Building Material Overview
With the advent of modern civilization and development of scientific knowledge, there has been an upsurge in demand for developing newer materials for novel applications. In fact, with the technological leaps in recent times, focus has been on developing the materials required to perform in stringent conditions - high temperature & pressure, highly corrosive environment, higher strength but without much weight implications etc. which the conventional materials failed to service. This ushered in 'engineered material', devising material properties catering to the application needs. And the innovation was not limited to developing materials with novel properties alone but it also addressed the method of manufacturing - improved processing techniques, effective use of energy while processing and more importantly with the least environmental impact. Advanced materials with combination of properties for specific end uses became a reality.
Over the last thirty years composite materials, plastics, and ceramics have been the dominant emerging materials. The volume and number of applications of composite materials has grown steadily, penetrating and conquering new markets relentlessly. Modern composite materials constitute a significant proportion of the engineered materials market ranging from everyday products to sophisticated niche applications.
Today high performance fibre reinforced plastics (FRP) are starting to challenge those ubiquitous materials such as steel & aluminium in everyday applications as diverse as automobile bodies and civil infrastructure. It would be naive to suggest that FRP will dislodge those materials from their dominant roles. However, continuous advances in the manufacturing technologies and performance of FRP have intensified the competition in a growing range of applications leading to significant growth in its market acceptance. For any given application and industry sector, the final choice is often a competitive outcome of alternative solutions, including advances in alternative materials such as aluminium alloys and metal-composite hybrids. Each type of composite brings its own performance characteristics that are typically suited for specific applications.
Increasingly enabled by the introduction of newer polymer resin matrix materials and high performance reinforcement fibres of glass, carbon and aramid, the penetration of these advanced material forms has witnessed a steady expansion in usage. The increased consumption has reduced the product cost. High performance FRP can now be found in such diverse applications as composite armouring designed to resist explosive impacts, fuel cylinders for natural gas vehicles, windmill blades, industrial drive shafts, support beams of highway bridges and even paper making rollers. An examination of the diversity of some of these newer applications and the socio-commercial considerations that underpin their introduction gives an instructive insight into the future place of high performance FRP.
The development of a composite component involves both material and structural design. Unlike conventional materials, the properties of the composite material can be varied considering the end application. Properties (stiffness, thermal expansion etc.) can be varied continuously over a broad range of values by suitable selection of resin, fibre, their ratio, additives etc.
Commonly used polymer matrix composites comprise a thermosetting resin matrix in combination with a fibrous reinforcement. Some advanced thermoplastic resins are also used, whilst some composites employ mineral filler reinforcements, either alone or in combination with fibrous types. Cellular reinforcements (foams and honeycombs) are also used to impart stiffness in conjunction with ultra lightweight. Whilst the use of composites will be a clear choice in many instances, material selection in others will depend on factors such as working lifetime requirements, number of items to be produced (run length), complexity of product shape, possible savings in assembly costs and on the experience & skills of the designer in tapping the optimum potential of composites.
Lightweight corrosion resistant materials such as FRP could provide an important contribution to the safe, economical development of resources. The need for new markets has spurred renewed efforts in reducing the cost of both raw materials and manufacturing processes, making composites more competitive to use in civil infrastructure applications. The mechanical properties of composite laminates are listed in Table-I.
Indian efforts centre around developing cost effective building materials as well as for catering to the housing needs of urban & rural poor. In this context, certain developments concerning glass fibre reinforced polymer composites, natural fibre composites, industrial waste based composites have assumed importance. The key restricting factors in the application of composites are initial costs due to raw materials and also inefficient conventional moulding processes.
Various key product applications being developed in the building & construction industry are prefabricated, portable & modular buildings, exterior cladding panels, interior decorations, furniture, bridges and architecture mouldings. Various proven composite products being used in the housing sector are bathtubs & basins, drainage channels, manhole covers, pits, farm buildings, doors, door frames & windows, cabinets, housing modular, sheeting roof and flat, structural members, portable toilets, ponds & fountains, water storage tanks etc.
Composites for Structural Applications
Composites have long been used in the construction industry. Applications range from non-structural gratings and claddings to full structural systems for industrial supports, buildings, long span roof structures, tanks, bridge components and complete bridge systems. Their benefits of corrosion resistance and light weight have proven attractive in many low stress applications. Composites present immense opportunities to play increasing role as an alternate material to replace timber, steel, aluminium and concrete in buildings.
