Enhancing Crack-Resistant Behavior of Concrete Addis Ababa University Addis Ababa Institute of Technology (AAiT) School of Multi-Disciplinary Engineering Center of Materials Engineering (CME) Enhancing the Cracks-Resistant Behavior of Concrete Materials: Combined effects of TiO 2 Nanoparticles and Waste Plastics Fiber By Belete Balta Addis Ababa, Ethiopia June, 2020