Abstract: Compared with drilling and blasting and mechanical rock breaking,microwave assisted rock breaking is considered as a promising new method for hard rock excavation because of its advantages such as selective heating,high efficiency and strong controllability. In order to explore the influence of water on the assisted rock-breaking effect of microwave radiation on quartz sandstone with low wave-absorbing capacity,1. 4 kW microwave radiation was applied to quartz sandstone with different water content for 0~ 300 s to explore the relationship between temperature rise,damage and water content. According to the damage factors represented by wave velocity,such as damage factor Dm,surface temperature difference FT after microwave irradiation and Brazilian splitting tensile strength σt,the influence rule of temperature rise damage was comprehensively analyzed. The results show that the quartz sandstone in microwave radiation drying state presents a rapid temperature rise in the early stage,a slow and stable trend in the later stage,and the temperature difference increases first and then decreases. In addition to saturated water,the temperature rise rate of specimens with different moisture content in 90 s radiation increased from fast to slow down and opened a gap at 6 h after absorbing water (average moisture content 1. 88%). The change amplitude of FT,Dm and σ t does not change gradients with the increase of immersion time. The wave velocity and the damage factor Dm represented by the immersion time (water content 1. 69% ~ 1. 88%) show an " inflection point" of decrease and increase. The average decrease in the former increased by 5. 18%,while the latter increased by 0. 092,σt has increased by 25. 9%. The temperature rise damage process in rock microwave field is the result of multi-scale and multi-medium comprehensive response under the influence of water-rock coupling. Specific water content (1. 69% ~ 1. 88%) and radiation duration (more than 90 s) can promote the generation of thermal stress gradient after microwave absorption of quartz sandstone,thus causing pore damage and reducing ultimate tensile strength,making it more vulnerable to destruction. The analysis results can provide a reliable reference for the study and analysis of microwave radiation heating damage to hard rock under similar conditions.

Key words: microwave radiation,quartz sandstone,moisture content,heating and damaging,tensile strength