Document Type : Original Article


Materials Engineering Department, Zagazig University. Zagazig, EGYPT


Mode I1 fracture toughness of hybrid fiber reinforced concrete HFRC has been experimentally
investigated. The effect of crack length to depth ratio, a\w, was studied. The mechanical properties
of different hybrid fiber reinforced concretes were deteimined in an attempt to relate the
parameters of concrete type to its fracture toughness. Three different fiber types (steel "S", glass
"G" and polypropylene "PF"') were used. The volume fraction Vf was kept constant equal to 1.5%
for all FRCs with different configurations. These configurations are steel fiber only with 1.5% Vf
(SFRC), steel fiber with 1% VF in addition to glass fiber with 0.5% Vf (SGFRC), and steel fiber
with 1% Vf in addition to polypropylene fiber with 0.5% Vf(SPPFRC). The crack length to depth
ratio was equal to 0.3, 0.4 and 0.5 for fracture toughness specimens. The cement content was 450
kg/m3 for all mixes. The fracture toughness Kllc was determined according to fornula of Watkins
model by using cracked cubes 150 X 150 X 150 mm. Results of the present workindicated that,
the addition of short fibers slightly increase the compressive strength of FRC. The presence of
fibers significantly increases 'the splitting tensile strength of FRC for different types of fibers. For
Plain concrete Knc was not dependent on the value of dw, i.e. intrinsic property. On the other
hand, The mode I1 fracture toughness (KIrc) for all FRCs mixes, decreases with the increase in the
ratio alw due to the absence of fibers to connect the two surfaces of pre-crack.