IV.QUANLYmr AN D A U T U - XAY OI/NG & QUAN LY VAN HANH CAU TRONG 0 6 THj
AN MON C 6 T T H E P DO DONG DIEN RO TRONG CAU DUfdNG SAT DO TH! VA BIEN PHAP KIEM SOAT
STRAY-CURRENT-INDUCED CORROSION IN REINFORCED OF URBAN RAILWAY BRIDGE AND MITIGATION METHODS K S . D A N G C O N G M I N H - T T i S . D O A N V A N M d N
V i e n K t i o a Inpc v a C o n g n g h § GTVT, ITST
T6m tat: Bai bao niy iJe cap (ten si/ Sn mbn c6t tfiep trong be tong gSy ra bfli dong dien r6 cua he th6ng dien (Jong luc kfio tau dien. B^ bdo cung cip ttiong tin v6 ngu6n cOa dong dien ril, cO chi Sn mon, anh hudng 6%r\ cau triic. Bai bao cQng
dua ra phUdng phap phdt hien va bi§n phdp kiem scat dong dien rd. .^^
^ Abstract: The paper menfions the corrosion of reinforcing in concrete strucbire of Urtan railway bridge by stray c»- Bent tt provides information on the sources of stray current, the mechanism of corrosion, the effects on structures. Tlie fdocument also provide the methods for detection and mitigation of stray current induced corrosion on steel m concrete.
Gidi t h i e u c h u n g
C6t th6p trong BTCT ttiong ttiucmg Ithdng bj an m6n do n§m trong m6i truOng co do ki^m cao (PH hon 12,5), tren bi m | t c6t tii§p hinh th^nh I6p thu dong bin vimg bao ve khoi s i ; i n mon. Cdt thdp b i t d i u bj Sn m6n khi:
- C6 khi§m khuy§t khi thi cong nhu 16 rdng hay v i t niJit;
- €)0 k i l m bj giam do Ccic phan ung vdii khi hay c h i t I6ng;
- S I ; tham nhap ciJa ion cio vupt nguQng cho phep.
Ngoii an mon a § n hda hay con goi la an mdn gal- vanic, khi do dbng dien t u sinh ra tCr cac p h i n umg hoa h9c, c6t thdp con bj an m6n do co d6ng dien ti!r b§n ngoii t i c dong vao. Trong moi truicmg cd ddng dien, cot thdp khong bj an mdn khi ddng dien di v i o nhung se bj Sn mdn khi ddng dien di ra {kim loai trd thanh an6t). An mdn dang n i y do ddng dien rd g i y ra, cof chl d^ng i n mdn nay dupc trinh b i y trong p h i n sau.
Ddng di^n rd duoc d\nh nghTa l i ddng dt^n khdng ch^y theo mach didn dupc chl dinh. T i c hai i n mdn do ddng dien rd r i t ldn, theo ly thuydt thl v6i ddng didn 1A trong 1 nam cd the l i m tieu hao 9kg thep. Trong khi cic p h i n Ung dien hda chl co dien t h i i n mdn vai trim mV thi dien thd i n mdn do ddng didn dd cd the hing chyc vdn. Do vay an mdn do ddng didn rd cd tiie nhanh hon c i c dang an mdn khac hang t r i m d i n hing nghin t i n .
1. Ngudn c u a d d n g d i e n ro (Sources of stray currents)
Hd thdng didn ch^y d i u keo cua t i u didn l i ngudn cOa ddng didn rd trong cdt thep. Hd thdng n i y l i he th6ng ddng mpt chidu cd didn thd khoang 1500 d i n 3000V(1). P h i n tdn ddng didn trong mach quay \a\
ngu6n p h i t thdng qua du€mg ray va mpt p h i n nhd thflng qua BTCT h o i c d i t . S y nghen mach di#n trdn dudng ray l i m i n h hudng ddn thdng didn v i t i n g ddng di$n rd. Bdn cgnh dd, s y khdng c i c h didn hay cich di$n kdm ciJa hd thdng ray vdi bd tdng cung l i m ting ddng didn rd. D d tdn ciJa ddng didn rd do t i u didn g i y ra cd g i i th r i t k h i c nhau ttr v i i ampe d i n h i n g nghin ampe.
