Experimental Study On Mechanical Properties Of Basalt Fiber Concrete Based On Acoustic Emission Method

Over the years,the technology of concrete is developing continuously,so in the field of civil engineering,fiber reinforced concrete has made great achievements,and substitute ordinary concrete.Among them,Basalt Fiber(BF)as a new green material,has high tensile strength,corrosion resistance,good combination with concrete and other characteristics,it has become a research focus in the domain of Fiber concrete.Some scholar studies have shown that the damage of fiber concrete not only occurs at the macro scale,but also at the micro damage.So,it is very necessary to study the macro damage and the micro injure of the basalt fiber concrete.Based on acoustic emission technology,this paper studied the compressive and flexural properties of basalt fiber reinforced.In order to study the mechanical properties of basalt fiber concrete,we designed five different volume fraction,six different lengths and three different diameters were prepared to study the strengthening effect of basalt fiber on concrete specimens,the failure mechanism of the specimen is described and the reinforced and toughening mechanism of the fiber is revealed by the acoustic emission phenomenon.The research work of this paper are as follows:(1)The addition of basalt fiber reduces the fluidity of concrete,especially for the specimen with too long fiber length or large mixing amount,the drop in concrete slump is even more pronounced,the reason is that the random distribution of fibers increases the bond between the aggregates,cause the fluidity of cement to become poor.(2)Basalt fiber can effectively improve the mechanical properties of concrete.Fiber reinforced concrete with diameter of 17,length of 6mm and volume fraction of 0.2% has the highest compressive capacity,which is improved by 39.2% compared with plain concrete.Fiber reinforced concrete with diameter of 13,length of 15 mm and volume fraction of 0.4% has the highest flexural capacity,which is improved by 53.05%compared with plain concrete.(3)The acoustic emission parameters(damage anchor point,ringing number,energy and hit count)of the compressive and flexural specimens of plain concrete and basalt fiber concrete under load were observed.It was found that the failure of the specimen was divided into three stages.Initial stage: acoustic emission event number is less,the signal is weak.Fracture propagation stage: the number of acoustic emission events increased compared with the initial stage,some high amplitude signals begin to appear.Failure stage,the number of acoustic emission events has increased dramatically,and the point of maximum damage appears.At this time,macroscopic transfixion fractures appear,the specimen is destroyed.(4)In the process of compressive test of basalt fiber concrete,the acoustic emission b value represents the ratio of small events to large events,in the other words,the increase of b value represents the generation and development of micro-cracks inside the specimen,while the decrease of b value represents the coalescence of cracks inside the specimen.The acoustic emission b values of all specimens in this test tend to decrease between 75% and 80% of the ultimate load.So,b values can be used to analyze the fracture precursor of the specimen.In addition,the specimen with a volume fraction of0.2% has the highest compressive strength,its acoustic emission b value is also slightly larger than that of other specimens with the same size and different dosage.The indicates that the addition of basalt fiber prevents the formation of microfractures,and inhibited the crack penetration.(5)Acoustic emission parameters(rise time,ringing count,time of duration and amplitude)of basalt fiber concrete specimen in the process of flexural failure were calculated,to map the AF-RA curve,to identify the flexural failure mode of concrete.The results show that the higher the flexural strength of the specimen,the more proportion of shear cracks,the ratios of tensile cracks is reduced.The reason is that the addition of fiber inhibits the formation of tensile crack,reflects the fiber anti-crack effect.