Study On The Mechanical Properties Of Short Cut Aramid Fiber Reinforced Cement Mortar Composites

In this thesis, short cut aramid fiber was selected as reinforce material and the samples were prepared by two-step fiber dispersion, the mechanical properties also researched under quasi-static and high strain rate . The influence of cement additives, fiber length and volume content were researched to the quasi-static mechanical properties; considered of the interface fiber bonding strength with cement mortar, low temperature plasma was used to modify the surface of aramid fiber, the bending strength was researched with different treatment power and time. Split Hopkinson Pressure Bar was used to research dynamic mechanical properties of short cut aramid fiber reinforced cement mortar under high strain rate, the influence of fiber volume content and strain rate were also preliminary researched.The result of short cut aramid fiber reinforced cement mortar mechanical properties under quasi-static showed that: sodium carboxymethyl cellulose can effectively improve the fiber disperse in the solution, then improve fiber disperse in cement mortar. Silicon powder can fill up the big holes and pores in the cement, increase the samples'compactness, both of the two factors can improve the samples'compress strength. The fiber too short or long both cannot effectively increase the samples'bend strength, the bend strength comparatively best when the fiber length was 5~8mm, increased about 20%. Fiber volume content increased from 0vol% to 5vol%, the samples'bend strength increased from 2.6MPa to 8.3MPa, compress strength also increased from 29.5MPa to 54.3MPa, continue increase the fiber content, the samples'bend strength did not increase, but compress strength decreased. Consider both of the bend and compress strength, fiber volume content selected 5vol% best. In order to improve the aramid fiber interface bond strength with cement mortar, low temperature plasma was used to modify the surface of fiber. Result showed that: low temperature plasma can effectively treatment the fiber surface morphology. When the power was 100W, time was 20min, the fiber bonding strength with cement mortar was increased, and the tensile strength of fiber did not decrease severity. Added the fiber which were treated by low temperature plasma can increase the cement mortar's bend strength, when treatment power was 100W, the samples'bend strength increased from 8.3MPa to 10.5MPa, increased about 26.4%. When treatment time was 20min, the samples'bend strength increased from 8.3MPa to 9.7MPa, continue increase treatment power and time, the samples'bend strength decreased.In this thesisφ14.5mm Split Hopkinson Pressure Bar was used to research the short cut aramid fiber reinforced cement mortar composites'dynamic mechanical properties under high strain rate, the strain rate select 900 to 1800s-1. Result showed that: cement mortar was a strain rate sensitive material, the samples'dynamic mechanical properties and failure strain energy density increased with strain rate, the stress-strain curve trend showed from hardening to softening. Fiber volume content was 3%, the strengthening of fiber reinforced cement mortar increased most, the strengthening effect decreased with the strain rate, the toughening effect increased with fiber volume content and the strain rate. The strain rate has less impact on the ascent stage, but can significantly affect the descent stage. With the strain rate increase, the descent stage decreased gradually slowly, the sample s'failure strain energy density and toughness increased clearly.