DEVELOPMENT OF AN EFFICIENT METHOD OF PREDICTING REMAINING STRENGTH CAPACITIES OF CORRODED CONCRETE STRUCTURESUndergraduate research proposal report submitted in partial fulfilment of the degree of Bachelor of Science in EngineeringRathnayake R.M.M.
C. : EG/2012/2054Supervisor: Dr. J.M.R.S. Appuhamy23524853492500Department of Civil and Environmental EngineeringFaculty of EngineeringUniversity of Ruhuna3rd June 2016DEVELOPMENT OF AN EFFICIENT METHOD OF PREDICTING REMAINING STRENGTH CAPACITIES OF CORRODED CONCRETE STRUCTURES Supervisor:Dr. J.
M.R.S. AppuhamyExamination Committee: Dr. G.G.T. Chaminda (Chair) Dr.
G.S.Y. De Silva Dr.
K.S. Wanniarachchi Dr. T.N. Wickramarachchi Ms. S.N.
Malkanthi Dr. T. Rengarasu Dr. Champika Ellawala Dr. Vidura Vithana Dr. B.M.
L.A. Basnayake Dr. Cyril KariyawasamPREFACEThis report consists of the research proposal related to undergraduate research thesis. This report consists four chapters.
In first chapter it is described about introduction and background of the research under several topics. Introduction to the research is discussed under first tropic. Significance of the study to address present prevailing problems is discussed under the second tropic. Third topic is discussed about objectives of the research to be achieved.
In second chapter it is thoroughly discussed about researches done so far addressing a relative situation to the study. Conclusions of those researches are taken into the account to avoid weaknesses of the study. In third chapter it is discussed about the method that the research going to be continued. Here all the test and methods are described to approach the ultimate objectives.
This report is attached with the activity plan to fulfill each objective and references to have more information on the research under fourth chapter.Rathnayake R.M.M.C. (EG/2012/2054)Department of Civil and Environmental Engineering,Faculty of Engineering,University of Ruhuna.
ACKNOWLEDGEMENTWe would like to acknowledge our thesis advisor, Dr. J.M.R.S. Appuhamy for his guidance, suggestions and encouragement throughout the research process.
We are also thankful to the head of the department Dr G.S.Y. De Silva and the coordinator of the research projects Dr G.G. Thushara Chaminda for their contribution to encourage us to do such researches to evaluate future problems. Finally we are thankful to the technical officers and the people who helped us so far for the research for their support.
Rathnayake R.M.M.C.
(EG/2012/2054)Department of Civil and Environmental Engineering,Faculty of Engineering,University of Ruhuna.CONTENTS TOC o “1-3” h z u CHAPTER 1- INTRODUCTION AND BACKGROUND….
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.. PAGEREF _Toc452573122 h 11.1Introduction….
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.. PAGEREF _Toc452573123 h 1 1.1.1 Corrosion of steel reinforcement embedded in concrete……………………1 1.
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3Significance of the research2CHAPTER 2- LITERATURE REVIEW….
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..42.1 Residual bearing capacity of corroded rc elments..
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.42.1.1Effect of corrosion level.
