Reinforced concrete poles are commonly used as street lighting and electrical transmission poles. Typical concrete lighting poles experience very little load due to torsion. The governing design loads are typically bending moments as a result of wind on the arms, fixtures, and the pole itself. The Canadian pole standard, CSA A14-07 relates the helical reinforcing to the torsion capacity of concrete poles. This issue and the spacing of the helical reinforcing elements are investigated. Based on the ultimate transverse loading classification system in the Canadian standard, the code provides a table with empirically derived minimum helical reinforcing amounts that vary depending on: 1) the pole class and 2) distance from the tip of the pole. Research into the minimum helical reinforcing requirements in the Canadian code has determined that the values were chosen empirically based on manufacturer’s testing. The CSA standard recommends two methods for the placement of the helical reinforcing: either all the required helical reinforcing is wound in one direction or an overlapping system is used where half of the required reinforcing is wound in each direction. From a production standpoint, the process of placing and tying this helical steel is time consuming and an improved method of reinforcement is desirable. Whether the double helix method of placement produces stronger poles in torsion than the single helix method is unknown. The objectives of the research are to analyze the Canadian code (CSA A14-07) requirements for minimum helical reinforcement and determine if the Canadian requirements are adequate. The helical reinforcement spacing requirements and the effect of spacing and direction of the helical reinforcing on the torsional capacity of a pole is also analyzed. Double helix and single helix reinforcement methods are compared to determine if there is a difference between the two methods of reinforcement. The Canadian pole standard (CSA A14-07) is analyzed and compared to the American and German standards. It was determined that the complex Canadian code provides more conservative spacing requirements than the American and German codes however the spacing requirements are based on empirical results alone. The rationale behind the Canadian code requirements is unknown. A testing program was developed to analyze the spacing requirements in the CSA A14-07 code. Fourteen specimens were produced with different helical reinforcing amounts: no reinforcement, single and double helical spaced CSA A14-07 designed reinforcement, and single helical specimens with twice the designed spacing values. Two specimens were produced based on the single helical reinforcement spacing. One specimen was produced with helical reinforcement wound in the clockwise direction and another with helical reinforcement in the counter clockwise direction. All specimens were tested under a counter clockwise torsional load. The clockwise specimens demonstrated the response of prestressed concrete poles with effective helical reinforcement whereas the counter clockwise reinforced specimens represented theoretically ineffective reinforcement. Two tip sizes were produced and tested: 165 mm and 210 mm. A sudden, brittle failure was noted for all specimens tested. The helical reinforcement provided no post-cracking ductility. It was determined that the spacing and direction of the helical reinforcement had little effect on the torsional capacity of the pole. Variable and scattered test results were observed. Predictions of the cracking torque based on the ACI 318-05, CSA A23.3-04 and Eurocode 2 all proved to be unconservative. Strut and tie modelling of the prestressing transfer zone suggested that the spacing of the helical steel be 40 mm for the 165 mm specimens and 53 mm for the 210 mm specimens. Based on the results of the strut and tie modelling, it is likely that the variability and scatter in the test results is due to pre-cracking of the specimens. All the 165 mm specimens and the large spaced 210 mm specimens were inadequately reinforced in the transfer zone. The degree of pre-cracking in the specimen likely causes the torsional capacity of the pole to vary. The strut and tie model results suggest that the requirements of the Canadian code can be simplified and rationalized. Similar to the American spacing requirements of 25 mm in the prestressing transfer zone, a spacing of 30 mm to 50 mm is recommended dependent on the pole tip size. Proper concrete mixes, adequate concrete strengths, prestressing levels, and wall thickness should be emphasized in the torsional CSA A14-07 design requirements since all have a large impact on the torsional capacity of prestressed concrete poles. Recommendations and future work are suggested to conclusively determine if direction and spacing have an effect on torsional capacity or to determine the factors causing the scatter in the results. The performance of prestressed concrete poles reinforced using the suggestions presented should also be further investigated. Improving the ability to predict the cracking torque based on the codes or reducing the scatter in the test results should also be studied.

