Dr. T.Ch. Madhavi, Professor & A. Mohan, Research Scholar, Civil Engg, SRM Institute of Science and Technology, Ramapuram, Chennai
What Is Textile Reinforced Concrete?
Textile Reinforced Concrete which was first introduced in the 1990s is emerging as a valuable construction material and is being widely used in construction projects as it can take any form since it is extremely versatile. It is an innovative composite material with a combination of fine grained concrete and multi-axial mesh like textile fabrics as reinforcements. It is a cementitious material where reinforcement consists of high strength non-corrosive textile fabrics. TRC is light, stable, and sustainable. It is a composite material that takes advantage of the non-corrosive nature of fiber materials.
Difference Between RCC, FRC and TRC
Concrete is well known for its very high compressive strength, but the high bending tensile strength which is essentially required for many structural members is provided only by reinforcing steel. If the concrete is not properly mix-designed and consolidated, the steel easily undergoes corrosion once cracks appear in concrete due to tensile forces. This problem is over come in TRC by using a textile fabric instead of using a metal cage inside concrete. Textiles replace conventional steel reinforcement and overcome the weakness of steel to corrode which is a major advantage of TRC over steel reinforced concrete. Thus, the basic difference between textile reinforced concrete and conventional reinforced cement concrete is that, the steel reinforcing bars in conventional concrete are replaced with 2D or 3D textile materials.
Unlike fiber reinforced concrete containing short fibers, textile reinforced concrete provides a higher degree of effectiveness because the fiber bundles are arranged in the direction of the main tensile stresses. Thus, TRC overcomes the shortcomings of both conventional RCC and FRC, wherein the reinforcement bars and short-cut fibers are replaced with textile meshes to improve durability, ductility and design control. Figure 3 shows the stress-strain relations of TRC as compared with other concretes.
It is seen from Fig.3 that the TRC posses a linear plastic behaviour with strain hardening. The carbon textile reinforcement undergoes brittle failure at the ultimate limit strain.
Characteristics & Features of TRC Components
- Textile reinforced concrete can be used to produce different types of thin, cost effective, and lightweight structural and non-structural components.
- TRC can be used to build slender, lightweight, modular, and freeform structures.
- Components made with TRC can be slender/thin, with high tensile strength and malleability. Another important feature of TRC is the permeability of concrete/mortar into the textile. It is important to ensure that there are sufficient openings in the textile for the concrete to flow through it without disturbing the textile shape. The placement of the reinforcement is vital to provide strength to the concrete. TRC is proven to be a suitable solution for the strengthening of existing structures.
- TRC does not corrode like steel and will retain its strength even after the formation of small cracks in concrete. TRC can also provide a protective layer, due to its corrosion free property, for an existing old structural member or can retrofit a member which lost its strength.
- In TRC, reinforcement cover is not needed and also TRC provides good bond force compared to steel bars in normal concrete.
- TRC has been successful in overcoming the problem of corrosion of steel bars in concrete.
- Due to high tenacity of textile fibers the concrete becomes more flexible and durable.
- Can be used for designing slender structural members and filigree elements.
- Has low-shrinkage.
- Has high compressive and tensile strength.
- Has better freeze–thaw resistance characteristics.
- Is eco-friendly.
- Lacks fire resistance
- Sensitive to pressure
- Textile reinforced concrete provides high strength in compression
- Textile reinforcement also increases the tensile strength of the concrete member.
- TRC is a strain-hardening composite.
- Amount of concrete can be reduced in TRC members compared to normal reinforced concrete; because of which, significant load on the structure can be reduced.
- Has enhanced tensile strength due to the thin and long fibers that are woven in a specific direction to act as reinforcement.
- Since steel is excluded in TRC, corrosion can be completely prevented.
- Chemical attacks on reinforcement are negligible compared to normal steel reinforcement.
- Compared to conventional reinforced concrete, TRC has better crack control and TRC members show multiple micro cracks of 50 to 100 nm width.
