Glass Reinforced Plastic

Gulf Construction, June 2010105

RP (glassfibre reinforced plastic)composite rebar is the next-genera-tion material for concrete reinforce-

ment in the region and with the recentacceptance of the material in theInternational Building Code (IBC), the con-struction industry can expect to see wideruse of GRP in these applications.

In view of the soil conditions prevalent inthe region, GRP rebar is the naturalchoice, given the numerous advantagesoffered by the material. GRP compositerebar offer corrosion resistance (impervi-ous to the action of salt ions and alkalinityinherent in concrete) and are light inweight (approximately 25 per cent theweight of an equivalent steel bar).

As the rebar do not contain metal, they willnot cause any interference in contact withstrong magnetic fields or when operatingsensitive electronic instruments. In otherwords, they are transparent to magneticfields and radio frequencies. Further, thelevel of thermal expansion is comparable toconcrete due to the high silica content(greater than 75 per cent) of GRP rebar. TheGRP rebar are also electrically and thermallynon-conductive. ASTM D7205 describes testmethods for determining tensile modulusand strain properties of GRP rebar usingAmerican Concrete Institute (ACI) designguidelines.

The savings in construction and life-cyclecosts with GRP rebar are multi-fold:• Instead of low-permeability concrete withadded corrosion inhibitors, conventionalconcrete can be used; • Costs incurred in using expensive mem-branes can be eliminated; • Reduced weight leads to lower installationtime; • Savings of at least 45 per cent in total costof maintenance and demolition; and• Savings of at least 15 to 20 per cent in theoverall life-cycle cost.

The development of key codes and stan-dards has catapulted the commercial accept-ance of GRP rebar in the industrialisedcountries. And with GRP composites finallyrecognised by IBC, it can be considered awatershed in the global building and con-struction sector, including the region!

Standards & acceptanceNorth America is the acknowledged leader

in the use of GRP rebar for concrete rein-forcement. The concept initially mooted inthe early 1990s paved the way for extensivetrials and successful commercialisationtowards the end of the millennium. The ACIand Japan Society for Civil Engineers (JSCE)

The case for manufacturing as well as use of GRP composite rebar inthe Gulf region is very strong, given the region’s resources andenvironmental conditions. S SUNDARAM* elaborates.

G Composite rebar ‘ideal for Gulf’

have formulated design guidelines for theuse of GRP rebar, while the CanadianNetwork of Centers of Excellence onIntelligent Sensing for Innovative Structureshas published a design guide and manualson the subject.

In April 2008, the American CompositesManufacturers’ Association (ACMA)announced an effort to introduce GRP com-posites into the IBC – a model building codedeveloped by the International CodeCouncil (ICC) – to promote acceptance ofcomposites in building and construction.The ICC final hearings were held inSeptember 2008 wherein building officials“approved” as submitted, item FS196-07/08.

The new section of the 2009 IBC stipulatesthe proper use of GRP for building con-struction and will enable architects, speci-fiers and buyers to appreciate the benefits ofGRP as a viable product. The code changeprovides recognition of GRP composites formany building applications and includesappropriate requirements to allow their usein a manner intended by the code alongside

traditional building materials. Also in 2008, a team composed of ACMA

members and the University of Miami suc-cessfully submitted new standards for the useof GRP rebar in concrete, to the ACI. Aftera rigorous process, ACI’s Committee 440adopted the new standards designed to pro-vide fibre-reinforced polymer rebar manufac-turers with critical tools to aid engineers inspecifying composite rebar for structuralapplications. Coupled with the ACI designspecification (ACI 440.2R-06), the standardsenhance the use of GRP composite rebarand render it easier for manufacturers to pro-duce them and have them qualified onpotential jobs. The standards include:• 440.5-08: specification for constructionwith fibre-reinforced polymer reinforcingbars;• 440.5M-08: metric specification for con-struction with fibre-reinforced polymer rein-forcing bars;• 440.6-08: specification for glassfibre-rein-forced polymer bar materials for concrete

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Composite rebar used at Nakheel’s Palm Cove Canal in Dubai Waterfront, UAE.

Glass Reinforced Plastic

Gulf Construction, June 2010107

resin, fibre orientation and quality controlduring manufacturing playing a major rolein their mechanical characteristics. Thenew design philosophy adopted for GRPcomposite rebar allows consideration to begiven to either composite rupture or con-crete crushing as the mechanism that con-trols failure and is based on limit-statedesign principles, followed by checking forfatigue endurance, creep rupture enduranceand serviceability criteria.

ApplicationsThe following aspects have to be factored in

when designing with GRP concrete rebar:• Direct substitution of GRP rebar in con-crete structures designed with steel rebar isgenerally not practical;• GRP rebar have a lower modulus of elas-ticity and shear strength, thereby limitingapplications to short spans of secondarystructural elements; and• GRP rebar applications are generally con-fined to reinforcement of concrete and notrecommended to be used as a pre-stressing orpost-tensioning element.

