Kinh Nghiem TK-TC-SC Ket Cau BTCT Chiu Tac Dong an Mon Cua Moi Truong Bien

7/23/2019 Kinh Nghiem TK-TC-SC Ket Cau BTCT Chiu Tac Dong an Mon Cua Moi Truong Bien

1/9

Mt s Kinh nghim thit k vthi cng sa chakt cu cng trnh b tng ct thp b hhng

do tc ng n mn ca mi trng bin vit namSOME EXPERIENCE ON DESIGNING AND REPAIRING FAILED

REINFORCED CONCRETE STRUCTURES CAUSED BY CORROSION

OF VIETNAMS MARINE ENVIRONMENT

TS. Phm Vn KhoanThS. Nguyn Nam ThngKS. Nguyn ng KhoaKS. Trn NamVin KHCN Xy dng-B Xy dng

ABSTRACT: Corrosion situation causing failure in reinforced concrete structures in marine

areas in Vietnam has become very serious. Corrosion of reinforced steel damaging reinforced

concrete structures is a widespread problem. Now, there is a few constructions in coastal

atmosphere (1 to 30 km from water edge) with 50 to 60 durability, most of the others in upper

marine and estuary near marine, in the land atmosphere areas (0 to 1 km from water edge) are

corroded and damaged after from 15 to 20 years. On average, the structures durability in the

above mentioned areas is from 40 to 50 percent of designing requirements. Suffering due to

corrosion is serious, cost on repairing failed constructions caused by corrosionaccounts for 30 to70 percent of prises of making new constructions. To solve corrosive resistance and protection of

reinforced concrete constructions in marine areas in Vietnam, this article introduces some

experience on designing and repairing failed reinforced concrete structures caused by corrosionof Vietnams marine environment. This has been researched, developed matter and applied

effective for the last few years by IBST (Vietnam Institute for BuildingScience and Technology)

1. Vn n mn vhhng cng trnh b tng ct thp vng bin Vit Nam

Kt qu nghin cu v kho st ca Vin KHCN Xy dng 1, 2, 3, 4, 8cho thy cccng trnh b tng ct thp (BTCT) xy dng vng bin nc ta phi gnh chu tcng n mn mnh ca mi trng bin, trong ph bin v nguy hi nht l hintng xm thc clorua gy n mn v ph hu ct thp trong cc kt cu BTCT.

Hin nay, trn khp vng bin c nc c hng nghn cng trnh BTCT c xydng trong khong thi gian t trc nm 1990 ang b n mn v ph hu ct thpnghim trng. Trong s , c rt nhiu cng trnh cn phi sa cha ln mi c thtip tc ko di c tui th phc v. Qu trnh n mn ct thp c th bt u ngayt khi hm lng ion clorua xm nhp vo min b tng cn ct thp khng ln,khong 0,60 0,80 kg/m3 btng. Do sn phm n mn (g st) n th tch 4 6 ln sgy ng sut lm nt b tng bo v dc theo cc thanh ct thp b n mn, to iukin thun li cho s xm nhp ngy cng nhanh ion clorua vo bn trong b tng, ynhanh tc n mn v ph hu ct thp.

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2/9

Bc tranh chung v n mn v ph hu kt cu cng trnh BTCT do ion clorua nhsau :

o Cc phn kt cu BTCT nm cc vng nc ln xung v sng tp, kh quyn trnmt nc bin v mt nc sng gn bin, kh quyn trn b (cch mp nc 0 1km) chu xm thc clorua rt mnh, vi nin hn khong 1520 nm v tuthucvo cht lng b tng, v tr lm vic ca kt cu min b tng cn ct thp c th

b xm nhp ti 0,94 3,60 kg Cl-

-/m3b tng. V vy c rt nhiu kt cu b nmn v ph hu ct thp rt nghim trng sau khong 1520 nm s dng.

o Cc phn kt cu BTCT nm vng kh quyn gn b (t 1 30 km) chu xmthc clorua kh mnh, vi nin hn s dng 20 30 nm, min b tng cn ct thpc th tch t ti 0,63 1,41 kg Cl-/m3 b tng v ct thp cng b ph hu nng nsau khong 20 30 nm s dng.

