Evaluation Of Mechanical Properties Of Cement Materials And Low Energy-consumed Crashing Mechanism

Cement industry is an important basis for economic construction and structuralengineering. It is also one of major industries of energy resource consumption andpollutant emissions. Fragmentation of raw materials and grinding of cement clinkeris one of the largest energy-consumed aspects of cement production. Therefore, it isof great practical significance to minimize the energy consumption of thefragmentation. The manner and energy consumption of crushing are related with themechanical properties of cement materials. In this work, based on the contrarianthinking of materials strength science and fracture mechanics, the effect ofmechanical properties of materials, loading mode and temperature on the strength ofmaterials and energy consumption of crushing were studied. Small energy-consumedtheory was proposed, which was that the largest surface energy was got withminimal energy consumption, or in a given condition of surface energy, the energyconsumption was minimum. Then it was explored new ways and new methods tolow energy-consumed, as follows.(1) The mechanical properties of raw material and dry kiln cement clinker such ashardness, strength, elastic modulus and so on, were tested. The relationship ofcrushing resistance and mechanical properties for dry kiln cement clinker wasdiscussed. Brittleness and energy dissipation of materials were analyzed. It wasfound that the mechanical characteristics of dry kiln cement clinker were highhardness, low strength, and elastic modulus lower than the raw materials. Lowstrength led to its crushing resistance low. And high hardness was made it difficult tofine grinding. It was the main reason of clinker grinding energy consumption morethan raw materials.(2) Based on Oliver-Pharr model, depth sensing indentation technique was used toevaluate the hardness and elastic modulus. Then it was applied to cement clinker androck computing. The elastic modulus of calculate and dynamic tested modulus werecompared, to verify the reliability of the results. At last, according to loading and unloading curve and residual indentation morphology, crushing resistance andenergy dissipation rate of the materials were analyzed. The energy dissipationfraction of clinker is62.33%, which is more than that of granite and limestone. It isexplained why the grinding of clinker consumes a lot of energy. It was indicated thatthe clinker was one of quasi-brittle materials which have a certain plasticity andgreater energy dissipation capacity.(3) Multi-angle compression fracture tests were designed with acoustic emissionmonitoring. The optimal tensile and shear loading conditions were studied for singleparticle of the clinker. The optimal angle of low energy-consumed crushingmechanism was45°by theoretical derivation. And the test environment of impactcompression, direct compression and cyclic compression was designed. Based onthree major theories of Rittinger, Kick, and Bond, energy consumption of cementclinker was evaluated, to compare the effect of different evaluation theories anddifferent loading ways on energy consumption. Finally, it was found that thecompression load way between5000~10000N for10times had lowest energyconsumption.(4) The impact of equipment was made for different impact angles tests of cementclinker particle. The impact load and displacement curve of the process, impact peakforce and impact indentation morphology were studied with the impact angleschanged. In impact crushing experiment, it was showed that the depth of damagearea increased with the increase of impact angle, which made significantly residualstrength lower. Under the nearly same impact velocity, the smaller the impact angle,the higher the impulse, the longer contact time, and the peak impact force ismaximum value with impact angle of45°. When the impact angle is45°, the area ofdamage surface for cement clinker was most serious damage and fracture was causedby the composite stress of the compressive stress and shear stress. It was veryimportant in engineering applications to many grinding equipments.(5) By high-temperature stress relaxation of cement clinker, the brittle-ductiletransition temperature can be determined in the second heating process of cement clinker. With the temperature from800℃to1200℃, the stress decreased from60%to Below40%. Particularly under the conditions of1200℃, the level of stressrelaxation increases obviously. Some gas and liquid was equivalent to a lubricant toreduce friction between particles of clinker. So the stress was reduced. It was shownthat from800℃to1200℃, the elastic modulus decreases, and the stiffness ofclinker decreased. The elastic modulus is very sensitive to temperature change.When temperature increases from800℃to1200℃, the elastic modulus of cementclinker decreased from24.50GPa to7.57GPa. The deformation of the clinker in thistemperature is largest, and the plastic deformation obvious. The residual strengthincreased with temperature decreasing. When the temperature was800℃, damageof cement clinker sample was brittle fracture. As the temperature increases, thedamage extent of the clinker was larger. Clinker at high temperature has low stiffnessand large deformation capacity. When the temperature was1200℃, the fracturesurface was caused by shear failure.(6) Elastic deformation, extend crack initiation, crack unstable propagation of thedamage process of clinker were simulated by the numerical simulation of RFPA2D.Compression tests of different angles were simulated. And the destruction process ofhigh temperature for clinker, were simulated by different material properties. Therupture force and the minimum energy path were analyzed to achieve load form ofthe model. It was shown that the numerical simulation of particles of cement clinkerwas consistent to one of real test. With the elastic modulus from E=47.28Gpa~E=1.43Gpa decreasing, the maximum failure load decreased. When the liquid fractionfrom0%to10%increased, the maximum failure load decreased, and the crushingwork also decreased.