Nghien CLPU anh hipang cua cac yeu to dac tru'ng den mipc do cacbonat hoa betong
Study on effect of typical factors on carbonation of concrete
Ngay nhan bai; 12/9/2014 Ngay sira bai: 17/11/2014 Ngay chap nhan dang: 28/01/2015
Tran Van Mien, Le Van Hai Chau
T O M T A T ;
Hi?n nay, t5nh hinh nghien ci3u ve cacbonat h6a b&t6ng trong n\idc con h^n che, Tac hai cua qua trinh cacbonat hoa betong gay ra cho c6ng trinh la van de lau dai mdi the hien ro. Vi?c nghien ciiu ve cacbonat hoa betong c6 the keo dai hang chuc nam ttidng ditdng v6i tudi thp cua c6ng trinh. Bai bao nay trinh bay nghien ciiu anh hiJdng cua cac yeu to die trUng chi phoi q u i trinh cacbonat hoa betong, bao gom: nong dp khi CO^ cua moi tnl6ng, thdi gian tac dpng cua moi trifdng va ti 1? nildc/xi mang (N/X) cua betong. Kit q u i nghien cifu cho thay ti 1? N/X gay 5nh hifdng manh den qua trinh cacbonat h6a betong, va miic dp cacbonat hoa bSt6ng tang \in khi nong d6 CO^ v i thdi gian tac ddng cQa moi trifdng tang lin.
Tii khoa: Cacbonat hoa, bitong, n6ng do khi CO^
ABSTRACT
At present, there is limited research on carbonation of concrete in Vietnam. Carbonation aggression on the concrete is very slow, it takes long time and through the service life of the concrete structure. In this paper, effects of the typical factors including CO^
concentration, exposure time and W/C ratio on the carbonation of the concrete was presented. The results show that W/C ratio strongly affects to the carbonation of the concrete, and, the carbonation increases with increasing exposure time and CO^
concentration.
Keywords: Carbonation, Concrete, CO^ concentration PGS. TS. TrSn Van Mien
Bp mon V^t lieu xSy ditng - Khoa Ky thu^t xay di^ng
Trifdng Dai hoc Bach Khoa - Dai hgc Quoc Gia Thanh pho Ho Chi Minh.
D i d d n g : 0903810481 Email :[email protected] ThS. Le Van Hai Chau
BQ mon Vat lieu xay difng - Khoa Ky thuat xay dUng.
Trifdng Dgi hpc Bich Khoa - Dai hpc Quoc Gia Thinh pho Ho Chi Minh.
1 . Gidi t h i e u
Cac cau kien betong c6t t h e p (BTCT) la mot trong nhifngvat lieu xay dUng quan trong nhat du'oc sil dung tren the gidi do gia thanh li vh de dang thi cong. Khi ket cau BTCT lam v i | c trong mol tru'dng co nong do CO, cao nhU thanh thim noi 6 nhi^m va dieu kien khi hau cd lOi cho qua trinh cacbonat hoa xay ra, hien tuong cacbonat hoa betdng x3y ra lam gi5m d 6 pH cCia Idp betong bSo vi theo thdi gian, p h ^ vd \dp mhng thu dong bcio vi cot thep, thuc day phSt sinh an m o n cot t h ^ p trong BTCT va hinh thanh cac vet nut trong ket cau BTCT, hau quS \h lam gi^m tuoi tho cua ket cau BTCT [1,2].
