Discussion and Possible Improvements
The obv guideline uses a deflection of 1.75 mm for precracking, which is the mean deflection for the determination of ultimate limit state calculation. Most other authors use the deflection for service state calculations (e.g. 0.5 or 1.0 mm). This approach might be more realistic. But the discussion under 2.1 should be kept in mind.
Beams with cross section of 150 x 150 mm and a span of 450 mm will not give such a realistic bending situation as beams with 600 mm span, which are recommended by DAfStb .
The influence of humidity, shrinkage and creep of concrete in the compression zone has not been investigated in detail yet. Small temperature changes in our test environment also result in small changes of deformations. Unfortunately it was not possible to test 50 and 60 % loaded specimens in parallel due to limited test facilities. Therefore long-time experience with 50 % is lacking.
The supports were improved by installation of supporting rollers.
Up to now for most tests one mix design has been used. 2015 a RRT started with other mix designs and fibre dosages.
Concrete Mix Design
A common used mix-design for FRC was used for all tests: 370 kg/m3 CEM II A-S/42.5 R, w/c = 0.5, 1747 kg/m3 Danube sand and gravel 4/16.
Consistency was controlled by different dosages of Sika Viscocrete 1020X at 450 mm on the spread table, 28 days compressive strength reached 60 MPa, first peak strength about 6 MPa. The fibre dosage was quite low. About the same amount of fibres, calculated by volume, was added for steel (30.0 kg/m3) and polymeric fibres (4.5 kg/m3) in all tests reported here.
For these tests 9 different fibres, representing commonly used types, were used, 8 synthetic macro fibres and one type of a typical steel fibre as Ref. . As structural synthetic macro fibres did improve since 2006, when the tests started, it makes no sense to identify specific fibres. The fibres vary in their material composition and dimensions. The results should mainly give an overview on possible creep deformations with different fibres.