This study was undertaken to analyze the flexural and splitting tensile strengths and the ductility of abaca fiber-reinforced concrete composites. Abaca fibers are natural fibers of vegetable origin prepared from the abaca plant which is a native plant of the Philippine Islands. The purpose of the study was to investigate how various volume-fractions of the abaca fiber in the concrete mix could affect the mechanical properties of the concrete matrix.
A concrete design mix containing a volume ratio of 1.0 part Type I Portland...cernent and 3.0 parts sand was utilized in the preparation of laboratory test samples. Abaca fibers were cut to 1 to 1.5 inches long and randomly mixed with the concrete at 0 .2% and 0.4% volumefractions. The fibers were not chemically treated and no admixtures were used. The test samples were cast into concrete cylinders and flexural beams. Standard ASTM procedures in casting of flexural beams and concrete cylinders and the curing of 28-day concrete samples were followed. The center-point loading method of the flexural test and the splitting tensile test were utilized. The scanning electron microscopy technique was used to examine and analyze some failed concrete samples.
The study revealed that the addition of abaca fibers decreased the mean flexural and splitting tensile strengths of the concrete matrices. However, increases in ductility of the matrices were attained as a result of the addition of abaca fibers at 0.2% and 0.4% volumefractions.
The Scanning Electron Microscope (SEM) micrographs revealed that increasing the fiber volume-fraction influenced the growth rate of dehydration precipitates in the form of CH (calcium hydroxide) crystals. At the 0.2% volume-fraction, smaller density of precipitates grew into large crystals, while at the 0.4% volume-fraction, the dehydration precipitates were much more dense which were made up of small sized crystals.
It was concluded that the addition of abaca fibers to the concrete mix decreased the mean flexural and splitting tensile strengths of the concrete matrix. The modulus of elasticity was increased and consequently improved the ductility of the concrete matrix. The abaca fibers in the concrete mix acted as a medium to slow down and stop the propagation of cracks by deflecting and absorbing some of the crack energies. This contributed to the strength of some localized ductility in the concrete matrix.