Quantitative kinetic and structural analysis of geopolymers Part 2. thermodynamics of sodium silicate activation of metakaolin

Zhang, Zuhua and Provis, John L. and Wang, Hao and Bullen, Frank and Reid, Andrew (2013) Quantitative kinetic and structural analysis of geopolymers Part 2. thermodynamics of sodium silicate activation of metakaolin. Thermochimica Acta , 565. pp. 163-171. ISSN 0040-6031

Abstract

The paper describes the outcomes of a study using isothermal conduction calorimetry (ICC) to characterize the geopolymerization kinetics of metakaolin activated with sodium silicate. Two exothermic peaks are observed in the calorimetric curves for all systems reacting within the temperature range 20-40°C. The peaks are assigned to the dissolution of metakaolin, and the formation of geopolymeric gels with disordered structure, respectively. Compared with the use of NaOH solution to activate metakaolin, the presence of soluble silicate in the activator hinders the reorganization of the local structure of geopolymeric gels and also suppresses the formation of zeolites or zeolite precursors. The ICC data are used via a thermochemical model to quantify the reaction kinetics of geopolymerization, by assuming that the geopolymeric gels have an analcime-like local structure and taking into account the speciation of the silicate monomers and dimers in the activator. Decreasing the modulus from 1.6 to 1.0 increases the fractional reaction extent from 0.12 to 0.26 after 72h at 25°C. When the modulus is 1.2, increasing the reaction temperature from 20°C to 35°C results in an improved reaction extent from 0.24 to 0.35. The rapid polymerization that occurs at 40°C appears to hinder the further reaction of MK and consequently results in a lower reaction extent than at 35°C. Combined with the findings from previous analysis of systems where NaOH was used to activate MK, the concentration of available Na+ appears to have a more pronounced influence on the extent of geopolymerization than temperature and the concentration of soluble Si. The higher reaction extent of the solid precursor particles with the soluble Si from the activator results in binders with more compact microstructure and higher mechanical strength. Considering the longer-term utilization of geopolymers, the addition of soluble silicate to the activator will delay the transformation of amorphous raw materials to locally ordered materials, potentially providing advantages in terms of microstructural stability in service.


Statistics for USQ ePrint 23763
Statistics for this ePrint Item
Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: © 2013 Elsevier B.V. Published version deposited in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Date Deposited: 17 Jul 2013 23:45
Last Modified: 03 Aug 2014 22:51
Uncontrolled Keywords: geopolymer; isothermal conduction calorimetry; kinetics; sodium silicate
Fields of Research : 03 Chemical Sciences > 0307 Theoretical and Computational Chemistry > 030703 Reaction Kinetics and Dynamics
09 Engineering > 0905 Civil Engineering > 090503 Construction Materials
03 Chemical Sciences > 0303 Macromolecular and Materials Chemistry > 030305 Polymerisation Mechanisms
Socio-Economic Objective: B Economic Development > 87 Construction > 8703 Construction Materials Performance and Processes > 870399 Construction Materials Performance and Processes not elsewhere classified
Identification Number or DOI: 10.1016/j.tca.2013.01.040
URI: http://eprints.usq.edu.au/id/eprint/23763

Actions (login required)

View Item Archive Repository Staff Only