In order to solve the problem that the built-in parallel bond model in the discrete element software cannot adequately simulate the post-peak fracture behavior of quasi-brittle materials, a linear cohesive model was established. First, two particles are used to simulate the interface constitutive behavior in different modes. The results show that the new model can better simulate the behavior of Mode-I fracture, Mode-II fracture, and Mixed-mode fracture. Then, the influence of micro-parameters on the newly constructed constitutive model is analyzed, which provides a basis for the determination of micro-parameter values. Finally, the proposed softening model is applied to a three-point bending test of mortar, and the fracture behavior obtained is compared to the acoustic emission results. The simulation results also show that the constitutive model we built can be used to simulate the fracture behavior of quasi-brittle materials such as mortar and concrete.

Mass concrete structures under long-term loads are susceptible to time-dependent fractures, which pose a threat to their structural integrity and safety. In order to study the crack growth rate of concrete materials under long-term constant load, the data were processed according to the calculation method of fatigue crack growth rate. The relationship between the crack growth rate and strength factor in the stable growth stage was obtained using the Paris formula. The experimental data and theoretical analysis show that the time-dependent fracture curve CMOR(t)-t of the standard three-point bending beam specimens could be divided into three stages. The relationship between the crack propagation rate da/dt(t) in the second stage and the intensity factor K(t) could be well described by the Paris formula. The life of crack growth of a standard three-point curved beam is inversely proportional to the level of constant load. These conclusions can provide data support for further studies on crack extension life under long-term constant load.

Slurry-infiltrated fiber concrete (SIFCON) has excellent potential for application as a new material with good crack resistance, impact resistance, and seismic performance. In this paper, SIFCON blocks were cast in a single pour using the custom-made two-dimensional directional steel fiber placement device, followed by compressive testing. Based on the test results, the effects of fly ash substitution rate, steel fiber aspect ratio, and steel fiber volume fraction on the compressive bearing capacity and ductility of SIFCON blocks were investigated. The results indicate that the custom-made device in this paper effectively achieves the directional placement of steel fibers, offering a cost-effective solution that optimizes the construction process. Regarding the test results, it was observed that the compressive bearing capacity of SIFCON blocks decreases linearly with increasing fly ash substitution rate, while the addition of fly ash improves the ductility of the blocks. Notably, a 31% decrease in bearing capacity was noted when the fly ash substitution rate increases from 0% to 40%, whereas the ductility ratio increased by 99% for the same substitution rate range. Furthermore, the results revealed a positive correlation between the bearing capacity and ductility of SIFCON blocks with higher steel fiber aspect ratios and volume fractions. Specifically, the bearing capacity increased by 19% and 33% with steel fiber aspect ratio increments from 33 to 70 and volume fraction increases from 10% to 14%, respectively. Additionally, the ductility ratio of the test blocks increased by 104% when the aspect ratio of the steel fibers increased from 33 to 70, and by 37% when the volume fraction of steel fibers rose from 10% to 14%.

Concrete structures frequently experience sustained loading during service, which may lead to crack propagation and eventual failure. In this study, three-point bending beams with heights of 200 mm and 300 mm were subjected to sustained load levels of 0.82, 0.84, and 0.86 of the peak load. The crack propagation process was monitored using the Digital Image Correlation (DIC) technique to capture full-field displacement and strain distributions. Analysis of the crack opening displacement (COD) and the fracture process zone (FPZ) revealed that concrete exhibits brittle fracture behavior under sustained loading, with the FPZ not fully developed at creep failure. The crack propagation process was further characterized into three stages. In the initial stage, crack development is mainly governed by viscoelastic deformation. In the intermediate stage, both viscoelasticity and the gradual decay of cohesive stresses within the FPZ contribute to crack growth. In the final unstable acceleration stage, crack propagation is dominated by cohesive stress degradation. Importantly, the crack length at creep failure closely matches the corresponding crack length on the descending branch of quasi-static loading, indicating a direct link between time-dependent creep fracture and quasi-static post-peak behavior. These results provide new insights into the time-dependent fracture mechanics of concrete, revealing the evolution of damage under long-term loading. The study emphasizes material behavior, including FPZ development and stage-wise crack propagation, offering a mechanistic understanding of creep fracture beyond the evaluation of measurement techniques.

To optimize the design of concrete beams and assess the performance of new materials, four-point bending tests were conducted to examine the bending behavior of alkali-activated concrete (ALAC) beams with different reinforcement ratios. The cracking load, displacement, and crack width were measured using the Digital Image Correlation (DIC) method and compared with results obtained through traditional methods. The findings demonstrate that DIC significantly outperforms traditional techniques in determining crack load, displacement, and crack width, particularly in capturing crack initiation and propagation. As the reinforcement ratio increases, the mid-span displacement at the peak load decreases for ALAC beams. At the same reinforcement ratio, the ALAC beam exhibits 1.07 times the bearing capacity, 1.4 times the mid-span displacement, and 0.72 times the maximum crack width compared to ordinary Portland cement concrete (PCC) beams. The cracking load, calculated using a plasticity coefficient of 1.17 for the section resistance moment, aligns closely with the experimental results. Furthermore, the formulas for mid-span displacement and maximum crack width in ordinary concrete beams can also predict the corresponding properties of ALAC beams. These findings validate the mechanical behavior and application potential of ALAC beams under various reinforcement ratios.