Concrete Durability in Persian Gulf.pdf

7/27/2019 Concrete Durability in Persian Gulf.pdf

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CONCRETE DURABILITY ISSUES IN THE PERSIAN GULF

Dr. Mohammad ShekarchiProfessor at the Construction Materials InstituteUniversity of TehranTehranIRAN

Engr. Farid MoradiGraduate Student at the Construction Materials InstituteUniversity of TehranTehranIRAN

CBM-CI International Workshop, Karachi, Pakistan Dr. M. Shekarchi and Engr. F. Moradi

ABSTRACT: The Persian Gulf is one of the most aggressive exposure conditions for thedurability of reinforced concrete structures in the world. In this region, chloride diffusionand chloride induced reinforcement corrosion usually leads to a reduced service life ofconcrete structures, which consequently affects the overall economy of the Persian GulfStates.

This paper presents a summary of the state of durability of concrete structures, and repairof affected structures in the Gulf region. Durability and service life based design is oneof the best methods to improve performance of reinforced concrete in a harsh environment.DuraPGulf is a relatively new service-life design model. It provides a realistic predictionof corrosion initiation for reinforced concrete structures in the Persian Gulf region. Thedevelopment of the model and its calibration is described.

1. INTRODUCTION

Concrete is the most used construction material in the Gulf States. This material is moredurable against severe conditions compared to other construction materials. However, dueto the use of unsuitable components, poor workmanship, lack of curing, and lack of knowledgeabout the mechanism of deterioration, many structures (predominately those exposed toaggressive environments) show early deterioration.

The Persian Gulf region has a very severe exposure condition for reinforced concrete whencompared to other marine environments. In the last couple of decades, the region hasexperienced significant growth in construction (e.g., industrial and urban construction).Most of this construction uses reinforced concrete. Many structures are showing signs ofdurability governed distress. Lack of understanding of durability factors in the initial designand construction is the prime cause [1].


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The synergistic effects of physical and chemical mechanisms (e.g., corrosion of steel rebar,

sulfate attack, carbonation of concrete, crystallization pressure of salts in pores, hydraulicoverload, etc.) have contributed to the deterioration of concrete structures in the Gulf. Inaddition to these factors, climatic factors that involve large fluctuations in temperature andhumidity affect concrete durability in the Persian Gulf states. Extreme temperature andrelative humidity with daily and monthly variation intensify some mechanisms of deterioration.

The Iranian coast is one of the most unknown coastal stretches of the world. Even if Iranianscientists have explored it, the results of the exploration are hardly accessible. It is probablynot because of a lack of studies but rather a lack of publications resulting from the studies[2]. For this reason, this paper describes the geographic, climatic, and other specificationsof the Persian Gulf region that affect the durability of reinforced concrete structures.

The development and calibration of the DuraPGulf model, which is a service-life predictionmodel, is described. The research programs on the performance of reinforced concrete inthe gulf region have been performed by the Construction Materials Institute (CMI) at theUniversity of Tehran since 2002.

2. ENVIRONMENTAL CONDITIONS PERSIAN GULF

The Persian Gulf is a semi-enclosed sea only connected through the narrow Strait of Hormozto the Oman Sea and the Indian Ocean. The Gulf is 990 km long and has a mean depth of31 m. The tides occur in the Gulf diurnally and semi-diurnally with a tidal range of 2-4m at the northern Persian Gulf and 1-2 m at the rest [3]. A comparison of the ionicconcentration of the gulf and other seas shows the higher salinity of the Gulf water; on

average it is around 38.9 g/lit [4]. Due to this tide cycle, many chemicals are emitted intothe sea, which increases contamination, salinity, and temperature of the Gulf water. Theseemissions cause damage to the ecosystem, and industrial structures run the risk of beingadversely effected.

Hot-dry, hot-humid, and salty environments present a challenge to reinforced concreteconstruction in the Persian Gulf. For concrete structures located in a warm climate, thehigh ambient temperature is an aggravating factor because heat is a driving energy sourcethat accelerates both the onset and the progress of the deterioration mechanisms. Theclassical law connecting heat and the rate of chemical reactions states that for each increaseof ten degrees Celsius in temperature, the rate of chemical reactions is doubled [5].

