Punching strength behavior of reinforced concrete slabs with chips waste tire rubber

Every year waste in millions of tons is accumulated in the globe and much of it is non-biodegradable in nature, e.g., waste vehicle tires. In addition, waste recycling is energy consuming and pollution producing. Moreover, in this research, an experimental study is carried out to explore the behavior of chips rubberized concrete (CRC) in punching shear of flat plates. The experimental program comprises 10 specimens designed to fail by punching. The investigated parameters were the model type column, chips rubber ratio that used instead of coarse aggregate. Two cases are classified according to shape of column; square and rectangular. Each case consists of five specimens, the first specimen casted by normal strength concrete (NSC) and the other casted with CRC, by 5%, 10%, 15%, and 20%. The experimental results present that increasing chips rubber instead of coarse aggregate in two cases studies (square, and rectangular column) from zero to 20% shows a drop in the punching shear capacity by range of 13.54%, and 18.52%, and a reduction in the initial and secant stiffness by (16.06%, 25.19%), and (24.44%, 26.88%) respectively. Also, using 20% chips waste rubber increased the central deflection of two cases at service load by (37.39%, 47.28%), and increased the central ultimate deflection of the plates by about (24%, 24.58%) respectively. Furthermore, 20% replacement of coarse aggregate by rubber increased the ductility by (20.38%, 15.60%), and increased the energy absorption index significantly by 41.41%, and 28.75%, and led to decrease cracks width at service load by 36.11%, and 44.12% for the two cases respectively. From comparison between theoretical and experimental results one can get three equations relate the deficiency of punching shear capacity and chips rubber ratio, and concluded that the optimal replacement was by using 10% to15%. It can be inferred that the experimental results for square columns (S-R) specimens at all replacement percentages from zero to 20% less constrictive than ACI-code equations, whereas for rectangular columns (R-R) specimens the ACI-code equations can be used to replace 15%, after that the correction factor must be applied.