1. f Ts. NGUYN MNH PHT620.4422LY THUYT NV HNG IN MN BNG raG HP
TRONGDNG L*G L: ` H XUT BN XY DUNG V H NI- 2007
2. LI NI UTrong nhng nm gn y, Un nng cao chIt llzg v tui th cho
cc cng trnh xy dng, c bit l cc cng trnh xy dng Dng bl U khu Uc Uen
bh lun c mt ngha h Sc to ln. Nhn chung U cc cng trnh xy dng, Uc s
dng Dt liu mt cch hp l, qu trnh th cng m bo chIt lng U trong tng
trng hp c th c ch trng z cc bin php bo U thch hp th tu th s c nng
ln ng e. Trn c S , cho php khai thc c trit tnh nng S dng ca Ut liu,
gim b*t c cc ch ph u tu bSa cha hng nm s em li hiu qu hnh ,Ct10.Trn
thc t: g quy UIn nng Cao chct lng U tu th cho cc cng trnh xy dng
cng c ngha l phi gi quy nng Cao kh nng chhg n mn cho b tng U b tng
c thp trong cc k c'u xy dng. Thc cht l Un phi nm c nhng h bi u cc
qu trnh n mn, b cch khc phc nhng nhc cir71 ca lo Ut liu ny khi S
dng trong cc mi trng c tc ng n mn, t ra cc bin php ci thin tnh nng
ca Ut liu theo hng nng cao tnh bn ca chng trn C s nguyn Ut liu Sn c
trong nc o ph hp U iu hin thc tca Vit Nam.Chnh U Dy nghin cu u n mn
v chzg n mn cho b tng- b tng c thp nhm tng cng bn U ho di tu th cho
cc cng trnh xy dng ang l mt trong nhng nhim U ca tht c nhiu c quan
nghin cu trong c nc quan tm.Cuz Sch cp C UIn ny ch yt c dng lm ti
liu hctp cho cc Snh Din ngnh cng ngh Dt liu xy dng, cc hc Un-cao hc
chuyn ngnh Dt liu xy dng. Ngoi ra, c h)S dng lm ti liu tham kho cho
Cc k S, cn b k thut lm Uc trong lnh Dc xy dng ni chung.
3. Mc d r c,gng tch gp knh nghim U tham kho hin ca nhng nh
nghin cu trc, Song khng th) trnh khi nhng hn chic u ni dung ln hnh
thc. Rlt mong nhn c nhng hin ng gp qu bu ca ng nghip U ng o bn c
hcun Sch c hon thin hn trong ln ti bn Sau. Mi gp xin gi u: Phng Bin
tp sch Khoa hc K thut - Nh xu bn Xy dzg, 37 L i Hnh - H Ni. n tLO.'
04.9741954.Xn chn thnh cm n!Tc gi
4. PHN M UTNG ouAN v` NGHIN cu N MN V BIN PHP GHNG N IVIN Guo B
TNG V B TNG c THP0.1. TNH HNH NGHIN CU CHNG N MN'B TNG V B TNG CT
THP TRN TH GIIVic nghin cu v d bn ca b tng v b tng ct thp c nhiu nh
nghin cu quan tm. Theo V.M. Moskvin, Cng trnh ca Vila "nghin cu
nguyn nhn ho hc ph hu v Cc bin php nng Cao kh nng chng n mn ca cc
Cht kt dnh rn trong nc" l Cng tI"1nh nghin Cu khoa hc u tin v n mn.
Nhng nm u ca th ki XX Vin nghin cu bn cc cng trnh thu li bin ca Nga
do nhng k S xy dng ni ting nh A.R. Shuliachenko, V.I. Chamomskij
kho St nhng Cng trnh b tng v b tng ct thp ti cc hi cng chu u v nc
Nga. H i n kt lun rng bng xi mng pooclng khng th ch to b tng Ct thp
bn vng trong mi trng bin. S nng Cao c b tngChi c th mang li tui th
cho cc cng trnh n 20, 30 nm. Nhng-nghin Cu v s dng b tng v b tng ct
thp trong cc x nghip cng nghip c thc hin vo u th ki XX nh Cng trnh
nghin Cu ca E. Raba1`d [5]. c bit l Cng trnh nghin cu ca A.A.
Bajkov l cng trnh nghin cu c gi tr ln trong lnh vc ny. ng phn tch
nguyn nhn gy n mn b tng v nhng bin php p dng trong thc t Chng n mn.
Kavatosi trong cng trnh nghin cu ca mnh da ra loi ph gia tng hp Siu
do (Furylacol - Ca(N03)2) ch to va bn trong mi trng Chu tc ng Xm
thc ca cc mui gy n mn. G. Bachacp trong mt cng trnh khc cng b vic s
dng du nha thng vi hm lng 0,15% Ch to va v b tng c kh nng chng n mn
Cao [6].
5. Cc nghin cu u c nhng kt lun thng nht v nguyn nhn n mn l do
cc sn phm thu ho ca xi mng b tan vo mi tr`l1g hoc tc dng vi cc mui,
axt c trong mi tmlig to ra nhng hp cht c tnh tan mnh hoc n th tch
gy nn s ph hu kt cu ni b cc cng trnh. Cc Cng trnh nghin Cu cng nh
gi c hiu qu ca cc bin php chng n mn: Dng ph gia v c hot tnh, dng xi
mng c bit... Cc bnh lun v nguyn nhn gy n mn v gii hn bn ca kit cu b
tng v b tng ct thp dng trong cc mi tnrng ny Vn cn nhiu Vn phi tranh
Ci ko di cho n nay.0.2. TNH HNH NGHIN CU CHNG N MN B TNG V B TNG CT
THP VIT NAM ,Nhiu cng trnh xy dL_n1g bng b tng ct thp nc ta`sau mt
thi gian khai thc b n mn v ph hoi trong cc mi trng c tnh cht n mn.
iu i hi phi c cc bin php phng nga hn ch s n mn ca cc kt cu b tng v
b tng ct thp. Nh nc ta ban hnh Cc tiu Chun nh nc: TCVN 3993 : 85
"Chng n mn trong xy dng, kt cu b tng v b tng ct thp - Nguyn tc c bn
thit k"; TCVN 3994 : 85 "Chng n mn trong xy dng - Kit cu b tng V b
tng ct thp - Phn loi n mn"; TCXD 149-86 "Bo v kt cu xy dng khi b n
mn". Tuy nhin, cc Tiu chun ny cha Cp n tt c cc loi n mn, Cc mi trng
n mn, do vic p dng cng b hn ch v cha pht huy c tc dng trong thc
t.Nhn thc c tnh Cp bch ca vic chng n mn b tng v b tng Ct thp, nc ta
c nhiu c quan khoa hc nghin cu Vn ny. Cc ti nghin cu cha quan tm
nghin cu v l thuyt, m ch yu vo Cc bin php c th chng n mn cho cng
trnh kt Cu b tng v be tng ct thp. Cc nghin cu tp trung vo vic chng
n mn ca mi trng lng, ch yu l mi trg bin, v nc ta c hn 2000 km b bin
v cng ngy cng c nhiu Cng trnh quan trng c xy dng trong mi trng
bin.Trong nhng nm cui thp ki 60 c mt S nh nghin cu tin hnh kho st h
hng ca Cc kt cu b tng ct thp cng Hn Gai v Hi Phng c xy dng t nm
1914 [4], v cng a ra nhn xt l cn phi c quy nh ring cho cng tc thit
k v thi cng b tng v b tng ct6
6. thp Vng bin, phi khc vi kt Cu nm Su trong ni a. V vt liu xi
mng, khi chng ta chi c hai loi xi mng l .i mng pooclng v xi mng
pooclng puzolan, do tc gi kin ngh nn dng Xi mng pooclng puzolan
trong cng trnh bin. Nhng nghin cu u tin nhm tm ra bin php bo v Cng
trnh bin cng c tin hnh t nhng nm u ca thp ki 80, nhng sau khng c
trin khai p dng.Vin Khoa hc Cng ngh Xy dng (VKHCNXD) - B Xy dng t
nhng nm u ca thp ki 80 trin khai nghin cu lnh vc chng n mn b tng bo
v ct thp, t c mt S thnh qu nht nh theo hng S dng ph gia c ch n mn v
sn ph b mt kt Cu i vi cng trnh bin. Nm 1994, B Khoa hc Cng ngh v Mi
trng giaocho VKHCNXD nghin cu tng th cc iu kin k thut cn thit bo_V
Chng n mn v m bo bn lu cho kt cu b tng v b tng ct thp Xy dng Vng
bin ph hp vi iu kin t nhin, kinh t v x hi Vit Nam ( ti mang m S TL
- 40/94). Trn c S cc kt qu nghin cu ny, bin Son nhng chi dn k thut
cn thit cho cng tc xy dng v sa cha cng trnh lm bng b tng v b tng ct
thp Vng bin nc ta. VKHCNXD cng Xy dng tiu chun ngnh v Vn ny, nhng
cho ti nay vn cha c ban hnh [4].Vin Khoa hc Cng ngh Giao thng Vn ti
trong mt S cng trnh nghin cu v n mn b tng a ra nhiu kin phn tch tnh
hnh h hng kt cu b tng v b tng ct thp do n mn, chi ra cc nguyn nhn v
ra bin php bo V nh l: dng cc ph gia k nc (du tho mc), nc thi b giy
nhm nng cao Chc cho b tng. Tng cng bo v mt ngoi kt Cu b tng bng cc
lp son ph Chng thm nh: Sn bitum - cao Su, Sn bitum - epoxy.Vin Khoa
hc Thu li Quc gia thnh Cng trong ti S dng ph gia bentnt tng chng
thm, gim n mn ct thp i vi cc cng trnh thu li.Vo nhng nm cui ca thp
ki 90 c mt ti V cng ngh Vt liu mang m S KC-05-13A v trin khai ch to
cc t hp b tng v va c ph gia c ch n mn v bo v ct thp trong mi trng
bin Vit Nam. ti ny bao gm cc nhnh ti: Nghin cu cht c ch n mn ct
thp, nghin cu dng ph gia ZKJ, nghin Cu dng ph gia bentnt ci tin,
nghin cu dng ph gia khong SISEX, nghin cu dng SP melamin7
7. foocmaldehit sunfomat [MFS], nghin cu dng ph gia polyme
trong b tng.Mc ch a cc loi ph gia trn vo b tng l tng cng c Chc,
chng thm cho b tng, t d ngn nga hoc hn ch n mn. Cc phng php c ch n
mn, bo V catt thng phi hp vi cc phng php Chng n mn b tng, nhm bo V
chng n mn cho kt cu b tng ct thp ni chung.Lin tc trong Cc nm t 1995
n nm 2000 c nhiu hi ngh khoa hc v chng n mn cho cc cng trnh xy dng
c t chc cc c quan nh VKHCNXD, VKHCNGTVT, Trng i hc Xy dng H Ni. Tuy
nhin Cc ti u tp trung vo cng tc chng n mn cho cc cng trnh bin, cha
c mt hi ngh chnh thc no ni v n mn ca cing trnh Xy dng dn dng v cng
nghip.Ngoi nhng ti trn, cn c mt s nghin cu. khc v chng n mn v tng
tui th cho cng trnh b tng v b tng ct thp trong mi tnrng bin v Vng
Ven bin. Trc y nh nc ta c mt S cn b khoa hc sang cc nc bn (Lin X,
Ba Lan, Tip Khc, Rumani...) lm nghin cu sinh, nghin cu cc ti v n mn
b tng trong nc bin.Tuy c mt S kt qu nghin cu v b tng v b tng ct thp
trong mi trng bin nc ta nhng cho n nay vn cha trin khai p dng c
nhiu vo sn fut. Chng ta nghin cu sn xut c mt S loi xi mng bn trong
mi trng nc bin nh: Xi mng chng Sunfat, xi mng bari v c s dng mt S
Cng trnh b tng ct thp trong nc mn hoc chu nh hng ca nc mn.Nm 2000
nh nc cho php VKHCNXD thc hin mt S d n k thut, kinh t v chng n mn v
bo V cc cng trnh b tng v b tng ct thp vng bin. ti ny c trin khai
hai nm 2000 - 2001. Hy vng rng cc d n c thc hin s c thm nhiu kt qu
ng dng vo cc cng trnh xy dng.Nh vy, nc ta v ang quan tm nhiu n vn n
mn v chng n mn b tng v b tng Ct thp. Tuy nhin Vn ny mi chi tp trung
vo Cc cng trnh xy dng mi trng bin, m cha quan tm n vn chng n mn cho
cc cng trnh Xy dng cc mi trng khc.
8. Chng 1 L THUYT CHUNG V N MNB TNG V B TNG CT THP1.1. KHI NIM
V N MNB tng xi mng sau khi cng rn bao gm hai thnh phn: xi mng v b
khung ct liu. I-la thnh phn ny lin kt vi nhau to thnh mt khi vtIng
chc v c kh nng chu lc. Khi b tng S dng trong mi trng c tc ng xm
thc, nu khng c nhng bin php bo v n s b n mn. Trc ht thnh phn xi mng
b ph hoi V n d b n mn hn ct liu. Khi xi mng b n mn th lin kt gia xi
mng v`i ct liu cng b ph hoi v cui cng b tng b ph`hu. D0 vy, c th ni
n mn xi mng cng c ngha l n mn i vi b tng. 'B tng c th b n mn ho hc
c ba mi. trng S dng: Lng, rn v kh.- n mn trong mi trng lng Xy ra
khi b tng tip Xc vi nc bin, nc chua phn, nc khong, nc ngm hoc nc
thi ca cc nh my v X nghip cng nghip. Cc loi nc ny thng cha cc nhn t
c tnh cht gy n mn. n mn trong mi trng lng l loi n mn rt ph bin i vi
cc cng trnh xy dng, c bit l cc cng trnh xy dng mi trng bin, cc cng
trnh lm vic trong n , di t c nc ngm. Cc nh my, x nghip sn xut c s
dng ho cht. l i tng nghin cu c rt nhiu ngi quan tln.- n mn trong mi
trng kh xy ra khi b tng tip xc vi cc loi kh c cha tc nhn gy n mn,
thng gp cc khu vc xung quanh cc nh my c s dng v ch bin ho cht hoc
cc cng trnh c tip xc vi khng kh bin v trong mi trng kh hu Ven bin.-
n mn trong mi trng rn xy ra khi b tng tip xc vi mt S loi ho cht nh
phn khong, thuc tr su. Nhng n mn trong iu kin ny cng chi din ra khi
cc ho cht b m [3].
9. n mn b tng s nh hng ln in bn ca kt cu cng trnh b tng v b tng
ct thp. S ph hoi cng trnh Xy dng do b n mn gy nn tn tht rt ll V
kinh t. Chnh v vy, c nhiu nh khoa hc trn th gii quan tm nghin cu v
cp n cc vn c lin quan n n mn b tng v b tng ct thp trong nhiu ti liu
khoa hc.Tu theo tc dng ca cc tc nhn n mn nhiu hay t, s n mn c phn
ra ba mc : n mn mnh, n mn trung bnh v n mn yu [6]. S n mn b tng rt
a dng v din ra rt phc tp, cc qu trnh n mn ny xy ra do nhiu nguyn
nhn khc nhau. S n mn c th do tc ng xi mn ca dng chy, n mn do sinh
vt bm trn b mt kit cu btng, do thay i cc iu kin vt l hoc c s tc ng
ca hin tng din ho. Tuy nhin, nguyn nhn ch yu gy n mn b tng l do c s
thay i v mt ho hc trong thnh phn ca xi mng di tc ng ca cc hp cht ho
hc c trong mi trng. Trong thnh phn ca xi mng c cc sn phm thu ho nh
Ca(OH)2 v CSAH d ho tan, chng tan vo nc, lm cho cu trc b tng b rng,
do cng b tng gim v c th b ph hu. Mt khc, chng c tnh hot ng ho hc
mnh, d tng tc vi mt S hp cht ho hc ca mi tnrng (cc axt v mui...),
to thnh cc sn phm mi d tan trong nc ho`n hoc n th tch nhiu, gy ni
ng Sut ph hoi kt cu btng, hoc to thnh cc cht v nh hnh, ri rc, khng
c tnh cht kt dnh.Qu trnh n mn din ra mnh hay yu tu thuc vo c tnh ca
xi mng, loi v lng dng ph gia trong xi mng, nng ca cc tc nhn ho hc
trong mi trng nh hng ng k n qu trnh n mn. Cc yu t nh trng thi v
nhit mi trng, mc ti trng lm vic ca cc kt cu... cng c nh hng ng k n
mc n mn.Trong cc yu t k trn th c tnh ca x mng v c ca b tng l yu t c
nh hng rt ln n s n mn. Khi b tng b rng, s thm thu ca nc tng ln, dn
n s xm nhp ca cc tc nhn n mn, do `c iu kin tip Xc v tng tc vi cc sn
phm thu ho ca xi mng. Cc sn phm thu ho cng d b n mn th n mn b tng
cng mnh hn. Khi b tng b rng cng to iu kin cc tc nhn n mn ct thp
trong b tng.S n mn b tng v b tng ct thp rt a dng v din ra phc tp,
tuy nhin s n mn thng tn ti ba dng c bn l n mn loi I, n mn 'loi II v
n mn loi III [6]. Khi xt bn cht cc qu trnh n mn btng,10
10. ta thy rng s n mn din ra khng n thun mt loi ring bit, m qu
trnh ph hu thng quy t hai hoc c ba loi n mn, nhng mc khc nhau,
trong c mt loi n mn din ra mnh hn. S phn loi y da trn tnh vt tri ca
mi loi n mn trn. Khi nghin cu mt cch y v n mn cn phi tnh n n mn
chnh v ph ng thi dil ra. Cng vi S n mn b tng bi cc tc nhn ca mi
trng cn n mn ct thp trong lng b tng. Di y trnh by mt S vn c bn v cc
loi n mn .1.2. C TRUNG CA QU TRNH N MN1.2.1. n mn loi In mn loi I
din ra do s ho tan ca cc sn phm thu ho ca xi mng (ch yu l cc
hydroxyt canxi v aluminat canxi ngm nc) b ho tan, c bit hydroxyt
canxi tan mnh nht, do loi n mn ny cn c gi l qu trnh kh kim. xi mng
c c trng l kt cu khng ng nht v c cu trc v cc thuc tnh ca chng,
trong c thuc tnh b ho tan. Khi hydroxyt canxi tan vo dung dch lm
dch chuyn trng thi cn bng ca cc sn phm thu ho trong h xi mng - nc.
ho tan ca hydroxyt canxi trong nc nhit d 20C l l,18g/I, tnh theo
lng CaO. Theo Moskvin s c mt ca cc mui trong dung dch c nh hng ang
k n tnh ho tan ca hydroxyt canxi. Khi cc mui cha mt trong cc ion O
hoc Hi th ho tan gim i, cn khi cc mui Cha cc ion khc loi th s lm
tng ho tan ca hydroxyt canxi. iu ny c khng nh, khi tng NaCl hoc
KCl, tan ca hydroxyt canxi tng ln r rt.S ho tan ca cc sn phm thu ho
va lm kt cu xi mng b rng Va lm mt n nh cc sn phm thu ho khc. Theo
Ivanov [6], 2CaO. SiO2.aq l km bn nht trong cc Silicat canxi ngm nc
c to ra do s thu ho xi mng. N chi bn Vtng trong dung dch bo ho Vi.
3Ca0.2Si02. aq l khong c bn mi trng c nng hyroxit canxi 2 1,1 g/l.
