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Showing 1-5 of 12 Abstracts search results

Document: 

SP314

Date: 

March 6, 2017

Publication:

Symposium Papers

Volume:

314

Abstract:

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.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-314

DOI:

10.14359/51689772


Document: 

SP314-07

Date: 

March 1, 2017

Author(s):

Anto Sucic and Medhat H. Shehata,

Publication:

Symposium Papers

Volume:

314

Abstract:

Consideration of using high volume of Recycled Concrete Aggregate (RCA) in conventional concrete applications is rare due to the physical properties of RCA and its corresponding drawbacks. In the rare instance where RCA is utilized, replacement levels typically do not exceed 15-20% in order to minimize on the drawbacks. To take another approach, this paper presents results from a study aimed at maximizing the RCA replacement levels, while making only minor adjustments in mix design, to achieve both equivalent strength and durability performance of RCA concrete to their virgin aggregate counter parts. In order to investigate higher replacement levels, 15 MPa concrete criteria were followed to produce a high-volume, low-risk concrete readily produced in the ready-mix industry. Concrete specimens were tested for compressive strength, drying shrinkage, and effects of released alkalis from RCA on triggering disruptive expansion, if used with sand that marginally meets the alkali-silica expansion limit. Through modifications in mix design, the drawbacks of RCA (reduced strength, increased drying shrinkage, and promoting ASR potential) were successfully mitigated at coarse RCA replacement levels up to 100%.

DOI:

10.14359/51689737


Document: 

SP314-03

Date: 

March 1, 2017

Author(s):

Ayman Moustafa and Mohamed A. ElGawady

Publication:

Symposium Papers

Volume:

314

Abstract:

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.

DOI:

10.14359/51689741


Document: 

SP314-08

Date: 

March 1, 2017

Author(s):

Yasser Khodair and Bhagiratha Bommareddy

Publication:

Symposium Papers

Volume:

314

Abstract:

This paper studies the fresh, hardened, and durability characteristics of Self-Consolidating Concrete incorporating Recycled Concrete Aggregate (SCCRCA). Twenty concrete mixtures were divided into five different groups, with constant water to cementitious materials ratio of 0.38, based on the Recycled Concrete Aggregate (RCA) content: 0, 25, 50, 75, and 100% of natural coarse aggregate (NCA) replaced by RCA. All mixtures were designed to have slump greater than 500 mm (19.7 in). The Portland cement was substituted by different percentages of Fly Ash (FA) and Ground Granulated Blast Furnace Slag (S), while the control mixtures were prepared using 100% Portland cement. The fresh concrete properties of all mixtures were investigated, such as: flowability, deformability; filling capacity, and the ability to resist segregation. Moreover, the compressive strength at 3, 14, and 28 days, the tensile strength, and the free shrinkage up to 80 days were studied. Partial replacement of Supplementary Cementitious Materials (SCMs) for cement reduced the 28-days-compressive strength of SCCRCA mixtures compared to those of the control mixtures. Based on the outcomes of this research, replacing the natural coarse aggregate (NCA) in SCC by more than 75% RCA is not recommended. However, this percentage might change depending on a variety of factors.

DOI:

10.14359/51689736


Document: 

SP314-02

Date: 

March 1, 2017

Author(s):

Osama Youssf, Mohamed A. ElGawady, Julie E. Mills, and Xing Ma

Publication:

Symposium Papers

Volume:

314

Abstract:

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 (ERC) when compared with conventional concrete. This paper presents empirical models able to predict the CRC characteristics (f’CRC, f’TRC, and ERC). 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 ERC, 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.

DOI:

10.14359/51689742


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