Factors such as water to cement ratio, moisture, mixture, presence and depth of rebar, and dimension of specimens, all of which affect apparent resistivity of concrete, were analyzed by experimental and modeling methods. Cylinder and rectangular prism concrete specimens were used in the experiments exposed in a high moisture room, laboratory room temperature, high humidity and outdoor weather environments. Single rebar and four rebar specimens were used to study the rebar effect on the apparent resistivity. Modeling analysis was employed to verify and explain the experimental results. Based on the results, concrete with fly ash showed higher resistivity than concrete with just ordinary Portland cement. Rebar presence had a significant effect on the measured apparent resistivity at some of the locations. The results could be used as a guide for field apparent resistivity measurements and provide a quick, more precise and easy way to estimate the concrete quality. / by Yanbo Liu. / Thesis (M.S.C.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.

The corrosion of the reinforcing steel in concrete by de-icing salts is one of the major issues concerning the durability of reinforced concrete. Different methods have been used to protect the reinforcing steel, but still corrosion of reinforced structures continues to be a big problem causing enormous costs in their restoration and rehabilitation. The continuity of the pores of concrete plays a crucial role in the corrosion of the reinforcing steel. The ingress of corrosive species, such as chloride ions, oxygen and water, through the pores of the concrete cover cause the breakdown of the passive layer formed on the steel by the high pH of the concrete. The use of supplementary cementitious materials (SCM) in the production of high performance concrete (HPC) improves its resistance to corrosive species as a result of the pozzolanic reaction which forms more calcium silicate hydrates (C-S-H). Most of the studies about the corrosion of the reinforcement in HPC have been carried out in sound concrete. However, very few works have been reported on the corrosion of steel in cracked concrete. The crack pattern on HPC is very distinct from that formed on ordinary portland cement (OPC) concrete, which may result in different corrosion mechanisms of the reinforcing steel. The objective of the present work consisted in the evaluation of the corrosion of reinforcing steel in cracked HPC and OPC concrete under different exposure and loading conditions. For that purpose, two sets of beams of HPC (containing fly ash or slag) and two sets of OPC concrete were cast. The difference between the OPC concretes was the date of casting. Three sets of reinforcing steel probes were embedded in each beam at different locations. All the beams were cracked at midspan by the four-point method. Eight beams of each concrete were coupled in pairs and partially immersed in a solution of de-icing salts every two weeks. In this way, one set of the corrosion probes was non-submerged (top) while the other two were completely submerged (one at the crack level and the other at the bottom). Two pairs of beams were subjected to static loading whereas the other two were under cyclic loading. The corrosion potentials readings were taken daily by a data acquisition system, whereas the corrosion rates were determined by the Linear Polarization technique using a corrosion monitoring system. According to the results obtained, the corrosion rates of the submerged and non-submerged probes are very low. This behaviour is observed for the four concretes and for both loading conditions. The type of loading did not influence the corrosion rates of these probes, which were in the same range for all the concretes. On the other hand, the probes close to the crack showed higher corrosion rates, especially those under cyclic loading. In general, the OPC concrete cast during the winter presented the highest corrosion rates for both loading conditions, followed by the OPC concrete cast in the summer (as were both HPCs), then by HPC-Slag and HPC-Fly Ash, which showed the lowest values. In most of the cases there was a good agreement between the corrosion potentials and the corrosion rates, so that the OPC concretes exhibited the most negative values. The lower corrosion of the probes in the HPC-Fly Ash and HPC-Slag beams was ascribed to the continued pozzolanic activity, which may result in the self-healing of the crack with time. The probes close to the crack in the dynamically loaded beams experienced higher corrosion than those in the static beams. In some cases the corrosion rate reached values above 100 mm/year. The lower corrosion of the probes in the static beams was attributed to the self-healing of the crack. The formation of additional microcracks in the dynamic beams during cyclic loading may be responsible for their higher corrosion. The corrosion potential of the rebar cage shifted to more negative values during cyclic and static loading. This change in the potential was associated with stress concentration of the reinforcement surface, making it more active. Although the shift in the potential was not really significant, this may have important consequences in practice where the concrete is subjected to higher loads.

