For durability and serviceability reasons, design of FRC structures has to avoid too high long term deformations and creep rupture. Therefore more knowledge regarding creep of cracked FRC is necessary. Up to now no international specification for tests is available. Numerous tests according to the Austrian Guideline “Fibre reinforced Concrete” have been performed with different fibres, but same dosage. Unnotched beams with a span of 450 mm, precracked to 1.75 mm deflection were loaded with 50 % of short time residual load, which was stepwise increased to higher levels.
The results give a clear indication, how cracked FRC will behave under sustained load. However, the test results may only be applied to the fibre dosages and the quite high crack mouth opening displacement used in these tests prior to the creep test. Creep and shrinkage of the concrete was not eliminated from the data.
The used testing equipment stood the test. The supports have been improved recently. The influence of the storage climate has still not proved satisfactory.
Following above stated test conditions it may be concluded for the tested fibres: Beams with low quality synthetic fibres will not withstand a sustained load of 50 % of short time residual strength. Beams with most synthetic fibres will perform well at a load level of 50 %, but experience problems at a load level of 60 %. Creep rupture may occur immediately or after some years of loading. Therefore, it is difficult to predict the creep behaviour in advance. Beams with some synthetic fibres tend to suffer very high deformations not ending up in failure before some years of loading have passed. Beams with the hooked end steel wire fibres started with a slip out from the matrix and creep rupture occurred within several hours at load levels of 75-85 %.
Acknowledgments These tests were partly sponsored by members of the committee working with the guideline “Fibre Reinforced Concrete” of the Austrian Society for Construction Technology (obv): obv, Gueteverband Transportbeton, KrampeHarex Fibrin, Forta, Adfil, Grace, Bekaert, Cemex, Arcelor Bissen, Asamer & Hufnagel and Transportbeton.
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