Manoj Vasudev - Product Engineer – Repairs and Protective Coatings, Fosroc India
Vinay Kumar - Product Engineer – Grouts & Adhesives, Fosroc India
The demand for structural strengthening of ageing structures is growing rapidly in buildings, industrial structures, infrastructure projects like bridges, dams, etc. Structural Strengthening also helps in the conservation of heritage structures. Bridges are an important infrastructure for the country’s transportation requirements. Based on the material used, they can be broadly classified as RCC Bridges, Masonry Bridges, Steel Bridges, Composite Bridges, etc. Typical challenges faced by bridges in their service life are corrosion, increase in loading conditions, natural calamities like earthquakes and floods, accidents, and impact loads, among others. The effect of these can be seen in the formation of cracks, spalling, deflections, etc. in RCC bridges, and joint failures, settlement cracks, crown failure, etc. in masonry bridges.
The Fiber Reinforced Polymer system (FRP) is effective in enhancing the capacity of structures. Benefits include high strength to weight ratio, which means no additional loads to structure, non-corrosive in nature, ease of application, time and labour saving, etc. Limitations include poor fire resistance, needs protection, compatibility issues with masonry structures, non-breathable, and poor bonding with moist substrates, etc.
The Fabric Reinforced Cementitious Matrix system (FRCM) also known as textile reinforced composite (TRC) is a type of structural strengthening system in which High Strength Fiber Grids are embedded in specially designed cementitious mortars to form a composite. The fibres used could be carbon, glass or basalt. The cementitious matrix is specially formulated to have dimensional stability (shrinkage compensation), and the capacity to embed the grids and establish a bond with the substrate.
This system overcomes the limitations of conventional FRP systems with its benefits of breathability, compatibility with substrates (concrete as well as masonry), relatively better thermal protection, adhesion to moist substrates, repair and strengthening using the same system, etc.
FRCM system can be used for (but not limited to) flexural strengthening of girders, deck slabs, etc., shear strengthening of girders or beams, axial load enhancement of piers, and strengthening of arches. It prevents formation of plastic hinges and improves overall capacity. Fosroc has introduced the FRCM system under its brand name Nitowrap CF (CS) - a high strength carbon fiber grid embedded with specially designed cementitious matrix. A lot of research studies have been conducted to understand its application and efficiency.
A research conducted on masonry arches to understand the behaviour aimed to establish the improvement in load capacity of masonry arches by application of Nitowrap CF (CS) on them. Figure 1 shows the application of Nitowrap CF (CS) on the intrados of the arches.
Figure 2 shows the testing of control arch with no FRCM. Figure 3 shows the testing of arch with one layer of Nitowrap CF (CS). The results showed 67% increase in failure load for the arches, thereby demonstrating the efficiency of Nitowrap CF (CS) in enhancing the capacity.
Fosroc is pursuing many more research projects and real time experiments for the systems to generate more reliable data and instil confidence in these systems so that they can be adopted for strengthening major infrastructures across the country.
Conbextra Cable Grout
Pre-stressing technology is being adopted for ease and speed of construction of infrastructure and building projects. Cable duct grouting is an important activity for effective transfer of loads. The present practice of using site batched grouts poses challenges of durability and performance. In site batched grouts there were issues during the application and performance over a period of time. The main issue of site batched grouts is consistency in the mix, bleeding and segregation during pumping, voids formation after the grouting is complete inside the ducts, and loss of prestress due to void formation, which leads to corrosion. Hence, there was a requirement for a solution to address these issues.
Prepacked grouts are more convenient to use than site batched grouts for long-term performance and durability. Cable grout is a specially formulated cement powder mix, designed for grouting of cables in post tensioned concrete. The mix is based on Portland cements and additives, free from sand which imparts high flow characteristics, negligible bleed, and controlled expansion in the plastic state, whilst minimizing water demand.
As a protection to the tendons, it is structurally important for the durability and performance of prestressed bridges and buildings. If grouting is not done as per the specific requirements, the tendons will start corroding due to which there will be loss in the prestress, which will lead to under- performance of the structure and ultimately failure of the structure.
Conbextra Cable grout offers specifications that comply to MORTH and EN447, thereby satisfying all the stipulated parameters such as efflux time, bleeding and strength requirement.
Advantages of Prepacked Cable Grout
- In prepacked, only addition of water is required
- Controlled technical properties
- Well formulated and well-established required parameters for cable grout
- Elimination of batch variations due to human error in site proportioning which can lead to changes in the constituents of grout materials
- Follows strict compliance of the specifications of MORTH and EN447
- Ease of handling and application of the grout
- Maintains consistency and workability of the grout
- Saves time on site trails and increases productivity in construction jobs
- Avoids frequent maintenance of the cable ducts
- Can be formulated into high strength grouts
- Consistency in the results of the technical parameters
- Supports application and handling
- Proven product for critical and smaller gap applications without segregation and bleeding which cause voids
- Elimination of corrosion of the tendons