1. Introduction
One of the most critical structural components is the column, which is normally built to withstand compressive loads [
1]. It is possible for a frame-structured building to collapse completely if its most dominant structural member, such as a column, fails [
2]. Reinforced square columns are commonly used to support infrastructures such as buildings and bridges because of their low cost and ease of construction. This component’s strength and rigidity may deteriorate over time [
3]. Engineers have used a variety of methods to modify, reinforce, and repair older structures over the past few decades. Reinforcing square concrete columns with square jacketing [
4] is common. Square jacketing saves time and money by not requiring any formwork or modification that is time-consuming and costly [
5]. Only a small portion of the cross section is effective because square jacketing generates confinement pressure only at the corners. Cementitious composites should be developed to improve the square jacketing procedure as a result of this research.
Cementitious composites are one of the most widely used materials in infrastructure development worldwide due to their abundant resources, mature manufacturing process, and high flexibility [
6]. Cementitious composites such as Ferrocement, Fibre reinforced cementitious composites (FRCC) and engineered cementitious composites (ECC) are being widely used in different site conditions as a jacketing material [
7]. The ferrocement jacketing method is a state-of-the-art technique that has been used for many years as an effective, cost-efficient, and widely available material [
8]. It is constructed of mortar and steel wire mesh and is generally cast in extremely thin layers to give it whatever shape is required. This jacketing is simple to apply to an RC column and does not need any sophisticated methods [
9]. Strength, toughness, fracturing, crack control, and fatigue resistance are a few of the many improved technical properties that can be attributed to the uniform distribution of reinforcement [
10]. Kaish et al. utilised a ferrocement jacket to strengthen square RC column specimens under axial compression [
3,
4]. They also tested the jacketed RC column under eccentric loading to evaluate its performance [
3]. The application of ferrocement jacketing systems to strengthen axially loaded unreinforced concrete cylinders was also reported later [
11]. Several types of improved ferrocement jacketing systems to strengthen square RC columns were also proposed [
12]. However, the fabrication of the ferrocement jacket presents numerous challenges. The time-consuming nature of this is one of the most critical concerns. It takes more time to cast and also around 4 weeks to cure in order to create a hard and dry surface, and many activities are disrupted, particularly in the workplace for safety concerns [
13]. In this case, the prefabricated jacketing system could effectively mitigate the issues of using the conventional jacketing method. Kai et al. [
1] investigated the application of prefabricated cementitious composites to construct cylindrical concrete composite column stubs. They utilised the glass fabric mesh to prepare the prefabricated cementitious composite. Prefabricated engineered cementitious composite tubes were also utilised for the seismic strengthening of RC columns [
14]. However, prefabricated ferrocement jackets were not investigated in detail to repair or strengthen axially loaded concrete members.
The prefabricated jacketing system is a part of automation in the construction industry [
14]. In this method, components are prefabricated and prepared in the factory which are later assembled as a jacket for the structural element [
15]. This ensures uniform quality, improved working environment, increment in productivity and work efficiency with reduced costs, replacing humans in dangerous environments, and automation, which reduces waste and factory lead times [
13]. Although Fibre-Reinforced Polymer (FRP)-based prefabricated jackets have been used from as early as the 1990 s in Japan [
16], their lack of good bonding [
17], the possibility of brittle failure modes [
16], their inability to allow the detection of possible damage on the reinforced concrete substrate over time [
18], and lack of design code [
19] puts into question its practical usability. Moreover, the adhesive needs a temperature above 10 °C to start the hardening process [
20]. Therefore, the hardening process delays in cold weather [
21]. On the contrary, utilising cementitious composites like ferrocement in the prefabrication method would produce an inexpensive material less sensitive to high-temperature that needs an expansive agent, in particular, to establish the bond between the interstice of ferrocement and the underlying substrate [
22]. However, due to a lack of proper design, installation techniques, and relative research, this prefabrication technique has yet to be adopted by the construction industry. The proper design of the prefabricated jackets consists of the size, shape, connection method, and the mortar that connects the jacket with the existing column [
23].
Prefabricated ferrocement has been used as early as the 1970s in order to build structures such as water tanks, sunshades, secondary roofing slabs, and shell elements [
24]. Eventually, prefabricated ferrocement was utilised for constructing hydraulic flumes, roofing, and developing low-cost housing [
25,
26]. However, very few researchers experimented with the usage the prefabricated ferrocement as a repairing and strengthening material. Due to the availability and physical characteristics of ferrocement, combined with the ease of handling and workability of prefabrication, prefabricated ferrocement jackets are able to strengthen structural components effectively and efficiently.
Concrete elements built 30–40 years ago are mostly low-strength concrete, especially when brick chips are used as coarse aggregates [
3,
4]. These concrete columns may need strengthening when they deteriorate due to various factors such as corrosion, earthquakes, and floods [
27], structural factors such as overload, as well as other environmental factors [
28]. In this study, prefabricated ferrocement jackets (PFJ) are developed and the performance of a PFJ confined column is compared with non-jacketed concrete specimens. The goal of this research is to understand the behaviour of precast ferrocement jackets when used for repairing and strengthening sub-standard low-strength concrete stub columns. The progression of cost-effective and resilient retrofitting procedures may greatly reduce maintenance needs [
29], enhance life-saving protection, and extend the service life of concrete structures [
30].
Novelty of This Research
Ferrocement has been used for decades as a sustainable and affordable material for repairing, strengthening, and even constructing structural components. However, applying a cast-in-place ferrocement jacket for the repair and strengthening of concrete columns is time-consuming and labour-intensive. Previous research on ferrocement jacketing does not provide an answer to this aspect. The installation of prefabricated jackets to repair/strengthen diminishes the drawbacks of using ferrocement jackets cast in situ. Therefore, in this study, wearable prefabricated ferrocement jackets have been investigated for the structural repair and strengthening of square concrete stubs. The jackets differed based on the shape (‘L’ and ‘U’) in order to repair the damaged specimens and strengthen the undamaged specimens. The results from this study will help to assess the applicability and feasibility of using prefabricated jackets as suitable repairing and/or strengthening techniques.