1,721,012 research outputs found
Comparative Investigation of Detection Techniques for Chloride-induced Corrosion of Loaded Reinforced Concrete Slabs
No full textThis study involved a comparative investigation of chloride-induced corrosion detection techniques on loaded reinforced concrete slabs which were exposed to deicing salts and wetting-drying cycles to simulate typical aggressive environments in cold climates. The studied techniques involved linear polarization technique, galvanostatic pulse technique, electrochemical impedance spectroscopy, half-cell potential and concrete electrical resistivity mapping. The results showed that concrete quality and moisture content have a direct effect on corrosion activity, and these properties are represented well with concrete electrical resistivity. The galvanostatic pulse technique was shown to correlate well with electrochemical impedance spectroscopy, which was used as a benchmark for corrosion rate measurements in this study; however, the galvanostatic pulse technique was not capable of detecting corrosion activity in saturated concrete accurately. The results of this research do not support the criteria provided by the ASTM C876-09 standard for using half-cell potentials to estimate the probability of reinforcing steel corrosion in reinforced concrete structures
Comparative Investigation of Detection Techniques for Chloride-induced Corrosion of Loaded Reinforced Concrete Slabs
No full textThis study involved a comparative investigation of chloride-induced corrosion detection techniques on loaded reinforced concrete slabs which were exposed to deicing salts and wetting-drying cycles to simulate typical aggressive environments in cold climates. The studied techniques involved linear polarization technique, galvanostatic pulse technique, electrochemical impedance spectroscopy, half-cell potential and concrete electrical resistivity mapping. The results showed that concrete quality and moisture content have a direct effect on corrosion activity, and these properties are represented well with concrete electrical resistivity. The galvanostatic pulse technique was shown to correlate well with electrochemical impedance spectroscopy, which was used as a benchmark for corrosion rate measurements in this study; however, the galvanostatic pulse technique was not capable of detecting corrosion activity in saturated concrete accurately. The results of this research do not support the criteria provided by the ASTM C876-09 standard for using half-cell potentials to estimate the probability of reinforcing steel corrosion in reinforced concrete structures
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Concrete resistivity : interim observations on potential aggregate impacts
No full textThe electrical properties of concrete are used as a surrogate to assess fluid transport in concrete because resistivity can be measured rapidly and economically. While resistivity has been measured for nearly a century, the recent rise in handheld, battery-operated testing tools coupled with the desire to quantify the transport performance of concrete has caused a sudden spike in interest in resistivity measurement as a quality control or quality acceptance tool. Standards have been developed with an emphasis on the role of sample conditioning and many state highway agencies (SHAs) have explored the use of resistivity. Some SHAs have reported that the use of certain aggregates tended to reduce the resistivity values when compared with other aggregates with all other factors being equal. This report examines one fundamental assumption of the resistivity testing (i.e., that the aggregate is resistive or non-conductive). It explores the implications if the aggregate is conductive using both an analytical and finite element approach to determining the impact of aggregate with a lower resistivity and discusses a procedure to account for aggregate resistivity
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Seismic performance of aging prestressed transmission pole with simulated soil foundation
Get PDFThe Cascadia Subduction Zone has recently been identified as a source for an impending great earthquake. The potential of a large earthquake has created widespread interest into the resiliency of lifelines within the potentially affected areas. One critical lifeline is the electrical distribution and transmission systems which relies on legacy infrastructure components that were designed and constructed without regard to the seismic hazard. Of particular interest is the resiliency of prestressed concrete poles used for transmission towers within the region. Through material and structural testing of existing full scale specimens, moment capacities have been analyzed and compared to simulated earthquake moment demands. The structural testing allowed for an innovative solution to produce simulated site response through fabricating soil representative springs using steel plates. The soil simulated springs allowed for full scale testing with non-fixed base motions such as rotation and translation. After the conclusion of testing three different specimens, it was found that the poles remaining in the field are considerably vulnerable to site conditions but would structurally survive a subduction zone like earthquake
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Dual Purpose Utilization of Titanium Alloy Bars for Impressed Current Cathodic Protection and Near Surface Mounted Retrofit in Reinforced Concrete Beams
Get PDFMany older reinforced concrete bridges and buildings in the United States are considered deficient due to past design codes that are not conservative, increased loading, and deterioration of structural components. Deterioration is most commonly caused by corrosion, which reduces the steel cross sectional area and damages the concrete cross section. To rehabilitate deficient structures, supplemental structural materials are added to the members to permit the application of higher loads. One acceptable structural strengthening approach is the use of Grade 5 (Ti-6Al-4V) titanium alloy bars (TiABs) in near surface mounted retrofit (NSMR) applications in reinforced concrete bridge elements. To prevent and combat corrosion, impressed current cathodic protection (ICCP) systems are widely deployed with the use of Grade 1 or Grade 2 titanium anodes. These two remediation efforts are generally undertaken as separate actions. This research proposes a novel combined approach whereby the supplemental strengthening material is used integrally within the cathodic protection system.