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42.1.3Effect of bond deterioration…
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……………42.2 Acceleratted corrosion of reinforcement……………………………………………………….52.2.1Impressed current technique………………………………………………………………….52.2.2Effect of impressed current density on the load-bearing capacity………………62.3 Eorrosion rate monitoring7CHAPTER 3- METHODOLOGY…………………………………………………………………83.1 Proposed methodolagy83.1.1 Sample preparation………………………………………………………………………………83.1.2Preparation of Formwork……………………………………………………………………..83.1.3Reinforcing Steel…………………………………………………………………………………83.1.4Concrete Mix Design…………………………………………………………………………..93.1.5Proposed accelerated Corrosion by impressed current technique………………103.1.6Corrosion monitoring…………………………………………………………………………10 3.1.7The approach to determine remaining strength capacities of corroded……….11 CHAPTER 4- ACTIVITY PLAN………………………………………………………………………..124.1 Activity diagram………………………………………………………………………………..12REFERENCES………………………………………………………………………………………………….13LIST OF TABLESTable 3.1: Details of raw materials for concrete………………………………………………………10LIST OF FIGURES TOC h z c “Figure” Figure 1.1: Chloride induced corrosion……..……………………………………….…… PAGEREF _Toc452510276 h 1Figure 1.2: Intermediate process of strength reduction…………………….………………2Figure 2.1: Relationship between bond strength and corrosion………………………………….4Figure 3.1: Dimensions of the samples…………………………………………………………………..8Figure 3.2: Sample chart…………………………………………………………………9Figure 3.3: Configuration of Reinforcement……………………………………………..9Figure 4.1: Activity diagram……………………………………………………………12ABBREVIATIONS AND ACRONYMSBS– British StandardsRC– Reinforced ConcreteCHAPTER 1INTRODUCTION TO THE RESEARCHINTRODUCTIONCorrosion of steel reinforcement embedded in concreteThe deterioration of concrete structures can be recognized in different ways, such as by corrosion of reinforcement, freeze-thaw damage, etc. The corrosion of reinforcing steel is a major durability issue of existing concrete structures. Generally, reinforcing steel and the surrounding concrete area are damaged by corrosion. Finally, it affects both the serviceability and load-carrying capacity of existing reinforced concrete structures.The reinforcing steel in concrete structures corrodes mainly due to carbonation, chloride ingression and any other chemical ingression. The deterioration process in reinforced concrete structures due to corrosion can be categorized into two phases, namely, initiation and propagation. The initiation phase starts when chloride, carbonation or both begin to penetrate the concrete. The thin oxide layer formed on the surface of the embedded steel prevents from corrosion. The propagation phase starts by the passivation of the thin oxide layer on the surface of steel; this is the start of the active corrosion condition of the reinforcing steel. The corrosion of steel is getting in an active state when the pH value decreases. The summation of the time, from penetration until the threshold value is reached and the time from propagation until a maximum acceptable corrosion depth is reached, can be illustrated as the service life of the structure. During the propagation phase of the corrosion, a reduction in the steel cross-sectional area, which affects both the ductility and the strength of the steel, and a volumetric expansion, which causes spalling of concrete and loss of bond strength in between the concrete and steel (due to both a weak interface layer and the disengagement of ribs), can be seen. These effects may reduce the anchorage capacities and the composite interaction and change the geometric properties, due to a loss of the concrete cross section. Finally, this causes changes in the overall stiffness of the structure, and a reduction in load carrying capacity can be observed. Several researchers have studied the relevant corrosion mechanisms and the corresponding structural behaviour of deteriorated reinforced concrete structures. They pay significant attention to the accurate modelling of the bond strength and the corresponding mechanisms of corroded reinforced concrete structures.Flexure or bending is commonly find in structural elements such as beams and slabs which are transversely loaded. Flexural strength is measure of the tensile strength of OPC concrete, in other words it is a measure of a resistance against failure in bending. Although the probability of the structures being flexure deficient is low. Corrosion is caused by the destructive attack of chloride ions penetrating by diffusion or other penetration mechanisms from the outside, by incorporation into the opc concrete mixture, by carbonation of the cement cover, or their combination (Cabrera, 1996). Carbonation of concrete or penetrations of acidic gases into the concrete causes of reinforcement corrosion. Besides these there are few factors, some related to the concrete quality, such as w/c ratio, cement content, impurities in the concrete ingredients, presence of surface cracking, etc. and others related to the external environment, such as moisture, bacterial attack, stray currents, etc., which affect reinforcement corrosion (Castro et al., 1997). Uncontaminated cover concrete provides a physical barrier that prevents