Bridges account for a major sector of the construction industry and have attracted strong interest for the utilization of high performance FRP. FRP has been found quite suitable for repair, seismic retrofitting and upgrading of concrete bridges as a way to extend the service life of existing structures. FRP is also being considered as an economic solution for new bridge structures. Design approaches and manufacturing efficiencies developed for road bridge applications will benefit their introduction into a broader range of civil construction fields.
Decks for both pedestrian and vehicle bridges across waterways, railways and roadways are now a commercial reality in both North America and Europe, with some pedestrian bridges being built entirely from composites. Because of the superior durability of composite, only cosmetic maintenance requirements are expected for at least 50 years. The composite bridge decks are quite suitable for replacing conventional/old bridge decks having super structure intact. The replacement can be carried out in a short time with minimal disturbance to the traffic.
Among a wide array of composite products, pultruded profiles such as gratings, ladders, cable trays, solid rods & other sections are used in many structural application with Class I flame retardancy. Pultrusion is the most cost-effective method for the production of fibre-reinforced composite structural profiles. It brings high performance composites down to commercial applications such as lightweight corrosion-free structures, electrical non-conductive systems, offshore platforms and many other innovative new products. Pultruded sections are well-established alternative to steel, wood and aluminium in developed countries and are fast catching up in other parts of the world. Structural sections have ready markets in oil exploration rigs, chemical industries etc. The amount of energy required to fabricate FRP composite materials for structural applications with respect to conventional materials such as steel & aluminium is lower and would work for its economic advantage in the end. The pultruded products are already being recognized as commodity in the international market for construction.
In pursuit of developing advanced performance materials for building & construction, railways, automobiles, bio-medical etc., the Advanced Composites Programme was launched by Technology Information, Forecasting & Assessment Council (TIFAC), an autonomous organization under the Department of Science & Technology (DST), Govt. of India. Under a project of the aforesaid programme, FRP Pultruded profiles (industrial gratings, solid rods for electrical insulation, cable-trays, ladders etc.) with excellent surface finish and flame retardancy as per international standards have been developed by M/s. Sucro Filters Pvt. Ltd., Pune. The profiles developed have met all the desired properties. Table II lists the mechanical/ chemical properties of FRP pultruded sections vs. other structural materials. Table III lists out the characteristics of the pultruded products.
Repair, Retrofit & Rebars
Composite plates are successfully used to repair masonry beams, columns, buildings and other structures damaged/weakened by impact, earthquake or subsidence and can usually be adhered in place by hand without the need for heavy lifting equipment. Such repairs can be carried out much more rapidly than traditional techniques.Composite reinforcing bars may be used to replace steel in conventional reinforced concrete in order to prevent "concrete cancer" problems resulting from internal corrosion of the reinforcement. The use of composite rebars is justified where the nature of the construction would render possible future repairs inaccessible or otherwise unduly costly.
Composites as Building Material
The composite is an ideal material for the manufacture of prefabricated, portable and modular buildings as well as for exterior cladding panels, which can simulate masonry or stone. The translucent roof sheeting is now supplied in a variety of colours and profiles to suit both commercial and domestic building needs. In interior applications, composites are used in the manufacture of shower enclosures and trays, baths, sinks, troughs and spas. Cast composite products are widely used for the production of vanity units, bench tops and basins. Realistic simulation of marble in various colours, onyx and granite can now be achieved with cast composites using resin, filler and proper processing technology. The availability of highly fire resistant phenolic composites opens up the opportunity for new, safer and cost effective building techniques.
This area holds priority for the induction of composites in place of conventional materials being used in doors & windows, paneling, furniture and other interiors. Components made of composite materials find extensive applications in shuttering supports, special architectural structures imparting aesthetic appearance, large signages etc. with the advantages like longer life, low maintenance, ease in workability, fire retardancy etc. The key restricting factors in the application of composites are initial costs due to raw materials and also inefficient conventional moulding processes. Industry & design experts are of the view that with the adoption of advanced technologies and some extent of standardization, these problems could be easily taken care of.
