An mon be tong cot thep bai xam thyc khi eacbonie va SLP can thiet cua viec nghien CLFU ve van de nay tai Viet Nam
Pham Sdn Tung
ABSTRACT
In order to clarify the corrosion of reinforced concrete initiated by the invasion of carbon dioxide, this article will give an overview of the earbonation by examining some following areas: the causes and consequences of the earbonation, the chemical-physical process of the invasion of CO^, the factors that affect the earbonation depth, the impacts of this process on microstructure and propeties of the cementitious matrix. Besides, some important experiments and equipements which are necessary for the carbonation's research are also mentioned. In addition, throughout the whole article, the author would like to express the importance of studying the earbonation of reinforced concrete in the world in general and, in particular, in Vietnam at the present time.
The research in this domain will help to understand profoundly the problem of earbonation, so that the accurate empirical or numerical modellings predicting the earbonation rate can be provided to draw adequate measures for the earbonation prevention.
Key words : reinforced concrete,
corrosion, earbonation, earbonation depth, empirical modelling, numerical modelling, microstructure.
Pham SoTi Tiing
Ngdien cuu sinh chuyen nganh Xay dung - Institut National des Sciences Appliquees de Rennes, France
Email: son-tung.phamfi; insa-rennes.fr
Oat van de
Be tong di/gc phat minh vao cuoi the l<y 19 khi chat ket dinh la voi hot bat dau duoc thay the bdi xi nnang Portland. Sau do vao khoang nam 1870 nhOng thanh thep du'oc cho vao be tong de bu tri/ cho kha nang chiu keo rat kem ciJa loai vat lieu nay, va BTCT ra ddi. Nhd cd tinh du viet do ket hgp tinh chat chiu nen tot cua be tong va chju keo tot cua thep nen tCf sau 1900, BTCT bat dau dirge sir dung rong rai trong xay difng de thay the cho cac ket cau kim loai. Ngay nay BTCT hien dien trong hau het tat ca cac cong trinh dan dung, cong nghiep, thuy lai, quoc phdng.
Thanh phan eg ban cua be tong bao gom xi mang, ni/6c, cot lieu min (cat), cot lieu tho (da, sol). Ngoai ra tuy theo yeu cau cua cong trinh ma c6 the co them cac chat phij gia khac. Trong BTCT, be tong ngoai vai trd chiu irng suat nen con c6 mot vai tro v6 cirng quan trgng khac la bao ve cot thep khdi si/xam thgc ciia mdi trudng.
C6 nhieu tac nhan xam thuc, trong do pho bien nhat la khi CO^, khi SO^ va ion Chlorure (CI ).Tai cac thanh pho va khu cong nghiep, khiSO^ chii yeu sinh ra do ngudi dan ddt than hoac dau. Xam thgc ion CI da so chi xay ra ddi vdi cac cong trinh ven bien. Do dd co the noi rang an mdn Cacbonic la pho bien nhat doi v6i BTCT khi tinh trang d nhiem CO^da trd thanh mot van decap bach tren toan the gidi. CO^ gay tac hai khong nhdng vdi sde khde con ngudi ma con ca vdi tudi thg ciia cac cdng trinh xay ddng.Trong mdi trudng khdng cd tinh xam thgc, ket cau BTCT cd the lam viec tren 100 nam. Ngugc lai, trong mdi trudng cd tinh xam thUc COj, hien tdgng an mdn cot thep va be tdng dan tdi nift vd, pha hiiy cdng trinh chi sau 10-30 nam sir dung, tuy theo chat lUdng vat lieu sir dung va mdc dp xam thuc cua mdi trudng.
