Workability and strength of coarse high calcium ﬂy ash geopolymer
, T. Chareerat
, V. Sirivivatnanon
Department of Civil Engineering, Khon Kaen University, Khon Kaen 40002, Thailand
CSIRO Manufacturing and Infrastructure Technology, North Ryde 2113, Sydney, Australia
Received 10 February 2006; received in revised form 1 August 2006; accepted 11 November 2006
Available online 27 December 2006
In this paper, the basic properties viz., workability and strength of geopolymer mortar made from coarse lignite high calcium ﬂy ash
were investigated. The geopolymer was activated with sodium hydroxide (NaOH), sodium silicate and heat. The results revealed that the
workable ﬂow of geopolymer mortar was in the range of 110 ± 5%–135 ± 5% and was dependent on the ratio by mass of sodium silicate
to NaOH and the concentration of NaOH. The obtained compressive strength was in the range of 10–65 MPa. The optimum sodium
silicate to NaOH ratio to produce high strength geopolymer was 0.67–1.0. The concentration variation of NaOH between 10 M and
20 M was found to have a small eﬀect on the strength. The geopolymer samples with high strength were obtained with the following
practices: the delay time after moulding and before subjecting the sample to heat was 1 h and the optimum curing temperature in the
oven was 75 °C with the curing duration of not less than two days.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Geopolymer; High calcium ﬂy ash; Lignite; Workability; Strength
Manufacturing of Portland cement is an energy inten-
sive process and releases a large amount of green house
gas to the atmosphere. It has been reported that 13 500
million ton is produced from this process worldwide, which
accounts for about 7% of the green house gas produced
annually . Eﬀorts have, therefore, been made to promote
the use of pozzolans to replace part of Portland cement.
Recently, another form of cementitious materials using
silicon and aluminum activated in a high alkali solution
was developed . This material is usually based on ﬂy
ash as a source material and is termed geopolymer or
alkali-activated ﬂy ash cement [3–7]. The mortar and con-
crete made from this geopolymer possess similar strength
and appearance to those from ordinary Portland cement.
It is also well known that geopolymers possess excellent
mechanical properties, ﬁre resistance and acid resistance
The work on this geopolymer so far has been based on the
normally used type-F low calcium ﬂy ash [2–6]. It is known
that high calcium ﬂy ash contains a reasonable amount of
silica and alumina. This high calcium ﬂy ash could also be
suitable for use as a base material for making geopolymer.
The annual output of lignite ﬂy ash from Mae Moh
power station in the north of Thailand is around 3 million
tons. This ﬂy ash contains a high percentage of calcium and
is being used quite extensively for construction in Thailand.
The knowledge of the use of high calcium lignite ﬂy ash in
producing geopolymer would be beneﬁcial to the under-
standing and to the future applications of this material.
2. Materials and experimental details
Lignite ﬂy ash (FA) from Mae Moh power station in
the north of Thailand, sodium hydroxide (NaOH) of three
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Cement & Concrete Composites 29 (2007) 224–229