Methodology for Predicting the Residual Resource of Reinforced Concrete Structures with Annular Section and an Aggressive Environment Inside

Abstract A methodology for predicting the residual service life of reinforced concrete structures with an annular cross-section and an aggressive environment inside has been developed. It includes the determination of the most intense corrosion process and the assessment of its kinetics, and the calculation of the limit value for the structural characteristics in the critical zone and the residual service life as the time required for reaching this limit value. A formula for calculating the residual recourse is proposed. The corrosion intensity was assessed using thermodynamic analysis; the limit value of the structural characteristics in the critical zone was calculated using the finite element method. The methodology was tested during the inspection of a 90-meter-high reinforced concrete chimney of a coke production facility that had been in operation for 70 years. It has been established that the aggressive environment is gaseous, the most aggressive components of which are acid gases, namely sulphur anhydride and nitrogen oxides, which neutralize the calcium hydroxide of concrete and form compounds that do not have binding properties. Concrete corrosion advances in a concentric front from the inner surface to the outer one, with a corrosion front advance rate of up to 2.4 mm/year. The corroded concrete layer loses its strength and protective properties to the reinforcement. The analysis of the stress-strain state of the structure revealed that the critical structural zones are at the levels of about +25 m (for the entire structure) and +80 m (for the upper part of the structure) with an initial wall thickness of 220 and 180 mm, respectively, and a lining that was lost 15 years ago. The limit value of the wall thickness, after which the probability of reaching the limit state becomes high, is 112 and 25 mm, with a residual life of 30 and 12 years, respectively. It is recommended that the chimney be overhauled as soon as possible, the damage be repaired and the lining be restored, or that the structure be dismantled and a new one built after 10 years at the latest.