SỮA CHỮA CÁC KẾT CẤU BỊ HƯ HỎNG DO MÔI TRƯỜNG BIỂN VÀ BỊ CÁCBÔNÁT HOÁ Ở PHÁP VÀ ÚC

Hội nghị khoa học tòan quốc lần thứ hai về Sự cố và hư hỏng công trình Xây dựng REPAIR TO STRUCTURES DAMAGED BY MARINE ENVIRONMENT AND CARBONATION IN AUSTRALIA AND FRANCE SữA CHữA các KếT CấU Bị HƯ HỏNG DO MÔI TRƯờng biển và bị cácbônát hoá ở pháp và úc Laurent Bouet Civil Engineer. Technical Service Manager Sika Limited Vietnam ABSTRACT: Reinforced concrete has been widely chosen and used all over the world for its both technical performances and aesthetic properties. But, concrete is a “living” material, that is subject to aggression which are commonly the carbonation process and the chlorides and sulfates attacks when these structures are exposed to marine environment. This paper present the repair concept of two projects where concrete structures have been damaged by such attacks: Opera HouseSydneyAustralia: Substructure repair work of this famed project. Theatre Des ArtsRouenFrance: Facade repair work for which the specific aspect of the concrete finish had to be maintained Tóm tắt: Bê tông cốt thép đã được chọn và sử dụng rộng rãi trên khắp thế giới vì tính năng kỹ thuật cũng như tính thẩm mỹ của chúng. Nhưng bê tông là một vật liệu “sống” và là đối tượng chịu sự tấn công của quá trình cácbônát hoá và sự ăn mòn của clorua và sulfát khi những kết cấu này tiếp xúc với môi trường nước biển. Tài liệu này trình bày giải pháp sửa chữa của hai dự án nơi mà kết cấu bê tông đã bị hư hỏng do ăn mòn trên ở hai công trình: Nhà Hát Nhạc Kịch Sydney úc: sửa chữa kết cấu hạ tầng cho dự án nổi tiếng này. Nhà Hát Des ArtsRouenPháp: sửa chữa mặt tiền mà vẫn giữ nguyên diện mạo đặc thù của lớp bê tông hoàn thiện 1. Sydney Opera House – Australia Substructure repairing process. Introduction Reinforced Concrete had offered a lot of opportunities to architects to express them self and achieve beautiful building which become city or country landmark such as The Sydney Opera House (picture 1). Danish Architect Jorn Utzon had designed a beautiful freestanding, sculptural tripartite Opera House. Sitting Bennelong Point, virtually in the Sydney Harbour, the Opera House is completely exposed and overlooked by the great Sydney Harbour Bridge. Sydney Opera House construction started in 1957 and was completed in 1973. The structure is made of cast in situ concrete, tileclad concrete and precast elements. Due to its location, Sydney Opera House is subjected to both urban and marine environment which have conducted the concrete structure to present signs of deterioration less than 15 years after the project was completed. The part of the structure which has been suffering the most from marine environment is the promenade substructure beams and columns standing only less than 2 meters above sea level (picture 2). Substructure Repair programCause of damage In 1991, a diagnosis of the structure concluded that the main cause of the damages was the concrete carbonation process, low concrete covers in some locations and of course the effect of chlorides onto steel reinforcement. Due to the reinforcement rust expansion, the concrete had started to crack and consequently to spall. The survey did not show that the visible cracks had a structural origin. Substructure Repair programRepair Procedure. Some repair works consisting of crack surface patching had been previously applied but showed a poor durability. Due to relatively large volume of the repairs, the solution of cast and pour was chosen based on technical and practical considerations. The approved repair work program of 1991 was as follows: Chipping off all cracked and spalled concrete making sure that allloose adhering material was removed. At the edge locations, right angle cuts to concrete surface were provided to avoid feather edging of repair material. The concrete was broken down all around the reinforcement leaving a space of at least 10 mm in order to insure proper mortar cover. (picture 3) Reinforcements were prepared to eliminate any trace of rust. When required, additional rebars were put in place by welding of splicing onto existing one. Corrosion inhibitor slurry, Sika Monotop 610 was brush applied to the reinforcement. A watertight wooden formwork was placed Non shrink grouting mortar called Sikagrout, was selected based on its mechanical properties, non shrinkage behavior and to its resistance to marine environment aggression due its silica fume content that enhance overall durability and especially resistance to sulfate. Sikagrout, once mixed with water using a slow speed electric mixer, was then poured into the formwork in a continuous operation (picture 4.) Free face of grout was water cured. Thanks to Sikagrout early high strength development, the formwork was removed as early as 24 hours after the grout being poured. Finally, the repaired sections were wrapped in a plastic sheet, in order to assure grout proper curing and therefore optimal grout durability to be achieved (picture 5). Picture 3. Surface Preparation Picture 