Study On The Weakening Effect And Mechanism Of Granitoid Rocks Under Microwave Irradiation

Mechanical rock breaking has been widely applied in engineering construction for its advantages of low damage on surrounding rock,high automation,high penetration rate,et al.When facing hard rock,nevertheless,it has the weaknesses of excessive cutter wear,low penetration rate,long construction period,high cost,et al.In recent years,many scholars have found that rock can be effectively weakened by microwave heating,thus proposing a new approach known as microwave-assisted mechanical rock breaking.That is weakening the rock using microwave irradiation before breaking it with mechanical ways,thereby raising the penetration rate and reducing the cutter wear.Taking Granitoid rocks and basites as researching object,this paper distinguished the microwave sensitivity of 14 common rock-forming minerals based on their heating rate under microwave irradiation of different powers and studied the influence of mineral species,crystal form,chemical components,microwave power and mineral form on heating rate.Meanwhile,the weakening law,and mechanism and influencing factors of granitoid rocks under microwave irradiation were studied by comparing the physical and mechanical properties of 5 types of igneous rocks before and after microwave irradiation.Conclusions are as follows:(1)Different minerals have different microwave sensitivities.Rock-forming minerals involved in this paper can be sorted into 3 groups:hypersthene,hornblende2#and biotite3#are the most sensitive to microwave,followed by hedenbergite1#,hedenbergite2#,biotite1#and biotite2#,while quartz,orthoclase,plagioclase,muscovite,diopside,forsterite and hornblende 1#are the least.Common ore-forming minerals are more sensitive than rock-forming mineral and are sorted as extreme sensitive group.(2)Heating rate of minerals is related to mineral types(species and subspecies)and chemical components(mainly Fe content).Mineral species has the greatest influence on its sensitivity.Mela minerals are more sensitive than leuco ones(while some mela minerals contain little Fe,their microwave sensitivity is similar to leuco ones);As for minerals in the same species,their sensitivities are related to their crystal forms;As for minerals in the same species and with the same crystal form,their sensitivities are decided by Fe content.(3)When the mineral is heating under microwave treatment,its temperature is linear to irradiation time.The heating rate is linear to the microwave power while the sensitivity remains unchanged.Given the same microwave power,the heating rate of mineral block is higher than that of mineral powder between 1.2 and 2.1(mean value is 1.7);The internal temperature of the mineral block is greater than its surface temperature between 1.6 and 2.4(mean value is 2).(4)The weakening effect of diabase,quartz monzonite2#and alkali feldspar granite is optimized with the increase of microwave power.Given the same microwave parameter,diabase has the best weakening effect,followed by quartz monzonite2#,and alkali feldspar granite the worst.Generally,the more sensitive minerals rock contains,the higher temperature which has a positive correlation with the temperature difference between the microscopic minerals it reaches,as well as a better weakening effect it has.(5)The granitoid rocks can be effectively weakened under certain microwave conditions by this experiment.The weakening mechanism of granitoid rocks is not only related to sensitive minerals such as biotite,but also to the heat transfer between quartz and biotite and thermal expansion characteristics of quartz under microwave irradiation.When microwave energy is small,the lower the overall temperature of the rock,as well as a smaller volume of deformation biotite and quartz,rock weakening effect is not obvious;with the increase of the microwave energy,biotite continues to heat up and transfer some of the energy to the quartz which is also rapidly increasing.At this time,the action of biotite and quartz promotes the obvious weakening effect of the rock.At this stage,the expansion of quartz accounts for the main part of the total expansion,which plays a leading role in the weakening of the rock.With the increase of the microwave energy,the volume of quartz no longer changes with the increase of temperature.However,there is still a structural water escaping from biotite between 800 and 1000?,its volume will expand significantly,which further promotes the weakening of the rock.(6)The weakening effect of granitoid rocks is related to the relative content of biotite and quartz.Generally,when given the same content of quartz,a higher content of biotite can cause a greater reduction of rock strength;when given the same content of biotite,the influence of quartz content on strength reduction in unclear in this paper.