https://doi.org/10.14311/APP.2022.33.0624 Acta Polytechnica CTU Proceedings 33:624–630, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague REDUCTION OF DISSOLVED OXYGEN IN MINIMIZING CORROSION Mary Grace Ventanillaa, Jason Ongpenga, ∗, Nishida Takahirob, Keiyu Kawaaic a De La Salle University, Department of Civil Engineering, 2401 Taft Avenue, 0922 Manila, Philippines b Port and Airport Research Institute, Nagase 3-1-1 Yokosuka-shi, 239-0826 Kanagawa, Japan c Ehime University, Bunkyo-Cho 3 Matsuyama-shi Emime 790-0826, Japan ∗ corresponding author: jason.ongpeng@dlsu.edu.ph Abstract. Concrete structures are susceptible to corrosion especially when exposed to marine environment. In order to minimize the corrosion in reinforced concrete, reduction of dissolved Oxygen (DO) in mixing water is recommended. The DO is the measurement of the amount of free Oxygen that is dissolved in water which is proportional to the corrosion rate of steel bars inside concrete. In this paper, the use of industrial waste/by-products, agricultural waste, natural minerals, and green inhibitors as additive for cement in reducing the DO level of the mixing water was explored. Candidate materials from different types of agricultural waste, industrial waste, natural minerals, and green inhibitors. The percentage difference of DO were computed for all types of materials as ash or powder or extract in room temperature. This is the percentage difference of DO level in distilled water and the solution mixed with the candidate material having a mass ratio of 3 : 2 and/or 3 : 1. Results showed that more than 90% reduction of DO level were achieved when mixed with ginger extract, ginger powder, aloe vera extract, ginger pulp, and rice hull ash. Future experimental studies using the candidate materials producing reinforced concrete specimens with high reduction of DO level in mixing water is recommended. Keywords: Corrosion, dissolved oxygen, waste. 1. Introduction Concrete is considered as most extensively used con- struction material globally and each component has contributed to an environmental impact [1]. It is made up of aggregates (coarse and fine) and paste (cement and water). Concrete industry is one of the largest consumers of natural resources, therefore at- taining reliable, vigorous, sustainable and economical concrete products has been proposed. Cost of con- crete products has increased over the years resulting to increase in the shortage of aggregates and wors- ens situation. Use of industrial and agricultural by- products have gained interests as a potential replace- ment to concrete manufacturing process [2] since they are rich in silica as well as alumina which are suited as supplementary cementitious material and superior reactivity [3]. Through the years, there is scarcity of natural resources. To address such issues, substitu- tion to concretes components could be an answer to environmental impacts, however, substitute materi- als should impart comparable or enhanced attributes compared to the natural concrete [2]. Several factors affect the durability of reinforced concrete structures such as change in temperature that could lead to cracks due to shrinkage, amount of moisture that could permeate concrete, physical factors (strength, resistance to wear and tear, and abrasion), chemical factors like aggressive agents that could interfere with the cement paste and biological factors (organisms) that could damage concrete. One way of achieving durable concrete is to study corro- sion which can be defined as "destruction of metal by either chemical, electrochemical or electrolytic reac- tion within its environment" according to American Concrete Institute. It is a global problem that deteri- orates the durability of concrete structures [5]. Also, corrosion of steel in concrete is one of the main rea- sons for premature failure where in marine environ- ment, chloride ingress is the probable cause for break- ing the passivating layer and the onset of extreme corrosion [6]. Most marine structures are susceptible to corrosion as it is located near marine environment and may trigger chloride intrusion [7]. Nowadays, it is necessary to inspect and alleviate corrosion to ex- tend serviceability of RC structures and is accepted worldwide [4]. Three parameters that greatly affect corrosion of reinforcing bars in concrete are shown in Figure 1. These are Oxygen, pH level, and the per- meability of concrete. In this research, reduction of Oxygen through dissolved Oxygen (DO) level in mix- ing water is the main focus to prevent corrosion inside concrete. Additives such as industrial waste/by-products, agricultural waste, natural minerals, and green in- 624 https://doi.org/10.14311/APP.2022.33.0624 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 33/2022 Reduction of Dissolved Oxygen in Minimizing Corrosion Figure 1. Graph showing relationship of Embodied Carbon for cements by clinker content, source [4] hibitors are considered as candidate materials in re- ducing the DO level of mixing water that could affect concretes resistivity to corrosion. The selection of these materials is based on the result of related stud- ies utilizing them as replacement to cement or aggre- gate that enhances concrete’s durability. Industrial wastes are known to have high pH level which is be- ing measured under varying temperatures to enhance its reactivity [8]. Since these wastes no longer have in- dustrial application, converting them to construction materials could improve its properties. In addition, agricultural waste is also found to contain minerals that could improve various properties of concrete. Natural minerals as admixture could enhance resis- tance of concrete to chloride penetration [9]. Plant extracts are also considered as these were proven to be good corrosion inhibitors [10]. Shown in Table 1 is the process of accumulation of the candidate ma- terials from previous researchers. Numerous literatures are available considering cor- rosion in reinforced concrete structures. However, researches associated with Oxygen - reducing mate- rials haven’t been thoroughly studied. Using key- word searches "Oxygen", "permeability", "concrete" and "corrosion" resulted to 34 published journals. It is evident that researches concerning on the effects of DO in concrete corrosion has an average of only two publications per year and in which approximately one publication per year under Cement and Concrete Re- search. This study introduces the use of waste ma- terials, plants and natural minerals to contribute sig- nificantly in the performance of reinforced concrete, particularly, in the reduction of Oxygen that can in- hibit corrosion on the steel bars. 2. Apparatus and materials 2.1. Dissolved Oxygen meter Sufficient amount of free Oxygen at the initial curing stage is critical in the formation of the passive layer protecting the reinforcing steel bars [26]. There is a relevant connection when aggregates in concrete have open porosity as it could increase the permeability of Oxygen [27]. Corrosion rate of steel is higher on areas with high Oxygen contents. Measuring the Oxygen level of water at a certain location can be used to foresee the performance of different alloys in the same environment [28]. Oxygen permeability in reinforced concrete is high using deformed bars which makes it more susceptible to corrosion than plain bars since cracks begin at the ribs of the rebars and eventually becomes surface cracks [29]. DO is the measure of the amount of free Oxygen that is dissolved in water. Fac- tors such as atmospheric pressure, temperature and salinity determine the amount of Oxygen that can be dissolved physically in water. Rate of corrosion pro- cess on the reinforcing steel bars in concrete can be controlled by DO on pore solution, thus, reduced DO could enhance corrosion resistance [30]. 2.2. Candidate materials Materials were chosen based on its effect on the per- formance of concrete. Related studies as presented in Table 1, utilized the use of these candidate materials as an additive or replacement to either cement and aggregates. Table 2 to 4 summarize the candidate 625 M. G. Ventanilla, J. Ongpeng, N. Takahiro, K. Kawaai Acta Polytechnica CTU Proceedings Corrosion inhibitors Candidate materials Process of Accumulation Source Wastes Industrial waste Blast Furnace Slag Acquired from industry as it is a by-product of steel manufacturing [11] Bottom Ash Acquired from industry as it is aby-product of coal power plants [12] Fly Ash Acquired from industry as it is aby-product of coal power plants [13] Granite / Marble Dust Acquired from industry producing marble / granite as tiles [14] Waste Glass Powder Crushing, Sieving using Ball Mill [15] Wood Waste Ash Incineration, Combustion [16, 17] Agri- cultural waste Coconut Husk Ash Burning under controlled temperature orincineration, pyrolysis [18] Rice Husk Ash Burning under controlled temperature or incineration, through annealing furnace [19] Corn Cob Ash Burning under controlled temperature [20] Sugarcane Bagasse Ash Burning under controlled temperature or incineration, combustion, acquired from sugar mill [13, 17] Seashell Cleaning, Drying, Crushing /Pulverizing, Furnace [21] Natural Volcanic Ash Readily available on areas near volcanoes [22] minerals Natural Zeolite Mining [23] Plant extracts Water Hyacinth Extraction, Drying, Grinding [24] Aloe Extraction [10] Ginger Extraction, Drying [25] Table 1. Process of accumulation adapted from previous researches. Agricultural wastes Specimen Ash Powder3 : 2 3 : 1 3 : 2 3 : 1 Bagasse ash Bagasse ash AW-BA-2 AW-BA-1 Coconut husk ash Coconut husk ash AW-CHA-2 AW-CHA-1 Corn cob ash Corn cob ash AW-CCA-2 AW-CCA-1 Rice hull ash Rice hull ash AW-RHA-2 AW-RHA-1 Shells Oyster shell AW-SS-A-OS-2 AW-SS-A-OS-1 AW-SS-P-OS-2 AW-SS-P-OS-1 Yellow cockles AW-SS-A-YC-2 AW-SS-A-YC-1 AW-SS-P-YC-2 AW-SS-P-YC-1 Strombus sicad AW-SS-A-SC-2 AW-SS-A-SC-1 AW-SS-P-SC-2 AW-SS-P-SC-1 Brown scallop AW-SS-A-BS-2 AW-SS-A-BS-1 AW-SS-P-BS-2 AW-SS-P-BS-1 Clamrose big AW-SS-A-CB-2 AW-SS-A-CB-1 AW-SS-P-CB-2 AW-SS-P-CB-1 Granular ark AW-SS-A-GA-2 AW-SS-A-GA-1 AW-SS-P-GA-2 AW-SS-P-GA-1 Distant scallop AW-SS-A-DS-2 AW-SS-A-DS-1 AW-SS-P-DS-2 AW-SS-P-DS-1 Green mussel AW-SS-A-GM-2 AW-SS-A-GM-1 AW-SS-P-GM-2 AW-SS-P-GM-1 Table 2. Agricultural wastes as candidate materials in reducing DO level. 