PSI - Issue 11

Iara Silva et al. / Procedia Structural Integrity 11 (2018) 130–137

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Iara Silva et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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6.1. Identification of cracks

Cracks, in general, can be classified by two criteria, activity and opening. The classification of fissures in activity was considered relevant because it is directly linked to the cause of this pathological manifestation. Inactive cracks are understood as those in which the opening remains constant and the responsible cause, after a certain time, ceased to exist. Whereas, the active cracks are those that present opening variation and the responsible cause for their formation continues acting in the structure (Souza and Ripper (1998)), being able to evolve to a macro crack or disruption. Regarding the opening of cracks, the practical concepts of micro and macro cracks were considered. Micro cracks are fine, continuous gaps on the surface and along the concrete pieces and macro cracks are thicker openings that indicate a rupture, discontinuity or separation in parts. In addition, consideration has been given to the manufacturer's recommendation for the product used for the treatment, which is indicated for cases where the gaps of the static cracks are less than 0.4 mm. The objective of this study was to evaluate the possibility of cracks recovery in concrete sleepers through a treatment for their cracks and subsequent application on the track. Therefore, it was not considered the recovery of concrete sleepers already installed in the railroad, but only those still in the factory, inspected immediately after manufacture. The sleepers selected for this recovery treatment were those that, shortly after factory inspection, presented cracks considered stable. And the defects did not demonstrate significant depth and extension, were not too thick, pr esented no evidence of pieces’ surface separation or formation of cracks webs and, in which case, did not appear in positions considered critical - in the rails’ support region near the shoulders and very close to the ropes. The presence of very long, lon gitudinal and active micro or macro cracks, located in the region of rails’ settlement, near the shoulders and between the prestressed cables or originated from them (Fig. 1), was a reason for the disposal of the sleeper, which was not allowed to be recovered or reused. 6.2. Criteria for recovery

a

b

Fig 1. (a) macro cracks between prestressed cables; (b) micro cracks starting from the prestressed cables, with large longitudinal extensions.

Therefore, the concrete sleepers selected for this treatment had some inactive, thin and elongated cracks on their surface in random directions. On the other hand, the presence of longitudinal macro cracks and macro cracks between the prestressed cables and the rail settlement region caused the piece to be rejected.

6.3. Procedure Execution

The diagnostic technique used was visual inspection, performed simply with the naked eye or, when necessary, with the aid of optical instruments to enhance the visual capacity. Then, the cracked sleepers, which obeyed the established criteria, were submitted to the painting crystallization treatment.