Effect of bar yielding and heat on bond behavior between steel bar and high-strength concrete containing waste PET by pullout and beam tests: Experiments and predictions

Abstract

In this work, the effect of elevated temperatures and steel bar yielding on bond behavior between steel bar and high-strength concrete containing waste polyethylene terephthalate (WPET) was addressed in the pre- and post-yielding phases via the pullout and beam tests. For that end, 36 and 12 specimens were manufactured for the pullout and beam tests, respectively. Variables considered in this work were content of WPET particles used in place of natural fine particles in concrete (0 and 10%), diameter of steel bars (12 and 16 mm), embedment length (5 and 10 times the bar diameter), and exposure temperature (25, 200, and 600 °C). Then, the effect of these factors on different parameters including the concrete compressive strength, steel bar-concrete bond behavior, bond failure mode, and bond stress-slip graph was explored. The results of both types of tests indicated that partially replacing the natural fine aggregate of concrete with WPET and increasing the exposure temperature had a reducing effect on the steel bar-concrete bond strength. In the specimens without WPET, using a bar with a greater diameter led to higher bond strength than using a bar with a lower diameter for low exposure temperatures (25 and 200 °C); however, for high exposure temperatures and in the presence of WPET, an inverse trend was observed. In addition, the reducing effect of these factors (high temperatures and polymeric waste aggregate) was more significant in the specimens reinforced with a bar of a greater diameter. The effect of the bar yielding was in the form of a drastic reduction of the maximum bond strength relative to that of the similar specimens without the bar yielding. Moreover, in the case of the yielding of bars, bars with a greater diameter had higher bond strength than those with a smaller diameter. A factor equal to 1.04 was proposed based on the obtained results to convert the bond strength results of the beam test into those of the pullout test. Finally, a four-line prediction model for the unyielded bond strength was developed, and a reduction factor was developed based on a formula proposed by fib Model Code 2010 to consider the effect of the bar yielding.