Recycling of steel fibres and spent equilibrium catalyst in ultra-high performance concrete: Literature review, research gaps, and future development

Abstract

Recently the Ultra-High Performance Fibre Reinforced Concrete (UHFRC) presents remarkable advantages compared to the other types of concrete. Compared to the ordinary concrete, higher packing density was achieved using refine aggregates which resulted in increasing density by the percentage of 15% and consequently compressive strength of 160%. Additionally, higher durability focusing lower water absorption factor of 1 and chloride ion diffusion of 1 mm were reported. The main drawback is related to the initial cost of this material which are mainly related to the higher prices of cement and steel fibre which limited to use it frequently. Based on this fact the paper is prepared by introducing potentialities of using some recycled materials which can be utilized for producing some eco-efficient and affordable UHPFRC. Emphasis is given for employing Recycled Steel Fibre (RSF) from end-life tires for reinforcing cementitious matrix concrete and spent Equilibrium catalyst (Ecat) from the oil refinery company to be partially replaced by sand and/or cement in concrete mixtures.Detrimental effects of RSF by 4% decreasing the compressive strength was reported in the literature for producing HPC due to adverse effects of rubbers and synthetic particles attached to the RSF. Consequently, maximum volume of these particles was suggested no to be more than 5%. Tensile properties improvement of HPC was reported using RSF by increasing ductility and postcracking behaviour with higher than 1% volume of friction RSF. Regarding to the effects of RSF on the early age concrete, 67% of shrinkage was reported to be occurred at the end of 4 days casting. Higher affinity for water absorption of Ecat was fund to be important factor in decreasing workability of fresh mortars which affects the initial and final setting time. Compressive strength improvement about 45% was reported when 15%–20% of cement was replaced by Ecat.