Examination of the effect of waste pet and fiber additives on mechanical properties and crack formation of concrete

In this thesis, the mechanical properties of waste PET, polyester fiber and copolymer fiber reinforced concretes were determined and the internal structure of the concrete was evaluated by image processing method after the instrumented weight reduction test. For this purpose, 100x100x100 mm cube samples and 100x100x150 mm prismatic beam concrete sample mixtures were prepared, with 0.5%, 1.0% and 1.5% ground PET bottles, Polyester (PLY) and Copolymer fiber (KPF) additives in proportion to the volume of witness concrete and cement. After the ultrasound transmission velocity test and Schmidt hammer test were performed on the concrete samples, three-point loading test was performed on the prismatic beam samples, and the pressure test and instrumented weight reduction test were performed on the cube samples. In order to evaluate the post-experimental deformations (crack development) of concretes containing additives in different ratios, thin sections were made and these sections were examined by image processing method. While decreases in strength were detected in parallel with the increase in the concrete compressive strength, with the three-point loading test, the samples with 1.0% and 1.5% KPF additives (6.65-6.78 MPa, respectively) were obtained with higher flexural strengths than the witness sample (6.56 MPa). From the macrostructural analysis of the specimens subjected to the instrumented weight reduction test, it was determined that the PET-added specimens could not prevent the concrete specimens subjected to dynamic loads from breaking apart, whereas the PLY and KPF-added concretes prevented the concrete from breaking under dynamic loads. In addition, from the thin section examination, it was seen that the concrete with additives gave better results than the witness sample in terms of crack area, diameter, length and width.