Effect Of Short Fibers And Pre-tension On Mechanical Performances Of Basalt Textile Reinforced Concrete

Basalt Fabric Reinforced Cementitious Matrix Composite(BFRCM),called Basalt Textile Reinforced Concrete(BTRC)as well,is a new class of building materials,which has outstanding advantages of high strength,large strain capacity,excellent durability,and has been gradually applied to civil engineering.Research on reinforcing effect and mechanism of short fibers and pre-tension on mechanical performances of BTRC have a large significance on application of BTRC in engineering.The main works of this paper are as follows:(1)A mortar having large flow-ability and plastic viscosity was designed according to mix proportion of standard ECC,and mix process for dispersing short fibers in mortar evenly was also tested.The flow-ability of mortar mixed by adding sands before and after short fibers were measured,and the mortar mixed by adjusting initial water binder ratio to 0.22,0.25 and 0.28 followed by adding 2.0vol.%short carbon and glass fibers were also tested.(2)The tensile testing of basalt textile consisting of one and three warp yarns were performed by MTS load frame with a gauge length of 100 mm,and two,three and five layers of BTRC with different volume content(0.5vol.%?1.0vol.%?1.5vol.%)of short carbon,glass and steel fibers were also tested by tensile testing,pre-tensioned five layers of BTRC with 0.5vol.%short carbon or steel fibers were also perf-ormed by the same method.The influence and reinforcing mechanism of short fibers and pre-tension on tensile mechanical performances of BTRC were analyzed.(3)Five layers of BTRC with short carbon and steel fibers ranging from 0.5vol.%to 1.5vol.%by 0.5vol%and pre-tensioned alone were tested by static four-point bending testing utilizing MTS load frame,and influence of fibers type and content on flexural mechanical performances of BTRC were analyzed.(4)Full-field strain distribution of tensile and flexural specimen surfaces were obtained by Digital Image Correlation(DIC)analysis,and the strain development with testing process,the effect on crack pattern of short fibers and pre-tension were also described.This study result say,adding sand after short fibers with initial water binder ratio of 0.22 lead to the best improvement on fibers dispersal in mortar,and flow-ability is largest.The mechanical properties of basalt textile obtained from three warp yarns are reasonable.Layer of basalt textile in BTRC have an significant influence on mechanical performances;as for tensile testing of five layers of BTRC,three types of short fibers and pre-tension can increase tensile crack stress,with increasing volume content of short carbon fibers tensile crack stress increase,while ultimate load and toughness increase first and then decrease,reaching optimal value at 1.0vol.%;with increasing content of short steel fibers the ultimate load and toughness increase constantly,at 1.5vol.%reach a maximum;short fibers have no obvious influence on ultimate strain.Pre-tension alone can also increase crack stress,ultimate load and toughness,with short fibers together the ultimate load and toughness increase further,while ultimate strain decrease slightly with pre-tension alone.Reinforcing mechanism of short fibers and pre-tension can divide into enhancement on matrix and interface between matrix and textile;short fibers can improve matrix strength,and the bridging effect of short carbon and glass fibers and anchor effect of short steel fibers enhance interfacial performance,and increase effectiveness factor.Pre-tension can produce pre-compressive stress of matrix,and the restrain of matrix on radial expansion of warp yarn owing to poisson's effect lead to larger interfacial contact force and friction force and improve interface performance;short fibers improve matrix strength,so the interfacial force is more outstanding.According to DIC analysis on tensile testing,the strain at cracks is large than other no-crack region,and increase gradually with growing tensile strain,while the strain at critical crack increase quickly post ultimate strain,and strain at other cracks decrease due to descent of tensile stress.Short glass,steel fibers and pre-tension increase crack numbers with decreasing crack spacing and width,short carbon have no influence on crack number,at the same time,crack shape change from line to curve owe to the restrict on crack propagation of fibers bridging-effect.According to four-point bending testing result,the following can be saw:short fibers and pre-tension increase flexural crack stress and flexural strength of BTRC,and the enhancement of pre-tension perform best;flexural strength increase first and then decrease with increasing content of short carbon and steel fibers,and get superior value with 0.5vol.%carbon fibers or 1.0vol.%steel fibers,so there are optimal volume content of short fibers,which is different with varied types of fibers.There are obvious increase at absorbed energy and ultimate strain of BTRC with short carbon,steel fibers and pre-tension,and pre-tension has a most outstanding improvement,With increasing content of short carbon and steel fibers,both the absorbed energy and ultimate strain increase first and then decrease,and reach a maximum at 1.0vol.%.Based on DIC analysis of four-point bending testing,we can see:short fibers and pre-tension improve crack pattern with increasing crack number and decreasing crack spacing.There in an increase first and then descent at crack number with increasing content of short fibers,and reach a maximal value at 1.0vol.%with smallest crack spacing;strain at cracks diminish with short steel fibers and pre-tension,short steel fibers and pre-tension reduce crack width obviously,and short fiber has no outstanding influence on crack width.