the direct exposure of the steel surface to the outside environment. It also provides a highly alkaline chemical environment that protects steel from corrosion.Corrosion of steel reinforcement embedded in concrete is an agent problems on durability of reinforced concrete structures. Chloride induced corrosion is one of the major problem for RC structures especially which are exposed to Marian environment. In this process Chloride irons penetrate the cover of the RC member by a combination of diffusion and capillary action and they gradually permeate until they reach the steel surface as shown in figure 1.1.8648701273810Sourcehttp://www.corrosion-club.com/images/corrosioncell.gif00Sourcehttp://www.corrosion-club.com/images/corrosioncell.gifFigure SEQ figure * ARABIC s 1 1.1: Chloride induced corrosionHowever, Natural corrosion process of RC elements takes long time bout 10-15 years (Malumbela, Moyo & Alexander 2012) to indicate significant structural damages. Therefore it is necessary to implement an accelerated corroded technique in order to evaluate experimental results within a short time of period. There are several techniques that accelerate the corrosion of reinforcement. Impressed current technique is the most common method experienced in past history. Some researchers have been adding some modification for this technique to get results within a very short time period.Corrosion effect on load bearing capacityUltimate load bearing capacity is reduced with increase in the degree of corrosion (Revathy, Suguna & Raghunath 2009). Intermediate process between corrosion and reduction of ultimate load carrying capacity is shown in figure1.2. Many of researches has done focussing one or combination of this intermediate process to determine residual strength or service life of RC structures (Cairns et al. 2006 sited in Sallehuddin & Cairns 2013).3760470-91440Sallehuddin & Cairns 20130Sallehuddin & Cairns 2013Figure 1.2: Intermediate process of strength reduction.OBJECTIVESDevelopment of an efficient method of predicting remaining strength capacities of corroded concrete structures.SIGNIFICANCE OF THE RESEARCHCorrosion damage of RC structures is an argent problem that needs to be addressed. This damage is a large drain on the economy. For the purpose of maintenance and repair options, their residual service life should be determined. Still there is no any standard procedure to determine remaining moment capacity of corroded RC structures. For assessing the condition of corrosion-damaged RC structures, the remaining carrying capacity of such structures should be estimated. To meet this objective, the study on the residual strength capacity of reinforced concrete beams that were subjected to different degrees of corrosion damage was undertaken.CHAPTER 2LITERATURE REVIEWRESIDUAL BEARING CAPACITY OF CORRODED RC ELMENTSEffect of corrosion levelIn order to ensure safety of RC structures whose reinforcing steel has been severely corroded, it is necessary not only to repair the damage appropriately, but also to evaluate strength of RC members according to the degree of rebar corrosion. “The effects of rebar corrosion on the strength of RC members reinforced with them can be evaluated by three factors; The losses in the effective cross-sectional area of concrete due to cracking of cover concrete; The losses in the mechanical properties of rebar due to their reduced cross-sectional areas; The bond strength and rigidity between corroded rebar and concrete.”(Lee 1999)The strength of RC members damaged by rebar corrosion can be analysed by finite element analysis if material models representing the relationships between the degree of rebar corrosion and the bond properties and mechanical properties of corroded rebar can be derived. The purpose of this study is to investigate quantitatively and experimentally the relationship between the degrees of rebar corrosion and the flexural strength of RC beams damaged by rebar corrosion. Also, results of experiment on RC beams damaged by rebar corrosion were compared with the results of finite element analysis.The effect of uniform corrosion, causing extensive cracking, staining and spalling of concrete cover. In this crack width measured using Crack Microscope with an accuracy of 0.02mm. The initiation of corrosion is likely to occur at the stirrup reinforcement surface which has the minimum concrete cover. In Corroded beams red and brownish-red colored rusts were observed in different amounts and at different locations. All corroded beams developed surface cracks. The crack pattern seen in Corroded specimen, the crack that propagated perpendicular to the corroded steel bars was observed on the extreme tensile face of the beam to where corrosion agents drawn into the concrete (Chaitanya & Krishna 2014). Ultimate load carrying capacity of the RC elements are reduced with increase in the degree of corrosion. (Chaitanya & Krishna 2014). He has found that at a at corrosion levels of 31%, theoretical load-bearing capacity exceeded the measured capacity by 30%. But at lower levels of corrosion (around 5%) theoretical capacity was found to be similar to the measured capacity (Azad, Ahmad, and Azher, 20010).Effect of mass loss of reinforcementCorrosion will