Hp cht CaO.SiOZ.aq bn trong cc dung dch c nng hydroxyt canxi thp
hn, nhng n chi hon ton bn Vftng trong dung dch c Cco 2 0,05 g/l (
pH = ll). Khi nng ca hydroxyt canxi nh hn gi tr11
11. ny th cc sn phm s phn hu v tch ra Ca(0H)2, hydroxyt canxi
mi tch ra li tip tc tan, lm cho kt cu gim chu lc. Niu gim nng
hydroxyt canxi xung di 0,05 g/l th Cc Silicat canxi hon ton b phn
hu, kt cu btng hon ton b ph hoi.Trong S cc aluminat canxi ngm nc,
loi km bn nht l 4Ca0. Al2O3.l9H20. Ngc li, 2Ca0.Al2O3.H20 c ho tan
nh nht. Gii hn bn ca nhm cc khong ny nh sau:Loi khong: . - Nng
Ca(OH)2: 2Cao.A1,o,.H,o O, 17 - O,315g/l 3Cao.A1,o,.6H,o
0,315-l,l5g/l 4Cao.Al,.o,.19H,O l,l5g/lT y, c th a ra nhn Xt rng cc
sn phm Silicat canxi ngln nc v aluminat canxi ngm nc c hm lng oxyt
canxi thp bn vtlg hn. Tuy nhin, cc sn phm thu ho thng tn ti cc dng
c bn l 3CaO. 2Si02.nH20 v 3CaO.Al203.6H2O. l nguyn nhn dn n s mt n
nh ca xi mng khi nng ca hyroxyt canxi gim i, hay ni cch khc l hin
tng n mn ho tan din ra. HVn quan trng ca n mn loi I l tc ho tan. V
vy, nh gi cng ca n mn loi I, cc nh khoa hc a ra bin php xc nh tc ho
tan. Phng php c nhiu nh khoa hc thc hin l phng php nghin nh xi mng
ri X l bng lng nc d hoc dng nc thay i. c kt qu xc nh gn vi iu kin
lm vic ca cng trnh b tng v b tng ct thp, ngi ta tin hnh bng cch cho
nc thm qua mu b tng th nghim v di ra b mt mu.Cc yil tinh hng ti qu
trnh n mn loi I Thnh phn khong. ca xi mng pooclng gy nh hng ln nht
ti tc n mn v tnh lin tc ca qu trnh n mn loi I. Khi xi mng c nhiu
khong C38 v CaO t do, s ho tan cng mnh. Mt khc, vi cu trc ca clinke
xi mng cng nh hng ti s n mn v chng c nh hng ti qu trnh thu ho ca xi
mng. - Loi ph ga cho vo x mng rlh hng ng k ti tcc n mn loi I. Khi
dng xi mng pooclng pha ct nghin, trn trepen v trn puzolan-ct12
12. nghin th kh nng b n mn nh hn So vi xi mng pooclng. Khi dng
xi mng pooclng - puzolan c hiu qu ln nht, mt khc n cn nng cao tnh
chng thm V.A. Kind [5] th nghim v xc nh c lng hyroxyt canxi trong
Xi mng c ch to t cc loi xi mng khc nhau qua 28 ngy m ng cng nh
Sau:Loi xi mng Lng CaO, % Xi mng pooclng khng ph gia 9,37 70% Ximng
pooclng + 30% trepen 2,92 60% Ximng pooclng + 40% trepen 1,5 50%
ximng pooclng + 50% trepen 0,85Cc yit ti cng ngh khc nh thi gian ng
cng, nhit ca mi trng bo dng v nhit ca mi trng tip xc vi btng c tc
ng ln n tc ho tan ca Ca(0H)2,` v cc nhn t ny nh hng ti s to thnh cc
,sn phm thu ho, cng nh s hnh thnh_cu trc ca btng. Thi gian rn chc
cng di, nhit bo dng cng cao th kh nng chng n mn loi I cng c ci
thin. nh hng ca nhit bo dng n lng hydroxyt canxi c trong ximng c
gii thiu bng l.l.Bng 1.1. nh hng ca nhit bo dng n bn ca xi mngLoi
Xi mng kh kim (CaO), g/kg Sau 2 ngy rn chc TCP`"8 20C 40CKt qu
trong bng l.l cho thy: nhit bo dng cao xy ra phn ng Silict ho chuyn
t hydroxyt canxi t do thnh Silicat canxi ngm nc, bn trong mi trng n
mn loi I.Phng php bo dng cng nh hng n mc n mn ho tan khi dng cc loi
ximng khc nhau (bng 1.2).Vic chng hp c bit c hiu qu lm gim mc n mn
i vi xi mng pha ct nghin. iu ny hon ton d hiu, bi v`1 iu kin chng h
nhit Cao phn ng Silicat ho din ra mnh.13Khng c ph gia 21 24 30 i C
30% trepen 18 l4 8 I
13. Bng 1.2. nh hng ca chng hp btng n n mn loi I_ _ Nng CaO,
mg/I, bo dng trong iu kin Lol xl mng pooclng (X.P) _ _ _ _ ` V Chmg
hp lu kln thngXimng khng c ph gia 393 555 220 602 152 416 122
139X.P ct (25% Ct nghin)X.P. puzolan (25% trepen)X.P. xi (25% Xi
nghin)Thi gian rn chc cng nh hng ti s thay i bn ca b tng xi mng khi
chu tc ng n mn loi I. Qua th nghim, Moskvin a ra kt lun: Khi tui ca
btng tng ln, xi mng pooclng khng ph gia s khng nh hng ti bn ca
chng, nu loi b c hin tng Cacbonat ho b mt. Ngc li, bn ca b tng xi
mng pooclng pha ph gia c nng ln (bng 1.3). Bng 1.3. nh hng ca loi
xi mng ti s kh kim cc tui khc nhaul xl m ng IIE Ximng pooclng khng
ph gia 1 l l l l ,l 5 1,26 0,82 0,45 l ,22 1,0] 0,75 0,73Ngoi cc yu
t c bn c nh hng ti bn ca Va ximng v btng di tc ng n mn loi I nh
trnh by trn th s n mn cc kt cu btng dng ny cn Chu nh hng bi tnh cht
mi mn ca dng nc, cng ca nc... Ximng pooclng puzolan Ximng pooclng
puzolan-ct 1.2.2. n mn loi II1.2.2.1 . Bn cht ca n mn loi IIn mn
loi II c phn bit khc vi n mn loi I ch n khng chi l s ho tan ca cc
sn phm ca xi mng, m ch yu do tng tc ca cc axit hoc mui trong mi
trng vi cc sn phm thu ho ca Xi mng to ra cc hp cht tan mnh hn cc sn
phm thu ho ban u, khng c cng . Mc ph hoi mnh ca n mn loi II l do s
tc ng ng thi ca cc qu trnh ho hc n s phn hu Ca(0H)2 lm tng dng k mc
ph hoi kt cu btng.14
14. Trong S cc tc nhn gy n mn loi ny th axit l tc nhn ph hoi
mnh nht, tip theo l cc mui axit v cc hp cht c kh nng tng tc vi cc
sn phm thu ho ca xi mng c tnh hot ng ho hc mnh. Di y trnh by mt S
vn c bn V Cc qu trnh n mn loi II:1.2.2.2. n mn d axit cacbonicS tc
dng gia dioxit cacbon trong khng kh vi hydroxyt canxi trong d xi
mng l ph bin nht ca qu trnh n mn loi II. Khi trong nc C hm lng khi
CO2 nh chng s tc dng vi hydroxyt canxi to ra Cacbonat canxi'(CaCO3)
kt tinh bn vfmg trn b mt b tng lm cho s n mn gim di, n lp y cc l
rng v bao bc quanh Ct thp ca b tng, bo m n nh cho kt cu b tng v b
tong ct thp. Khi nng ca C02 tng ln nhiu, CaCO3 li bin thnh
Ca(HC03)2. Sn phm mi Sinh ny c tan ln hn nhiu so vi hydroxyt canxi.
Hn th na, phn ng gia axit cacbonic v Cacbonat Canxi din ra nhanh
trong khi s khuch tn ca Ca(0H)2 t trong ra b p cho s mt lp mng ph
Cacbonat canxi li din ra chm. Trong trng hp ny kt cu b tng b ph hoi
nhanh hn..Nhng nghin Cu do I.E. Orlov [6] thc hin v l thuyt do ng a
ra v tc dng ph hu Cacbonat c hnh thnh trong nc cha axit cacbonic
chi ra rng: TC ca phn ng ti l vi bnh phng hm lng axit cacbonic.Cng
ph hoi ca axit cacbonic ph thuc vo cc yu t nh: L'l1g kh C02, lc ion
dung dch, loi xi mng, thi gian bo dng btng v din tch mt tip xc ca
xi mng vi cc tc nhn gy n mn.TC n mn do axit cacbonic trong mi trng
mui Na2S04 1,5% Cn ph thuc vo cc yu t nh lng kh C02, lc ion trong
dung ch.Nghin cu ca nhiu tc gi cho thy s ra tri ca Ca(0H)2 trong b
tng dng Xi mng pooclng nhanh hon btng dng xi mng pooclng puzolan, V
b tng dng Xi mng pooclng puzolan Sinh ra t hydroxyt can xi hn. Xi
mng pooclng pha bt Vi cng c bn trong axit cacbonic cao hn Xi mng
pooclng thng.Thi gian bo dng cng di th n mn cng kh din ra do lp
Cacbonat ho Cng dy. Theo nhng quan st ca Moskvin, cc cng
trnh15
15. b tng v b tng ct thp Sau khong 3 thng rn chc ngoi khng kh,
lp Cacbonat ho trn b mt kt cu c Chiu dy chng Vi Cm. Bng nhng S liu
thc nghim Moskvin chi ra rng din tch mt. phn ng nh hng ng k n nng
cc i ca bicacbonat, ngha l n c nh hng r nt n s n mn kt cu b tng v b
tng ct thp.1.2.2.3. n mn ca cc axit khcTrong s nhng axit V c thng
gp (tr axit cacbonic) tc dng ln xi mng v b tng nh axit clohydric,
axit Sunfuric, axit nitric v cc axit hu c nh axit axctic, axit
lactic... khi b tc dng bi cc axit ny xi mng s b ph hu.Theo mc n mn
ca cc axit phn ra ba nhm theo mc gim dn nh Sau:+) Nhm I l cc axit,
khi phn ng vi cc sn phm thu ho ca xi mng hnh thnh cc sn phm dng gel
nh ioxit silic, hyroxyt st, hyroxyt nhm v mt lng khng ng k cc cht
trong Sut nh mui Canxi. Cc axit ny l axit clohyric, axit Sunfuric v
axit nitric. Phn ng ca cc axit ny vi cc sn phm thu ho ca xi mng din
ra nh Sau:Ca(OH)2 + H2S0,, (hoc HCl hoc HNO3) - CaSO,, (hoc CaCl2;
hoc Ca(NO3)2 + nH2O) nCa0.Si02 + pH2S0,, + nH20 -> nCaS0,, +
mSi(0H),, + nH2O+) Nhm II l Cc axit vi tan ca sn phm to thnh nh hn
1 g/l v c nng thp. Cc sn phm thuc nhm ny l HZSO4, Fc(0H)3,
Al(OH)_,... Khi c mt ca cc mui canxi, nhng axit ny s lm cho n mn d
xi mng gim i.+) Nhm III bao gm cc axit cha gc mui`canXi m ho tan nh
hol 0,002g/I nh axit oxalic, hyrotluoric v fluoxilixic. Cc axit ny,
khi tng tc vi cc hp cht ca ximng, Sinh ra sn phm dng gel, c tc dng
ngn cn s xm nhp ca tc nhn gy n mn lln chm ng k tc h hng Cng trnh.
