Abstract
The fracture energy of the high-performance fiber-reinforced cement-based composite (HPFRCC) can be modified within wide limits by the variation of the amount of steel fibers added to the fresh mix. First of all, considering the actual engineering conditions in Qingdao, the materials commonly used in Qingdao were selected. The optimal reference mix proportion of the HPFRCC cementing material was proposed through determination of fluidity and flexural strength. Based on the optimal mix proportion, the uniaxial tensile, fracture, and dry shrinkage properties of HPFRCC with different steel fibers are systematically studied. Stress-strain diagrams of the different samples were measured under the uniaxial tensile test, wedge splitting test, and three-point bending test. The steel fiber content was varied between 0 and 200 kg/m3. The load bearing capacity and the fracture energy were determined experimentally. In addition, moisture loss as a function of time and shrinkage was determined in an environment of 20°C and 50% RH (relative humidity). The results indicate that the maximum load increases significantly in the HPFRCC series reinforced by 150 and 200 kg/m3 of steel fibers. Both have a hardening branch developed after the first crack deflection due to the high percentage of fibers bridging the crack surfaces. The load bearing capacity and fracture energy increased almost linearly with the steel fiber content. It was found that the three-point bending test is more applicable in measuring the fracture energy of HPFRCC than the wedge splitting test. The addition of steel fibers decreased the moisture diffusion and consequently the drying shrinkage of HPFRCC, and there was minimum weight loss and deformation when the steel fiber content was 150 kg/m3. The results obtained will be presented and discussed.
Highlights
Concrete is the most widely used building material, but its brittleness increases with its strength
During the test, it can be seen that when the load of the common cement mortar reaches the peak value, small cracks appear along the direction of the main cracks, and the cracks gradually extend to a certain length with the wedge-shaped plate, and
From the load-CMOD curves, it can be seen that after the curve passes through the peak point, it descends approximately linearly in a gentle slope, which is very different from the curve of the ordinary mortar specimen. is is mainly due to the uniform and disordered distribution of the steel fiber inside the specimen after mixing with the steel fiber, so that the specimen does not fully develop along the direction of the main crack reserved in the specimen after reaching the cracking load, but at the same time, there are transverse cracks, which can be obtained from the corresponding failure image of the specimen (Figure 11(b))
Summary
Concrete is the most widely used building material, but its brittleness increases with its strength. E related research results show that the addition of the steel fiber into the cement matrix can greatly improve the fracture toughness and fracture energy of concrete [12,13,14,15,16]. Ren et al [39] studied the influence of different steel fiber contents and types on the fracture energy and fracture toughness of ultrahigh-performance cement-based composites. To fully understand the influence of different steel fiber content on the fracture and dry shrinkage properties of HPFRCC, this paper first uses Qingdao local materials as the base material and obtains the best mix proportion of the matrix materials through the fluidity and flexural strength test; the steel fiber is added on the basis of this best mix proportion and is made into the HPFRCC studied in this paper. En, the load crack opening displacement curve, fracture energy, and dry shrinkage performance of HPFRCC with different steel fibers are compared and analyzed, and the influence of HPFRCC with different steel fiber content on the fracture performance and dry shrinkage performance is discussed, which lays a solid foundation for HPFRCC to be widely used in practical projects
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