Performance of oxygen/argon plasma-treated steel fibres in cement mortar

Abstract

Steel fibres are used widely to control initiation and growth of cracks in concrete. However, the bond between steel fibres and the cement matrix in steel fibre-reinforced concrete (SFRC) is almost always purely physical. A viable approach to reduce cracking in fibre-reinforced concrete is to supplement the physical bond between fibres and cement matrix with a relatively uniform chemical bond along the fibres' surface. However, despite the promising results reported for other types of fibres, little attention has been paid to chemical surface treatment of steel fibres to improve their ability to bond with concrete. In this study, an oxygen/argon plasma treatment process is investigated as a potential technique to improve the bond between steel fibres and a cementitious matrix. Several variations in treatment parameters are made in order to identify the optimal treatment conditions. The results of X-ray Photoelectron Spectroscopy and surface energy measurements confirm that plasma treatment can significantly increase the fibres’ surface energy and consequently the strength of the fibre-cement bond. The improved bond between steel fibres and concrete is confirmed by the results of fibre pull-out tests, as well as the reduced average crack size observed in restrained drying shrinkage tests. Moreover, the results indicate considerable decrease in the volume of permeable voids in SFRC due to plasma treatment of steel fibres.