Concrete future - Concrete Mix Design, Quality Control and Specification - page 294

13.4.2 Other significant properties
The drying shrinkage of this geopolymer concrete is much lower than for
Portland-cement-based concrete with typical 56-day values of approxi-
mately 300 microstrain or less. The drying shrinkage will normally be less
than that achieved for a Portland-cement-based concrete even incorporat-
ing a shrinkage reducing admixture as shown in Figure 13.1. The prod-
uct also has a very low heat of hydration. The limited thermal and drying
shrinkage makes it well-suited for thick and heavily restrained concrete
elements and should enable a significant reduction in the quantity of crack
control reinforcement.
While creep has not been directly measured, prestressed girders were
cast using this proprietary geopolymer concrete in 2011. The prestress was
transferred after 3 days. The girders were left unloaded for 100 days. The
girders were loaded with W80 wheel load (8 tons) in accordance with the
Australian bridge standard (AS 5100) and continuously measured for deflec-
tions over the subsequent 15-month period, as shown in Figure 13.2a. The
hogging prior to load and deflection under sustained load were monitored
using embedded vibrating wire strain gauges and the results are shown in
Figure 13.2b. The structural behaviour in the girders was consistent with
the compressive strength and modulus indicating no unusual deformation
properties.
Precast reinforced beams were cast for the Global Change Institute at
the University of Queensland. AECOM modeled the beam in RAPT based
on an uncracked condition under self-weight and the measured mechani-
cal properties. The expected deflection under the test load of 5 × 2 ton
blocks equally spaced was calculated to be 3.0 mm. The actual maximum

700

EFC
Blended
Eclipse

600

500

400

300

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100

0 0

7 14 21 28 35 42 49 56

Days after Initial Reading

Figure 13.1 Drying shrinkage of geopolymer, 30% fly ash, and shrinkage reduced
concretes.