Investigation of measures for the prevention of corrosion of steel in concrete structures

In this study, which was done with the intention of developing reinforced concrete products that are resistant against corrosion, efficiencies of additives in the inhibition of reinforcement corrosion in reinforced concrete samples evaluated by producing reinforced concrete samples that contain various additives and partially corroded steel reinforcements from old buildings were used to build reinforced concrete samples. Cathodic protection processes with external current and galvanic anode were applied on these samples; and the efficiency of cathodic protection on preventing corrosion is evaluated.Reinforced concrete samples were poured in the form of a cylinder lollipop with measurement of 70x40 mm by planting steel reinforcements into the concrete. A total of seven different sample groups for each and every corrosion inhibiting additive were produced. Also, three control sample groups for each one these different sample groups were also produced. In the first group of samples, silica fume which has the trademark of Tecno Silica, was added to the concrete mortar mixture. In the second group of samples, organic and inorganic based mixture inhibitor which contained nitrogen and which has the trademark of Sika Ferrogard-901, was added into the concrete mortar mixture. In the third group of samples, emulsion which is of silane and siloxane composition and which has the trademark of Sika Gard-703 W was spread on the outer surface of the concrete. In the fourth group of samples, special amino alcohol based, organic or inorganic mixture inhibitor which has the trademark of Sika Ferro Gard-903 was spread on the outer surface of the concrete. In the fifth group of samples, epoxy resin based coating material which has a solvent with two components and which has the trademark of Tecno bond 650 was spread onto the outer surface of the steel reinforcement. In the sixth group of samples, steel reinforcements were covered with zinc by the use of hot dipped galvanize method. In the seventh group of samples, cement based, polymer modified coating material which has the trademark of Sika Monotop 610 and which contains silica fume and corrosion inhibitor was spread onto the outer surface of the steel reinforcement. Rest of the groups were produced as control samples that do not contain additives.Samples were put through accelerated corrosion by being kept in a salty water solution which had a concentration of 50 gr. Cl- /liter for three months. During this three month period, half-cell potential measurements and corrosion current density measurements were taken regularly. Gecor 8 apparatus was used when measuring the corrosion current density. Lolipop samples which were put through the three month long accelerated corrosion test were broken at the end of this test. Reinforcements were removed and the surfaces of these samples were cleaned. Then, the micro structure of these samples were studied under an Olympus optic microscope with 200 enlargement.The affects of those additives which had been added to the concrete mortar mixture on the compressive strength and splitting tensile strength of concrete were evaluated at the end of a 28 day curing time. The affects of the coating material that were spread on the surface of steel reinforcements on the adherence durabilities of reinforced concrete samples were determined at the end of both 28-day curing period and 90-day accelerated corrosion experiments.Pressure endurances of samples that have Sika Ferro Gard-901 and Tecno Silica trademarked silica fume additive were determined to be 33.5 Mpa and 30.6 Mpa respectively. Pressure endurances of control samples, that belong the samples mentioned above, were determined to be 28.5 Mpa and 27 Mpa respectively. Splitting tensile strengths of samples that have Sika Ferro Gard-901 and Tecno Silica trademarked silica fume additive were determined to be 3.85 Mpa and 4 Mpa, respectively. Splitting tensile strength of control samples that belong to the samples mentioned above were determined to be 2.9 Mpa and 2.9 Mpa, respectively. It has been determined at the end of pressure endurance and splitting tensile strength experiments that Sika Ferro Gard-901 and Tecno Silica concrete additive increased both the pressure endurance and splitting tensile strength of the concrete. This conclusion was reached when Sika Ferro Gard-901 and Tecno Silica additives were compared to the samples.At the end of the adherence strength experiments which were performed after the end of the curing period, it was determined that Sika Ferro Gard-901, Zinc coating and Tecno Silica silica fume increased the adherence strength of reinforced concrete samples, Tecno Bond 650 epoxy based coating and Sika Monotop 610 coating decreased the adherence strengths of reinforced concrete samples and Sika Ferro Gard-903 inhibitor and Gard-703 emulsion did not change adherence strengths of reinforced concrete samples very much. At the end of the accelerated corrosion period, adherence strengths of samples that contain Sika Ferro Gard-901, zinc coating, Tecno Silica silica fume, Tecno bond 650 epoxy coating, Sika Monotop 610 coating, Sika Ferro Gard-903 and Sika Gard-703 W were determined to be 5.27 Mpa; 5.44 Mpa; 4.88 Mpa; 4.16 Mpa; 4.18 Mpa; 5.22 Mpa; 5.29 Mpa respectively. The adherence strengths of control samples that belong to the samples mentioned above are determined to be 3.88 Mpa; 3.8 Mpa; 4.17 Mpa; 3.83 Mpa; 3.74 Mpa; 3.91 Mpa, 4.03 Mpa respectively.At the end of the accelerated corrosion period, corrosion current density of samples that contain Sika Monotop 610, Zinc coating, Tecno Bond 650 epoxy coating, Sika Ferro Gard-901, Sika Ferro Gard-903, Sika Gard-703 W and Tecno Silica silica fume were determined to be 0.14 µA/cm2; 0.36 µA/cm2; 0.19 µA/cm2; 0.29 µA/cm2; 0.42 µA/cm2; 0.20 µA/cm2; 0.31 µA/cm2, respectively. The corrosion current density measurements of control samples that belong to samples mentioned above were determined to be 0.56 µA/cm2; 0.57 µA/cm2; 0.60 µA/cm2; 0.56 µA/cm2; 0.76 µA/cm2; 0.52 µA/cm2, 0.68 µA/cm2 respectively.Additionally, at the end of accelerated corrosion period, half-cell potential values of samples that contain Sika Monotop 610, Zinc cladding, Tecno Bond 650 epoxy cladding, Sika Ferro Gard-901, Sika Ferro Gard-903, Sika Gard-703 W and Tecno Silica silica fume were determined to be -411 mV,-666 mV,-192 mV,-542 mV,-575 mV,-315 mV,-433 mV, respectively. The half-cell potential