A novel model based on the three-parameter Weibull function is proposed to describe the three-stage fatigue deformation behavior of plain and fiber-reinforced concrete. The fatigue strain at a particular stress between zero and the maximum fatigue stress can be modeled using the proposed model, and all the model parameters have clear physical meanings. This model is validated via comparison of its results with previously reported results of compressive, tensile, and flexural fatigue tests. Cases of application of the model to plain concrete and fiber-reinforced concrete with high ductility are examined in order to investigate the variation of the model parameters. Additionally, a deformation-based method for prediction of the fatigue life of concrete is presented, and the prediction results demonstrate that the proposed model can be successfully applied to the estimation of the fatigue life of concrete materials.

Graphene and graphene oxide (GO) sheets have great potential to improve the properties of traditional cement-based building materials. This research studied the effects of graphene and GO sheets on the flexural and compressive strength of cement paste. After dispersion into water with an effective surfactant, graphene and GO sheets can be stored stably for several days. As the proportion of graphene and GO sheets increased from 0% to 0.1% by weight, the mechanical properties of the nanocomposites were improved significantly. With the addition of 0.05% by weight graphene sheets, the flexural strength of the samples increased by 38% and 23% at 7 and 28 days, respectively. The compressive strength of specimens was also improved by the addition of graphene sheets. However, the results showed that high content of GO sheets has an adverse impact on the mechanical properties. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analysis showed that the addition of graphene sheets improved pore-diameter distribution and formed a compact microstructure of cement paste.

This study investigates the effect of high temperature on microstructure and mechanical properties of high-toughness fiber-reinforced cementitious composites. Pore size distribution, microstructure, and mechanical properties are tested after exposure to 20, 200, 400, 600, and 800°C. The variation of chemical compositions after elevated temperatures leads to color changes of fibers and matrix, which can be clearly verified from energy dispersive X-ray analysis (EDAX). Furthermore, pore size of the composites decreases gradually at 200 and 400°C. Compressive strength varies consistently with the microstructure, showing that fire damage does not inevitably lead to the deterioration of mechanical properties. However, residual flexural properties decrease significantly because of the melting of PVA fiber. As a covering layer of the structures, the composites exhibits excellent fire protection to reinforced concrete columns.

Ultrahigh toughness cementitious composite is a cementitious material that exhibits the characteristic of pseudo strain hardening under uniaxial tension, and has potential use in structures that experience repeated or fatigue loads. A series of quasi-static, dynamic, and fatigue tests were performed to evaluate the frequency effect on the compressive fatigue behavior of this material; in this paper the results are reported. It is found that the fatigue life and deformation pattern are influenced by loading frequency. The relationship between the secondary strain rate, the secondary strain rate per cycle, and the fatigue life is illustrated and equations applied to predict the fatigue life of specimen are developed. The failure strain of each loading frequency is found to follow the Weibull distribution. Based on the distribution of the static failure strain at the same stress level, a probabilistic model of the fatigue failure strain is proposed to describe the frequency effect, which gets a considerable agreement with the experimental results.