The behaviour of strain-hardening cement composites under biaxial compression

[摘要] ENGLISH ABSTRACT: Reinforced concrete is susceptible to cracking. This makes it less durable thanit would be had it been crack-free. Ingress of harmful substances into reinforcedconcrete through cracks – which causes corrosion of steel – is not desirable.This can be mitigated by the use of fibre reinforced-concretes or mortarsshowing strain hardening properties accompanied by improved ductility andmultiple cracking under tensile loading. Such materials are called Strainhardeningcementitious composites (SHCC's).At Stellenbosch University, work has been done in previous years on SHCC todetermine its behaviour under various loading conditions. Some of the aspectsof the material that have been studied are the behaviour under uni-axial tensileloading, uni-axial compression and shear. The behaviour of SHCC under biaxialstresses was investigated to enable the prediction of the material behaviourunder complex stress conditions.Square plate specimens of nominal dimensions 100 x 100 x 20 mm were castand subjected to biaxial compressive loading at stress path angles of 00, 150,300 and 450; which were equivalent to vertical/horizontal stress ratios of 0/1,0.27/1, 0.58/1 and 1/1 respectively, at ages 23 to 33 days. Comparisons weremade between specimens tested using steel platens and those tested usingVesconite sheets. Those tested using Vesconite yielded lower failure stresses.Vesconite was used to reduce the retraining effect of the frictional forcebetween the specimens and the steel platens.Poisson's ratios were calculated for specimens tested using steel and thosetested using Vesconite. The values for Vesconite were found to be higher thanfor steel. Additionally, the values for the uni-axial case were different from thoseobtained for other stress ratios. This could have been due to the assumptionmade that plane stress was realised and that Elastic moduli in tension and in compression was the same. The possibility of the existence of a triaxial stressstate could render the calculated Poisson's ratios incorrect.Shear slip type failure accompanied by wedging was observed. Vertical to neardiagonal cracks were evident on the front faces of the specimens for the stresspath angles of 00 to 450 respectively. The observed crack patterns showedclosely spaced multiple micro-cracking on the narrow edges of specimensindicating Strain-hardening behaviour. The stress-strain curves also showed aslight indication of strain-hardening where tensile strains were measured.

[发布机构] Stellenbosch University