The aim of this study was to analyze the influence mechanism of aeolian sand on the mechanical property of concrete and establish the time‐varying compressive strength model. Test studies on the development of concrete’s compressive strength with aeolian sand from the Mu Us Desert were carried out. Influence mechanism of aeolian sand on the strength of concrete was revealed by using the nuclear magnetic resonance (NMR) to analyze the pore ratio and structures of aeolian sand concrete (ASC) and using the X‐ray single crystal diffraction (XRD) to calculate the relative contents of hydration products semiquantitatively. Results show that the strength first increases and then decreases with the increase of aeolian sand content, where 20% was the best replacement ratio. With less than 20% content, it promoted the strength by changing the pore structure of concrete and accelerating the cement hydration speed based on its filling effect and chemical activity; when the content was more than 20%, it led to a decrease of strength because of an increase of harmful pore ratio and a weakening of the interface transition zone (ITZ), where the stress concentration and damage when loading are easier to occur. At last, a time‐varying compressive strength model of ASC considering the harmful pore ratio variation and heterogeneous nucleation effect was established based on the discussion, published date, and American Concrete Institute (ACI) model, which agrees well with the experimental results and can easily predict the strength of concrete.

It is highly significant to theoretically assess the effect, under load, of initial stress and structure on the mass damage of rock mass. In this reported study, first a multi-factor coupling damage constitutive model under the action of joint-load was established by fully considering the non-uniformity, anisotropy and initial structure of a rock mass based on the Weibull distribution and D-P criterion. The relationship between the damage evolution and joint angle in the rock mass was elaborated. Then, a jointed rock mass strength criterion was built in line with the D–P criterion and the limit state of rock mass failure by the method of multivariate function total differential as based on the constitutive model. The results showed that the established constitutive model was in good agreement with the test results, which accurately reflected the damage characteristics of jointed rock mass during the entire loading process. The initial damage value of the rock mass increased with increasing joint dip angles, and the damage evolution of the jointed rock mass could be divided into the initial, stable, accelerated and failure damage stages. Comparing the results of this approach with other methods it was found that the strength criterion better reflected the effects of minimum principal stress σ₃, volume stress σ_m, shear stress J₂^1/2 and joint dip angle β on rock mass strength than other existing strength criteria, which showed that the proposed method offered important guiding principles for the engineering practice.

This study aims to reveal the impact of immersion duration on the internal structural damage and mechanical property degradation of coal rocks. Coal rocks from the post-mining area of Liangshuijing Coal Mine were selected as the research subject. Physical and mechanical tests were carried out on these with different immersion durations (0 d, 15 d, 30 d, 60 d, 120 d, and 240 d) using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), acoustic emission (AE), digital image correlation (DIC), and compression testing, further elucidating the damage degradation mechanisms of water-immersed coal rocks. The research demonstrates that changes in the pore structure of coal rocks can be divided into two stages as the soaking time varies: the stage of water swelling (saturation process) and the stage of soaking damage (long-term immersion process). The water swelling stage of coal rock extends from surface drying and contraction to water swelling, and the soaking damage stage of coal rock extends from expansion to soaking damage. During the stage of soaking damage, the water showed dynamic changes from macropores to mesopores to micropores, with a gradual increase in the number of micropores. The AE count and cumulative count of coal rock decrease first and then increase, and the four stages’ acoustic characteristics and macroscopic characterization phenomena appear. The mechanical properties declined. After 240 d of immersion, the uniaxial compressive strength and elastic modulus decreased by 48.93% and 29.53%, respectively, and the plastic characteristics were enhanced. These research results provide a beneficial reference for understanding and predicting the instability and destruction of water-immersed coal rocks.