626 vol. 33/2022 Reduction of Dissolved Oxygen in Minimizing Corrosion Industrial wastes Specimen Ash Powder3 : 2 3 : 1 3 : 2 3 : 1 Blast furnace slag Blast furnace slag IW-BFS-2 IW-BFAS-1 Bottom ash Bottom ash IW-BA-2 IW-BA-1 Fly ash Fly ash IW-FA-2 IW-FA-1 Marble / Granite waste dust Marble / Granite waste dust IW-WWA-2 IW-WWA-1 Table 3. Industrial waste as candidate materials in reducing DO level. Natural mineral Specimen ASH Powder3 : 2 3 : 1 3 : 2 3 : 1 Volcanic pumice Volcanic pumice NM-VP-2 NM-VP-1 Natural zeolite NATURAL ZEOLITE NM-NZ-2 NM-NZ-1 Natural mineral Plants Specimen Extract Powder3 : 2 3 : 1 3 : 2 3 : 1 Aloe vera Aloe vera P-AV-2 P-AV-1 Ginger Ginger extract 1 P-GE1-2 P-GE1-1 Ginger extract 2 P-GE2-2 P-GE2-1 Ginger pulp P-GP-2 P-GP-1 Ginger powder P-GPW-2 P-GPW-1 Water hyacinth Water hyacinth P-WH-2 P-WH-1 Table 4. Natural and plants as candidate materials in reducing DO level. materials based on their ratio with water and type whether powder, ash or extract. A reducibility effect in the DO was found using 3 : 1 and 3 : 2 mass ratio (Water : Specimen Ratio), therefore, it was adapted and was considered that it may have a possibility in obtaining the same effect when combined with con- crete [31]. Candidate materials that were burned, powdered and extracted have composition similar to cement and aggregates that may replace them or be added to enhance concrete properties. Usually, those mate- rials that were burned and became ash are associated with cement properties, powdered materials are asso- ciated with aggregates while extracted materials may serve as coating to metals to reduce corrosion. In this study, candidate materials are used as an addi- tive to mixing water in reducing DO level. Figure 2 shows the DO meter used and the sample candidate materials. 3. Methodology Candidate materials were gathered from different sources such as industrial plants, farms, quarries and plantation. Industrial wastes were readily available since these are by-products being disposed, whereas, agricultural wastes were burned to form ash which can produce properties similar to cement. Moreover, minerals are also readily available as they are part of natural resources while plants, on the other side, were gathered from plantation and were extracted. 3.1. Mixing Procedure 300ml of distilled water was used to determine the baseline value of DO to identify the percentage dif- 627 M. G. Ventanilla, J. Ongpeng, N. Takahiro, K. Kawaai Acta Polytechnica CTU Proceedings Figure 2. DO meter and sample candidate materials. Figure 3. Candidate materials for DO testing. ference of DO when mixed with the candidate mate- rials. DO of water was found out to be 5.08ppm. DO of the mixture were measured by placing 100grams and 200grams of materials into a bottle with 300ml of distilled water (3 : 1 and 3 : 2 ratio), stirred until thoroughly mixed to form a solution. At room tem- perature (average 26 degrees Celsius), DO level was measured using DO meter. Except for the case of gar- lic powder and RHA, the ratio used was 10 : 1 since these materials were observed to be low density, thus, bagasse ash and wood waste ash were tested only in 3 : 1 ratio. Figure 3 shows how the specimens were prepared prior to DO testing. 3.2. Percentage difference of DO The equation used to determine the DO is shown be- low. %DOdif f = DOwater − DOsolution DOwater · 100 (1) where: • DOwater = DO level of distilled water at room tem- perature • DOsolution = DO level of mixed solution at room temperature 3.3. Results and Discussion Shown in Table 5 are the materials with highest DO level reduction represented by the percentage differ- ence resulted to a reduction of more than 90% which include ginger extract, ginger powder, aloe vera, gin- ger pulp, and rice hull ash. Materials DO diff.(ppm or mg/L) % DO diff P-GE-1 4.99 98.23 P-GE-2 4.98 98.03 P-GPW 4.97 97.83 P-AV-1 4.96 97.64 P-AV-2 4.91 96.65 P-GP-1 4.81 94.69 AW-RHA 4.77 93.90 Table 5. Top percentage DO difference of the can- didate materials. 628 vol. 33/2022 Reduction of Dissolved Oxygen in Minimizing Corrosion 4. Conclusion Corrosion inside concrete is very complex with a lot of factors contributing to it. In this study, the objec- tive is to reduce the DO level of mixing water that can reduce the corrosion of steel rebars inside con- crete. Identification of candidate materials from agri- cultural waste, industrial waste, minerals, and plants were made in the region. 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