The Study of Mechanical Properties and Chemical Groups of Composite Concrete

The use of hemp fiber is capable of increasing the compressive and tensile strength, along with enhanced ductility in concrete. Shell ash also contains calcium compounds that improve the properties of concrete. Therefore, this study aimed to measure the compressive and tensile strengths of concrete as well as the chemical functional groups of hemp fiber. To achieve this, hemp fiber (additive) and 6% shell ash (filler) were added to the concrete mixture, targeting a design strength of 25MPa. The results showed that the average compressive strength of concrete after 28 days obtained a minimum value of 25.668MPa with 0.5% fiber and the maximum strength was 33.446MPa with 1.5% fiber. The split tensile strength test of the concrete after 28 days obtained a minimum value of 1.982MPa, and a maximum of 2.831MPa. These results showed that adding hemp fiber at approximately 1.5% to concrete improved the compressive strength by 4.74% and the split tensile strength by 3.47% compared to conventional concrete. Furthermore, the FTIR test showed that the shape of the wavelength spectrum diagram and the area of chemical bond peaks were the same among hemp, plastic, and other natural fibers.