Electronic Thesis and Dissertation Repository


Master of Engineering Science


Civil and Environmental Engineering


Nehdi, Moncef L.


With increasing world population and urbanization, the depletion of natural resources and generation of waste materials is becoming a considerable challenge. As the number of humans has exceeded 7 billion people, there are about 1.1 billion vehicles on the road, with 1.7 billion new tires produced and over 1 billion waste tires generated each year. In the USA, it was estimated in 2011 that 10% of scrap tires was being recycled into new products, and over 50% is being used for energy recovery, while the rest is being discarded into landfills or disposed. The proportion of tires disposed worldwide into landfills was estimated at 25% of the total number of waste tires, which represents fire hazards and grounds for breeding of disease carrying mosquitoes. Moreover, waste generated during construction and demolition in the United States in 2014 was about 353.6 million tons. This is expected to increase worldwide with ageing civil infrastructure. Recycling tire rubber and demolition concrete as recycled concrete aggregate (RCA) poses technological challenges. Tire rubber tends to float during concrete mixing and placing due to its lower density, while RCA tends to absorb mixing water, causing loss of workability and shrinkage stresses.

In the present study, tire rubber and tire steel-wire along with RCA can be preplaced in the formwork, eliminating the problems above. Subsequently, a flowing grout is injected to fill inter-granular voids. This preplaced aggregate concrete (PAC) offers multiple sustainability advantages. It incorporates about 50% more coarse aggregate than normal concrete, thus reducing the demand for cement and the associated greenhouse gas emissions from cement production. The dense granular skeleton of PAC has a unique stress transfer mechanism, which better resists shrinkage and thermal contraction stresses due to the physical contact between granular particles. Moreover, the mixing and pumping energy of concrete and the associated labour are greatly reduced since only the smaller grout fraction is mixed and injected.

In this experimental study, 21 eco-efficient preplaced aggregate concrete mixtures were made with recycled concrete aggregate, along with 10%, 20%, 30%, 40% and 50% of scrap tire rubber, and 0%, 0.25%, 0.5% and 1.0% of tire steel-wire fibre. The mechanical properties of specimens from each mixture were explored, including compressive, tensile and flexural strengths, elastic modulus, post-crack behaviour, and impact resistance. While tire rubber decreased the mechanical strength and elastic modulus, combined tire rubber and steel-wire fibres provided the preplaced aggregate concrete with superior post-crack behaviour, higher toughness and better impact resistance. The Weibull distribution was found to be an effective tool for predicting the impact resistance of PAC mixtures. It is believed that the proposed sustainable technology of preplaced recycled aggregate concrete incorporating recycled tire rubber and tire steel-wire fibres can offer an eco-efficient construction procedure for pavements, sidewalks, road barriers, and other non-structural concrete. Further refinements, including the use of effective supplementary cementitious materials or geo-polymer grout can further enhance the mechanical strength and overall eco-efficiency of this technology.