4. Sikagrout pouring 2. Theatres Des ArtsRouen–France. Repair to Original Technology Introduction Numerous buildings have been built in west of France in 19501960 as part of the reconstruction program after the 2nd WWR. Several architects, among them Le Corbusier, August Perret, Luigi Nervi have been designing reinforced concrete structures (mainly apartment and public buildings) with a non painted exposed concrete finish surfaces (pictures 6 and 7). Picture 6. Cast in place reinforced Picture 7. Precast micro concrete concrete with exposed aggregates panels with large exposed stones. But, a lot of these structures, today 40 to 50 years old, are now in need to be refurbish in consequence to the following degradation process: ? Carbonation of concrete to depth up to 50mm ? Marine environment exposure and chlorides penetration to concrete in a particularly rainy climate ? Corrosion of reinforcement not anymore naturally protected by alkaline concrete ? Expansive rust creates cracks in concrete ? Gaz (carbon dioxide), Water and Chlorides (rain) penetrates even more and deeper accelerating the degradation process which conduct to concrete spalling. Theatres Des Arts of Rouen (picture 8) is among the numerous building to receive refurbishment in France in a market estimated to 400 millions USD per year. Built in 1960, Theatre Des Arts facades combine exposed aggregates finish reinforced concrete and large pink marbles elements. Picture 8. Theatres Des ArtsRouen France Rouen’s Theatre Des Arts is typical of the post war architecture style and therefore it has been registered as part of French Architecture Heritage. This meant that any refurbishment had to follow strict aesthetic and technical rules that could meet the general requirement to “repair to original” A team composed of architects, contractors and Sika Company as the repair material supplier was asked to develop a patented process to refurbish that building with the goal of providing a solution to meet both durability and aesthetic needs. Rouen’s Theatre Des Arts was particularly damaged with numerous concrete spalling (pictures 9 and 10) and exposed corroded reinforcement. (picture 11) Picture 9 10. Concrete spalling Picture 11. Reinforcement corrosion The approved repair system was as follows: ? Surface preparation by sandblasting andor shipping cracked spalled concrete. (picture 12); ? Application to exposed reinforcement of a ready to use 1 component corrosion inhibitor (picture 13); ? Addition of new rebars (if required); ? Patching of high performance ready to use repair mortar to damaged areas. (High strength, impermeable Sikatop mortars) (pictures 14 15); ? Application on still fresh mortar of specially formulated repair microconcrete with pigments to match initial aspect (pictures 16 17); ? Sponge finishing of still fresh micro concrete; ? After drying and hardening of micro concrete and repair mortar, a new sandblasting is performed (picture 18); ? Spray Application on all surface of Sika Ferrogard 903, penetrating corrosion inhibitor to inhibit corrosion in areas where no damaged is seen yet but where concrete is already carbonated. (picture 20) Sika Ferrogard 903 is a multifunctional type of corrosion inhibitor which interact with the steel reinforcement surface. It forms a protective layer which act as a barrier for oxygen. It displaces chlorides ions from steel surface but it does not modify concrete performances and aspect. (picture 21); ? Application of transparent concrete protective coated against CO2 penetration and acting as graffiti barrier. Picture 12. Concrete chipping Picture 13. Sika Monotop 610 corrosion inhibitor applied to reinforcement Picture 14. Sikatop repair mortar application Picture 15. Mortar applied Picture 17. Micro concrete application to still fresh Sikatop mortar Picture 16. Micro concrete mixing Picture 18. micro concrete finishing Picture 19. Sandblasting of hardened repair Picture 21. Action mechanism of Sika Ferrogard 903 to steel Picture 20. Sika Ferrogard 903 , penetrating corrosion inhibitor spray application Picture 23. Theatres Des Arts after refurbishment completion Picture 22. Aspect of repaired concrete surface The satisfactory aspect of Theatres Des Arts facades (picture 22 23) after refurbishment completion has led to more repair program of building with an exposed aggregates aspect. 3. Conclusion Reinforced concrete can be affected by several attacks especially carbonation phenomenon and chlorides attack (in a marine environment) which often lead to corrosion of reinforcement and consequently concrete cracking and spalling. Repair techniques which can combine technical and aesthetic requirements do exist but still need a good cooperation and team work between the actors involved in that process including contractorapplicator, architect and material supplier. A good analysis of degradation causes, a proper selection of repair solution combined with their proper application shall lead to optimal repair durability and together aesthetic requirement..

