Creep Coefficient Results
Considering the inherent scatter of creep, and the intrinsic scatter of the material together with the fact that each specimen was tested under different conditions of width and load, it is difficult to draw obvious conclusions from a direct analysis of the results. To overcome these drawbacks, the analysis of the creep coefficient is proposed.
Fig. 6 u(t) — time curves of the specimens: a S1/PF_0.25Pi and 1.50Pi; b S2/PF 0.25Pi and 1.50Pi; c S1/SF_0.25Pi and 1.50Pi; d S2/SF_0.25Pi and 1.50Pi
For the purpose of this research, the creep coefficient (u(t)) at a time t defined in terms of crack width is the ratio between the crack at t time t in phase 2 (w‘c) and the initial crack width (w°c), as indicated in expression:
The evolution of the creep coefficient is presented in Fig. 6 for each beam. The curves are grouped by stages S1/PF (Fig. 5a), S2/PF (Fig. 5b), S1/SF (Fig. 5c) or S2/SF (Fig. 5d).
Using t = 90 days as reference, a value of y(t = 90) between 0.5 and 4.0 is reached for all the specimens of both conditions S1 and S2. PF creep coefficients for 90 days (ut!90) ranged between 1.5 and 4.0 for both S1 and S2 campaigns, although in the former an asymptotic value of the creep coefficient was reached during the secondary stage. In this stage, creep is not significantly affected by the wp value. Moreover, at similar loading level and for wp < 1.50 cracked PFRC can be expected to experience creep coefficients of around twice those of SFRC.