Textile reinforced concrete is composed of high strength fibers which are in the form of textiles. The TRC material must have higher Young’s Modulus than the concrete surrounding it. Textile fabric must have high tensile strength, and high elongation before breaking.
Types of Textile Fibers
Alkali Resistant Glass (AR Glass): These are derived from organic non-metallic raw materials which are melted at 1250oC to 1350oC to form molten glass. This molten glass is fabricated by wet-spinning process. The advantage of AR Glass is its adhesion to concrete and low cost.
Basalt: Basalt is a natural fiber extracted from volcanic rock. Basalt fibers are manufactured similar to glass fibers. Basalt fibers have good tensile strength and are cost-effective. Basalt has high temperature resistance. The drawback of basalt fiber is when it is exposed to alkali solution, it deteriorates and reduces its strength.
Carbon: Carbon fibre is produced from an organic polymer resin called polyacrylonitrile. Carbon textile fibers give the optimal mechanical behavior. Carbon has good tensile strength and low heating expansion. But it has poor adhesion to concrete and is not cost effective. These problems can be overcome with AR Glass and Basalt fibers.
Polypropylene Fiber: Polypropylene and nylon fibres are good in increasing the impact strength. They possess high tensile strength, but low flexural strength due to low elasticity. Properties of some of the textile fibers commonly used are listed in the Table 1.
Geometry of Fabric
The textile is made of yarn that is made of continuous strand of filaments. The yarn is woven, glued, braided or is left non-woven depending on the strength requirement. With the advancements in textile technology a wide variety of fabrics with different types of fibers making the fabric are available. The textile fabric gives great flexibility in the geometric design. The fabric structure differs by the way the yarns are connected together. Fabrics can be produced by different methods, such as weaving, knitting, breading and non-woven (Figure 4).
Weft Insertion Knitted Fabric: In the weft insertion knitted fabric, the yarns in the warp direction are knitted into stitches to assemble together the straight yarns in the weft.
Short Weft Knitted Fabric: In the short weft knitted fabric, the warp yarns are also knitted into stitches but in this case, they bind together a set of yarns which are laid-in intermittently in both the weft and the warp directions in a zigzag form. In the case of the short weft knit, two different fabric types can be prepared (Peled and Bentur, 2000).
- The (short) weft yarns (the reinforcing yarns) parallel to the applied load, and
- The (short) weft yarns at an angle to the applied load.
The yarn should remain straight, when the fabrics are used in matrices. The load carrying capacity of the fabric is estimated generally by considering the longitudinal yarns, which are in the loading direction. The textile fabric must be oriented in the correct direction so that the stresses in the member are carried safely. The perpendicular yarns are considered as non structural and are meant to hold the longitudinal yarns. Different types of yarns, textile weaves, and shapes can be used to support different types of loading. AS mentioned earlier, the textile mesh used for reinforcement must be open enough to allow concrete to pass through during concreting.
On the other hand, variations of the geometry in a fabric could reduce the strengthening effect resulting in drastically reduced efficiency. The fabric density affects the crimped structure of the warp yarns in the woven fabric, the number of joints, and the penetrability of the cementitious matrix in the fabric.
Some Applications of TRC
- TRC would be a great material for different types of structural engineering and architectural applications such as in buildings, bridges, marine structures, mines, facades systems, etc., where corrosion may be a problem.
- Can be used to create any irregular shape with free-form surfaces and enhance the style and architectural design of modern buildings and shell structures.
- Can be used for load-bearing structure reinforcements, and to strengthen or repair existing buildings.
- Carbon fabric can be used as textile in TRC to heat buildings since carbon fiber is a conductor of heat.
- TRC is effective in making precast elements and lightweight structures.
- Can be used for storage tanks, sandwich walls, and silos.
- A large-scale pavilion roof was constructed at RWTH Aachen University, Germany. The roof was engineered using 4 thin and double curved textile reinforced concrete pieces in the shape of hyperbolic paraboloid [Fig 5(a)].
- In 2015, a pedestrian foot-over and cycle path bridge was constructed with carbon fibers in Albstadt Ebigen [Fig 5(b)].
- In 2015, textile reinforced concrete sandwich facades were used at Mannheim [Fig 5(c)].
- In 2016, a high curtain wall was made of TRC to protect high pylons in Istanbul.
- In 2016, repair works were carried out using TRM for the world heritage site of Aachen Cathedral.
Life Cycle Assessment (LCA) is helpful to determine the impacts of building materials on the environment. The sustainable potential can be defined using two factors: input–output and durability. The first factor consists of processes, inputs, and outputs encountered over the life cycle of a product viz., extraction, production, application, maintenance, demolition, disposal, reuse, and recycling. To start any process, energy and natural resources are the essential inputs, while emissions, waste, and by-products within each process are the resulting outputs. Thus, embodied energy is the total energy used over the life cycle of a product. It is ideal to use building materials having the least possible embodied energy in sustainable design and building construction practices.
Building materials are produced and designed to be serviceable during an expected life cycle. Hence, a longer life cycle is more preferable. Longer durability of building materials is more preferable as it can reduce the extraction and production of new materials, retrofitting or rehabilitation, demolition and reconstruction resulting in reduced energy consumption, emission of pollutants and waste production (Portal et. al., 2015). TRC, with its durability and long life contributes significantly in reducing life cycle costing.
Sustainability Aspects of TRC
Concrete is the second most used material in the world, after water. According to a report of World Business Council for Sustainable Development, global concrete production was estimated to be approximately 25 billion per year. Increasing use of concrete, leads to increase in cement consumption. The global production of cement is responsible for 7-9% of all CO2 emissions, which has a significant effect on global warming and climate change. The uses of steel reinforcement represent a significant proportion of this impact. TRC provides a solution by replacement of steel and also reducing consumption of concrete. Construction industry is in need of a sustainable material and TRC can provide the solution to meet this demand.
Textile Reinforced Concrete is environmentally sustainable material as its design allows for reduction in concrete consumption significantly based on the results of various life cycle assessments. TRC is light in weight, stable and also sustainable. TRC members are generally thinner than conventional reinforced concrete members. While typical steel reinforced concrete panels are 100 to 300 mm thick, TRC panels can be made of 50 mm thickness. TRC components do not require additional thick protective cover since Textile reinforcement material is non-corrosive. TRC produces thin, slender components meaning lesser consumption of building materials. Thin and slender TRC components have lower weight and higher load carrying capacity with high durability even under extreme environmental conditions. Thus, its use lowers CO2 emissions and conserves natural resources in the production of concrete.
TRC can be used for strengthening the old structures and extend their life span instead of demolishing them. Since TRC extends the life span of structures, it cuts down the maintenance and rehabilitation charges. This material can make significant contribution to sustainable construction. Basalt has the least cumulative energy demand, whereas carbon has the least environmental impact. (Portal et al., 2015)
Limited research has been done to fully understand the potential of textile reinforced concrete and its increased usage. Lightweight construction is also being explored slowly to realize the potential of TRC. In spite of its many intrinsic properties and strength, as of now, TRC has been applied to limited extent only and needs to be marketed really well for its adoption by city planners, architects, contractors, engineers, and researchers for its extensive application in the field. TRC may serve as a panacea to a host of problems in building construction. Moreover, standardization is required which would further fuel its adoption rapidly.
Conventional construction materials are not able to meet the requirements of new age construction industry. Textile reinforcement is one such development which can be used in the place of conventional main steel reinforcement. TRC gives better choice and flexibility in the design of structural components. Replacement of conventional steel reinforcement with textile fibers will help in realizing innovative architectural designs which were considered impossible before. Corrosion and acid attack prevention make TRC more durable and contribute to creating more sustainable buildings having good strength.
In conclusion, after a detailed analysis it is observed that TRC is more environmental friendly and cost effective solution. TRC will be the new age material for future generations and is essential to be implemented in construction projects. Statistics indicate that the need for strengthening and repairing of buildings will increase drastically in the near future and application of TRC for this purpose also is very much needed.
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