Results of Creep Tests
Test results are available now up to more than 3200 days or 8 years. The results show higher deformation for cracked beams reinforced by synthetic fibres at the same load level and therefore wider cracks than for SFRC. Some cannot sustain a
Fig. 5 Creep deformation of the 4 beams with type A polymer fibres, leading to creep rupture after different period of time. Note The creep load is 50 % of the load at 1.75 mm up to 90 days, and then increased to 60 %. The absolute values of creep load are not the same for all 4 beams
Fig. 6 Creep deformation of one beam with type F polymer fibres, leading to creep rupture after 2300 days. Load level 60 %. Total deflection before tertiary creep very low. The other two beams are still carrying the sustained load after 2694 days
Fig. 7 Creep deformation of one beam with type E polymer fibres, leading to creep rupture after 2770 days. Load level 60 %. Total deflection before tertiary creep is moderate. The other two beams collapsed after 190 and 260 days
high percentage of post-crack load for extended periods and fail due to creep failure.
Some typical results of individual specimens are shown in Figs. 5, 6, 7, 8, 9 and 10.
Figure 5 gives an overview of 4 test results for a typical synthetic fibre in 2006. All 4 samples could not withstand the 60 % of short time load.
Fig. 8 Creep deformation of three beams with type G polymer fibres: Beam 1 experienced creep rupture after 313 days. Load level 60 %. Notice Absolute sustained load applied was 60 % higher, than for beam 2 and 3. Beam 2 collapsed after 2041 days. Beam 3 was still carrying the sustained load. The test was finished at the collapse of beam 2. For both load level 60 % had been changed to 65 % after 2013 days
Fig. 9 Creep deformation of one beam with type B polymer fibres, leading to creep rupture after 1400 days. Load level 60 %. Very high total deflection. The other two beams collapsed after 1062 days at 11 mm deflection and 3000 days at 5.5 mm deflection
Fig. 10 Creep deformation of one beam with a typical steel fibre, at load level 4 (50 % up to 85 days, 60 % to 3180 days, 70 % to 3190 days, after that the load was increased to 80 %)
While beams with type F fibres (Fig. 6) show low deformation and only one collapsed up to now, the beams with type E fibres (Fig. 7) showed slight, but ever increasing secondary creep, which ended up in creep rupture after 190-2770 days.
Figure 8 shows the influence of the load applied, relatively always 60 %, but absolutely for beam 1 with 60 % difference (10.44 kN instead of 6.42 kN).
The crack width for one specimen reached nearly 10 mm (Fig. 9). But the most alarming fact is that beams with some types of fibres can fail after a long period of testing, e.g. after 6 or 7 years (Figs. 6 and 7). Up to 1.5 years or even longer the graphs of deformation-time still show low rates of creep deformation.
Beams with common steel fibres (low carbon cold drawn wire fibre with hooked ends) are still performing excellently (Fig. 10) at load levels of 60 and 70 %. Note, that the concrete properties will have changed after 3200 days. Beams at 28 days with the same steel fibres under 75 % and up to 85 % of the residual load were tested as well. They failed within minutes due to fibre pull out at this load level.