Ahmad Shoaib Amiri
University of Nebraska-Lincoln, Class of 2020
From Herat
From Herat
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University of Nebraska-Lincoln
Jamia Millia Islamia
Ahmad Shoaib Amiri of Herat receives University of Nebraska-Lincoln degree
Ahmad Shoaib Amiri of Herat was among 723 graduates who received degrees from the University of Nebraska-Lincoln during a virtual graduation celebration Aug. 15. Amiri earned a Master of Science f...
August, 17 2020 - Verified by University of Nebraska-Lincoln
Graduate Research Assistant at College of Engineering University of Nebraska
Explored concepts of structural health monitoring (SHM)
Used non-destructive testing (NDT) methods to detect various structural issues in bridge decks
Collaborated with faculty advisor, consultants, and officials from Nebraska Department of Transportation (NDOT)
Produced well-written and high-quality reports and presentations
Provided leadership and training for undergrad students
October 2018 - March 2020
A Comparison Between Ultrasonic Guided Wave Leakage and Half-Cell Potential Methods in Detection of Corrosion in Reinforced Concrete Structures
Corrosion of reinforcing steel bars (rebar) in reinforced concrete decks can lead to serious structural issues in bridges. Ultrasonic Testing (UT) methods provide small wavelengths that can be used for early detection of several types of deterioration. The recently-developed Ultrasonic Guided Wave Leakage (UGWL) Method utilizes steel as the waveguide and measures the energy leaked into the surrounding concrete. Previous studies completed at University of Nebraska-Lincoln demonstrated that the measurements of the leaked energy using receivers from the concrete surface can successfully identify early stages of various flaws such as corrosion, delamination, and cracking. In this method, the longitudinal waves are generated along the rebar by a transmitter placed directly on the rebar, and recorded by an array of receivers on the concrete surface. Previous studies have shown promise in testing stretches of concrete decks as long as 10 feet using a single transmitter and an array of sensors placed 6 inches apart.
The primary goal of this Master’s thesis is to demonstrate that the recently developed UGWL method has several advantages over the commonly used Half-Cell Potential (HCP) method in the detection of corrosion in reinforced concrete (RC) bridge decks. To achieve this goal, laboratory experiments as well as a pros-and-cons analysis is conducted. Laboratory specimens are placed in a corrosive environment by submerging them in 10% NaCl solution. These slabs were then monitored for 6 months. During this period, UGWL and half-cell potential data were collected every 6 days. After testing was completed, chloride threshold levels (CTLs) were measured on cores taken from the specimens. The secondary goal of this thesis is to develop a quantitative correlation between UGWL data and CTLs, similar to those established between HCP and CTLs in the literature.
The experimental results demonstrated that the UGWL technique detected the corrosion activity approximately 21 days sooner than the HCP method. The findings also suggest that chloride content determined after the completion of the corrosion process, which lasted for 6 months, exceeded the standard chloride threshold levels; confirming that the selected method of inducing corrosion in the lab was successful.
August 2020 -
Publications
A Novel Structural Health Monitoring Method for Reinforced Concrete Bridge Decks Using Ultrasonic Guided Waves
This article presents the latest improvements in a recently developed nondestructive testing (NDT) approach for early detection of various flaws (corrosion, delamination, and concrete cracking) in reinforced concrete (RC) bridge decks. The proposed method involves the use of internal steel reinforcement as a wave guide for transmitting ultrasonic waves through the system and the measurement of leaked energy from the surface of the concrete. This paper builds upon the progress made in the previously published phases of the project and aims to further explore the capabilities and practicality of the proposed NDT method. Specifically, the limits of propagation distance, effect of bidirectional reinforcement, methods of attachment and coupling of the sensors to the reinforcement and concrete, and suggestions for optimal sensor arrays are discussed in this paper based on the findings from the most recent laboratory tests and pilot field tests. The results show that with careful placement of sensors and data interpretation, early stages of localized corrosion and delamination can be detected, even when bidirectional and multiple layers of reinforcement are present. For field applications, an angled seat made of fast-setting Hydrocal gypsum cement is recommended, and it is projected that the optimal angle of attachment is 33 degrees or less from the vertical axis.