Ngay nay, thanh pho va khu cong nghiep xuat hien ngay cang nhieu, hien tUong cacbonat hoa betong t r d thanh mot van de nghiem trong va can nghien eHu mot each chi tiet de dUa ra nhu'ng bi^n phap sCra chfla cho cdng trinh BTCT da du'a v i o sir dung cung nhif la de xuat glai phap d ^ phdng trSnh hien tUong cacbonat cho nhCmg cong trinh xay difng mdi ngay tif giai doan thiet ke [3]. & cac nifdc phat tnen, co hon mot nCra cac cdng trinh dang bl h u hai nang do bj an m d n cdt t h e p (mdt phan trong sd nay do tac ddng cua qua trinh cacbonat hda betong bSo ve cot thep), va tieu tfin hon I t i USD di siia chfla hay lam han che mu'c dp h u hai c^a nhflng ket cau BTCT nay [4, 6,8],
Hi6n nay, tinh hlnh nghien cflu ve cacbonat hda betong trong nudc cdn han che. Tac hai cua qua trinh cacbonat hda betdng gay ra cho cdng trinh la van de lau dai mdi the hien rd, cho nen viec nghien cflu, t i m hieu mat rat nhieu thdi gian, cd the k^o dai hang chuc nam tuong duong vdi tuoi tho cOa mdt cdng trinh.
B^i bao nay trinh bay n g h i i n cflu i n h hudng cfla cac yeu t d dac trflng chi phdi qua trinh cacbonat hda betdng, bao g d m : ndng dp khi COj cua mdi trfldng, thdi gian tac ddng cfla mdi trfldng va ti le nfldc/chat ket dinh (N/X) cua betdng. Nghien cflu dupc thuc hien dua tren
10.2015S||Q[i:OBSI3 7 1
3 ti le N/X khac nhau, ba ndng do khi CO, khac nhau (3000ppm, 4000ppm va SOOOppm). Mau bi t d n g sau khi dijc, thao khudn, va dudng hd tieu chuan cho d ^ n khi dat cudng dp thiet ke, duoc dua vao tfl mdi trudng giau khi CO^ mau se chiu tac ddng cua mdi trfldng nay 14; 28 va 42 ngay de danh gia mflc d d cacbonat hda xay ra ddi vdi betdng.
2. Qua trinh cacbonat hoa betdng Tac ddng cua CO, den cac san pham hydrat hda cfla xi mang dan den mdt sd thay ddi cd lien quan den vl cau trflc xi mang, lam cac ti'nh chat cda be tdng bien ddi t f l t f l
Theo S.L.Meyers [5,7], C^S thuy hda ra C^SH (CjSjH,), sau do C,SH phan fltig vdi CO^ de tao thanh CaC03 va CSH theo cac phSn flng sau:
2C^S-^6H,0 -^ C^SJii,+3Ca{0H\ (1) CjSH+CO, ^ CaCO,+CSH+HjO (2) Trong khi do, C2S phan OVig trflc tiep vdi CO, de tao ra cac s i n pham cflng loai vd^ qua trinh cacbonat hda cfla C^SH:
2 C j S + 4 H p -^ C^S^H^+Ca{0H)j (3) Trong gial doan t h f l hai cua qua trinh, CSH (hydrated monocalclum silicate) phSn flng vdi COj vh H,0, tao thanh CaCO, va silic ngam nUdc (silic vd ^ n h hinh);
CSH+CO,+H^O - . CaCO,+Si(0H), (4) Trong qua trinh nay, CaCO^ xuat hien chu y^u 6 dang thfl hlnh cua canxit, vi nd dn dmh hdn dang a rag on it.
C^c aluminate ngam nfldc (CjAH) cung bi cacbonat hda'
4CjAH-H4CO,-^CaCO3+4AI(OH),+10H,O(51 S i n ph^m hydroxit nhdm AIIOHlj cCia phan lfng tr^n tao thSnh nhdm oxit (AljOj) do nhom oxit cd ket cau dn d m h hon C^c s3n pham cua p h i n flng tren tiep tuc phan huy khi nong d d CO, tang, tao thanh KaCO,JM,0,).