reduce the cross-section of the steel and the concrete, and thereby the load carrying capacity of the structure (Ahmad 2003 sited in Azard 2010). Pitting corrosion is more dangerous than uniform corrosion. Without necessarily being evident from the surface of the member, it may progressively reduce the cross sectional area of the rebar to a point where the rebar can no longer withstand the applied load leading to a catastrophic failure of the structure. Effect of bond deterioration 3198495756920Al-Sulaimani 1990Al-Sulaimani 1990Initially bond strength is increased by a small amount of corrosion but starts to decrease with further increases in corrosion level (Al-Sulaimani et al. 1990 sited in Sallehuddin & John 2013) as shown in figure 2.1.Figure 2.1: Relationship between bond strength and corrosion.There are two mechanisms by which corrosion may affect the bond between reinforcing bars and concrete (Stanish 1997). Most of the corrosion products that accumulate on the bar surface occupy a larger volume than that of the original un-corroded metal which is causing cracking or spalling of the concrete cover. Loss of cover inevitably implies loss of confinement and reduction in bond strength at the interface zone between the two materials. We can summarized factors which are affected for the bond strength as Adhesion between the concrete and the reinforcing elements, Gripping effect resulting from the drying shrinkage of the surrounding concrete, Frictional resistance to sliding and interlock on the reinforcing elements subjected to tensile stress, Effect of concrete quality and strength in tension and compression and Mechanical anchorage effects of the ends of the bars through the development length (Nawy 1996 cited in Stanish 1997).The basic problem associate with the deterioration of reinforced concrete as a result of corrosion is not only that the reinforcing steel reduces in mechanical strength, but also the products of corrosion exert stress within the concrete that cannot be resisted by the limited plastic deformation capacity of the concrete and the concrete therefore cracks. This leads to the weakening of the bond and anchorage between concrete and reinforcement which directly affects the serviceability and ultimate strength of concrete element within structures (Azad et al. 2010). ACCELERATTED CORROSION OF REINFORCEMENTImpressed current techniqueThe process of natural steel corrosion is very slow. Current density due to natural steel corrosion is often between 0.1 and 10 ?A/cm2 (Andrade & Alonso 2001 cited in malumbela et al. 2012). The level of impressed current density has varied greatly from 3 ?A/cm2 to 10400 ?A/cm2 between researchers to speed up laboratory corrosion tests. Researchers continue to use various modifications with impressed current technique to accelerate steel corrosion so as to shorten the needed testing time.Corrosion is the gradual deterioration of a metal due to its reaction with the surroundings. Chloride-induced corrosion does not begin until a stabilized chloride threshold is reached in the concrete matrix. Corrosion of RC structures is highly in?uenced by the microstructural properties of the concrete. For example, a higher electrical resistivity of the concrete prevents electron transfer between anode and cathode resulting in a longer initiation period. Further, concrete cured properly with low w/c ratio results in lesser permeability and reduced diffusion of corrosion causing agents. Initiation of corrosion may be attributed to carbonation or chloride ion ingress, two major corrosion causing agents. Corrosion mechanism involved depends mainly on the type of corrosive agent. The type of corrosion mechanism involved determines the period of propagation, which directly relates to the service life of RC structures (Mahima & Moorthi 2018)Some researchers opted to mix concrete with chlorides ranging from 1% (Mangat & Elgarf 1999 cited in Malumbela et al. 2012) to 5% (Maaddawy & Soudki 2003 cited in Malumbela et al. 2012) by weight of cement. Some researchers immersed their cured samples in tanks with NaCl solution with concentration from 3% to 5% by weight of the solution. (Cairns, Du & Law 2008 cited in Malumbela et al. 2012).Adding chlorides to concrete results in uniform distribution of corrosion agents around the steel. Under natural steel corrosion limited faces of a structure are often exposed to chloride attack. In addition, chlorides and other deleterious compounds are purposely excluded from concrete mixes in practice. In an attempt to better represent natural steel corrosion, some researchers contaminated selected faces of their cured specimens with chlorides. (Weber 2014).Effect of impressed current density on the load-bearing capacityMass losses of steel due to steel corrosion up to7%, the level of current density had little effect on the load-bearing capacity of RC beams (Mangat & Elgarf 1999 cited in Malumbela et al. 2012). At mass losses of 10% and beyond, load-bearing capacity of RC beams decreased significantly with increase in the level of the impressed current density. according to their results, at a mass loss of steel of 20%, current density of 1000 ?A/cm2 induced a loss of load-bearing capacity of 60% compared to 78% when a