To measure creep in tension under drying conditions, two specimens
were tested at a concrete age of 64 days. One was loaded at
50% and one at 70% of the average compressive strength of the concrete
measured at 64 days, both for a period of 30 days. The self-adhesive
aluminum sheet was removed when testing under drying conditions.
3. Experimental results
Experimental results for autogenous shrinkage observed for compression
and tension creep tests at 64 days are presented in Fig. 6.
The corresponding results for tests carried out at 7 days are presented
in Fig. 7. Drying shrinkage results for specimens tested at 64 days are
presented in Fig. 8.
In Fig. 6 the evolution of autogenous shrinkage is very small. The
fluctuations observed can be attributed to temperature variations in
the test room during creep tests. This result is not surprising considering
the concrete age (64 days) at the loading time.
Fig. 9 presents specific creep curves (strain vs. time per unit of
applied stress) for basic creep tests in compression and in tension
for a concrete age of 64 days at loading. Fig. 10 presents specific
creep curves for drying creep tests performed in compression and in
tension for a concrete age of 64 days at loading. Fig. 11 shows specific
creep curves for basic creep tests in tension and compression for concrete
loaded at an age of 7 days. Fig. 12 shows specific creep curves
for basic and drying creep tests in compression for concrete loaded
at an age of 64 days at 50% and 70% of its compressive strength at
loading. Fig. 13 presents the corresponding specific tension curves
for concrete loaded at an age of 64 days at 50% and 70% of the tensile
strength at loading.
Note that specific creep curves for creep under drying conditions
were obtained by subtracting the elastic strain and the drying shrinkage
strain from the total strain and divided by the loading stress.
Considering Figs. 9–13, the following comments can be made:
1. Specific creep curves for basic creep in tension are similar for the
two loading conditions (50% and 70%). Thus, basic creep in tension
can be considered to exhibit linear viscoelastic behavior up to a
loading level of at least 70%.
2. Specific creep curves for loading levels of 50% and 70% in compression
are close, considering the usual scattering related to this type