Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
6 results
Search Results
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 ANALYTICAL STUDY OF THE BEHAVIOR OF COMPOSITE DOVETAIL METAL DECKING FLOOR SYSTEMS FOR THE DEVELOPMENT OF PRACTICAL DESIGN GUIDELINES(2022) Pase, Tara; Phillips, Brian M; Fu, Chung C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Prior testing and industry practice have shown composite metal floor systems – floors systems constructed from concrete composite with metal decking – behave stiffer than the current state-of-the-practice simplified calculations and estimations predict. Specifically, the dovetail decking does not have the quantity of available research and universal design guidance compared to the more common trapezoidal composite decking; this lack of a more accurate design standard has made the calculation of the non-linear stiffness behavior of the dovetail composite deck floor systems under small to intermediate strains inaccurate, and therefore limits its use for long-span configurations where deflection limits (i.e., serviceability limits) control the design.The objective of this research is to create an analytical model of the flexural behavior of re-entrant dovetail composite decking floor systems for service (i.e., deflection) and strength (i.e., ultimate capacity) limit states and to understand the unique mechanical behavior of the slab system. By creating a more accurate analytical model of the flexural behavior of the dovetail composite deck system, a robust design guide table for engineering use is developed for a multitude of variables typically seen in construction, including but not limited to: various loads, deck gauges (thicknesses), concrete strength, concrete depths, etc. The flexural behavior of the composite metal deck is modeled based on its material properties and the following base assumptions: the composite slab is in pure bending; plane sections remain plane and are orthogonal to the neutral axis; the laws of static equilibrium apply; and loads are assumed to be static. Application of this composite theory to determine the moment-curvature relationship using a numerical strain-compatibility computer-based solver is compared against physical tests to validate and calibrate the theoretical assumptions that make up the basis for the calculations. The resulting flexural behavior derived from this numerical strain-compatibility method has a multitude of uses including but not limited to: the derivation of a robust design table for a number of decking gauges, common slab thickness values, concrete strength ranges, and so forth; and variable stiffness properties for use in simplified finite element plate models. The real-world purpose for this new numerical strain-compatibility model is to provide robust design guidance and engineering resources for practicing structural engineers, without a time-consuming and expensive finite element model. With the numerical strain-compatibility analysis, an engineer can accurately analyze and specify composite concrete slabs in building projects without being limited by shorter spans or thicker slabs due to inaccuracies in deflection calculations.Item Investigation of Delayed Ettringite Formation Damage Process Using Simultaneous Neutron and X-ray Tomography(2019) Feuze Lekem, serge alain; Amde, Amde M; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Delayed ettringite formation (DEF) is a significant deterioration process in concrete which involves the growth of ettringite [Ca6Al2(SO4)3(OH)12 ·26H2O] crystals leading to cracking and reduction of compressive strength. Conditions leading to DEF are well known and include among others cement chemistry, presence of humidity, heat curing of concrete structures, and the presence of cracks. The mechanisms and kinetics by which deterioration occur is still not well understood despite numerous investigations. Understanding the mechanism and kinetics of concrete deterioration due to DEF is important in order to prevent such costly deterioration and to improve concrete durability. In this research, concrete specimens were prepared with type III Portland cement and under different conditions that were designed to either promote or inhibit DEF. These consisted of a control set, a set subjected to a heat cycle and a third set made with elevated potassium content of 1.72% and also thermally cycled. They were tested periodically up to 380 days by conventional methods such as expansion and weight change measurements and compressive strength testing. Scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDAX) confirmed the presence and the morphology of ettringite in voids at different ages. Simultaneous neutron and X-ray tomography, a new nondestructive microscopic method was used to scan the specimens at regular intervals in order to assess the feasibility of the method in monitoring the progress and characterizing DEF induced damages. The linear regression analysis of the correlation of expansion with weight change data revealed that expansion and deterioration process occurred in three distinct successive stages. In the first stage, the ettringite fills the pores with little or no expansion; in the second, the expansion appears to be creep due to expansive stresses in the filled pores and in the third stage, crack propagation leads to significant expansion and loss of compressive strength. The results of the linear regression also revealed that the mechanism of DEF is the replacement of pre-existing calcium hydroxide crystals. Through non-linear curve fitting, the kinetic of deterioration was modeled using the Kolmogorov-Avrami-Johnson-Miehl model. The simultaneous neutron and X-ray tomography allowed visualization of the interior of the specimen due to enhance phase segmentation. MATLAB routines were developed to allow for correction for beam hardening and to enhance phase segmentation. The study showed that with improved resolution, proper sample sizing, the method can be effectively used to characterize concrete damage due to expansive phases.Item Flexural Fatigue Behavior of Fiber-reinforced Concrete Based on Dissipated Energy Modeling(2014) Aramoon, Ehsan; Goulias, Dimitrios; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)After a century of study of fatigue phenomena in concrete, most of the proposed models for predicting the fatigue life of concrete are not sufficiently precise. The traditional models for predicting fatigue life of concrete are only based on the strength-related parameters such as stress level. The high variation of concrete's strength has led to highly scattered fatigue test result and, consequently, reduced the predictive quality of fatigue models. Recently, several studies have focused on incorporation of new damping-related parameters in fatigue life models to improve the predictability of these models. Damping properties have a crucial effect on dynamic motion and energy dissipation capacity in fatigue life, and therefore they seem to be an important factor in characterizing fatigue as a dynamic motion. The general objective of this research was to acquire a comprehensive understanding of the fatigue behavior of concrete in terms of energy dissipation and, consequently, develop a more statistically reliable approach to characterize the fatigue properties of concrete such as fatigue life. To achieve this purpose, damping properties of several concrete mixtures, with or without fiber reinforcement, were studied. A fatigue model based on dissipated energy concept was developed. The new model is then compared to traditional model. The results show that the new fatigue model has better predictive quality than the traditional approach.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 Characterization of Pore Structure and Crack Propagation in Concrete Using X-Ray Computed Tomography(2004-12-13) Hunter, Opio Konata; Amde, Amde M; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis utilized the method of computed tomography to quantify the pore structure and the development of cracks in concrete specimens due to delayed ettringite formation. The pore structure is responsible for the passage of harmful substances through the concrete matrix, while delayed ettringite formation causes expansion and internal cracking in concrete structures; particularly in prestressed and precast concrete elements. Computed tomography is a relatively new technique that can be utilized to determine the pore structure and crack propagation in concrete specimens within the mm to micrometer range. The experiment was successful in quantifying the pore structure in the specimens. The pore sizes and total porosity of each specimen were determined along with the pore size distribution on diameter and volume. A comparison was then made with the mercury intrusion porosimetry technique. However, the second objective of analyzing internal cracking due to delayed ettringite formation was not met.