The climate is tropical at the eastern Iranian coast, in Qatar, and in the United Arab Emirates.Along the remaining coast, there is a subtropical climate. Temperatures can vary by asmuch as 30C, and the relative humidity may range from 40 to 95% during a typical summerday. The minimum to maximum temperature range is from 3 to 50C, and the relative



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humidity may be as high as 95% or as low as 5%. The combination of these values result

in exposure conditions that are very detrimental to concrete materials, members and structures.These exposures cause damage due to thermal and mechanical stresses [1].

3. CONCRETE CONSTRUCTION IN THE PERSIAN GULFREGION?

The Persian Gulf is self-explanatory, and hot weather is an inherent part of the region. Itis an aggressive environment for both fresh and hardened concrete. Experiences have shownthat despite the aggressive effect of hot weather, the low quality of concrete construction,unskilled labor, and lack of proper supervision in the hot climate have also been mainreasons for the poor performance of concrete structures in Persian Gulf states.

Also phenomena that propagate the micro and macro crack (e.g., drying and plastic shrinkage,creep, impact of overloads, etc.) have led to a reduction in both the strength and durabilityof structures in the harsh environment of the Gulf. Cracks are a direct pathway for thepenetration of ions into concrete. It is important to consider the permeability of concretewhen assessing the durability of the material as well as the structural member.

Reinforcement corrosion is the main cause of concrete deterioration in marine environments.Chloride, which is the most common ion in seawater, penetrates into the bulk of concreteand degrades the alkali protective layer of reinforcement, with the result that the embeddedsteel starts to corrode and produce rust, which is massive as compared with steel. Therusted steel creates interior tensile stress and expands by up to seven times the originalvolume, which leads to the cracking and spalling of concrete covers [6].

Due to the above phenomenon, many structures suffered damage only 510 years afterconstruction. These structures were built in the 1990s, (e.g., Folad Jetty in the Persian Gulf,Bandar-Abbas Port, Iran), and portions of these structures have essentially become non-functional.

In an effort to repair and retrofit some of these structures, many new materials (such as

mineral and chemical admixtures) were used in the concrete mixtures for repairs. Thesewere used to improve the properties of fresh and hardened concrete. Although these additiveshelped in improving the properties of fresh and hardened concrete, because of the mismatch

between the existing concrete and the repairing concrete, these accelerated the deterioration

of concrete structures instead of improving the potential problems. For example, silica-fume, as a super-pozzolanic admixture, decreases the bleeding of fresh concrete, which

increases the probability of plastic shrinkage, which induces early crack of concrete, etc.



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The above experience does not mean that admixtures should not be used in concrete mixtures

used for repairing or retrofitting. This implies that care should be taken to better understandthe chemical compatibility between the admixtures and the cement type of the concretemixtures being developed for the repair concrete and existing concrete. The development

of new guides with instructions and updating of the existing guides has improved theefficiency of the admixtures used for repair work. For example, if modified concrete withadditional silica-fume cures well, it will have a positive effect on the corrosion of steel in

concrete by increasing the electrical resistivity [7, 8]. Engineering codes of practice (e.g.,Construction Industry Research and Information Association (CIRIA-1984) [9] in the UK,Building and Housing Research Center (BHRC-2006) [10] in Iran, and Saudi Arabian Oil

Company (ARAMCO-1994) [11]) have compiled some specifications for durable concrete.These codes reduce chloride diffusion in the marine structures that have built around the

Gulf region. Table 1 presents specifications for durable concrete in the Gulf region.

Table 1 Specifications for durable concrete in the Gulf region


Construction considerations include cooling the concrete with chilled water and ice, notplacing concrete on hot and windy days when humidity levels are low, are other criteria forhot weather concreting. Utilizing guides for hot weather concreting have significantly

improved the quality and performance of concrete structures in the Gulf region.

With the aging of concrete structures reaching the end of their service life, maintenance and

repair are important to increase the serviceability of the structures. Repair and rehabilitation

of deteriorated concrete structures are essential not only to utilize them for their intendedservice life but also to assure the safety and serviceability of the associated components

[12]. Figure 3.1 shows schematically the factors that affect the compatibility of concretesubstrate and repair materials [13].


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Figure 3.1 Factors affecting the durability of concrete repairs.

Usually repair mortars applied to hardened concrete substrates have a tendency to shrinkon drying. Because of the restraint provided by the substrate at the interface and/or theperiphery of an enclosed patch repair, drying shrinkage cannot proceed freely, and may leadto cracking, spalling and even premature failure of repaired surfaces. It is an example forincompatibility between both materials. Incompatibility between the hardened concreteand repair material, contrary to improving structural affairs, intensifies premature deteriorationand leads to early deterioration. A case study was undertaken collect information on thedamaging effects of poor repair methods and materials.

