Master of Science (M.S.)

 

2017

Name: Nicolas D'Amico

Title: Photogrammetric Techniques for Evaluation and Analysis of Concrete Structures and Specimens

Department: Civil and Environmental Engineering, UML

Abstract: Photogrammetric methods such as structure from motion (SFM) have the capabilities to produce models with accurate geometric, surface and mechanical informationby generating point cloud models (PCM). PCM can be used for visual inspection and data registration in condition assessment. Laboratory concrete specimens and in- situ reinforced concrete structures (e.g., buildings and bridges) were constructed and evaluated for demonstrating the practical usage and geometric accuracy of PSM. Results show that photogrammetric methods can be used for remote sensing and nondestructive testing (NDT) in maintaining againg civil infrastructure. From this research, it is found that photgrammetric methods are capable pf delivering PCM with geometric accuracy less than 5% error in surface crack profiling, damage assessment, area and volume estimation, and data registration. Estimated mechanical properties from PCM can also be correlated and used in finite element analysis for condition assessment.

Here is the full text of Nick's Master's thesis.

Here is the presentation for Nick's Master's thesis defense.

 

2016

Name: Viet Le

Title: Detecting and Quantification of Damage from ASR Gels using Multiphysical Nondestructive Evaluation

Department: Civil and Environmental Engineering, UML

Abstract: With its discovery in 1940, alkali-silica reaction (ASR) has been recognized as a debilitating plague to concrete structures. Due to the production of ASR gels that swell by imbibing water from their surroundings, an expansive pressure is exerted within a cementitious composite, resulting in damages such as map cracking, spalling, deformations, and reductions in mechanical strength. Unfortunately, structural health monitoring (SHM) of civil infrastructure for major issues like ASR require an immense amount of manpower far greater than the current supply of civil engineering professionals in today's society. A potential solution for this issue lies in the developments for nondestructive evaluation (NDE) of civil infrastructures which has proven to be an effective approach for collecting information on the condition of a material, a component, or a system. Changes in the material properties of a structure afflicted with ASR can be quickly and harmlessly determined by using noninvasive measurement technologies and in-depth analytic techniques. In this study, a continuous wave imaging radar system along with synthetic aperture radar (SAR) imaging algorithms, an ultrasonic testing instrument, and an open-ended coaxial probe for dielectric measurement were utilized in order to non-destructively detect and quantify damages from ASR gels on 25 x 25 x 285 mm mortar bars stored in a 1N NaOH solution at 80-deg. C for 7, 14, 21, and 28 days. Nondestructive detection of the damage from ASR gels was carried out by observing the differences between mortar bars made from reactive aggregates susceptible to ASR and a control group made from a nonreactive aggregate. Amplitudes from the SAR images of mortar bars made from reactive aggregates were found to be greater than those from SAR images of mortar bars made from a nonreactive aggregate. In addition, lower ultrasonic pulse velocities for the mortar bars made from reactive aggregates indicated periods of peak damage due to the evolution of cracks caused by the swelling of the ASR gels. Quantification of damage from ASR gels was achieved by using a linear function to model the ratio between total SAR amplitude and length expansion percentage with respect to time stored in the NaOH solution. In addition, the evolution of ASR gels with time and their effects on the measurements using the NDE methods were observed from a multiphysical perspective in their increasing and decreasing trends for ultrasonic pulse velocity, total SAR amplitude, and dielectric constant. Several mechanisms including the evolution of crack damage, moisture influence from ASR gels, and cement hydration were considered in order to characterize the damages from ASR gels on the mortar bars for each time period of storage in the 1N NaOH solution at 80-deg. C.

Here is the full text of Viet's Master's thesis.

Here is the presentation for Viet's Master's thesis defense.

 

2014

Name: Qixiang Tang

Title: Finite Element Analysis for the Damage Detection of Light Pole Structures

Department: Civil and Environmental Engineering, UML

Abstract: Light pole structures are commonly installed in everywhere of human society. Aging of light poles is unstoppable and inevitable, and eventually cause failures of light poles. Potential failures of light poles are detrimental to public safety since they bring risks to nearby residents and damage adjacent structures. Effective damage detection methods for light poles are hence required. Any change in structural properties (e.g., mass, stiffness) can lead to differences in the dynamic response of structures, such as modal frequencies and mode shapes. Inversely, changes in dynamical responses can be used as indicators for damage detection. In this study, a straight steel tubing light pole was used as an example. The relationships among damages and dynamic responses (modal frequencies and mode shapes) were determined by observing the differences in dynamic responses between intact and artificially damaged finite element models (developed by ABAQUS) of the example light pole. Inversely, damage detection methods were developed by using determined relationships. Proposed methodology was to use sensitive modes which were determined for three common damage locations, to localize damage. Then, use linear regression equations to qualify damage level and size. A damage detection methodology using mode shapes are also proposed in this study.

