Civil Engineering Reference
In-Depth Information
13.4.1 Mechanical properties
This geopolymer has been used on a number of different projects in
Australia and a total volume of over 4000 m³ has been poured to date.
It is not “labcrete”! Test specimens have been taken during actual pro-
duction and a summary of the average mechanical properties are given in
Table 13.1.
While the most common concrete grades used are 32 and 40 MPa (equiv-
alent to fcu of 40 and 50 MPa), cylinder strengths up to 70 MPa have
been measured. Since the geopolymer binder consists entirely of fly ash and
ground-granulated blast-furnace slag (GGBS), there has been a common
perception that geopolymer concrete would develop its strength very slowly
or require heat curing. Portland cement systems containing high volume
replacement of fly ash or GGBS and many geopolymer binders do develop
compressive strength slowly. However, this particular geopolymer concrete
develops its strength quite rapidly with design strength typically achieved
after 7 days under laboratory conditions. Strength development at early
age (up to 3 days) is sensitive to ambient temperature, but adequate early
strength would be expected if the concrete temperature is above approxi-
mately 20°C.
The data available suggest that geopolymer concretes in general includ-
ing this proprietary geopolymer tend to have higher tensile and flexural
strength relative to the compressive strength than Portland-cement-based
concrete. This appears due to the strong bond of the geopolymer gel to the
aggregate particles (Concrete Institute of Australia 2011) and would be
expected to improve crack resistance of geopolymer concrete.
Several researchers have reported a significantly lower elastic modulus for
geopolymer concrete than for comparable OPC concrete. For example, Pan
et al. (2011)
found the reduction was about 23% for typical strength grade
compared to the equations given in AS 3600. Accordingly those geopoly-
mer concretes were outside guidelines given in Australian Standard 3600
and ACI Committee 363. However, the elastic modulus of this proprietary
geopolymer concrete has been found to be comparable to Portland-cement-
based concrete as shown in Table 13.1. The Poisson's ratio has been found
to range between 0.19 and 0.24, which is slightly higher than would be
expected for Portland-cement-based systems.
Table 13.1
Mechanical properties of geopolymer production concrete
Compressive
strength
(MPa)
Tensile
strength
(MPa)
Flexural
strength
(MPa)
Elastic
modulus
(GPa)
Std.
deviation
Shrinkage
(microstrain)
Poisson's
ratio
Mix
32 MPa
38.1
3.7
4.5
6.2
300
31.8
0.20
40 MPa
55.6
4.3
6.0
6.6
230
38.5
0.24
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