o Cc phn kt cu BTCT thng xuyn b ngp trong nc bin mc d b xm thcclorrua rt mnh, min b tng cn ct thp c th tch t ti 1 5kg Cl-/m3b tng,thi gian phc v kh lu, nhng ct thp hu nhcha b hoc mi ch b n mnrt nh. Chng hn, kt qu kho st gn y ti cc phn kt cu ngp trong nc

bin v ca sng ven bin nhCng Hn Gai sau hn 100 nm, Cu b tng (cugia) Phan Thit trn 90 nm, cu PhHi Phan thit trn 85nm ch pht hinthy ct thp chm b g nh, b tng cha b nt v. i vi cc cng trnh c ninhn ngn hn, nhCng Thng v Vng Tu trn 15nm, Cng Nha Trang trn15nm, Cng Sng Hn trn 35nm, Cng Ca Cm gn 30 nm u cha phthin thy ct thp b n mn. Hin tng ny c gii thch l do lng oxy hotan trong nc bin thp nn khng kh nng oxy ho ct thp.

o Ngoi ra, cc kt qu kho st cho thy tc xm thc ion S O42-vo trong b tng

vng ngp nc v nc ln xung rt chm, v vy cha pht hin thy hintng b tng b ph hu do n mn sunf t ti cc cng trnh c nin hn 15ntrn 100 nm k trn.

Nhvy, tnh trng n mn v ph hu kt cu BTCT cc vng nc ln xung vsng tp, kh quyn trn mt nc bin v mt nc sng ven bin, kh quyn trn b (cch mp nc 0 1 km) v gn b (cch mp nc t 1 30 km) l rt ph bin vgy thit hi nghim trng cho nn kinh t nc ta. Tnh hnh thc tin t ra vn cp bch phi nghin cu v trin khai p dng cc gii php thit k v thi cng sacha cho cc kt cu b tng ct thp v ang b hhng do tc ng n mn cami trng bin nc ta.

Di y xin gii thiu mt s kinh nghim thit k v thi cng sa cha cc cngtrnh BTCT b h hng do tc ng n mn ca mi trng bin nc ta do VinKHCN Xy dng nghin cu v trin khai ng dng c hiu qu tt trong nhng

nm gn y.

2. Mt s kinh nghim thit k sa cha kt cu BTCT b hhng do n mn

Nhn chung cc kt cu BTCT khi b n mn ct thp v nt vb tng bo v uko theo s suy gim kh nng chu lc v c th mt hon ton kh nng chng nmn. Do vy, phng n thit k sa cha kt cu BTCT b hhng do n mn cnphi m bo t ng thi cc yu cu sau y:

- Kh nng chu lc ca kt cu;



3/9

- Kh nng phng chng n mn;- iu kin lm vic bnh thng

2.1. Thit k m bo kh nng kh nng chu lc ca kt cu

Cc phng n di y c th p dng i vi cc kt cu cn gia c tng cng khnng chu lc. Tuthuc vo tnh trng v mc hhng c th chn mt trong cc

phng n thit k gia c sau:a) Gia c khng m rng tit din

- p dng cho kt cu b hhng cc b;

- Din tch ct thp cn gia c xc nh theo kt qu tnh ton kh nng chu lc;

- Lin kt thp mi vi thp cbng hn hoc buc, chiu di hn hoc buc theoquy phm hin hnh.

- V d minh ho thit k sa cha cc b kt cu ct hnh 1 ;

Hnh 1. V d thit k sa cha hhng cc b kt cu ct BTCT ti cng trnh sa cha chng n mn kt cu BTCT Nh ngh L Li Sm snThanh Ho (nm 2002)

Hnh 2. V d thit k gia c c m rng tit din kt cu dm BTCT ti cng trnh sacha chng n mn kt cu BTCT Nh ngh L Li Sm snThanh Ho (nm 2002)

b) Gia c m rng tit din

Thp dc c o 16

Thp dc mi o 16

Lin kt hn gia

11

Ct BTCT c

B tng kh chng n mn

Trt hon thin XM - Plime,

M300, dy tb 60mm

M200, dy tb 20mm

thp mi v thp c(Lh= 100mm, a= 500mm)