FRP Doors & Door Frames
With the scarcity of wood for building products, the alternative, which merits attention is to promote the manufacturing of low cost FRP building materials to meet the demands of the housing & building sectors. The doors made of FRP skins, sandwiched with core materials such as rigid polyurethane foam, expanded polystyrene, paper honeycomb, jute/coir felt etc. can have potential usage in residential buildings, offices, schools, hospitals, laboratories etc. As structural sandwich construction has attained broad acceptance & usage for primary load bearing structures, the FRP doors can be manufactured in various sizes & designs using this technology.
The principal fabrication technique employed is contact moulding or hand lay-up process. The front & back sheets of the doors are fabricated separately. Wooden inserts are placed between two sheets for various fittings. The PU foam is sandwiched between the sheets by in-situ foaming process followed by painting & polishing to meet aesthetic requirement. Proper usage of additives imparts fire retardant properties to the doors. In addition, usage of composite material for the doors makes them totally water & termite resistant. FRP doors are much cheaper than the wooden ones. The FRP doorframes can also be fabricated by contact moulding.
The FRP doors & doorframes have been designed & developed using the aforesaid technology by the RV-TIFAC Composite Design Centre (CDC), Bangalore under the Advanced Composites Programme. The FRP doors developed by CDC conform to BIS specifications (IS:4020). After successful field trials and users’ feedback, the technology for FRP door has been transferred to over 50 entrepreneurs for commercial exploitation.
The rapid expansion of the use of sandwich construction in many fields has yielded a more precise knowledge of design methods, test procedures & manufacturing techniques of cost-effective composite products. A low-density core made of honeycomb or foam materials provides a structural performance with minimum weight. Other considerations such as sound insulation, heat resistance, vibration-damping etc. dictate the particular choice of material used as core material.
The fibre glass veil facing used while moulding the panels for suspended ceilings increases panel stiffness and resists puncturing. Due to their easy printability, the veil imparts good panel aesthetics. The suspended ceilings are used to cover up electrical wiring, ducting, piping and fittings. The veil with an optimum porosity contributes to improved acoustical quality of the working or living space.
FRP Modular Toilet Units for Indian Railways
FRP Modular Toilet Units for Railway Coaches were developed under a project of the Advanced Composites Programme in partnership with Hindustan Fibreglass Works, Vadodara with design and technology support from IIT-Bombay. The Industrial Design Centre of IIT-B helped in design drawing, fabrication of modular toilets with improved aesthetics & ergonomics. IIT-B also extended support in terms of structural design of FRP toilets, reinforcement lay-up, mould design & fabrication, selection of suitable raw materials, testing & mechanical characterization and quality assurance norms for fabrication. Three types of FRP toilet units were developed as per the space availability in ICF coaches.
The FRP toilet unit consists of four parts : the flooring trough, one L-shaped side-wall, one C-shaped side-wall & roof. These parts are fastened by self-tightening screws. The FRP toilet is light in weight, corrosion resistant, fire retardant, has longer life with easy maintainability. Due to its modular design, the whole toilet unit can be installed inside the coach in a short timeframe. The following features were provided in the toilet .
FRP sandwich door with rigid PUF core, lipped with pultruded FRP frame on all four sides of the door
Special PVC sheet with improved anti-skid and anti-abrasion properties for the flooring
Concealed type Ki-tech flexible conduits with aluminium core encased within two HDPE layers
FRP toilet units are now fully operational in passenger coaches of Indian Railways. The performance of four nos. FRP toilets, which were fitted to an AC-II tier coach of Mumbai Rajdhani Express in October 2001, has been extremely satisfactory. Based on the initial field trials, FRP toilets have been inducted by the Indian Railways for many important trains on regular basis. The project bagged the Certificate of Merit under the National Award for Excellence in Consultancy Services–2001 by DSIR, Govt. of India.
Natural Fibre Composites as Building Materials
Natural fibres, as a substitute for glass fibres in composite components, have gained interest in the last decade, especially in the housing sector. Fibres like flax, hemp or jute are cheap, have better stiffness per unit weight and have a lower impact on the environment. Structural applications are rare since existing production techniques are not applicable and availability of semi-finished materials with constant quality is still a problem.
The moderate mechanical properties of natural fibres prevent them from being used in high-performance applications (e.g. where carbon reinforced composites would be utilized), but for many reasons they can compete with glass fibres. Advantages and disadvantages determine the choice. Low specific weight, which results in a higher specific strength and stiffness than glass is a benefit especially in parts designed for bending stiffness.
