Effects of microballoons' size and content in epoxy on compressive strength and modulus

Five slabs containing volume of microballoons ranging from 33.4 to 51.5% and all belonging to a size range of 65-100 mu m were made. In order to study the effect of size range, another slab, but belonging to a broader range of 44-175 mu m, was also cast, where in the microballoons' content was 40.1% by volume. The first set of five slabs showed a decrease in compressive strength from 82.4 to 58 MPa as the microballoons' content increased. A similar trend was observed for modulus values also. The work further showed that the samples from the narrower size range display a higher strength. Microscopic examinations revealed crushing of microballoons for the highest microballoons' case while for the least microballoons bearing sample, deformation marks were visible on the epoxy matrix.