Use of cooper slag for surface treatment of slip-critical high-strength bolts

Introduction. The article discusses the results of testing slip-critical high-strength bolts whose contact surfaces are treated using copper slag having a fraction of 0.5–2.5 mm (this processing method was used directly on the construction site for the installation of roof steel structures covering a concert hall). An additional assessment of the bearing capacity of the samples was carried out factoring in local damage to the friction surfaces detected around bolt holes during installation.

Aim. In this work, the actual friction coefficient μ of friction joints was determined when processing contact surfaces using a copper slag of a fraction of 0.5–2.5 mm in order to confirm the design friction coefficient of μ = 0.42.

Materials and methods. The manufacturing and testing of samples of friction joints were carried out following company standard 006-97 «High-strength bolts in steel structures of bridges». Each sample comprised a stack of three steel C355 plates having a thickness of 16, 25, and 16 mm (GOST 27772-2015), tightened using a high-strength bolt M27 (10.9) (GOST 52644). The control tests of three groups of samples where contact surfaces were treated differently were carried out: № 1 – factory, № 2 – treatment using copper slag of a fraction of 0.5–2.5 mm, № 3 – treatment using copper slag of a fraction of 0.5–2.5 mm, with an artificial defect created around the bolt hole.

Results. On the basis of the obtained test results, it was concluded whether the further treatment of the surface of friction joints using copper slag can be employed directly on the construction site.

Conclusions. The treatment of friction surfaces using a copper slag of a fraction of 0.5–2.5 mm offered a friction coefficient μ at or above that of the design value (0.42) (in these specific conditions, even including the identified local defects modeled during testing). Although such treatment remains unregulated by regulatory documents, it is gaining great popularity. Therefore, it is necessary to carry out additional research on the use of copper slag (including various fractions) in order to substantiate the introduction of this method in regulatory documents.

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