Utilizing Coal Fly Ash & Recycled Glass in Developing Green Concrete Materials

(Aggregate Research 5-26-2011) The environmental impact of portland cement concrete production has motivated researchers and the construction industry to evaluate alternative technologies for incorporating recycled cementing materials and recycled aggregates in concrete.
 
One such technology is based on using pulverized glass as sand or pozzolan.
 
Currently in the US, more than 600,000 tons/year of recycled glass bottles are stockpiled due to prohibitive shipping costs from recycling locations to glass melting factories {1}. This project proposes the use of this waste material along with fly ash (another industrial byproduct with landfill rate of 42.4 million tons/year in developing durable and environmentally positive concretes that can be used for various transportation applications.
 
The research findings can lead to development of recommendations and specifications that pave the way for adoption of this green technology. Green concrete materials produced based on outcomes of this research can be used in various transportation-related applications such as highway barriers, pavements, piers, platforms, and buildings.
 
The main challenge in producing durable glass-based concretes is the deleterious alkali-silica reaction (ASR) between glass particles and the cement past matrix that leads to formation of expansive ASR gel, and cracking of concrete. To mitigate ASR, application of 6 different fly ashes in replacement levels of up to 40% of portland cement in concrete will be evaluated. To optimize fly ashes in replacement levels of up to 40% of portland cement in concrete will be evaluated.
 
To optimize fly ash content and minimize it’s negative effects on early-age strength, it is important to determine exactly how fly ash mitigates ASR and what ash properties (e.g., composition, fineness, glass content) determines its effectiveness.
 
As such, this research seeks two major technical objectives:
 
1- Understanding the mechanism by which fly ash mitigates ASR;
 
2- Identifying factors that most significantly determine fly ash effectiveness against ASR.
 
This information will assist material designers in selecting the best available fly ash type and content in glass concrete. Also, the results can be applicable to other cementitious materials (e.g., slag, recycled glass powder) to evaluate their effectiveness against ASR.
 
In addition, the results will shed light on the strengths and shortcomings of ASTM C1567 test as a tool in determining the required pozzolan content to mitigate ASR.
 
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