Enhancement of the cracking resistance and toughness characteristics of concrete with recycled synthetic inclusion

The main intent of this research was to determine the feasibility of utilizing recycled plastics and tires, through mechanical size reduction, as soft reinforcing inclusions in concrete.; Plastic flakes obtained through size reduction of high-density polyethylene and mixed plastic wastes were used at relatively high volume fractions as replacement for fine aggregate in light-weight concrete, and as an additive at relatively low volume fractions in normal-weight concrete. Plastic inclusions were effective in enhancing the flexural toughness, post-cracking impact strength and resistance to shrinkage cracking of light-weight concrete. The flexural strength of light-weight concrete could be maintained at an optimum plastic volume fraction; the compressive strength, however, was reduced in the presence of plastics. The positive effects of plastics could be attributed to their micro crack arrest and deflection, and particularly crack bridging effects. In compression, the adverse effects of stress redistribution and concentration resulting from the presence of low-modulus inclusions seem to overshadow any positive effects resulting from the interaction of plastics with cracks. In normal-weight concrete, relatively low volume fraction of plastic flakes had significant effects on reducing the restrained shrinkage crack widths; slight improvements in flexural toughness were also observed in the presence of plastics. Various aspects of the long-term performance of both the light-weight and normal-weight plastic-concrete composites under severe exposures were also investigated. While long-term performance was generally good, plastic flakes at relatively high volume fractions were observed to have adverse effects on de-icer salt scaling resistance; the normal-weight concrete with optimum plastic flake content exhibited satisfactory scaling resistance.; Tire inclusions were observed to be dimensionally unstable in concrete under moisture effects; coated tire particles at relatively low volume fractions, however, performed satisfactorily in reducing restrained shrinkage crack widths in normal-weight concrete.