Cdt thdp bd tdng bj anh hudng bdi ddng didn rd (Hlnh 1.1) gdm cac k i t c i u c i u v i h i m ciia hd thdng tau didn ho$c t t i t c i u thdp ciJa c i u tnic bdn canh nhu dudng dng, cdt thep mdng n h i , cdt thep ciJa c i n g n g i m , t i vpt dudng s i t . . .
• y v v * -
Hin tl 1.1: Ddng iJiin ro tren c6t thip cua h$ tttdng tiu (S&t n^n.
2. N g u y d n ly a n m o n c u a d o n g d i e n r o (Principles o f stray current corrosion)
An mdn cOa thep trong bd tdng trong s u x u i t hidn cua ddng didn rd la khac so vdl i n mdn cua thep trong mdi trudng didn ly trung tinh nhu d i t v i nudc bdi vl mdi trudng kidm bao quanti cdt thdp trong be tdng d i n tdi thg ddng hda bd mat cdt thdp.
Khdng phai d d n ^ didn rd ludn g i y ra i n mdn cdt t h ^ . S u p h i hijy cdt thdp phg thudc vao nhidu ttidng sd nhu ddng dien di vao ho$c di ra khdi cdt tt>dp, d$
Idn cua ddng dien va k h o i n g thdf gian m i nd x u i t hien, s u g i i n doan cua ddng didn rd, trang t h i i cua thep, ham luong ion cio trong bd tdng va didn trd s u i t ciJa be tdng. Elidn lucmg c i n d l khoi m i o q u i trinh an mdn se cao hcfn ndu mat dp ddng didn rd t t i i p , ndu bd tdng khdng chOa ion d o hoac ndu ddng didn rd khdng lien tue. i n h hudng ciJa mot sd thdng sd duoc trinh b i y dudi d i y .
2.1. Mit dd dong vi khoing thdi gian xuit hi$n cua ddng di$n rd
Khi g i i m mat dd ddng d i n tdi g i i m tfnh i n mdn cua ddng didn rd. Co nghidn ci^u da chl ra r i n g trong viia xi mang khdng cd cio, s u an mdn cua cdt thdp khdng x u i t hidn sau 14 t h i n g lien Uic i p ddng mot c h i i u v(X m$t do ddng 1A/m^ v i tdng dien lupng hdn 10.000A.h/m*.
Tuy nhien, chi 10 ngay vdi mat d ^ ddng 10A/nf v i didn lupng 2200A.h/nf la diJ de b i t dau cd sir an nrtdn."
NGUdl XAY DUNG s 6 THANG 9 & 10 - 2015
IV. QUAN LY Dir AN PAU TU - XAY DtfNG & QUAN LY VAN HANH CAU TRONG 0 0 THI Trong mdt thCr nghiem tuong lu vdi thdp dy ling luc
bao quanh bdi vQa, khdng thiy su an mdn ciJa cdt thdp sau 33 tuin vdi ddng DC cd mit do ddng nhd hdn 269mA/ m^ Vdi mat dd ddng td 1.08 tdi 1.61 A/mf, sy an mdn quan sit thiy trdn 50% b i mit ciJa cdt thdp sau 33 tuin. Tuy nhien vdi mit dd ddng 10.8A/m*
i n mdn lim niii Idp vQa xung quanh cdt thdp chl sau hai tuin.'^'
Khoang thcri gian ngit ddng cd inti hudng cd Id vdi cdt thdp vl didn lupng ddi hdi d l bit diu i n mdn cdt thdp ldn hdn dipn lupng ddi hdi de duy tri an mdn.
Mdt sd thi nghidm chi ra ring vdi m|t dp ddng tir 1 tdi 10A/m' inh hudng cd Ici cua sy ngit ddng chi cd ttie quan sit dupc vdi be tdng chua lupng ion do thip hdn 0.4% khdi lupng. Vdi lupng ion do cao hen, bit diu an mdn l i qui nhanh de cd the quan sat dupc inh hudng cd Ipi khi ngit ddng.""
2.2. Him luong ion do trong be tdng Sy xuit hidn him lupng nhd ion do cd th^ din tdi giim dien luung ddi hdi d l bit diu sy i n mdn. Trong trudng hpp ciu true be tdng chuia ion do thim chi vdi lupng nhd hdn muic dp d l bit diu cd su i n mdn dilm, thi sy xuit hidn cua ddng didn rd cd t h l cd npuy hilm.