1

2

3

4

6

Thp dc c o 165

Thp dc mi o 16

1

2

5

6

3

Mt ct 2-2

2

2

2

1

3

4

5

6

8

7



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- p dng cho kt cu b hhng ton din hoc kt cu chu lc ln

- Din tch ct thp cn gia c xc nh theo tnh ton;

- Lin kt thp hnh mi vi kt cu c thc hin bng gng kt hp vi hn;

- Lin kt thp trn mi vi thp cthc hin bng hn.

- V d thit k gia c sa cha ton din kt cu dm minh ho hnh 2.

2.2. Thit k m bo kh nng phng chng n mn lu di cho kt cu

Cn c kt qu kho st nh gi hhng thit k phng n phng chng n mnlu di cho cc kt cu b n mn v khng cn nng lc phng chng n mn(bao gm c kt cu v khng kh nng chu lc).

o Trng hp kt cu b tng ct thp b n mn

Phng n thit k chng n mn cc b : p dng cho trng hp kt cu b nmn v hhng cc b. Loi bphn b tng b nt, bong l, nhim mn xungquanh cc thanh ct thp b n mn, to khong trng ti thiu 20-30 mm lmsch g ct thp (v d xem hnh 1). Sn chng n mn ct thp. Chn v lp yphn b tng c bbng b tng hoc va mi c tnh nng tho mn yu cuthit k chng n mn bng 1, c th chn theo mt trong cc phng n sau:

- B tng chng thm;

- B tng phun kh;

- Va bm khng co;

- Va rt t chy chng n mn clorua:cho trng hp ct thp b n mn nng,min b tng cn ct thp b nhim ion Cl-trn 2,0 kg/m3, kt cu c ct thpdy, cu to phc tp, kh x ltheo cc phng n khc.

Phng n thit k chng n mn ton din:p dng cho trng hp kt cu b nmn v hhng trn din rng. Cch lm nhsau :

+ Loi bcc phn b tng b nt, bong l, b nhim mn xung quanh v dctheo cc thanh ct thp b g, to khong trng ti thiu 20-30 mm ;

+ Lm sch g ct thp v sn chng n mn ct thp ;

+ Gia c b sung thm thp mi theo (nu kt cu khng m bo kh nng chulc);

+B sung b tng hoc va mi c tnh nng tho mn yu cu thit k chng n mn bng 2, v d xem hnh 2 v 3. C th chn theo mt trong cc phng n sau:

- B tng chng thm;- B tng phun kh;

- Va bm khng co;

- Va rt t chy khng co.

- Va rt t chy chng n mn clorua:cho trng hp ct thp b n mn nng,min b tng cn ct thp b nhim ion Cl -trn 2,0 kg/m3, kt cu c ct thpdy, cu to phc tp, kh x ltheo cc phng n khc.



5/9

o Trng hp kt cu khng cn nng lc chng n mn (in hnh l cc tr nghp chiu dy b tng bo v mng, khng t mc v chng thm):

i vi kt cu c lp b tng bo v mng, khng t mc theo yu cu thit kchng n mn bng 1 th bo v mt ngoi bng lp b tng phun kh, va trtchng thm hoc sn chng thm ngn chn s xm nhp ca nc, oxy v cc

cht xm thc vo kt cu. Chiu dy lp b tng, va gia c mi c tnh ton sao cho tng cng lp b tng

bo v cv lp bo v mi t yu cu bo v ti thiu theo quy nh bng 1.C th chn mt trong cc phng n sau:

- B tng chng thm;

- B tng phun kh;

- Va bm khng co;

- Va rt t chy khng co.

