Material Factor Analysis And Acoustic Emission Parameter Characterization For Mechanical And Fractural Properties Of Manufactured Sand Concrete

As one of the main components of cement concrete,natural sand accounts for about 20%-40% of concrete.Due to the fact that natural sand has the characteristics of small reserves and non-renewable in the short term,with the rapid development of transportation infrastructure construction,the supply of natural sand is in short supply,the price of natural sand is soaring,and resources are facing depletion.At the same time,the phenomenon of excessive mining of natural sand leads to ecological environment damage,and the quality problem of natural sand is increasingly prominent.Manufactured sand(MS)has the characteristics of abundant raw materials,economical and environmental protection,making MS a reliable substitute for natural sand.In this thesis,the working properties and mechanical properties of manufactured sand concrete(MSC)were studied,and the effects of glass fiber,basalt fiber,and steel fiber on the mechanical properties and fracture properties of MSC were analyzed.Based on acoustic emission technology(AE)and fracture toughness,the fracture mechanics characteristics of MSSC notched beams to be characterized under different loading modes,providing theoretical and data support for the application of MS in practical engineering.The specific research work carried out in this thesis is as follows:(1)The influence of water-cement ratio,replacement rate of MS,and stone powder content on the working performance and mechanical properties of MSC was analyzed,and the influence rule of each factor on the performance of MSC was obtained,and the coupling effect between each factor was clarified.Using water-cement ratio(0.41,0.44,047),MS replacement rate(20%,60%,100%),stone powder content(0%,5%,10%)as the key influencing factors and levels,and the three-factor and three-level test design was carried out based on the response surface method.And the change law of concrete working performance and mechanical properties under different factors at different levels was studied through slump test,compression test and bending test,and the damage process was characterized and analyzed by AE technology.The results show that with the increase of stone powder content,the working performance and mechanical properties of concrete increase first and then decrease;with the increase of the replacement rate of MS,the strength of concrete also increases,and the internal damage of concrete decreases;The stronger the interaction between the reduction of ash ratio and the increase of the replacement rate of MS,the more favorable it is to the strength of concrete,and the more unfavorable to the working performance.(2)The influence law of fiber type,dosage and length on the strength of MSC was analyzed,and the enhancement mechanism of fiber on the strength of MSC was explained by combining the AE technology.Based on the compression test and bending test of MSC,the influence of types of fibers(steel fiber,basalt fiber,glass fiber),fiber content(0%,1%,2%),and fiber length(6mm,13 mm,20mm)on the mechanical properties were analyzed.The results show that the three kinds of fibers can enhance the strength of MSC,and the order of reinforcement effect is from high to low: steel fiber > glass fiber > basalt fiber;basalt fiber and glass fiber MSC have brittle damage in the bending test,and the toughening effect of MSC is worse than steel fiber;while the toughening effect of steel fiber is more obvious,the addition of fiber can effectively reduce the early damage of MSC;the MSC with the content of steel fiber is 1% and the length of steel fiber is 6mm has the highest strength.(3)The fracture characteristics of the MS and natural sand concrete notched beams were studied by different loading methods,and the fracture process of the concrete notched beams was characterized by combining the AE technology and fracture toughness index,and the fracture characteristics of the MSC and natural sand concrete were analyzed.And the difference between the fracture characteristics of three-point bending and four-point bending cutting beam is clarified.The results show that the MSC exhibits better fracture toughness under the action of bending load,has better control ability to cracks,and the synergistic effect of MS and steel fiber is better;and the three-point bending test is more serious than the four-point bending fracture test.The cumulative AE parameters have a strong correlation with the fracture toughness index,and the cumulative AE parameters are more sensitive to the specimen fracture.