concrete construction industry

CBM-CI – Int. Workshop, Karachi, Pakistan

Dr. E. Limuswan

NORWAY – CONCRETE CONSTRUCTION INDUSTRY – CEMENT BASED MATERIALS AND CIVIL INFRASTRUCTURE (CBM - CI) Dr. Odd E. Gjørv Prof. Norwegian University of Science and Technology NTNU Trondheim NORWAY ABSTRACT: This paper presents some recent developments and experiences with high performance concrete for important concrete infrastructures in Norway. Many of these concrete structures are located in severe environments, and recent experience has shown that the specification of a high strength or high performance concrete has not necessarily been sufficient for ensuring a proper durability. However, the combination of a probability-based durability design in combination with performance-based concrete quality control during concrete construction appears to provide a better basis and strategy for ensuring a more controlled durability and service life.

1.

INTRODUCTION

Roughly speaking, Norway is a small country, but it has a long and broken coastline of more than 2,000 km (1,243 mi), characterized by many deep fjords and numerous inhabited islands. From the early 1900s, therefore, reinforced concrete has been a common construction material for concrete infrastructures in a very harsh and difficult marine environment. Along the Norwegian coastline there are more than 300 large concrete bridges and more than 10,000 harbor structures, most of which are made of concrete. Since the early 1970s, 34 major concrete structures have also been installed for oil and gas explorations in the North Sea, most of which were produced in Norway. For many years, the deterioration of concrete structures in a severe marine environment, mostly in the form of chloride-induced corrosion of embedded steel, has been a big problem and challenge for the Norwegian construction industry [1, 2]. To meet this challenge, there is consolidated effort in the form of research and development of HPC materials and their application in the civil infrastructure. The production of the very demanding offshore concrete structures has also been very important for this development. In addition, Norway has been one of the biggest international producers of condensed silica fume, the effect of which has also been very important for the development of high performance concrete. In this paper, a brief description of the some recent developments in Norway in the area of High Performance Concrete (HPC) is described. Also presented is the some of the experiences in field application and use of HPC in Norway’s civil infrastructure.


2.

DEVELOPMENT AND APPLICATION OF HPC

2.1

Offshore Structures

Dr. E. Limuswan

When the first concepts for fixed offshore concrete structures for the North Sea was introduced in the late 1960s, the technical community of the international oil industry showed much scepticism. At the same time, however, the results of a comprehensive field investigation of more than 200 conventional concrete sea structures along the Norwegian coastline were published, demonstrating that the general condition of these structures was quite good, even after service periods of up to 50-60 years in severe marine environments [3,4]. These results contributed, therefore, to convincing the most skeptical international operators that concrete could be a possible and reliable construction material for offshore installations in the North Sea. However, the appearance of corrosion on embedded steel that typically took place on all conventional concrete sea structures after a service period of 5-10 years was not acceptable to the offshore technical community. Therefore, in order to gain acceptance for the first offshore concrete platform, both increased concrete quality and concrete cover beyond that required by current concrete codes in combination with much stricter programs for quality assurance and quality control had to be introduced. After the first breakthrough for use of concrete for offshore installations in the North Sea, rapid development took place. Thus, during the period from 1973 to 1995, altogether 28 major concrete platforms containing more than 2,500,000 m3 (3,750,000 yd3) of high performance concrete were installed, and by 2007, there were 34 concrete structures in the North Sea, most of which were produced in Norway. Primarily as a spin-off from the research on and application of high performance concrete for all these demanding offshore concrete structures, high-performance concrete was also successively applied to a number of land-based concrete structures in Norway. These applications included a variety of structures such as bridges, harbor and coastal structures, underground construction, water treatment plants and storage facilities for aggressive waste and chemicals. In addition, high performance concrete was applied to a variety of concrete products. Mostly, however, high performance concrete was applied to bridges and harbor structures.

