An Experimental Study on Splicing with Helical End Rebar

Abstract

The bond behaviour between reinforcement and concrete is critical for strength, ductility, and serviceability of reinforced and precast structures. Conventional anchorage systems often face limitations such as long development lengths, premature slip, and radial cracking, compromising joint reliability in precast construction. The system combines chemical adhesion, frictional resistance, and mechanical interlock, while the aluminium sleeve with polymer-modified grout enhances confinement, reduces splitting cracks, and improves durability. This study investigates a novel anchorage system using helically ended rebars embedded in grout-filled aluminium sleeves and confined within M40 concrete cylinders. Pull-out tests were conducted on 10 mm of grade Fe415,12mm of grade Fe500, helical and straight rebars with embedment length of 130 mm,190mm using NS-1Powergrout is a non-shrink grout to ensure dense packing and efficient stress transfer by using a dowel element. The experimental results, including load–slip curves and peak bond strengths, were validated through load displacement curves. The findings confirm that the proposed helical bar–sleeve system ensures enhanced bond efficiency, reduced embedment requirements, improved ductility, and greater reliability for precast and space constrained reinforced concrete applications.

Introduction

The bond between reinforcement bars and concrete is crucial for the performance of reinforced concrete (RC) structures. It allows stress transfer, strain compatibility, crack control, and prevents bar slip under service loads, ensuring effective structural behavior. Bond develops through chemical adhesion, friction, and mechanical interlock of deformed bar ribs. Bond strength affects anchorage, splicing, and overall structural ductility and serviceability, particularly important in precast construction where joint performance is critical.

Traditional anchorage methods face challenges like insufficient embedment length, premature slip, cracking, and durability issues, especially in precast elements with limited space and complex stresses. To address these, this study investigates a novel anchorage system using helically ended rebars embedded in grout-filled aluminium sleeves within concrete. The helical ends improve mechanical interlock, while the grout and sleeve provide confinement, uniform stress distribution, and crack resistance, enabling shorter development lengths and better bond efficiency.

Materials Used

• Grout: Non-shrink, polymer-modified grout (NS-1 Power Grout) used to fill the sleeve, ensuring dense packing, strength, and durability.

• Aggregates: Clean natural river sand (fine aggregate) and crushed granite (coarse aggregate), conforming to IS standards.

• Cement: Ordinary Portland Cement (OPC) 53 grade, used for M40 grade concrete.

• Reinforcement: High-yield deformed steel bars of 10mm (Fe-415) and 12mm (Fe-500) diameter, with straight and helically wound ends to enhance anchorage.

• Sleeves: Aluminium sleeves (40mm and 60mm diameter) create annular space around rebars for grout placement and confinement.

Methodology

• Concrete Mix Design: M40 grade concrete with a mix ratio of 1:1.325:2.53 (cement:fine aggregate:coarse aggregate), water-cement ratio 0.4, achieving ~49.8 N/mm² compressive strength after 28 days.

• Development Length: Calculated as 130mm for 10mm bars and 190mm for 12mm bars, based on grout bond strength and steel grade.

• Laboratory Tests: Cylindrical concrete specimens with centrally embedded aluminium sleeves and grout-filled helically ended rebars were cast, cured for 28 days, and subjected to pull-out tests to evaluate bond strength and anchorage performance.

This innovative system aims to improve bond reliability, reduce slip, and enable shorter anchorage

Conclusion

From the experiments results the conclusions drawn are listed below: 1) Helical end rebars improved peak load capacity by 15-20% for overlapped specimens (S2 vs S1, S6 vs S5) and by 75-100% for dowel specimens (S4 vs S3, S8 vs S7). 2) Dowel connections with helical end (S4) achieved almost equal strength to overlapping helical rebars, showing their effectiveness. 3) Overall, the use of helical ends enhances bond strength, load transfer and structural safety making them preferable in anchorage and dowel applications.

References

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Copyright

Copyright © 2025 Ganesh B, Srilakshmi P, C B K Rao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.