BTC n mn thay i tu thuc vo d ho tan ca cc sn phm to thnh. ho tan ca
cc sn phm ny cng mnh th tc ph hu cng nhanh. Sn phm thu ho ca ximng
l khng thay i, nn tc n mn ph thuc vo loi axit c trong mi
trng.16
16. Khi so snh bn ca btng dng cc loi ximng khc nhau Moskvin a
ra kt qu th nghim c gii thiu bng 1.4 v minh ho trn biu thc nghim
(hnh l.l).Bng 1.4. S0 Snh tc n mn vi cc loi xi mng khc nhauKhi c tc
dng ca loi axit Loi cht kt knh HzS04Ximng pooclng 0,94 Ximng chu
axitGh ch: Tc ll m!! tnll tlleo lrlg CaO vi 3 loi xinrzg du, tnh
blzg llzg N6120 i vi xmrzg Clzu axt.T bng S liu trn ta thy Ximng
pooclng c bn km nht, xi mng pooclng puzolan c bn cao hn khng ng k
so vi ximng pooclng thng, cn xi mng chu axit c chng n mn tt nht.Mt
yu t khc nh hng ti tc n mn ca cc axit V C l nng ca axit v tc dng nc
Chy qua b mt ximng.Hnh 1.1.' Sph thuc ca ring lllg CaO tclz ra t x
mng vo tc tllin dungdch HCl (pH = 2) 1 - 100ml/gi;2 - 300ml/gi;3 -
600ml/gi;_4 - 800ml/gi 17
17. Khi chu tc ng ca axit c nng m c (pH = 1), btng dng Xi mng
pooclng puzolan c bn nh hn vi btng dng xi mng pooclng. Ngc li khi
nng ca axit yu (pH Z 4) bn ca ximng pooclng puzolan li ln hn khi
dng xi mng pooclng. Tc dng chy cng nhanh th s n mn din ra cng
mnh.1.2.2.4. n mn ca cc dung dch mui manhMui manh c bn l hai loi
mui clorua manh v Sunfat manh. Chng thng c trong nc ngm, nc bin. S
n mn ca loi mui ny ch yiu do chng tng tc vi hydroxyt canxi c trong
ximng. Nhng phn ng chnh din ra gia hyroxyt canxi c trong ximng vi
cc mui manh nh sau:MgS0, + Ca(OH)2 + 2H2O = CaSO,.2H20 + Mg(0H)2
MgCl-_, + Ca(OH)2 = CaCl2 + Mg(0H)2_ Trong hai trng hp ny hyroxyt
manh c to ra c ho _tan rt nh (l8,2 mg/I) nn chng kit ta li. Nhng
quan st v trng thi ca cc kit cu b ph hu do mui manh chi ra rng trn
b mt v trong cc l rng tch t cc cht v nh hnh mu trng (hyroxyt manh).
B tng cng b thm nhiu v hm lg hyroxyt canxi trong Ximng cng nhiu th
cht V nh hnh mu trng ny c to ra cng nhiu v cc tnh cht c hc ca kt cu
btng cng b suy gim. Tuy nhin, cng c mt s tc gi kho st v chi ra rng,
trong mt s trng hp hyroxyt manh c tc dng lm chn kn cc l rng trong
btng, gp phn nang cao cng ca n.S n mn ca cc mui manh cng chu nh hng
bi cc loi xi mng khc nhau. Khi so Snh cc loi ximng dng nu trn chu
tc dng cria mui clorua manh, th ximng aluminat c bn cao nht, cn i
vi hai loi Ximng pooclng v ximng pooclng puzolan th s So snh li ph
thuc vo nng ca mui tc ng vo btng. Khi nng mui thp (l-2%) th hai loi
ximng c bn tong ng, nhng khi nng cao (khong trn 5%) th bn ca ximng
pooclng li cao hn xi mng pooclng puzolan. iu ny c th c gii thch
rng, khi dung dch mui xm nhp vo bn trong xi mng, hyroxyt canxi s
tng tc vi chng, to ra hyroxyt manh, lp cc mao qun, c tc dng cn tr s
xm nhp ca dung dch mui Xam nhp tip vo trong, nhng lng sn phm18
18. ny Sinh ra t xi mng pooclng puzolan khng cn tr s xm nhp mnh
m ca mui manh c nng cao. C th ni s n mn xi mng pht trin nhanh khi
dung dch MgCl2 c nng trn 2% v c th cho php S dng btng trong mi trng
mui ny vi nng khng V qu 5000mg/I.1.2.2.5. n mn ca dung dch k`mTheo
nhng ti liu cng b th bn thn kim khng c tc dng n mn btng, nhng khi
btng trong dung dch kim long, sau tip xc vi khng kh, trong btng s b
Cacbonat ho sinh ra cc mui Cacbonat (Na2CO,,) kt tinh ph v cu trc
btng. Trong dung dch kim dc, tuy ho tan ca Ca(0H)2 c gim i r rt,
nhng lng OH Sinh ra li lm cho cc oxit v Silicat b ho tan, t n n ph
hoi b tng. Nh vy c th ni n mn do kim c trong xi mng xy ra trong lng
khi b tng, gia cc cu t vi nhau. Bn than clinke lun cha mt lng Cc
cht kim (Na20, K20). Trong ct liu b tng, c bit l trong ct thng cha
oxit silic V nh hnh (opan, chanxedon, thu tinh ni la), chng c th tc
dng vi kim trong xi mng ngay nhit thng, lm cho b mt ht ct liu n ra,
to ra mt h thng cc Vt nrt. S ph hoi ny Xy ra Sau khi hon thnh cng
trnh Xy dng khong 10-15 nm.1.2.3. n mn loi IIILoi n mn ny l s tch t
cc mui, c hnh thnh t s tng tc ca cc sn phm thu ho ca xi mng vi cc
hp cht ca mi trng loc c Xm nhp t bn ngoi, lm tng th tch nhiu, gy ni
ng xut ph hoi kt cu xi mng. c tnh C bn ca n mn loi III l thi k u sn
phm xut hin do tng tc ca cc hp cht ca mi trng v sn phm thu ho ca xi
mng cn t, chng kt ta trong cc l rng v mao qun trong cu trc b tng,
nng Cao c chc v gp phn lm tng bn ca kt cu. Nu sn phm ny khng tng
thm th kt cu khng b ph hoi. Nhng v Sau sn phm Sinh ra cng nhiu,
chng gy ni ng Sut, ph hoi kt cu v m ng cho cc tc nhn n mn xam nhp
tip vo Su bn trong b tng v nhanh chng ph hoai b tng.S ph bin ca loi
.n mn ny l S xm nhp ca cc hp cht t nhin v cng nghip ho cht cha dng
cc hp cht Sunfat.19
19. 1.2.3.1. n mn ca cc mut SunfatMui Sunfat thng gp trong a S
cc loi nc t nhin. Trong nc Sng, h hm lg Sunfat tnh theo ion SOZ
thng khng v`t qu l00mg/[. Trong nc khong ngm hm lng ny tng ln rt
ln. c bit trong nc bin vi mn 33-35g/I lng S022 thng l 2,5 - 2,7g/l.
Mt s ngnh Sn xuat ho cht c dng axit sunfuric nh ngnh luyn cc, snxut
Sunfat amon, sn xut phn khong v nhiu ngnh cng nghip khc cng gp dng
n mn ny. Tuy nhin, s n mn chi ng k khi nng SO2 ln hn 4250mg/1.Qu
trnh n mn ho hc din ra nh Sau:u tin l s tng tc ca Sunfat manh vi
hyroxyt canxi theo phng trnh:MgSO4 + Ca(0H)z + 2H20 = CaS04.2H2O +
Mg(0H)2Khi trong mi trng c cha mui Na2SO_,, th u tin l tng tc
caSunfat natri vi hyroxyt canxi theo phng trnh: I Na2SO4 + Ca(OH)2
+ 2H2O = CaSO4.2H2O + 2NaOHSn phm CaSO4.2H20 c hnh thnh tng th tch
2,34 ln' so vi hyroxyt canxi. Sau khi c to ra, CaS0,,.2H20 li tng
tc vi 3Ca0.Al2Og.6H20 to ra 3CaO.Al203.3CaS,,.31H20 (mui ettringit)
theo phng trnh:3Ca0.Al20,I6H20+3CaSO,,.2H2O + l9H20 =
3CaO.Al203.3CaS04.3lH20Ettringit kt tinh v nm li trong cc l rng ca
xi mng v b tng, tng th tch gp khong 4,8 ln So vi tng th tch ca cc
hp cht Sinh ra n. Chnh v s n th tch ca cc sn phm ny m cu trc ca b
tng c th b ph V.1.2.3.2. Cc yit tnh hng ti n mn sunjat Mc n mn xi
mng v b tng ca cc chit gc Sunfat chu nh hng ca nhiu nhn t. - Hm lng
C3A c nh hlg ln nht n tnh n mn Sunfat ca xi mng v s c mt ca chng s
to ra phn ng vi cc mui Sunfat to thnh ettringit. Lng C3A cng nhiu
th lng ettringit Sinh ra cng ln,cu trc b tng cng b ph hoi nhanh
chng. Xi mngpooclng_ c hm '20
20. lng C_,S cao s c d bn chng Sunfat tt hon So vi loi Xi mng
pooclng c nhiu khong CSS. iu ny c gii thch l do trong xi mng alit,
aluminat canxi ngm nc c thu ho trc khng tan trong dung dch hyroxyt
canxi bo ho, v vy chng phn ng vi thch cao to ra ettringit, tng th
tch, ph v kt cu b tng (bng 1.5).Do nhng nh hng ln ca thnh phn khong
ca xi mng n tnh cht n mn Sunfat nn nhiu quc gia a ra tiu chun khng
ch hm lng khong: CSA S 5%; C3A + C4AF S 22%; C35 S 50% cho xi mng
chng n mn trong mi trng ny. 'Cc nh khoa hc qua th nghim kt lun rng
khng Chi thnh phn khong ca clinke c nh hng ti bn Sunfat ca b tng m
tnh cht vi cu trc ca chng (thnh phn pha) cng c nh hng ti tnh cht
ny. iu kin v cng ngh Sn xut, nht l ch lm ngui, c nh hng ln ti bn
Sunfat ca cc loi xi mng.Bng 1.5. nh hng ca thnh phn khong trong
clinke xi mng pooclng, %, n bn Sunfat ca b tngp15 8 25 52 Th 15 8
50 27 - 15 8 70 7 -5 15 25 55 Cao 30 10 nh gi nh hng ca cc loi ph
gia khong hot tnh, cc nh khoa hc th nghim So Snh s n mn ca ba loi
xi mng: xi mng pooclng, xi mng pooclng puzolan v xi mng pooclng xi
thng qua vic Xc nh bin dng ca cc mu th nghim Sau 3 thng ngm ngp
trong cc dung dch mui Sunfat natri v Sunfat manh (hnh 1.2).Cc kt qu
th nghim cho thy bn ca cc mu t xi mng pooclng puzolan Cao hn so vi
xi mng pooclng, cn xi mng pooclng xi cho ...bltt nht. iu ny c th
gii thch: Khi dng cc ph gia khong hot tnh,"~'lb--c.vuv`.gv-g..