June 2020 -
Articles
Prototype System for Implementing the Ultrasonic Guided Wave Method on the Field
Until recently, there were no methods for structural health monitoring of new reinforced concrete bridge decks, or diagnosis of existing ones, with the sensitivity to detect the early onset of various types of deterioration. Past and current Nebraska Department of Transportation (NDOT) - UNL collaboration on this topic by the research team has developed a novel technique and succeeded in answering this gap. This method involves leakage of ultrasonic guided waves (UGW). In this method, the waves leaked from the wave guide (steel rebar) are detected by an array of receivers (R) placed on the surface of the concrete. Based on the location of the R, the increase or decrease in the amplitude of the detected waves, if read in the frequency domain, can be compared to theoretical expectations and a prediction can be made on the type, size, and location of one of the following flaws: corrosion, delamination, and cracking in concrete independent of rebars. While these accomplishments are exciting, they have all taken place in the controlled environment of a laboratory. By leaving the end of the rebar exposed, the attachment of the transmitter to the rebar has not been an issue, it was accomplished by simple grease-coupling. Also, by avoiding interference from the environment, signals have been clear and repeatable; and no issues were observed with damage to the equipment over time. As such, the next step is to make this method more practical by developing ways to overcome issues that will occur on the field. The ultimate goal of this project is to make the previously developed innovative testing method, namely the use of the leaked ultrasonic guided waves for the early detection of multiple flaws in reinforced concrete bridge decks, more practical and field-application ready.
June 2020 -
Research Projects
Seismic stability analysis of historical construction: a case Study-Wazirpur Tomb
The non-engineered construction of masonry structures has been proved to be the most vulnerable during earthquake and have cited maximum damage during past earthquakes in India [4]. India is a country which is known for its culture and historical importance, therefore the need for an extensive monitoring and stability assessment of historical monuments is required. The historical monuments have been built without taking into consideration the effect of seismic parameters mentioned in latest Indian Standard of Earthquake Resistant Design of Structures. The present study is an attempt to assess the vulnerability & the stability of the historical masonry structures against the horizontal forces produced by major earthquakes using finite element (FE) simulation technique [1, 2]. The Wazirpur Tomb - an example of historical construction has been considered for the present study. The construction of box-like structure of the tomb has been done using locally available sandstone & lime mortar. The Response Spectrum Analysis [3] has been carried out & the response in terms of engineering parameters, such as natural frequency of structure, displacements, stresses etc. have been noted & discussed. The maximum stresses obtained from FE simulation technique have been compared with the permissible compressive & flexural stresses.
References
1.
Betti M, Galano L (2012) Seismic analysis of historical masonry buildings: The Vicarious Palace in Pescia (Italy). Buildings 2:63–82Google Scholar
2.
Betti M, Galano L, Vignoli A (2015) Time-history seismic analysis of masonry buildings: a comparison between two non-linear modelling approaches. Buildings 5:597–621Google Scholar
3.
IS:1893 (2016) Criteria for earthquake design of structure-part 1 general provisions & buildings. Bureau of Indian Standards, New Delhi, DecemberGoogle Scholar
4.
Agarwal P, Shrikhande M (2011) Earthquake resistant deisgn of structures. PHI Learning Private Limited, New DelhiGoogle Scholar
Articles
Detection of Flaws in Asphalt Overlaid Concrete Decks Using Ultrasonic Guided Waves
Background The research proposed here builds on the achievements of a previous NOOT project. The novel, nondestructive ultrasonic guided wave leakage (UGWL) based testing method we developed recently promises to be able to detect the onset of corrosion and delamination in reinforced concrete bridge decks earlier than any other nondestructive testing (NDT) method (Garcia, Erdogmus, et al. 2017 and 2019); however, the effects of asphalt overlay on the method's effectiveness remains unclear. With this project, we aim to investigate the effect of asphalt overlays on the feasibility of the recently developed UGWL method. In this section, the background and the motivation for the proposed work are summarized. Reinforced concrete bridge decks are highly susceptible to deterioration, mainly due to corrosion of the rebars and the subsequent propagation of issues, such as delamination, cracking, and spalling. According to the Federal Highway Administration (FHWA 2014), 145,890 out of the 610,749 highway bridges (24%) in the U.S. are structurally deficient. Yunovich et al. (2001) state that corrosion and delamination problems account for approximately 40% of all