Development of geopolymer concrete compositions

Introduction. Global warming and the cement industry’s significant contribution to carbon dioxide emissions (7–8 % of the total) make the search for environmentally friendly alternatives to Portland cement an urgent challenge. One of the most promising alternatives is geopolymers — heat-free binders produced through the alkaline activation of aluminosilicate raw materials. Geopolymers outperform conventional cement in terms of energy efficiency, resource conservation, and environmental performance, and their structure and chemical composition fundamentally differ from those of traditional cements. The use of geopolymers in construction can substantially reduce costs and improve the environmental situation in the regions.

Materials and methods. The materials investigated included fly ash, ash-and-slag mixture, ground granulated blast-furnace slag, potassium and sodium silicate solutions used for the preparation of the geopolymer binder. An IR 5081-5 press was employed to determine the strength of the binder specimens, while the strength of geopolymer concrete was tested using a TP-1-350 press. Frost resistance was evaluated using an accelerated method in a climate chamber. Water permeability was determined with an AGAMA-2PM testing apparatus.

Results. The study presents the results of a comprehensive investigation into the selection of geopolymer binder and concrete compositions as alternatives to conventional heavy concrete based on cement binders. The developed geopolymer concrete compositions correspond to concrete strength classes B15, B20, B22.5, B25, and B30. The effect of heat and moisture treatment on the strength characteristics of the geopolymer binder was examined.

Conclusions. Chemical and physico-mechanical analyses of the geopolymer binder components were carried out. The influence of the type of silicate solution and of the heat-and-moisture curing regime on the binder strength was investigated. Rational compositions of geopolymer binders and corresponding concretes were developed. Test results on water resistance, compressive and flexural strength, porosity, and frost resistance were obtained, and the workability of geopolymer mixtures (cone slump) was evaluated. According to the findings, geopolymer binder compositions up to class B30 can be successfully applied in the construction industry as an environmentally friendly alternative to Portland-cement concretes.

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