Construction Materials Institute Research Projects Durability of Reinforced Concrete Structures in Persian Gulf Abstract Corrosion of steel reinforcements in concrete has become the main factor in early, premature deterioration and failure, of concrete structures. This deterioration process is responsible for huge financial costs spent on the repair and maintenance of RC structures annually. Is this regard, Persian Gulf region is if more importance, due to its hot climate which makes one of the most aggressive exposures for concrete structures. Construction of concrete structures in Persian Gulf has increased during past decades due to its special and strategic location (widely Gas and Oil industries). Unfortunately, today, many of these structures are suffering from steel reinforcement corrosion. Concerning the severity of the problem, Construction Materials Institute at the University of Tehran started a Research project on Durability issue in Persian Gulf in 2001 and in conjunction with the Iran’s Management and Planning Organization. The main goals of these projects were: 1- Establishing the First Academic Exposure Site in Persian Gulf region. 2- A complete and conceptual test design and concrete specimens preparation. 3- Periodic Sampling of Concrete Specimens, Testing and Analyzing for Chloride diffusion in concrete. 4- Developing DuraPGulf software to predict the service life of concrete structures based on time to corrosion initiation. This paper presents a brief look at several aspects of this extensive research project at the Construction Materials Institute. Keywords: Corrosion, concrete, durability, Persian Gulf, Exposure site, DuraPGulf 1- Introduction 1-1- Persian Gulf Region 1-1-1-Geography Persian Gulf, located in the south of Iran is a shallow marginal sea of Indian Ocean that lies between southwestern of Iran and the Arabian Peninsula, has an area of 225,000 square kilometers. Its length is about 990 km, its width varies from 300 km to 180 km at the strait of Hormoz and the depth rarely exceeds a depth of 90 m.
Transcript
Construction Materials Institute
Research Projects
Durability of Reinforced Concrete Structures in Persian Gulf
Abstract
Corrosion of steel reinforcements in concrete has become the main factor in early, premature deterioration and failure, of concrete structures. This deterioration process is responsible for huge financial costs spent on the repair and maintenance of RC structures annually. Is this regard, Persian Gulf region is if more importance, due to its hot climate which makes one of the most aggressive exposures for concrete structures. Construction of concrete structures in Persian Gulf has increased during past decades due to its special and strategic location (widely Gas and Oil industries). Unfortunately, today, many of these structures are suffering from steel reinforcement corrosion. Concerning the severity of the problem, Construction Materials Institute at the University of Tehran started a Research project on Durability issue in Persian Gulf in 2001 and in conjunction with the Iran’s Management and Planning Organization. The main goals of these projects were: 1- Establishing the First Academic Exposure Site in Persian Gulf region. 2- A complete and conceptual test design and concrete specimens preparation. 3- Periodic Sampling of Concrete Specimens, Testing and Analyzing for Chloride diffusion in concrete. 4- Developing DuraPGulf software to predict the service life of concrete structures based on time to corrosion initiation. This paper presents a brief look at several aspects of this extensive research project at the Construction Materials Institute. Keywords: Corrosion, concrete, durability, Persian Gulf, Exposure site, DuraPGulf
1- Introduction
1-1- Persian Gulf Region
1-1-1-Geography Persian Gulf, located in the south of Iran is a shallow marginal sea of Indian Ocean that lies between southwestern of Iran and the Arabian Peninsula, has an area of 225,000 square kilometers. Its length is about 990 km, its width varies from 300 km to 180 km at the strait of Hormoz and the depth rarely exceeds a depth of 90 m.
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1-1-2- Climate
Persian Gulf has a notoriously unpleasant climate. Temperatures are high, though winters may be quite cool at the northwestern extremities. The sparse rainfall occurs mainly as sharp downpours between November and April and is higher in the northeast.
1-1-3- Construction in Persian Gulf
Due to strategic location of Persian Gulf, many structures and infrastructures have been constructed in this region within past decades. Today, many of these structures suffer from corrosion damages which may affect the economy of Persian Gulf. The main reasons for the poor performance of concrete structures are poor workmanship and lack of knowledge of the deterioration mechanisms which result in insufficient planning and wrong estimation of environmental effects.
1-1-4- Corrosion in Persian Gulf
Today, many of new and old concrete structures in coast of Persian Gulf and Oman Sea are suffering from corrosion. Extensive Inspections on marine structures have been carried out during last 4 years in this region. Observations prove the severity of corrosion issue in this region.
