Fly ash and zinc slag blended geopolymer: Immobilization of hazardous materials and development of paving blocks

Abstract

The potential for practical application of fly ash, zinc slag and their blends for geopolymer synthesis at ambient temperature have been investigated in this paper. Fly ash is an alumino-silicate byproduct suitable for geopolymer reaction, but its low reactivity at ambient condition is the restriction of its bulk utilization. Above limitation can be overcome by blending with zinc slag (ZS). Additionally, ZS contains heavy and toxic metals (Pb, Zn, Cr, Cd, As), which can be stabilize in Al-Si based geopolymer network structure. Isothermal conduction calorimetry (ICC) is used to monitor the geopolymer reaction with time. Slag rich specimens are characterized with higher rate of reaction with augmented peak. The mineralogy and microstructure of the geopolymers have been examined through X-ray diffraction and scanning electron microscope. The detected chief reaction product is N-(C)-AS -H and C-(N)-AS -H 1 type hydrated gel. Continual improvement of compressive strength of the geopolymers with increasing slag content is explained with higher degree of reaction, formation of more reaction products and development of compact microstructure. According to toxicity characteristic leaching procedure (TCLP), toxic metals leaching is within permissible limit. Paver blocks using 40−80 wt% ZS has been developed, which meets IS 15,658: 2006 standard and comply with US-EPA specification.

Quarry Waste as Precursors in Geopolymers for Civil Engineering Applications: A Decade in Review

“…Various papers have included blast furnace slag as a precursor for producing geopolymers containing quarry waste [29,33,34,36,37,43,[53][54][55][56][57][58][59]. The potential of using geopolymers consisting of copper mine tailings and slag for pavement construction was investigated [33].…”

Fly Ash-Based Geopolymer Building Materials for Green and Sustainable Development

“…Kaur et al [21] indicated that approximately 1.2 times more compressive strength could be obtained when a combination of NaOH and Na 2 SiO 3 was added to fly ash, compared to the use of NaOH only. The compressive strength increased as NaOH concentration increased from 8 to 16 M. Thus, the increase of NaOH concentration caused a significant acceleration of dissolution reactions, promoting the early stages of the geopolymerization process [24,25]. A maximum compressive strength of 40.42 MPa was obtained when fly ash was activated with 16 M NaOH and mixed with a sand to fly ash ratio of 3:1 [21].…”

“…The curing temperature and aging period not only play a significant role as accelerators of the chemical reactions, but also determine the extent of those reactions [30,36]. The aging periods mostly used to test the compressive strengths of geopolymer materials are 7 and 28 days [21,25,[37][38][39][40][41][42].…”

“…Wang and Zhao [32] demonstrated that a dosage of 25 wt% of fly ash or slag was crucial to obtain excellent flame retarding efficiency. Nath [25] developed a fly ash and zinc slag (40−80 wt %) blended geopolymer for the immobilization of hazardous materials and paving blocks. Furthermore, fly ash-based geopolymer spheres were evaluated as a methylene blue adsorbent material by Novais et al [44].…”

“…The properties of geopolymers are very similar to OPC when formed under appropriate conditions [46]. However, there is a strong difference between Portland cement hydration and alkali activation of fly ash [24,25]. Alkali activation is similar to the chemistry involved in the synthesis of large groups of zeolites [11].…”