4. CASE STUDY

This case study examined the damaging effects of poor repair methods and materials.Repairs are usually undertaken to improve the condition of the existing structure and increasethe useful service life of the facility. The results of the case study showed that poorperformance of the parent concrete and incompatibility of repair material with the concretesubstrate accelerated the deterioration of the repaired structure.

For this case study, Jetty No. 2 of petrochemical company of Bandar-e Imam, located onthe northwestern coast of the Persian Gulf in a semi-closed region of Khowr-e Musa, wasselected. This is a reinforced concrete marine structure that was constructed in 1976. After15 years the structure started showing signs of distress and major deterioration. The severe



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environmental conditions, hot-dry climate of the region, lack of periodic maintenance, and

lack of knowledge about the deterioration mechanism contributed to the distress anddeterioration of the structure. At the time of the design and construction of this structure,the parameters affecting the long term durability of concrete in the hot weather of the Gulf(e.g., limiting the maximum w/cm ratio, influence of admixtures, chemical compatibilitybetween the admixtures and the cement, use of accelerators like chloride calcium) were notwell understood.

Repair work was undertaken some 15 years ago without proper attention to compatibilitybetween repair materials and the existing concrete substrate. Unfortunately, no documentationor data was logged for the repair work. Figure 4.1 shows some examples of distress resultingfrom the incompatibility of the repair methods with the concrete substrate. The patterns

of cracking, spalling, and other deterioration demonstrated that there were damagingmechanisms in progress. These could be attributed to the chemical, physical, andelectrochemical incompatibilities of the repair material (e.g., longitudinal cracks that areevidence ofcorrosion of steel bars and/or drying shrinkage of repair materials, debondingof interfacial surfaces between repair parts and concrete of the structure, efflorescence ofrepair material, incipient anodes, etc.) and the existing concrete substrate surfaces.

This case study demonstrates that although repairs are conducted intending to mitigatedeterioration and increase the remaining service life of the facility, if not done carefully andproperly with attention to details regarding the compatibility of materials, the repair itselfcould contribute to the acceleration of distress and deterioration of the structure. Furthermore,

it is essential that all documentation and data on repair materials and methods of repairwork be carefully recorded and maintained for future reference.



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Figure 4.1 (a) Longitudinal cracking on a repaired surface; (b) Efflorescence of repair material;(c) Debonding of repair material and substrate concrete.


(a)

(b)

(c)


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For the case study structure in particular, another consideration that did not receive attention

was the difference in the quality of the precast and in-situ concrete in the structure. Figure4.2 shows two chloride profiles, one for an in-situ beam in the structure and the other fora precast girder in the structure. These profiles were taken at the same age. The chloridelevels in the beam are much higher than the chloride levels in the girder. Data from theconstruction time showed that proper curing and extended aging of the concrete in the girderbefore first exposure to the severe environment resulted in the low chloride contents ascompared to the beam member in the structure. This shows the importance of proper curingand aging of concrete prior to exposure to severe environmental conditions.


Figure 4.2 Comparison of chloride profiles between an in-situ beam and a precast girderin the same structure.

5. DESIGN FOR DURABILITY AND SERVICE LIFE

Rresearch at the Construction Materials Institute (CMI) at the University of Tehran hasshown that the minimum durability requirements in current concrete codes are not enoughto ensure the long-term performance of concrete structures in marine environments withhot weather climate conditions like those of the Gulf. Design of reinforced concretestructures without considering performance and durability under severe environmental

conditions is likely to lead to deterioration of the structures during their service life.

Traditional methods of structural design are based on the strength of the structure and donot include interactions with environmental factors. This interaction is essential for the


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coastal structures of the Gulf region. Not considering concrete cover cracks and their effect

on the durability of concrete limits the treatment of durability to only the environmentalfactors.

Fortunately, effort is now being focused on Durability and Service Life Based Designmethods. These consider durability as one of the limit states in the design of concretestructures. Durability and Service Life Based Design is a performance based design thattakes into account the probabilistic nature of the environmental aggressiveness, the degradationmechanisms, and the material properties in the finished structure. This design process canbe divided into eight stages that can be summarized as: required performance, defensestrategy, maintenance strategy, design, construction, maintenance plan, use, and maintenance[14].