,IRlng hydoxyt canxi trong Xi mng.tlti'g.:;2
21. Hnh 1.2: Tllll bn drlg ca Cc mu 30 X 30 X 100mm rl`ong
dullg dch nng 5% ca cc mui.' a) Trollg Sullfat nat', b) T0I1g
suIf^at maIlIie^,' l, 2, 3 - khi hm lng CJA ban u 10,3%; 4, 5, 6 -
khi hm lng C_,A ban u l 7,8%; 1,4 - xi mng pooclng; 2,5 - xi mng
pooclng puzolan (20% puzolan); 3,6 - xi mng pooclng xi (50% xi).Khi
xt s nh hng ca nng v loi mui Sunfat n s n mn xi mng cho thy: cc loi
mui c nng > 250 mg/I mi c kh nng n mn r rt, v khi nng cc mui cng
cao th s to thnh hydro Sulfo aluminat tricanxit cng nhiu. Trong cc
loi mui Sunfat th mui Sunfat canxi c tc n mn ln hon cc loi mui
Sunfat khc. iu ny c gii thch bng s to thnh nhiu CaSO,,.2H20, to iu
kin Sinh ra nhiu ettringit. S to thnh hydro Sulfo aluminat
tricanxit lm cho cu trc ca Xi mng tr nn ti Xp.V nh hng ca cc loi
mui V.V. Kind [5] khng nh rng, trong 3 loi mui: Sunfat natri,
Sunfat canxi v Sunfat manh th tc n mn ca loi mui th ba ln nhat. ng
da ra s liu S.o Snh khi ngln cc mu xi mng ch to t xi mng pooclng c
hm lng CSA 10% trong cc mi trng mui c nng 2% th mu ngm trong Sunfat
manh b ph hoi trc, chi Sau cha y 3 nm.Cng xt S nh hng ca cc loi mui
gc Sunfat ti s n mn xi mng v btng A.I. Panpherova chi ra rng S n mn
ca mui amoni Sunfat l nguy him hn. iu ny c gii thch l khi b Sunfat
amon tcdng th nng ca cation tng ln v s c mt ca NHT , t thc y phn
Liig gia Sunfat amon vi hydroxyt canxi to ra CaSO,,.2H2Oi v22
,"
22. 2NH,,OH. Hydroxyt amon tan nhanh vo mi trng v mt phn tch ra
khi amoniac bay hi.Cc yu t iu kin mi trng nh tnh kh m c chu k lin
tc, nhit khng kh v tnh chuyn ng ca dng nc... cng c nh hng n S n mn.
Tnh kh m lin tc lm tng ng k tc n mn. Khi nhit thay i, cng nh khi c
S chuyn ng ca dng chy th mc n mn S tng ln.1.2.4. n mn ct thp trong
b tngNgoi hin tng n mn b tng, trong cc mi trng s dng, c bit l mi
trng nc bin v nc ngm cn xy ra hin tng n mn ct thp. Ct thp trong b
tng b n mn ch yu l n mn in ho. Trong mi trng bin n mn ct thp cn do
tc dng xm thc ca cc ion Cl` ngm vo b tng ct thp t mi trng bn ngoi,
hoc do ln trong vt liu ch to b tng (ct, ').Khi ct thp c t trong b
tng c chc cha b Cacbonat ho, mi trng kim trong b tng cao l iu kin
thun li hnh thnh trn b mt ct thp mt lp oxt mng ngn cn qu trnh gi
thp (n mn). Lp mng oxyt mng ny c gi l mng "th ng", khi b mt ct thp
tn ti dng th ng. Hin tng n mn chi xy ra khi lp mng "th ng" b xuyn
thng (lp b tng bo v b rng). Vic n mn ct thp s dl n n th tch, lrn nt
v lp b tng bo v v ph hu ton b b tng ct thp+ n mn ct thp trong b tng
thng din ra dng n mn in ho. dng n mn ny cc nguyn t St trong Ct thp
tch khi mng li tinh th v tr thnh ion mch in trong dung dch, di tc
dng ca ion 0H` trong mi trng to ra cc sn phln gi khc nhau di dng
cng thc chung: xFeO.yFe20g.ZH2O. Cc sn phm gi St ny c th Vl
Fe3O4.Fe(OH)2.Fe(OH)3, Fe(OH)3.3H20. Cc sn phm ny c tnh xp, tch t
trn b mt ct thp vi th tch ln gp 4 - 6 ln So vi cc thnh phn ban u,
chnh v vy gy ni ng Sut ph hoi cu trc b tng dc theo v tr t thp, lm
cho cc tc nhn xm thc d dng xm nhp vo bn trong, tng nhanh qu trnh n
mn b tng v ct thp. Qu trnh gi chi c th xy ra nu nh b tng kh nng dn
in nh mt lg ngm nc nht nh v`1 lc ny c s phn cc. cch bit gia Catt v
ant (hnh 1.3).23
23. B mt b tngdy lp b tng bo V ChiuxFeOyFezO, + H20 40 + O, +
H20 H20Ani cc b Catt cc bHnh 1.3: S qu trnh gli ci thp do n mn rl
hoQua y, chng ta thy rt r kh nng chng thm ca lp b tng bo v ng Vai
tr rt quan trng i vi qu trnh gi ca ct thp.. B tng khng cht, lp bo v
khng chiu dy cn thit hin tng gi cng mnh. mi trng kh ro, do b tng
khng kh nng dn in nn ct thp t b gi, cn trong mi tnrng ngm nc hon
ton th b tng c th dn in, nhng nc li ngn cn S thm nhp ca oxy qua be
tng nn ct thp cng t b gi.+ n mn ct thp trong b tng cn c th do thm
ion CIT. S c mt ca ion Cl_ trong mi trng bin l nguyn nhn ch yu lm
tng tc ^ n mn ct thp trong b tng. Tc n mn thp ln do ion Cl` lm gim
in tr ca dung dch in li trong b tong. Mc khc, khi ion Clo khuch tn
n b mt ct thp, chng c th to nn s n mn bng cch ho tanlp th ng hoc
khuch tn qua lp oxy ny. S c ch qu trnh ngmn ct thp trong b tng c mt
ion clo c trnh by hnh 1.4.c trng n mn thp khi c Clo to ra cc "l"
trn b mt kim loi (micropilc), lm ti l in tch Catt/ant ln nn mt dng
n mn cc b rt cao. Chi c ion Clo dng t do mi gy ra n mn ct thp v s
khuch tn ca chng trong cu trc xp ca btng. Cng tim n nguy c n mnt
thp mnh m hn.24
24. B tng Fe(OH)2 CI' HMng th ngCatt (+)- - Ct thp e Ant (-)
eHnh 1.4: C Chll mn in ho thp trong b tllg khi c mt on CloCng ging
nh qu trnh Cacbonat ho, tc thm ion Clo ph thuc vo bn cht xi mng, cc
ph gia khong, v cht lng b tng (c trlrng bi bn Chng thm). Kh nng thm
ion Clo ti l vi hm lng khong CSA c trong xi mng. V vy, xi mng
pooclng c kh nng bo v ct thp cao hon Xi mng bn Sunfat. V nguyn tc,
cc ph gia khong tro bay, tro xi hoc mui silic a vo xi mng pooclng s
lm`gim ti l thnh phn CSA nn gim kh nng c nh ion clo. Song yu t quan
trng hn l b tng c tro bay, tro xi hoc mui silic c h S khuch tn ion
nh hon nhiu So vi b tng xi mng pooclng. V vy b tng c ph gia khong
ckh nng bo V ct thp cao hn nhiu so vi b tng Xi mng pooclng. S`kh m
lin tip l mt trong nhng diu kin khc nghit nht kch thch s n mn.S n
mn Ct thp cng chu tc ng ca hin tng Cacbonat ho b tng. bn lu ca cng
trnh b tng ct thp c bo m nh lp btng bo v v mt vt l v ho hc ct thp
khng b n mn. Bn Cht ca s ngn cn qu trnh n mn l do c mi tmng kim cao
ca nc chit btng (pH .>. 13). S gim kim ca mi trng trong lp btng
bo V n ngng thu ng ca St (pH 11,4) xy ra do qu trnh ra tri kim hoc
qu trnh Cacbonat ho btng. T gim kh nng bo v ct thp ca btng.25
25. C Ch Cacbonat ho btng gy n mn ct thp l hin tlg Chung i vi
mi cng trnh BTCT khi b tng tip xc vi mi trng khng kh, hoc trong nc
Cha kh C02. Trong khng kh lun Cha Cht ioxyt Cacbon (CO2) vi ti l
trung bnh l 0,03% theo th tch, hm lng kh C02 ny tu thuc vo p sut v
nhit ca mi trng khng kh. Kh C02 trong khi quyn tc ng trn cc vng cha
Vi Va xi mng to ra Cacbonat canxi (CaCO3) v dn n s st gim tnh kim
(pH) ca b tng xung. Cc sn phm ca qu trnh Cacbonat ho lln thay i cu
trc xp ca b tng v lm gim Chng thm, dn n s n mn ct thp trong b tng.
