The series of photographs shows expansion of fly ash geopolymer concrete blocks heat-cured and then immersed in an extreme alkali medium at 80 degrees Celsius for 14 days. The blocks heat-cured at 200 degrees Celsius display only limited fine cracking indicating low expansion, compared to the others.
Fly ash generated by coal power generation can be repurposed into geopolymer concrete. However, a critical durability problem has been low resistance to alkali attack.
Researchers at the University of Johannesburg have found that high temperature heat-treatment at 200 degrees Celsius can halve this harmful mechanism in fly ash geopolymer concretes.