Service life prediction is currently an area of significant international research, and thereare a number of different definitions published for the term service life. Degree ofreliability of the structure for its intended service is the key component in defining servicelife. Figure 5.1 describes definition of service life schematically.


Figure 5.1 Schematic explanation of the service life of a structure.


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Computer based models have been developed to predict the service life of concrete structures

exposed to chloride attacks like marine environments and/or deicing salts for road structures(e.g., bridges). Examples of computer based service-life models for concrete structuresinclude Life365, DuraNet, and DuraCrete.

These models predict service life based on a study on chloride corrosion in North Americanand European coastal regions and/or exposure of structures to deicing salts. Before the2000s, there were no computer-based models to predict service life in the Persian Gulfregion. This was largely due to a lack of data for modeling concrete durability and chloridediffusion in the climatic conditions of the Persian Gulf region.

The Durability of Reinforced Concrete Structures in the Persian Gulf Region (DuraPGulf)

model [15] was developed as a first model for service life of concrete structures in the Gulfregion. This model was developed at the Construction Materials Institute (CMI) at theUniversity of Tehran. For the calibration of this computerized model, data on chloridediffusion in the climatic conditions of the Persian Gulf region was collected by carefullycontrolled experimentation.

For the collection of data, a comprehensive and complete set of field experiments wereconducted under actual field and exposure conditions. The objective was to collect datato study the effects of different parameters such as the water to cement ratio, Pozzolanicmaterials (e.g., silica-fume) content, curing conditions, exposure conditions, environmentaltemperature, and surface coating on chloride diffusion.

6. COMPUTER BASED MODEL - DuraPGulf

For the collection of data for the model, 120 prism specimens measuring 151560 cmwere exposed to the marine environment of Bandar-Abbas city, which has one of harshestexposure environments for the durability of concrete in the Persian Gulf. The specimenswere tested after 3, 9, and 36 months of exposure and will be tested after 80 months ofexposure. The test specimens have been placed in five different exposure conditions: (1)atmospheric, (2) buried, (3) submerged, (4) tidal, and (5) splash zone (Figure 6.1).



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Figure 6.1 Samples are exposed in several zones: (a) atmospheric, (b)buried, (c)tidal, (d) submerged, (e) splash.

The mixture proportions for the concrete used in the Iranian Gulf coast region were designedto cover a wide range of construction applications. To study the effect of curing period onthe durability, test specimens were cured for 0, 3, 7, and 28 days and then exposed to thesevere exposure conditions.


(a) (b)

(c) (d)

(e)


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Crank's solution of Fick's second law [16], which is the best definition for the diffusion of

chloride ions, has been used to fit close correlation curves to the data, which measured thechloride concentration in bulk concrete. This model uses the Moving Least Squares method(MLS) as a statistical method for data regression to predict the chloride diffusion coefficient(Dc) and surface chloride content (Cs) for new cases, with the result that it will be ablepredict the service life of a reinforced concrete structure. Figure 6.2 shows the homepageof the software. This software takes into account the effects of structure properties (e.g.,water to cement ratio, cover thickness, etc), site conditions including the temperature andhumidity profile, exposure conditions, curing period, and type of coatings by allowing theuser to input the data regarding these variables. The output from the computerized modelincludes time of corrosion initiation, variations in chloride profiles during the predictedservice life, and/or recommendations for required structural properties for the design servicelife of the structure being analyzed.

The service life of a concrete structure in a marine environment consists of two definitestages, the initiation period and the propagation period [17]. Modeling and research on thepropagation period is a time-consuming process as it has a complex formulation and isinfluenced by the nature of concrete cracking in the field condition. For this reason, mostresearch on the prediction of service life has focused on the initiation period. The DuraPGulfmodel also is also limited to prediction of the initiation period of service life withoutconsidering the propagation period. After the initial calibration of the model is completeand is found to be satisfactory, future work at the Construction Institute at the Universityof Tehran will attempt to model and include the propagation period stage.


Figure 6.2 Homepage of the DuraPGulf model.


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7. SUMMARY AND CONCLUSIONS

The durability of reinforced concrete is one of the main challenges for the constructionindustry in coastal areas of the Persian Gulf. This region has hot weather and severeexposure conditions, and is one of the harshest environments as compared to other marineenvironments. Rapid deterioration of newly constructed structures has initiated a focus onthe durability-based design of concrete structures. The time and money invested in repairson concrete structures in the Gulf Region is very heavy and thus more effort is now beingexpended on the design and construction of new structures that are based on durabilityconsiderations that take into account the harsh environmental conditions of the Gulf.

