Experimental Study On Compressive And Electric Properties Of Red Mud-coal Metakaolin Geopolymer Under The Acid Environment

With the rapid development of industrialization and urbanization,the problem of environmental pollution has attracted more and more attention,and the problem of pollution in the field of environmental geotechnical engineering has also attracted more and more scholars’ attention.Especially in engineering construction,after geotechnical engineering materials are affected by typical pollutants,their compressive strength decreases and structural changes cause the material to lose its value.Therefore,the change of the mechanical properties of geotechnical engineering materials after pollution is one of the key issues in environmental geotechnical engineering research.This paper relies on the National Natural Science fund project-Study on Physical and Mechanical Properties and Mechanism of Red Mud-Coal Metakaolin Geopolymer of [51879180] to carry out the series research,selecting two kinds of solid waste red mud and coal measures kaolin as raw material preparation of geopolymer as the research object,the sulfuric acid solution and hydrochloric acid solution as the acid pollutants to study the compressive properties and electrical properties of the red mud-coal metakaolin geopolymer in acidic environment.This paper selects Si/Al=1.2,Na/Al=1.0 ratio to make red mud-coal metakaolin geopolymer test block,chooseing p H=2 sulfuric acid solution and hydrochloric acid solution as the soaking solution.Compressive strength and electrical tests of the red mud-coal metakaolin geopolymer test block corroded by two acid solutions and 6 immersion ages were carried out to explore the compressive and electrical properties of red mud-coal metakaolin geopolymers in acidic environments.In addition,by testing the macroscopic parameters such as acid consumption and quality of the red mud-coal metakaolin geopolymer in acidic environment,as well as its chemical composition and microstructure,it revealed the damage mechanism of the acidic environment to the red mud-coal metakaolin geopolymer,and the following conclusions were obtained:(1)The unconfined compressive strength test results show that when the immersion time in acidic solution is less than 3 d,the compressive strength of the red mud-coal metakaolin geopolymer has a greater decline rate.When immersed for 3 d to 112 d,the compressive strength first increased slightly and then decreased with the extension of immersion age,and the peak appeared at 14 d of immersion;During the whole process,the compressive strength of red mud-coal metakaolin geopolymer in sulfuric acid solution was higher than that in hydrochloric acid solution,and the test blocks had better corrosion resistance in hydrochloric acid environment.The stress-strain curves of red mud-coal metakaolin geopolymer in acidic environment are all softening type,which can be divided into four stages: compaction stage,elastic stage,plastic deformation stage and failure stage.(2)Electrochemical impedance spectroscopy test results show that the equivalent circuit model of red mud-coal metakaolin geopolymer in acid environment is: R(Q(RW))(QR);The Nyquist of different acidic solutions included a small capacitance arc in the high frequency region and a large capacitance arc in the intermediate frequency region,and the capacitance arc in the intermediate frequency region first increased and then decreased after soaking for 3 d to112 d.The data of electrochemical impedance spectroscopy were fitted,and the results showed that there was a good correlation between the electrochemical parameters(the resistance of pore solution,the transfer resistance of solid-liquid interface)and the compressive property parameters(the compressive strength,elastic modulus).(3)In an acidic environment,the resistivity of the red mud-coal metakaolin geopolymer first increases and then decreases when it is immersed for 3 to 112 days,and the peak appears at 14 days of immersion.Moreover,the resistivity has a good correlation with its compressive performance parameters(compressive strength,elastic modulus).(4)From chemical composition and microstructure analysis,it is confirmed that the structure of red mud-coal metakaolin geopolymer gradually heals after soaking for 3 d to 14 d,and more amorphous silicate aluminate polymer is formed,which leads to the increase of compressive strength.After soaking for 14 d to 112 d,the zeolite phase was formed,and the amorphous silicate aluminate polymer depolymerized,and the microstructure became loose,leading to the decrease of compressive strength.