Ion do trong bd tdng lam giam didn trd suit ciJa nd, tao didu kidn thuan Ipi cho su di chuyin cua ddng didn rd. Them vio dd, ddng didn rd cd thl dua ion do tdi b i mat cua thep, cd the lam tang mde dp an mdn dilm ban diu giy ra bdi Ion elo v i md rpng vung i n mdn '*'.
Khi him lupng ion cio trong be tdng ting, mat dp ddng ddi hdi cho an mdn giim dang ke. Trong sy xuit hidn cua mdt lupng nhd Ion elo 0.1 tdi 0.2 % khdi lupng, him tupng khdng du d l gay an mdn diem, vdi mit dd ddng nhd hun 1 Nm^ cd the bit diu sy an mdn.(2) Ddng (Spn rd se kich thich an mdn dilm ban diu bdi lim ctio didn thd cdt thep cao hdn didn thi cit thdp ban diu.
2.3. Di0n trd suit ciJa bi tdng
Gidn trd suit ciJa be tdng la mdt thdng s6 quan trpng ddi vdi sy i n mdn ciia cdt thdp bdi vi nd ting cudng hoac can trd su di chuyen ciia ddng di^n rd. Bd tdng cd didn trd suit eao se bao vd cdt thdp tdt hon bdi vi nd giam cudng dp cQa ddng didn rd.
3. Anh hirdng cua ddng dien rd den k i t cau (effects of stray currents on structures)
3.1. Snh hudng cua ddng diin Idn lien lien kitgiOa thip vi be tdng
Khi ddng dieri di qua be tdng tdi thep, bd tdng se din mdm di tai b i mit cua cdt thdp bdi vi sy tap trung chit kilm tai dd. Sy mdm di cua be tdng tai b i m|t ciJa cdt thdp, diJ thdng thudng chl l i mot ldp mdng, thyc td da du de phi huy tidn kit giOa edt thdp v i be tdng v i do viy lim yiu di hoae phi huy kit ciu. (5)
Cic nghidn edu da cht ra anh hudng ciHa ddng m^t chidu Idn lidn kit giiia thdp v i bd tdng. Tai mat dp ddng td 1.08 din 10.8A/m^ luc lidn kit ed t h i giim ding k l sau vii thing.(6) Nghidn cufu cung chi ra ring bd tdng bj mIm di tai bd mat ciia cdt thdp, nguydn nhin bdi sy tfeh tg cua ion natri v i ion kali tai bd mat thdp. Tai mde dd thip hon cua mat dd ddng td 0.054 tdi 1.94A/m^ Iyc lidn kit khdng giim trong 4
nim nghien cdu.
3.2. Ndt be tdng
Ndt be tdng xung quanh cdt thdp l i kit qua toA;
tidp ciia mdt sd qui trinh an mdn t^i bd mat cdt thep.
Vj tri bd mat cdt thdp bj i n mdn la vj trf m i t^i dd ding didn rd di ra khdi edt tlidp.
3.3. Phan dng kiem - siiic
Mdt sd quan sit tai trg bd tdng dd cua mpt ga tau dien da chi ra phan dng kidm - silic phi hoai bd tong va nguyen nhin l i do phan dng niy dupc tang Idn boi irih hii&ng c6a ddng didn rd. Sy ting cao phin ung kidm - silic l i do cic ion kidm tham thiu vio bd mat thep dudi tie ddng cua gradien dien thd dupe tao ra.
4. Phu'dng phap phat hl^n dong didn rd. (stray current detection methods)
4.1. Do didn thi/si/ Uiay dSi bit thudng Anh hudng cua ddng dipn rd Idn cdt thdp cua kit ciu cd the phit hidn bang do didn thi cdt thdp trong bd tdng. Su thay d6i bit thudng ciia di0n thi theo m gian td mdt vii gid ddn mdt ngiy se cho biit sy hiln didn ddng didn rd.(4)
Mdt sd tidu chuin dua ra gii trj thay dii dien thl m i tai dd khdng bj inh hudng cOa ddng <J$n rd. EN 50162, djnh nghta gii tri thay dii tdi da l i 200mVciio cdt thdp trong kit ciu bd tdng khdng cd bio v$ catlt.
fil bio vd cdt thdp khdi ddng didn rd, lEC 62128-2 quy djnh khdng cin cd bidn phip gi thdm ndu suthay doi gia trj didn thd trung islnh trong gid cao diem khdng vupt qua lOOmV.
