Graduation Semester and Year

2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Nur Yazdani

Abstract

ABSTRACT: Corrosion of rebar is considered the leading cause of deterioration in concrete structures. When steel rust, it occupies larger volume and creates pressure on the concrete, leading to cracking and spalling. As the cross-section is being compromised, the structural capacity of the reinforced concrete structure is reduced. Corrosion is a slow natural electrochemical process that affects the long-term performance. However, sometimes premature catastrophic failure occurs due to corrosion, especially in chloride environments. Moreover, the cost of repair and replacement of deteriorated structures has become a major liability for management agencies. Consequently, it is important to determine the level of corrosion at early stages to minimize maintenance costs. While visual inspection is the simplest way to identify the corrosion, it is only useful when corrosion products reach their threshold value, not at the initiation stage of corrosion. Conversely, electrochemical methods, such as Half-Cell Potential (HCP) and Linear Polarize Resistance (LPR), can locate corrosion activity, but they are quasi-non-destructive methods. On the other hand, Ground Penetrating Radar (GPR) detects corrosion through its reflective wave in the form of maximum amplitude and two-way travel time. Apart from GPR, iCOR is also able to detect corrosion activities, such as corrosion rate, and concrete electrical resistivity, in a short time without any physical connection to rebars. iCOR, moreover, uses Connectionless Electrical Pulse Response Analysis (CEPRA) method. The current study was designed to evaluate the difference in Non-Destructive Evaluation (NDE) data between non-corroded and corroded concrete beams and to quantifying the amount of corrosion that occurred in the steel rebars in concrete. A total 36 beams of 36 in. (914 mm) X 15 in. (381 mm) X 8 in. (203 mm) sizes with 4 design parameters were prepared for the present study. The parameters were concrete clear cover, rebar diameter, concrete strength and porosity, and duration of corrosion. For concrete clear cover, ranges from 1.5 in. (38 mm), 2 in. (50 mm), and 3 in. (75 mm) were considered as these are the required clear covers provided in ACI 318-19 code for interior beams (building), bridge deck and structure exposed to soil respectively. Three different rebar diameters 0.375 in. (10 mm), 0.875 in. (22 mm), and 1.25 in. (32 mm) were selected. Concrete compressive strength of 2.7 ksi (18.62 MPa) with high porosity 4.5% and 6.8 ksi (46.88 MPa) with low porosity of 1.5% were additionally selected as one of the parameters. Furthermore, corrosion durations of 10, 20, and 30 days were selected. Accelerated corrosion (induced current) technique was used to corrode steel rebars faster. As components of accelerated corrosion direct power source, anode (steel rebars), cathode (stainless steel), and electrolyte solution (5% NaCl solution) were incorporated. Next, after each 10-day interval, all of the beams were scanned with both GPR and iCOR devices. The thickness of the concrete cover, the size of the embedded rebars, the age of the building, and the concrete's compressive strength were all shown to have a substantial effect on the change of the concrete rusting. From the scan result analysis, it was evident that the reflected amplitudes rose when corrosion levels increased, concrete coverings decreased, rebar diameters increased, and concrete strength decreased. In addition, corrosion rates and potentials were decreased by increasing corrosion duration, rebar diameter, concrete strength, and concrete cover. In contrast, as the concrete resistivity increased, corrosion period, rebar diameters, and concrete clear cover increased. Furthermore, a statistical analysis was performed using a multivariable regression model to quantify the amount of corrosion. Corrosion in reinforced concrete structures can be measured using this quantitative corrosion degradation model, which represented a major advancement. This quantitative study may be used to evaluate the loss of steel rebar cross-section, allowing for the quick and nondestructive way of determination of the remaining capacity of the reinforced concrete structures.

Keywords

Reinforced concrete, Non-destructive evaluation, Accelerated corrosion, Ground-penetrating radar, iCOR, Two-way travel time, Amplitude, Steel rebar, Rebar mass loss, Multivariant regression model

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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