Here is the full text of Qixiang's Master's thesis.

Here is the presentation for Qixiang's Master's thesis defense.

 

Name: Ross Gladstone

Title: Ranging and Sizing of Concrete Targets using Radar Images (incomplete)

Department: Civil and Environmental Engineering, UML

Abstract: This research investigated the use of Synthetic Aperture Radar (SAR) imaging for the surface and subsurface characterization of reinforced concrete (RC) slab specimens. The motivation was to develop SAR imaging to be used for the conditional assessment of corroded steel reinforcing bars in RC bridges or other structures with RC slabs. The ultimate goals of this research were to develop a post-image processing technique to: (1) extract surface and subsurface information from RC slab specimens (e.g., steel reinforcing bar locations), (2) extract information about corroded steel reinforcing bars embedded in RC slab specimens (e.g., corrosion assessment), and (3) enhance SAR images of RC slab specimens (e.g., improve signal-to-noise ratio). The SAR system utilized a monostatic radar antenna at a center frequency of 10 GHz and collected SAR images of non-corroded RC slab specimens at 40, 80, 120, and 160 cm. The range dependence of non-corroded RC slab specimens was determined using results obtained at these ranges. 30 SAR images at 40 cm were then used to locate non-corroded steel rebars using a post-imaging processing technique that extracted the peak responses. One of these SAR images was then enhanced using the Discrete Wavelet Transform (DWT). It was found that the DWT could increase detectability and decrease noise. The Daubechies 5 wavelet was used to decompose the SAR image four times and different detail coefficients were removed. Lastly, 30 images of an artificially corroded RC slab specimen were obtained. The maximum values from the peak response were compared to half-cell potential measurements for that specimen. It was found that there was a coorelation between SAR images and the probability of steel rebar corrosion.

 

2013

Name: Justin Wilson

Title: Artificially Accelerated Corrosion Test and Half-cell Potential Monitoring of Reinforced Concrete Slabs

Department: Civil and Environmental Engineering, UML

Abstract: Monitoring of corrosion is one of the greatest challenges facing civil engineers today. All structures require monitoring to ensure they can operate safely under service loads. Reinforced concrete structures need a special kind of monitoring because corrosion can severly damage the structure and cause failure. Many types of testing exist such as destructive testing and ultrasonic testing. The half-cell potential method offers a standardized way to test for the level of corrosion without destroying the specimen. An adapted version of the modified Southern Exposure Test was performed and reasonable results were obtained with the hafl-cell potential method. The time history of the measurements was plotted, effect of spatail location and concrete cover proved, and the current density was calculated and plotted for each week of the experiment.

Here is the full text of Justin's Master's thesis.

Here is the presentation for Justin's Master's thesis defense.

 

Name: Hao Liu

Title: Dielectric Modeling of Cement Paste and Mortarg

Department: Civil and Environmental Engineering, UML

Abstract: Dielectric properties of cementitious materials (cement paste, cement mortar, and concrete) are key parameters in radar simulation and radar sensor are used in condition assessment of structures in Civil Engineering as one nondestructive testing (NDT) method. However, due to heterogeneity of cementitious materials, it is difficult to understand, measure and model dielectric properties of these materials. In this thesis, several dielectric models were applied on oven-dried and room-condtioned hydrated cement paste panels. Modeling results are used for fitting experimental results obtained using open-ended coaxial probe at room temperature 21-25 deg.C with 25-30% relative humidity. In use of homogeneous models, dielectric constant of cement paste panels at the frequency of zero and infinity, and relaxation time were calculated and compared. In use of heterogeneous models, how shapes of inclusion materials and selection of host and inclusion material influence dielectric properties of mixing material was also investigated.

Here is the full text of Hao's Master's thesis.

Here is the presentation for Hao's Master's thesis defense.

