· Polypropylene fibres improve the plastic shrinkage cracking of concrete.
· Initial cracking flexural strength increases with the addition of polypropylene fibres @ 0.7 kg/m³ but the strength remains constant till 1.5 kg/m³. After that strength may decrease.
· Cocktail fibres @ 60 kg/m³ of steel fibres + 1.5 kg/m³ of PP give the highest initial cracking flexural strength.
· Fibres reinforced concrete gives the highest final cracking flexural strength i.e. an improvement in post cracking behaviour of concrete.
· Maximum compressive strength is achieved when only steel fibres are used. Compressive strength decreases with increase in polypropylene fibres
Toutanji et al. (1997), studied the effect of curing environments and that of testing direction relative to casting direction on the mechanical properties of fibres-reinforced concrete. From this investigation it was concluded that:
· In comparison to moist curing, steam curing did not seem to increase first-crack or ultimate flexural strength of steel fibres concrete. However, steam curing was found to increase the compressive strength and to reduce compressive and flexural toughness indices. Air curing, on the other hand, was noted to reduce first-crack and ultimate flexural strength significantly and to reduce flexural toughness slightly. This seemed to indicate that steam curing causes bonds between steel fibres and concrete to become brittle, and air curing is less effective in enhancing flexural behaviour.
· Steel fibres concrete specimens with relatively high flowability (workability), tested in the direction perpendicular to casting direction, exhibited reductions in flexural first-crack strength, flexural ultimate strength, and flexural toughness of 14%, 22%, and 30%, respectively, as compared to specimens tested in the direction parallel to casting direction.
· Steel fibres concrete specimens with relatively moderate and low flowability, tested in the direction perpendicular to casting direction, exhibited insignificant reductions in flexural first-crack and ultimate strength (for certain cases less than 10%), compared to those tested in the direction parallel to casting direction. However, significant reductions of 20% and 14% in flexural toughness were noted for mixtures with moderate and low flowability, respectively.
Parveen et al. (2013), investigated the effect of variation of polypropylene fibres ranging from 0.1% to 0.4% along with 0.8% steel fibres on the behaviour of fibrous concrete. The mechanical properties of the concrete such as compressive and tensile strength had been investigated. The experimental results shown that: