ZEMCH 2015 - International Conference Proceedings | Page 781

The concrete reinforced with industrial steel fibres( ISF) was realized with hooked end fibres( length / diameter = 50) while the recycled steel fibres( RSF) are characterized by an average equivalent length Leq = 12.63 mm, average diameter Φav = 0.33 mm with an equivalent aspect ratio Leq / Φav = 41.21( C. O. V.= 13.23 %).

Mix-design As discussed by the authors in previous papers( Aiello et al. 2009; Centonze et al. 2012), the workability represents a main issue during the optimization of the mix because of the tendency of the recycled steel fibres to bundle within the fresh concrete. Furthermore, this rheological property is negatively affected as the quantity of fibres increases( ACI 544.1R 1996; Mohammadi et al. 2008; Yazici et al. 2007). In order to limit this tendency, it was used a forced mixing because the generated friction can allow a better distribution of fibres into the mixture. Moreover, the use of this mixer in the laboratory scale is advantageous in view of the transfer to larger scale applications. The mixing stages of the materials were carried out by introducing the aggregates and then, gradually, water and cement. Then the admixture was introduced and at the end, when the mixture reached a sufficient workability the fibres were added( Fig. 6). The reinforced mixture was developed on the basis of the optimal rheological and mechanical properties obtained for the plain concrete( PC). Two reinforced mixtures were realized for comparison purposes: the first one with recycled steel fibres( RSFC) and the other with industrial steel fibres( ISFC). The mix design applied for each one is summarized in the following Table 1. The cement content( CEM II A-LL 42.5R), the water content and the w / c ratio were always constant for each mix, equal to 300 kg / m3, 180 l / m3 and 0.58 respectively. It was also used a water reducing admixture( Creactive No. W. A. 135), which allowed higher fluidity avoiding segregation. For a better comparison of the reinforced concrete mixtures, the content of steel fibres was constant in terms of % v( volume of concrete), taking into account the different densities of the two utilized types of fibres: 6.9 kg / dm3 for RSF and 7.82 kg / dm3 for ISF.

Application of steel fibres derived from scrap tires as reinforcement in concrete 779