Mac duan mdn CO^ vdi BTCTda vadangdudc nghien ctru nhieu tren the gioi nhung dViet Nam cac nghien cdu ve qua trinh xam thuc nay cdn kha khiem tdn va chu yeu mdi chi di/ng d viec bao ve cdng trinh khdi su an mdn CO^ ndi rieng va cac loai xam thuc khac ndi chung thdng qua cac tieu chuan ve cudng do be tdng, mac chong tham, chiing loai xi mang, phu gia, loai cot thep, chat lugng thiet ke, thi cdng, bien phapxirii, sir dung cdng trinh..., chd chua t h u c s u d i sau vao nghien eiru ban chat, sUanh hudng ciia an mdn CO^tdi cau triic vat lieu, hay kha nang d u doan dd xam nhap ciia tac nhan xam thuc. Neu cht tuan theo mdt quy pham xay dung chung ve chong an mdn thi cd the dan tdi tinh trang bao ve cdng trinh qua mdc can thiet gay lang phi (khi mdi trudng khong thgc sd gay an mdn hay khi suxam thuc ciia CO^ cd Igi thay vi cd hai), hoac dudi mdc can thiet (danh gia thap mdc do anh hudng ciia CO^ tdi tudi thg cdng trinh). Vi vay nghien eiru sg anh hudng ciia an mdn CO^tdi cac tinh chat ciing nhu ket cau ciia vat lieu de tif dd CO kha nang phan doan chinh xac sd xam nhap ciia CO^ tuy theo mdi trudng, vat lieu, the loai cdng trinh la rat quan trong.
Bai viet trddc het se de cap tdi ban chat hda-ly va cac giai doan ciia qua trinh an mdn cacbonic, nhung khd khan trong viec ddi pho vdi hien tuong nay, ban chat cung nhu nhirng du nhugc diem ciia cac md phdng thde nghiem va md phdng so, de t d dd thay dugc trien vong nghien cdu ve van de nay tai Viet Nam.
Cor che hoa-ly cua an mon BTCT boti xam thiTc CO^
Ndng do CO^ trong khi quyen bien doi tijy theo viing. 6 ndng thdn ndi khdng khi trong lanh thi nong do CO^ ve mat the ti'ch vao khoang 0,03%. d thanh pho, con so nay CO the len tdi 1%. Vdi mire do d nhiem khdng khi ngay cang tang nhu hien nay thi tai mot so thanh pho Idn d Viet Nam nong do CO, tham chi vUdt qua
Q9.2QM^mmm^if 81
I'Vlci tnxarig ben Vung be tong dS
bl cacbonhoa Ducmg bien
Vung be tong chira cacbonhoa
Hinh 1: So do xam thuc CO,
BTCT chua bl an mon
••^'li i^^•• e ^ v V
ngoai I
"iKhi cacbonic bat I
-I dau charn ten cot thep ' Gi sat xuat V^t nut xuat hien hien \
t^^t- Z-l.
Then sjan "u benh" Tl'i6i gian "phar benh"
H'mh 2: so do qua trinh an mon CO, gay huhong BTCT 1% la chuyen binh thL/6ng, dac biet la nhQng dja diem co mat dp giao thong day dac, vi du nha:
be mat cua cac ham ehui la mpt trong nhu'ng noi CO nong dp CO^ rat cao, hay nhCfng ngoi nha mat pho noi thaong xuyen chiu canh tac dUdng.
Nhu'ng cong trinh xay dUng nay chiu sU an mon CO^ hang gid, hang ngay trong suot cuoc ddi cua chung.
Khi COj tham nhap vao BTCT thong qua cac 16 rong hinh thanh trong qua trinh do be tong.
Op rong cua be tong ngoai viec phu thupc vao vat lieu con phu thuoc vao qua trinh thi cong (dam be tong, thdi gian bao dudng am). Do do dp rong khac nhau thi SL/ xam nhap cua CO^
cung khac nhau, cang it 16 rong thi cang kho khan cho CO^ xam nhap. Neu be tong bi ngap nude hoan toan dan tdi khong con 16 r6ng thi khi CO, se khong the xam nhap vao dupc.
Sau khi xam nhap, khi CO, se hoa tan vao nUdc CO sin trong be tdng de trd thanh dung dich Axit:
C O , + H , 0 ^ H , C 0 3 (a) Moi loai BTCT luon cd mpt dp ngam nude
nhat dinh tuy theo dp am cung nhu nhiet dp moi trudng nen kha nang hda tan CO, khi thanh CO, dung djch la khac nhau. Neu be tdng qua khd thi CO^ khong the chuyen hda thanh dung djch axit.
Nhu vay, sU xam thUc CO, dien ra thuan loi
nhat khi be tdng khdng qua udt (khiCO^ khdng the xam nhap) cung nhu khdng qua khd (khi CO^ khdng the chuyen hda thanh dung dich).
