A factorial experimental analysis of using wood fly ash as an alkaline activator along with coal fly ash for production of geopolymer-cementitious hybrids

Wenlin Yvonne Lin; Arun Kumar Prabhakar; Babu Cadiam Mohan; Chi-Hwa Wang

doi:10.1016/j.scitotenv.2019.135289

A factorial experimental analysis of using wood fly ash as an alkaline activator along with coal fly ash for production of geopolymer-cementitious hybrids

Sci Total Environ. 2020 May 20:718:135289. doi: 10.1016/j.scitotenv.2019.135289. Epub 2019 Nov 23.

Authors

Wenlin Yvonne Lin¹, Arun Kumar Prabhakar², Babu Cadiam Mohan¹, Chi-Hwa Wang³

Affiliations

¹ Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.
² NUS Environmental Research Institute (NERI), National University of Singapore, 1 Create Way, Research Wing-06-06, Singapore 138602, Singapore.
³ Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore. Electronic address: chewch@nus.edu.sg.

PMID: 31839313
DOI: 10.1016/j.scitotenv.2019.135289

Abstract

Alkaline activated materials such as geopolymers and cementitious materials derived from pozzolanic reactions offer several advantages over the currently widely used Portland cement, especially in terms of environmental sustainability and physiochemical properties. However due to the need of an alkaline activator, such as NaOH or KOH, which result in high production cost and requires skilled personnel, they have not been deeply explored and put to use. Here in this study, wood fly ash, a by product of wood combustion is used as an alternative source of alkaline activator for producing such alkaline activated materials along with coal fly ash, where the resulting geopolymer-cementitious hybrid (GCH) was characterized physico-chemically through electron microscopy, BET, FTIR, XRF & XRD. However, the leaching of heavy metals from the wood fly ash could potentially pose an environmental concern. Therefore, the focus of this study is to reduce the leachability factor of wood fly ash involved in the alkaline activated process and to understand the effects of various factors (i.e. water-to-ash ratio (w/a), method of curing, type of alkaline activator and ash sieving) on the leaching process, through factorial experimental analysis. The leaching patterns of various elements such as Pb, Zn, Cr, As. Hg, Se were studied along with the contributing factors and results showed that the dominant factor was the type of alkaline activator (i.e. Wood Fly Ash versus Na₂SiO₃). By comparing the leaching data to Denmark's leaching criteria, the best performing GCH sample was found to be 0.3DI_p_s (0.3 represents the w/a ratio, "p" denotes that samples were precured and "s" denotes sieving).

Keywords: Coal/wood fly ash; Factorial experimental design; Geopolymer; Green binder; Heavy metal immobilisation; Pozzolanic.