Structural Performance of Alkali-Activated Soil Ash versus Soil Cement
Publication: Journal of Materials in Civil Engineering
Volume 28, Issue 2
Abstract
Alkaline activation of fly ash (FA) was used to improve the mechanical performance of a silty sand, considering this new material as a replacement for soil-cement applications, namely, bases and subbases, for transportation infrastructures. For that purpose, specimens were molded from mixtures of soil, FA, and an alkaline activator made from sodium hydroxide and sodium silicate. Uniaxial compression tests showed that strength is highly increased by the addition of this new binder. The results described a high stiffness material, with an initial volume reduction followed by significant dilation. All specimens have clearly reached the respective yield surface during shearing, and peak-strength Mohr–Coulomb parameters were defined for each mixture. The evolution of the microstructure during curing, responsible for the mechanical behavior detected in the previous tests, was observed by scanning electron microscopy. These results were compared with soil-cement data obtained previously with the same soil at similar compaction conditions. The main difference between both binders was the curing rate, with alkali-activated specimens showing a more progressive and long-lasting strength increase. This was analyzed taking into account the chemical process responsible for the behavior of the mixtures.
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Acknowledgments
The authors would like to acknowledge the staff at the Chemical Engineering Department of University of Porto, in particular, Professors Fernão Magalhães and Adélio Mendes, for allowing the use of particle size analyzer; the company Pegop—Energia Eléctrica SA, which runs the thermoelectric-power plant of Pego, for the supply of FA; the Electronic Microscopy Unit at the University of Trás-os-Montes e Alto Douro for the SEM, EDS, and XRD analysis; the MCTES/FCT (Portuguese Science and Technology Foundation of Portuguese Ministry of Science and Technology) for their financial support through the SFRH/BPD/85863/2012 scholarship; the Agência Nacional de Inovação for their support through the ECOSOLO project (FCOMP-01-0202-FEDER-038899); and to Marco de Laureto for the help in the laboratory work.
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Published In
Journal of Materials in Civil Engineering
Volume 28 • Issue 2 • February 2016
Copyright
© 2015 American Society of Civil Engineers.
History
Received: Dec 9, 2014
Accepted: Jun 22, 2015
Published online: Aug 13, 2015
Discussion open until: Jan 13, 2016
Published in print: Feb 1, 2016
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