Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item NON-DESTRUCTIVE TESTING FOR QUALITY ASSURANCE OF CONCRETE & PERFORMANCE PREDICTION OF BRIDGE DECKS WITH MACHINE LEARNING(2022) Ghahri Saremi, Setare; Goulias, Dimitrios DG; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Non-destructive testing (NDT) methods are particularly valuable in the quality assurance (QA) process since they do not interfere with production of concrete and reduce testing time and cost. NDTs can provide early warnings in meeting strength requirements at early ages of concrete as well as long term strength. NDTs are also valuable in providing evaluation of health of in-service infrastructures such as bridge and pavement. The results of this study can be used for potential adoption of an NDT-based QA plan. Their adoption in QA will provide the opportunity to test a larger portion of concrete during assessment without a significant increase in QA cost and testing time. To achieve that purpose, the selected NDTs should be fast, accurate, reliable and simple to run. The NDT methods explored in this study included infrared thermography, ultrasonic pulse velocity (UPV), fundamental resonance frequency, rebound hammer, ground penetrating radar (GPR), and ultrasonic pulse echo (UPE). Different sets of NDTs were selected in each experimental study undertaken in this dissertation appropriate to the research objectives and goals in each case. For strength gain monitoring, (i.e., maturity modeling during early ages of hydration), the suggested NDTs need to provide an assessment of the mechanical properties of concrete. To assess the concrete quality during production and/or construction the selected NDTs should rapidly identify potential issues concerning uniformity and/or the presence of production and placement defects. For evaluating the condition of concrete bridge decks with asphalt overlays, GPR response was used to detect layer thickness and concrete quality and to evaluate reinforcement condition. For addressing the transition from lab to field results, machine learning modeling was used to predict the structure condition. Therefore, two artificial neural network (ANN) models were proposed and assessed in this study to predict the condition of bridge decks in Maryland and Massachusetts. Thus, the objectives of this research were to identify and assess alternative NDT methods that can be used in: i) monitoring and/or estimating strength gain (i.e., maturity modeling) in concrete; ii) evaluating concrete uniformity and production quality; iii) detecting and measuring the extent of delamination in concrete slab representing small scale field conditions; iv) evaluating GPR in assessing the condition of pavement layers, concrete quality and reinforcement in bridge decks; and v) employing machine learning modeling to predict the condition of bridge decks.Item PROJECT MANAGEMENT MATURITY IN THE CONSTRUCTION INDUSTRY OF DEVELOPING COUNTRIES (THE CASE OF ETHIOPIAN CONTRACTORS)(2011) Yimam, Abadir Hassen; Skibniewski, Miroslaw J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research has studied the maturity of PM in the construction industry of developing countries; in the course, the research has also identified two major gaps in the existing maturity models and, proposed a PM maturity model to address the gaps and adapt it to the developing countries context. Using the model, maturity assessment of contractors in Ethiopia is undertaken and, low level of PM maturity (Informal practice of the basic processes) is found. Further, the research found ISO certified contractors‟ PM maturity to be higher than those which are not. Similarly, the PM maturity of contractors which took part in Capacity Building Program is found to be higher than those which did not take part .Likewise, Road contractors PM maturity is found to be higher than Building contractors. Moreover, the research found higher maturity level for material, procurement, cost, financial, time, and human resource management. Risk and safety management are found to be the least matured PM areas.Item CONCRETE SHRINKAGE PREDICTION USING MATURITY AND ACTIVATION ENERGY(2009) Clarke, Christopher Steven; Goulias, Dimitrios G.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shrinkage is a complex material response that often affects concrete in an adverse manner. The characteristics of the natural environment in which concrete is placed and the rate of strength development have been used to model the rate of shrinkage development. Furthermore, concrete maturity has been used to predict the rate of strength development of concrete cured at different temperatures. This study sought to find a correlation between activation energy based concrete maturity and concrete shrinkage. A single concrete mixture was tested to determine the apparent activation energy of the mixture and the shrinkage under varying environmental conditions. A shrinkage model incorporating relative humidity and temperature was developed to predict the shrinkage of the concrete mixture. A relationship between concrete shrinkage and activation energy based maturity was investigated.Item EARLY AGE STRENGTH PREDICTION FOR HIGH VOLUME FLY ASH CONCRETE USING MATURITY MODELING(2008-11-21) Upadhyaya, Sushant; Goulias, Dimitrios; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of fly ash in concrete has received significant attention over recent years due to environmental concerns regarding its disposal and on the other hand its potential use as a cementitious material, with its ability to provide significant benefits to concrete. While a fly ash content less than 25% of total cementitious content is routinely used in concrete, high-volume fly ash (HVFA) contents are not common used due to perceived lower early-age strengths. The objective of this research was to demonstrate that the beneficial effects of high in-place hydration might be able to compensate the slower rate strength gain of HVFA concrete that is typically observed when tested in standard laboratory conditions, in this effort, the maturity-based technique was used. In addition, different methods (match-cured cylinders and pullout testing) were used to estimate the early-age in-place strength of HVFA concrete to confirm the maturity predicted strengths. The results have shown that the standard and field-cured cylinder strengths underestimate the in-place concrete strength. Higher in-place temperatures due to the mass characteristics of structural elements resulted in increased early age in-place strengths, adequate for construction scheduling, as measured by match-cured cylinders,pullout testing, and the maturity approach. Furthermore, an extensive investigation on the use of the traditional and alternative maturity principles was examined in order to first identify it's applicability to these types of mixtures and, then identify potential adjustments to the maturity modeling as applicable to HVFA concrete mixtures. Two primary directions were followed, the constant and variable ultimate strength (Su) for multiple curing temperatures. Another objective of the study was to examine alternative methods of predicting activation energies (AE) for these cementitious systems, as compared to the traditional method identified by the maturity process. Among them, the setting time approach of mortar was considered. Finally, a maturity-based approach was developed for estimating in-place strength of HVFA mixtures to assist the construction industry in implementing the results of this study.