Fracture Models and Effect of Fibers on Fracture Properties of Cementitious Composites—A Review

Cementitious composites have good ductility and pseudo-crack control. However, in practical applications of these composites, the external load and environmental erosion eventually form a large crack in the matrix, resulting in matrix fracture. The fracture of cementitious composite materials causes not only structural insufficiency, but also economic losses associated with the maintenance and reinforcement of cementitious composite components. Therefore, it is necessary to study the fracture properties of cementitious composites for preventing the fracture of the matrix. In this paper, a multi-crack cracking model, fictitious crack model, crack band model, pseudo-strain hardening model, and double-K fracture model for cementitious composites are presented, and their advantages and disadvantages are analyzed. The multi-crack cracking model can determine the optimal mixing amount of fibers in the matrix. The fictitious crack model and crack band model are stress softening models describing the cohesion in the fracture process area. The pseudo-strain hardening model is mainly applied to ductile materials. The double-K fracture model mainly describes the fracture process of concrete. Additionally, the effects of polyvinyl alcohol (PVA) fibers and steel fibers (SFs) on the fracture properties of the matrix are analyzed. The fracture properties of cementitious composite can be greatly improved by adding 1.5–2% PVA fiber or 4% steel fiber (SF). The fracture property of cementitious composite can also be improved by adding 1.5% steel fiber and 1% PVA fiber. However, there are many problems to be solved for the application of cementitious composites in actual engineering. Therefore, further research is needed to solve the fracture problems frequently encountered in engineering.

Mechanical Properties of Hybrid Ultra-High Performance Engineered Cementitous Composites Incorporating Steel and Polyethylene Fibers

This paper presents the authors’ newly developed hybrid ultra-high performance (HUHP) engineered cementitious composite (ECC) with steel (ST) and polyethylene (PE) fibers. From this point on it will be referred to as HUHP-ECC. The volumes of steel and PE fibers were adjusted to obtain different mechanical properties, including compressive strength, tensile, and flexural properties. We found that tensile and flexural properties, including bending strength and ductility indexes, increased with higher PE fiber amounts but reduced with the increased ST fiber volume. Notably, the compressive strength had the opposite tendency and decreased with increases in the PE volume. The ST fiber had a significantly positive effect on the compressive strength. The fluidity of HUHP-ECC improved with the increasing amount of ST fiber. The pseudo strain-hardening (PSH) values for all the HUHP-ECC mixtures were used to create an index indicating the ability of strain capacity; thus, the PSH values were calculated to explain the ductility of HUHP-ECC with different fiber volumes. Finally, the morphology of PE and ST fibers at the fracture surface was observed by an environmental scanning electron microscope (ESEM).

The Behavior of Pseudo Strain-Hardening Cementitious Composite (PSH2C) Using Synthetic Fibers under Uniaxial Tensile Loading

The application of pseudo strain-hardening cement composites (PSH2C) to structural systems depends primarily on the tensile response of the materials, which is a direct function of fiber and matrix characteristics, the fiber content or volume fraction. In general, improved response of material is observed with an increase in the fiber volume fraction, as long as the fiber content does not impede mixing. This paper addresses the direct tensile response of pseudo strain hardening cement composites (PSH2C) reinforced with PET fibers, which belongs to a class of discontinuous short fiber reinforced cement based composites characterized by a strain hardening and multiple cracking responses under direct tensile loading. The variables are different types of fibers (PET, PET+PE, PET+PVA).

The Seismic Behavior of Pseudo Strain-Hardening Cemetitious Composites Coupling Beams with Polyvinyl Alcohol Fiber

This paper addresses the seismic behavior of pseudo strain hardening cementitious composite (PSH2C) coupling beams with different failure modes in hybrid coupled shear wall. Test variables included the ratio of steel coupling beam strength to beam-wall connection strength. The results show that Specimen PSH2C-SCF exhibits a better stable behavior in comparison with Specimens PSH2C-SBVRT and PSH2C-FCF.

Panel Shear Strength of Steel Coupling Beam-Pseudo Strain Hardening Cementitious Composite Wall Connection

Hybrid coupled wall systems, where steel coupling beams couple two or more pseudo strain hardening cementitious composite (PSH2C) shear wall can be used in medium and high-rise construction subjected to earthquake. This paper addresses the panel shear strength of steel coupling beams - PSH2C shear wall connection. Test variables included the connection detail in hybrid coupled shear wall system. The results show that Specimens PSH2C-PSFF and PSH2C-PSFFT exhibits greater panel shears strength than Specimen PSH2C-PSF.

Stud Bolt Effects on the Bearing Performance of Pseudo Strain-Hardening Cementitious Composite (PSH2C) Wall-Steel Coupling Beam Connections

Recently, hybrid coupled shear system, where steel coupling beam couple two or more RC shear walls are frequently applied for medium and high-rise building subjected to earthquake. This paper addresses the seismic performance of PSH2C wall - steel coupling beam with stud bolts in the connection region. Test variables included stud bolts in embedded steel coupling beam and types of material, such as PSH2C and concrete, in the wall. The results show that PSH2C wall – beam connections (PSH2C-ST and PSH2C-SB) exhibit better hysteretic response than normal concrete wall – beam connections (HCWS-ST and HCWS-SB).

The Influence on Horizontal Ties of Steel Coupling Beams

Hybrid coupled shear wall system with steel coupling beams has known as the effective lateral load resisting system for tall buildings subjected to earthquake. This paper addresses the influence on horizontal ties of steel coupling beams in pseudo strain hardening cementitious composite (PSH2C) hybrid coupled shear wall. Test variables included the connection detail and types of material, concrete and PSH2C, in the connection region. The results show that Specimen PSH2C-SB and PSH2C-SBVRT exhibits a better stable behavior than Specimens HCWS-SB and HCWS-SBVRT.

The Apparent Density, Tensile Properties and Drying Shrinkage of Ultra High Toughness Cementitious Composites

A new class of high performance fiber reinforced cementitious composites called Ultra High Toughness Cementitious Composites (UHTCC) is developed in the last few years. It is a pseudo strain hardening material with maximum tensile strain capacity more than 3%, yet the fiber volume fraction no more than 2%. The multiple cracking patterns accompanying pseudo strain hardening behavior are obtained which implies high ductility, energy absorption capacity, and toughness. A remarkable characteristic distinguish it from conventional high performance fiber reinforced concrete is the maximum crack width of multiple cracks which is about 60µm under ultimate tensile load. Such micro-cracks are often small enough to prevent the intrusion of aggressive agents. From a durability point of view this composite can be considered as an effectively uncracked material. The performances of this new material, including the apparent density, the uniaxial tensile property, and the drying shrinkage performance, are experimental studied in this paper.