VAHBEHOMNAY
NANG CAO CHAT LUONG BE TONG CONG TRINH BIEN
PCS. TS Li Xudn Roanh, ThS. Tg Duy Long*
I Tom tat ' Be tdng cot thep cdng trinh bien ludn bi tdc ddng cda cdcyiu to tu nhien nhudong chdy, tdc dong vdt nSi gay mai mdn, va
ddp, chdn ddng, bi dn mon do tdc ddng cua mot so chat trong nudc bien, bisinh vdt tdc ddng... Be khong che chat lugng vd gia tdng do ben ca hoc cua be tdng, bdi viit ndy neu lin bdn chat cua qud trinh dn mon vd gidi phdp tich ale chong dn mdn cho be tdng viing bien.
Jit khoa: fle tdng, c6t thip, cdng trinh biin, tdc ddng, dn mdn.
Summary:
Reinforced concrete of marine structures is always attacked from environment such as flow, wave, and erosion by sea water and so on that leading to failure or reduce the strength of structures. This article will discuses the causes of erosion and alterna- tive methods to prevent the attack from outside to concrete structures.
Keywords: Reinforced, concrete, marine structures, attacked
Nhdn ngdy 16/4/2013, chinh sda ngdy 25/5/2013, chap nhdn dang ngdy 28/5/2013.
\fiet Nam c6 during bcr bi^n dai h(Ai 3.260 km trai dai tCf Mong Cdi d^n Ha Ti^n, tren do, nhufng cdng trinh quan trong da dUtfc xay diAig nham khai thac nguon Itfi Xii vung bien. NhuTng cdng trinh nay thong thUcfng dUtfc xay di/ng tijr thep tong htfp, be tdng cot thep va mot so loai vat lieu cong nghiep khac, trong do loai vat lieu be tong cot thep chiem ty le kha cao. Trong moi trifo^g nUdc man khi kho va ifdt, mot so thanh phan cilia nifdrc bien da tham nhap vao khol be tong gay ra cac phan uTng hoa hoc.
tao do xdp trong be tong, lam be tong giSm yeu kha nang chiu life. Ngoai y^u to tren, do be tdng vCing ni/drc bien con bj tac dong cua dong chay, sinh vat, vat noi... den ket cau, gay mat on dinh do ben. Bai viet trao doi cung ban doc nhuTng van de ky thuat ve ctf che an mon va gidi phap chong an mon cua vat lieu trong vung nUdrc man tac dong.
1. Cd che an mon be tdng cdt thep trong vung nUdc man Nude biln thdng thudng chiia trung binh khoing 3,5%
d e mudi hda tan gdm, ty le phan tram cic chat nhU sau: NaCl - 2,37%; MgCtj - 0,32%; MgSQ, - 0,22%; Ca50, - 0,13% cdn lai t i KCl v i KjSO,. Ngoai r a, cdn mdt sd lUOng nhd CO^ va O^ hda tan. Dp pH ciia nUdc biln vao khoing 8,0. Neu cd nhieu CQj hda tan thi pH ed the nhd hon 7,0. Trong d c chat ndi tren, cd tiem nang an mdn manh vcri be tdng la MgCt^; MgSO^ va CO^.
Co che an mdn dupe md t i nhusau:
1.1 .Tic ddng i n mon be tdng (a) Tdc Hdng ciia CO^
Khi COj tac dung vdi mdt sd thanh ptfln ciia xi mang thi sinh ra cac phin Ung hda hpc tao thanh chat mang tinh tan nhuCafHCO,)^, CaS0,.2HjQ.
(b) Tdc dong cQa MgC^ MgSO^
NhUng biln doi co bin tao ra san pham bj rUa trdi hoac lam pha vd d u true v i dp ben ciia da xi ming la: Hda tan
Bi tdng cdt thip bi dn mdn tdnudc bien vd sinh vdt biin
1.2 Tac dong I n mdn cdt t h ^ trong be tdng Theo k i t q u i nghien cUu eua nhieu tac g i i tren t h i gidi CaCI^; Ca(HC03)j; CaS0^.2HjQ trong nUde, trUong nd do tao va thdng nhat nguyen nhan an mdn cdt thep ed the tUdcylu khoang ettringine tim co sd cho sU mat on djnh kit d u . td t i e dpng sau:
6 2 HQCVI^NCANBOQUANLYXAYDUNGVADQTHI
-Thinh phin hda hpc ciia dung djch nude chiet trong be tdng, anh hudng tdi dang an mdn dilm hoac an mdn t o i n dien;
• Dd am trong be tdng cd tie dung tao mdi trudng dien ty;
- Khi nang tham thau oxy va tham gia phin Ung tao gi, phu thudc dp dac chic va d u tao 16 rong cCia be tdng;
- Nhilt dp cCia mdi trucmg ed tic dung thuc day cac q u i trinh phin Ung v i trao ddi chat.
