Nano-indentation Character Of Interfacial Transition Zone Between Steel Fiber And Cement Paste

Steel fiber reinforced cement based materials is a typical heterogeneous and multi-scale heterogeneity,it can be seen as the three-phase composites consisting of steel fiber,cement base and the interface transition zone.The interface transition zone play a bridge role and connect the steel fiber and cement base material these two completely different properties to form a whole.So far,about the macro mechanical performance of fiber reinforced cement matrix composites have made great progress and the research results are also very rich.But the research on the internal working mechanism is relatively very lack.And because the material of the whole macro mechanics performance(such as strength,ductility,creep,shrinkage and fracture,etc.)are closely related with its interface on the mechanical properties of nanometer scale.So the research on interface transition nano mechanical properties and for better control and improvement of the macroscopic mechanical behavior is significante.Based on the national natural science foundation project(code:51478367),interface transition zone(ITZ)of nano mechanical properties are studied under different water cement ratio.The main work and achievements are as follows:(1)The itz is observed by scanning electron microscope(SEM),to explore the trend of microstructure characteristics changing with different distance from the steel fiber.The results show that when the distance from the fiber surface is 10?m,we did not see the orientational calcium hydroxide crystal and larger pores,the overall microstructure is relatively dense;when the distance is 20?m,we can see large hole and calcium hydroxide crystal,the overall microstructure is relatively loose.(2)The P-h curves of itz were determined via nano indentation test.The distribution of elastic modulus and hardness were calculated and mapped in a 2D plane by the Oliver-Pharr method.The result indicated that,?The interface width are all about 40?m;? with the distance increasing,elastic modulus and hardness values drop first and then rise.what s more,the water/cement ratio is higher,the elastic modulus and hardness is lower;? the lowest modulus and hardness is 20?m from the steel fiber.(3)The frequency distribution was determined by a deconvolution method.The results showed that ?Water cement ratio will affect the distribution of phase.In the itz,we can fitting holes,hydrated calcium silicate gel,high density and low density hydrated calcium silicate gel,calcium hydroxide these distribution of the peaks.But we can not t fit the hole distribution of the peak in matrix;? the water cement ratio affects volume fraction of each phase.In low water cement ratio,the main hydration products is HD C-S-Hgel.In high water cement ratio,the main hydration products is LD C-S-H gel.With the increase of water/cement ratio,the content of porosity and low density C-S-H gradually increased,while high density C-S-H reduced.(4)Comparing itz of steel fiber elasticity modulus(indentation hardness)trend with polypropylene fiber and concrete respectively.Research shows that:?the steel fiber and polypropylene fiber itz thickness and trend are not the same:the elastic modulus in polypropylene fiber increases with the increase of space,while the trend of the steel fiber is appearing to drop first;?the steel fiber and concrete itz trend are not the same:the elastic modulus in lightweight aggregate increases,while the trend of steel fiber appear to drop first;?the irz of steel fiber,polypropylene fiber and aggregate are all belong to the weak links.(5)Prediction of steel fiber reinforced cement base composite elastic modulus as a whole.Firstly,using the coating theoretical analysis to get two-phase elastic modulus value,which containing steel fiber and interfacial transition zone,Secondly,using the homogenization theory to analyze the equivalent modulus of matrix,Thirdly we can obtained the macro elastic modulus of the steel fiber reinforced cement matrix composites and compare with the test results.The results show that the homogenization theory is applicable to calculate the macro elastic modulus of composites,and the influence of the interface transition zone on the whole elastic modulus value can't be ignored.Finally,based on the full text,some further recommendations for further research are put forward.