Solutions From Bajaj Reinforcements For Fibre Reinforced Wet Shotcrete
A shotcrete layer in Tunnel constructions ensures preliminary support and safe working environment for all workers inside tunnel. The role of shotcrete layer is to stabilise the deformations required to mobilise the ground’s inherent strength. Additions of fibres in shotcrete layer provide an excellent way of stabilising deformations by transforming the brittle nature of concrete to a ductile behaviour. Fibres are used in concrete as structural reinforcement, which provides excellent resistance to the post cracking capacity of concrete. For stabilisation of UG and surface excavation, the fibres in FRS layers are able to take part in the transfer of stress and hence act as primary structural reinforcement.
Recommended Use Of Fibre Reinforcement In Shotcrete As Per Rock Classes
FibreTuff – “Macro Synthetic Structural Fibres” are heavy duty synthetic fibres specially engineered for use as replacement of steel fibre in a range of applications, including ground supported slab (both internal and external), sprayed concrete (Shotcrete) and precast concrete units. It is manufactured from polymeric materials, which have diameters greater than or equal to 0.9mm+-0.05mm as per EN14889-2 and have Young’s modulus between 9-12 GPa, Tensile strength of 500-600 MPa. Macro synthetic fibres are often fully embossed to achieve mechanical bonding with the concrete and they come in length of 30-60mm. Cross sectional shapes are typically circular or rectangular or elliptic or continuously deformed. Fibre Tuff is supplied loose in plastic Bags.
Fibre Tuff features a unique continuous embossed surface, enabling the fibre to achieve maximum bond with the cement matrix for optimum performance.
Benefits Of Fibre Tuff In FRS
Bajaj makes Structural Macro synthetic fibres, Fibre Tuff are commonly used is wet shotcrete due to its specific advantage over plain shotcrete with wire mesh reinforcement.
Ductility, toughness, energy absorption capacity.
SNFRS behaves nicely as crack resistant in hardened shotcrete.
SNFRS helps to increase productivity and speed of construction.
SNFRS ensures safety as no workmen needs to work under unsupported overburden for fixing a wire mesh.
SNFRS adheres to all excavated surface upon proper robotic spraying and thus no void is expected, which is common in wire mesh shotcreting as shadow formation
Use of SNFRS can greatly reduce rebound losses compared to conventional wire mesh reinforced shotcreting in tunnel.
Use of SNFRS will ensure lower shotcrete consumption as it follows the excavation profile, which is not possible in wire mesh reinforced shotcreting.
Use of Macro Synthetic Fibre like Fibre Tuff in wet shotcreting for transportation tunnel is preferable as in case fire fibre may melt only and thus concrete may not get cracked or spalled, which is mostly observed when steel fibre reinforced shotcrete is used.
Consumption of Macro synthetic structural fibre in wet shotcrete is less costly than that of steel fibre to attain similar performance due to its less consumption.
Handling & storage of Macro synthetic fibre is easier than steel fibre.
Corrosion is a huge problem when spraying with steel fibre, which reduces the energy absorption capacity. This problem is faced within acouple of years or less, well under the life span of 50 years.
Commercial Advantages For Both Owner & The Constructor
Direct cost benefit through savings of materials due to low rebound loss and low shotcrete consumption during spraying and adhesion on rock surface along the excavation profile.
Cost savings through reduction of reinforcement consumption while changing from Wire mesh to Fibres.
Savings through no use of labour cost when use of SNFRS against wire mesh, which needs labour to fix it.
Indirect cost savings in reduction of cycle time when SNFRS can be directly sprayed on rock surface and its faster, safe operation.
Thickness of SNFRS can be less than that with wire mesh reinforced shotcrete. Thus ensure cost savings.
In case of using Bajaj Fibre Tuff, inventory is controlled greatly as it is locally produced at Nagpur, supplied only required quantity and thus can avoid bulk import at any time.
Factors Related To Mix Design And Use
Fibre length should not exceed 60% of pump line diameter
Good distribution of fibres depends on good dosing method and speed as well as the mixer.
The use of fibres may reduce workability; this can be offset by the use of plasticising admixtures.
Fibre Tuff is now used by many Tunnel Builders in India. Bajaj Reinforcement LLP always proposes Joint field demonstration and testing as per standards when all necessary support will be extended by Technical Team.
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