Dudi t i c ddng eiia d c yeu td bj mdi trudng t i n cdng, b& tdng cdt thep giim dp ben thudng xly ra qua 2 giai doan nhu sau: Giai doan tfeh tu mam b§nh t i khoang thdi gian dau khi chii y l u xly ra d c qua trinh thIm thau tie nhanxam thpc tU mdi tnidng biln v i o be tdng, tieu bieu nhu ion CI-, SO^'", Mgj+, Na+, CO^... Trong giai doan niy, kit d u chua ed dau hilu hu hdng dang ke, van bao dam kha ning chju tuc v i cdng nang sU dung ban dau. Giai doan pha hi^y va phat triln hu hdng bat dIu tU thiri diem be tdng v i cdt thep bj an mdn din tdi gly nUt vd hoac mIm hda be tdng, gl cdt thep, glim khi ning chju Ipc cOa kit d u hoac cdng nang sU dung eua cdng trinh. Toan bd thdi gian ciia giai doan 1 v i giai doan 2 t i tudi thp sd dung cua cdng trinh. Thdi gian keo dai qua trinh tfeh tu mIm binh trong mdi trudng biln ed t h i la 5,10, 30 nim hoic l i u hon ttiy thudc vao mdi trUimg, chit lUong t>e tdng va cdng trinh ndi chung, gill phap thiet k l , dieu kien sU dungcdngtrinh.
Be tdng bdo vi bi ndt, cdt thip bi gidm tiet dien thi ket cau ddn ddn bl suy gidm khd ndng chiu luc Ddi vdi trudng hpp an mdn cdt thep, trong qui trinh tich tu dieu kien gi thi hau nhu kit d u chua bj hU hai. Tuy nhien sau khi bj gi, dan tdi be tdng b i o ve bj nUt, cdt thep bi giim tilt dien thi kit d u din dan bi suy giam kha nang chiu luc.
Trong giai doan gi thep thi dp pH va ndng dd Cl- la cac tic nhln xuc t i c nen khdng true t i l p i n h hudng tdi tdc dp glcot thep
An mdn be tdng do phin iimg kiem - silic hoac i n mdn sunphat neu ed xay ra cung phai qua mdt thdi gian tham thau chat x l m thpc va tich tu sin pham phin Ung d l tao Ung suit phi vd be tdng. Hu hdng dang niy, neu cd trong mdi trUdng nude biln tdi thieu cung phll sau 10-15 nam mdi cd the xay ra.
2. Gili phip thiet ke khic phuc sU an mdn be tdng bien hidn nay cd the i p dung d Vilt Nam
2.1. Yeu cau ve vSt tieu dau vio va lua chon thanh phan be tdng
(a) Chiing fogiximang diing trong moi trUifng biin Theo ket qui nghien cUu cdng bd tren the gidi, thdng qua cac tieu chuan thilt k l ma d e hiep hdi be tdng ACI, FIP, CEB, RILEM... dIu khuyen d o nen sUdung xi mang pooctang vdi ham tupng C^A = (6-9)% hoic xl mang pooclang - xi, puzolan.
Xi mang ben sunphat (C^A 5%) khdng dupe neu nhU mdt yeu d u bat bude.
ib) Cot lieu dimg cho be tdng
Cdt lieu nhd: Ve chiing loai cdt lieu nhd trong cic quy pham qudc te deu thdng nhat nen ehpn loai d t die, chic, cd nguon gdc tu nhien, dilu niy phu hpp vdi TCVN 1770-1986.
- Xet dudi gdc do ning cao tinh chdng tham cho b% tong thi theo kit qui nghien edu nen Uu tien diing loai cat cd cd hat trung phdi hpp vdi ham lupng xi mang trong be tdng de dim bio lUdng hat mjn d n thiet cho yiu d u chdng thIm.