Dp am mdi trudng thuan Ipi nhat cho qua trinh an mdn CO^ la khoang 65%. [1]
Trong nude, dung dich H^CO^ la axit yeu va se t u phan ly theo 2 budc sau :
H^COj+OH ^ H C O ^ + H p (b) HCO3 + OH" ^ CO^ + HjO (c) Qua trinh nay lam giam nong dp ion OH,
do dd dp pH giam theo. De giU can bSng mdi trudng kiem nhU ban dau, mpt trong nhUng thanh phan quan trpng nhat cua be tdng la Ca(OH)^ se phan ly de tao ra ion OH":
Ca{0H)jp*Ca'"+20H" (d) Ion Ca^' tao thanh se ket tua vdi CO^^ de tao
thanh eanxi cacbonat CaCO^ dong rSn:
Ca^'+CO^-^CaCO^ (e) Qua trinh tren cung xay ra tuong t u vdi mpt
thanh phan quan trpng khac cua be tdng la C-5-H (calcium silicate hydrate) thdng qua phan Lfng sau:
C.S^H^ + xHjCOj -^ xCaCO, +
+ySiO^ .tH^O + (x - 1 + z)HjO (0 San pham euoi cung cua qua trinh eacbon
hda la canxi cacbonat ddng ran va nude. Canxi cacbonat tao thanh se khien cho 16 rong cua be tdng giam di, han ehe su xam nhap cua CO, the khfva the dung dich.Toc dp xam nhap cua khi CO^
cung bj giam dang ke do nUdc tao thanh. NhUvay cd the ndi CalOH)^ va C-S-H giong nhU nhUng ngudi linh canh chien dau chong lai sUxam nhap cua COj.Tuy nhien qua tr'inh nay chi tiep tue xay ra cho den khi nao be tdng khdng cdn thanh phan Ca(OH)^ va C-S-H nUa, luc dd CO^ lai tiep tue tien vao sau hon cho den khi gap loi thep.
Su xam nhap CO^ dien ra kha phdc tap va bao gom nhieu bUdc khae nhau. Oe don gian hda nen trong 6a so tai lieu pho thdng hien nay, qua trinh nay thudng ehi duoc tdm gpn bang mdt phan Ung tong quat:
Ca(OH)j + COj -^ CaCOj + H^O (g) Tuy phan Ung nay khong hoan chinh vi nd khdng eho thay duoc toan bp ban chat su xam thue cua CO^, nhUng nd cd Ipi the la bang each don gian nhat 6a chi ra dupc sU hinh thanh canxi cacbonat va giai phdng nude,
Sau khi CO, gap Idi thep, day la lue bat dau phat trien su an mdn kim loai. Thdng thudng cot thep dupc bao ve trong mdi trudng kiem nhd eac Idp dxit va hydroxit sat tren be mat (be day khoang 10^ den 10' |am). Khi tinh kiem giam, dp pH giam dl dan tdi su khdng on dinh cua Idp bao ve nay. Khi cot thep khdng dUOc bao ve nUa se hinh thanh caegi Scit lam the tich thep tang len va gay nut, vd cdng trinh.
Nhu vay qua trinh an mdn CO^ cd the chia thanh 2 giai doan rieng biet:
- Giai doan xam thUe CO,: day la luc CO, bSt dau xam nhap vao BTCT cho tdi khi nd «an» het cae chat bao ve Ca{OH)^ va C-S-H de tdi dUOc cot thep. Day la giai doan ehiem nhieu thdi gian nhat va bat dau ngay khi cdng trinh dUOc thi cdng.
- Giai doan an mdn kim loai: sau khi CO, eham tdi loi thep thi qua trinh an mdn se xay ra rat nhanh, phu thupc ehu yeu vao chat lUpng thep cung nhu phuong phap bao ve thep.
Cd the noi giai doan xam thuc cua CO, chinh la thdi gian «u benh» edn giai doan an mdn cot thep la thdi gian «phat benh». Giai doan «u benh» chiem nhieu thdi gian va can dupc quan tam nghien cu'u nhieu nhat vi nd giup rut ra dUOc eac phuong phap bao ve cdng trinh hUu hieu trUde khi xay ra giai doan «phat benh» khi ma su pha huy cdng trinh se xay ra khdng the tranh khdi.
