Ground penetrating radar for assessment of reinforced concrete wastewater treatment plant
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Ground penetrating radar for assessment of reinforced concrete wastewater treatment plant Paola Machado Barreto Manhães1,2 · José Tavares Araruna Júnior1,3 · Genda Chen2 · Neil Lennart Anderson3 · André Bezerra dos Santos4 Received: 25 March 2020 / Revised: 15 July 2020 / Accepted: 28 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract During their long-term service, wastewater treatment plants deteriorate due to rebar corrosion in concrete structures. This paper presents a case study of ground penetrating radar (GPR) survey performed on a reinforced concrete (RC) structure in sieving unit of the wastewater treatment plant in the City of Fortaleza, Brazil. The RC structure was subjected to both the sulfuric acid attack from the oxidation of hydrogen sulfide present in the wastewater gas and the cyclic dry–wet salt-fog environment due to its proximity to the ocean. The survey results suggest that the amplitude of electromagnetic waves from a GPR scan and the determined dielectric permittivity values can be used to monitor steel rebar corrosion in a concrete structure by rapidly detecting any growth of inherent faults. The results indicate that the rebar condition can be assessed through slices at different times/depths obtained from a three-dimensional (3D) survey. Based on this study, it is recommended that the upper RC slabs in sieving unit of the plant be demolished and the lower slabs be preserved. Keywords Wastewater treatment plant · GPR · Rebar corrosion · Concrete deterioration
1 Introduction Corrosion on sanitation facilities has caused not only the loss of concrete mass but also structural capacity, ultimately leading to structural collapses [1]. Concrete deterioration in wastewater treatment systems is a result of a range of abiotic chemical reactions and biotic processes on cementitious materials used in the production of concrete. Concrete deterioration advances from carbonation (CO2) and H 2S acidification during the initial stages that convert hydrated calcium
silicate (CaO.SiO2.2H2O) and portlandite (Ca(OH)2) into CaCO3, Ca(HS)2 and S0 [2]. These processes reduce the pH of concrete from around 12 (fresh concrete) to 9, and provide favorable conditions to the biological production of sulfuric acid from oxidation of hydrogen sulfide present in the sewer gas phase during later stages [3]. Jiang et al. [2] suggested that biotic processes, caused by bacteria and fungi, lead to the formation of two important corrosion products: gypsum and ettringite, according to the following reactions:
CaO ∙ SiO2 ∙ 2H2 O + H2 SO4 → CaSO4 + Si(OH)4 + H2 O, (1)
* Genda Chen [email protected]
H2 SO4 + CaCO3 → CaSO4 + H2 CO3 ,
(2)
1
H2 SO4 + Ca(OH)2 → CaSO4 ∙ 2H2 O (gypsum),
(3)
Department of Civil and Environmental Engineering, Pontifical Catholic University of Rio de Janeiro, Rio de Janeiro, Brazil
2
Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO, USA
3
Department of Geoscienc
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