Mechanical properties of concrete containing a high volume of tire-rubber particles

Due to the increasingly serious environmental problems presented by waste tires, the feasibility of using elastic and flexible tire-rubber particles as aggregate in concrete is investigated in this study. Tire-rubber particles composed of tire chips, crumb rubber, and a combination of tire chips and crumb rubber, were used to replace mineral aggregates in concrete. These particles were used to replace 12.5%, 25%, 37.5%, and 50% of the total mineral aggregate's volume in concrete. Cylindrical shape concrete specimens 15 cm in diameter and 30 cm in height were fabricated and cured. The fresh rubberized concrete exhibited lower unit weight and acceptable workability compared to plain concrete. The results of a uniaxial compressive strain control test conducted on hardened concrete specimens indicate large reductions in the strength and tangential modulus of elasticity. A significant decrease in the brittle behavior of concrete with increasing rubber content is also demonstrated using nonlinearity indices. The maximum toughness index, indicating the post failure strength of concrete, occurs in concretes with 25% rubber content. Unlike plain concrete, the failure state in rubberized concrete occurs gently and uniformly, and does not cause any separation in the specimen. Crack width and its propagation velocity in rubberized concrete are lower than those of plain concrete. Ultrasonic analysis reveals large reductions in the ultrasonic modulus and high sound absorption for tire-rubber concrete.     

Laboratory waste minimization by recovery of silver as nano-silver colloidal dispersion from waste silver chloride

The use of cyclic experiments, where the product of one reaction becomes the starting material for the next experiment, was proposed as an effective protocol for waste minimization in an educational lab. A simple, cheap and pollution-free method was developed for recovering silver as nano-silver colloidal dispersion from waste silver chloride in the laboratories of the Faculty of Health, Safety and Environment. Silver nanoparticles of the size 5–18 nm were recovered in the presence of sodium borohydride as a reducing agent and polyvinylpyrrolidone as a stabilizer agent. The nano-silver particles were studied for their formation, structure, stability and size using UV–Vis spectroscopy, transmission electron microscopy and dynamic light scattering techniques. The antibacterial assays of nanoparticles showed satisfactory results for Escherichia coli ATCC25922, Staphylococcus aureus ATCC 29213, and Acinetobacter baumanii (Clinical isolate). A laboratory experiment was designed in which students synthesize yellow colloidal silver solution from chemical waste silver chloride and estimate particle size using visible spectroscopy.     

Transformer oils as a potential source of environmental exposure to polychlorinated biphenyls (PCBs): an assessment in three central provinces of Iran

Environmental Science and Pollution Research - Polychlorinated biphenyl (PCB) contamination of oils from all transformers of the national electrical grid in Tehran, Qom, and Alborz, three central...