NhuTng kho khan trong viec doi pho vdi xam thiTc cacbonic
Dau hieu de nhan biet mpt cdng trinh BTCT bian mdn CO, la su xuat hien tren be mat be tdng nhung dUdng gi, nhUng vet nUt dpc theo cac dudng dat cot thep, nhUng cho vd cue bd, hay tham chi la sU xuat hien cua cot thep gi sau khi Idp be tdng bao ve da bi bong trde het. Cd the ndi rang an mdn cot thep la nguyen nhan hang dau gay hu hdng eho eac cdng trinh. Mot diem can neu rd la viee eham sde eac cdng trinh cho dij eo can than den may cung khdng the biet dupe ed sU xuat hien cua qua trinh eacbon hda hay khdng. Nd ehl cd the nhan biet dupe khi cd su xuat hien cua cac dau hieu tren. Lue do thudng da qua mudn va
8 2 ' ^ ' ^ ^ ' ^ ^ " ^ ^ 09.2012
Mpt cdng thUc khac cua tac gia Smolczyk [3]:
, N 1 K =7.(10.- -0,175)
Hinh 3: xam thifc CO^ lam an mon BTCT gay ha hong cong trinh phai mat rat nhieu tien va thdi gian de sda ehCfa.
Khac vdi nhUng hong hdc lien quan den loi thiet ke hay thi cdng thudng de dang 6\jqc sCra chUa va cho SLTa chUa ton tai ben lau, thi viec sda chUa nhUng sU co lien quan den an mdn cdng trinh thudng rat khd khan, Vi du, doi vdi nhung cdng trinh giao thdng nhU cau BTCT, mpt khi 6a xay ra hien tUpng an mdn thi gan nhu chi cdn each pha huy xay mdi de dam bao an toan. Do dd den thdi diem hien tai, phuong phap phdng ehdng ngan ngUa ngay trong thdi gian «u benh» de tranh giai doan «phat benh» la phuong phap hUu hieu nhat de doi phd vdi an mdn CO^. SU khd khan trong viee doi phd vdi an mdn CO, edn the hien d cho chung ta khong the ap dung mpt each may mdc kinh nghiem cua cong trinh nay vao cdng trinh khac bdi sU khac nhau ve tinh nang cdng trinh, ket cau, vat lieu, phuong phap xay dUng va sU bien doi cua tac nhan xam thuc. Chinh vi nhUng li do nay ma viec tim hieu nhdng yeu to anh hudng tdi qua trinh caebon hda eung nhu nhdng anh hudng cua qua trinh nay den eau true vat lieu la vd CLing quan trpng de t d d d cd the dua ra cae md phdng, dU doan tuoi thp cdng trinh, t d dd cd eac bien phap thiet ke, thi cdng hpp ly.
Mo phong thiTc nghiem dUa tren cac yeu to anh hUdng tdi qua trinh xam thUc cacbonic BTCT
Cae yeu td nay tuy kha da dang nhUng cd the tong ketve 3 loai ehinh :
- Anh hudng cua vat lieu sCr dung - Anh hudng cua qua trinh thi eong - Anh hudng cua mdi trudng
Doi vdi vat lieu sd dung, anh hudng Idn nhat den t d loai xi mang sCr dung, cap phdi be tdng va tl le nUde/xi mang. Dp tham cua CO, giam dang ke khi ti le xi mang trong be tong tang len. Dieu nay de hieu vi sd dung nhieu xi mang hon se khien dp chat cua vat lieu tang len gay khd khan cho CO, xam nhap. Do dd, mot so nghien cdu bang thuc nghiem eho ra md phdng dU doan dp xam nhap eua CO, dua vao thdng so mac be tdng.Ti le nudc/xi mang cang eao thi dp tham cua CO^ cang Idn. Vi the viec ha ti le nUde/xi mang cd the giam dp tham CO^, tuy nhien dieu nay cd nhUpe diem la lam cho tinh cdng tac eua be tdng giam, dong thdi ed
kha nang gay ra thieu nUdc eho cac phan Ung hydrat hda trong qua trinh hinh thanh be tdng.