T>)Mgtan(h)
tfinh 4.1: Vidu v^iJodi$nth^ (^Ithip theo thdi gian. Mi gian do ^ong"*^
ngiy da chl ra cic gi^ tri I6n nhit, trung binh vk nhd nh&t trong 1 giO (Ws6 do trong 1 giSy). Bien (h^ c6t Mp dddc do vdi diSn cut 6 xit Idm loai Mn trong b§ tdng. Mng so cho My (a/ ifffin r^y c6 sd tdn tai cua ddng &in ri.
Mdt sd nhi nghidn cdu sir dung v i dua ra tl mi iicm cho sy do didn thd d l xic djnli anh hudng cOa ddng dien rd trdn cdt thdp bd tdng nhu trong bing dudi'":
Bing 1: Anh hudng cOa ddng di$n rd dupc chip
nhin trin cot thip bi tdng
ThAng s6 Di^n tiie
Sl/phancLlc
Tf^ngthdithAp Thu ddng
Ktifing ion do
ton do W
HoatirOng HoatdOno
Gii trj trtn V(CSE) 0.5 0 5-l!x[Ci%Ik i<hAng dp dung 0.05
Giilrtdirli V(CSE)
-i.in
• 1 . 1 0 -1.1C)
.
(*) gia tri thinh -0.95 ddi vdi thdp du ling luc
NGUOl XAY DUNG SO THANG 9 & 10 - 2015IV- QUAN Vi DJ AN OAU JlS - XAY Dl/NG & QUAN LY VAN HANH CAU TRONG B 6 THj
c i f i L " ' * " cue SO s4nh C u / C u S O .
5. Bl^n p h i p Kiem soit d o n g d i e n d d t r o n g k e t cSu ( s t r a y c u r r e n t m i t i g a t i o n In e x i s t i n g s t r u c t u r e s ) Bi^n ph4p i<i|m s o i t d6ng dien ro ciia tSu di#n bao g6m:
- C i c h dien cho ray - LiSrl kk dien
- T h i « bj ngan dSi c h i l u ddng di#n - B4o v ^ catat
- LiSn kSt cuQng b i i t 5.1. Cich aiSn cho ray
Trong he thdng t ^ u di#n, ddng dien r6 giSm d i n g ke b6 SI/ c i c h d i ^ n giua duCftig ray v i v i t iieu n§n (Hlnh 5.1).
^ ^
Hlnti 5.1;
Hinh mlnh hgasU cich di$n cua iJU&ng
ray
5.2. Lien ket dl$n
Biy l i bi^n phap sdm nhit dutfc sd dung d i kilm soit ddng didn rd cua h$ thdng t i u didn, c i c lidn kdt giua c6t thep v i cue i m cCia ngudn didn mdt chidu tai mdi ga t i u . Bidu niy cung c i p m$t Hen kdt didn cho ddng di$n rd quay vd ngudn v i do v i y giim ddng dien rd trong bd tdng (Hlnh 5.2).
Clrc^iwng i N Q U d N | C w S m
Hinti 5.2: LiSn kk (Ji$n tai m0t ga tku 5.3. Thiit bi ngin ddi chiiu ddng dl$n Bi trinh cho sy hlnh thinh mach di^n, thiit bj ngin d i i chiiu ddng di^n cd t h l duti^ l i p d i t t^l mdi tidn kit didn. NhOng thidt bi^ niy cd dien trd eao d mdt chiiu v i di^n trd thip d chidu khic. NhCing loai thiit bj ngin d i i chidu ddng c^pn dua ra trong bing:
Bdng 2 Dang
0 1 ^ tif
DIos
Rd le 1 ^ song song v<}l dios
TtilMbl cho chinh liAJ kitfmsoit(]i$Rtt)£
D9c ( f i l m Ddi hoi nguiin xoay chi^u i i v ^ h^nti rcf le, rd le p l i i i d^n t o i n bd 66t\g di^n, c6 Vni c h ^ ngat mach
06\ hdi phdi c6 di^n thg t6i thi^u 0.4V a§
i h di^n, c6 dign trd, \k mk bi Si chdng l5i qud ddng vd si/ c6 di6n dp ngifdc Odi hdi mOt rd le nhd hdn bdi ddng dl$n chO y^u di qua dios vd nd Id mOt tfil^t bi chdng s\f co diOn dp ngutjc Cd thfi d ^ todn bO ddng di^n rd nhutig tudng ddi ak
5.4. Bao v$ cat6t:
lwl$c dd bio vd ca tdt l i mOt bidn phip cd Ipi d l
kilm soit ddng didn rd. Nhung ddng dien rd thudnp qua Idn d l cd t h l dung bidn phip kiem soit bing andt hy sinh, bdn c^nh dd he thdng ddng dien ngoii Idn trong ttiinh phd dudng nhy se tao ra i n h hudnp tdi cae thidt bj khac. Do v i y bidn ptiip bao vd catdt c6 hieu q u i gidi h^n.