current density of 4000 ?A/cm2 was used.The current density isn’t that caused a larger reduction in load-bearing capacities at higher levels of steel corrosion, but rather the product of current density with time (Azad et al. 2007).They further asserted that a higher value of corrosion current density for a lesser period of time would be as damaging as a lesser value of current density for a longer corrosion period. He found that average mass loss of steel of 1% to relate to loss in load-bearing capacity of 1.4%. However Mangat ; Elgarf (1999) and Azad et al. (2007) was agreed that, at large mass losses of steel (;10%), calculated values of load-bearing capacity, using measured average mass losses of steel, had little relation with experimental results. CORROSION RATE MONITORINGSome researchers have measured the actual level of steel corrosion at the end of accelerated corrosion tests (Malumbela et al. 2012). This was done by removing corroded steel bars from concrete specimens, cleaning them and measuring levels of steel corrosion as mass losses of steel or as corrosion pit depths. In real structures, however, it is uncommon for corroded steel bars to be removed from structures. Faraday’s Law is therefore often used to estimate the level of steel corrosion. Once the Icorr is known, the accumulated charge (Q= Icorr*t) can be calculated over the total exposure time. Faraday’s law is given bellow.m = AQ/zF QUOTE AQzF Where m is the mass of the steel consumed (grams), Q is the charge in coulombs, F is 96,500 coulombs, z is the ionic charge (2 for Fe ? Fe2++ 2e-) and A is the atomic weight of the metal (56 g for Fe).Finally, Considerable research has been devoted to corrosion of reinforcement in reinforced concrete dealing with various issues related to corrosion process, its initiation and damaging effects. After the review of available literature and noting the areas where further work is needed, the following conclusion can be drawn; Ultimate load carrying capacity, deflection and stiffness of the RCC elements are reduced with increase in the degree of corrosion. Reduction in cross section of reinforcement, yield strength and cracks along the reinforcement are the main contributing factors for strength degradation of RCC element. As the degree of corrosion increased, the beam failure mode changed from ductile mode to brittle mode. To accelerate the corrosion process, generally current is impressed in the specimens immersed in electrolyte made with 3.5-5% NaCl mixed in water. Salt spray method or alternate drying and wetting may also be used for induced corrosion. Small level of sustained load has little effect on rate of corrosion. The results of an accelerated corrosion tests on bare steel bars are in good qualitative agreement with results from steel bars embedded in aged concrete. An attempt has been made in this study to review the literature available and to carry out experimental investigation effectively to determine the effect of corrosion on flexural capacity and performance of cantilever beam with a TMT bars as reinforcement.Rectification MethodsConsistent success in concrete repair begins with the recognition that each repair situation is defined by a unique combination of circumstances shaped by engineering, exposure, constructability, cost, and time considerations. The installation method must deliver the selected repair material to the prepared substrate with predictable results. The properties of repair materials generally specified are compressive strength, bond strength, shear strength, and those properties that influence volume changes, such as drying shrinkage, modulus of elasticity, and coefficient of thermal expansion. Other properties such as resistance to freeze and thawing, low permeability, or sulfate resistance may be specified. The repair material must fully encapsulate exposed reinforcing steel, achieve satisfactory bond with the substrate, and fill the prepared cavity without segregating. If these requirements are not achieved, the repair will not perform its intended purpose. Bonding of the repair material with the existing substrate depends upon the repair material reacting with, and interlocking to, the profile of the prepared concrete surface. Some materials may require a bonding agent to insure intimate contact with prepared surfaces. If the repair material is self-bonding, it must have sufficient binder (e.g. cement paste, epoxy resin) to thoroughly wet out the substrate. Force must be applied to drive the repair material into intimate contact with the prepared surface. The type of force will vary with the application method. In trowel applied systems, the repair material is forced into the prepared surface by the pressure applied to the trowel by the finisher or cement mason. In cast-in-place systems, the pressure is provided by initial vibration, or hydraulic pressure developed by concrete or grout pump. High velocity pneumatic placement techniques develop exceptional forces through impact. The dry packing process generates pressure when the rodding tool pounds the material against the substrate. The requirement that the repair materials be mixed and applied without segregating is equally important. Any segregation of material components will