2.2

Bridges

For long-span bridges, both high strength and low weight are important. For most concrete bridges built in Norway during recent years, design strengths of 65-75 MPa (9,300 - 11,000 psi) based on normal weight and 60-65 MPa (8,800 - 9,300 psi) based on lightweight concrete have typically been applied. For cantilever bridges, the use of normal weight or lightweight concrete has sometimes varied from one span to another. In recent years, two floating bridges for strait crossings have also been built, where a 65 MPa (9,300 psi) type of lightweight concrete was used for the floating pontoons. Many of the Norwegian concrete bridges are exposed to very severe marine environments, so in spite of the high performance concrete, chloride penetration and steel corrosion have still proved to be a challenge for the long-term performance [1]. For many of the durability problems, it has been possible to relate the problems to a lack of proper quality control and problems during concrete construction. The durability specifications were only based on prescriptive requirements to the concrete composition and execution of concrete work, the results of which cannot be verified and controlled during concrete construction. Also,


Dr. E. Limuswan

specification of a high strength concrete does not necessarily yield a concrete with high resistance against chloride penetration [5]. In some cases, a deep chloride penetration occurs during concrete construction before the concrete has gained sufficient maturity and density [1].

2.3

Harbor Structures

In recent years, both design and execution of concrete work have generally improved. However, recent field investigations of relatively new concrete structures in Norwegian harbors have revealed that an uncontrolled chloride penetration still represents a big challenge. For concrete harbor structures, the exposure conditions are even more severe than that of concrete coastal bridges. Also for such structures, therefore, a high chloride penetration was observed during concrete construction before the concrete has gained sufficient maturity and density [1]. At early ages, most types of concrete are very sensitive and vulnerable to chloride penetration [6], and this may represent a special problem when the concrete construction work is carried out during cold and rough weather conditions, which may often be the case along the Norwegian coastline.

3.

RECENT TRENDS

For harbor structures, bridges and offshore structures that have been exposed to severe marine environments for some time, recent experience has shown that the specification of high strength or high performance concrete has not necessarily been sufficient for ensuring durability. Although the overall condition of concrete structures in the North Sea appears to be quite good [7,8], some of the structures have already experienced a deep chloride penetration [9]. For some of them, corrosion has also taken place, very costly repairs have been carried out, and additional protective measures applied to retard further chloride penetration. Many of the observed corrosion problems can be related to a lack of proper quality control or special problems during concrete construction. While it is relatively easy to control the resistance of concrete both against freezing and thawing and expansive alkali reactions by following established precautions and procedures, electrochemical corrosion of embedded steel still represents the most critical threat to the durability and long-term performance of concrete structures in chloride containing environments. Therefore, to gain a more controlled durability and service life of new important concrete infrastructures in Norway, a probability-based durability design in combination with performance-based concrete quality control during concrete construction have recently been introduced [10,11]. A probabilistic approach to the durability design of concrete structures was developed in the European research project “DuraCrete” in the late 1990s [12]. Later on, further development and simplification of the results from this project provided the basis for new recommendations and guidelines both for durability design and performance-based concrete quality control of new important concrete structures in Norwegian harbors [10,11]. Although a probability-based durability design does not guarantee a given service life, such a design provides the basis for an engineering judgment of all those factors that are considered relevant for the durability, including the scatter and variability of all factors involved. Hence, a good engineering basis for comparing and selecting one of several technical solutions for a given environment is obtained, and durability requirements can be specified that are possible to verify and control during concrete construction. Extensive experience has shown that many


Dr. E. Limuswan

of the durability problems that occur after some time can be related to lack of proper quality control and special problems during concrete construction. Upon completion of a new structure, therefore, it is very important to provide documentation of achieved construction quality and durability before the structure is handed over to the owner. As part of the durability design, the owner must also be provided with a service manual for a regular condition assessment and preventive maintenance of the structure. For concrete structures in chloride containing environments, it is the regular monitoring of the real chloride penetration and evaluation of the future corrosion probability in combination with protective measures during the service period that provide the ultimate basis for achieving a more controlled durability and service life. In Oslo harbor, a new large city development project with a service life requirement of 300 years is currently under construction. To provide the best possible utilization of high performance concrete in all concrete substructures located in water depths of up to 20m, a probability-based durability design in combination with a performance-based concrete quality control are currently being used to ensure a proper durability [13].

4.