To achieve this goal, a number of technical challenges were overcome, including selection and deployment of appropriate materials, development of construction techniques, and creation of an electrically conductive structural grout (ECSG). The approach was demonstrated in the laboratory to show how the system works, both structurally and cathodically, and how the different components interact. Two cases were considered for typical structural deficiencies: lack of flexural reinforcing steel and insufficient shear reinforcing steel (widely spaced stirrups). TiABs were selected as the near surface mounted retrofit (NSMR) material to provide the required additional strength, as well as to function as the anode in an impressed current cathodic protection (ICCP) system. To enable the multi-functional system, an ECSG was developed using carbon fibers. The grout was demonstrated to adequately bond the TiABs to the concrete substrate and to achieve the required level of resistivity to allow electrons to flow within the ICCP system. Two full-sized reinforced concrete beam specimens were constructed with reinforcing deficiencies in the Structural Engineering Laboratory at Oregon State University. The beams were constructed with high-levels of sodium chloride in the concrete to simulate the long in-service life conditions that produce chloride contents at which corrosion freely occurs. The reinforcing steel within the beams was specially constructed to electrically isolate each of the bars enabling measurement of the electrical influence and interactions of the different bars. NSM-TiAB bars were installed on the specimens and electrochemical tests were conducted to investigate the use of the TiABs as an anode in an ICCP application.
ICCP was achieved with cathodic potentials maintained in the linear region of the cathodic polarization curve of the steel rebar. The 100 mV criterion was satisfied, thus establishing that cathodic protection locally protected the existing steel, and demonstrating the capabilities of this material to prevent further structural deterioration and extend the service lifetime. The beam specimens were then tested to failure to assess structural performance. Both specimens were observed to demonstrate larger and predictable strength increases. The results of this study demonstrate the feasibility of combining structural strengthening within an ICCP system using TiABs, which has not previously been considered. This new potential offers a more economical rehabilitation strategy that can restore or increase strength and prevent deterioration from corrosion which can preserve existing infrastructure
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Influence of Concrete and Construction Parameters on Chloride Test Measurements and Critical Chloride Threshold Limits
Get PDFThe issue of chloride-induced corrosion of reinforcing steel in concrete and its economic impacts are well-known. Chlorides that cause reinforcement corrosion can be from constituent materials used to prepare concrete or can enter the hardened concrete when the structure is exposed to chloride environments. To minimize the risk of reinforcement corrosion, specifications and documents published by the American Concrete Institute (ACI) limit the amount of admixed chlorides that can be present in concrete. These limits are referred to as allowable admixed chloride limits (Climit) and are commonly used as acceptance criteria for concrete in new construction. The initial admixed chloride concentration (Ci), that is the chlorides contained in all constituent materials of concrete, should be less than the Climit value. The Climit value should be significantly lower than the critical chloride threshold, Clcrit, the concentration of chlorides responsible for initiating corrosion on steel surface. To determine Ci, most ACI documents require using either the American Society for Testing and Materials (ASTM) standard C1152, “Standard Test Method for Acid-soluble Chloride in Mortar and Concrete,” or C1218, “Standard Test Method for Water-soluble Chloride in Mortar and Concrete.” The test outcomes of the ASTM C1152 and C1218 test methods represent the acid-soluble chloride (ASC) and water-soluble chloride (WSC) concentrations, respectively, in concrete. While the applicability of the ACI Climit values to accept or reject concrete seems simple, there are challenges.
