Mechanical properties and structure of fly ash modified basic oxygen furnace slag based geopolymer masonry blocks

N. T. Sithole, F. Okonta, F. Ntuli

Research output: Contribution to journalArticlepeer-review


The objective of this research was to investigate the effect of Fly ash as a source of Si and Na on the mechanical performance of the Basic Oxygen Furnace Slag based (BOFS) geopolymer. BOFS has the lowest SiO2, Al2O3, Na2O content compared to other aluminosilicate sources (fly ash, metakaolin, granulated blast furnace slag and mine tailings); which have been used to effectively in geopolymer synthesis. SiO2 and Al2O3, contents of BOFS are respectively 5-7 times and 6-8 times lower than those of fly ash, metakaolin and granulated furnace slag (GBFS). This study evaluated the potential use of fly ash as a source of Si and Al to improve the mechanical performance of a BOFS based geopolymer. The influence of varying amount of Coal Fly Ash (FA) (10-50%) on UCS was studied. The effects of several factors on the UCS of BOFS geopolymer were also investigated. The test variables were molarities of sodium hydroxide (NaOH) (5 M, 10 M and 15 M); the solid to liquid ratio (20 %, 25 % and 30 %); and the curing temperature (20°C, 40°C, 80°C and 100°C). It was established that most favorable conditions for the geopolymer synthesis were FA was 10% of the mixture, 5M NaOH and 80°C curing temperature. Attempts has been made to relate the microstructure of BOFS/FA based composite with properties of geopolymer. Aggregation was identified as the main particulate process as established by the evolution of the particle size distribution (PSD) and its derived moments during the geopolymerisation process. The morphology of the particles appeared flaky and fluffy. The developed composite met the minimum requirement of ASTM C34-13 for a structural clay load bearing non exposed masonry and load bearing exposed side construction masonry.

Original languageEnglish
Pages (from-to)372-383
Number of pages12
JournalJournal of Solid Waste Technology and Management
Issue number3
Publication statusPublished - Aug 2020

All Science Journal Classification (ASJC) codes

  • Waste Management and Disposal


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