Phin flng Cacbonat hda cfla Ettringite cung dflpe x^t den-
'CjA(CS)3Hj,+C,0^CaC0^+AI,0,+H,0+CaS
0 4 . 2 H , 0 (6) Mdt sd t i n h chat cfla betdng bi thay ddi
trong qua trinh cacbonat hda. Cac tfnh chat bi anh hfldng bao gfim; do ben co hoc, dd ben hda hoc, Cfldng dd b^ mat, dp rong, d d co ngdt,
Od ben cO hoc cua betdng (cudng do keo, nen va module d^n hdi) tang trong qua trinh cacbonat hda. Qua trinh cacbonat hda cdn ihm tang t i n h b^n sulphate cua betdng nhung khdng lam tang k h i nang chong an mdn trong mdi trudng nfldc axit. Dd rdng g i i m do mdt p h i n cua cac Id rdng bi lap day bdi CaCO^ hinh Ihanh trong qua trinh cacbonat hda.
Hau h^t cac nghien cuu da chl ra rang su cacbonat hda cua cac s i n pham thfly hda trong xl mang khdng 5nh hfldng tdl qua trinh cacbonat hda cua pha long trong cac Id hdng cOa betdng. Qua trinh cacbonat hda cua pha Idng trong cac Id hdng cau true betdng chi cd Ca(0H), tham gia p h i n flng-
Ca(0H),-H CO, — CaCO,+ H,0 (7)
Bang 1:Thdnh phan hda va khoang cua SlO: ^<^
: i w !5*
FcA 1 SO, M ^ CS l*.l 1 iN* ( ^ t*.l
-'• - ' - j ^ ^ ^ l ' "
I V
-*
64 1 la.i mang PCSO
1*.) i-.i 1 , ^ C«0
0-2 1 tklS t « M | C K Bang 2-Cap phdi betdng s f l d u n g trong nghien cflu
Ky hieu
M300 M400 M500
N/X
0,50 0,45 0,43
X kg 390 428 450
N Lit 193 193 193
0 kq 1183 1179 1165
C kq 576 570 549 X : X i m a n g ; N Nfldc; C: Cat, 0 Oa
Khi cd sflxuat hien cua Ca(HCOj)^ cac phan flng xay ra la:
Ca(0H),+ CO, -> CaC0j+H,0 (8) Ca(0H),+ COj-i-H^O - • Ca(HCO,), (9) Khoang CalHCO,), hinh thanh trong dung dich. vi vay cd the xay ra p h i n iJTig:
Ca(HC03),-i- Ca(OH)^ — 2CaC03-H2H,0 (10) 3. Nguyen vat lieu sfl dung va thflc n g h i e m
Nguyen vat l i i u s f l d u n g trong nghien cflu g d m : cat sdng cd modun d d Idn M^, = 2,2; da dam cd D^^ = 20mm, xl mang PC50, phu gia sieu hda deo vh nfldc sach. Thanh phan hda cfla xi mang PCSO dfloc the hien d b i n g 1,
Mau betdng sfl dung 1^ m i u lap phflong canh lOOmm, hdn hop betdng dfloc thiet ke cap phdi theo ACl 211 vdi d d sut thiet ke la SN=8 2cm, ti le nudc/chat ket dinh (N/X) la 0,43, 0,45 va 0,5. Cac mau betdng sau khi dflpe dflc trong khudn 1 ngay, thao khudn, dfldng hd trong nflde t h i m 27 ngay. C i p phdi betdng sfl dyng trong nghien cflu dupc the hien d bang 2.
Cac mau thi nghiem sau khi due va dfldng hd se dupc lau khd be mat va dat vao budng CO, de khao sat qua trinh Cacbonat hda trong 14,28va42ng^y,
4 . Ket q u i nghien cflu
4.1. Anh hudng cua ti le N/X den chieu sdu cacbonat hda betdng
Trong nghien cflu nay, cac mau betdng (BT) lap phu'dng eCia 3 cap phdi khac nhau cd l l le N/X lan luot la 0,5, 0,45 va 0,43 duOc sfl dung cho qua trinh cacbonat hda n h i m xae dinh mdi lien he gifla tl sd nay va kha nang cacbonat hda trong betdng. Ket qua nghien cflu dUoc the hien trong eac bang 3,4 va 5.
