Mobilization of oxyanion forming trace elements from fly ash based geopolymer concrete

1 online resource (200 pages) : PDF

2012

University of North Carolina at Charlotte

The suitability of fly ash based geopolymer concrete as a replacement for ordinary Portland cement (OPC) concrete depends on the mobility of elements from the material. Due to the alkaline nature of geopolymer concrete, there is a potential for the release of oxyanion forming elements such as As, Cr and Se which are characterized by their high mobility in the alkaline environment. In this study, geopolymer concretes were produced with varying amount of hydrated lime and subjected to tests that include pH dependence test, Dutch availability test, tank test, water leach test, mineralogical, microstructural analysis and geochemical modeling using PHREEQC/PHREEPLOT. The results of this study confirmed that As and Se and other oxyanion forming elements exhibit higher mobility in the alkaline pH. Further investigation using the Dutch availability and tank test showed that As have the highest mobility from all the geopolymer concretes. It also reveals that the mobility of As and Se reduces with time as the element becomes depleted in the matrix. Mobility of the two elements was observed to be lowest in the geopolymer concrete with 1% hydrated lime which suggest that the addition of 1% hydrated lime lead to reduction in the mobility of As and Se. Cr on the other hand have the same low mobility from all the geopolymer, this suggest that hydrated lime addition has no effect on the mobility the element. Finally, PHREEQC/PHREEPLOT identifies species of leached elements as As (5), Se (6) and Cr (6). These species of As and Se have low toxicity whereas the species of Cr is of the more toxic form, but it is released in level far below the Maximum Concentration Level (MCL) set by EPA for drinking water.

doctoral dissertations

Environmental engineering

Ph.D.

Coal Fly Ash
Geopolymer Concrete
Leaching
Oxyanion Forming Elements
Phreeqc/phreeplot
Xrd/sem

Infrastructure & Environmental Systems

Ogunro, Vincent

Daniels, John
Tempest, Brett
Pando, Miguel
Ozelkan, Ertunga
Orozco, Carlos

Thesis (Ph.D.)--University of North Carolina at Charlotte, 2012.

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Sanusi_uncc_0694D_10405

http://hdl.handle.net/20.500.13093/etd:270