Qua trinh thi cdng anh hudng tdi kha nang xam thUe eua CO, thdng qua dp dam chat, thdi gian bao dUdng am, xU ly nhiet. Ngoai ra, be tdng due sin thudng c6 kha nang ehdng xam thue CO^ cao hon so vdi be tdng do tai cho nhd qua trinh thi cdng dupe quy ehuan hda.
Anh hudng eua mdi trUdng tdi qua trinh eacbon hda la do sU thay doi nong do CO^ trong khdng khi, sU thay doi nhiet dp va dp am. Ket luan ve anh hudng cua nhiet ddtdi kha nang xam thuc cua be tdng den nay edn nhieu mau thuan giUa cac nghien cdu tren the gidi. Mdt so tac gia cho rSng nhiet dp tang lam giam kha nang tham CO^ do lam eham lai tdc dp chuyen doi t d CO, khi sang CO^ dung dich. Mdt so khac lai cho rang nhiet dp tang lam bay hPi nUdc va cae 16 rong khi tang len, khi CO, de dang xam nhap vao hon, do dd dp xam thuc cua CO^ tang len,
Oa cd rat nhieu md phdng dUa ra de d u doan tuoi thp cdng trinh dUa tren cac yeu to anh hudng neu tren. Day dupc gpi la cae md phdng thUe nghiem xuat phat t d viec thi nghiem thay doi lan luot tdng yeu to de xem xet sU anh hudng tdi mUc dp xam thuc C0_, roi dung nhUng phuong phap phan tich thong ke (ehang han nhu phuong phap hoi quy) de xac dinh mdc dp lien quan, phu thude giCfa cae yeu td va dua ra cdng thUc hpp li nhat. Tong hpp ehung lai, cae md phong nay cd the dUa ve mdt cdng thUc so hpe chung nhat dudi dang:
x=KvT
x: do sau xam thUc cua CO, t : thdi gian xam thuc
K la he so phu thude vao tinh chat be tdng, qua trinh thi cong va dae diem mdi trudng.
Hien nay cd rat nhieu eac eong thde thuc nghiem loai nay do cac tac gia khac nhau dUa ra, va di nhien ket qua eua ehung la khac nhau.
Lay vi du cdng thde eua Loo [2]:
K=300.(R,„
".{c,r'-
' • ( t w c )R^g: cudng dp chiu nen 28 ngay cua be tdng (MPa)
C^: nong dp CO^ trong khdng khi (kg.m ^) t^^^: thdi gian bao dUdng am (ngay) f: nhiet dp (°C)
N/X la ti le nudc/xi mang.Trong cdng thUc cua Smolczyk khdng xuat hien nong dp CO, bdi nd ehi ap dung eho cac cdng trinh trong mdi trUdng tU nhien. Rd rang day la mdt nhUOc diem vt cho du trong mdi trudng t u nhien nhung neu nong dp CO, thay doi thi ket qua khdng cdn chinh xac.
Lpi the cua nhUng cdng thde nay la de sd dung, khi d cdng trudng ngudi kisuchi viec nhap cae thdng so dau vao la cd the tinh ra thdi gian «u benh» ehi bang mdt phep tinh. Tuy nhien nhUng md phdng thuc nghiem nay thudng chi dung vdi mdt loai vat lieu nhat djnh, trong mdt dieu kien thi eong va mdi trUdng nhat dinh. Lay vidu, eudng dd chiu nen cao cua be tdng chua chJc da the hien that su kha nang chong tham CO, tot vi hien nay ngUdi ta ed the eho mdt sd chat phu gia de tang cudng dp chiu nen, nhung nhdng chat phu gia nay lai lam giam nong dp eua Ca(OH)j va C-S-H thdng qua cae phan Ung hoa hoc, do dd tang dd tham thau CO^. Ngoai ra, nhung md phdng thuc nghiem nay khdng tinh den qua trinh dien bien phUe tap eua an mdn cacbonic, nhU sU tao thanh cua nude va CaCO^ lam giam dan dan dp rong, thay doi the tich, hay su thay doi dien tich rieng be mat eua eau true vi mo trong be tdng, cung nhU sU thay doi dd ngam nude, kha nang khuech tan dung dich CO, va cac ion. Vi vay, nghien edu anh hudng cua an mdn CO, tdi cae tinh ehat vat lieu la rat can thiet de ed the tien tdi nhdng md phdng ehinh xac hon.
