PSI - Issue 37

Jesús Toribio et al. / Procedia Structural Integrity 37 (2022) 1001–1006 Jesús Toribio / Procedia Structural Integrity 00 (2021) 000 – 000

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1. Introduction Prestressed concrete technique in civil engineering requires the use of heavily cold drawn pearlitic steels in the form of commercial prestressing wires. If they are surrounded by a corrosive environment, there is a decrease of the effective net section of the wires, so that the cohesion between steel and concrete is weakened. Corrosion products accumulation occupies a volume several times of that corresponding to the original material. Montemor et al. (2003) and Yüzer et al. (2008) demonstrated that the increment of volume of the corrosion products contributes to the appearance of stresses capable to generate cracking in the concrete. In addition, long-term material degradation can occur (Nykyforchyn et al., 2009) due to the simultaneous action of applied stresses and aggressive environment . It is seen that Cl – ions can induce the fracture of the passive film that would be formed at a pH of 12.5, as discussed by Hredil and Toribio (2014), Tang et al. (2012) and Li and Sagüés (2002), so that the pH inside the pit would decrease (Hredil and Toribio, 2014), thus enhancing hydrogen embrittlement, a really dangerous phenomenon in prestressed concrete structures as motorway viaducts where accidents are reported by Vehovar et al. (1998) due to the harmful action of hydrogen on the prestressing steel wire. Research on hydrogen embrittlement of cold-drawn pearlitic steel for prestressing wires has been published in the matter of notched specimens (Toribio, 1992; 1993; 1996) and cracked ones (Toribio and Lancha, 1993; 1998; Toribio and Ovejero, 1999; 2001; 2007; Toribio et al., 2004). However, in the scientific literature there is a clear scarcity of data on hydrogen embrittlement of smooth wires of cold drawn pearlitic steel, mainly due to the big scatter of experimental results, although some classical references can be found (Cherry and Price, 1980), as well as more recent ones (Hredil et al., 2015; Hredil and Toribio, 2016) In this research framework, the present paper studies the environmentally-assisted microstructural integrity of initially-smooth samples of cold drawn pearlitic steel wires (commercial prestressing steel wires). 2. Experimental procedure Mechanical properties of the commercial prestressing steel wires (cold drawn pearlitic steel) used are as follows: Young’s modulus E= 208 GPa, yield strength  Y = 1.49 GPa and ultimate tensile strength (UTS)  R = 1.83 GPa. An evaluation was made of the fracture behaviour exhibited by initially-smooth samples of cold drawn pearlitic steel ( commercial prestressing steel wires ) subjected to constant extension rate tensile (CERT) tests in aggressive environment promoted by a corrosion cell with a three electrode assembly: (i) metallic sample or working electrode, (ii) reference electrode ( saturated calomel electrode ) and (iii) counter-electrode (platinum electrode), cf. Fig. 1.

Fig. 1 Testing device.