Correlation of strength to apparent porosity of geopolymers – Understanding through variations of setting time

•Effect of molar ratio on compressive strength was investigated for geopolymer mortars.•Short, 2h long heat treatment time was applied.•Sample with Na2O/Al2O3=1, SiO2/Al2O3=2.9 surpassed 80MPa at 28days.•Uncertainty of apparent porosity determination increased with setting time.•Setting time was pri...

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Bibliographic Details
Published in:Construction & building materials 2015-09, Vol.93, p.983-988
Main Authors: Balczár, Ida, Korim, Tamás, Dobrádi, Annamária
Format: Article
Language:English
Subjects:
Aluminum oxide
Analysis
Apparent porosity
Binding
Building materials
Compressive strength
Construction materials
Geopolymer
Mechanical properties
Microstructure
Moisture content
Polymers
Porosity
Portland cement
Setting time
Silicon dioxide
Strength
Strength of materials
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Summary:•Effect of molar ratio on compressive strength was investigated for geopolymer mortars.•Short, 2h long heat treatment time was applied.•Sample with Na2O/Al2O3=1, SiO2/Al2O3=2.9 surpassed 80MPa at 28days.•Uncertainty of apparent porosity determination increased with setting time.•Setting time was primarily controlled by the alkali concentration. The research focused on manufacturing a novel binding material system featured by adequate strength. The molar ratio of the components was optimised to reach this favourable property together with a cost-cutting reduction of heat treatment time. Compressive strength and the relation of apparent porosity to setting time were studied and evaluated. Four sets of samples were prepared, and the SiO2/Al2O3 as well as the Na2O/Al2O3 molar ratios were varied over a wide range. As a result, the compressive strength of the samples (51.3 and 81.4MPa at 7 and 28days age, respectively) surpassed the highest strength class of Portland cements (52.5MPa). There was a strong relationship between the uncertainty of apparent porosity determination and setting time, furthermore, the setting time was controlled primarily by the alkaline concentration of the activating solution and secondly by the soluble silica or water contents.
ISSN:0950-0618
DOI:10.1016/j.conbuildmat.2015.05.059