Mo phong so va nhufng anh hudng cua qua t r i n h xam thUc cacbonic t d i cau true BTCT - llnh vUc con rong m d cho nghien cdu
Cac anh hudng eua qua trinh eacbon hda tdi BTCTcd the dUOe ehia ra lam cac nhdm sau :
- Vi cau true
- Cudng dp chiu nen eua be tdng - Od ngam nUdc eua be tdng
- Cac tinh chat khueeh tan eua khi, nude, dung dich va ion
- Dp eo rut cua be tdng
Trong dd anh hudng tdi vi cau true la quan trpng nhat vi nhung anh hudng khae thudng la he qua eua sU thay doi vi cau true trong qua trinh eacbon hda be tdng. The hien rd nhat cua su thay doi VI eau true la 16 rong giam, giup can trd sUxam nhap cua CO,. Vi du dp rong cua vua xi mang khi bi eacbon hda da giam khoang 10% den 15% [4].
Nguyen nhan cua sU thay doi dp rong nay la do the tich eua eac tinh the CaCO^ tao thanh Idn hon so vdi the tieh cua cac tinh the Ca(OH), va C-S-H trong be tdng ban dau [5]. Qua trinh nay eung lam thay doi sU phan phdi to rong. Thong thudng so lupng nhUng 16 r6ng ed ban kinh nhd hpn 0,1 pm giam di (do CaCO, tao thanh bjt kin eac 16 r6ng).
NhUng dong thdi cung ed mpt sd lUpng Idn cac 16 rong cd ban kinh tren 0,1 jjmtang len, dieu nay cd the giai thieh bdi su eo rut cua be tdng gay ra
09.2012 ^l^nil^^'i 8 3
mdt so vet nut [6], hien tupng nay lai lam tang sU khueeh tan dung dich axit H^CO, cung nhu cae ion khae, do dd thuc day qua trinh an mdn.
ThUe nghiem tim hieu ve nhung anh hudng nay la rat can thiet vi chung giup eho ra eac thdng so phuc vu eho viec md phdng qua trinh tham thau cua CO^. Mdt so thi nghiem thudng dung nhu do dp rong be tdng bang phuong phap tham nude, do dp dac cua be tdng bang phuong phap tham khi, phan tich nhiet vi sai de biet duoc su bien doi cac thanh phan cua be tdng, dudng dang nhiet hap phu-giai hap phu vdi chat bi hap phu la hpi nude hoac nito de t d do cd the rut ra kha nang ngam nude, sU phan phoi 16 rong eung nhu dien tich rieng be mat cua be tdng. Ngoai ra edn ed each nghien cUu gian tiep bang mdt so phuong phap khdng pha huy nhu kiem tra sieu am hay phan tich eac tinh chat truyen nhiet, dien cua be tdng...
Da phan eac phuong phap nay ddi hdi may mde hien dai va kha ton kem. Vi du mdt may phan tieh nhiet vi sai cd gia khoang it nhat 30.000 euros, nhUng may hien dai cd the len tdi 100.000 euros [7]. Phan ti'ch hap phu - giai hap phu dang nhiet ddng vdi hoi nude ddi hdi phai ed them buong dieu phdi dp am de lap kem vdi may phan tich nhiet vi sai. Phan tieh hap phu - giii hap phu dang nhiet tinh vdi hoi nUde yeu eau cd budng dieu hda dp am nhiet dd, hien cd gia khoang 20.000 euros cho mdt budng dung tich 335 lit[8]. May phan tich hap phu - giai hap phu dang nhiet Nito cd gia it nhat 20.000 euros (hang Micromeritics, Hoa Ky), hon nUa viee sd dung thi nghiem nay edn phai kem theo nito Idng d nhiet dp -195,79°C. Ngoai ra eac may phan tich dp phan phdi 16 rong bang thuy ngan, may phan tieh eac tinh chat nhiet hoc, may do the tich that bang khi Helium, may kiem tra sieu am...
cung deu ddi hdi mdt khoan dau t u kha tdn kem.
