Effect of crumb rubber on the punching shear behaviour of reinforced concrete slabs with openings

This study aims to evaluate the mechanical properties of concrete incorporated with crumb rubber (CR), i.e. rubberised concrete, and investigate the punching shear behaviour of rubberised concrete slabs with openings adjacent to columns. For this purpose, four concrete mixtures with different percentages (0%, 5%, 10% and 20%) of CR as volume replacement for fine aggregates were prepared. Twelve slabs were cast (i.e. three slabs for each mixture). One slab had no opening, the second slab had an opening with a size of 100x100 mm2 and the third slab had an opening with a size of 150x150 mm2. Results showed that the use of CR exerted a negative effect on the mechanical properties of concrete. Meanwhile, the addition of up to 5% CR caused a slight reduction in the compressive strength, tensile strength and flexural strength of rubberised concrete. The experimental results indicated that the punching shear strength and stiffness of rubberised concrete slabs decreased with increasing CR. However, the toughness of the test specimens increased by using CR content up to 5% and then declined for 10% and 20% CR contents. Openings in flat slabs adjacent to the column face cause a significant reduction in punching shear strength, and punching shear strength decreases with an increase in opening size. Finally, the accuracy of four design code equations, namely ACI 318-2014, ECP 203, BS8110 and Euro -2 in predicting the punching strength of rubberised concrete slabs with or without openings is evaluated and compared with the experimental results.