PSI - Issue 60

Harikrishna S et al. / Procedia Structural Integrity 60 (2024) 700–708 Harikrishna S / Structural Integrity Procedia 00 (2019) 000–000

706

The following inferences were made from assessment of location.

• The entire middle wall was not damaged, but more than half portion has distress locations. Major damages happened on portions which were submerged in sulphur. • Sufficient cover was there for the reinforcement rods for the wall. Despite that, sulphur intrusion happened. • The depth of carbonation of concrete extended up to the 80-90% of clear cover confirming prevalent acidic environment and loss of flexibility of concrete. • The results of strength tests on core samples from bottom portion of walls indicated high strength. So, chances of delamination/damage there is negligible. Usually that area was immersed in molten sulphur. It is inferred that minor crystallization of sulphur in concrete pores may have happened. This confirms that absence of air can reduce chances of corrosion to large extent. 6.0 Probable damage mechanisms No precise conclusive damage mechanism [3] was established in the case. Probable damage mechanisms can be sulphur attack on concrete and sulfidation of steel. a. Concrete • The moisture might have percolated into the pit through minor seepage from ground or from leakages in steam coils inside the pit. • The traces of any oxidised sulphur may have dissolved in this moisture to form sulphuric acid/ sulphurous acid. • The acid might have an ingress into concrete through openings in acid resistant bricks and reacted with dicalcium silicate/ tri calcium silicate & tetra calcium aluminate to form corrosion products that occupy much higher volume than original concrete. • This may have resulted in bulging of concrete thereby causing bulges in brick wall also. These formation of corrosion products may have resulted in loss of strength of concrete. b. Reinforcement steel • Sulfidation is the corrosion of carbon steel resulting from their reaction with sulphur compounds in high temperature environment. This mechanism is also called sulfidic corrosion. 7.0 Repairs The centre partition concrete wall is severely deteriorated and needed to be repaired & refurbished. The scope was finalised considering following parameters. • Ensuring proper shoring/scaffolding during dismantling jobs • Full depth removal of damaged & deteriorated concrete. • Replacement of damaged reinforcement bars and binding with old bars • Installing bonding agents to surface of old concrete to ensure proper bonding with repair mortar. • Installation of new acid resistant lining bricks The following jobs were carried out subsequently. • All damaged/ deteriorated / loose RCC material on the wall was chipped off till reasonably good concrete were observed and the entire wall was cleaned.