Experimental Study On Shear And Splitting Tensile Properties Of Aligned Steel Fiber RPC

Reactive Powder Concrete（RPC）a new type of structural material was first developed in 1990s.It has attracted much attention from engineers due to its excellent strength（compressive strength is higher than 150 MPa and tensile strength is equal to or higher than 8 MPa）,durability and fatigue resistance,as well as a unique strain-hardening response involving multiple micro-cracks.It is found that the orientation and distribution of steel fibers have great influence on the mechanical properties,especially the tensile properties and toughness of RPC members.The improvement of the tensile strength of composites will be lost if the fiber are poorly distributed and perpendicularly orientated to the load direction.Therefore,it is very important to study the orientation and distribution of steel fiber to improve the performance of RPC.To study the influence of fiber distribution on the mechanical properties of RPC members under quasi-static loading,the modified double-plane direct shear test and split tensile test was carried out on aligned steel fiber-reinforced reactive powder concrete（ASFRPC）specimens and conventional steel fiber-reinforced reactive powder concrete（SFRPC）specimens at three types of steel fiber with different contents,V_f,of 1.0%,1.5%and 2%and three types of steel fiber with different lengths,l_f,of 13mm,16mm and 20mm.The main research contents and results are as follows:（1）The modified double-plane direct shear test combined with image analysis method（DIC）were carried out on specimens with different orientations,different contents and different lengths and shear behaviors including the shear strength and shear load displacement curves were then measured.The experimental results show that the orientation and distribution of steel fibers have great influence on the shear properties.The shear strength,peak deformation and shear toughness of the aligned steel fiber specimens are significantly higher than that of the randomly distributed specimens.In particular,when the specimen enters the post peak state,the equivalent residual shear strengthf_p1,2.、f_p1,5.、f_p,2.0 is also higher than the random distribution.Therefore,the aligned steel fiber used in RPC shear structure has high safety and reliability.（2）The fiber spacing on the shear plane of ASFRPC and SFRPC specimens is analyzed,and the number of steel fibers on the failure section is counted.Based on the fiber spacing theory,the relationship between the above parameters and fiber content is analyzed.The results show that the ASFRPC specimen has smaller fiber spacing,more steel fibers play an effective role in bridging when shear deformation occurs,and the bonding area between the fiber and the matrix at the cross section is larger,so as to absorb more energy in the process of overcoming the bonding force,which shows higher shear strength and toughness.（3）The split tensile test was carried out on specimens with different orientations,different contents and different lengths.The experimental results follow:Orientation coefficient of steel fibers has not a strong impact on the split tensile strength.Due to the small size of the specimens,which limits the movement area of a single fiber,the unidirectional arrangement efficiency of the fiber is low under the action of magnetic field,and the splitting tensile strength of aligned steel fiber RPC specimen is only slightly higher than that of disorderly distribution.