Dr Mohit Raina, Senior Expert-Textile Reinforced Concrete, ITA, RWTH Aachen, Raina Industries Pvt Ltd, tells us why the use of textile reinforced concrete in construction is an idea whose time has come.
While textile reinforced concrete (TRC) is new to India, it has great potential in the construction of a multitude of structures, from outer facades and partition walls in buildings to jaalis and water tanks. Dr Mohit Raina, Senior Expert-Textile Reinforced Concrete, ITA, RWTH Aachen, Raina Industries Pvt Ltd, who began his textile research in 2000 at VJTI in Mumbai and now specialises in the field of TRC, shares some vital facts about the material in conversation with SHRIYAL SETHUMADHAVAN.
The Indian construction industry employs 32 million and its market size is estimated at Rs 248,000 crore. While it contributes to 11 per cent of GDP, much of its growth is fuelled by the rise of the middle class and the need to develop substantial infrastructure. Currently, extensive amounts of steel-reinforced concrete are being used for building across India. A major challenge faced by steel-reinforced concrete is corrosion resistance in peninsular India. The temperature in coastal regions often exceeds 30°C with high levels of humidity; annual rainfall averages between 1,000 and 3,000 mm. Such extreme climatic conditions cause deterioration of reinforced structures, resulting in restoration and rehabilitation expenses. In such a scenario, TRC is the most viable solution.
Composition and properties
TRC is an innovative composite material that uses high-strength fine-grained concrete and mesh-like textile reinforcements, mainly consisting of AR glass or carbon fibres. Unlike steel, textiles are not susceptible to corrosion, thus it is possible to minimise concrete cover to only a few millimetres. A normal steel reinforced concrete requires a minimum cover of 20 mm from all directions for the steel reinforcement. As a result, slender concrete constructions can be built, meeting the needs of modern architecture with both economic and environmental advantages. Since 1999, the Collaborative Research Centre 532 (called SFB 532) at RWTH Aachen University has been investigating the basic principles of TRC. After 12 years of research, the material was unveiled for use. PPP projects have been undertaken and pilot buildings set up for applications ranging from pedestrian bridges to sandwich and ventilated facades. The material has proven itself and has received the necessary permissions as well. (For material development, please see figure on Development of TRC). Based on successfully employed and awarded pilot projects, the material and the production technology possess a Technology Readiness Level (TRL) of 7.
TRC has the following advantages:
The application of TRC allows economic savings in terms of material, transport and anchorage costs and thus has been used for thin-walled and lightweight ventilated façade systems in recent years. At present, small panel sizes of 0.5-3.0 m2 are state-of-the-art in the application of TRC in Germany. Panel sizes of up to 7 m2 can also be realised in combination with bracing stud-frame systems.
TRC comprises 'textile' reinforcement, which does not corrode and highly increases the life of the buildings and projects where this material is incorporated. Further, the flexible textile reinforcement renders an enormous amount of design freedom. While the material can be repaired and replaced, textile reinforcement is also used in retrofitting and building renovation projects.
For the production of TRC, various types of textiles and fibre materials are used. The textile reinforcement structures have to be especially designed to take resulting strains in the building member. Hence, the textiles must be positioned correctly during the manufacturing of the concrete building members. Choosing the correct textile structure is essential. The textiles are produced using a warp knitting process with inserted reinforcement fibres. The advantage of warp-knit fabrics is the biaxially stretched position of the filaments. The fibres in warp-and-weft direction lay on each other - non-crimpedand - are bonded with a knitting thread. Non-crimped fibres provide best results for reinforcement. The warp knitting process allows variations in material and local additional reinforcement depending on variation in machine setups. Textile reinforcement can be used in a coated or uncoated state. Coating allows for higher load-bearing capacity and increased durability, especially for glass-fibre material. Common coatings consist of epoxy based resins.
The matrices used for TRC generally meet special demands regarding production techniques, mechanical properties and durability of the reinforcement material. In most cases, a small maximum grain size (< 5 mm) is used. An essential aspect for TRC matrices is the full penetration of the technical textiles to guarantee good bonding as well as loading behaviour. Hence, the consistency of the matrix has to be adjusted for the properties of the textile, geometry of the specimen and production technique. Production techniques are casting (highly flowable consistencies are required), lamination, spraying or pultrusion (rather plastic consistencies are required).
The textile component, as reinforcement, provides the necessary high tensile strength in a concrete matrix. This leads to appropriate load-carrying capacity for applications in the building sector. The reinforcement can be realised with short fibre or long fibre textile structures. The initial reinforced concrete comprised short fibre, generally glass fibres, which were introduced into the concrete matrix. These short fibre reinforcements provide localised reinforcement.
But owing to their random placement, they reduce crack propagation in concrete and are not suitable as elements carrying loads. Research has been carried out to use long fibre or filaments as structural reinforcement. However, issues such as filament breaks and filament dispersion during handling of such filaments in a concrete matrix are known.
Textile structures provide a suitable solution to the reinforcement within concrete matrices. These textile structures are engineered to provide high tensile requirements and act as a replacement for steel reinforcement. The textiles used involve materials such as alkali-resistant glass, carbon and Aramid. The fibres are required to have features such as small relaxation under permanent load, appropriate and constant adhesion between reinforcement and concrete, low cost of production and the possibility of processing easily on textile machinery. The fibres mentioned can be used in filament or twisted filament form. These filaments are a better choice because they possess only a small structural elongation. Features that play a vital role are the applied size on the filaments, the thickness of the filaments and the number of filaments.
Concrete mixing and pouring techniques in India are highly dependent upon the type of building construction and geographical location. However, there is still scope for innovation in terms of different concreting techniques such as pouring, centrifugal manufacturing, lamination and spray concrete for normal building components such as facades. Use of multiple construction techniques can provide the much-needed product differentiation within the construction components market. TRC research will give impetus to different concreting techniques, thus furthering the development of state-of-the-art concreting practices.
Barriers to TRC in India
There has been reluctance in India to integrate new products like TRC, which are now established in the West. Health and safety are still major issues on construction sites as the industry is unorganised with dependence on cheap, illiterate labour and low automation. There has been a substantial rise in pre-casting applications in the last decade, but this forms only a small percentage of the total construction market.
Two aspects govern the cost of manufacturing TRC in India. On one side, material costs play a vital role. The materials need to be imported with an import duty of about 30 per cent. Second, labour costs are a determining factor. TRC products currently manufactured in Germany are affected by the very high labour costs in the country, which are 97 per cent more than that in India. However, the lack of good vocationally trained labour in India deters the growth of TRC solutions. Clearly then, automation in manufacturing is also a solution for the manufacture of TRC in India.
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