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 [r]
Trang 1An 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
Trang 2ÍVlci 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 ' hien \ Gi sat xuat V^t nut xuat hien
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 nhúng
noi CO nong dp CÔ rat cao, hay nhCfng ngoi nha
mat pho noi thaong xuyen chiu canh tac dUdng
Nhúng cong trinh xay dUng nay chiu sU an mon
CÔ hang gid, hang ngay trong suot cuoc đi 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 CÔ
cung khac nhau, cang it 16 rong thi cang kho
khan cho CÔ 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 nhaụ Neu be tdng qua
khd thi CÔ 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 (khiCÔ khdng the xam nhap) cung nhu khdng qua khd (khi CÔ khdng the chuyen hda thanh dung dich)
Dp am mdi trudng thuan Ipi nhat cho qua trinh
an mdn CÔ la khoang 65% [1]
Trong nude, dung dich H^CÔ la axit yeu va
se t u phan ly theo 2 budc sau : H^COj+OH ^ H C O ^ + H p (b) HCO3 + OH" ^ CÔ + HjO (c) Qua trinh nay lam giam nong dp ion OH,
do đ dp pH giam theọ De giU can bSng mdi trudng kiem nhU ban dau, mpt trong nhUng thanh phan quan trpng nhat cua be tdng la CăOH)^ 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 CaCÔ 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:
C.S^H^ + xHjCOj -^ xCaCO, +
+ySiÔ tH^O + (x - 1 + z)HjO (0 San pham euoi cung cua qua trinh eacbon
hda la canxi cacbonat đng ran va nudẹ 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 CÔ
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 CăOH)^ va C-S-H nUa, luc đ CÔ lai tiep tue tien vao sau hon cho den khi gap loi thep
Su xam nhap CÔ dien ra kha phdc tap va bao gom nhieu bUdc khae nhaụ 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:
CăOH)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 CÔ, 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 loaị 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 naỵ 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 CÔ 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 cúu 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 khdị
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
Trang 3, N 1
K =7.(10.- -0,175)
Hinh 3: xam thifc CÔ 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
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 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
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 đ, 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 CÔ cang Idn Vi the viec
ha ti le nUde/xi mang cd the giam dp tham CÔ,
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 CÔ cao hon so vdi be tdng do tai cho nhd qua trinh thi cdng dupe quy ehuan hdạ
Anh hudng eua mdi trUdng tdi qua trinh eacbon hda la do sU thay doi nong do CÔ trong khdng khi, sU thay doi nhiet dp va dp am Ket luan ve anh hudng cua nhiet đtdi kha nang xam thuc cua be tdng den nay edn nhieu mau thuan giUa cac nghien cdu tren the gidị Mdt so tac gia cho rSng nhiet dp tang lam giam kha nang tham CÔ do lam eham lai tdc dp chuyen doi t d CO, khi sang CÔ 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
đ dp xam thuc cua CÔ 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 nhaụ
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 CÔ 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
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 đ 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 CaCÔ tao thanh Idn hon
so vdi the tieh cua cac tinh the CăOH), 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
Trang 4khueeh tan dung dich axit H^CO, cung nhu cae
ion khae, do đ 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
Da phan eac phuong phap nay đi 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 tích hap phu - giai hap
phu dang nhiet đng vdi hoi nude đi hdi phai
ed them buong dieu phdi dp am de lap kem vdi
may phan tich nhiet vi saị Phan tieh hap phu
-giii hap phu dang nhiet tinh vdi hoi nUde yeu
eau cd budng dieu hda dp am nhiet đ, 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 đi 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 hdạ 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 sdcđuoctúnghien
edu anh hudng cua an mdn CÔ 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,
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 đ 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 nudẹ De lam dupe dieu nay đi 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 nhúng 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, đng thdi keo theo su bien doi cua nhieu tinh chat khae nhUcUdng dp chiu nen va dp ngam nđc 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 mdị
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 đi vdi cdng thde
tinh toan dua tren eac tinh chat cua vat lieu, mdi trudng, phuong phap thi cdng Du cd thuan Ipi
thuc nghiem nay khdng bao quat 6U0c toan bp
qua trinh hda-ly cung nhU cae anh hUdng eua xam thuc CÔ len cau true be tdng, do đ 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 đpc 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,
đ a mc a ova mat dp dan cUđng 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 đ 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 cdụ
TAI LIEU THAM KHAO
1 Verbeck G., 1958, Carbonation of hydrated Portland cement, ASTM special publication, n°205:17-36
2 Loo ỴM., Chin M.5, Tam CT, Ong K.C.G, 1994, A carbonation
prediction model for accelerated carbonation testing of concrete,
M3gazme of concrete, Voị46, n^M: 191 -200
3 Chaussadent I , 1997, Etat des lieux et reflexions sur la carbonatation du beton armẹ 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 http://www.directindustrỵcom/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 theorỵ Concrel library of J.S.C.E: 131-146
12 Bary B., Sellier Ạ, 2004, Coupled moisture-carbon dioxlde-caldum transfer model for carbonation of concretẹ Cement and Concrete Research 1859-1872
8 4 ^sitivii^:^ 09.2012