Sd lieu nghien cflu anh hfldng cua t i le N/X den ehieu sau cacbonat hda betdng d cac bang 3, 4 va 5 cho thay r i n g , khi t i sd N/X trong betdng tang t f l 0,43 den 0,5 thi kha nang BT bi cacbonat hda eung tang dang ke. Cu the la d nfing dp C02 dat SOOOppm tai thdi diem 42 ngay ij thi d d sau cacbonat hda eCia BT cd tl sfi N/X = 0,5 la 1,505mm Idn hon 57,3% so vdi 0.957mm cua cap phdi ed N/X = 0,43. 6 cac nfing dp C02 dat 3000ppm va 4000ppm thi tang lan luot la 49,5% va 54,8%. Khdng p h i i t i t ea ludng nUdc trong hon hop BT deu phue
Hlnh 1 Buong li khi CO, tac dong cacbonat hoa belong Bang 3: Anh hUdng eua tt le N/X den chllu sau cacbonat hda eiJa betdng sau 14 ngay IJ trong bufing giau khi CO,, m m
Bang 4: Anh hfldng eOa tl le N/X den ehi&j sau cacbonat hda ei!ia betdng sau 28 ng^y 0 trong bufing giau khi CO,, m m
M U M l M H ^ ^ H I ^ ^ ^ H
3 0 0 0 4 0 0 0 SOOD
0 8 9 5 0 9 . i : 1 o i :
Q'06 c e s 0 816
0.W8 0 669 0.69! Bang 5: Anh hfldng eCia ti le N/X den chilu sau cacbonat hda ei^a b i t d n g sau 42 ng^y i^
trong budng g i i u khi C O , m m
{ 4 0 0 0 1 MOO
j 1.096
! i l 5 1 I '0.5
0.865 091S 1078
0,7Jj 1 0,856 0,957 1 vy cho qua trinh hydrat hda eCia xi mang, mi se ed mdt lupng nude d u sau khi hon hop BT ninh ket, luang nudc d u nay bay hoi tao t h i n h cae Id rdng va he t h d n g mao q u i n bin trong BT.
Chinh nhflng h i t h d n g 16 rdng n i y se lam tSng t f i c q u a t r i n h k h u y e c h tan eCiakhlCO, vao trong BT, dan den quS trinh cacbonat hda c i c thSnh phan trong betdng. Chinh vl vay, mat d d 16 rfing se tang khi luong nudc tang hay ndi e i c h khic la t i so N/X tang Du xi mang \i thanh p h i n chO i yeu bj cacbonat hda trong b i t d n g nhflng m ^ '
7 2 SSiSSIiaS 10.2015
sd nghien cflu g i n dSy k h i n g dinh r i n g ham Iflpng xi mang khdng i n h hfldng nhieu den khS nang bj cacbonat hda trong betdng neu cac cap phdi cd d d sut khdng doi hay ndi c i c h khae la t l sd N/X khdng ddi. Vi vay, cd the ndi rang t i sd N/X i n h h u d n g trflc t i ^ p den d p sau cacbonat hda cua BT, Tfl sd l i i u thfle nghiem trinh bay d b i n g 3 , 4 va 5, d d sau cacbonat hda x(mm) cua BT cd quan he vdi tl sd N/X nhU sau
x = - 7 , 5 6 x N / X ^ - H 1 . 2 3 x N / X - 2 , 7 5 O D Trong d d :
X la chieu sau betdng bi cacbonat hda, m m ; N/X la ti le nfldc/xi mang sfl dung trong cap phfii BT.
