CoatingsPro Magazine

MAY 2015

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COATINGSPRO MAY 2015 61 Science Behind It Fiber-Reinforced Polymers By Brad Erickson, S.E., Simpson Strong-Tie Engineering Manager for Composite Strengthening Systems F or the Cumberland Bridge project in Cumberland, Md., the contractor needed to repair and protect more than 250 concrete columns. Te engineer from the Maryland State Highway, the client on this project, chose to use a fber-reinforced polymer (FRP) solution to do so. W hy? What Is FRP? Trad it ion a l met hod s for repa i r i ng conc rete i nc lude add i ng steel pl ates a nd jac kets or reba r a nd conc rete, but t hose t y pes of met hod s c a n add a sig n i f ic a nt a mou nt of weig ht t h at cou ld potent i a l ly i mpac t t he fou nd at ion of t he st r uc t u re. For t h is t y pe of projec t, a n FR P solut ion m ade more sense. A n FR P solut ion consists of a n e x ter n a l ly bonded s ystem t h at feat u res a h ig h st reng t h /st i f f ness -to -weig ht rat io. It is a l ig ht weig ht, low-i mpac t solut ion desig ned to prov ide a cost- ef fec t ive a lter n at ive to t rad it ion a l ret rof it met hod s a nd to i nc rea se t he l i fe of t he conc rete repa i rs t h at were per for med. It is idea l for ret rof it solut ions bec au se it c a n ea si ly confor m to t he e x ist i ng sh ape of t he st r uc t u re, wh ic h, i n t h is c a se, consisted of conc rete colu m ns. T he FR P fabr ic f rom Si mpson St rong-Tie comes i n 12- or 24 -i nc h (31 or 61 c m) w idt hs a nd is del ivered d r y to t he jobsite i n rol l s. T he epox y is del ivered i n fac to - r y- sea led buc kets. It consists of t wo components a nd h a s a 2 A :1B volu met r ic m i x rat io. T he i nst a l ler m i xes t he epox y, pr i mes t he su r faces, sat u rates t he fabr ic, a nd t hen "w raps" t he st r uc t u ra l element a nd a l lows it to c u re. I n te r m s of c apac it y, t y pic a l ly comp osite st re ng t h - e n i ng s y ste m s prov ide st r uc t u r a l re i n force me nt a nd a re u s e d to sup p or t add it ion a l she a r a nd f le x u r a l de m a nd s on colu m n s , b e a m s , s l a b s , w a l l s , a nd pi le s. T h i s a l so i nc lude s s e i sm ic /w i nd ap pl ic at ion s (i .e., to add re i n force me nt t h at he lps t r a n sm it t he l ate r a l a nd upl i f t force s i n t he s e e ve nt s). FR P solut ion s c a n a l so b e u s e d for colu m n a x i a l con f i ne me nt , wh ic h i nc re a s e s t he de si g n st re ng t h of t he conc rete to sup p or t h i g he r compre s sion load s a nd con f i ne t he colu m n conc rete. FR P s y ste m s a re u s e d to re si st te n sion force s wh i le m a i nt a i n i ng compat ibi l it y b et we e n t he comp osite m ate r i a l s a nd t he su b st r ate. I n e s s e nce, it ac t s ju st l i k e i nte r n a l ste e l re i n force me nt but i s i n st a l le d on t he e x te r ior of t he e le me nt it i s prote c t i ng or st re ng t he n i ng. How Was It Used? For this project, the column heights var ied in size f rom 15 to 30 feet (5 –9 m). Most were round, but there were a lso a number of square columns on the jobsite. Because of the number of columns, more than 100,000 square feet (9,290 m²) of FR P fabr ic was used to w rap each of the columns. With t wo layers of FR P fabr ic, that equated to approx i- mately 53,000 square feet (4,924 m²) per layer. T he coatings crew used severa l products to complete the coatings system on the columns. Inc lud ing the infor- mation prov ided in the feature ar tic le, the products star ted w ith F X- 406, a zinc-r ich pr imer. It is a single-com- ponent, fast-dr y ing coating desig ned to protect steel f rom cor rosion w ith the sacr if icia l ga lvanic protection of zinc. It was used in this repair situation because the high zinc content prov ided the super ior cor rosion protection of steel. T hen they applied the F X-752 epox y bond ing agent, a 100 percent solids, t wo -component, moisture-tolerant epox y system desig ned to increase the bond bet ween f reshly placed repair mor tars or concrete mi xes and ex ist- ing concrete. W hi le the bond ing agent was sti l l tack y, the concrete columns were restored to their or ig ina l section using F X-263 R apid-Hardening Ver tica l /O verhead Repair Mor tar. For ming was not required as the mor tar was troweled into place. T he crew a lso used F X-778 high-mod- u lus trowel g rade epox y to achieve the smooth exter ior f inish needed before the next step in the process. T he CSS carbon f iber fabr ic was saturated w ith an epox y saturant using a mechanica l rol ler to ensure that f u l l f iber satura- tion was achieved. T he mater ia l was then rol led into place on each column. In the final step, Simpson Strong-Tie FX- 480, a protec- tive epox y coating, was applied to ever y column over two layers of fabric. FX- 480 is a high-solids, two-component, high-build, moisture-tolerant epox y coating designed to protect the concrete from abrasive environments. It was colored light gray to blend in w ith the existing structure. Once dried, it provided a tough tile-like finish. Overall, the fber-reinforced polymer coating system wrapped the concrete columns, ofering a viable retroft solution to meet the client's needs. CP

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