The tensile strength and tensile damage characteristics of concrete/steel fiber reinforced concrete have been studied for decades due to their great importance in structural design and safety analysis. Splitting tensile test methods such as ASTM C-496 [
1], ISO 4108 [
2], BS 1881-117 [
3], etc., are frequently adopted to measure the tensile strength and investigate the corresponding fracture characteristics of concrete materials [
4,
5]. For common concrete, according to quasi-static tensile splitting tests, the influences of water-cement ratios, porous structure, types of cement, aggregates sizes and samples sizes on the tensile strength of concrete have been extensively researched [
6,
7,
8,
9]. Meanwhile, the dynamic tensile fracture pattern and mechanical response of concrete has been studied by the dynamic Brazilian test [
10], which has shown that the impact velocity plays a significant role in the failure pattern of concrete specimens. Through building mechanical models, Carmona and Aguado [
11] have indirectly determined the tensile stress–strain curve of concrete with a splitting tensile test, Hoang et al. [
12] have investigated the crack propagation process in the splitting plane and obtained the distribution of residual tensile strength as crack propagation, and Olesen et al. [
13] have analyzed splitting tensile fracture and the compressive crushing/sliding failure during the test, In addition to experiments, numerical methods are also one of the most important methods for studying concrete structures, e.g., Giuseppe Fortunato et al. [
14] and Luciano Ombres et al. [
15] used a nonlinear constitutive relation (concrete damage plastic model) in a numerical model to study the mechanical and damage behavior of concrete structures under load. For steel fiber reinforced concrete, Prisco et al. [
16] have identified corresponding post-cracking behavior, Abrishambaf et al. [
17] have investigated the tensile stress-crack width law during post-cracking stage, and Boulekbache et al. [
18] have studied the post failure mechanism of fiber reinforced concrete during splitting test based on digital image correlation. In addition, Olivito and Zuccarello [
19] have studied the tensile strength of steel fiber reinforced concrete with respect to fiber content and mix-design variations, and Denneman et al. [
20] have obtained a close estimate of the true tensile strength of fiber reinforced concrete from an adjusted tensile splitting test procedure, Shalchy and Askarinejad et al. [
21,
22] have studied the nanostructure of the cement/fiber interfaces, and the corresponding mechanical properties.
In addition to the aforementioned studies, the tensile mechanical behavior of concrete-concrete interface is also a research focus for scientists. Generally, the interface, which is weaker than both sides of materials, widely exists in repaired structures [
23,
24], composite structures [
25] and Chinese high-speed railway track slab structures [
26]. Based on splitting tensile tests, Tschegg and Stanzl [
27] have measured the adhesive power of interface between old-new concretes, and Tayeh et al. [
28] have investigated characteristics of the interface between old concrete and steel fiber reinforced concrete. Chandra Kishen and Subba Rao [
25] have analyzed the fracture properties of concrete-concrete, transversely cold jointed interface beams. Shah and Kishen [
29,
30] have studied the fracture behavior of concrete-concrete interface by acoustic emission technique and analyzed nonlinear fracture properties of the interface.
Although various studies have been carried out in this area, the performance of the interface between different material properties in concrete was largely overlooked. First, the existing of interface between two types of concrete will cause a reduction of the strength; therefore, a quantitative comparison for the tensile strength value of interface and intact concretes is necessary and also a suitable numerical model to describe the mechanical response of the sample or structure with interface should be built. Second, the reinforcement method (such as using steel fiber) for the interface should be investigated. However, most of researchers [
16,
17,
18,
19,
20,
21,
22] have considered to put steel fiber inside the concrete to form an intact sample or structure and ignored to study the reinforcement behavior of the steel fiber for the interface between different types of concretes (Similar to planting steel fiber in the interface). These respects are quite important for interface structure design and safety evaluation. In particular, some interface cracking phenomena have been observed in high-speed railway track slab structures during operations. As shown in
Figure 1, the prefabricated track slab is installed on the support layer by pouring the filling layer on site. The filling layer is composed of asphalt mortar for CRTS I/II track slabs or concrete for CRTS III track slab (
Figure 1a). Cracks generally emerged in the interface due to the reason that the interface is the weakest part in the whole structure (
Figure 1b,c). Therefore, a systematic investigation is carried out in this study for quantitative analysis strength reduction of the interface and the reinforcement behavior of the steel fiber on the interface through a series of tensile splitting tests on four types of cubic concrete samples, including high strength concrete (used for track slab), low strength concrete (used for filling layer), cementation of low and high strength concretes (interface) and cementation of low and high strength concretes with steel fibers (interface reinforced by steel fiber which may be a possible improvement method).
The paper is organized as follows: first, samples preparation and experimental procedure are introduced; second, the tensile strength, initiation cracking point and damage properties of the concretes are analyzed and compared; third, the numerical simulations with finite element method (FEM) are conducted; finally, conclusions are drawn based on the tests and numerical simulations.