 

Name: Shafique Ahmed

Title: Mechanical Analysis of Reinforced Concrete Beams for Structural Health Monitoring

Department: Civil and Environmental Engineering, UML

Abstract: Damage assessment and condition evaluation of existing civil infrastructure systems are essential to the decision making in routine structural maintenance and disaster remediation. To determine internal conditions using surface strain measurement is a critical, real-life engineering problem, in view of the popularity of using surface strain measurement for structural health monitoring. The objective of this study is to develop a damage detection methodology to relate surface measurement (e.g., strain) with the internal condition (e.g., healthy or damaged) of structures using a singly-reinforced concrete beam as an example. Numerical approach is applied in conducting a parametric study in this research. A finite element model of a benchmark singly-reinforced concrete beam specimen was created using a commercial finite element analysis package, ABAQUS. The model was validated in laboratory four-point bending test, using fiber optic strain sensor measurement. Artificial damages were modelled by rebars volume reduction, and four types of artificial damages are considered. From the simulation results, relationships between the change in surface strain and intensity of internal damage are developed. It is found that damage introduced in the rebar embedded in a reinforced concrete beam can be accurately located using the surface stress difference. Nonsymmetric damages yield more contour area of surface stress change than the symmetric damages.

Here is the full text of Shafique's Master's thesis.

Here is the presentation for Shafique's Master's thesis defense.

 

Name: Carlos Jaquez

Title: Analysis of Accelerated Corrosion Experiments on Reinforced Concrete Slabs using Half-cell Potential Measurements

Department: Civil and Environmental Engineering, UML

Abstract: Corrosion of steel reinforcement is known to be the primary cause of deterioration for reinforced concrete structures. It is one of the foremost factors that a?ect the durability of concrete structures. The corrosion of steel reinforcement is most commonly caused by the action of chloride ions on the steel reinforcement. These chloride ions cause the breakdown of the passive film formed around the reinforcement due to the highly alkaline environment of the concrete. Damage to the concrete eventually manifests itself in the form of cracking and eventually spalling of the concrete. End of service life for the corrosion affected structures is characterized by the loss of concrete cover of the reinforcement. At this stage, the reinforcement is no longer protected against further degradation from corrosion. In this research, corrosion in reinforced concrete structures is induced by means of accelerated corrosion experiment. Reinforced concrete slabs were cast with various different cover thickness for the steel reinforcement (1.5-in, 2.0-in and 2.5-in) and the effects of chloride induced corrosion studied and analyzed by means of half-cell potential measurements. A separate accelerated corrosion experiment was performed on an individual steel rebar to measure the anticipated mass loss from corrosion. These results were compared against the analysis of the half-cell pottential data and correlated. Furthermore, a cover meter survey was performed on the reinforced concrete slabs to determine the reliability of the cover meter sensor when corrosion is known to be present in the reinforcement. The sampling rate for the half-cell potential measurements was 8 inches while the sampling rate for the cover meter survey was 5 inches.

Here is the full text of Carlos' Master's thesis.

 

2011

Name: Alice Chow

Title: Measurement and Modeling of Hydration Heat in Concrete Specimens

Department: Civil and Environmental Engineering, UML

Abstract: Concrete is known as a heterogeneous material made of complex chemical compositions. The development of concrete temperature during early age is crucial on its long term durability. Cracking can occur, if the concrete temperature rise too high or if there is large temperature difference between interior and exterior of concrete during early hydration stages. This premature failure can lead to undesired results which may associate with quality concern, time consuming and extra cost. In this research, the effect of ambient temperature and adiabatic temperature are considered during the temperature measurement within concrete cylinders at early age; the first 45 hours and the first 70 hours. Concrete specimens were manufactured under various water-to-cement ratios (w/c) (0.40, 0.45, 0.50, 0.55 and 0.60). A Fabry-Perot (FP) fiber optic temperature sensor and type K thermocouple sensor were embedded into concrete cylinders to monitor the temperature development during early-age hydration in the first experiment. Two FP sensors were inserted in the second experiment. Each concrete cylinder was insulated in styrofoam chamber. A sampling rate of 20 second was used in all experiments. From the experimental result, it is found that FP fiber optic temperature sensors are reliable. Temperature profiles are used for calculating the apparent activation energy (Ea) and the heat of hydration (H(t)) of concrete, which can help us to better understand cement hydration.

Here is the full text of Alice's Master's thesis.