The DuraPGulf Model has been developed based on the local data on this environment, andis anticipated to help engineers to design reinforced concrete structures with a betterunderstanding of the expected durability performance. It is expected that the DuraPGulfModel will continue to be improved as more experience is gained through its use and theobserved field performance of the structures over their immediate service life.

ACKNOWLEDGMENTS

The authors would like to acknowledge the technical and financial support of ConstructionMaterials Institute (CMI) at the University of Tehran, the Ports and Shipping Organizationof Iran, and the Management and Planning Organization of Iran.

REFERENCES

[1] Neville, A., Good Reinforced Concrete in the Arabian Gulf, Materials and Structures, Vol.33, December 2000, pp. 655-664.

[2] Hpner, Th., Ebrahimipour, H., & Kazem Marasch, S. M.,Five Intertidal Areas of the PersianGulf, Wadden Sea Newsletter, 2000-2, pp. 30-33.

[3] Zwarts, L., Wadden en wadvogels in de Golf, Waddenbulletin 1991-2, pp. 65-68.[4] Chini, M., Study on the Effect of Silica Fume and Water to Binder ratio on the Diffusion of

Chloride Ion in Persian Gulf Region (In Persian), M. s. Thesis, University of Tehran, Iran,June2004,127 pages.

[5] Mehta, P.K ., Concrete in Marine Environment, Taylor & Francis Books, 2003, 206 pages.[6] ACI 222R-01,Protection of Metals in Concrete against Corrosion, Reported by ACI Committee

222, American Concrete Institute (ACI), 2005, 41 pages.[7] Ghalibafian M., Shekarchi M., Zare, A., & Tadayon M., Chloride Penetration Testing of

Silica Fume Concretes under Persian Gulf Conditions, The 6th CANMET/ACI International

Conference on Durability of Concrete, Thessaloniki, Greece, 2003, pp. 737-753.[8] Shekarch, M., Tadayon, M., Hoseini, M., Chini, M., Montazer, SH., Alizadeh, R. & Ghods,P. Application of the Water Absorption as a Criterion for the Durability of Concrete Structuresin Marine Environments, 4th

international Conference on Concrete under Severe Conditions,CONSEC04, Seoul, Korea, 2004, pp. 369-376.



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[9] CIRIA, The CIRIA Guide for Concrete Construction in the Gulf Region, Spec. Pub.31,

Construction Industry Research and Information Association, Ministry of Housing andConstruction, Department of the Environment, London, 1984.

[10] BHRC-PN S 428, Code of Practice for Concrete Durability in the Persian Gulf and OmanSea (In Persian), Building and Housing Research Center, Ministry of Housing and UrbanDevelopment, Tehran, Iran, 2006, 87 pages.

[11] ARAMCO, The Saudi Arabian Oil Company concrete specification09 SAMSS-097, Clause5.1, Saudi Aramco, Dhahran, Saudi Arabia, 1994.

[12] Maslehuddin, M., Alidi, S. H., Mehthel, M., Shameem, M., Ibrahim, M., Performanceevaluation of repair systems under varying exposure conditions, Cement & Concrete Composites,Vol. 27, 2005, pp. 885897.

[13] Emmons, E. H., Vaysburd, A. M., & McDonald, J. E., ARational Approach to DurableConcrete Repairs, Concrete International, Vol. 15, No. 9, 1993, pp. 40-45.

[14] DuraCrete, Probabilistic Methods for Durability Design, Document BE95- 1347/R0, The

European Union Brite EuRam III, Contract BRPR-CT95-0132, Project BE95-1347, CUR,Gouda, 1999.

[15] Alizadeh, R., Ghods, P., Chini, M., Hosseini, M., & Shekarchi M.,Durability Based Designof RC Structures in Persian Gulf Area Using DuraPGulf Model, First International Conferenceon Concrete Repair, Rehabilitation and Retrofitting (ICCRRR 2005), Cape Town, SouthAfrica, pp. 391-394.

[16] Crank , J ., The mathematics of diffusion , Clarendon Press, Oxford, UK, 1975.[17] Maage, M., Helland, S., Vennesland, E. and Carlsen, J.E.,Service Life Prediction of Existing

Concrete Structures Exposed to Marine Environment, ACI Material Journal, Vol.93, No.6,1996, pp. 1-8.


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Concrete Durability in Persian Gulf.pdf