De cd the cd dUde cac thong so tdt nhat phuc vu cho md phdng thi mpt phdng thi nghiem duoc yeu cau nen cd day du cac loai may tren, vi moi loai thi nghiem deu cd Uu, nhupe diem rieng nen chung ed the bo sung eho nhau nham cho ra ket qua tdt nhat. Vidu phan tieh hap p h u - g i a i hap phu dang nhiet vdi hoi nude thudng cht ehinh xac vdi cac vi 16 r6ng cd ban kinh t u 1 nm den 22 nm, vdi nito thudng ehi chinh xac vdi 16 rong cd ban kinh 2-32 nm, cdn phan tich vdi thuy ngan chi ehinh xae vdi cac 16 rong Idn cd ban kinh td 30 nm tdi 60 pm.
Mdt vi du khac la do dp rong bang phuong phap tham nude thudng kha nhay cam vdi nhieu sai so, do do do dp rdng vdi may do the tich that bang khi Helium cd the giup kiem tra dp rdng ehinh xac han, tham chi cd the biet duoc the tich vat chat ran trong be tdng bien doi velupng nhuthe nao trong qua trinh eacbon hda. Ben canh nhung thi nghiem tren, se la mpt Ipi the neu cd the kiem tra suthay doi cau true vi md cua be tdng bang kinh hien vi dien tu", hoac bang chup tia X.
Qua vao nhUng thdng sdcdduoctu'nghien edu anh hudng cua an mdn CO^ tdi vat lieu, dUa vao dien bien hda-ly (cac phuong trinh a, b, c, d, e, f, g), eung nhudUa tren thUe te la cae phan dng hda hoc trong qua trinh eacbon hda khdng xay ra tdc thdi ma can mdt thdi gian nhat dinh,
nhUng md phdng bang phuong phap sd ra ddi, trong do chu yeu sd dung phuong phap phan t d hUu han, phuong phap the tich hUu han hoac phuong phap sai phan hUu han. NhUng md phdng sd noi tieng nhat cd the ke den Saetta [9], phdng thi nghiem cau dudng Paris [10], lshida[11],haycuaBary[12].
Cae md phdng so nay mac du khae phuc dupe nhUng nhUOc diem cua cac md phdng thUe nghiem nhUng cd nhupc diem Idn la sU pho bien kem, da so ehi gidi han trong ndi bd mdt sd phdng thi nghiem. Tham chi cho du chung ta eo mudn mua cung khdng dUpe vi hien nay edn ehua cd mdt phan mem md phdng sd nao ve xam thuc COj dupe dua ra thi trUdng. Do dd ehung ta hoan toan cd the t u nghien cdu d Viet Nam de dua ra dUde mdt phan mem md phdng sd ve xam thuc CO, phu hpp vdi khi hau nUde ta, cac phUPng phap thi cdng cung nhu dac diem eua vat lieu trong nude. De lam dupe dieu nay ddi hdi phai cd mdt su dau tu Idn do yeu eau ve cac loai may mdc, thi nghiem 6a neu d tren. Dieu nay hoan toan cd the lam dUpe trong bdi canh nude ta dang day manh cho dau t u khoa hpe, md ra nhu'ng trung tam nghien cdu khoa hpe hien dai vdi day du cac trang thiet bi tan tien. SU dau tU nhU vay la cd loi vi nhdng may mdc tren khdng ehi phuc vu eho nghien cUu qua trinh xam thuc C0_, ma cdn dung dupe trong rat nhieu cac nghien cUu khac.