- Va trt chng thm

Bng 1. Cc yu cu ti thiu v thit k bo v kt cu chng n mntrong mi trng bin 9

Kt cu lm vic trong vng

Kh quynS

T

T

Yu cu

thit kNgpnc

(4)

Ncln

xung

Trn mtnc

Trn b,

01 km cchmp nc

Gn b,

130 kmcch mp

nc

1 Mc b tng, Mpa 30 40 40 50 30 40 50 25 30 40 25 30 40

2 chng thmnc, at

8 10 10 12 8 10 12 6 10 12 6 10 12

3 Chiu dy lp b tngbo v ct thp, mm

- Kt cu ngoi tri

- Kt cu trong nh

- Nc bin

- Nc l ca sng

50

40

40

30

70

60

60

50

60

50

50

40

40

30

50

40

40

30

30

25

40

30

30

25

25

20

4 m rng vtnt, mm- Kt cu ngoi tri- Kt cu trong nh

0,1-

0,05-

0,1 0,1

0,1 0,15

0,1 0,15

5 Cu to kin trc - B mt kt cu phng, khng gy ng nc, khng gy tch hi mv bi.

- Hn ch s dng kt cu BTCT dng thanh mnh (chp, lan can chnnng)

- C kh nng tip cn ti mi v tr kim tra, sa cha.



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2.3 . m bo iu kin lm vic ca kt cu

Cn c kt qu kho st nh gi iu kin lm vic ca kt cu. Trong phng n thitk sa cha cn c bin php ngn chn hoc loi bcc yu t gy tng tc nmn v hhng nhcng trnh b qu ti, thm t, ng nc, m t ko di

3. Kinh nghim thi cng sa cha kt cu BTCT b hhng don mn

3.1 Vt liu s dng

a) B tng phun kh:Vt liu s dng ch to b tng phun kh, thnh phn btng phun kh c chn theo ch dn kthut xy dng B tng phun kh - Chdn kthut thi cng v nghim thu.

b) B tng chng thm:Vt liu ch to v thnh phn b tng chng thm chn theoCh dn kthut chn thnh phn b tng cc loi, hoc B tng Ch dn kthut thi cng x lcc vt nt, r, thm nc bng cng ngh bm p h, va ximng.

c) Va bm khng co:ly theo ti liu B tng Ch dn kthut thi cng x lccvt nt, r, thm nc bng cng ngh bm p h, va xi mng

d) Va rt t chy khng co:Chn loi va t chy khng co trn sn p ng yu cukthut ca TCXD 258:2001

e) Va t chy chng n mn clorua:p ng yu cu kthut bng 2 thnh phn cpphi va c th sb chn theo bng 3 di y.

Bng 2. Yu cu kthut ca va t chy chng n mn clorua

TT

Ch tiu kthut n vYu cut c

Phng phpkim tra

1 chy (sau 60 pht ) cm 20 Nht k Suttard2 tch nc (sau 90 pht) % 0 TCVN 3109:19933 Cng nn tui 28 ngy daN/cm

2 400 600 TCVN 3121:1979

4Tnh khng co ( bin dng tui 28 ngy)

mm/m 0,0010,05Ch dn k thut chnthnh phn b tng cc loi

5 thm ion clorua culng 1.000 AASHTOT-277

Bng 3. Thnh phn va t chy chng n mn clorua

T l pha trn vt liu, phn n v

TT

Cng

va tui28 ngy(daN/cm2)

Lng/rn Xi mng Ct Cht cch nmn

Ph giakhongsiu mn

Ph giasiu do

Phgian

1600

0,18-0,20

100 100 0,8-1,0 10-15 1,5- 2 8-10

2500

0,18-0,20

100 125 1,0-1,2 10-15 1,5- 2 8-10

3400

0,18-0,20

100 150 1,2-1,4 10-15 1,5- 2 8-10



7/9

Ghi ch:

- Trc khi s dng cn trn th nghim va t yu cu k thut bng 2;

- Xi mng s dng loi PC40 hoc PCB40;

- Ct s dng c ht t 0,30 2,0

- Cht c ch n mn: Dng ph gia canxi nitrit dng lng, nng NO2-30%

- Ph gia khong siu mn: dng silicafume hoc metacaolanh hoc dng c tnh nngtng ng;

- Ph gia siu do dng bt

- Ph gia n dng AC-89 hoc loi tng ng.

