M.Tech. (Civil Engineering) / Every year, millions of Rands are being spent in rehabilitation, repairs and maintenance of reinforced concrete structures projects around the country due to corrosion. There are a number of studies and investigations that have been done recently to address the effect of corrosion on reinforced concrete structures. Concrete provides an ideal environment for steel, supplying both physical and chemical protection from corrosive attack. The effect of corrosion on reinforced concrete structures contributes to the reduction of steel cross sectional area, weakening the bond strength between steel and concrete and thereby reducing the ductility, deflection capacities and load carrying capacity of the structure. In this research, five series of three samples each of reinforced concrete beams were fabricated, some with reduced cross-sectional area and with exposed bars to simulate loss of bonding through spalling. The structural performance of these beams was tested in terms of maximum load carrying capacity, deflections and ductility ratio. The main conclusions are as follows:  As little as 1 % loss in mass of tension steel resulted in a load carrying capacity decrease of 6.9 %  Beam deflection increased by a factor of 1.5 times when the steel mass loss level was 14%  5 % steel loss in mass resulted in a 16.5 % decrease in relative ductility.

The Florida Department of Transportation (FDOT) has been using supplementary cementitious materials while constructing steel reinforced concrete marine bridge structures for over three decades. It has been found from previous studies that such additions in concrete mix makes the concrete more durable. This research was conducted to better understand the corrosion propagation stage of steel rebar embedded in high performance concrete exposed to high humidity environment. Reinforced concrete samples that were made with binary mixes, and ternary mixes were considered. None of these concretes had any admixed chloride to start with. An accelerated chloride transport method was used to drive chloride ions into the concrete so that chlorides reached and exceed the chloride threshold at the rebar surface and hence the corrosion process initiated after a short period of time (within few days to few months). Once corrosion has initiated the corrosion propagation can be studied. Electrochemical measurements such as rebar potential measurements, Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Pulse (GP) measurements were taken at regular intervals (during and after the electro-migration process) to observe the corrosion propagation in each sample. During the propagation stage, reinforcement eventually reached negative potentials values (i.e., Ecorr≤ –0.200 Vsce) for all the samples. The corrected polarization resistance (Rc) was calculated by subtracting the concrete solution resistance from the apparent polarization resistance measured. The Rc values obtained from LPR and GP measurements were converted to corrosion current (as the corroding area is unknown), and these corrosion current values measured over time were used to obtain the calculated mass loss (using Faraday’s Law). A comparison was made of the calculated corrosion current obtained using the LPR and GP tests. A comparison of mass loss was also obtained from the values measured from LPR and GP tests. From the experimental results, it was observed that the corrosion current values were largely dependent on the length of solution reservoirs. For specimens cast with single rebar as well as three rebars, the most recent corrosion current values (measurements taken between July 2018 to October 2020) in general were larger for the rebars that are embedded in specimens prepared with SL mix, followed by specimens prepared with FA, T1, and T2 mixes respectively. The range of corrosion current values (most recent) were 0.8-33.8 μA for SL samples, 0.5-22.5 μA for FA samples, 0.8-14.8 μA for T1 samples, and 0.7-10.4 μA for T2 samples respectively. It was also found that the calculated mass loss values were larger for rebars that are embedded in specimens (single rebar and three rebars) prepared with SL mix, followed by specimens prepared with FA, T1, and T2 mixes respectively. The range of calculated mass loss values were 0.07-1.13 grams for SL samples, 0.06-0.62 grams for FA samples, 0.12-0.54 grams for T1 samples, and 0.06-0.40 grams for T2 samples respectively. A variety of corrosion related parameters (Ecorr, Rs, Rc, and Icorr) and calculated theoretical mass loss values observed, were due to the changing parameters such as concrete compositions, concrete cover thickness, rebar diameter, total ampere-hour applied, and reservoir size. The specimens showed no visual signs of corrosion such as cracks or corrosion products that reached the concrete surface. The actual size of the corroding sites was unknown as the specimens were not terminated for forensic analysis. The size of the corroding sites could affect how much corrosion products are required to crack the concrete. It is speculated that the corrosion products in liquid form penetrated the pore structure but did not build up enough to cause cracks. No cracks or corrosion bleed outs were observed within the monitored propagation period of approximately 1600 days. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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When damaged, military airfields must be repaired quickly so that flying operations can resume. Due to their rapid-setting and high-strength properties, epoxy-based polymer concretes (PC) may provide a good alternative to the portland cement concrete (PCC) rapid repair mixes currently used by the United States Air Force (USAF) for their Rapid Airfield Damage Recovery (RADR) operations. Epoxy-based PCs use epoxy polymers in place of portland cement to bind together aggregate and form the composite concrete. A commercially available epoxy-based PC, referred to as Commercial Product "B" in this thesis, was tested according to the procedures stated in the Tri-Services Pavements Working Group (TSPWG) Manual M 3-270-01.08-2. This manual defines testing protocol to be used for rapidsetting rigid repair materials intended for use on rigid airfield pavement spall repairs. These tests include various ASTM standards for compressive strength, flexural strength, slant-shear bonding strength, modulus of elasticity, coefficient of thermal expansion, and slump. Commercial Product "B" was not able to set and cure within the time limits set by the TSPWG manual, but otherwise surpassed final compressive strength, flexural strength, slant-shear bonding strength, and slump requirements. However, its modulus of elasticity was below the acceptable range, and its coefficient of thermal expansion was several times higher than the maximum allowed value. In addition, a second epoxy-based PC currently under development by Luna Labs and D.S. Brown was tested for compressive strength and, in most mix designs, surpassed the minimum requirements. This PC was also field tested in a series of four (4) 2-feet by 2-feet by 8-inch deep patches placed within an 8-inch thick PCC slab. Three of these patches did not meet minimum compressive strength requirements and none of them exhibited good bonding between the PC repair material and the original PCC slab. Finally, the effect of the surface moisture content of PCC on the bonding strength and chloride ion penetration resistance when PCC is bonded to PC was tested by casting Commercial Product "B" against ordinary PCC under two different moisture conditions: surface saturated dry (SSD) and PCC that had been conditioned at 10% relative humidity (RH) for 48 hours. The bonded samples underwent three- and four-point bond flexural testing and rapid chloride penetration testing (RCPT). The bond flexural testing showed that Commercial Product "B" bonds to PCC better when the PCC has been conditioned at 10% RH rather than being at SSD conditions. No statistically significant difference was detected for RCPT between bonded samples cast under the two surface moisture conditions, but did show that samples of PCC bonded with Commercial Product "B" are less susceptible to chloride ion penetration than samples comprised entirely of PCC. The results of this thesis show that PC may be useful to the USAF for repair airfields as short term repairs, but further work is required to ensure they meet all standards set by TSPWG for rapid repair materials. They also demonstrate that, when possible, a PCC repair surface should be dried completely before PC repair material is cast against it. / Master of Science / When damaged, military airfields must be repaired quickly so that flying operations can resume. Due to their rapid-setting and high-strength properties, epoxy-based polymer concretes (PC) may provide a good alternative to the portland cement concrete (PCC) rapid repair mixes currently used by the United States Air Force (USAF) for their Rapid Airfield Damage Recovery (RADR) operations. Epoxy-based PC use epoxy polymers in place of portland cement to bind together aggregate and form the composite concrete. To test whether epoxy-based PC can be used for RADR or other airfield repair operations, a commercially available epoxy-based PC, titled Commercial Product "B" in this thesis, underwent a battery of tests as specified for potential rapid repair materials in the Tri-Services Pavements Working Group (TSPWG) manual for testing protocol for rapid-setting rigid repair materials. Commercial Product "B" was not able to set and cure within the time limits set by the TSPWG manual but otherwise surpassed final strength, bonding, and workability requirements. However, it is not nearly as stiff as ordinary PCC and it expands and contracts far more than PCC when it undergoes temperature changes. In addition, a second epoxy-based PC currently under development by Luna Labs and D.S. Brown was tested for compressive strength and, in most mix designs, surpassed the minimum requirements. This PC was also field tested in a series of four (4) patches placed within a PCC slab. Three of these patches did not meet minimum compressive strength requirements and none of them exhibited good bonding between the PC repair material and the original PCC slab. Finally, the effect of the surface moisture content of PCC on the bonding strength and resistance to chloride ions, often found in de-icing agents, when PCC is bonded to PC was tested by casting Commercial Product "B" against ordinary PCC under two different moisture conditions: surface saturated dry (SSD) and PCC that had been conditioned at 10% relative humidity (RH). The bonded samples underwent bond flexural testing and rapid chloride penetration testing (RCPT). The bond flexural testing showed that Commercial Product "B" bonds to PCC better when the PCC has been conditioned at 10% RH rather than being at SSD conditions. No statistically significant difference was detected for RCPT between bonded samples cast under the two surface moisture conditions but did show that samples of PCC bonded with Commercial Product "B" are less susceptible to chloride ion penetration than samples comprised entirely of PCC. The results of this thesis show that PC may be useful to the USAF for repair airfields as short term repairs, but further work is required to ensure they meet all standards set by TSPWG for rapid repair materials. They also demonstrate that, when possible, a PCC repair surface should be dried completely before PC repair material is cast against it.

