Bajaj FibreTuff–MacroSynthetic StructuralFibre

 

Kush Bajaj

Director
Bajaj Reinforcements LLP

 

Kush Bajaj, Director, Bajaj Reinforcements LLP sits with Civil Engineering and Construction Review for a short interview to introduce Fibre Tuff – their new synthetic fibre.

Civil Engineering and Construction Review:  What Property of concrete does Bajaj Fibre Tuff improves?

Kush Bajaj: With the development of synthetic fibre, synthetic macro-fibre has been used widely in civil engineering. Due to some limitations of steel fibre, macro synthetic fibre could be a better solution for enhanced performance, such as facilitating lightweight concrete structure, high corrosion resistance, better residual (post-cracking) flexural strength, smaller crack width and improved performance in impact, abrasion along with more of a levelled surface than traditional steel fibre reinforced concrete. Synthetic macro fibre, such as Bajaj Fibre Tuff is a new type reinforcement material in concrete.

Fibre reinforced concrete (FRC) can be subjected to harsh conditions, including very high static stresses, high temperatures, dynamic loading and a very corrosive environment. When designing a surface support system, such as a fibre reinforced concrete, it is important to understand how the system behaves and the mechanism of loading to which that FRC support may be subjected.  Concrete requires a rotation capacity in order to follow ground movements while the arching effect in the surrounding rock mass develops. The fibre reinforcement within the concrete overcomes the brittleness of it and provides the necessary ductility after the concrete cracks, to prevent a sudden failure. Due to the load bearing capacity available after cracking, the failure mechanism is transformed from a brittle mode characteristic of unreinforced concrete to a nearly elastoplastic mode. Therefore, energy absorption or residual strength performance criteria (post crack performance) are generally required to specify and rate FRC performance.

CE&CR: What are the field of application for Bajaj Fibre Tuff?

Kush Bajaj: Bajaj Fibre Tuff has a high tensile strength (say 550+MPa) and a relatively high modulus of elasticity (say 13GPa). Unlike polypropylene ´micro´ fibres, they can significantly increase the post-cracking capacity of concrete and are starting to be used in place of steel fibres in a range of applications, including ground-supported slabs (both internal and external), sprayed concrete, small precast concrete units and composite floor slabs on steel decking, Blast wall.

They are particularly suitable for providing nominal reinforcement in aggressive environments such as marine and coastal structures, as they do not suffer the problems of staining and spalling that can result from the corrosion of steel. In addition, because they are non-conducting, they have been used in tram and light railway developments. The properties of the fibres are covered by BS EN 14889, Fibres for concrete, Part 2, Polymer fibres – Definition, specifications and conformity.

CE&CR: How is your product better than steel fibre?

Kush Bajaj: Bajaj Fibre Tuff yields outstanding residual strength and energy absorption capacity, which often outperforms SFRS, especially at larger displacements, due to the lower Young’s Modulus compared to steel fibre. It performs extremely well at both small and large crack widths but their ability to resist corrosion means that MSF can withstand higher deformations and larger crack widths without detrimental loss of performance. This is also achieved by using longer fibres up to 50 mm, which is possible because the length of macro synthetic fibres is not limited by the hose or nozzle diameter.

Steel fibres, due to their inherent stiffness are limited in length, typically to 30-35 mm to avoid line blockage, which in turn leads to a rapid performance loss through pull-out with increasing crack widths. In contrast, high performance macro synthetic fibres show a high post crack performance level even at very large displacements.

Maximum allowable crack widths when using steel bars or steel fibres are small, because cracks act as points of rapid ingress of corrosive media to the reinforcement. Maximum acceptable crack widths are about 0.006 inches (0.15 mm) or just 0.004 inches (0.10 mm). In contrast, crack width control is not critical for durability when using macro synthetic fibres since they are not susceptible to corrosion. Crack width limits might have to be considered though for water-tightness or structural capacity. Recent research has shown that the addition of macro synthetic fibres to steel rebar reinforced concrete reduces crack widths and crack spacing by 30% in bending. Thus, MSF can add a significant gain of design life to steel reinforced concrete structures.

Most mix designs for shotcrete, and sometimes also for precast segments, focus on durability and corrosion protection to provide high resistance against chemical attack over their service life, which in tunnelling is typically between 80 to 120 years. To achieve this goal, the mix design often contains large proportions of pozzolanic binders, which can develop significant post-hardening of the concrete over time. This leads to embrittlement of the fibre concrete matrix, which is responsible for post-crack performance loss when using steel fibres.

The change in behaviour with age is due to a change from a ductile high-energy pull-out mode of post-crack fibre performance into a brittle low-energy rupture mode of the fibre itself, because of rupturing of steel fibres at crack widths, which exceed the elongation capacity of the fibre. The fibres break rather than being pulled out of the concrete matrix. This effect leads to performance degradation by primarily affecting the capability to react to a change of loading conditions while the structure is aging. Typical examples for changed loading conditions in tunnelling are nearby underground or subsurface construction, seismic loading, or changes in hydrological conditions or tidal effects.

Macro synthetic FRC (Bajaj Fibre Tuff) is largely unaffected by this phenomenon since post-hardening or changes in paste hardness make little difference to the behaviour of the fibre within the composite beyond the first few days of hardening. The performance of macro synthetic FRC evident at 28 days is, therefore, unaffected over time.

In addition to above all dosage of steel fibre is approximately 8 time higher in weight than macro synthetic fibre; thus in order to achieve similar performance steel fibre are added 8 time more, which increases the cost. Macro Synthetic fibres are very economical option when it’s come to compare with steel fibre.

CE&CR: Bajaj Fibre Tuff Claims to reduce carbon footprint. What aspect of this product follows through with the said claim?

Kush Bajaj: Carbon emission while manufacturing steel fibre or rebar is high because of higher energy consumption, whereas with synthetic fibre, it’s negligible. Synthetic fibre concrete reinforcements deliver a 70% reduction in carbon footprint compare to steel fibre and steel bar reinforcements. Environment impact assessment shows that by using macro synthetic reinforced fibre concrete and fibre shotcrete one can minimise environmental impact using proven reinforcements technologies.

CE&CR: Considering the other synthetic fibres available in the Indian market, what influenced you to make synthetic fibre – the Fibre Tuff?

Kush Bajaj: Bajaj Reinforcements LLP is the sole manufacture of synthetic fibre in India. Quality and the service are strictly practised in our premises. Synthetic fibre available in the market are either imported or supplied through supplier/agent therefore the quality can’t be certified or assured with every batch of fibre.

We are proud manufacturer of heavy structural synthetic fibre with high tensile strength and young modulus. Compare to imported fibre. Bajaj Fibre tuff are easily available in the market and economical too.

 

 

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