Concrete is strong in compression; however, it is quite fragile in tension. To overcome this flaw, concrete is frequently reinforced with bars typically made of low grade, low carbon steel. The environment inside of concrete is favorable for steel; unfortunately when passive steel is exposed to chlorides, active corrosion can initiate, resulting in damage to the structure. One source of chloride contamination is through anti-icing agents which are used to inhibit the formation of ice on roadways, ensuring safe driving conditions. This represents a serious concern from both the cost associated with rehabilitation (Canadian infrastructure deficit in 2003 was $125 billion [1]) and as a safety concern to the public. In Canada, 5 million tonnes of road salts are used each year [2], of which Ontario uses 500 to 600 thousand tonnes [3]. As a result, the Ministry of Transportation Ontario (MTO) has requested a study of four frequently used anti-icing agents: 25.5% NaCl, 31.5% MgCl2, 37.9% CaCl2 and 32.6% multi Cl- (12% NaCl, 4% MgCl2 and 16% CaCl2). The objective of the study is two-fold, the first is comparing the effects of the solutions on steel embedded in concrete (high pH environment) and the second is to compare the effects of the anti-icing agents to a variety of construction steels in atmospheric conditions (neutral pH). Macro-cell and micro-cell corrosion in concrete were tested using both modified ASTM G109 prisms and concrete beams with 6 embedded black steel bars. Unfortunately, these tests proved inconclusive; all of the steel remained passive. This was a result of casting a high quality concrete in laboratory conditions which ultimately lead to minimal diffusion of the anti-icing solutions. Therefore, it is recommended that for short term corrosion testing (<2 years), poor quality concrete or cement paste should be used. Micro-cell testing in synthetic concrete pore solution contaminated with the anti-icing solutions was conducted in order to obtain results in the period of the M.A.Sc. program and to directly observe the corrosion. The initial concentration of Cl- in each solution was 0.00% Cl-; this was incrementally increased by 0.005% Cl-/week. Potentiostatic linear polarization to resistance measurements and pH measurements were used to monitor the corrosion on a weekly basis. The results of this test showed that MgCl2 has the most detrimental effects due to the drop in pH (from 13.5 to 9.1) caused by Mg replacing Ca in Ca(OH)2 to form the less soluble Mg(OH)2. The transition from passive to active corrosion initiated at 0.7, 0.4-0.9, 0.6 and 0.6% Cl- for NaCl, MgCl2, CaCl2 and multi Cl-, respectively. The active corrosion current densities were 11mA/m2 for NaCl, CaCl2 and multi Cl-, whereas MgCl2 had active corrosion rates of ~100 mA/m2. One bar exposed to CaCl2 showed corrosion rates as high as 600 mA/m2. This was a result of crevice corrosion between the shrink fitting and the rebar. Once the expansive corrosion products broke through the shrink fitting and ample supply of oxygen became available, allowing the corrosion rates to spike dramatically. The following steels were tested directly in the diluted solution in a cyclic corrosion chamber: stainless steels: 304L, 316LM, 2101, 2205, 2304, XM28; corrosion resistant steel reinforcing bars (rebar): galvanized rebar, guard rail (galvanized plate steel) and MMFX; carbon steels: black steel rebar, box girder, drain, weathering steel. The reinforcing bars were virgin steels whereas the remaining steels were components from the field. The testing regime followed SAE J2334 using the anti-icing solutions diluted to 3% by wt. Cl- as the immersion liquid. Unfortunately, the mutli Cl- solution was not tested due to time constraints. The mass change per unit area was measured every five cycles. All stainless steels exposed to all anti-icing solutions exhibited similar changes in mass per unit area, less than 10 g/m2. All plain carbon steels including weathering steel exhibited mass changes per unit area of more than 1000 g/m2 with some variability between the various anti-icing solutions and steel types, although the black steel rebar typically outperformed the other carbon steels. The corrosion products of MMFX were non-adherent, resulting in inconclusive results. The galvanized layer on the guard rail, which had been exposed to the environment in service, proved to be more protective than the fresh zinc coating on the galvanized rebar. When exposed to the MgCl2 solution, the mass change of both new and used galvanized steels was comparable to that found in the stainless steels. When exposed to NaCl solutions, the galvanized guard rail also exhibited this trend, whereas the new galvanic coating did not, suggesting that with exposure to the atmosphere a galvanic coating will protect the steel against NaCl. In all cases galvanized steel exposed to CaCl2 solutions exhibited mass changes per unit area of less than 100 g/m2 this is considered moderate, as this value is one order of magnitude higher than the stainless steels and one order of magnitude lower than the carbon steels exposed to the same test. It is recommended that galvanic coatings be utilized in areas heavily exposed to anti-icing solutions. The weathering steel offers no advantages over carbon steels when directly exposed to anti-icing solutions. Furthermore, in areas with high amounts of exposed galvanized steel, CaCl2 should be avoided. Between the four solutions tested, NaCl solutions are recommended as the anti-icing agents that, overall, causes the least amount of damage to both the reinforcing steel in concrete and to exposed metallic components. NaCl is followed by multi Cl- and CaCl2. Even though MgCl2 causes less damage when directly exposed to carbon steels and galvanized steels than CaCl2, it is much easier to repair external components than internal components. Therefore, MgCl2 is not recommended.