Va trt chng thm:Vt liu ch to v thnh phn cp phi chn s b theo bng 4.

Bng 4. Thnh phn va trt chng thm

T l pha trn vt liu, phn n v

TT

Mc va,

chngthm tui28 ngy

Lng/rn Ximng

CtPh giasiu do

Ph giakhong

siu mn

Phgia

plime

Ph gian

1 200, B8 0,140,16 100 180 0,2-0,3 5-10 10-15 6-8

2 300, B10 0,140,16 100 150 0,2-0,3 5-10 10-15 6-8

3 400, B12 0,140,16 100 150 0,2-0,3 5-10 10-15 6-8

4 500,B14 0,140,16 100 125 0,2-0,3 5-10 10-15 6-8

Ghi ch:

- Trc khi s dng cn trn th nghim va t yu cu mc v chng thm

- Xi mng: Loi M200,B8 v M300,B10 dng xi mng PC30 hoc PCB30; loi M400,B12M500, B14 dng xi mng PC40 hoc PCB40;

- Ct s dng c ht t 0,30 2,0

- Ph gia siu do dng nc chm ninh kt, nng cht kh 40%;

- Ph gia khong siu mn: dng silicafume hoc metacaolanh hoc dng c tnh nngtng ng;

- Ph gia plime gc latex hoc acrylic

- Ph gia n dng AC-89 hoc loi tng ng

f) Sn chng n mn ct thp:Dng sn epoxy bin tnh hoc sn chng n mn ximng plime. Yu cu sn chng g phi c kh nng chng n mn cao v linkt bm dnh tt vi c b tng v ct thp v phi p ng yu cu k thut theoASTMD 3963/D 3963M-01.

3.2 Thit b thi cng

a) Thit b phun kh:Cc thit b dng cho cng ngh phun kh b tng chn theo tiliu B tng phun kh - Ch dn kthut thi cng v nghim thu.

b) Thit b bm va lng khng co:Chn theo "B tng - Ch dn kthut x lccvt nt v thm bng cng ngh bm p hva xi mng"



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c) My nh g ct thp:Dng my nh g cm tay, in 1 pha, cng sut 550 800W, chi a loi phng v loi bt.

d) My khoan b tng:S dng my khoan in xoay p, cng sut 750 1150 W,mi khoan 18 38

e) My ct thp cm tay, in 220V, cng sut 750 - 900 W.

3.3 Qui trnh cng ngh thi cng

Qui trnh cng ngh thi cng sa cha kt cu BT&BTCT b hhng do n mn ctin hnh theo trnh t sau y:

a) Chng kt cu:Khi thc hin vic sa cha hoc gia c kt cu, c bit l ivi cc kt cu b gim yu kh nng chu lc, nht thit phi tin hnh chngkt cu v gii phng hon ton hoc mt phn kt cu cn sa cha khi trngthi chu lc. Cc kt cu chu lc ti ln c th chia ra x ltng phn thit din.Tuthuc vo ti trng tc dng ln kt cu, c th chng kt cu bng ct gc chc 80mm, hoc yu cu phi c ct chng thp kh nng chu ti vm bo an ton cho thi cng.

b) c ta b tng:c ta kthut loi b phn b tng dc theo cc thanh ct thpb g, to khong trng sao cho c th nh sch c g ton b thanh ct thp cnsa cha.

c) Ty g ct thp:Ct thp phi c nh sch g bng bn chi, chi st, my nhg cm tay hoc phun ct.

d) Khi cn c th phi phun hoc qut cht bin i g lm sch hon ton g trnb mt ct thp v bo v ct thp trong khi ch phun hoc b tng.

e) Hn hoc ni b sung ct thp:Theo bn v thit k sa cha, tin hnh hn giacng lin kt vng chc ct thp cv mi. Trong trng hp khng th hn linkt gia ct thp cv mi th c th dng t hp bu lng cng cao khoan chn

su vo phn b tng c lin kt vi thp gia cng. Bin php ny thng pdng cho cc kt cu c kch thc ln gia c bng thp hnh.

f) Qut sn bo v ct thp:Thng s dng cc loi sn chng g c ngun gc tEpoxy, xi mng v xi mng-Plime.

