Characteristics of early-damaged cement stone and the creep behavior after damage

The cement used in roadway is in the state of long-term compression, and its creep characteristics have been extensively studied. However, the cement paste will be affected by stress after construction and cause early damage, and the creep behavior after damage has not been involved. To solve this problem, 5 groups of 10 cement stone specimens were prepared for early damage and post-damage creep tests. The results show that the damage amount at each stage can be calculated by establishing a complete damage solving equation, and the creep behavior after damage can be effectively characterized by the modified Nishihara model after introducing damage factors. With the decrease of the stress ratio (100% - 60%), the axial strain, transverse strain, Poisson's ratio and the damage amount of the cement stone specimen decrease, while the elastic modulus increases. The 80% stress ratio (the damage amount is 0.50) of early cement stone specimen is the damage threshold value, and the effect of early damage below this value on later creep property is far less than that of the damage above the threshold value. The internal cracks of the specimen under the acoustic emission observation increase with the increase of the damage amount from compaction to generation of fine cracks and then gradually penetrate to failure. With the decrease of damage amount, the creep failure strength of cement stone specimen showed a trend of rapid increase at first and then stable, while the primary damage strain and primary creep strain showed a trend of rapid decrease at first and then slow decrease, both of which changed at 0.50 damage amount. The instability modes of cement stone specimens are divided into energy storage instability and dissipative energy instability. The stress concentration of high and low damage specimens occurs at large and small cracks respectively in the creep stage.

Automated summary

The study on early damage and post-damage creep behavior of cement stone specimens revealed that the modified Nishihara model with damage factors effectively characterizes the creep behavior after damage, and the 80% stress ratio serves as a threshold value for early damage. The study also showed significant differences in the impact of damage amount on later creep behavior below and above the damage threshold value.