S 1.2.5. n mn b tng v b tng ct thp trong mi trng binTrn th gii cng
nh Vit Naln c rt nhiu cng trnh nghin Cu v n mn b tng v b tng ct thp
trong mi trng bin. Ni chung, cn nhiu kin khc nhau V bn cht ca qu
t1'nh n mn b tng v b tng ct thp. iu ny c th c gii thch: Do qu trnh
n mn trong mi trng ny din ra chm v theo nhng c ch khc nhau. Cc kt
qu th nghim nhanh cha din t ng bn cht ca hin tng ph hu kt cu trong
thc t.Theo Ks Mohta [6], n mn trong mi trng bin c chia lm ba vng
chnh (hnh 1.5):c! thp BtngVng kt quyn Tc dng m mn Vng thu chiu c
hc, Va pln xung7Mc nuc ttlpn mntlo hc v V sinh oi vi b tng Phn b cc
lp n mn ho hc: 1. Tc ng ca C0,2. Tc ng ca Mg 3. Tc ng ca SO,Vng
ngpHnh 1.5.' S d m t n mn b tng ci thp trong mi trng bin26
26. - Vng thng xuyn ngp nc: y ch yu Xy ra n mn ho hc v n mn Vi
Sinh mc nh i vi b tng.- Vng thu triu ln xung (gia hai mc nc): y xy
ra qu trnh n mn ho hc v n mn vi Sinh i vi b tng, n mn ct thp, tc ng
ph hu vt l v va p, mi mn c hc.- Vng khng kh bin (khng kh c cha cc
mui phan tn): Ch yu l n mn ct thp, dn ti lm n1t n, ph hoi lp b tng
bo V.Be tng v b tng ct thp c xay dng trong nc bin hoc vng ven bin
chu tc dng trc tip ca cc yu t xm thc ca mi trng bin m c trng l bn
loi yu t xm thc Sau:- Cc yu t ho hc: Nc bin c Cha cc ion khc nhau
ca cc loi mui k trn.- Cc yu t bin ng ca nc bin v thi tit: Nc thu
triu ln xung nn mt S b phn b kh m lin tip.- Cc yu t Vt l: Nhit bin
i.- Cc yu t c hc: Tc ng ca Sng xi mn trn b mt b tng.Tc ng phi hp ca
cc yu t ny lm cho b tng v b tng ct thp trong mi trng bin b n mn
mnh. Xt v bn Cht c mt s dng n mn chnh Sau y:- n mn ho hc b tng
trong nc bin.- n mn Ct thp trong kh quyn bin v vng c mc nc ln
xung.- n mn b tng do vi Sinh vt bin.Trong cc dng n mn ny th n mn ho
hc ca b tng ong mi trng bin l nguy him nht V n va ph V cu trc b tng
va to iu kin cc tc nhn ho hc xm nhp vo n mn Ct thp.Cc cng trnh b
tng ct thp khi S dng trong mi t1'ng bin, nu khng c bin php bo v c
hiu qu th b n mn mnh, v mi trng nc bin c cha cc hp Cht ha hc c tnh
cht n mn cao i vi c b tng v ct thp. C th ni y l loi n mn tng _hp.c
im ca nc bin l cha nhiu mui, tng hm lng cc mui ho tan trong cc i
dng khong 34 - 35%, v tng quan hm lng- ca chng rt bn vng. Lng mui
ho tan trong nc bin nh hn So vi i dong v bin i trong mt gii hn rng.
Hm lng mui (%) ln27
27. nht l NaCl (77-79), Sau n MgCl2 (10,5 - 10,9), MgS0,, (4,4
- 4,8), CaSO4 _(3,4 - 3,6). Tng lng mui clorua l 88-89% v cc mui
Sunfat l 10,5%:` pH = 8,2 - 8,3..Ngoi ra trong nc bin cn c cc hp
Cht ho hc nh nitrit, nitrat, photphat, ioxit silic, cng nh cc loi
mui bromua, iotua... Qu trnh n mn b tng trong mi trng nc bin o nhiu
phn ng ng thi v ph thuc ln nhau vi cc c ch khc nhau: Ho tan khi ngm
chit; Cc phn ng trao i kim; kt ta cc hp cht ho tan; kt tinh Cc mui
gin n. Cn c vo Cc mui ho tan ch yu trong nc bin (MgClz, MgS0,,) cc
phn ng chnh gy ra ph hu b tng c trnh by tm tt:Mgcl, + Ca(oH), -
Mg(OH), + CaCl2Hoc: Mgso, + Ca(oH), - Mg(oH), + Caso, .2H,o Hoc:
Mgso, + [Ca(oH), + 3Cao.A1,o,CaSo,.18H,o] -Mg(OH)z +
3Ca0.Al2Og.3CaS04.3lH20 (etringit gy n th tch). Hoc Mgso, +
[Ca(oH), + 3Cao.2Sio,.3H,o] -4Mg0.Si02.8H20 + CaS0,,.2H20 (Sn phm
ho tan) i vi b tng ngm trong nc bin, Moskovin a ra S phnI vng theo
s u tin tc ng ca cc ion khc nhau. iu ng ch l tcdng ca mi loi ion
khng c tnh tan, chng hn monoclorualuminat canxi (C3A.CaCl2.l0H2O),
khi c mt ca SO2 tr nn khng n nh v phn hu to thnh ettringit
(3C_a0.A120,.3CaSO,,.3lH2O). Khi c mt caI mui Cacbonat v silic ho
tan th ettringit li chuyn thnh hp cht mi,(CaC03,
CaS0,,.CaO.Si02.l5H2O). Chnh t s giao thoa ca cc ion khc_ nhau nn
mc xm thc ca nc bin yu hn nhiu So vi nc chaion Sunfat. Mc xam thc
yu ca nc bin cn c gii thch do vai tr ca ion clo lm tng tan ca thch
Cao v ettringit, nn hn Ch s kt tinh chng, hn ch gin n ln gy ph hu b
tng.Nguyn nhn chnh lm ph hu btng trong mi trng bin l do cc mui
Sunfat n mn xi mng. V mt nguyn tc, bn n'mn Sunfat ca btng tng khi
gim thnh phn QA v ph thuc khng nhiu vo hmilng QS ca ximng.28
28. 1.2.6. n mn ca nc thi cng nghip1.2.6.1. Nc thi cng nghip v
s n mn b tngTrong nc thi cng nghip, nht l nc thi ca cc nh my phn
khong thng Cha cc hp cht ho hc c tnh n mn mnh, c tc ng ph hoi b tng
rt a dng. Tuy nhin, theo quan im phn loi ca Moskvin th nimn trong
mi trng nc thi cng nghip c th l n mn loi I nh cc Cng trnh thp lm
ngui, b cha, ng dn nc..., n mn loi II nh axit v C v hu c, mui ca cc
axit mnh v.v. Cc cng trnh c tnh cht n mn loi III nh kim, mt s
monome (b trng hp tng th tch)... S n mn c th tn ti ng thi c hai
loi, v i khi c ba loi. Thnh phn Cc hp cht n mn trong nc thi cng
nghip tu thuc tng ngnh sn xut.Kt cu b tng ct thp trong mi trng cng
nghip cng chu tc ng n mn ca mi trng hu c lng (v d nh cc axit bo). S
n mn ca nc thi cng nghip cng c th khng do tng tc vi hp Cht ca Xi
mng, nhng li nh hng n bn do thuc tnh hp ph. Cc hp cht c tinh hp ph
ny hp ph tren b mt pha rn ca xi mng. Sau mt thi gian chng to thnh
lp n hoc a phn t, chng hp ph thm nhp vo cc phn khuyt tt, cc khe h
ca Vt rn cho nn c ca chng b gim i. Cc hp Cht c tnh hp ph l dung dch
nc ca cc cht hot tnh b mt (x phng, cc cht ty ra v Sinh, cng nh cc
Sn phm ca ngnh ho du).Tuy nhin theo nh gi ca nhiu nh khoa hc th S n
mn cc mi trng cng nghip nh cc nh my c dng axit v cc nh my sn xut
phn bn l nguy him nht.1.2.6.2. Tnh chi ca nc thi _cng nghip Vit
NamQua kho st v tnh cht ca nc thi cc nh my v x nghip Cng nghip Vit
Nam cho thy: a S cc cng trnh Xy dng bng b tng v b tngct thp trong
cc nh my v Cc x nghip cng nghip ni chung v cc nh my phn khong ni
ring sau mt thi gian S dng ngn. u b h hng nng. Nguyn nhn dn n S ph
hu cc cng trnh l do chng tip xc vi nc thi c cha hm lng cc ho cht
ln, vi cc29
29. ho cht trng thi m t hoc tip xc vi cc ho cht dng kh. c bit
Nh my Phn m v Ho cht H Bc, s ph hoi ca cc tc nhn ho hc ca mi trng
din ra rt nhanh. Phn xng Sn xut lu hunh mi c xy dng v a vo sn xut
cui nhng nm 1970, n nm 1992 phi sa cha ln, n nm 2002 phi xy
dngli.Theo S liu kho St ca trung tam mi trng - Trng i hc Xy dng H
Ni, tnh cht ca nc thi mt s nh my v x nghip khu vc H Ni c mt S c tnh
nh Sau:Bng 1.6. Tnh cht ca nc thi cc nh my khu vc H NiTnh cht nc
thiTng hm lng mui mg/ILoi nh my Nng muiln nht, mg/INh my dt nhum n
3850 NHT, 21-29 Nh my CN thc phm n 2600 NaCl, 78 Nh my c kh ho cht
- HIS, 332Nh my phn khong n 10 800 NH*, 8820 Theo bo co tng hp tnh
hnh cng nghip nhim trng im ti Thnh ph H Ch Minh ca y ban Mi trng
Thnh ph H Ch Minh th S nhim nc thi ca Cc nh my thuc pha Nam tng i a
dng, tuy nhin cc thng S lin quan n n mn b tng cng tong t nh nc thi
khu vc H Ni. in hnh nh Nh my sn xut bt git VISO pH n 9,0 Cl`
4l5mg/I, v SO2 l 170 mg/1. x nghip Ru Bnh Tay c pH l 4,7.B tng
trong cc nh my phn khong thng b ph hoi nghim trng bi nhiu nguyn nhn
khc nhau, trong d S n mn ho hc l nng nht. Theo kt qu nghin Cu ca
Mohan Rai [6] s ph hng cc kt Cu btng trong mt s nh my sn xut phn
khong rt trm trng vthng din ra theo ba dng c trng t ba dng phn
