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