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Thames Tideway Tunnel –Thermal Assessment and On-Site Thermal Monitoring
Thames Tideway Tunnel, the biggest infrastructure project ever undertaken by the UK water industry, has been designed to upgrade London’s 150-year-old sewer network. The under-construction 25 km tunnel will intercept wastewater and stormwater and divert them into treatment plants to prevent the release of untreated effluent into the River Thames. The East Section, one of three work packages, consists of six worksites, including the construction of two lengths of tunnel of approximately 10 km, deep shafts, maritime works and structures connected with the existing system.
The main structures were designed considering environmental aggressiveness related to sewage and contact with saline water, but the durability of the main structures must also consider the risks from “Alkali-Silica reaction [ASR]” and “Delayed Ettringite Formation [DEF]”.
DEF is a result of high early temperatures (commonly above 70 ℃–80 ℃, in accordance with the BRE IP 11/01) in the concrete during hardening which prevent the normal formation of ettringite during hydration. Several years, or even decades, after concrete hardening, suitable conditions may allow the formation of higher volume ettringite that may cause cracking.
The risk of DEF has been monitored on the Thames Tideway Tunnel (East Section) from 2018 and numerous thermal assessments were done considering dimensions of the structures, type of formwork, pouring methodology, expected weather and rate of rise.
This paper highlights the “real life” conditions and associated main parameters which have a significant impact on the fresh concrete temperature and thus on the peak temperature.
Also detailed in this paper are long-term expansion measurements carried out on cores retrieved from a massive structure to demonstrate that there is only a negligible risk of DEF despite the thermal monitoring detecting that the peak temperature accidentally exceeded the specified maximum of 75 °C.
Thames Tideway Tunnel –Thermal Assessment and On-Site Thermal Monitoring
Thames Tideway Tunnel, the biggest infrastructure project ever undertaken by the UK water industry, has been designed to upgrade London’s 150-year-old sewer network. The under-construction 25 km tunnel will intercept wastewater and stormwater and divert them into treatment plants to prevent the release of untreated effluent into the River Thames. The East Section, one of three work packages, consists of six worksites, including the construction of two lengths of tunnel of approximately 10 km, deep shafts, maritime works and structures connected with the existing system.
The main structures were designed considering environmental aggressiveness related to sewage and contact with saline water, but the durability of the main structures must also consider the risks from “Alkali-Silica reaction [ASR]” and “Delayed Ettringite Formation [DEF]”.
DEF is a result of high early temperatures (commonly above 70 ℃–80 ℃, in accordance with the BRE IP 11/01) in the concrete during hardening which prevent the normal formation of ettringite during hydration. Several years, or even decades, after concrete hardening, suitable conditions may allow the formation of higher volume ettringite that may cause cracking.
The risk of DEF has been monitored on the Thames Tideway Tunnel (East Section) from 2018 and numerous thermal assessments were done considering dimensions of the structures, type of formwork, pouring methodology, expected weather and rate of rise.
This paper highlights the “real life” conditions and associated main parameters which have a significant impact on the fresh concrete temperature and thus on the peak temperature.
Also detailed in this paper are long-term expansion measurements carried out on cores retrieved from a massive structure to demonstrate that there is only a negligible risk of DEF despite the thermal monitoring detecting that the peak temperature accidentally exceeded the specified maximum of 75 °C.
Thames Tideway Tunnel –Thermal Assessment and On-Site Thermal Monitoring
Lecture Notes in Civil Engineering
Ilki, Alper (editor) / Çavunt, Derya (editor) / Çavunt, Yavuz Selim (editor) / Denis, Pierre-Edouard (author) / Chaizemartin, Alexandre (author) / Chapin, Hugo (author) / Gibb, Ian (author) / Linger, Lionel (author)
International Symposium of the International Federation for Structural Concrete ; 2023 ; Istanbul, Türkiye
2023-06-01
11 pages
Article/Chapter (Book)
Electronic Resource
English
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