Polypropylene engineered cementitious composites (PP-ECC) exhibit superior strength and strain hardening under tensile deformation, which is expected to enhance the anti-cracking performance and self-confinement of the plastic hinge region in structural columns. However, there is still a lack of fundamental studies on the compressive behavior of a reinforcement-confined PP-ECC column. This paper presents a proof-of-concept experimental study on the confined PP-ECC column and hybrid normal strength concrete (NSC)-ECC column. Two sets of reinforcement-confined columns were designed: a pure PP-ECC column and a hybrid C30-PP-ECC column. Then, static compression tests were carried out to prove the effectiveness of the confinement in enhancing the peak strength of the hybrid column with respect to pure PP-ECC columns. However, the deformability improvement was not remarkable, with an increase of only 3.2% from samples containing no stirrups to those containing stirrups at a volumetric ratio of 1.6%. An equation was proposed to predict the peak strength of the confined PP-ECC columns. This equation considered the contribution from the tensile capacity of PP-ECC to the circumferential confining effect of the columns. The hybrid column delivered better deformability but smaller peak strength compared with the pure PP-ECC columns. Some mechanical features of the hybrid column were discussed.

Introduction

In recent years, the engineered cementitious composite (ECC) has demonstrated evident advantages for crack resistance and tensile strain hardening [1–۴]. Currently, polyvinyl alcohol (PVA) and polyethylene (PE) fibers are commonly used in ECCs. With the application of PVA and PE fibers, the tensile stress and ultimate deformability of an ECC can be larger than 3 MPa and 5%, respectively [5,6]. On the basis of advances with this material, many composite components or structures were developed and investigated to improve the structural deformability and crack resistance [7–۹]. Choi et al. [10] reviewed the mechanical properties of ECC and its application in different structural components, such as beam-wall connections, coupling beams in walls, shear walls, and columns. Due to the excellent strain hardening behavior and ductility of ECC materials, these composite structures exhibited better deformability and energy dissipation capacity when used as reinforced ECC columns and ECC beam-column connections. The specimen failed after the ECC was crushed but only at very large deformation. However, the high cost of PVA and PE fibers hinder the large-scale promotion of ECC in practical engineering.