Ăn mòn bê tông cốt thép bởi xâm thực khí cacbonic và sự cần thiết của việc nghiên cứu về vấn đề này tại Việt Nam

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<b>An mon be tong cot thep bai xam thyc khi </b>

<b>eacbonie va SLP can thiet cua viec nghien </b>

<b>CLFU ve van de nay tai Viet Nam </b>

<b>Pham Sdn Tung </b>

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

<b>Oat van de </b>

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
<i>lieu nay, va BTCT ra ddi. Nhd cd tinh du viet do ket hgp tinh chat chiu nen tot cua </i>
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.

<b>Cor che hoa-ly cua an mon BTCT boti xam thiTc CO^ </b>

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

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<i>I'Vlci tnxarig ben </i>
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

<i><b>••^'li i^^•• e ^ v V </b></i>

ngoai I

"iKhi cacbonic bat I

<i>-I dau charn ten cot thep ' </i> hien \ Gi sat xuat V^t nut xuat hien

<i><b>t^^t-</b></i>

<i><b>Z-l. </b></i>

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*Cá"+20H" (d)
Ion Cấ tao thanh se ket tua vdi CÔ^ de tao

thanh eanxi cacbonat CaCO^ dong rSn:

Cấ+CÔ-^CaCÔ (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:

<i>C.S^H^ + xHjCOj -^ xCaCO, + </i>

+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
<i>hda nen trong 6a so tai lieu pho thdng hien </i>
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
<i>don gian nhat 6a chi ra dupc sU hinh thanh </i>
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.

<b>NhuTng kho khan trong viec doi pho vdi </b>
<b>xam thiTc cacbonic </b>

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

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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 ehCfạ
Khac vdi nhUng hong hdc lien quan den loi thiet
<i>ke hay thi cdng thudng de dang 6\jqc sCra chUa </i>
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
<i>trinh giao thdng nhU cau BTCT, mpt khi 6a xay ra </i>
hien tUpng an mdn thi gan nhu chi cdn each pha
huy xay mdi de dam bao an toan. Do đ 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 CỘ 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 đ cd eac
bien phap thiet ke, thi cdng hpp lỵ

<b>Mo phong thiTc nghiem dUa tren cac </b>
<b>yeu to anh hUdng tdi qua trinh xam thUc </b>
<b>cacbonic BTCT </b>

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,„

<i>".{c,r'-</i>

' • ( 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 đ
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 CăOH)j va C-S-H
thdng qua cae phan Ung hoa hoc, do đ tang đ
tham thau CỘ 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 CaCÔ 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 đ 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.

<b>Mo phong so va nhufng anh hudng cua </b>
qua t r i n h xam thUc cacbonic t d i cau true
<b>BTCT - llnh vUc con rong m d cho nghien cdu </b>

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

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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 CỘ 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...

<i>Da phan eac phuong phap nay ddi hdi </i>

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,
<i>thi nghiem 6a neu d tren. Dieu nay hoan toan cd </i>
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.

<b>Ket luan </b>

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
<i>nhUng nha thiet ke can d\J doan trUdc 6fjgc </i>
mdc dp xam thuc cua CO,, t d do dua ra dUde
eac bien phap bao ve thieh hpp. Rat nhieu eac
<i>md phdng thUc nghiem da ra ddi vdi cdng thde </i>
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
<i>thuc nghiem nay khdng bao quat 6U0c toan bp </i>
qua trinh hda-ly cung nhU cae anh hUdng eua
xam thuc CO^ len cau true be tdng, do dd eho ra
<i>ket qua sai so nhieu, khdng ap dung 6aoc rong </i>
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.

<b>TAI LIEU THAM KHAO </b>

1. Verbeck G., 1958, Carbonation of hydrated Portland cement,
ASTM special publication, n°205:17-36

<i>2. Loo Y.M., Chin M.5, Tam CT, Ong K.C.G, 1994, A carbonation </i>

prediction model for accelerated carbonation testing of concrete,
<i>M3gazme of concrete, Voi.46, n^M: 191 -200 </i>

3. Chaussadent I , 1997, Etat des lieux et reflexions sur la
carbonatation du beton arme. Rapport du Laboratoire Central
des Fonts etChaussees Pans

4. Ngala V., Page C, Parrot L, 1995, Diffusion in cementitious
materials, further investigation of cfiloride and oxygen diffusion in
well-cured cement pastes, Cement and Concrete Research: 819-826
5. Papadakis V.G., Vayenas C.G. et Fardis M.N., 1989, A reaction
engineering approche to the problem of concrete carbonation.
AlChEJournal, 35(10): 1639-1650

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.

8.

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.
Concrel library of J.S.C.E: 131-146

12. Bary B., Sellier A., 2004, Coupled moisture-carbon
dioxlde-caldum transfer model for carbonation of concrete. Cement and
Concrete Research. 1859-1872

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