CONCLUDING REMARKS

Both in Norway and many other countries, the lack of proper durability and long-term performance of many important concrete infrastructures not only represents technical and economic problems, but dalso has a great impact on available resources, environment and human safety [14]. In recent years, therefore, extensive research has been carried out in many countries to obtain better control of the various deterioration processes of concrete structures in severe environments, and never before has so much knowledge and experience regarding durability and service life been available. It is a great challenge for the professional community, therefore, to utilize and transform more of all this knowledge and information into good engineering practice for achieving a more controlled durability and service life. For concrete structures in severe environments, recent experience has shown that the specification of a high strength or high performance concrete does not necessarily ensure a proper durability. However, the combination of a probability-based durability design and performance-based concrete quality control appears to provide a better basis and strategy for ensuring a more controlled durability and service life for concrete structures. REFERENCES [1] Gjørv, O.E., Durability and Service Life of Concrete Structures, Proceedings of First fib [2] [3] [4] [5]

Congress 2002, Session 8, Vol. 6, Japan Prestressed Concrete Engineering Association, Tokyo, 2002, pp. 1-16. Gjørv, O.E., The Durability of Concrete Structures in the Marine Environment, in Durability of Materials and Structures in Building and Civil Engineering, ed. by C.W. Yu and J.W. Bull, Whittles Publishing, ISBN 1-870325-58-3, 2006, pp. 106-127. Gjørv, O.E., Durability of Reinforced Concrete Wharves in Norwegian Harbours, Ingeniørforlaget, Oslo, 1968, 208 p. Gjørv, O.E., Steel Corrosion in Concrete Structures Exposed to Norwegian Marine Environment, Concrete International, 1994, Vol. 16, pp. 35-39. Årskog, V, Ferreira, M., Liu, G. and Gjørv, O.E., Effect of Cement Type on the Resistance Against Chloride Penetration, Proceedings of Fifth International Conference on Concrete Under Severe Conditions: Environment and Loading, ed. by F. Toutlemonde, K. Sakai, O.E. Gjørv and


[6]

[7]

[8] [9]

[10] [11] [12] [13]

[14]

Dr. E. Limuswan

N. Banthia, Laboratoire Central des Ponts et Chaussées, Paris, ISSN 1628-4704, 2007, pp. 367374. Guofei, L. and Gjørv, O.E., Early Age Resistance of Concrete Against Chloride Penetration, Proceedings of Fourth International Conference on Concrete Under Severe Conditions: Environment and Loading, ed. by B.H. Oh, K. Sakai, O.E. Gjørv and N. Banthia, Seoul National University and Korea Concrete Institute, Seoul, ISBN 89-89499-02-X 93530, 2004, pp. 44-55. Moksnes, J. and Sandvik, M., Offshore Concrete in the North Sea - A Review of 25 Years Continuous Development and Practice in Concrete Technology, Proceedings of Odd E Gjørv Symposium on Concrete for Marine Structures, ed. by P. K. Mehta, CANMET/ACI, Ottawa, 1996, pp. 1-22. Durability of Concrete Structures in the North Sea: State-Of-The-Art-Report, Féderation Internationale de la Précontrainte - FIP, London, 1996. Sengul, O. and Gjørv, O.E., “Chloride Penetration into a 20 Year Old North Sea Concrete Platform”, Proceedings Vol. 1, Fifth International Conference on Concrete under Severe Conditions – Environment and Loading”, ed. by F. Toutlemonde, K. Sakai, O.E. Gjørv and N. Banthia, Laboratoire Central des Ponts et Chaussées, Paris, ISSN 1628-4704, 2007, pp. 107-116. Recommended Specifications for Increased Durability of New Concrete Harbor Structures, Norwegian Association for Harbor Engineers, TEKNA, Oslo, 2. edtition, 2007, 18 p. (In Norwegian). Practical Guidelines for Service Life Design of New Concrete Harbor Structures, Norwegian Association for Harbor Engineers, TEKNA, Oslo, 2. edition, 2004, 48 p. (In Norwegian). DuraCrete: General guidelines for durability design and redesign, The European Union – Brite EuRam III, Project No. BE95-1347: Probabilistic performance based durability design of concrete structures, Report No. T7-01-1, 1999. Årskog, V. and Gjørv O.E., A New City Development Project in Oslo Harbor With 300 Years Service Life Requirement, Proceedings of Fifth International Conference on Concrete Under Severe Conditions: Environment and Loading, ed. by F. Toutlemonde, K. Sakai, O.E. Gjørv and N. Banthia, Laboratoire Central des Ponts et Chaussées, Paris, ISSN 1628-4704, 2007, pp. 851862. Gjørv, O.E. and Sakai, K., (eds.) Concrete Technology for a Sustainable Development in the 21st Century, E & FN Spon, London and New York, ISBN 0-419-25060-3, 2000, 386 p.