This thesis involves the consideration of the reinforced concrete beam as a composite beam with incomplete interaction. The influence of bond slip and loading condition on the formation of cracks is studied analytically. / Thesis / Master of Engineering (ME)

yes / This paper presents a relatively simple column strengthening procedure using unbonded wire rope and T-shaped steel plate units. Twelve strengthened columns and an unstrengthened control column were tested to failure under concentric axial load to explore the significance and shortcomings of the proposed strengthening technique. The main variables investigated were the volume ratio of wire ropes as well as geometrical size and configuration of T-shaped steel plates. Axial load capacity and ductility ratio of columns tested were compared with predictions obtained from the equation specified in ACI 318-05 and models developed for conventionally tied columns, respectively. The measured axial load capacities of all strengthened columns were higher than predictions obtained from ACI 318-05, indicating that the ratio of the measured and predicted values increased with the increase of volume ratio of wire ropes and flange width of T-shaped steel plates. In addition, at the same lateral reinforcement index, a much higher ductility ratio was exhibited by strengthened columns having a volume ratio of wire ropes above 0·0039 than tied columns. The ductility ratio of strengthened columns tested increased with the increase of flange width, thickness, and web height of T-shaped steel plates. A mathematical model for the prediction of stress–strain characteristics of confined concrete using the proposed strengthening technique is developed, that was in good agreement with test results.

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