bridge deck repair costs; and Arndt et al. (2011) identify the highway bridge corrosion related repair costs to be around $8.3 billion, with $2 billion of this just for the repair of bridge decks. There are several NDT methods gaining more popularity to help with these issues, but most of these methods can only detect flaws after they reach a certain size, at which point, structural behavior may already be compromised and the deck has to be replaced. In the past few years, in collaboration with NDOT, we have developed a novel NDT method that is capable of detecting the onset of rebar-concrete separation (mechanical delamination) and rebar corrosion (chemical delamination). This method utilizes a commercially available ultrasonic testing system; however, we developed innovative techniques for placing the transmitters and receivers, as well as for the analysis of the data. Due to the unique placement of sensors, instead of measuring the ultrasonic waves directly (the sensors on two ends of a steel pipe or both sensors on the concrete are common placements); we measure the leaked energy. The transmitter (T) is placed at the end of the steel rebar using the rebar as a waveguide. This allows the ultrasonic waves to propagate for longer distances within the boundaries of a linear element. The receiver (R) on the other hand is placed on the concrete's surface. As a result of this arrangement, the leaked energy from the ultrasonic guided waves propagating through the rebar are measured from the surface of the concrete. Using this technique, which we refer to as "ultrasonic guided wave leakage (UGWL) method", we were able to detect delaminations as small as 0.008" and record signals up to 10 and 14 feet away from the transmitter on a lab specimen and on an actual bridge deck, respectively. For the analysis/post-processing, we utilize the energy or the amplitude, instead of the typically measured velocity. This allows smaller changes in condition to be detected more clearly. Thus far, we have tested this method only on reinforced concrete lab specimens and a bridge deck without any membrane or asphalt overlay.To make sure the idea is adequately tested with reinforced concrete decks first, we have intentionally kept asphalt out of the scope thus far, per mutual agreement between the Pl and the NDOT. Meanwhile, given the high cost of bridge deck failures, NDOT's philosophy is to add an asphalt overlay to bridge decks based on age (i.e. when they are 10 years old) as a precaution. As a result, there is an urgent need to study the feasibility of the UGWL method with the inclusion of an asphalt overlay, to ensure it remains feasible and applicable to Nebraska's infrastructure. It is also further identified through discussions with NDOT that, given the complex and multi layered construction of asphalt-overlaid reinforced concrete bridge decks, currently there are no effective NDT methods to detect issues underneath the asphalt and membrane layers. If our method proves successful, it will provide a highly valuable tool to NDOT's capabilities for inspection and maintenance. There are a few studies on the ultrasonic testing of asphalt based on our preliminary review. Tigdemir et al. (2004) have demonstrated the possibilities of applying ultrasonic methods on asphalt-concrete specimens to estimate fatigue life. Khazanovich et al. (2005) have shown that ultrasonic testing techniques can provide a simple, quick, and objective procedure for evaluation of surface distresses in asphalt concrete pavements. Hoegh et al. (2012) demonstrated that ultrasonic tomography could detect delamination between new and old asphalt layers, as well as delamination of lifts within new asphalt pavements. Pahlavan et al. (2016) investigated the influence of asphalt on fatigue crack monitoring in steel bridge decks using guided waves; however, they concluded that the type of asphalt greatly affects the extent of propagation of guided waves. Haser et al. (2015) monitored the viscosity of asphalt binders, while Zargar et al. (2017) evaluated the air voids in asphalt. Finally, a very recent study by McGovern et al. (2018) evaluated the life expectancy of asphalt pavements. These studies render the use of ultrasonic testing on asphalt more promising, while in the past, the high attenuation of ultrasonic waves in asphalt has been stated as a concern. It should be noted that none of these studies attempted the exact procedure we aim to investigate; therefore, our proposed work remains novel. A more in-depth literature review regarding the characteristics of asphalt and their effects with respect to our method and objectives is included in the proposed scope of work. Objectives The ultimate goal of the project is to expand the capabilities of the recently developed novel UGWL testing method to detect flaws in asphalt overlaid reinforced concrete bridge decks. Two objectives will help achieve this goal: 1. To determine the effects of the asphalt overlay on the testing method 2. To understand to what extent we can detect the flaws in reinforced concrete decks when there is an asphalt overlay 2. To determine if we can use the "asphalt" as a waveguide in addition to or instead of the rebar.
Research Projects