Natural fibre composites (NFC) can be used as a substitute for timber as well as for a number of other applications. It can be moulded into sheets, boards, gratings, pallets, frames, structural sections and many other shapes. They can be used as a substitute for wood, metal or masonry for partitions, false ceilings, facades, barricades, fences, railings, flooring, roofing, wall tiles etc. It can also be used in pre-fabricated housing, cubicles, kiosks, awnings, sheds/shelters. Natural fibres due to their adequate tensile strength and good specific modulus enjoy the right potential for usage in composites thus ensuring a value-added application avenue. The maximum tensile, impact and flexural strengths for natural fibre composites reported so far are 104.0 MN/m2 (jute-epoxy), 22.0 kJ/m2 (jute-polyester) and 64.0 MN/m2 (banana-polyester) respectively.
Although the tensile strength and Young’s modulus of natural fibre like jute are lower than those of glass fibres, the specific modulus of jute fibre is superior to that of glass and on a modulus per cost basis, jute is far superior. The specific strength per unit cost of jute, too, approaches that of glass. The need for using jute fibres in place of the traditional glass fibre partly or fully as reinforcing agents in composites stems from its lower specific gravity (1.29) and higher specific modulus (40 GPa) of jute compared with those of glass (2.5 & 30 GPa respectively). Apart from much lower cost and renewable nature of jute, much lower energy requirement for the production of jute (only 2% of that for glass) makes it attractive as a reinforcing fibre in composites. Table IV gives the properties of a few natural fibre.
Jute-coir composites provide an economic alternative to wood for the construction industry. It involves the production of coir-ply boards with oriented jute as face veneer and coir plus waste rubber wood inside. A very thin layer of jute fibres impregnated with phenolic resin is used as the face veneer for improved aesthetics and to give a wood like finish.
The orientation & uniformity of jute fibre improve with carding and this also helps in better penetration of resin into the fibre. The coir fibre contains 45.84% lignin as against 39% in teakwood. Therefore, it is more resistant than teakwood against rotting under wet and dry conditions and has better tensile strength. The composite boards namely, coir-ply boards (jute + rubber wood + coir) as plywood substitute and natural fibre reinforced boards (jute + coir) as MDF substitute can be used in place of wood or MDF boards for partitioning, false ceiling, surface paneling, roofing, furniture, cupboards, wardrobes etc. These boards have been employed as doors & door frames as an alternate to conventional material like wood, steel etc.
Bamboo Composite Boards & Laminates
Bamboo is one of the fastest renewable plant with a maturity cycle of 3-4 years, thus making it a highly attractive natural resource compared to forest hardwoods. Bamboo offers good potential for processing it into composites as a wood substitute. Bamboo laminates could replace timber in many applications such as furniture, doors & windows and their frames, partitions, wardrobes, cabinets, flooring etc.
Bamboo laminates are made from slivers milled out from the bamboo culm. After primary processing comprising cross cutting, splitting and 2-side planing, the slivers are treated for starch removal and prevention of termite/borer attack. The slivers are then subjected to hot air drying followed by 4-side planing for attaining uniform thickness. These slivers are coated with glue on the surface and are arranged systematically. They are subjected to a curing in a hot press (6’X4’ 2-day light) at temp. ~ 70 0C using steam & pressure ~ 17 Kg/cm2. The pressed laminate (panels/tiles) is then put through trimming, sanding & grooving machines to give a pre-finish shape. The flow chart & intermediate quality control parameters for manufacturing bamboo composites are enclosed.
The project on production of bamboo composites & laminates is based on the following premises.
Value-added products from Bamboo
Cost-effective compared to good solid wood sections for furniture
Diversification from traditional plywood to bamboo based products
Complete range of bamboo composite laminates for furniture, flooring tiles, boards, door & window frames to replace the use of timber for domestic as well as international market
Bamboo composite based flooring tiles, boards (used for partitions, cupboards, racks, door & window panels) and blocks (used for furniture, rails & styles for doors & windows etc.) as wood substitute would help develop & promote high value-added products from bamboo
Bamboo composite laminates with a low-temperature curing resin system for reduced energy requirement
Promotion of eco-friendly use of bamboo while building a sustainable infrastructure for plant multiplication, propagation and cultivation
Boosting the usage of bamboo based products in India towards generating good employment & income opportunities at rural level
Towards an effective bamboo utilization and exploring the value-addition potential, the project on development of bamboo composite laminates was launched by the Advanced Composites Programme of TIFAC in partnership with M/s. Emmbee Forest Products Pvt. Ltd., Manabari with technology support from the Department of Polymer Science & Technology, University of Calcutta. The project aimed at developing value-added products from bamboo with an innovative resin system for reduced processing energy requirement. Bamboo based products such as flooring tiles, laminate boards, blocks (for door & window frames, rails & styles, furniture etc.) as wood substitute are being developed under the project.