- Cit dung trong d e cdng trinh biln v l co bin phii thda man ehi tieu ky thult cCia TCVN 1770:1986, ngoii ra d n phll d i p Ung mot so yeu cau bd sung sau:
• Nen ehpn loai d t cd M^> 2,0 cd cap phdi hat hpp 1;>' d i m b i o yeu d u chdng tham nude;
• Dd ben hda hpc dupe thd bang phuang phip nglm - sly trong dung djch MgSQ, sau 5 chu ky cd hao hut trpng tupng 18% (ap dung cho be tdng nglm trong nude bien);
• Cat khdng dUpc cd tiem nang gay phin ufng kiem - silic khi xac djnh theo cac phUdng phap thd ASTM C 289 va ASTM C277;
• Ham luong ion Cl- trong cat phai d mUe sao cho tong luong Cl- trong b l tdng 0,6 kg/m^ ddi vdi b l tdng cdt thep va 0,3 kg/m^ doi vdi be tdng cdt thep Ung suit trudc. NIn ehpn cat cd ham lupng Ct- tdi da l i 0,05% khdi lUOng eat cho be tdng cdt thep va 0,01% khdi lupng cat cho be tdng cdt thep Ung suat trudc. Chi tieu niy khdng ap dung vdi be tdng thudng khdng cdt thep.
• Ham lupng SQ^ trong cat phii d mUc sao cho tdng tUpng SOj trong be tdng 4% ham lUpng xi mang. Gidi han chi tieu naycdthedatdmUc 0,5% khdi luong d t v i n phu hpp thpc t l . - Cdt lieu Idn cho be tdng d vung bien ve nguyin tic phll thda man TCVN 1771:1987, ngoai ra phll d i p Ung cac yeu d u bd sung sau:
- Nen sU dung cdt lilu Idn cd ngudn gdc da dam cacbonat hay granit, han che dung sdi cho cac cdng trinh dudi nUde va nOi mUe nUdc thay doi;
- Kfeh thudc hat Idn nhat tdi da la 40mm va phii thda man ddng thdi cac yeu d u sau:
Q Khdng Idn hon 1 /3 chieu day bin.
o Khdng Idn hon 3/4 khoing each glUa 2 cdt thep.
o Khdng tdn hon 1 /5 khoing each nhd nhat glUa hai thanh coppha.
- Ham lucmg thoi det 15% ddi vdi cdng trinh tilp xuc vcri nudc biln;
- Dp mil mdn trong tang quay khdng Idn hon Mn-lll theo TCVN 1771:1987 (Ip dung cho phan cdng trinh chiu sdng, chiu m i l mdn);
- Cdt lilu tdn khi thU theo cic phuong phip ASTM C289,
S631 2013 Xl^lV D l ^ G & B& T H 5 3
VAHOEHOMNAY
C227 v i C586 khdng dUOc ed khi nang gly phan Ung klem- silic va kiem- cacbonat;
- Ve kha ning ben hda hpc, thi nghiem theo ASTM C88, ddi vdi cdng trinh nglm trong nUdc bien yeu d u sau 5 chu ky ngam - say 6 dung dich MgSQ, hao hut trpng lupng 18%;
- Ham lupng ion Ct- trong cot lieu Idn phai d mdc sao cho tong lupng Cl- trong be tdng khdng tdn hon 0,6 kg/m' ddi vdi be tdng cdt thep va 0,3 kg/m' ddi vdi be tdng cot thep Ung suit trude. Khdng che nguyen lieu, nen sUdung cdt lieu khdng nhilm man, Cl- 0,01%;
- Ham luong SO, nen khdng che d mUc 0,5% khdi lupng cdt lieu va tdng lupng 50^ trong be tdng 4% ham lupng xi mang.
(c) NUde cho be tong
d Viet Nam yeu cau ky thult ddi vdi nUdc do be tdng duoc quy djnh bdi TCVN 4506:1987.
(d) Cot thep
Yeu d u ky thuat cho thep cdt be tdng vung bien ve co ban ed the chap nhan theoTCVN 3101:1979, TCVN 1651-1985.
2.2. Ylu cau trong thi cong (a) Cong tde trdn vCra be tong
Bl tdng trdn deu, cd dp deo theo yeu cau thiet ke v i gldl ban thdi gian do va dam nam trong thdi gian ninh ket ban dau ciia be tdng. TrUdng hpp do be tdng trong nUde ed trdn phu gia, be tdng khdng dam thi thdi gian phu thudc vao phu gia pha trdn quyet djnh.
(b) Dam bi tong
Be tdng phai dUOc dam ky, dudi h i t khf trong vUa ra. Mat khic, chon dp sut eiia vUa hop ly de khdng sinh 16 hong chUa nude trong vUa.
(c) Ke tgo ldp bdo vi dung quy dinh
Con ke ed the dUde tim tU cic loai vat lieu khdng gay an mdn cdt thip, khdng bj tp an mdn trong mdi trUdng bien, dii khi nang bao ve cdt thep tuong duong nhU tdp be tdng bao v l v i phai bam dinh chat che vdi phan be tdng xung quanh, khdng dUpc tao nen cac dudng tham cho d e tac nhan xam thuc. Trong dieu kien Viet Nam, tot nhat t i che tao bang vUa xi ming - eat t j le 1:1,5 tdi 1:2; ty le N/X<0,4. Thdi diem thfch hpp de dijc eon ke la trudc khi lap dUng cdt thep khoing 7-10 ngiy v i can duoc bao ve trUde tie ddng eua nUde va gid bien.
(d) Cong tdc dUdng ho be tong
0 Viet Nam, quy djnh ve bao dUdng be tdng dUdc neu trong TCVN 5592:1991, thcri gian bao dudng tuy theo viJng va miia khf hlu, dao ddng ehu yeu tU 3 - 6 ngay. Sd thdi gian nay duoc xic dinh ti^ylu cau dat chi tieu dat cudng dp va sUhinh thanh tdt cau true ciia be tdng.
- Thdi gian bao dudng am theo quy djnh theo TCVN 5592:1991 theo viing khf hiu, cUdng dp bao dudng tdi ban trln 60% cudng dp 28 ngiy
- Trong thdi gian bio dudng phai cd bien phap bio v l tranh kha ning bao mdn ciia sdng bien cung nhu cic chin ddng CO hoc khac tac ddng len be mat kit d u .
- Ddi vdi b l tdng cdt thep va be tdng cdt thep u^g suit trudc tuyet ddi khdng diing nude biln d l bao dudng, ddng
thdi phll cd bien phap phdng ngCra han ehl tdi da khi nang tiep xuc vdi nUde va hat nUdc bien trong vdng 3 ngay dau bao dudng.
- PhUcmg phap b i o dudng ap dung theoTCVN 5592:1991, Khi do be tdng mat de, kinh nghiem cua mdt sd nhi thau da dung cay va re beo sen de che phCi mat be tdng sau khi dam xong. Phuong phap nay giU am cho mat be tdng kha tdt.
3. Cac giai phap huTu hieu chdng xam thUc cho b l tong vung bien
Chong xdm thuc cho be tong vung bien Can eU vao co che tac dung ed the liet ke chung theo tUng nhdm nhusau:
Nhdm T. Ning cao dp die chic va khi nang chong tham thau ciia ban than be tdng bang phu gia.
+ SU dung phu gia hda deo, sieu d6o giam ty le N/X.
-I- SU dung phu gia khoing hoat tinh tao san pham thuy hda mdi eua da xl mang va lam tang dp die chic
+ SU dung phu gia chdng tham gdc polymer.
Nhdm 2: Nang cao tinh chat bao ve cdt thep cho be tdng bang phu gia Ue che an mdn.
Nhdm 3: Bao ve trUc t i l p cdt thep trong be tdng.
-f- Son phCi cdt thep, ma cdt thep (Son huu CO gdc epoxy, vinyl chloride va polyethylene. Ma kirn loai kem, nhdm, ddng, nikel, Sdn polime hoac xi mang - potime);
+ Bao ve eatot bang ddng ngoai hoac lap dat anot hi sinh;
+ SU dung thep hpp kim, thep khdng ri lam cdt thep trong b l tdng.
Nhom 4: Bio ve tang cUdng chong tham thau mat ngoai.
+ Tam be mat bing polime;
-nSdn phu be mat;
-I-Trat, phun vUa chdng tham;
+ Bpe ket d u bang coppha kim loai.
