Concrete presents different internal micro-structure and damage characteristics because of the different content of steel fibers and the randomness of its distribution. Therefore, the failure process of steel-fiber-reinforced concrete (SFRC) should be divided into different stages and the damage types should be classified to further clarify the strengthening mechanism of steel fibers. The role of volume fractions of steel fibers in the splitting-tensile strength of concrete was investigated by split tensile tests for concrete with four different volume fractions of steel fibers (0.0%, 1.0%, 1.5%, 2.0%). The acoustic emission energy and horizontal displacement of concrete in the splitting-tensile process were monitored by combing digital image correlation (DIC) and acoustic emission (AE) techniques, and the microscopic failure mechanism of SFRC was analyzed emphatically. The results showed that the addition of steel fibers improved the splitting-tensile strength of concrete. With the increase of the volume fraction of steel fibers, the splitting-tensile strength of concrete increased first and then decreased, and reached the maximum value of 5.294 MPa when the content was 1.5%. It was observed that the overall failure mechanism could be divided into four stages: slow accumulation of elastic energy (I); rapid accumulation of elastic energy (II); rapid accumulation of dissipated energy (III); a slow decrease of elastic energy and a slow increase of dissipated energy (IV). Tensile failure dominated the failure process of concrete splitting-tensile resistance, while there was a part of shear failure.
Keywords: acoustic emission; digital image correlation; failure mechanism; splitting-tensile strength; steel-fiber-reinforced concrete.