For preventing bamboo composites from any deterioration by moisture absorption and imparting long-term storage life, a water based acrylic pre-coat has been developed. This pre-coat would prevent any fungal attack during transit for the reconstituted wood sections for furniture. Further, a UV cured melamine acrylate system as the finishing coat has also been developed for flooring tiles made of bamboo composites. A water based PU resin system has also been tried for final finish of the flooring tiles.
Various stages of bamboo processing starting from cross-cutting, parallel splitting, knot removal, two-side planning, anti-fungal treatment, drying, four-side planning, glue application and hot pressing were fine tuned. Products such as flooring tiles, furniture sections, reconstituted wood, air locked sections, mat boards etc. have been developed under the project.
Composite Materials towards Re-building & Rehabilitation
In the wake of disastrous damages by the earthquake in Gujarat, the Advanced Composites Programme has contributed to the national efforts of re-building and rehabilitation. Under the TIFAC Rehab Project for Kachchh, the following initiatives were taken up for the quake affected people.
392 low-cost semi-permanent shelters (20’x12’) made of natural fibre composite materials such as jute-coir composite boards and rice husk particle boards with bamboo mat face veneer etc. were supported on MS angles & channels. For improved aesthetics and also to augment the thermal insulation, natural fibre composite board roofing of the shelters was covered with terracotta tiles.
In order to cater to the shelters, 128 community toilet blocks (4’x4’) made of modular FRP section for walls & roof were constructed.Fifteen shops (12’x8’) were constructed in the township along with a Post Office in the township, which has commenced its services. In addition to the semi-permanent residential shelters constructed at Bhuj, 25 school blocks-cum-community centres (24’x 20’) were also constructed at various locations in Kachchh.
The TIFAC Rehab Project was a model initiative of technology demonstration with novel building materials with the delivery in the quickest possible time addressing the crucial need for post-disaster relief.
Composite Building Materials – Technology Demonstration
For augmenting the reception block of Technology Bhavan campus in Delhi, the Advanced Composites Programme took initiatives by building a 3000 sq. ft. temporary structure for post office, CR section, technology demonstration-cum -display area and additional office space towards showcasing composite building materials. The array of products developed under the programme such as jute-coir boards, FRP doors, bamboo composite flooring tiles & rice husk particle boards for false ceiling were used in the construction of the shelter towards technology demonstration. Jute-coir composite boards, made of coir felt & waste rubber-wood as inside veneers and oriented jute as face veneer is a unique value-added application for agro-wastes and positioned as an effective wood substitute building material. While the shelter structure was fabricated out of standard steel sections, jute-coir boards were used for double-wall construction ensuring excellent thermal insulation. They were also used for roofing overlaid with terracotta tiles. Elegant looking bamboo composite tiles were used for the flooring. The door shutters made of sandwich panels of glass fibre reinforced polyester resin, have good aesthetic appeal with adequate mechanical strength and water resistance.
The most important feature governing the choice of material & form of construction for any component is its structural integrity. Whereas high specific strength and lightweight were often the dominant criteria to be achieved, particularly for aerospace applications, there is today an increasing emphasis on other criteria such as environmental durability, embedded energy, fire resistance.
Innovative thermoset and natural fibre composite products would go a long way in developing new application areas thus enhancing its market reach. India with an excellent knowledge-base in various resins, catalysts & curing systems coupled with an adequate availability of various raw materials can certainly carve out a niche in the upcoming technology of composite fabrication. Value-added novel applications of natural fibre composites would also ensure international market for cheaper substitutes. The products when locally manufactured would actually become cost competitive for other wood substitutes.
The Advanced Composites programme has improved the laboratory-industry linkages towards application development & commercialization by launching 30 projects across the country. The programme has been quite instrumental in bridging the knowledge gaps and bringing together the industries & the users for technology development, transfer & subsequent commercialization.