Heterogeneous fiber-particle composite subjected to principal stress rotation

Test results of 20 Engineered Cementitious Composite (ECC) plates under 4-point bending are reported. 13 plates were pre-cracked to allow rotation of the principal stress directions, in order to permit the study of shear and tensile stress transfer at multiple cracks. Coarse aggregates were investigated as a possible means to improve shear-transfer. When subjected to principal stress rotation, ECC exhibited a nearly orthogonal crack pattern, indicating little contribution from the shear transfer mechanism. A reduction in flexural capacity was observed, depending on the relative angles of principal tensile stress applied. When coarse aggregate was added to ECC, significant reductions in flexural capacity and flexural ductility were observed. In a situation when principal stress direction rotated, however, the test results show that coarse aggregate in the amount of 15% of the maximum packing density of the aggregate used was effective to control the orientation of secondary cracks in cracked ECC and to maintain a comparable level of flexural capacity irrespective of the reorientation angle of principal stress field and the angle of pre-existing cracks.