4.2. Anh hudng e^a nong dd khi CO^ den ehieu sdu cacbonat hda eda bitdng
De k h i o sat 3nh hudng eua ndng dd CO, d^n d d sau eaebonat hda, n h d m lam nghien cflu da d i k h i o sat eie cdng trinh cd sfl tiep xfle thfldng xuyen va lau d i i vdi khi CO, nhfl:
mdt sd ham de xe d chung cfl, sieu thi, ham Thu Thiem...de ed c i i nhin tfing quat ve mflc d d cacbonat hda trong d i l u kien thfle te de t f l d d lap phfldng p h i p md phdng trong phdng thf nghiem. Qua k h i o sat thay dfloc r i n g , ndng d d CO, d cac ham de xe k h o i n g 600 - 900ppm, neng h i m Thu Thiem ed m$t d d lflu thdng kha cao va cd cao trinh t h i p hon mi/c nflde bien nen ndng d d CO, t r f l lai trong h i m r i t Idn. Cu the, d hai dau h i m ndng d ^ CO, v i o k h o i n g 700ppm, va mac du ed h i thdng thdng gid hoat ddng lien tue nhflng 6 doan gifla h i m ndng dd CO, van d ngfldng rat cao l i k h o i n g xap xi 1500 ppm, eao gap 3 lan so vdi nfing do CO, d mdi trfldng khdng khi btnh thfldng l i 460 p p m . De nghien cflu v f l ^ sat vdi thfle te, vfla thue day nhanh qua trinh cacbonat hda phue vu cho cdng tac khSo sat trong dieu kien thdi gian khdng cho phep thi n h d m n g h i i n cflu chon mflc nfing do CO, tdi thieu la 3000ppm cao g i p 2 l i n dieu kien thfle te va cac mflc k h i c la 4000 v i SOOOppm. Ket qua t h i nghiem dfloc the hien trong cac b i n g bieu va hinh ben dfldi.
Hinh 2: Anh hUdng cua nong do khi CO^ den mifc do cadxinat hoa BT sau 14 ngiy dtrong budng giau khICO,
K^t q u i nghi&n eflu eho t h i y r i n g , sau 14 ngay d i u tien tiep xue CO, betdng b; eaebonat hda k h i manh. Cu t h ^ , khi t i n g ndng dd CO, trong eae budng t f l 3000ppm, 4000ppm va SOOOppm thi dd s i u eaebonat hda ciia b i t d n g m i c 300; 400 v i 500 t i n g l i n IflOt l i 16,6%;
40,5% va 59,6%, Hien tflong n i y x i y ra la do sau khi d u d n g h d am va phoi r i o nflde trong 24h
thi cie Id rdng trong b i t d n g trudc khi dem tiep xue CO, cd d p am tUdng ddi khoang 60%, nhiet dp trung binh trong budng khoang 25"C day l i dieu k i i n tdi flu cho qua trinh cacbonat hda trong b i t d n g . Mat khac, trong thdi gian nay cac k h o i n g trong xi mang van dang trong qua trinh thuy hda va d i n tdi flu hda cfldng dp cho betdng nen qua trinh eaebonat hda de xay ra hon so vdi cae thdi diem sau khi b i t d n g d i hoan thien eau true v i cfldng dp. Tfl n g i y 14 t r d di, qua trinh cacbonat hda cd b i l u hien cham lai. Cu thi, d t h d i diem 28 n g i y sau khi tiep xuc CO,, cac mac betdng 300,400,500 khi n g i m trong c i c budng cd nfing dfi CO, la 3000, 4000 v i SOOOppm ed dp sau cacbonat tang l i n Ifldt 13,1%; 15,6% va 16,7%, g i i m di k h i Idn so vdi thdi diem 14 n g i y Dieu nay chflng t d r i n g , cang ve sau thi eau true betdng c i n g h o i n thien hon, eac phan t f l trong eau true BT sit lai g i n nhau hon, d i e chac hon nen kha nang xam nhap cda CO, g i i m di d i n g ke l i m eho q u i trinh cacbonat hda yeu dl. Mat khac, cac ldp b i t d n g bi cacbonat hda ban d i u tao thanh eanxicacbonat CaCO, lap dan cae e i u true rdng b i n trong b i t d n g l i m eho cau true dac sit hon, g d p p h i n g i i m k h i nang khueeh tan CO, v i o b i n trong BT.
