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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
S. S. Araújo | G. N. Guimarães | A. L. B. Geyer
vices), and harder to use due to its analog readings, need of
constant maintenance, equipment fragility, calibration difficul-
ties and manual control by the testing operator.
7. In general, the strain gages and clip gages had more consis-
tent readings and lowest coefficients of variation and showed
important advantages such as a smaller need of external in-
tervention during testing and minimization of reading errors by
the operator. In case of strain gages, the bonding of the gage
to the concrete surface has various aspects that should be
closely watched, making its use more difficult. Also, the strain
gages have to be discharged after their use, and a second use
is not allowed, which increases testing costs. The clip gages
have the advantage of measuring both longitudinal and trans-
verse strains, show digital readings and are less susceptible to
calibration procedures. Clip gages are more practical, can be
reused several times and setting them up on the specimen is
easy and no great operator expertise is required.
Modulus of elasticity tests using different measuring devices showed
that even when following the criteria specified in code ABNT NBR
8522:2008 [3], variations in test results are relatively significant.
5. Acknowledgements
The authors wish to express special thanks to Laboratory Carlos
Campos Consultoria e Construções Ltda., to Laboratório de Fur-
Figure 7 – Modulus of elasticity versus concrete
type and specimen size (includes all
measuring devices)
C60
C30
Concrete
Static Modulus of Elasticity (GPa)
20
21
22
23
24
25
26
27
28
29
Size 100x200 (mm)
Size 150x300 (mm)
Figure 8 – Modulus of elasticity
versus strain measurement device and
specimen size (SG – strain gage, DI - dial
indicator, CG - clip gage and LVDT)
Static Modulus of Elasticity (GPa)
Size 100x200 (mm)
Size 150x300 (mm)
SG
DI
CG LVDT
Strain Measurement Device
16
18
20
22
24
26
28
30
1. The two specimen sizes used in this study had an effect on the
concrete static modulus of elasticity since the average modu-
lus obtained from 100 mm x 200 mm and 150 mm x 300 mm
specimens were 24.4 GPa and 26.2 GPa, respectively. The
average modulus obtained from 150 mm x 300 mm specimens
were 7% higher. However, code ABNT NBR 8522:2008 [3]
sets tolerance limits in item 8.2 which allows variation in results
of up to 10%.
2. Results using strain gages were similar to results using dial
gages since their average modulus were 27.6 GPa and 27.5
GPa, respectively. The results for clip gages and LVDTs
showed average modulus of 26.3 GPa and 19.8 GPa, respec-
tively.
3. For specimen size 100 mm x 200 mm, results showed largest
variability when dial gages and LVDTs were used. For 150mm
x 300 mm specimens, modulus results obtained from clip gag-
es and LVDTs presented larger variability.
4. For the two concrete types, 100 mm x 200 mm specimen re-
sults showed larger variability than 150 mm x 300 mm speci-
men results. The 150 mm x 300 mm specimens had smaller
coefficient of variability in the modulus tests.
5. Modulus values obtained using dial gages and strain gages
were higher than results obtained with clip gages and much
higher than those obtained with LVDTs.
6. Values obtained with LVDT were smallest than those obtain
with the other 3 devices. In general, LVDT was considered the
less accurate (greatest coefficient of variation among the 4 de-