Effect of specimen and aggregate sizes upon the fracture characteristics of concrete

Abstract

The paper describes an experimental study of the effect of test specimen size and coarse aggregate size on the fracture toughness and toughness index of plain and fibre reinforced concrete. The tests were carried out by means of notched and un-notched beams subjected to four-point bending and by means of the compact compression test specimen. Three coarse aggregate sizes, 5, 10,and 20 mm, were used in the study for both polypropylene and steel fibre reinforced concrete. The fracture toughness results obtained from the beam specimens were independent of the size of the coarse aggregate — this result is contrary to recently published research results. In the case of the compact compression test specimen results the maximum fracture toughness values were obtained for the 10mm aggregate mix and the minimum for the 20 mm aggregate mix — again these results are in conflict with other published results. The fracture toughness values increased with an increase in the size of the test specimen used. Although this result confirms earlier research it is contrary to that predicted by Fracture Mechanics theory. The toughness index of steel fibre reinforced concrete is approximately double that for polypropylene fibre reinforced concrete for the same volume of fibre. Both fracture toughness and toughness index results should be given to describe the fracture characteristics of fibre cement composites.