Hội nghị khoa học tòan quốc lần thứ hai Sự cố h hỏng công trình Xây dựng REPAIR TO STRUCTURES DAMAGED BY MARINE ENVIRONMENT AND CARBONATION IN AUSTRALIA AND FRANCE SữA CHữA KếT CấU Bị HƯ HỏNG DO MÔI TRƯờng biển bị các-bô-nát hoá pháp vµ óc Laurent Bouet Civil Engineer Technical Service Manager Sika Limited Vietnam ABSTRACT: Reinforced concrete has been widely chosen and used all over the world for its both technical performances and aesthetic properties But, concrete is a “living” material, that is subject to aggression which are commonly the carbonation process and the chlorides and sulfates attacks when these structures are exposed to marine environment This paper present the repair concept of two projects where concrete structures have been damaged by such attacks: - Opera House-Sydney-Australia: Substructure repair work of this famed project - Theatre Des Arts-Rouen-France: Facade repair work for which the specific aspect of the concrete finish had to be maintained Tóm tắt: Bê tông cốt thép đà đợc chọn sử dụng rộng rÃi khắp giới tính kỹ thuật nh tính thẩm mỹ chúng Nhng bê tông vật liệu sống đối tợng chịu công trình cácbônát hoá ăn mòn clorua sulfát kết cấu tiếp xúc với môi trờng nớc biển Tài liệu trình bày giải pháp sửa chữa hai dự án nơi mà kết cấu bê tông đà bị h hỏng ăn mòn hai công trình: - Nhà Hát Nhạc Kịch Sydney - úc: sửa chữa kết cấu hạ tầng cho dự ¸n nỉi tiÕng nµy - Nhµ H¸t Des Arts-Rouen-Ph¸p: sưa chữa mặt tiền mà giữ nguyên diện mạo đặc thù lớp bê tông hoàn thiện 1.Sydney Opera House – Australia Substructure repairing process Introduction Reinforced Concrete had offered a lot of opportunities to architects to express them self and achieve beautiful building which become city or country landmark such as The Sydney Opera House (picture 1) Danish Architect Jorn Utzon had designed a beautiful freestanding, sculptural tripartite Opera House Sitting Bennelong Point, virtually in the Sydney Harbour, the Opera House is completely exposed and overlooked by the great Sydney Harbour Bridge Sydney Opera House construction completed in 1973 started in 1957 and was The structure is made of cast in situ concrete, tile-clad concrete and precast elements Due to its location, Sydney Opera House is subjected to both urban and marine environment which have conducted the concrete structure to present signs of deterioration less than 15 years after the project was completed The part of the structure which has been suffering the most from marine environment is the promenade substructure beams and columns standing only less than meters above sea level (picture 2) Picture Promenade Substructure Picture General view of Sydney Opera House Substructure Repair program-Cause of damage In 1991, a diagnosis of the structure concluded that the main cause of the damages was the concrete carbonation process, low concrete covers in some locations and of course the effect of chlorides onto steel reinforcement Due to the reinforcement rust expansion, the concrete had started to crack and consequently to spall The survey did not show that the visible cracks had a structural origin Substructure Repair program-Repair Procedure Some repair works consisting of crack surface patching had been previously applied but showed a poor durability Due to relatively large volume of the repairs, the solution of cast and pour was chosen based on technical and practical considerations The approved repair work program of 1991 was as follows: - Chipping off all cracked and spalled concrete making sure that allloose adhering material was removed At the edge locations, right angle cuts to concrete surface were provided to avoid feather edging of repair material The concrete was broken down all around the reinforcement leaving a space of at least 10 mm in order to insure proper mortar cover (picture 3) - Reinforcements were prepared to eliminate any trace of rust - When required, additional rebars were put in place by welding of splicing onto existing one - Corrosion inhibitor slurry, Sika Monotop 610 was brush applied to the reinforcement - A watertight wooden formwork was placed - Non shrink grouting mortar called Sikagrout, was selected based on its mechanical properties, non shrinkage behavior and to its resistance to marine environment aggression due its silica fume content that enhance overall durability and especially resistance to sulfate - Sikagrout, once mixed with water using a slow speed electric mixer, was then poured into the formwork in a continuous operation (picture 4.) - Free face of grout was water cured - Thanks to Sikagrout early high strength development, the formwork was removed as early as 24 hours after the grout being poured - Finally, the repaired sections were wrapped in a plastic sheet, in order to assure grout proper curing and therefore optimal grout durability to be achieved (picture 5) Picture Surface Preparation Sikagrout pouring beam Picture View of repaired Picture 2 Theatres Des Technology Arts-Rouen–France Repair to Original Introduction Numerous buildings have been built in west of France in 1950-1960 as part of the reconstruction program after the 2nd WWR Several architects, among them Le Corbusier, August Perret, Luigi Nervi have been designing reinforced concrete