The corrosion of the reinforcing steel in concrete by de-icing salts is one of the major issues concerning the durability of reinforced concrete. Different methods have been used to protect the reinforcing steel, but still corrosion of reinforced structures continues to be a big problem causing enormous costs in their restoration and rehabilitation. The continuity of the pores of concrete plays a crucial role in the corrosion of the reinforcing steel. The ingress of corrosive species, such as chloride ions, oxygen and water, through the pores of the concrete cover cause the breakdown of the passive layer formed on the steel by the high pH of the concrete. The use of supplementary cementitious materials (SCM) in the production of high performance concrete (HPC) improves its resistance to corrosive species as a result of the pozzolanic reaction which forms more calcium silicate hydrates (C-S-H). Most of the studies about the corrosion of the reinforcement in HPC have been carried out in sound concrete. However, very few works have been reported on the corrosion of steel in cracked concrete. The crack pattern on HPC is very distinct from that formed on ordinary portland cement (OPC) concrete, which may result in different corrosion mechanisms of the reinforcing steel. The objective of the present work consisted in the evaluation of the corrosion of reinforcing steel in cracked HPC and OPC concrete under different exposure and loading conditions. For that purpose, two sets of beams of HPC (containing fly ash or slag) and two sets of OPC concrete were cast. The difference between the OPC concretes was the date of casting. Three sets of reinforcing steel probes were embedded in each beam at different locations. All the beams were cracked at midspan by the four-point method. Eight beams of each concrete were coupled in pairs and partially immersed in a solution of de-icing salts every two weeks. In this way, one set of the corrosion probes was non-submerged (top) while the other two were completely submerged (one at the crack level and the other at the bottom). Two pairs of beams were subjected to static loading whereas the other two were under cyclic loading. The corrosion potentials readings were taken daily by a data acquisition system, whereas the corrosion rates were determined by the Linear Polarization technique using a corrosion monitoring system. According to the results obtained, the corrosion rates of the submerged and non-submerged probes are very low. This behaviour is observed for the four concretes and for both loading conditions. The type of loading did not influence the corrosion rates of these probes, which were in the same range for all the concretes. On the other hand, the probes close to the crack showed higher corrosion rates, especially those under cyclic loading. In general, the OPC concrete cast during the winter presented the highest corrosion rates for both loading conditions, followed by the OPC concrete cast in the summer (as were both HPCs), then by HPC-Slag and HPC-Fly Ash, which showed the lowest values. In most of the cases there was a good agreement between the corrosion potentials and the corrosion rates, so that the OPC concretes exhibited the most negative values. The lower corrosion of the probes in the HPC-Fly Ash and HPC-Slag beams was ascribed to the continued pozzolanic activity, which may result in the self-healing of the crack with time. The probes close to the crack in the dynamically loaded beams experienced higher corrosion than those in the static beams. In some cases the corrosion rate reached values above 100 mm/year. The lower corrosion of the probes in the static beams was attributed to the self-healing of the crack. The formation of additional microcracks in the dynamic beams during cyclic loading may be responsible for their higher corrosion. The corrosion potential of the rebar cage shifted to more negative values during cyclic and static loading. This change in the potential was associated with stress concentration of the reinforcement surface, making it more active. Although the shift in the potential was not really significant, this may have important consequences in practice where the concrete is subjected to higher loads.

