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Open AccessArticle

Mechanical Properties of Geopolymers Synthesized from Fly Ash and Red Mud under Ambient Conditions

by Nevin Koshy 1,2,†, Kunga Dondrob 1,†, Liming Hu 1,*, Qingbo Wen 1 and Jay N. Meegoda 1,3
State Key Laboratory of Hydro-Science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100091, China
Department of Civil Engineering, Indian Institute of Technology Jammu, Jammu and Kashmir 190006, India
Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 071021982, USA
Author to whom correspondence should be addressed.
Joint first authors.
Crystals 2019, 9(11), 572;
Received: 20 September 2019 / Revised: 25 October 2019 / Accepted: 30 October 2019 / Published: 31 October 2019
(This article belongs to the Special Issue New Horizons in Zeolites and Zeolite-Like Materials)
Aluminosilicate gels form geopolymers and nanocrystalline zeolites which have comparable strength properties, making them a potential replacement for ordinary Portland cement. The study explores the use of two untreated industrial wastes, Class-F fly ash and red mud, for synthesizing geopolymeric material at ambient synthesis conditions. The high alkalinity present in the red mud was exploited for the dissolution of silica in the fly ash and red mud. The mechanical, mineralogical, microstructural, and pore characteristics were analyzed and the contributions of curing period, Si/Al, Na/Al, and liquid-to-solid (L/S) ratios on the compressive strength of the end products were also investigated. The alkalinity of the system due to the red mud was adequate for the dissolution of raw fly ash and the subsequent formation of aluminosilicate gels. The strength of the end product was directly proportional to the initial Si/Al ratio and the specimens with highest fly ash content exhibited highest compressive strength values after 28 days of curing. Furthermore, fly ash contributed to the formation and distribution of interstitial and capillary pores in the aluminosilicate matrix. The lowest L/S ratio of the initial mix resulted in the end product with the highest unconfined compressive strength. View Full-Text
Keywords: fly ash; red mud; geopolymer; characterization; unconfined compressive strength fly ash; red mud; geopolymer; characterization; unconfined compressive strength
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Koshy, N.; Dondrob, K.; Hu, L.; Wen, Q.; Meegoda, J.N. Mechanical Properties of Geopolymers Synthesized from Fly Ash and Red Mud under Ambient Conditions. Crystals 2019, 9, 572.

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