structures (mainly apartment and public buildings) with a non painted exposed concrete finish surfaces (pictures and 7) Picture Cast in place reinforced micro concrete concrete with exposed aggregates exposed stones Picture Precast panels with large But, a lot of these structures, today 40 to 50 years old, are now in need to be refurbish in consequence to the following degradation process:  Carbonation of concrete to depth up to 50mm  Marine environment exposure and chlorides penetration to concrete in a particularly rainy climate  Corrosion of reinforcement not anymore naturally protected by alkaline concrete  Expansive rust creates cracks in concrete  Gaz (carbon dioxide), Water and Chlorides (rain) penetrates even more and deeper accelerating the degradation process which conduct to concrete spalling Theatres Des Arts of Rouen (picture 8) is among the numerous building to receive refurbishment in France in a market estimated to 400 millions USD per year Built in 1960, Theatre Des Arts facades combine exposed aggregates finish reinforced concrete and large pink marbles elements Picture Theatres Des Arts-Rouen- France Rouen’s Theatre Des Arts is typical of the post war architecture style and therefore it has been registered as part of French Architecture Heritage This meant that any refurbishment had to follow strict aesthetic and technical rules that could meet the general requirement to “repair to original” A team composed of architects, contractors and Sika Company as the repair material supplier was asked to develop a patented process to refurbish that building with the goal of providing a solution to meet both durability and aesthetic needs Rouen’s Theatre Des Arts was particularly damaged with numerous concrete spalling (pictures and 10) and exposed corroded reinforcement (picture 11) Picture & 10 Concrete spalling Reinforcement corrosion Picture 11 The approved repair system was as follows:  Surface preparation by sandblasting and/or shipping cracked spalled concrete (picture 12);  Application to exposed reinforcement of a ready to use component corrosion inhibitor (picture 13);  Addition of new rebars (if required);  Patching of high performance ready to use repair mortar to damaged areas (High strength, impermeable Sikatop mortars) (pictures 14 & 15);  Application on still fresh mortar of specially formulated micro-concrete repair with pigments to match initial aspect (pictures 16 & 17);  Sponge finishing of still fresh micro concrete;  After drying and hardening of micro concrete and repair mortar, a new sandblasting is performed (picture 18);  Spray Application on all surface of Sika Ferrogard 903, penetrating corrosion inhibitor to inhibit corrosion in areas where no damaged is seen yet but where concrete is already carbonated (picture 20) Sika Ferrogard 903 is a multifunctional type of corrosion inhibitor which interact with the steel reinforcement surface It forms a protective layer which act as a barrier for oxygen It displaces chlorides ions from steel surface but it does not modify concrete performances and aspect (picture 21);  Application of transparent concrete protective coated against CO2 penetration and acting as graffiti barrier Picture 12 Concrete chipping 610 corrosion Picture 13 Sika Monotop inhibitor applied to reinforcement Picture 14 Sikatop repair mortar application Mortar applied Picture 15 Picture 17 Micro concrete application to still mortar Picture 16 Micro concrete mixing fresh Sikatop Picture 18 micro concrete finishing of hardened repair Picture 19 Sandblasting Picture 21 Action mechanism of Sika Ferrogard 903 to steel Picture 20 Sika Ferrogard 903 , penetrating corrosion inhibitor spray application Picture 23 Theatres Des Arts after completion Picture 22 Aspect of repaired concrete surface refurbishment The satisfactory aspect of Theatres Des Arts facades (picture 22 & 23) after refurbishment completion has led to more repair program of building with an exposed aggregates aspect Conclusion Reinforced concrete can be affected by several attacks especially carbonation phenomenon and chlorides attack (in a marine environment) which often lead to corrosion of reinforcement and consequently concrete cracking and spalling Repair techniques which can combine technical and aesthetic requirements exist but still need a good cooperation and team work between the actors involved in that process including contractor/applicator, architect and material supplier A good analysis of degradation causes, a proper selection of repair solution combined with their proper application shall lead to optimal repair durability and together aesthetic requirement./  ... diagnosis of the structure concluded that the main cause of the damages was the concrete carbonation process, low concrete covers in some locations and of course the effect of chlorides onto steel... welding of splicing onto existing one - Corrosion inhibitor slurry, Sika Monotop 610 was brush applied to the reinforcement - A watertight wooden formwork was placed - Non shrink grouting mortar... to be refurbish in consequence to the following degradation process:  Carbonation of concrete to depth up to 50mm  Marine environment exposure and chlorides penetration to concrete in a particularly