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TECHNICAL PAPER

Figure 7: Specimen and output required for the toughness test prescribed in IS: 17161.

[46]
curves summarized in Figure 8. It was observed that the fatigue creep . Several pre-cracked notched beams were loaded over
data in the S-N diagram shows wide scatter, though with a year or more under controlled conditions (see Figure 10).
an increase in dosage of fibres, the scatter decreases. More Typical results for an M40 concrete with 30 kg/m of hooked-
3
importantly, the fatigue life of concrete at relatively high loading ended steel fibres are shown in Figure 11, with the pre-cracking,
is improved significantly by the incorporation of fibres. Even with creep, recovery and residual stages. The important preliminary
a low dosage of steel fibres, the fatigue performance of concrete conclusions include that the creep deformation is higher
is significantly improved. Using the S-N model developed based when the initial cracks are wider, and for specimens which has
on the critical CMOD in design, the safety of the structure can undergone more crack propagation in the pre cracking stage
be further improved because the crack growth is prevented and can be 3 times the initial deformation for polymer FRC and
from becoming unstable under fatigue. The use of fatigue crack [17]
resistance in FRC pavement design is schematically shown in 1.1-3 times for steel FRC .
[18]
Figure 9, where the design approach of Nayar and Gettu is Overall, the application of fracture mechanics principles has
modified appropriately with the S-N curves. helped understand the failure of fiber reinforced concrete better,

The creep of cracked fiber concrete, or its static fatigue to formulate methods for rational characterization of toughness
[27]
response, is also being studied at IIT Madras , with long-term and to implement the constitutive relations of crack response
testing also done as part of the work of a RILEM Committee into structural design. Several stretches of grade slabs and roads
[45]
(RILEM TC 261-CCF . The creep fracture response is affected within IIT Madras have been designed based on the research
by the crack propagation, debonding and pullout, and the fibre output, and have been in use since 2007.

Figure 8: S-N curves for cracked concrete with different fibre dosages of Figure 9: Scheme for the incorporation of fatigue resistance of cracked
hooked-ended steel fibres, and comparison with data from literature FRC in pavement design

46 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026