5.5. Lien kit cddng bdc:
Bidn phip kiem soat ddng dipn rd thanh cdng nhit l i sd durig lien kit cudng bdc. Mot lidn k i t cudng biJlc l i lidn kit vdi m$t chinh luu kilm soit dien t h i mic ndi tidp vdi lidn kit didn (Hlnh 5.3).
C N t u c i k x i a n g a f n
Hinh S.a- Uin k§t cUOng dtifc St? dung mdt chinh luu
Idim soat diin thi.
0idn i p d i u ra ciJa chinh luu kilm soit didn t h i ty ddng cd g i i trj thay d i i phg thudc v i didn t h i do dupic gii}a kit c i u va dien cue so sinh. Niu didn t h i do dutK l i dutfng hdn g i i trj kilm soit c i i dit, didn i p d i u ra se ting Idn de cudng bCrc ddng qua dudrig ndi am nhieu hop. Vdi mdt ngudn mOt chidu mic ndi tidp vdi dudng ndi am, cdt thdp bd tdng dupe ndi vdl ci,ic am d l chac chin ring toin b$ ddng didn rd sd ducK din v i c i t thdp va sd khdng cdn ddng dipn rd trong be tdng. Chinh luu kiem soit phii 6udc tip d i t sao cho khdng cd lien kit didn gii)a cdt thdp v i eye i m khdng cd hoat dpng eua ddng didn rd, niu khdng h#
thing ray v i ndi d i t se bj i n mdn.Q
n i lifu tham khio
1 C Esvald, Moiim R^lway Traa. 2'"' ed. (Zalbonel, Die Nedertand MRT, 2002), 2 L Bertolini, M.Cars3ia, Rpedeterri 'tntluence ol stray amnS on Corrosion ol Steel m Concrefe" European Federation ot Cormsion (EFC) PiAlication, No.38' CoTTDSion of Reinfarcement in Concrete Meclianisms, Monitoring, Intiibilors and RehabitHbofl Teclwiques. eds M.Rarpacti et al, (Cambridge, UK Woodhead Publistiing U(iiited,2007):p[i.105-1ig.
3. S.CHall, IMattiew. Q.S)ieng, 'Presuessed ConoBte P^e Corrosion Reseach - A Smunary ol a Decade ol Actii/ibes" CORROSION/96, paper No 330 Houston TX, Nacei99G)
4. PGalimlierti, F.Gaddi, M.AIt)erizzJ, L,Lazzani, "Corrosion Monitonng System tor flfljifcreetf Concrete Transit Tumti" C0RROSI0tl98, paper No.643 {Houston TX.
Nace:1998).
5. E B.Rosa, B UcColum, 0.S Peters,' BeOol^ in Concrefe" Technolcvc Papers of Oie Bureau of Standaid. No 18, U.S.Department of Comnefce. GamnmenI Printing Office Wastiington. DC (1913).
6. C.E>Locl(e, "Convsm of Stee/ in Portland Cmeni Concrete: fimdament^
SfiK/ies", Corrosion effect of Stray Current and the Techniques for Evaluating Corrosion of Rebais in Concrete, ASTM S P 906, ed.V.Chak8r {West Constuhocken, PWSTM, 1996): PP5-14.
7. B.Bazzoni, M.C,Briglia, G-Cavallera, D.MeMia, F. Parara,
'Montonng ol Stray Cunent interference in the fl&nloited Concrefe Sfrudures o/theTum Underground HaSmy Loop" CORROSION/99, paper No 560 {Houston TX Nace.199g)
I N G U d l X A Y D I ; N G S O T H A N G 9 & 1 0 - 2 0 1 5