GRP rebar are produced by the pultrusionprocess and are specifically advantageous inconcrete construction in areas of poor load-ing-bearing soil conditions or active seismicsites that require lightweight reinforcement.

Due to the low modulus of elasticity, GRPrebar need to be supported at a spacing thatis two-thirds that of steel rebar.

Other uses include tunnelling and boringapplications requiring reinforcement of tem-porary concrete structures, typical examplesbeing underground rapid transit structures,underground vertical shafts and miningwalls. Specific examples of use in structuresbuilt in or close to seawater include quays,retaining walls, piers, jetties, piles, bulkheadsand offshore platforms.

GRP in the regionThe structural engineering division of the

civil engineering department at the UAEUniversity has done extensive research on thepotential use of GRP rebar in the UAE

through Efors, the licensed consultancy withthe university’s research centre. The depart-ment is working on some ongoing projects inReem Island and has been associated withother projects in Abu Dhabi, Fujairah, RasAl Khaimah and Ajman in the past five years.GRP rebar have already been used in marinedocks and waterfront structures such asNakheel’s Palm Cove Canal in DubaiWaterfront and in the Baker Hughes build-ing in Dubai.

The UAE is already familiar with the use ofGRP rebar and the Emirates Foundation isfunding a research project on the perform-ance of concrete structures using GRP rebar.What is required now is expanding the use ofthe composite rebar in numerous upcomingprojects in the region.

In terms of manufacture, there are a fewGRP processors in the region with pultrusionfacilities, of which Pultron (Jebel Ali, Dubai)and Saudi Pultrusion Industry (Al Khobar,Saudi Arabia) merit specific mention.

Pultron commenced its manufacturingactivities in the UAE earlier this year and willbe relying on its 20-year expertise in produc-ing quality GRP rebar at its main manufac-turing facility in New Zealand.

The availability of the requisite types ofglassfibre and resin (produced locally inthe region) for rebar ensures that theregion is self-reliant on raw materials andtechnology for mass production of GRPrebar. Further, in view of the region’sprevalent soil conditions, GRP rebar is thenatural choice and should be exploited toa greater extent.

The synergistic availability of materials,technology, design data and internationalstandards makes a strong case for more exten-sive use of GRP rebar in construction activi-ties in the region in the coming years, con-sidering its immense potential.

* S Sundaram is a freelance writer with over 25years experience in the global composites industry.He regularly contributes to several composites trademagazines in Europe, North America, Asia Pacificand the Middle East.

reinforcement; and• 440.6M-08: metric specification for glassfi-bre-reinforced polymer bar materials for con-crete reinforcement.

Concrete has high compressive strengthbut limited tensile strength. To overcomelimitations in tensile, reinforcing bars areused in the tension side of concrete struc-tures. Historically, steel rebar have been usedas a cost-effective reinforcement. However,insufficient concrete cover, poor design orworkmanship and the presence of largeamounts of aggressive agents including envi-ronmental factors can lead to cracking of theconcrete and corrosion of the steel rebar.While, steel rebar can last for decades with-out visible deterioration provided the con-crete is not subject to chloride ion attack,they are prone to rust when exposed to chlo-rides especially in coastal areas, locationswhere salt-contaminated aggregates are usedin the concrete mixture and sites with aggres-sive soil conditions. When corrosion occurs,the resulting products have a larger volume(two to five times) than the metal productfrom which they are originally derived. Theconcrete cannot sustain the tensile loaddeveloped from this volume increase andeventually cracks and spalls, leading to fur-ther deterioration of the steel.

The combination of ongoing deteriorationand loss of reinforcement properties resultsin significant and expensive outlays forrepair and maintenance, ultimately endan-gering the structure itself. A quick-fix cost-effective solution is the use of epoxy-coatedsteel rebar with stainless steel being a moreexpensive alternative.

Rebar using glassfibre in a resin matrix(generally vinyl ester or epoxy) providesuperior tensile properties and built-in cor-rosion resistance and are also economicallyfeasible from a life-cycle cost-benefit-analy-sis viewpoint.

The ACI 440 recommendations are basedon principles of equilibrium and compati-bility and the law of mixtures of the con-stituents (glassfibre and resin).The resin-glass interfacial bond characteristics areresponsible for transferring the stress fromconcrete to the reinforcement and fordeveloping the required stress in the rein-forcement for an equilibrium, particularlywhen concrete cracks. Service limits inGRP reinforced concrete such as deflec-tion, crack width and crack spacing aredirectly influenced by the bond propertiesof the reinforcement in concrete.

GRP rebar are anisotropic in nature withfactors such as type and volume of fibre and

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Composite rebar ... offercorrosion resistance.