Dispersion of carbon fiber in cement matrix is one of main challenges for fabricating carbon fiber reinforced cement based materials. In this study, the dispersion of carbon fiber was improved by pre-dispersion of carbon fiber in basic aqueous solution using different concentrations of CMC. The relationships of CMC concentration and pH solution toward carbon fiber dispersion in aqueous solution was evaluated by UVvis spectroscopy. In order to understand how carbon fiber is dispersed in cement matrix, morphology fiber carbon reinforced composite was examined. Experimental results show that aqueous solution of CMC is effective to disperse carbon fiber. In addition, dispersion of carbon fiber increases with increasing of pH of CMC solution.
Carbon Fiber Cementitious Composites (CFCC) is one of the most important materials in smart concrete applications. CFCC should be able to have the piezoresistivity properties where its resistivity changes when there is applied a stress/strain. It must also have the compressive strength qualification. One of the important additives in carbon fiber cementitious composites is dispersant. Dispersion of carbon fiber is one of the key problems in fabricating piezoresistive carbon fiber cementitious composites. In this research, the uses of dispersants are methylcellulose, mixture of defoamer and methylcellulose and superplasticizer based polycarboxylate. The preparation of composite samples is similar as in the mortar technique according to the ASTM C 109/109M standard. The additives material are PAN type carbon fibers, methylcellulose, defoamer and superplasticizer (as water reducer and dispersant). The experimental testing conducts the compressive strength and resistivity at various curing time, i.e. 3, 7 and 28 days. The results obtained that the highest compressive strength value in is for the mortar using superplasticizer based polycarboxylate dispersant. This also shown that the distribution of carbon fiber with superplasticizer is more effective, since not reacting with the cementitious material which was different from the methylcellulose that creates the cement hydration reaction. The research also found that the CFCC require the proper water cement ratio otherwise the compressive strength becomes lower.
Smart concrete is an innovative material because it can serve as a sensor without any additional sensors in it. It is reinforced with carbon fiber that has gone through the pyrolysis process at high temperature to produce carbon content above 90%. The carbon fiber used in this study was Polyacrylonitrile. The working principle of carbon fiber sensor works piezoresistivity that respond to changes in mechanical (stress and strain) to electrical impulses. The resistivity changes that will be converted into units of load on the display circuit system. Key to success of this research was the concrete formulations and systems were sensitive and accurate readings so that any small change in resistivity could be directly detected. Variations in carbon fiber were added to the 0-1% by weight of cement with interval 0.5. Fly ash was added as a filler to reduce the use of cement. Results obtained from dynamic cyclic testing showed that the compressive strength was the best in the concrete without carbon fiber, then decline in line with the increased number of carbon fiber. But inversely proportional to the resistivity of the concrete produced. Smart concrete must have a high sensitivity to changes in stress / strain, it should also meet the required concrete strength both press and flexible to avoid initial crack.
The purpose of this study was to determine the effect of 5% NaOH alkalization and soaking time for 1 hour, 2 hours and 3 hours on mechanical properties by tensile and impact testing and scanning electron microscope (SEM) on composites with sugarcane bagasse fiber reinforcement and epoxy matrix which have the potential as future wind turbine blades material. The method used in the manufacture of composites was a hand lay-up method with a volume fraction ratio of 60% epoxy matrix and 40% waste sugarcane bagasse fiber. The optimum results of this composite study showed the impact strength value on the composite with 5% NaOH soaking for 2 hours was 0.120 Jmm-2, the tensile strength value was on the composite with 5% NaOH soaking for 2 hours at 10.80 MPa. SEM analysis results on the tensile test fracture pattern showed that composites have failed in the form of fiber pull out and debonding which can reduce mechanical properties, especially in strength. In this study, it was concluded that the alkalization process of 5% NaOH for 2 hours had a significant influence on improving the mechanical properties of sugarcane-epoxy fiber composites.
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