铁元素含量及含水状态对砂岩微波辐射升温损伤的影响

Effects of iron content and moisture on the microwave radiation heating and damage of sandstone

为研究砂岩的铁元素含量与含水状态对微波辐射升温损伤的影响规律,开展了砂岩试件微波辐射对比试验,试验分为12组,包含3种铁元素含量和4种含水状态(干燥、自然、浸水24 h与饱和)。试验采用X射线荧光光谱测量(XRF)技术检测试件表面铁元素含量,通过实时红外热成像监测表面升温过程,运用对比方法分析辐射前后P波波速与抗拉强度的关联特征。试验结果表明:(1)干燥状态下,砂岩试件升温过程均呈前期缓慢、中期活跃、后期稳定的趋势;铁元素含量越高,升温速率峰值就越高(2.66,2.40,1.66℃/s)、也就越早达峰(70,100,110 s);(2)干燥、自然、浸水24 h状态下,升温速率峰值平均值分别为:2.26,3.34,3.24℃/s,达峰时间分别为:90,70,20 s;饱和状态下,升温速率峰值为1.3℃/s,达峰时间为80 s;(3)含水状态对砂岩结构损伤的影响最为显著,饱和状态砂岩辐射180 s的损伤大于其他含水状态辐射300 s的损伤;铁元素含量直接影响岩石表面温度分布的均匀程度,铁元素含量越高,岩石表面温差越大;(4)相较于干燥和自然含水状态,浸水24 h和饱和状态下砂岩辐射后巴西劈裂初始压密阶段占比增加,起裂模式由端部起裂向中心起裂转变。研究成果可为类似原生和再生状态下微波辅助破岩效果的研究提供借鉴与参考。

The laboratory tests of microwave radiation were conducted to study the influences of varying iron content and moisture conditions on the heating and damage of sandstone.Twelve groups of sandstone samples with varying iron content and moisture conditions(dry,natural,immersed for 24 hours,and saturated)were tested.The iron content on the sample surface was detected using X⁃ray fluorescence spectroscopy(XRF).Besides,the heating process by continuous 1.4 kW microwave radiation was monitored by real⁃time infrared thermal imaging.The correlation between P⁃wave velocity and tensile strength was analyzed before and after radiation.The results show that the temperature rise of sandstone samples with different iron contents was slow at the early stage,active in the middle stage,and stable in the late stage under dry conditions.The peak heating rate increased with the increase of iron content,reaching 2.66,2.40,and 1.66℃/s,respectively,and also achieving the peak earlier with 70,100,and 110 s,respectively.Compared with iron content,the increased moisture conditions significantly affected the temperature rise of sandstone under microwave radiation.When the moisture condition was dry,natural,and immersed for 24 h,the average peak heating rates were 2.26,3.34,and 3.24℃/s,respectively,achieving the peaks with time of 90,70,and 20 s.However,the heating of sandstone slowed down in the saturated state,which decreased the peak heating rate to 1.3℃/s and extended peak time to 80 s.The analyses of strength and wave velocity indicate that the moisture condition significantly affected the structural damage of sandstone.However,iron content directly affected the uneven temperature distribution of the sandstone surface.The damage to sandstone after 180 s of radiation in the saturated state exceeded that after 300 s of radiation under other moisture conditions.Besides,the temperature difference of the sandstone surface was positively correlated with iron content.By comparion with dry and natural moisture conditions,the initial compaction stage of radiated sandstone subjected to 24 hour water immersion and saturation was prolonged in Brazilian splitting test.Besides,the cracking initiation mode transitioned from end crack initiation to center crack initiation.The research findings can provide a reference for studying microwave⁃assisted rock breaking in original and regenerated states.