Effect of Normal and Rubberized Concrete Properties on the Behavior of RC Columns Strengthened with EB CFRP Laminates and Welded Wire Mesh under Static Axial Loading

The huge amounts of old and damaged tires spread worldwide has caused many complex environmental risks. The old tires have been converted to crumb rubber (CR) and tire recycled steel fiber (RSF) to facilitate their use. This study used CR to partially replace natural sand in reinforced (RC) columns. Externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) laminates, welded wire mesh (WWM), and RSF were used to enhance the axial behavior of the tested columns to overcome the concrete deficiencies resulting from the inclusion of the CR instead of natural sand. Eighteen columns were prepared and tested to discuss the effects of strengthening type, CR content, RSF, and strengthening area on the axial behavior of the RC columns. Certain columns were internally reinforced with WWM, while others were externally strengthened with EB CFRP laminates. Partially or fully EB CFRP laminates were used to strengthen the columns. Moreover, one column was cast with NC and 0.2% RSF to investigate the role of RSF in confining the column. The results demonstrated a concrete strength reduction for the rubberized concrete (CRC) as the CR content increased. Conversely, the strengthened columns experienced higher load capacities than the corresponding un-strengthened ones cast with the same concrete mix. Moreover, adding 2% RSF to the NC mix could enhance the column capacity, although it decreased the concrete strength. Furthermore, using two CFRP layers increased the load capacity and ductility of the strengthened columns. The strengthened column cast with 50% CR showed the highest load efficiency (334.3% compared to the un-strengthened one).

Mechanical Properties and Anti-Spalling Behavior of Ultra-High Performance Concrete with Recycled and Industrial Steel Fibers

Experimental investigations on the mechanical properties of ultra-high performance concrete (UHPC) incorporating two types of recycled steel fiber processed from waste tires and three types of industrial steel fiber were carried out for comparison. Mechanical properties of UHPC include compressive strength, splitting tensile strength, fracture energy, and elastic modulus. Their explosive spalling behaviors under high temperatures were also investigated. The results show that all types of steel fiber exhibit a beneficial effect on the mechanical properties and the anti-spalling behavior of UHPC, except that recycled steel fiber with rubber attached (RSFR) has a slightly negative effect on the compressive strength of UHPC. Compared to industrial steel fibers, recycled steel fibers have a more significant influence on improving the splitting tensile strength and fracture energy of UHPC, and the improvement of RSFR was much higher than that of recycled steel fiber without rubber (RSF). UHPC that incorporates industrial hooked-end steel fiber (35 mm in length and 0.55 mm in diameter) exhibits the best resistance to explosive spalling, and the second is the RSF reinforced UHPC. The positive relationship between the fracture energy and the anti-spalling behavior of steel fiber reinforced UHPC can be presented. These results suggest that recycled steel fiber can be a toughening material and substitute for industrial steel fibers to be used in ultra-high performance concrete, especially RSFR.