B i n g 6: Chieu sau cacbonat hda cua b i t d n g 0 trong bufing khi CO, ed ndng do 3000ppm,
Hinh 3' Anh hudng cda ndng do khi CO, den m cacbonat hda BT sau 28 ngay li trong buong giau khi CO,
Hlnh 4: Anh hudng ciia nong da khi CO^ den mifc do cacbonat hoa BT sau 42 ngay ii trong buong giau khi CO^
Tuy n h i i n d thdi diem n g i y t h f l 4 2 , t a nhan thay rang q u i trinh cacbonat hda tang t r d lai Cu the khi ndng dp tang l i n thi d p s i u cacbonat hda cua c i c m i c b i t d n g 300,400, SOO lan Iflpt tang 37,3%; 24,6% va 30,6%, X i y ra hien tflpng nay la do khi cang ve l i u d i l , ndng dp CO, cang t i n g thi c i c Idp betdng da bi cacbonat hda khdng the e i n t r d dfloc sfl xam nhap o at cfla khi CO, khi ndng dd tang l i n vl xuat hien phSn flng hda hoc sau:
CaCOj + CO, -H H,0 — Ca(HC03)^ (tan) (12) Ca(HCO,), + Ca(OH), - - CaCO, + H O (13)
I I H M D I 04:3 OJW 0.733 1
B i n g 7: C h i l u sau eaebonat hda cua betdng il trong bufing khi CO, cd ndng d d 4000ppm,
Bing 8' C h l l u sau cacbonat hda eua betdng u trong budng khi CO, cd ndng d p SOOOppm,
C i u trflc dac sit do eae Idp b i t d n g bi cacbonat hda tao ra b; pha v d tao t h i n h canxi hydro cacbonat hda tan duoc, len Idi v i o c i c Id rdng cua c i c Idp b i n trong phan flng vdi dung djch Ca(OH), lat tao t h i n h CaCO,, Khi ndng dp CO, c i n g tang len, gardien nfing d p cang Idn lam cho khi CO, se khueeh tan sau vao b i n trong di d i n g hon. Anh hfldng cfla ndng dd CO, den k h i nang eaebonat hda b i t d n g cd the dfldc the hien thdng qua edng thflc (14), cdng thflc nay thiet lap dfla tren thflc nghiem.
x = 0,0152x[CO2]°-''" (14) Trong dd:
X la ehieu sau b i t d n g bi cacbonat hda, m m ; [CO,] la ndng d d khi CO, trong budng u, ppm,
4.3. Anh hudng cua thdi gian tiep xue den chieu sdu cacbonat hda cua betdng
Mdi l i i n h i gifla thdi gian cacbonat hda va c h i l u s i u cacbonat hda da dfldc n h i l u n h i n g h i i n cflu xay dflng thanh cdng thfle gan dung, Trong dd, edng thflc t o i n hoc hien nay dfldc sfl dung n h i l u nhat la x^ = Kc x t ' " , trong dd:
x^, e h i l u s i u cacbonat hda (mm), t: thdi gian eaebonat hda (nam), K^; he sd eaebonat hda { m m / n i m " ^ ) . De k h i o sat moi lien quan gifla t h d i gian tiep xfle vdi CO, va ehieu s i u cacbonat hda, nhdm n g h i i n cflu sfl dung 3 m i c betdng u trong c i c budng cd ndng dp CO, khac nhau, sau cac thdi diem 14,28 va 42 ngay lay ra do chieu sau eaebonat bSng phuong phap dung chat chi thi phenolphtalein, Sd lieu t h u dudc the hien trong eae b i n g 6,7 v i 8.
