Preparation And Pressure-sensitive Study Of Carbon Fiber Cement Matrix Composites

As the most widely used construction material,cement-based materials inevitably suffer damage during the service phase due to load effects,fatigue effects,and environmental corrosion.Resistance strain gages,piezoelectric strain sensors and optical sensors as sensors for evaluation and monitoring are applied in construction with some disadvantages such as poor durability and low sensitivity.Therefore,cementitious composites with self-sensing properties are gaining more and more attention.By adding conductive fillers to cementitious materials to make cement composites have the ability to sense stress,strain,and damage under external loads.At present,carbon fiber,carbon black,steel fiber,and graphene have been widely used as conductive fillers.Carbon fiber has high strength,high modulus,low specific gravity,alkali corrosion resistance,and good electrical and thermal conductivity making it a widely used reinforcing material,while carbon black has the advantages of low cost,good electrical conductivity,and large specific surface area.Cementitious composites with carbon fiber and carbon black as conductive fillers have good self-sensing effect and can effectively monitor the health of the structure.In this study,carbon fiber cement composites,carbon fiber powder/carbon black cement composites,and oriented carbon fiber cement composites were prepared by combining carbon fiber powder,compounding carbon fiber powder/carbon black,and orienting carbon fiber.The prepared cement composites were also tested for flexural and compressive strength,X-ray diffraction analysis,infrared spectroscopy analysis,scanning electron microscopy test,and resistivity test.The incorporation of carbon fiber powder can improve the mechanical properties of cement composites.The enhancement effect of carbon fiber powder on the compressive strength of cement composites increased first and then decreased,showing a normal distribution.The compressive strength increased by 27.9% at 1.4 wt% of carbon fiber powder.The enhancement effect on flexural strength also increased and then decreased with the increase of carbon fiber powder,and the flexural strength was increased by 80.6%at 1.4 wt% of carbon fiber powder.After 28 days of maintenance,the resistivity of carbon fiber powder cement composites decreases with the increase of carbon fiber powder admixture;during the cyclic ballasting process,the change of resistance of cement composites with carbon fiber powder admixture of 1.2 wt% at the peak stress is 30%;the water content has a great influence on the resistivity of cement composites,and the saturation water content is around 6%.By XRD and IR spectroscopy,the incorporation of carbon fiber powder does not react with the cement components,no new chemical bonds are generated,and the mechanical property enhancement of the cement matrix is purely physical.The carbon fiber powder/carbon black cement composites were prepared by fixing the admixture of carbon fiber powder at 1.2 wt% and changing the admixture of carbon black.The admixture of carbon fiber and carbon black will improve the mechanical properties of the cement composites.At 0.6 wt% of carbon black admixture,the mechanical properties of the cement composites were improved the most with 18.1%increase in compressive strength and 94.6% increase in flexural strength.Under cyclic ballast,the maximum change in resistance at the stress peak was about 35% for 1.2 wt%carbon fiber powder/0.6 wt% carbon black cement composites,and the change in resistance at the stress peak was about 30% for 1.2 wt% carbon fiber powder cement composites with the doping amount of 1.2 wt% carbon fiber powder,and the piezosensitivity was slightly increased than that of carbon fiber powder cement composites during cyclic loading of carbon fiber/carbon black cement.An extrusion tool with a diameter of 5 mm was used to orient the carbon fibers in the cement mixture slurry,and the differences between the resistivity,mechanical properties,and pressure sensitivity of the oriented carbon fiber and ordinary carbon fiber cement composites were investigated.As observed by scanning electron microscopy,the carbon fibers were arranged in the same direction in the cement matrix after orientation;the flexural strength of ordinary carbon fiber cement composites was lower than that of oriented carbon fiber cement composites,and the compressive strength was higher than that of oriented carbon fiber cement composites;the resistivity of the cement composites with two different carbon fiber distributions decreased continuously with the increase of carbon fiber admixture;compared with ordinary carbon fiber cement composites,the Oriented carbon fiber cement composites have better pressure sensitivity with the same carbon fiber doping amount.