Experimental Study On The Acoustic Emission Characteristics Of High Performance Concrete Of Mechanism Sand Under Uniaxial Compression

With many advantages such as simple material extraction,high strength and durability,high performance concrete with mechanism sand is exposed to a variety of complex environments during service,which act to expand internal microcracks and deteriorate mechanical properties,thus affecting structural safety.Therefore,regular nondestructive testing of the working stresses in concrete structures is essential.In order to investigate the damage characteristics of machine-made sand concrete under uniaxial compression,this thesis uses a combination of indoor tests and numerical simulations to carry out an experimental study on the acoustic emission characteristics of machine-made sand high-performance concrete under uniaxial compression,and the main work and research results are as follows.(1)Four working conditions(natural drying for 30 days,long-term immersion in tap water for 30 days,long-term immersion in 10% sodium sulfate solution for 30 days and dry and wet cyclic erosion in 10% sodium sulfate solution for 30 days)and three stone powder contents(8%,9.5% and 11%)were selected as variables to carry out the acoustic emission characteristics tests under uniaxial compression and step-by-step unloading conditions.It was found that the masses of the specimens increased under both the long-term immersion in 10% sodium sulfate solution and the wet and dry cycles for 30 days;compared with the natural dry condition for 30 days,the compressive strength and acoustic emission signal parameters of the specimens under the long-term immersion in tap water for 30 days and the long-term immersion in 10%sodium sulfate solution for 30 days showed a decreasing trend,and the specimens deteriorated more rapidly under the long-term immersion in tap water for 30 days.The compressive strength and acoustic emission signal parameters of the specimens under the condition of dry and wet cyclic erosion of 10% sodium sulfate solution for 30 days showed an increasing trend;from the viewpoint of the stone powder content of the specimens,the compressive strength and acoustic emission signal parameters of the specimens increased with the increase of the stone powder content,but the acoustic emission activity was weak at the early stage of loading;the Kaiser effect occurred in the process of step-by-step loading and unloading of the specimens.(2)Using the accumulated ringing count and accumulated energy value as the damage variables,the damage evolution law of the high performance concrete with different working conditions and different stone powder content was analyzed under the step-by-step loading and unloading conditions,and it was found that the damage degree of the specimen was low in the first two loading and unloading stages,and increased significantly near the damage;the higher the stone powder content of the specimen,the lower the damage degree in the same loading and unloading stages;comparing with the natural drying The higher the content of stone powder,the lower the damage degree in the same loading and unloading stage;compared with the natural drying 30 days working condition,the damage degree of specimen is lower in the dry and wet cycle erosion 30 days working condition of 10% concentration sodium sulfate solution,and the damage degree of specimen is higher in the long-term immersion 30 days working condition of tap water and the long-term immersion 30 days working condition of 10%concentration sodium sulfate solution.(3)Two kinds of uniaxial compression processes were simulated by RFPA2 D,and the shear stress mechanical properties and acoustic emission characteristics of concrete damage process under two loading methods were analyzed,and it was found that the trends of strength and acoustic emission parameters in uniaxial compression process were close to the experimental results;in uniaxial compression with step-by-step loading and unloading,only a small amount of acoustic emission was obtained in the first two cycles.In the step-by-step uniaxial compression,only a small amount of acoustic emission signal was obtained in the first two cycles,and the acoustic emission signal started to increase significantly from the third cycle,indicating that the results of uniaxial compression test of concrete under RFPA2 D simulation are consistent with the indoor test results.