alter physical properties and reduce or negate the ability of the repair to fulfill its primary function – to restore the structure to its original condition to the fullest extent possible.CHAPTER 3 METHODOLOGY3.1 PROPOSED METHODOLAGY3.1.1 Sample preparationThis research consists three different series of RC beams to identify behaviour of structural performance from lower to higher level of corrosion. Details of the samples are given bellow.Series I- Miner corrosion levelSeries II- Moderate corrosion levelSeries III- Severe corrosion levelAll the samples are consist with same dimensions as shown in figure 3.1. Figure 3.1: Dimensions of the samplesEach and every test will be repeated twice, including the test of the control beams, which is not subjected to corrosion. Sample chart is in figure 3.2.Preparation of FormworkThe formwork will be erected locally using 75mm thick plywood. Reinforcing SteelNominal yield strength of 460MPa, T10 Hot rolled deformable steel bars will be used for longitudinal direction. R6 plain bars will be used as shear links or stirrups. Proposed reinforcement configuration is given in figure 3.3. Figure 3.2: Sample chartFigure 3.3: Configuration of ReinforcementConcrete Mix DesignConcrete mix design will be done according to BS 8110. Derails of the raw materials are given in table 3.1. Table 3.1: Details of raw materialsMaterials DescriptionsCement Ordinary Portland cement (OPC)Fine Aggregate River sandCoarse Aggregate Maximum 25mm size of Crushed natural dolomiteWater Tap water at room temperatureProperties of each raw materials will be tested in the laboratory. Based on the properties of the raw materials mix design will be carried out to get the slump in the range of 150mm-175 mm and strength in the range of 25 MP.Proposed accelerated Corrosion by impressed current technique.In this research, electrochemical corrosion technique will be used to accelerate the corrosion of steel bars embedded in the specimens. Here direct current impressed on the bar embedded in the specimens. Reinforcing steel bars which they need to corrode are connected to a positive terminal, and a stain less steel bar/plate is connected to a negative terminal. Reinforcing steel bars therefore become the anode and the stain less steel bar/plate becomes the cathode. Specimens will be immersed in NaCl solution which has concentration of 3.5% by weight (which simulate NaCl concentration of sea water) to provide electrical contact between the anode and the cathode. We will be avoided adding chlorides to concrete mixes in order to simulate natural corrosion on accelerated corrosion technique. Corrosion monitoringLevel of corrosion will be determined based on rate of mass loss of steel bars. Mass loss of steel bars will be calculated using faraday’s law. Faraday’s law is given bellow.m = AQ/zF Where m is the mass of the steel consumed (grams), Q is the charge in coulombs, F is 96,500 coulombs, z is the ionic charge (2 for Fe ? Fe2++ 2e-) and A is the atomic weight of the metal (56 g for Fe).The approach to determine remaining strength capacities of corroded RC beams.Corroded RC beams will be tested against bending shear and torsion. Then control samples which are not subjected to corrosion, will be tested. Then we will be identified percentage of loss of load bearing capacity of corroded RC beams with respect to that of control samples.This test procedure will be repeated at the mild, moderate and severe corrosion levels.Load versus deflection curve will be used to evaluate loss of stiffness of corroded RC beams at the three corrosion levels with respect to that of control samples.Mass loss of reinforcement bars and deterioration of bond between reinforcement and concrete will be evaluated.Finally an efficient model will be developed based on all the experimental results to determine remaining strength capacities of corroded RC beams.Here it will be assumed that there is no any structural damage due to impressed current applied from the external source.CHAPTER 4ACTIVITY PLAN4.1 ACTIVITY DIAGRAMFigure 4.1: Activity diagramREFERENCESAzad, A.K., Ahmad, S. and Azher, S.A., 2010, ‘Residual strength of corrosion-damaged reinforced concrete beams’, Concrete research 62(6), 405- 414.Malumbela, G., Moyo, P. ; Alexander, M.G., 2012, ‘A step towards standardizing accelerated corrosion tests on laboratory reinforced concrete specimens’, The south African institution of civil engineering 54(2) , 78–85.Naga, C. ; Krishna, B., 2014, ‘An Experimental Study of Flexural Strength of Reinforced Concrete Beam Due To Corrosion’, Mechanical and Civil Engineering 11 (4), 98-109.Revathy, J., Suguna, K. ; Raghunath, P.N., 2009, ‘Effect of Corrosion Damage on the Ductility Performance of Concrete Columns’, Engineering and Applied Sciences 2 (2), 324-327.Sallehuddin, S.A. ; John J.C., 2013, ‘Critical Study of Corrosion Damaged Concrete Structures’, Integrated Engineering 5(2), and 43-50.Stanish, K., 1997, ‘Corrosion effects on bond strength in reinforced concrete’, MSc thesis, Dept. of Civil Engineering, University of Toronto.Weber, B.W., 2014, ‘Accelerated corrosion of steel in dry-cast reinforced concrete pipes after initiation’, MSc thesis, Dept. of Engineering and Computer Science, University of Florida Atlantic.
