## 5 Conclusions  
The physical and mechanical properties of CGB are heavily impacted by long-term exposure to acidic mine water, and this impact is time-dependent. This study investigates the changes in acoustic emission characteristics and mechanical properties of the CGB, as well as the evolution of stress threshold for crack sprouting under different exposure times.  
Based on microscopic tests, this paper also analyzes the deterioration mechanism of the CGB after chemical ion erosion, and the main conclusions drawn are as follows:  
1. Chemical erosion damages the apparent structure of the CGB, leading to an increase, and then decrease in its mass and UCS over time. As the erosion time increases, the initial compression stage and yield stage of the CGB stress-strain curve are prolonged, and the elastic stage is shortened. This leads to a reduction in CGB's compression brittleness and the enhancement of its plasticity.
2. The acoustic behavior of the CGB when subjected to uniaxial compression demonstrates the impact of acidic chemical erosion on the AE-stress relationship. During the initial stages of chemical erosion, the swelling products produced by the acidic chemical erosion fill the pores, weakening the crack closure phase and decreasing the cumulative acoustic emission rate values. As erosion continues, calcium leaching leads to an increase in pore structure. Consequently, its deformation rapidly changes from microcrack closure to microcrack expansion, enlarging the macroscopic crack damage and sharply increasing the acoustic emission rate.
3. Chemical erosion ultimately causes the performance of the CGB to deteriorate. However, the stress threshold for microcrack initiation and macro crack extension increases and decreases as the microporous structure changes with the erosion time. After 60 days of immersion, the stress thresholds for microcrack initiation and macro-rack extension increase by 20% and 6%, respectively. However, as the immersion time increases to 150 days, the stress thresholds for microcrack initiation and macro crack extension decrease by 56% and 16%, respectively.
4. The mechanism of deterioration for CGB due to chemical ion erosion can be divided into two stages. In the first stage, the strength of the CGB is enhanced due to the hydration reaction and ettringite's filling and compacting effect. Later, the alkaline environment is destroyed, and ettringite accelerates decomposition and dissolution, causing the hydration reaction of the cementitious material to be weaker than the strength deterioration effect caused by acidic corrosion. As the load increases, microcracks are generated at the bond interface, especially the microfractures along the interface transition zone, resulting in strength degradation.  
Methodology, D.L. and H.P.; investigation, H.N.; resources, D.L.; data curation, G.Z. and D.L.; writing--original draft preparation, D.L.; writing--review and editing, D.L. and H.P.; visualization, H.N. and D.L.; supervision, H.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (No. 52374147, No. 52061135111, No. 51974296, and No. 41931284).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy restrictions.  
The authors declare no conflict of interest.