Research Of Performance Of Ultra High Performance-slurry Infiltrated Fiber Cementitious Composites

Ultra High Performance-Slurry Infiltrated Fiber Cementitious Composites(Ultra High Performance-Slurry Infiltrated Fiber Cementitious Composites,UHP-SIFCC)is a new type of fiber reinforced cementitious composite with high toughness and high strength.Its unique production process to ensure the realization of high fiber rate,and the high fiber ratio of the fiber interlock makes its performance have a greater improvement than the ordinary steel fiber cementitious composite.In the previous study,the Slurry Infiltrated Fiber Cementitious Composites is mostly used in ordinary cement slurry,in order to further improve the performance of cementitious composite,the article use the ultra high performance cementitious composite(Ultra-High Performance Cementitious Composites,UHPCC)as matrix material,combined with the forming process of Slurry Infiltrated Fiber Cementitious Composites.This paper studied the influence on mechanical properties of different types,different content and different length of steel fiber on Ultra High Performance-Slurry Infiltrated Fiber Cementitious Composites.And the mechanical properties of the specimens were measured under different curing conditions and different water cement ratio,different cement types.The strengthening and toughening effect of steel fiber was studied by means of bending load deflection curve.This drew the following conclusions:(1)The addition of high volume steel fiber can significantly improve the failure mode of UHPCC.The pure UHPCC has no signs of failure prior to bending and compression,and it has typical brittle failure.The incorporation of high volume ratio of steel fiber made of UHP-SIFCC specimens,the first step is cracking in the loading process,with the increase of the load the specimens can bearing load unceasingly,until the destruction of the specimen can maintain better integrity,and the bending specimen is not broken.The flexural strength and compressive strength are improved compared with the initial crack strength.(2)Fiber rate can significantly affect the compressive strength of UHP-SIFCC,the higher the fiber ratio,the higher the compressive strength.Under the same condition,the end hook fiber to enhance the UHPCC is better than recycled fiber.This is because the recycled fibers has different lengths,the interlocking effect of fibers on the bending of complex shapes can not make up for the lack of anchoring length.As for the end hook fiber,25mm end hook fiber reinforcement effect is better than the 13mm end hook fiber.Therefore,in the future UHP-SIFCC research,it is recommended to use long fiber.(3)The compressive strength of the UHP-SIFCC specimens made of cement with strength grade 52.5 is higher than that of the cement of 42.5.With the increase of the water binder ratio of UHPCC matrix,the compressive strength of UHP-SIFCC specimen decreases.(4)Compared with 7d standard,the curing strength of 28d standard is greatly improved.The lifting effect of strength of 90 degrees water curing 72h to 48h curing is small,the 90 degree hot water curing 2-3d intensity has stabilized.The strength of 28d normal temperature curing is close to the strength of 48h hot water curing,and the strength of 2d hot water curing is higher than the 28d standard curing.(5)The flexural strength of UHP-SIFCC increases with the increase of fiber ratio and fiber length.The flexural strength of the UHP-SIFCC specimen with the end hooked fiber is higher than that of the UHP-SIFCC specimen with the recycled fiber.The growth rate of flexural strength of UHP-SIFCC specimen is obviously higher than that of compressive strength,within the scope of this article.(6)The bending strength error of UHP-SIFCC calculated by composite material theory is within 30%,and the theoretical error of UHP-SIFCC specimen with short fiber is less than that of long fiber.(7)The flexural toughness of UHP-SIFCC was improved with the increase of fiber ratio and fiber length.The difference of bending energy consumption of UHP-SIFCC specimens with different fiber ratio is mainly reflected in the descending segment.The interval amplitude of damage energy with 8%and 6%fiber ratio is higher than the the growth rate of damage energy with 10%and 8%fiber ratio.This is because the high fiber rate makes the fiber spacing sharply reduced,and the fiber spacing has a greater impact on the bond strength between the fiber and the matrix,thereby affecting the flexural toughness of the specimen.(8)The load deflection curve of UHP-SIFCC specimen belongs to the strain hardening curve,and the failure process is divided into three distinct stages,that is,linear elastic stage,plastic rising stage and falling stage.There is no stress mutation during the failure process.In the falling section,the stress decreases slowly with the increase of strain.The specimens have better loading capacity at later stage and show excellent ductility.(9)By comparing several commonly flexural toughness evaluation methods,it is found that the ASTMC1018 toughness index method can not reflect the difference of the falling stage well for the UHP-SIFCC material.The PCER method and the initial and residual bending toughness ratio can well compensate for this defect.In general,the flexural toughness of specimens increases with the increase of fiber content and fiber length.