Fabric Reinforced Cementitious Matrix: Structural Strengthening Systems

structural strengthening in aging infrastructures
The need for structural strengthening in aging infrastructures is rapidly escalating across various sectors, encompassing buildings, industrial structures, bridges, dams, ports, and other important structures. This demand extends to the conservation of heritage structures, preserving national values and culture. These sectors face unique challenges stemming from factors like environmental exposure, and evolving safety regulations. Addressing these challenges is essential to ensure the continued functionality, safety, and longevity of vital structures that support economic activities and daily life. Innovative solutions like Fabric Reinforced Cementitious Matrix (FRCM) systems have emerged as effective systems for structural strengthening.
Er. Manoj Vasudev, Business Development Manager – Repairs & Protective Coatings, Fosroc India, Bengaluru And Dr. Manjunatha L, Assistant Professor, Department of Civil Engineering, Nitte Meenakshi Institute of Technology, Bengaluru

Bridges, which are crucial components of transportation infrastructure, contribute significantly to a country’s economic progress. Different bridge types, including RCC Bridges, Masonry Bridges, Steel Bridges, and Composite Bridges, face challenges such as corrosion, increased loading conditions, natural calamities, and accidents during their service life.

In the realm of buildings, both commercial and residential structures require attention to address aging-related issues and ensure the safety and comfort of occupants. Historical and heritage buildings, in particular, hold cultural and architectural significance and require preservation to maintain our national identity and heritage. Structural strengthening solutions can help mitigate common issues in buildings, such as foundation settlement, wall cracks, and structural instability, by enhancing their resilience and longevity.

Ports serve as crucial nodes in global trade networks, facilitating the movement of goods and commodities between countries. However, the harsh marine environment, constant loading and unloading activities, and exposure to saltwater can lead to corrosion and deterioration of port structures, including wharves, docks, and storage facilities. Structural strengthening solutions are necessary to maintain the integrity of port infrastructure and prevent disruptions in maritime trade.

Industrial facilities, including manufacturing plants, refineries, and warehouses, are essential for supporting industrial operations and production processes. These facilities often house heavy machinery, equipment, and storage systems, placing significant demands on their structural integrity. Aging industrial structures may experience issues such as foundation settlement, structural fatigue, and corrosion, which can compromise safety and operational efficiency. Strengthening these structures is crucial to ensure worker safety and prevent costly downtime.

Strengthening Approach

There are many methods of structural strengthening, namely, encasement, steel plate bonding, external bonded reinforcement (EBR), additional supports, external pre-stressing, etc, with each method offering advantages and limitations.

Traditional approaches to structural strengthening in EBR have typically involved the use of Fiber Reinforced Polymer (FRP) systems, which offer advantages such as high strength-to-weight ratio, corrosion resistance, and ease of installation. However, FRP systems have limitations, including poor fire resistance and compatibility issues with certain substrates. In response to these challenges, innovative solutions like Fabric Reinforced Cementitious Matrix (FRCM) systems have emerged as effective alternatives.

FRCM system under the brand name ‘Nitowrap CF (CS)

FRCM systems involve embedding High Strength Fiber Grids in specially formulated cementitious mortars, creating a composite structure that enhances the mechanical properties of the substrate. These systems offer benefits such as compatibility with various substrates, including concrete, masonry, and steel, making them suitable for a wide range of applications in ports, industrial facilities, and buildings. Additionally, FRCM systems provide improved fire resistance, thermal protection, and adhesion to moist substrates compared to traditional FRP systems.

FOSROC, a leading player in the construction industry, has introduced an FRCM system under the brand name ‘Nitowrap CF (CS).’ This system utilizes a high-strength carbon fiber grid embedded in a specially designed cementitious matrix. Rigorous research studies have been conducted to understand the application and efficiency of this FRCM system. One notable study is focused on concrete compression members, demonstrating the system’s efficacy in enhancing the axial load capacity of these members.

Laboratory Study

introduced an FRCM system under the brand name ‘Nitowrap CF (CS)
In this study, a comprehensive experimental program was conducted in the Structural Engineering Laboratory of the Department of Civil Engineering, Nitte Meenakshi Institute of Technology, wherein RC columns of 900 mm length with square and rectangular cross sections of 150mm x 100mm and 100mm x 100mm, respectively, were cast. Concrete of compressive strength 35 MPa after 28 days curing was used to cast the specimens.

Longitudinal reinforcement of 2% is provided using 8mm HYSD bars and 8mm diameter lateral ties spaced at 100 mm are provided. Keeping some specimens as unstrengthened columns as control specimens, other columns were strengthened using FRCM composite wraps to modify their original square cross section to circular cross section and rectangular cross-sectional shape into elliptical cross sections (Fig1) for effective confinement. The carbon fiber grid used in CFRCM is Nitowrap CF (CS) bi-directional carbon fiber grid with mesh size of 15mm c/c.

The testing is carried out in a sophisticated 2000 kN capacity loading frame with automatic data acquisition system. All the specimens were tested up to failure considering the axial monotonic loading with load eccentricity of 0 mm, 12.5mm, 25mm and 50 mm. Two LVDTs were used to obtain the deformation on tension side and compression side face of the column. The set-up is prepared to simulate the hinged condition at both ends of the column as shown in Fig 2.

introduced an FRCM system under the brand name ‘Nitowrap CF (CS)Figure 2: Testing CFRCM strengthened specimens
The behaviour of each column is meticulously observed, focusing on maximum load-carrying capacity, the effect of eccentricity of loading, load deformation behaviour, failure modes, and confinement efficiency of the strengthened columns. Ultimate load carrying capability, corresponding deformation of specimens strengthened with CFRCM are compared with unstrengthened columns.

The findings from this investigation proved that rectangular specimens modified to elliptical shape using CFRCM show increase in load-carrying capacity of around 43% compared to unstrengthened rectangular columns, whereas square columns modified to circular columns show an improvement of 115% compared to unstrengthened square columns. From this it is proved that circular shape is more effective in confining the concrete using CFRCM. All the CFRCM strengthened columns exhibited ductile failure compared to unconfined columns.

This study serves as a testament to the versatility of FRCM systems, showcasing their potential applications in various scenarios. The ability to strengthen girders, deck slabs, beams, piers, and arches, preventing the formation of plastic hinges, highlights the comprehensive nature of this innovative structural strengthening solution. As research and development in FRCM systems continue, their role in extending the lifespan and enhancing the resilience of aging structures becomes increasingly evident.

Acknowledgement:

We would like to express our sincere gratitude to Mr. Vijay Kulkarni, MTech-Structures, Segment Head – Grouts & Anchors, Adhesives, Repairs & Protective Coatings, Fosroc India, and to Vandana H V and Meghana A, PG Students, Department of Civil Engineering, Nitte Meenakshi Institute of Technology for their invaluable contribution to this article with their insights, feedback, and guidance.
ICCT, January- February 2024
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