g) Tng cng bm dnh gia b tng mi v b tng c:Cch lm nhsau:

- c nhm b mt b tng c, ra sch b mt bng nc, ro nc;

- Qut mt lp hxi mng st vi t l N/X nhhn hoc bng 0,3 hoc hximng polime acrylic, xi mng polime styrenbutadien ln b mt b tng c(tl polime 15n 20%khi lng xi mng). Polime to dnh h latex phi png yu cu kthut theo ASTMC 1509-90;

h) Thi cng b tng v va sa cha- b tng: Thc hin theo TCVN 4453:1995. Ch s dng ct liu kch

thc Dmaxkhng vt qu 1/3 kch thc nhnht ca khi v to lin kttt vi b tng c.

- Bm va lng khng co:Thc hin theo "B tng - Ch dn kthut x lccvt nt v thm bng cng ngh bm p hva xi mng"

- Rt va t chy khng co, va t chy chng n mn clorua: Ghp cp phatng t nhbm va lng khng co, ch khc l thay bm bng rt, nn ca rtv lthot kh phi b tr pha trn cng.



9/9

- Phun b tng kh:Thc hin theo "B tng phun kh - Ch dn kthut thicng v nghim thu"

- Bo dng b tng v va:Thc hin theo TCVN 5592:1991.

4. Kt lun

Kinh nghim thit k v thi cng trnh by trn y c c kt t kt qunghin cu v ng dng ca Vin KHCN Xy dng trong nhiu nm qua c hiuqu tt trong sa cha cc cng trnh BTCT b hhng do tc ng n mn ca mitrng bin nc ta.

Kinh nghim gii thiu c th p dng lp phng n thit k v thi cng sacha chng n mn cho cc cng trnh BTCT xy dng vng bin nc ta.

Mi thng tin cn thit xin lin h:Phng nghin cu n mn v bo v cng trnh-Vin KHCN Xy dng. T:04. 754 01 89, Fax:04. 836 11 97, D:0913522602

Ti liu tham kho

1. Bo co tng kt ti 26B.03.03 "Nghin cu cc bin php bin php chng nmn b tng ct thp bo v cng trnh vng ven bin"- Vin Khoa hc KthutXy dng, H Ni, 1990.

2. Bo co tng kt ti 02.15.05.R116 "Nghin cu mt s bin php kthut vcng ngh bo v cc cng trnh xy dng di tc ng n mn ca kh hu vngven bin Vit Nam"- Vin Khoa hc Kthut Xy dng, H Ni, 1994.

3. Bo co tng kt ti c lp cp Nh nc ms 40-94TL"Nghin cu cc

iu kin k thut m bo bn lu cho kt cu b tng v b tng ct thp xydng vng ven bin Vit Nam"- Vin KHCN Xy dng, H Ni, 1999.

4. Bo co Tuyn tp hi tho:Chng n mn v bo v cc cng trnh b tng v btng ct thp vng bin Vit Nam. H Ni, 5/1999, 88 tr.

5. TCVN 2737:1995:Ti trng v tc ng. Tiu chun thit k.

6. Chdn k thut chn thnh phn b tng cc loi, Nh xut bn Xy dng, HNi, 1998.

7. Chdn k thut xy dng:B tng phun kh - chdn k thut thi cng v nghimthu; B tng- chdn k thut thi cng x lcc vt nt, rthm nc bng cngngh bm p h, va xi mng; Sa cha khe co dn chn nc- chdn thit k v

thi cng, Nh xut bn Xy dng, H Ni, 1999.

8. Ti liu tp hun k thut chng n mn v bo v cc cng trnh b tng v btng ct thp vng bin , Vin KHCN Xy dng, H Ni, 10- 2002.

9. TCXDVN d tho Kt cu BT&BTCT Yu cu bo v chng n mn trong mitrng bin Vit Nam, Vin KHCN Xy dng, H Ni, 2003.


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Kinh Nghiem TK-TC-SC Ket Cau BTCT Chiu Tac Dong an Mon Cua Moi Truong Bien