Behaviour of Ferrocement Encased RC columns under concentric Loading

Abstract

In recent years, composite materials have gained significant attention for upgrading and rehabilitating concrete structures. Among the various strengthening methods, ferrocement jacketing has emerged as an effective solution for improving the performance of reinforced concrete columns. Since columns are the primary load-carrying elements in framed structures, any failure in these members can seriously affect the overall stability of the building and may even result in structural collapse. The present research examines the effectiveness of ferrocement jacketing in enhancing the strength of both square and circular reinforced concrete columns. For square columns, two strengthening strategies were investigated. The first method involved providing reinforcement at all column corners, while the second focused on minimizing stress concentration by converting sharp edges into rounded corners. These approaches were further studied using two different jacketing configurations: (i) ferrocement jackets consisting of three wire mesh layers and (ii) jackets with a single mesh layer supplemented by two additional mesh layers at the corners. For circular columns, the study evaluated the influence of varying confinement levels through the use of different numbers of galvanized iron wire mesh layers. The specimens were wrapped with single-layer, double-layer, and triple-layer ferrocement jackets to assess their effect on compressive strength enhancement. A total of 27 specimens were prepared for the experimental program, including 15 square columns and 12 circular columns. After an initial curing period of seven days, the columns were retrofitted with ferrocement jackets and then cured for an additional 28 days. Once curing was completed, all specimens were subjected to concentric axial compression testing to determine their load-carrying capacities.

Introduction

Reinforced concrete (RCC) is a widely used construction material that provides good structural performance and durability. However, existing RCC structures can deteriorate over time due to aging, increased loads, environmental effects, earthquakes, floods, corrosion, carbonation, poor design, and faulty construction. Since replacing major structural components is expensive and may affect the integrity of connected members, retrofitting and rehabilitation are often preferred solutions.

Retrofitting increases the strength, load-carrying capacity, ductility, and service life of existing structures. It can be performed globally by adding shear walls, infill walls, bracings, wing walls, wall thickening, base isolation, or mass dampers, or locally by jacketing columns, beams, beam-column joints, and strengthening footings. Among these methods, jacketing—particularly ferrocement jacketing—is an economical and effective technique.

Ferrocement is a thin composite material made primarily of cement mortar reinforced with closely spaced layers of wire mesh. It is generally 10–25 mm thick and has a high strength-to-weight ratio, low self-weight, good crack resistance, durability, water resistance, fire resistance, and ductility. It requires relatively little formwork and can be constructed with less skilled labor. These properties make ferrocement useful for strengthening and repairing RCC columns, beams, slabs, walls, roofs, water tanks, and other structures.

The main constituents of ferrocement are steel reinforcing mesh, Portland cement, fine aggregate, clean water, and suitable admixtures. Different types of mesh, such as square, expanded, and hexagonal mesh, can be used. Fine, well-graded sand and a low water-cement ratio are generally preferred, while admixtures such as silica fume, superplasticizers, polymers, and fibers can improve performance.

Ferrocement confinement is particularly useful for RCC column retrofitting. A ferrocement jacket placed around an existing column improves its strength, ductility, energy absorption, durability, and resistance to environmental attack. It also protects the existing reinforcement and reduces water and harmful-material penetration.

Columns are critical structural members because they transfer loads from beams to foundations. Their failure can lead to collapse of the entire structure. Columns may be classified according to shape (square, rectangular, circular, etc.), slenderness ratio (short or long), and design (spiral or tied columns). Short columns generally fail primarily in compression, while long columns are more susceptible to buckling. Their behavior is also influenced by effective length and end restraints.

The research focuses on improving the performance of RCC columns using ferrocement confinement. Previous studies indicate that square columns strengthened with ferrocement jackets may experience significant cracking at sharp corners. Therefore, rounding or strengthening the corners can reduce stress concentration and improve performance.

Main Research Objectives

1. Study the improvement in load-carrying capacity and ductility of square columns strengthened with ferrocement jackets.
2. Investigate the effect of reducing corner stress concentration in square columns through corner modification and ferrocement strengthening.
3. Study the effect of different percentages/layers of wire mesh on the strength and ductility of square columns.
4. Evaluate circular columns confined with one, two, and three layers of wire mesh.
5. Study the first-crack load and failure modes of the strengthened columns.

Conclusion

From the experimental investigation of ferrocement jacketed RC square and circular columns under concentric load, the following concluding remarks could be made: 1) Ferrocement confinement improves the ultimate load carrying capacity of RC column. 2) Ferrocement confinement increases the ultimate axial deflection and lateral deflection of RC column. 3) Strengthening the square column by making the corners rounded is more effective than strengthening the column by keeping their edges sharp. 4) It is better to strengthen the square column with three layers of wire mesh than strengthening them with single layer of wire mesh and two extra layers of wire mesh at each corner. 5) It is concluded that type RFCRC and RFCRCC type ferrocement jacketing technique is better than RFCS and RFCSC respectively. 6) Crack patterns of tested square specimen also confirm that type RFCRC and RFCRCC type is more effective than RFCS and RFCSC respectively. 7) It is good to strengthen the circular column with three layers of wire mesh than that of two layers and one layer. 8) Crack patterns of tested circular column specimen also confirm that CC3 type of ferrocement jacketing technique is more effective than CC1 and CC2.

References

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Copyright

Copyright © 2026 Umesh Kumar. 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.