First, neither the ACI documents nor the ASTM standards provide guidance on considering some minimum number of test samples for Ci testing regime. Concrete is a heterogeneous material, and if a minimum number of test samples are not considered then the variability in the test outcome could potentially affect the decision process for accepting or rejecting concrete. In this regard, an understanding of the influence of concrete mixture parameters on the statistics of the chloride test outcome is needed. Second, ACI documents that allow both ASTM C1152 and C1218 test standards report Climit values based on a near constant ratio. ACI 222R, Guide to Protection of Metals in Concrete Against Corrosion, considers the ratio between the WSC and ASC Climit to fall between 0.75 and 0.8. Limited information is available on whether the existing correlation for WSC and ASC Climit is applicable for cementitious systems with admixed chlorides. A better understanding of various factors that influence the chloride test outcome of different cementitious systems containing admixed chlorides is therefore needed. Third, there is no consensus on Climit values among different ACI documents. The disparity in Climit can be partially attributed to lack of understanding on a reliable Clcrit value. A wide variation of Clcrit values are reported in literature. While the Clcrit values reported in literature may provide some useful insights specific to the reported research study, they cannot be compared among different studies due to differences in many parameters, including but not limited to, the definition of corrosion initiation, the test setup, the corrosion onset detection technique, chloride measurement technique, and the nomenclature for Clcrit. Given that Clcrit serves as an important parameter not only for specifying the allowable chloride limits but also for service-life prediction models, a standardized test method that can be commonly used by everyone is needed for quantifying Clcrit is needed. Several factors must be accounted for to assess the reliability, repeatability, ease of testing, and timeliness of the test method. Significant research is needed. In addition to the challenges noted on Ci and Clcrit testing, challenges exist in reliably determining the chloride diffusion coefficient of concrete (Dc), one of the important input parameters to the service-life prediction models. While factors such as the binder type and water to cement ratio have been reported to significantly influence the chloride transport, limited effort has been put to assess the influence of concrete and construction variables, such as nominal maximum aggregate size (NMAS), aggregate mass proportions, binder content, surface finish, and degree of consolidation on chloride transport. Research is needed.
This dissertation reports findings from various experimental programs conducted to address the aforementioned challenges associated with testing of Ci, Clcrit, and Dc. A summary of these findings follow. An increase in NMAS can induce significant variation in Ci and can significantly decrease the mean value of Dc. The fine to coarse aggregate ratio and the binder content of concrete mixture are found to have little or no significant effect on Ci and Dc. A procedure has been reported to determine the minimum required number of test specimens for Ci and Dc test regimes for various concrete mixtures. Considering the minimum number of specimens for testing is needed to minimize the difference between the mean value of the Ci or Dc estimated from testing and the actual value. The Ci has also been found to be significantly influenced, in decreasing order, by the test method (i.e., ASTM C1152 or C1218), the total chloride concentration, binder type, the supplementary cementitious material (SCM) replacement level, and water to cement ratio. The ratio of WSC to ASC (w/a) has been found to vary from 0.08 to 0.77 for cementitious systems with admixed chlorides, which is significantly different from the 0.75 to 0.8 range reported in the ACI 222 document. Using the data generated from testing, empirical models have been developed as a function of various study parameters to predict the WSC and w/a. The WSC models are anticipated to assist the owners, engineers, and contractors in designing the concrete mixtures that meet Climit. The w/a models can be used to better correlate the WSC and ASC Climit values, if both Climit values were to be allowed in the future revisions of ACI documents. This dissertation also reports the conceptualization and development of a new test method, OCcrit, for quantifying Clcrit. A comprehensive investigation has been performed to identify the effect of corrosion activation criteria, mortar type, type of chloride exposure, concentration of chlorides in exposure solution, and pH of the exposure solution on the outcomes of OCcrit. Results indicate that Clcrit is on the order of 0.234% by weight of cement for systems composed of Type I/II cement meeting ASTM C150 requirements and reinforcing steel meeting ASTM A615 requirements. This value is only slightly higher than the ASC Climit published by 2019 version of ACI 222R and revisions may be need for Climit values. An optimal set of values have been proposed for various OCcrit test parameters, currently being implemented in a round-robin test across the U.S. for investigating the repeatability and reproducibility of OCcrit. Lastly, the effects of concrete surface finish and degree of consolidation on service life parameters, the surface chloride concentration (Cs) and chloride diffusion coefficient (Dc), have been investigated. The surface finish has been found to have no significant influence on Cs and Dc, when these parameters are estimated following ASTM C1556, “Standard Test Method for Determining the Apparent Chloride Diffusion Coefficient of Cementitious Mixtures by Bulk Diffusion.” The degree of consolidation has been found to significant influence the Dc, mainly due to its corresponding effect on concrete porosity
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