Equivalent Flexural Strength Of Steel Fibre Reinforced Concrete And Its Modelling From Fibre Distribution And Fibre Pull Out Load

Oleh :
Sholihin As ad - - Fak. Teknik

This thesis presents the laboratory tests about the assessment of flexural and equivalent flexural strength of steel fibre reinforced concrete (SFRC) and its dependence o n fibre factors (e.g. dosage, shape geometry, etc.) and concrete quality. The analysis is supported by fibre pull-out test, investigation of the cracked zone of the specimen, where fibres contribute to the material resistance against the tensile flexural stress and development of a calculation model for reconstructing the load deflection curve of four-point bending test. The work sequence are (1) the four-point bending test to investigate the dependence of fibre type and concrete quality to flexural and equivalent flexural strength, (2) the investigation of the craked zone of tested beams to evaluate the involved amount of fibres and their distribution, 3) fibre pull-out test to understand the fibre pull-out behavior as micro component of SFRC and (4) development of a calculation model based o n fibre pull-out load to reconstruct the load-deflection curves of the tested beams in four-point bending test. The four-point bending test covers series with various dosage of crimped and end-hooked steel fibres mixed in normal and high strength concrete, variation of sand content mixed with 40 kg/m3 of short and long end-hooked steel fibres in normal and high strength concrete and the comparison of specimen with 40 kg/m3 of different fibre types (short and long crimped steel fibres, short, medium and long end-hooked steel fibres, long crimped end-flatted and straight end-capped steel fibres). The evaluation of the cracked zone of tested beams evaluates the number of fibres, fibre position and fibre distribution in the crack and its relation to the recorded load-deflection curves. In the fibre pull-out tests the influences of fibre type, shape, geometry, matrix quality and its orientation to acting force are investigated. In addition the effect of fibre bonding in the matrix by treatment of fibre surface with laminated epoxy-cement is tested. The results show that the flexural and equivalent flexural strength of SFRC are determined by fibre geometry, fibre distribution in crack and concrete quality. The variation of sand content in concrete mixture influences fibre distribution and slightlv influence post cracking behavior of the four-point bending test result. Fibre pull-out test results indicate that pull-out load depends o n fibre geometry, inclination to acting force, embedment and concrete quality. These results are then used for the development of a model which basically explains the post-cracking behavior of SFRC as the interaction of force that necessary for increasing height and fibre pull-out load resulting from the increase of crack width. With this model, load-deflection curves are calculated o n the basis of determined fibre distribution in crack, the assoiated fibre pull-out load and propagated crack height. The calculated load-deflection curves are in good agreement with the measured curve. Therefore this model helps to understand post-cracking behavior, which is expressed as equivalent flexural strength, of SFRC.