1-2- Establishment of First Academic Exposure Site
CMI established first academic exposure site in Bandar-Abbas city, Iran in conjunction with BARCO Company in 2002. It was designed to provide Submerged, Tidal, splash, atmospheric and soil exposure conditions for concrete specimens. It is located near Fulad Jetty in order to provide enough protection on the site and specimens. 2- Experimental program 2-1- Materials The cementitious materials used in this study were Portland cement (PC) equivalent to ASTM Type II, silica fume (SF) obtained from Azna ferro-silicon alloy manufacture. The aggregates used were crushed limestone from Metosak plant and were graded according to ASTM C 33. The coarse aggregate had maximum size of 12.5 mm and specific gravity and absorption values of 2.79 and 1.9%, respectively. The fine aggregate had specific gravity and absorption values of 2.59 and 3.2%, respectively. The fineness modulus of fine aggregates was 3.2. Polycarboxylate ether polymer superplasticizer and lignosulphonate plasticizer were used for the mixes in order to improve the workability of fresh concrete. 2-2- Mixture proportions Four separate series of concrete mixes were developed at the water to cementitious ratios of 0.35, 0.40, 0.45 and 0.50. All series included four SF mixes with 5%, 7.5%, 10% and 12.5% silica fume and the control mix without any admixture. All series were proportioned to have the same total cementitious materials content of approximately 400 kg/m3 which is typical of those used in the
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marine concrete structures in Iran. 2-3- Specimen preparation, casting and curing The concrete mixtures were prepared in the laboratory of the Construction Materials Institute at the University of Tehran using a 0.1 m3 countercurrent pan mixer. The freshly mixed concrete was tested for air content according to ASTM C 231, pressure method; slump according to ASTM C 143 and unit weight in accordance with ASTM C 138. Cubes of 150×150×150 mm and prisms of 150×150×600 mm in dimension were cast in steel mold and compacted on a vibrating table. The 150 mm cubes were used for the determination of compressive strength while the prisms were supposed to be tested for chloride diffusion. The molds were covered with the burlap kept wet for 24 hours after casting. The specimens were removed from the molds and were allowed to cure in water saturated with calcium hydroxide at 21 °C for 28 days. After the curing period prism specimens were sealed on four sides using epoxy polyurethane coating to ensure one-dimensional diffusion. 2-4- Exposure condition The specimens were moved to an investigation site located in Bandar-Abbas, Iran and subjected to different exposure condition in Persian Gulf. The Gulf water is so saline due to the close nature and high evaporation rate. The climatic factors include large fluctuations in daily and seasonal temperature and humidity regimes. Temperature can vary by as much as 30 °C during a typical summer day and relative humidity can range from 40 to 100% within 24 hours. 2-5- Sampling and testing Sampling was carried out at the ages of 3, 9 and 36 months. Each time, 100 mm were cut from end of the prism specimens. The cut surface of the remaining part were coated and moved back to the exposure condition for future sampling. The 150×150×100 mm slices were taken to the laboratory for the determination of the chloride diffusion at the above ages. A nominal 45 mm diameter core was taken from each slice for chloride concentration profiles. Each core was grinned in 8 increments from the finished surface to an estimated depth of chloride penetration. The dust from each layer was collected and analyzed separately for acid-soluble chloride according to ASTM C 1152, “Standard Test Method for Acid-Soluble Chloride in Mortar and concrete” and ASTM C 114, part 19. The cross-sectional area of a 45 mm diameter core is large enough to represent the concrete so that there is no need to be concerned about variations from sample to sample due to varying aggregate contents. 150 mm cubes were tested in compression at 7, 28 and 154 days with accordance to DIN 1048. 3- DuraPGulf
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Durability based design of RC structures has received a great concern in the recent decades. In Iran, the need for a model for service life design of concrete structures in Persian Gulf region is highly necessary. I general, current version of DuraPGulf is a model based on time to corrosion initiation of steel bars in concrete. In this research, criterion for steel corrosion is the “chloride threshold value” on the surface of steel embedded in concrete. Time to chloride initiation is calculated based on solving the Fick’s second law of diffusion. It is supported with a user friendly interface that helps the users for easier use of the program. DuraPGulf database is based on the results obtained from a complete set of field investigations on chloride diffusion such as water to cement ratio, silica fume content, curing condition, exposure condition, environment temperature and surface coating. For a specific mix design, the predicted service life is calculated using n dimensional MLS method. The software would help engineers to design RC Structures with a better understanding of the durability concepts.
Further information on DurapGulf can be found: Durability
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Research Projects 4- Durability Team at Construction Materials Institute Supervisors
Late Dr.Mahdi Ghalibafian Professor
Dr. Mohammad Shekarchizadeh Assistant Professor, Director
Dr. AliAkbar Ramezanianpoor Professor
Dr. Mohsen Tadayon Assistant Professor
Current members
Alireza rafiee Graduate Research assistant, M.Sc
Hamed Layssi Graduate Research assistant, M.Sc
Farhad Pargar Graduate Research assistant, M.Sc
Farid Moradi Graduate Research assistant, M.Sc
Ali Doosti Graduate Research assistant, M.Sc
Previous members
Rouhollah aalizadeh PhD student @ University of Ottawa
Poorya Ghods PhD student @ University of Carleton
Hooman Chini PhD student @ NTNU, Norway
Meghdad Hoseini PhD student @ University of Alberta
Shabnam Montazer Namvaran Consultino Co.
Technicians
Mohsen Golzari Construction Materials Institute Mahmood Reihani Construction Materials Institute