Ket luan
Qua trinh carbon hda BTCT la mpt qua trinh phUe tap, ehju anh hudng eua nhieu yeu td moi trudng, vat lieu va phuong phap thi cdng. Ban chat cua qua trinh la cae dien bien hda-ly xay ra ben trong BTCT, gay ra su bien doi vi cau true cua vat lieu, ddng thdi keo theo su bien doi cua nhieu tinh chat khae nhUcUdng dp chiu nen va dp ngam nddc cua be tdng, kha nang khuech tan eua khi va dung dich. Neu chi la be tdng don thuan thi sU xam thuc cacbonic khdng nhUng khdng cd hai ma edn cd Ipi vi nd lam tang dp chat, giam 16 rong, va do do lam tang cudng dp chiu nen.Tuy nhien, vdi BTCTthi qua trinh nay lai gay ra anh hudng xau tdi cdng trinh vi lam giam dp pH trong be tdng khien cho cot thep mat kha nang tU bao ve, gay gi va ndt vd cdng trinh. Viec sda chua nhdng hu hdng do cot thep bi an mdn bdi xam thuc cacbonic rat ton kem va mat nhieu thdi gian. Cae eong trinh dViet Nam do ehat lUpng vat lieu kem va qua trinh thi cdng thudng cd nhieu sai sdt, lai bi tac dpng them cua an mdn CO, nen tinh trang hu hong cang dien tien nhanh.ThUcte eho thay nhieu chung c u d Ha Npi va thanh pho Ho Chi Minh sau vai chuc nam sd dung da bi xudng cap tram trpng vdi nhUng ket cau trP tdi sat ben trong ed the do bat cd luc nao khien ngUdidan ludn sdng trong lo so thi giai phap duy nhat de giai quyet la chd di dan de pha di xay mdi.
Oe phdng tranh cac hau qua nghiem trpng cua an mdn BTCT do xam thUe eacbonie thi nhUng nha thiet ke can d\J doan trUdc 6fjgc mdc dp xam thuc cua CO,, t d do dua ra dUde eac bien phap bao ve thieh hpp. Rat nhieu eac md phdng thUc nghiem da ra ddi vdi cdng thde tinh toan dua tren eac tinh chat cua vat lieu, mdi trudng, phuong phap thi cdng. Du cd thuan Ipi
la don gian de sd dung nhung cac md phdng thuc nghiem nay khdng bao quat 6U0c toan bp qua trinh hda-ly cung nhU cae anh hUdng eua xam thuc CO^ len cau true be tdng, do dd eho ra ket qua sai so nhieu, khdng ap dung 6aoc rong rai bdi chung chi dung doi vdi mdt loai vat lieu nhat dinh, trong mot moi trUdng nhat dinh, vdi mpt phuong phap thi cdng nhat dinh. Oe khac phuc nhUng nhupc diem nay, thdi gian gan day eac mo phdng sd bat dau ddpc nghien cdu nhieu hon. Md phdng so dUa tren cac phuong phap phan t d hdu han, the tich hdu han hoac sai phan hUu han. Du ed nhieu Uu viet nhUng hien nay cae md phdng so edn rat hiem va khdng dupe dUa ra thi trudng, khd den duac vdi ngUdi sd dung. Chinh vi vay mae du de tai an mdn CO, khdng phai la mpt de tai mdi tren the gidi nhUng van luon la mdt de tai ndng hoi vdi nhdng nghien cdu mdi lien tue dUOc dUa ra hang nam. Vdi mUc dp d nhiem khdng khi cao, dd a mc a ova mat dp dan cUddng due, Viet Nam la mdi trudng ly tudng cho sUxamthUc CO,, gay anh hudng khdng nhd tdi chat lUpng cae cdng trinh xay dUng. Do dd viee dau tU nghien cdu ve qua trinh nay la can thiet eho du dieu nay doi hdi mpt khoan dau tU Idn de md cac phdng thi nghiem hien dai vdi day du cac phuong tien may mdc phuc vu cho nghien cdu.
TAI LIEU THAM KHAO
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6. fvliragliotta R, 2000, Modelisation des processus physico-chimiques de la carbonatation des betons prefabnques-Prise en compte des effets de parois. These de doaorat, Universite de La Rochelle 7. http://www.directindustry.com/prod/setaram/simultaneous- thermal-analyzers-lga-dta-tga-dsc-28528-419407.html 8. http://www.weisstechnik.be
9. Saetta, Schrefter, and Vitaliani, 1993, The carbonation of conaete and the mecanism of moisture, heat and carbon dioxide flow through porous material, Cement and Concrete Research: 761-772 10. Thiery M., Dangia R, Villain G., Platret G., 9-11 dec 2003, Modelisation du processus physico-chimique de carbonatation des betons, Artes desjournees des sciences de Ungenieur du reseau des laboratoires des ponts et chaussees, Dourdan, France: 403-408 n . Ishida T„ Maekawa K., 2000, Modeling of pH profile in pore water based on mass transport and chemical equilibrium theory.
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