Influence of Specimen Size for Impact Testing of Fiber Reinforced Cementitious Composite by Charpy Test

To evaluate the behaviour of fiber reinforced cementitious composites under impact loads, different impact tests can be used, such as drop-weight, Charpy test, gas gun and others. The Charpy impact test was initially developed for metallic materials, however, unlike what is observed for metallic materials, there are no standards or technical procedures for cementitious materials or fiber reinforced cementitious composites. Thus, an experimental program was carried out to determine the influence of the specimen size on the energy absorption capacity measured by Charpy impact test. Composites specimens were produced with different dimensions and mixtures. The minimum dimension of the specimen was equal to twice the fibre length. The mixtures were fabricated with cement, fly ash, sand and polyvinyl alcohol (PVA) or polypropylene fibers (PP). The PP fibers used in the composite mixtures were 6 mm and 12 mm length and PVA fiber was 8 mm and 12 mm length. For comparative purposes, a reference plain mortar mixture was also produced. Mechanical behaviour of the specimens was measure by using bending and compression tests and impact behaviour by Charpy impact test. The results indicate that the bending behaviour under static loads, including the ultimate bending strength, deflection capacity and toughness, were improved by increasing the fiber length, in all the PVA and PP composites and by increasing the PP fiber content. The impact energy absorption of fiber reinforced cementitious composite depends on the fibre content and length. The result of impact energy absorption obtained by Charpy test using different specimen sizes cannot be comparable, because the impact resistance depends on the size specimen used in the Charpy test. In the specific case, when the specimen size increases, there is a decline in the energy absorption capacity for PVA fiber composite; conversely, the trend is opposite for mortar or when PP fiber is used.