measurements of control samples that belong to samples mentioned above were determined to be -619 mV, -502 mV,-323 mV,-611 mV,-605 mV, -631 mV, -543 mV, respectively.According to the data that has been obtained, no corrosion has been observed on steel reinforcements and on reinforced concrete samples that are Sika Monotop 610 coated, hot dipped zinc coated and Tecno Bond 650 trademarked epoxy coated. A very thin layer (between 0 ?m and 4 ?m) of oxide was observed on reinforced concrete samples that have Sika Ferro Gard 901 inhibitor additive. However, it was observed that the corrosion current density values which were measured remained at a level that did not create a risk in terms of the endurance of the concrete. Because of this, it was also observed that Sika Ferro Gard 901 additive was able to protect reinforced concrete structures very effectively even when these structures are exposed to environments that contained high levels of chloride for extended periods of time and was also able to prevent any danger from arising in terms of the endurance of the reinforced concrete. A thin layer of oxide (between 5 ?m and 10 ?m, between 5 ?m and 15 ?m, respectively) was observed in reinforced concrete samples that have Tecno Silica silica fume and Sika Ferro Gard 903 inhibitor additives. However, in micro structure studies that were done on control samples, a thicker layer of corrosion (between 25 ?m and 30 ?m) was observed on these samples.This has proven that Tecno Silica silica fume and Sika Ferro Gard 903 additives is able to protect reinforced concrete samples from agressive chloride ions and oxygen that can come from the surrounding area of a concrete structure very effectively. Generally, no corrosion has been observed in reinforced concrete samples that are coated with Sikagard-703 W. A very thin layer of corrosion (between 0 ?m and 3 ?m) was observed in a very small area. Additionally, it was also observed that corrosion current density values that are measured in reinforced concrete samples that contain Sikagard-703 remained at a level that did not pose a risk in terms of the endurance of the concrete. Whereas, a relatively thick layer of corrosion (between 20 ?m and 30 ?m) was encountered in control samples and local corrosion formations were observed in some areas of reinforcements.?14 used rebars are used to produce 200x200x200 mm cubic reinforced concrete samples to represent old reinforced concrete structures.Manufactured reinforced concrete sample is tested before switching on the external current and the half cell potential is measured -475 mV with Cu-CuSO4 reference electrode. This value indicates that the steel reinforcements were corroded. After switching on the external current the halfcell potential is mV. This value indicates that cathodic protection is fully covered and corrosion is stopped completely, because it is lower than potential criteria for reinforcement steels, which is -770 mV, and higher than the over protection limit, which is -950 mV.Reinforced concrete sample is tested before connecting with zinc anode and the half cell potential is measured -235 mV with Cu-CuSO4 reference electrode. This value indicates that the steel reinforcements are in the corrosion uncertainty zone. After applying the galvanic anode protection the halfcell potential ise measured as -363 mV. This value indicates that anodic dissolution of zinc is taking place and providing electrons for cathodic protection of steel reinforcements. However the power of zinc anode is not sufficient for the amount of reinforcements and because of this, the value is not lower than -770 mV. But studies indicate that in case of using a zinc anode, which is big enough, a full cathodic protection can be attainable and on going corrosion of reinforcements can be prevented.Economic evaluation of anti corrosion agents and cathodic protection processes, that are applied to reinforced concrete samples, is done. Coating of steel reinforcements with anti corrosion agents brings a small incremental cost around 0.06% (70 TL) - 0.33% (367 TL), but during service life a high saving ratio around 33% (747 TL) - 41% (920 TL) can be obtained annually. Concrete grout additives cost around 0.10% (123 TL) ? 0.6% (671 TL), but during service life a high saving ratio around 33% (747 TL) - 37% (834 TL) can be obtained annually. Splash coating of steel reinforcements with anti corrosion agents brings a small incremental cost around 0.019% (21 TL) - 0.022% (24 TL), but during service life a high saving ratio around 33% (747 TL) - 37% (834 TL) can be obtained annually.Cathodic protection processes which are applied to protect constructions from reinforcement corrosion brings a small incremental cost around 0.6% (625 TL) ? 0.6% (653 TL), but during service life a high saving ratio around 36.7%(834 TL) - 36.9% (834 TL) can be obtained annually. External current source a cathodic protection system should be established in the new buildings and galvanic anode cathodic protection system should be established in the old buildings in terms of affordability and application requirements.Tecno Silica silica fume inhibitor which added in concrete as an additive were more appropriate according to the comparison of the other additives. During the life of comparisons made between the structure of reinforcement coatings epoxy coating and hot dip galvanizing in terms of affordability came to the fore. Other values are close to each other, although the hot-dip galvanized coating adhesion strength showed superiority. Therefore zinc plating is thought to be more suitable for applications where adherence is very important. Comparision was made between Coatings used on the outer surface of reinforced concrete, Sika Gard 703 W showed a more favorable in terms of cost and corrosion protection.When necessary prevention process and materials applied to the building which has 411,6 square meters floor area, eighty flat and twenty storey in order to protect it from reinforcement corrosion, the building cost that is 112.322 TL will be increased 1164 TL or 1% more but increasing the service life of building, annual cost of per flat may be desreases high amount. So, if prevention methods are applied to our buildings, cost for per building will be recovered within a few years.Key words: Reinforced concrete, corrosion, half-cell potential measurements, compressive strength, corrosion current density measurements, micro-structure, inhibitor, silica fume, adherence, hot dipped zinc coating, epoxy resin.