Dp die chac eiia be tdng la mdt trong nhUng chi tieu quan trpng nhat lien quan tdi dp ben liu cua kit d u viing bien Be tdng cd khi nang chong tham thau cao se ngan d n sU chuyen djch eic tie nhan x l m thpc nhu CO^, CI-, SO/, Mg=*, 0 ^ H^O..- vao trong d u true va qua do lam cham tai ding k l qui trinh an mdn be tdng, cdt thep. Vdi be tdng thdng thudng cd ti le N/X>0,4; dUdng tupng tham thau ion Ct- d mdc trung binh la 2000-4000 coulombs. Neu mudn khdng che tupng ion Cl- tham thau d mUe thap hdn thi ti t | N/X phll giim xudng dudi 0,4. Trong trudng hpp niy thudng phii d n tdi phu gia
5 4 HQC VIEN C A N Bp QUAN LY XAV DUNG VA DO THI
hda dio. Be tdng xl ming - potime hole be tdng polime cd kha 5. Ket l u i n
nangehdng tham thau ion Cl-cao nhat, <1000 coulombs. Be Be tdng cdt thep vung nUde man ludn b j d c y e u tdmdl tdng vdi cac loai phu gia khoang hoat tinh siticafume cung cd trUdng tic ddng gly ra hU hai v l khi nang chju lUc v i tinh khi ning chdng tham thIu ion Cl- cao, dp tham thau d mUe rat tham. Viec sU dung vat tieu che tao vUa la yeu td quan trpng, thip, 100-1000 coulombs. ngoii ra d n cd d c giii phip bio ve be m i t chdng t i c ddng
xam thpc ciia mdi trUdng. Ky thuat thi cdng va dudng hd be p«i.j^^ tdng cung l i ylu to quan trpng dim bio chat luong khdi do die chac v l ddng nhat tao cho kit d u ed khi nang chdng tham tdt. »{)gi hoc Thuy lai
TAI Lieu THAM K H A O
1.CaoDuyTiin&nnk(1999):Bdocdot6ngkitdetdinghien cCru cdc diiu kien ky thudt nhdm ddm bdo dd ben Idu cho kit edu be tdng vd be tdng cot thip d vung bUn Viet Nam- Vien khoa hoc Cong nghi Xdy dUng.
2. Vien khoa hoc Cong nghi Xdy ddng (2003): Ndng cao do bin Idu cho be tong vd be tong c6t thep trong moi trUdng bien bdng sddung phu gia khodng vdt hogt tinh.
3. Hodng Pho Uyen, Nguyen Quang Phd, Nguyen Quang Binh: "Xdc dinh mdi quan he giCfa he so tham vd mdc chdng tham cua be tdng cdc cong trinh thuy lai" - De tdi nghiin ciiu khoa hoc (2009).
4. Nguyin Mgnh Phdt(2010): i^ thuyet dn mdn vd chong an mdn bi tdng - be tdng cot thep trong xdy dUng 5. Cao Duy Tiin: Hiin tugng dn mdn kit edu be tdng cot thip dudi tdc dong khihdu ven bien Viet Nam. Hdi thdo qudc tebi tong ben biin 1994.
6. AtwoodW.GandJohnsonALAiThedisir^egradoncfCement inseawater.Transacdon,fi6CE.V87,paperNol533,1924.
7. ASTI^ C33 - 93: Specification for Concrete Aggregate.
a Aflehta P.K: Durability of Concrete in marine Environment - A Review proceedings of Istlntemadonal corrferervx "PerfomarKe ofConaeteinmarineEnvironmenfSt/\ndrevisbysea.^'-65AO pubBcation,1980.
Bd ddc chdc cda bi tdng Id mdt trong nhiing chi tieu quan trong nhdt lien quan tdi do ben Idu cua ket edu vOng bien Tdm lai, d l b i o ve ho trp cho kit cau b l tdng va be tdng cdt thep vung bien, cd rat nhilu giii phap va cdng nghe khie nhau. De nang cao dp b i n liu cho be tdng, cd the i p dung cic giii phap thudc nhdm 1 v i nhdm 4 trln nguyen ly tang dp dac chic hole chdng tham d mat ngoii. Cdn de bio ve cdt thep thi d c bien phip da neu thudc c l 4 nhdm dIu true t i l p hay gian tilp dan tdi hilu q u i t i n g cudng cdt thep cho be tdng.
4. Stir dung phu gia BIFI-WP
Khi be tdng sUdung phu gia BIFI-WP se cli thien dupe tfnh cdng tic, glim lupng nUde trdn m i v i n giU dupe dd luu ddng, qua dd tam cho be tdng glim dupc 16 rdng, cudng dd tang, cudng dp cua be tdng khi sUdung phu gia da ting mdt cich ding k l (tren 20%). Khi nang chdng tham cOng dUoc tang len tU B4 d i n BB.
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