International Concrete Abstracts Portal

Editor: Moncef L. Nehdi

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. Likewise, in 2013, Americans generated about 254 million tons of trash. They only recycled and composted about 87 million tons (34.3%) of this material. On average, Americans recycled and composted 1.51 pounds of individual waste generation of around 4.4 pounds per person per day. In 2011, glass accounted for 5.1 percent of total discarded municipal solid waste in the USA. Moreover, energy production and other sectors are generating substantial amounts of sludge, plastics and other post-consumer and industrial by-products. In the pursuit of its sustainability goals, the construction industry has a potential of beneficiating many such byproducts in applications that could, in some cases, outperform the conventional materials using virgin ingredients. This Special Publication led by the American Concrete Institute’s Committee 555 on recycling is a contribution towards greening concrete through increased use of recycled materials, such as scrap tire rubber, post-consumer glass, reclaimed asphalt pavements, incinerated sludge ash, and recycled concrete aggregate. Advancing knowledge in this area should introduce the use of recycled materials in concrete for applications never considered before, while achieving desirable performance criteria economically, without compromising the long-term behavior of concrete civil infrastructure.

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In recent years, a very important environmental issue all over the world is the disposal of waste tires. One possibility being explored is to use rubber from waste tires to replace part of the natural aggregates in conventional concrete, resulting in a product called crumb rubber concrete (CRC). Recent research on CRC is focusing on using it in structures subject to seismic loads, due to its higher ductility, damping ratio, and energy dissipation compared to conventional concrete. However CRC can have lower compressive strength (f’_CRC), tensile strength (f’_TRC), and modulus of elasticity (E_RC) when compared with conventional concrete. This paper presents empirical models able to predict the CRC characteristics (f’_CRC, f’_TRC, and E_RC). The proposed models are verified through the results of 148 CRC mixes as well as compared with two previous models. The proposed models resulted in predictions of the CRC characteristics with only 10.7%, 12.6%, and 11.3% errors in the predictions of f’_CRC, f’_TRC, and E_RC, respectively. The proposed f’_CRC model reduced the mean, standard deviation and maximum error percentages by 24.6%, 5.8%, and 20.2%, respectively, compared with the nearest best predictions by previous models. The proposed models can aid structural engineers who are considering CRC as an environmentally-friendly alternative to conventional concrete in structural applications.

The disposal of scrap tires has become an international concern. In Canada and the USA, hundreds of thousands of tires have been stockpiled with some authorities banning its landfill. The construction industry can beneficiate substantial volumes of shredded and crumb tire. This article is an overview of recycling tire rubber in concrete. It is shown that concrete with 20-30 MPa incorporating crumb and chipped tire rubber particles can be produced with a tire rubber aggregate replacement content less than 20%. Such a rubcrete can have adequate workability and air content, relatively low compressive strength, tensile strength and modulus of elasticity, high impact strength, high ductility and fracture toughness, and reasonable freeze-thaw resistance. The major concern with rubcrete is the significant loss of compressive strength and stiffness at high levels of aggregate replacement with tire rubber particles. However, surface treatments to enhance the bond of tire rubber particles to cement paste represent an efficient approach for enhancing the mechanical properties of rubcrete. Replacing coarse and/or fine aggregate with tire rubber particles results in increasing the strain capacity of concrete. Significant increase in material ductility and ability to absorb energy with increasing tire rubber particle content was reported. It is shown that rubcrete has a clear potential where flexibility and ductility are sought after, for example in tunnel linings, shock barriers, etc.

Concrete is the world’s most used construction material, and although it offers many advantages over other building materials from an environmental perspective (e.g., durability, thermal properties), the negative environmental impact of traditional concrete is of growing concern as its use increases. This paper highlights significant findings from a recent study focused on identifying alternate materials to be used in concrete to mitigate its negative environmental impacts. This study specifically researched structural-grade concrete in which 100 percent of the portland cement was replaced with self-cementitous hydraulic fly ash and the aggregates were replaced with pulverized post-consumer glass from the container industry. In particular, this paper presents the results of mechanical (compressive and tensile strength, elastic modulus), and durability (ASR, absorption, abrasion, chloride permeability) tests performed on two such concretes made with fly ashes from power plants in Wyoming and Kansas. Overall, the fly ash/glass concretes tested in this research program showed promise for use in the construction industry. They exhibited 28-day unconfined compression strengths in excess of 4,000 psi (28 MPa); although their corresponding tensile strengths were somewhat lower than would be expected based on the behavior of conventional concretes. Relative to durability, the results of the ASR tests were mixed, depending on the manner in which the ASR testing was conducted. The absorption results and abrasion resistance of the two concretes were found to be similar to conventional concretes, and the permeability test results indicate a total charge passed of less than 1,000 coulombs, which correlates with “very low” likelihood of chloride ion penetration being an issue.

Green construction has been a very important aspect in the concrete production field in the last decade. One of the most problematic waste materials is scrap tires. The use of scrap tires in civil engineering is increasing. This article investigates the dynamic properties of concrete with replacement of fine aggregate with scrap tire. Two different rubberized concrete mixtures were designed. The first set; variable slump (VS) was designed to keep the mix proportions constant with rubber replacement as the only variable. The other set; constant slump (CS) was designed to keep the workability the same using superplasticizer. The compressive strength of the concrete was reduced by the use of rubber. The viscous damping ratio was investigated using free vibration tests with impact hammer on simply supported beams and drop weight tests. The replacement of up to 20% of sand with rubber resulted in an increase in damping with the increase being more in the CS beams as well. Beyond 20%, the effect on damping was insignificant. The average hysteresis damping was found to increase with the increase of rubber content. The fracture energy was found to increase with the increase of rubber content up to 20%. Microstructure investigation was also performed on the two mixes. It is concluded that the choice of the rubber content and the mixing process can have a significant effect on the dynamic properties of rubberized concrete. Recommendations for these two aspects were provided.