khong l Nitrat VAmon, Sunfat Amon v c bit l Clorua Amn. Kt qu phn
tich thnh phn ho hc ca cc mu Va Xi mng b ph hoi trong mi trng mui
amon c chi ra bng 1.7.30
30. Bng 1.7. Kt qu phn tch thnh phn mu b tng trong cc mi trnga)
Trong Sunfat amon, %Tng CaO CaO t do So, Ettringit pH Tng CaO 44,5
- 53 CaO t do Cl 3CaO.A1g0;.CaClg. XI-IZO pH 9,5 - 10,00 Tng CaO
42,0 - 55,5 ' CaO t do 2,0 - 2,5 N03 4,0 - 2,5
3Ca0.Al2O3.Ca(N03)2.xH20 3,5 - 2,5pH 10,0 - 10,5Xt v tnh cht ho hc,
cc hp cht ny S tc dng vi cc sn phm thu ho ca xi mng to thnh cc hp
cht n mn.S n mn trong cc nh my phn khong ng thi tn ti c ba dng n mn
loi I, loi II v loi III, nhng din ra mnh hn l hai dng n mn loi II v
loi III.Cc phn ng n mn ca ba dng phn khong ny u c S hin din ca nc
(H20) v phi c nc th cc phn ng mi xy ra. Nh vy, n mn Cht rn chi xy
ra trong m_i trng lng, hoc trong mi trng khng kh m, v cht rn phi c
tnh ho tan. ng thi, vai tr ca thm b tng ng vai tr cc k quan
trng.31
31. Chng 2 VT LIU XY DNG - I TNG B N MNA. CC YU CU CHUNG I VI B
TNG Xl MNG POOCLNG2.1. KHI QUTB tng xi mng pooclng c thnh phn l xi
mng pooclng, ct liu nh, ct liu th, cc cht ph gia v nc, nh lng theo
ti l trn, vn chuyn theo quy nh tiu Chun cng trnh.B tng xi mng
poclng c phn loi trong TCVN v ACI tui chu nn l 28 ngy v tnh d gia
cng ca b tng phi p ng cc yu cu thit k' yeu cu k thut hoc trong cc
quy nh c bit. B tng c in c Cng t 10 - 50 MPa, cn b tng cht lng cao
v rt Cao c cng t 50 - 200MPa.2.2. VT LIU c b tng m bo yu Cu cht lng
vt liu phi c ch u tin. Yu cu v vt liu c quy nh cho tng Vt liu ch to
b tng vi cng ngh ch to b tng thch hp.2.2.1. Xi mng pooclng Xi mng
poclng phi ph hp vi yu cu tiu chun quc gia hoc theo cc tiu chun khc
cho tt c cc b tng xi mng.Loi xi mng c bit ph hp vi cc yu cu trong
cc quy nh c bit. Nu khng c yu Cu no c nu trong cc quy nh c bit xi
mng phi ph hp vi yu cu ca AASPTI M85 loi I hoc loai II hoc
'ICVN...Tt c xi mng dng trong vic ch to b tng c ti ch i vi cc bmt
ca cc b phn ging nhau ca mt kt cu phi dng mt loi.32
32. Xi mng c bo v chng m trc khi dng, vn chuyn S dng ti cng
trng.Ngi sn xut b tng trn Sn, sn phm c Sn phi m bo cc phong tin
thch hp gi cho xi mng p ng cc yu cu ca tiu Chun xi mng, gi ring bit
vi cc xi mng khc ngn nga khng cho xi mng ngoi quy nh lt vo cng
trnh. Cn ly mu th xi mng ti phu can hoc trong tuyn Cp liu ngay trc
khi a vo phu.Ngi k S phi xc nh Cc ti l hn hp trn c S cc th nghim
thc hin vi Cc vt liu c S dng trong cng trnh. Cc ti l phi drn bo sn
xut b tng vi hm lng xi mng nm trong dung Sai .-I: 2,5% i vi cc loi
b tng ang sn xut. Lng xi mng dng phi ln hn lng xi mng ti thiu v nh
hn lng xi mng ti a do tiu Chun quy nh Sn xut c be tng c o v tnh d
gia cng quy nh m khng vt hm lng nc ti a.Hm lng xi mng, hm lng nc, c
ct liu th, st v trng lng gn ng ca Ct liu nh v th i vi mi loi b tng
phi theo chi dn.h.fr2.2.2. Ct liuKhi lng ct liu nh v tho c xc nh
trong thit k v da trn cc phng php tnh v th nghim quy nh.Cc khi lng
tong i ca Ct liu nh v th c tnh vi n v xi mng da trn vic S dng ct
thin nhin c mun mn trong phm vi 2,50 - 2,90 v Cc phng php b tng
khng cn n tn s chn ng cao.Khi dng ct c c ht th, lng tng i ct liu nh
phi tng ln. i vi ct mn hn, lng tng di ct liu nh phi gim.Khi lng ct
liu c tnh bng kilgam hm lng Xi mng v ,S lt nc cn thit cho mi loi be
tng quy nh, cc ti l ny khng c thay i trong khi tin hnh d n xy
dng.Khi lng theo m ca cc ct liu c thit k cn c hiu chinh khi lng i
vi m thc t.Khi nh lng ct liu i vi cc kt cu c khi lng b tng khng ln
(l5m3) nu khng th t c tnh d v gia Cng mong mun c th thay i khi lng
ct liu hoc dng ph gia nhng khng c trng hp no hm lng xi mng chi nh
ban u b thay i.33
33. 2.2.3. NcTrong cng tc b tng nc bo dng, ra ct liu v trn khng
c c du v khng c cha qu lg/lt clorit nh Cl, cng khng Cha qu 1,3 g/lt
Sunpht nh SO4 .Ngoi cc yu cu trn, nc bo dng b tng khng c cha cc tp
cht vi lng lm mt mu b tng hoc n mn b mt.2.2.4. Ph giaHin nay thng
dng Cc loi ph gia tng do gim nc v lm chm rn chc i vi b tng xi mng
Poclng, b tng ng Sut trc cc kt cu c Sn v ng b tng ct thp. Lng ph
gia S dng phi ph hp vi liu lng do nh sn xut quy nh, vi s chp thun
ca ngi k S. Lng ph gia S dng phi trong phm vi 0,15 ti 0,25% tng lng
xi mng cho mt m dn v ca b tng trn v cho php gim hm lng xi mng ti ti
a 10% ca lng quy nh vi cc yu Cu cng nn.Cc ph gia ho cht, khi S dng
phi ph hp vi cc yu cu ca AASHTO M194.Khng c dng cc ph gia ho cht c
bit thay xi mng, cc ph gia cha clorit nh Cl qu 1% theo trng lng,
khng c s dng trong b tng ng sut trc v b tng ct thp. Nu dng ph gia
ht khng kh, gim ti l nc - xi mng, lm chm hoc lm tng nhanh thi gian
ng Cng, hoc tng nhanh s pht trin cng chng phi c S dng vi ti l liu
lng do nh sn xut khuyin Co theo quy nh trong cc quy nh c bit theo
chi dn ca ngi k s.Liu lng cc ph gia phi c cn ong chnh xc cho tng m
b tng bng cc phong php c Chp thun. `Tr khi c quy nh khc i vi cht ht
khng kh, cc mu ph gia kiin ngh S dng phi do nh thu np cho ngi k S
trc v s dng v lm th nghim xc nh S ph hp vi cc tinh cht cn c. Cc ph
gia cha qua th nghim khng c S dng.Mi loi ph gia bt k u phi n nh v
tnh cht trong ton b qu trnh S dng n vo cng trnh. Nu thy rng cht ph
gia cung cp khng n nh V tinh cht phi ngng ngay vic S dng.Ph gia pha
ch dng lng, ph gia lng phi c kh nng mt ln ton b khi lng cn thit cho
mt m trn. Ph gia lng c cho vo34
34. nc trc khi vo mt m trn. Nu dng nhiu hn mt loi ph gia lng,
mi loi phi c pha ch bng thit b ring chng khng Chu nh hng ln
nhau.Cht ht khng kh: Cht ht khng kh cn ph hp vi cc quy nh ca ASTM
C260.Cht gim nc: Kh S dng cc cht gim nc liu lng cho php ca cht ph
gia khng Vt qu liu lng dn n S co ngt trong b tng khi kh qu 20% khi
c dng trong b tng ng Sut trc c Sn; 10% khi dng trong b tng ng Sut
trc ti ch; 10% khi dng trong b tng mt ng khng c Ct thp. . V `Cht
gim nc phi lm gim yu cu v nc ca b tng cho t nht 7% khi dng vi liu
lng ti a m nh sn Xuat khuyn Co. Khng c dng cht lm chm ng cng vi liu
lng ln m nh sn xut khuyn co. Cng ca b tng cha cht ph gia vi lng do
ngi k S chi nh tui 48 gi v lu hn khng c nh hn cng ca be tng tng t
khng c Cht ph gia. Ph gia khng c nh hng c hi n hm lng khng khi
trong b tng.2.3. YU CU V CNG NNYu cu v Cng nn l yu Cu quan trng v
ti thiu i vi b tng. Cng b tng ph thuc vo lng nc, cng ngh ch to b
tng, thnh phn v cht lng thi cng b tng.Khi b tng c Chi nh bng cng
nn, cn xc nh cht lng bng cch th Cc m th i vi cc Vt liu, c thit k
chnh xc vi cc thit b trn v cc phng thc thi cng d nh cho d n. Vic b
tng c Cng quy nh khng c bt u cho ti khi nh thu Sn xut mt m th theo
thit k hn hp c s dng v ph hp vi cc yu Cu V cng m th. Cng b tng c th
xc nh trn mu hnh tr hoc hnh lp phng c kch thc 15cm. Cng nn trung
bnh ca ba mu th b tng c lin tip, phi bng hoc ln hn cng nn quy nh
tui 28 ngy hoc tui quy nh c th l 3, 7, 14 hoc 90 ngy khng c qu mt
trong mu th c cng nh hn cng quy nh v mu th phi c cng it nht bng 90%
Cng quy nh th nghim theo AASHTO hoc theo tiu Chun quc gia (TCVN. .
