Towards the development of sustainable concrete incorporating waste tyre rubbers: A long-term study of physical, mechanical & durability properties and environmental impact

The dramatic increase in the demand for vehicle tyres and consequently the rapid rise in associated waste rubber has been a concern for several decades. Rubber disposal has adverse effects on the environment, human health and a detrimental effect on sustainable development across the world. This paper investigates the effectiveness of a sodium hydroxide treatment method for waste rubber in addition to the utilisation of silica fume to improve the interfacial transition zone between the rubber and cement matrix. This has been shown to have important implication for the long-term development of physical and mechanical properties of concrete aged for 2 years. This study emphasises that while satisfactory improvements are attained through the rubber treatment alone, the actual performance of rubberized concrete containing silica fume could only be investigated over the long term owing to the slow pozzolanic reaction and its dependency on the formation of calcium hydroxide. The pretreatment of rubber and more specifically the utilisation of silica fume improved the durability of concrete over rubber replacement levels from ~20% to 40%. Long-term thermal conductivity and sound permeability of concrete containing tyre rubber were shown to have important consequences in energy conservation and social sustainability in construction practice. Results reported on the cost efficiency and consequently the CO2 emissions of concrete containing rubber do not only enhance awareness of the development of sustainable construction materials but also lead a cleaner alternative waste management route for tyre rubber.