Experimental Study On Type Ⅱ And Composite Fracture Performance Of C40 Self-compacting Concrete

Self-compacting concrete（SCC）has been valued for its good working performance,especially as the underfill material for CRTSⅢslab ballastless track.However,cracks are unavoidable during the preparation and use.Because of the existence of cracks,the bearing capacity and service life of SCC are affected.Therefore,it is of great significance to study the fracture performance and crack resistance design of SCC.In order to study the type II fracture toughness and composite fracture properties of SCC,a SCC with a strength of C40 is designed.The type II fracture toughness of SCC is studied by using a semi-symmetric loading test.The design size of the test specimens is 200 mm×200 mm×100 mm,divided into single-edge notched specimens,double-edge notched specimens and unnotched specimens.Single-edge notched specimens have four types of seam height ratios of 0.1,0.2,0.3,0.4.Three seam-height ratios were set for the double-edge notched specimens,0.1,0.2,and 0.3 respectively.Three specimens were poured for each seam-height ratio,and three unnotched specimens were poured.At the same time,the three-point bending eccentric loading test was used to study the composite fracture performance of SCC.The specimens size was 400 mm×400 mm×100 mm.Four kinds of seam height ratios were set,which were 0.1,0.2,0.3,and 0.4.Compared with pouring15 test specimens,five kinds of eccentric loading distances are set,which are 0 mm,20 mm,40 mm,60 mm,and 80 mm.Digital image correlation method（DICM）was used to study crack mouth opening displacement（CMOD）,crack tip slipping displacement（CTSD）of SCC specimens,and fracture process zone（FPZ）.Combined with the finite element software ABAQUS,the stress intensity factor K of the semi-symmetrically loaded test specimens was calculated and the shape factor and T stress of the three-point bending eccentrically loaded test specimens were calculated.The generalized maximum tangential stress（GMTS）criterion and other related theories were used to predict the results of eccentric loading tests at three points.（1）Regardless of whether it is a single-sided or double-sided notched,the CMOD and CTSD increase with the increase of the seam height ratio.For the same test piece,whether it is a single-sided or double-sided notched,the CTSD is greater than the CMOD.For the specimens with the same seam height ratio,the CMOD and CTSD of the double-sided notched specimens are larger than the CMOD and CTSD of the single-sided specimens;（2）For specimens with the same eccentric loading distance,as the seam height ratio increases,the CMOD of the three-point bending eccentric loading specimen gradually increases,the CTSD also increases,and the FPZ at the maximum load moment gradually decreases;For specimens with the same seam height ratio,as the eccentric loading distance increases,the CMOD and CTSD of the three-point bending eccentric loading specimen decrease,and the FPZ at the maximum load moment gradually increases;（3）The finite element software ABAQUS was used to calculate the stress intensity factor K of the semi-symmetrically loaded test piece,and compared with the type II fracture toughness calculated by theory.It is found that the theoretical calculated value is in good agreement with the simulated calculated value,the maximum relative error is 7.7%,the minimum relative error is 0.5%,and the Type II fracture toughness of SCC is 1.94MPa m^{1 2};（4）The finite element software ABAQUS was used to simulate the shape factor and T stress of the three-point bending eccentrically loaded test specimens.For the test specimens with the same eccentric loading distance,the shape factor _IY,shape factor Y_II and T stress all increased with the increase of the seam height ratio.At the same time,for the specimen with the same seam height ratio,the shape factor _IY gradually decreases with the increase of the eccentric loading distance,and the shape factor Y_II increases first,reaches the maximum at b=40 mm,and then gradually decreases,and the T stress gradually increases;（5）The GMTS criterion,the maximum tangential stress（MTS）criterion,the minimum strain energy density factor（SED）criterion,the maximum energy release rate（Gerr）criterion mixing factor（M_e）-fracture initiation angle（?₀）theoretical curve and(K_II K_Ic)-(K_I K_Ic)fracture curve were compared with experimental values.AtM_e=0.8,the relative error between the fracture angle predicted by the GMTS criterion and the experimentally measured fracture angle is 1.2%,the absolute values of the relative errors between the fracture angles predicted by the MTS criterion,the SED criterion,and the Gerr criterion and the experimentally measured fracture angles were 14.4%,17.2%,and 20.8%,indicating that the fracture angle predicted by the GMTS criterion is more accurate than other theoretical predictions.At the same time,the absolute value of the relative error between the predicted value of the GMTS criterion and the experimental value(K_II K_I（28）0.2)is 2.0%,and the absolute value of the relative error between the predicted value of the MTS criterion,SED criterion,Gerr criterion and the experimental value(K_II K_I（28）0.2)is 45.4%,5.6%,and 6.2%.This shows that the GMTS criterion has a high accuracy in studying self-compact concrete I/II composite fractures.