#17: Develoment and properties of low-calcium fly ash-based geopolymer concrete

Curtin Research Report on Fly Ash-Based Geopolymer Concrete
Develoment and properties of low-calcium fly ash-based geopolymer concrete
by Djwantoro Hardjito and B.Vijaya Rangan
Research Report GC 1 (103 pages) (dec. 2005),
Report GC 2 (107 pages) (mar. 2006)
Faculty of Engineering, Curtin University of Technology
Perth, Australia

From 2001, we have conducted some important research on the development, manufacture, behaviour, and applications of Low-Calcium Fly Ash-Based Geopolymer Concrete. This concrete uses no Portland cement; instead, we use the low-calcium fly ash from a local coal burning power station as a source material to make the binder necessary to manufacture concrete. Concrete usage around the globe is second only to water. An important ingredient in the conventional concrete is the Portland cement. The production of one ton of cement emits approximately one ton of carbon dioxide to the atmosphere. Moreover, cement production is not only highly energy-intensive, next to steel and aluminium, but also consumes significant amount of natural resources. In order to meet infrastructure developments, the usage of concrete is on the increase. Do we build additional cement plants to meet this increase in demand for concrete, or find alternative binders to make concrete?

In this work, low-calcium (ASTM Class F) fly ash-based geopolymer is used as the binder, instead of Portland or other hydraulic cement paste, to produce concrete. The fly ash-based geopolymer paste binds the loose coarse aggregates, fine aggregates and other un-reacted materials together to form the geopolymer concrete, with or without the presence of admixtures. The manufacture of geopolymer concrete is carried out using the usual concrete technology methods. As in the case of OPC concrete, the aggregates occupy about 75-80 % by mass, in geopolymer concrete. The silicon and the aluminium in the low-calcium (ASTM Class F) fly ash react with an alkaline liquid that is a combination of sodium silicate and sodium hydroxide solutions to form the geopolymer paste that binds the aggregates and other unreacted materials.

This paper contains 2 reports. The first Report GC1 (curtin-flyash-GP-concrete-report.pdf) describes the mixes and the short term properties. The second Report GC2 (curtin_flyash_GC-2.pdf) provides the long term properties. See the conclusions below.

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Based on the test results, the following conclusions are drawn:
1. There is no substantial gain in the compressive strength of heat-cured fly ash- based geopolymer concrete with age.
2. Fly ash-based geopolymer concrete cured in the laboratory ambient conditions gains compressive strength with age.
3. Heat-cured fly ash-based geopolymer concrete undergoes low creep.
4. The creep coefficient, defined as the ratio of creep strain-to-instantaneous strain, after one year for heat-cured geopolymer concrete with compressive strength of 40, 47 and 57 MPa is around 0.6 to 0.7; for geopolymer concrete with compressive strength of 67 MPa this value is around 0.4 to 0.5.
5. The heat-cured fly ash-based geopolymer concrete undergoes very little drying shrinkage in the order of about 100 micro strains after one year. This value is significantly smaller than the range of values of 500 to 800 micro strain for Portland cement concrete.
6. The drying shrinkage strain of ambient-cured specimens is in the order of 1500 microstrains after three months. This value is many folds larger than that of heat- cured specimens, and the most part of that occurs during the first few weeks.
7. The test results demonstrate that heat-cured fly ash-based geopolymer concrete has an excellent resistance to sulfate attack.
8. Exposure to sulfuric acid solution damages the surface of heat-cured geopolymer concrete test specimens and causes a mass loss of about 3% after one year of exposure. The severity of the damage depends on the acid concentration.
9. The sulfuric acid attack also causes degradation in the compressive strength of heat-cured geopolymer concrete; the extent of degradation depends on the concentration of the acid solution and the period of exposure. However, the sulfuric acid resistance of heat-cured geopolymer concrete is significantly better than that of Portland cement concrete as reported in earlier studies.