Drying shrinkage of alkali activated fly ash: Effect of activator composition and ambient relative humidity

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Abstract

Alkali activated fly ash (AAFA) is an alternative concrete binder that could serve as a substitute for ordinary Portland cement (OPC) for certain engineering applications. While this material has significant environmental and durability benefits, its potential volume instability and propensity to shrinkage and cracking could be of great concern. The subject of the present paper is evaluating the magnitude of drying shrinkage in AAFA binders of different compositions and at various ambient relative humidities (RH). Four AAFA paste mixtures were prepared using class F fly ash and liquid sodium silicate activators with various alkalinity (pH) and silicate modulus (n=(SiO2/Na2O)molar). The results were also compared with an OPC paste with a similar initial porosity. All AAFA pastes were steam cured at 60°C for 24 hours, followed by 6 days of moist curing at 23oC, while the OPC specimens were moist cured at 23oC for 7 days. The shrinkage specimens were dried under nitrogen purge at different relative humidities. The results show that activators with intermediate pH and modulus led to AAFA binders with higher compressive strength, denser pore structure, and larger drying shrinkage. Regardless of the activating solution, AAFA pastes dried quicker, and reached equilibrium faster than OPC paste. AAFA pastes also lost more moisture, but generally exhibited a lower drying shrinkage than OPC at similar RH. Steam curing of AAFA for a longer period (7-day vs. 1 day) stabilized the structure of AAFA binders and lowered the drying shrinkage.

Original languageEnglish (US)
JournalSustainable Construction Materials and Technologies
Volume2016-August
StatePublished - Jan 1 2016
Event4th International Conference on Sustainable Construction Materials and Technologies, SCMT 2016 - Las Vegas, United States
Duration: Aug 7 2016Aug 11 2016

All Science Journal Classification (ASJC) codes

  • Civil and Structural Engineering
  • Building and Construction
  • Mechanics of Materials
  • Materials Science(all)

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