Not available / text

Concrete is strong in compression; however, it is quite fragile in tension. To overcome this flaw, concrete is frequently reinforced with bars typically made of low grade, low carbon steel. The environment inside of concrete is favorable for steel; unfortunately when passive steel is exposed to chlorides, active corrosion can initiate, resulting in damage to the structure. One source of chloride contamination is through anti-icing agents which are used to inhibit the formation of ice on roadways, ensuring safe driving conditions. This represents a serious concern from both the cost associated with rehabilitation (Canadian infrastructure deficit in 2003 was $125 billion [1]) and as a safety concern to the public. In Canada, 5 million tonnes of road salts are used each year [2], of which Ontario uses 500 to 600 thousand tonnes [3]. As a result, the Ministry of Transportation Ontario (MTO) has requested a study of four frequently used anti-icing agents: 25.5% NaCl, 31.5% MgCl2, 37.9% CaCl2 and 32.6% multi Cl- (12% NaCl, 4% MgCl2 and 16% CaCl2). The objective of the study is two-fold, the first is comparing the effects of the solutions on steel embedded in concrete (high pH environment) and the second is to compare the effects of the anti-icing agents to a variety of construction steels in atmospheric conditions (neutral pH). Macro-cell and micro-cell corrosion in concrete were tested using both modified ASTM G109 prisms and concrete beams with 6 embedded black steel bars. Unfortunately, these tests proved inconclusive; all of the steel remained passive. This was a result of casting a high quality concrete in laboratory conditions which ultimately lead to minimal diffusion of the anti-icing solutions. Therefore, it is recommended that for short term corrosion testing (<2 years), poor quality concrete or cement paste should be used. Micro-cell testing in synthetic concrete pore solution contaminated with the anti-icing solutions was conducted in order to obtain results in the period of the M.A.Sc. program and to directly observe the corrosion. The initial concentration of Cl- in each solution was 0.00% Cl-; this was incrementally increased by 0.005% Cl-/week. Potentiostatic linear polarization to resistance measurements and pH measurements were used to monitor the corrosion on a weekly basis. The results of this test showed that MgCl2 has the most detrimental effects due to the drop in pH (from 13.5 to 9.1) caused by Mg replacing Ca in Ca(OH)2 to form the less soluble Mg(OH)2. The transition from passive to active corrosion initiated at 0.7, 0.4-0.9, 0.6 and 0.6% Cl- for NaCl, MgCl2, CaCl2 and multi Cl-, respectively. The active corrosion current densities were 11mA/m2 for NaCl, CaCl2 and multi Cl-, whereas MgCl2 had active corrosion rates of ~100 mA/m2. One bar exposed to CaCl2 showed corrosion rates as high as 600 mA/m2. This was a result of crevice corrosion between the shrink fitting and the rebar. Once the expansive corrosion products broke through the shrink fitting and ample supply of oxygen became available, allowing the corrosion rates to spike dramatically. The following steels were tested directly in the diluted solution in a cyclic corrosion chamber: stainless steels: 304L, 316LM, 2101, 2205, 2304, XM28; corrosion resistant steel reinforcing bars (rebar): galvanized rebar, guard rail (galvanized plate steel) and MMFX; carbon steels: black steel rebar, box girder, drain, weathering steel. The reinforcing bars were virgin steels whereas the remaining steels were components from the field. The testing regime followed SAE J2334 using the anti-icing solutions diluted to 3% by wt. Cl- as the immersion liquid. Unfortunately, the mutli Cl- solution was not tested due to time constraints. The mass change per unit area was measured every five cycles. All stainless steels exposed to all anti-icing solutions exhibited similar changes in mass per unit area, less than 10 g/m2. All plain carbon steels including weathering steel exhibited mass changes per unit area of more than 1000 g/m2 with some variability between the various anti-icing solutions and steel types, although the black steel rebar typically outperformed the other carbon steels. The corrosion products of MMFX were non-adherent, resulting in inconclusive results. The galvanized layer on the guard rail, which had been exposed to the environment in service, proved to be more protective than the fresh zinc coating on the galvanized rebar. When exposed to the MgCl2 solution, the mass change of both new and used galvanized steels was comparable to that found in the stainless steels. When exposed to NaCl solutions, the galvanized guard rail also exhibited this trend, whereas the new galvanic coating did not, suggesting that with exposure to the atmosphere a galvanic coating will protect the steel against NaCl. In all cases galvanized steel exposed to CaCl2 solutions exhibited mass changes per unit area of less than 100 g/m2 this is considered moderate, as this value is one order of magnitude higher than the stainless steels and one order of magnitude lower than the carbon steels exposed to the same test. It is recommended that galvanic coatings be utilized in areas heavily exposed to anti-icing solutions. The weathering steel offers no advantages over carbon steels when directly exposed to anti-icing solutions. Furthermore, in areas with high amounts of exposed galvanized steel, CaCl2 should be avoided. Between the four solutions tested, NaCl solutions are recommended as the anti-icing agents that, overall, causes the least amount of damage to both the reinforcing steel in concrete and to exposed metallic components. NaCl is followed by multi Cl- and CaCl2. Even though MgCl2 causes less damage when directly exposed to carbon steels and galvanized steels than CaCl2, it is much easier to repair external components than internal components. Therefore, MgCl2 is not recommended.

No description available.

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 120-121). / xii, 282 leaves, bound ill. (some col.) 29 cm

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.