Vdi ndng dp khi CO, trong dieu kien t f l n h i i n thi k h i nang cacbonat hda BT khdng i n h hfldng d i n g k l theo t h d i gian. Tuy n h i i n , khi ndng do CO, d mflc eao, k h i nang cacbonat hda BT s i tang tl l i t h u i n theo t h d i gian. Cu
SSSESSDBiaSTa
Bang 9: He so cacbonat hda BT Kc, m m / n a m " '
iJnpry GasiDuagbiidi M K I O O
M K 4 0 0
M K » 0 2 564
the, d m i c 300 (N/X=0,5) c h i l u sau eaebonat hda BT tang cao nhat la 103,9% t f l t h d i diem 14 n g i y d i n 42 n g i y trong budng CO, cd ndng d d 1^ SOOOppm 6 m i e 400, 500 t h i con so dd l i 53,8% v i 41,8%. Dieu n i y l i tat nhien, vi thdi glan chtnh l i yeu to co b i n v i quyet djnh kha nSng cacbonat hda trong betdng. Theo cac nghien eflu trudc d i y , chieu sau cacbonat hda BT X dfloc chflng minh l i tl le vdi can b i c hai cua thdi gian t, v i trong n g h i i n cflu nay eung m d t l i n nfla k h i n g dinh quy l u i t tuong t f l n h f l vay, Ap dung theo cdng thflc x^ = Kc x t " ' , ta ed t i m ra dfldc hSng sd cacbonat hda Kc eCia tflng mac b i t d n g k h i c nhau theo b i n g 9, Vay, gia t n trung binh eiia h i sd cacbonat Kc c i c mac BT300,400, 500 l i n Iflpt l i 3.606; 2,899; 2,561 (mm/namW).
Tuy n h i i n , cfing thflc x^ = Ke x t ' " ed mdt han c h l l i c i c h i sd cacbonat hda Ke khdng gidng nhau d c i c m i c betdng k h i e nhau, loai xi mang k h i c nhau v i ndng dd k h i e nhau. N g h i i n eflu n i y d i d l x u i t edng thfle lien h i phii hop n h i t vdi t i t c i sfi l i i u thfle n g h i i m vdi sal sd t h i p n h i t cd t h i . Mdi lien h i gifla thdi gian va e h i l u s i u eaebonat hda BT dflpe the h i i n theo cdng thflc (15).
= 0,4726 x e ' ,0,0181 HI (15) Trong dd, x la e h i l u sau b i t d n g bj eaebonat hda (mm); t l i thdi gian fl (ngay).
5. K i t l u d n
N g h i i n cflu da k h i o s i t i n h hudng cua nhflng y l u tfi d i e trung d i n c h i l u s i u BT bi eaebonat hda, t f l k i t q u i thflc n g h i i m cd t h e rut ra mdt sd k i t l u i n sau:
• C h i l u sau BT bi eaebonat hda t i n g t i le t h u i n vdi tl sd N/X. Khi BT bi cacbonat hda, d d rong trong BT cung se g i i m do sU k i t tua cua CaCOj d i n d i n h i sfi k h u i c h t i n giam lam eho q u i trinh cacbonat dien ra c h i m hon ban dau M i t k h i c , he sd khueeh t i n trong b i t d n g cung b; thay ddi theo thdi gian va sfl thay dfii bat t h f l d n g cfla d d i m . Vi v i y , chu kj khd am trong c i c Id rdng b i t d n g eung i n h hfldng den qua trinh cacbonat hda trong betdng.
• Chieu s i u BT b\ cacbonat hda tang t i l i t h u i n vdi n d n g d d khi CO,. Khi nong d o khi CO, tang cao, sir khueeh t i n v i p h i n flng hda hpe gifla CO, v i Ca{OH), eung tang manh lam cho qua trinh eaebonat hda dien ra manh me.
• N g h i i n cflu da k i l m chflng lai mdi quan he c i n b i e hai cCia thdi gian t va c h i l u sau BT bl cacbonat hda l i t i l i thuan vdi nhau. Cdng thflc g i n dflng d u n g de ngoai suy d f l doan k h i n i n g eaebonat hda trong BT la x^ = Kc x t'^.Vlec xem x^t mdi quan he nay n h i n manh t i m quan
trpng cfla Idp betdng b i o : ve, vi c f l g i i m 'A chieu day Idp betdng b i o v i se d i n
! den g i i m '/i thdi gian pha . hijy Icp t h u d d n g b i o ve
cdt thep.
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