PSI - Issue 33

Fabrizio Pittau et al. / Procedia Structural Integrity 33 (2021) 630–645 Author name / Structural Integrity Procedia 00 (2019) 000–000

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(b) Fig. 13. Details of the coating application – specimen D.

3.4.2. Application The application of this coating was carried out in the following stages: • surface cleaning; • application of the epoxy primer; • application of two layers of epoxy-cement primer; • joint sealing; • sealing of metal parts.

Cleaning was carried out with a jet of compressed air to eliminate surface dust. The first layer, of epoxy primer, was prepared by mixing the two components with a drill mixer and adding water. The application took place by roller and hardening for the application of subsequent layers after 4 hours. The second layer, of epoxy-cement primer, was prepared by mixing the first two components in liquid phase and finally the third in powder, making sure that the mixture was free from lumps. The application took place by roller and hardening for the application of subsequent layers after 6 hours. The last layer, of epoxy-cement primer, was applied similarly to the previous one with the addition of silica sand to the mixture in order to obtain a trowelable mortar. Complete maturation is reached in 7 days. Finally, the sealing of the through metal parts was carried out by sprinkling the perimeter of the metal part with an abundant dose of fillerized primer. The requires 7 days for curing.

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Fig. 14. Specimen D.

4. Experimental Test The performed tests are designed to verify the resistance to negative pressures, or gas pressures that move from the inside of the specimen to the outside. The test therefore involves the injection of nitrogen at a pressure higher than the atmospheric one in order to create the required pressure gradient. The overpressure induced in the specimens was monitored during the individual tests thanks to a previously installed pressure gauge, which made it possible to detect these overpressures.