aggregates that are a significant ionic influence on the pore solution system, and a methodology is proposed that corrects for the change in ion concentration of a fresh pore solution due to the dilution and adsorption of aggregates
- …