Here is the presentation for Alice's Master's thesis defense.

 

Name: Jeremiah Otchere-Nyarko

Title: Model Test and Numerical Simulation for the Structural Health Monitoring of a Truss Bridge

Department: Civil and Environmental Engineering, UML

Abstract: Structural Health Monitoring (SHM) is one of the vital tools used by civil engineers to improve and monitor the health of civil infrastructure. It involves the acquisition, validation and analysis of technical data to facilitate lifecycle decision in the maintenance of structures. Data collected by SHM are converted by damage detection algorithms into useful information that helps in accessing structural integrity and performance. This study investigates how data obtained from physical experiment and numerical simulation of a laboratory truss bridge model can be used for SHM. In the numerical simulation work, three 3-D truss bridge models are created using the finite element method. The numerical truss bridge models are based on the geometry and material properties of a scaled truss bridge model used in the physical experiment. Artificial damage is introduced to the structure by reducing the cross-sectional area of a truss member at a 20% interval. The natural frequencies and displacement of intact and damaged truss bridge models are recorded and analyzed. The physical experimental setup consists of a bridge truss set, six force sensors (load cells), a load cell amplifier, a data acquisition system, and a personal computer. It produces real-time static and dynamic responses of the truss bridge model which has a span length of 42”, a width of 5”, and a height of 12”. Three loading cases are considered, including (1) unloaded intact, (2) loaded intact, and (3) loaded damaged truss bridges. A damaged truss bridge model is created artificially by the removal of one diagonal truss member. Fast fourier transform is used for frequency analysis.

Here is the full text of Jeremiah's Master's thesis.

Here is the presentation of Jeremiah's Master's thesis defense.

 

Name: Ibrahim C. Solak

Title: Dielectric Measurement and Modeling of Cement Paste Specimens

Department: Civil and Environmental Engineering, UML

Abstract: Dielectric properties of construction materials have become valuable information in the condition assessment of civil infrastructure using microwave and radar nondestructive evaluation (NDE) techniques and sensors. Multi-phase dielectrics are usually encountered when structures are made of cementitious composites (e.g., Portland cement concrete). In this thesis, the dielectric dispersion of cement paste and cement mortar samples in the frequency range of 0.5 GHz to 4.5 GHz was studied. Cement paste and cement mortar samples of various water-to-cement (w/c) ratios (0.35, 0.40, 0.42, 0.45, 0.50, 0.55) were manufactured and their dielectric constants were measured by a coaxial probe at room temperature 23 oC ± 2 oC with 25 % - 30 % relative humidity. Contact dielectric measurements were collected at different locations on each sample to study the dielectric heterogeneity of the cement paste samples. It was found that the measured relative complex permittivity varies even within one cement paste panel. The measured relative dielectric constant decreases with the increasing w/c ratio and measurement frequency. Change in dielectric constant due to the removal of evaporable water by oven drying cement paste samples was observed. The effect of the fraction of sand in cement mortar to its dielectric constant was investigated and modeled.

Here is the full text of Ibrahim's Master's thesis.

Here is the presentation for Ibrihim's Master's thesis defense.

 

2010

Name: Burak Boyaci

Title: Geometric Analysis of Finite Difference Time Domain Simulation for Damage Assessment in Ground Penetrating Radar Applications

Department: Civil and Environmental Engineering, UML

Abstract: Detection and characterization of damages in civil structures is vital for public safety. Microwave/radar NDT (Nondestructive Testing) techniques are suitable for in-depth assessment of concrete structures since electromagnetic waves can penetrate into dielectric materials like concrete. Ground penetrating radar (GPR) is one of the commonly used microwave/radar techniques for concrete structures. Numerical simulation provides valuable insights to understand the wave propagation and scattering phenom- ena in the GPR applications for subsurface defect detection and characterization. In this thesis, Finite Difference Time Domain (FDTD) methods are used. Delaminations with different sizes and at different depths inside a rectangular concrete slab with dif- ferent dielectric properties are modeled. From the simulation results, it is found that delaminations are detectable in all cases. Moreover, the curvature values of arch-like shapes obtained from B-scan images of concrete slabs are calculated. It is shown that the curvature value and the size of delamination are related. Finally, a procedure for estimating the size of subsurface delamination in concrete slabs is proposed.

Here is the full text of Burak's Master's thesis.

Here is the presentation for Burak's Master's thesis defense.