.).35
35. Vi m vt liu th yu cu thit b trn, phng thc v kich c ca vt
liu phi ging nh khi S dng trn cng trnh.Cng b tng dng cho Cng trnh S
c xc nh t cc th nghim trn cc mu th. Mt th nghim cng d phi gm c cng
d trung bnh ti thiu 3 mu th, ch to t Vt liu ly t mt khi duy nht ca
b tng. Khi mt mu th no cho thy r vic ly mu hoc th nghim khng ng n,
mu th d phi loi b v th nghim cng d phi ly cng ca cc mu Cn li.Cc mu
b tng th nghim c bo dng ti a im lm vic t nht trong mt ngy v Sau d
mang n im th khi cc mu c bo dng theo d m tiu chun cho ti thi gian
th nghim.Trong Cc trng hp cn thm s liu c th S dng phng php khng ph
hoi mu.2.4. YU CU V IU KIN BO DNG B TNGVic bo dng b tng nhm to ra
mi trrlg b tng pht trin cng v phi tun theo cc quy nh cht Ch.Tt c b
tng mi c du phi bo dng. Phng php bo dng phi theo yu cu ca tiu Chun
hoc bn quy nh rieng.Plzlrng php nlrc.' B tng phi gi lin tc m t bng
cch ti nc trong mt thi gian ti thiu l 7 ngy Sau khi b tng c c. C th
S dng bng, gi, thm hoc ct m ph ln lm mi trng bo dng gi m trong thi
gian bo dng.Khi S dng bng, gi, thm hoc ct ph ln gi m bng cch ti nc
vi mt vi nc to ra mt lp Sng ch khng thnh tia nc cho ti khi b mt b
tng c ph bng mi trng bo dng. m t Vi phun khng c a trc tip bng p lc
vo b tng v khng c php tch t trn b mt b tng vi khi lng ln to ra mt
dng hoc trn trn b mt. Cui thi ki bo dng cc b mt b tng phi lm Sch mi
th.Pllirong php dng [lp clli bcio dtrng mll.' Ton b b mt b tng phi
c phun ng u vi mt hp cht bo dng mu. Nu mng hp cht b h hi v bt c l
do g trc khi ht hn 7 ngy Sau khi dc b tng.36
36. Trong trng hp b mt c phn b h hi phi c Sa cha ngay bng Cch
thm hp cht bo dng.Hp cht bo dng mu hoc trng ph hp vi Cc quy nh ca
AASHTO hoc theo tiu chun quc gia.Hp cht bo dng phi ri ln cc b mt b
tng vi mc d 1 lt/ 1m2.Plllrlg php mng bo dng Chng thin.' B mt b tng
l ra khi hon thin phi c phun nc, dng mt vi phun m to thnh mt lp sng
ch khng phi thnh tia, cho ti khi b tng ng cng, sau ph mng bo
dng.Mng bo dng phi gi ti ch trong mt thi gian khng t hn 72 gi.Giy
chng nc phi gi ph hp vi cc yu cu k tlnut ca AASHTO M139. Cc tm do
(polietilen) phi ph hp vi cc quy nh ca AASHTO M171.Giy chng thm nc
hoc mng do phi lm thnh tng tm c b rng ph ton b b mt b tng.Tt c cc
khe ni ca cc tm phi gn kn vi nhau bng xi mng sao cho khe ni khng
thm nc. Khe ni phi ph ln nhau t nht 10cm.B. CU TRC V CNG CA B TNG
XI MNGCng b tng ph thuc vo dc ca b tng. Nng cao trnh d cng ngh, la
chn hp l thnh phn b tng s c cu trc hp l v dc v cng b tng cao. Nh
vy, gia cu trc v cng d b tng c mi lin h cht ch. Ci thin cu trc s n
n nhng bin di v Cng d b tng.2.5. CU TRC VI M CA B TNGHn hp b tng l
hn hp Cha cc thnh phn ch yu: Xi mng, nc, ct, ct liu ln (, Si). Ngy
nay khi a S b tng u c S dng ca ph gia th ph gia tr thnh th`nh phn
quan trng trong hn hp37
37. b tng, c tc ng n cu trc Vi m ca hn hp b tng. Khi nho trn cc
thnh phn khong vt ca xi mng s Xy ra phn ng thu ho, cc cht cu thnh
nn xi mng (thnh phn chnh C3S2, QS, CSAF, CSA) to nn cc cht ngm nc
((`,,SnH2O, CSH, C,AF.n2H2O, CFH, C3A.n,H2O, CAH v Ca(OH)2 v tr
thnh hn hp cht kt dnh gc trong hn hp b tng. Dung dch lin kt cc ct
liu nh (ct) to nn dung dch h kt dnh va xi mng (y l cht kt dnh th
Cp). Cui cng dng dch h kt dnh Va xi mng chui vo k h ca cc ht Ct liu
ny v Chng to ra cu trc hn hp b tng hon chinh. Tm li c th phn cu trc
hn hp b tng thnh cc cu trc con:- Cu trc xng ca ct liu ln.- Cu trc V
mo ca h kt dnh va xi mng (nhl mi trng lin kt cc ht ct liu >ln
trong Cu trc b xng khung).- Cu trc tip gip gia h xi mng v b mt ct
liu ln (vng tip gip ct liu): Vi khung Xog ct liu ln c biu hin qua
lc dinh va xi mng ln b mt cc ht ct liu ln (lc dnh ny Chi hnh thnh
khi kt thc qu trnh ninh kt v hn hp b tng c Cu trc n nh v mt hon ton
tnh do). Vng tip gip ny tn ti cc l rng do nc tch ra li v l vng yu
nht trong cu trc b tng. Ti y c th xut hin cc Vt nlt v cc Vng ng Sut
cc b du tin trong b tng khi chu lc v chu tc ng ca cc yu t mi trng
gy n mn.2.5.1. Cu trc Ct liu lnCu trc ct liu ln to nn khung chu lc
ph thuc cng bn thn ct liu ln, tinh cht cu trc (din tip xc gia cc ht
ct liu) v cng d lin kt gia cc ht. Tuy nhin, thng cng bn thn ca ct
liu ln l cao nn ta loi ra khi din yu t nh hng. Trong vic ch to hn
hp b tng ngi ta lun mong mun xy dng mt m hnh hn hp b tng trong cc
ht ct liu ln tip xc nhiu chiu vi nhau v c h kt dinh Va xi mng lin
kt gia chng. Xy dng m hnh ny nhm a cu trc ct liu ln tr thnh cu trc
Chnh, quyt nh tnh cht cu trc vi m ca be tng v quyt nh tnh cht chu
lc ca be tng. Lc ny cu trc ca va xi mng chuyn xung th yu v chi c
tnh Cht lin kt. V mt chu lc va xi mng Chi chu lc tng tc do lin kt
gia cc ht ct liu38
38. ln trong b khung m khng chu lc ni ti trong lng n. Cch xy
dng m hnh cu trc b tng nh Vy c kh nng to ra b tng mc rt cao v gim c
nhng tc ng V cng phc tp ca cu trc h kt dnh va xi mng vi tnh cht cu
trc vi m ca b tng. Tuy nhin, m hnh ny Chi thun tu l thuyt m rt kh
hay khng c kh nng to c trn thc t nhng n a ra nguyn tc cho tt c Cc
cng ngh b tng l tng mnh ca cu trc b xng khung ct liu trn c s:+ Tng
din tip xc gia Cc ht ct liu ln (gia hai ht vi nhau v ca cc ht xung
quanh mt ht).+ Khng gian h trong b khung xoig l nh nht.+ Chiu dy ca
lin kt h xi mng vi cc ht ct liu l hiu qu (chi nhm mc ch lin kt).Vy
cc yu t nh hng c bn ti cu trc b tng l ct liu (kich thc, tnh Cht b
mt), phng php thit k thnh phn b tng (Cp phi), c tnh k thut ca ct
liu, k thut tc ng c hc, ngoi ra C mt yu t quan trng d l tinh linh
ng ca dung dch h va xi mng (khi dung dch va xi mng cng linh ng do
th cu trc ct liu ln cng mnh). Nhng ton b tnh cht phc tp trong cu
trc vi m cai b tng li nm lin kt gia va xi mng vi cc ht ct
liu.2.5.2. Cu trc vi m ca xi mngCc ht xi mng c thu ho bi nc v qu
trnh thu ho thc hin dn t ngoi vo bn trong ngay tc khc to lp mng kt
dinh bao quanh ht xi mng m bn cht l lin kt ion gia phn t hn hp xi
mng v phn t nc, lp mng ny dy theo thi gian thu ho v ngoi n la lp nc
t do. Tuy nhin, lp mng lin kt ny li cn tr s tham nhp ca nc v cng vi
thi gian tnh linh ng ca cc phn t nc v xi mng gim dn do vy lm gim tc
thu ho. Lp lin kt ht xi mng - nc dy dn cng vi n lp nc t do bao ngoi
ht xi mng mng dn, thm vo s linh ng ca Cc ht xi mng do tc ng ca vic
trn hay tc ng c hc c iu kin gn nhau dn dn hnh thnh lin kt v xo b
ranh gii gia cc ht xi mng. Mang lien kt xi mng nc bao quanh cc ht
ct liu nh v ko chng vo hnh thnh cu trc h kt dnh va xi mng. C th m t
tm tt cu trc vi m ca va xi mng trong hn hp b tng nh Sau:39
39. Cc ht xi mng lin kt vi nc (loi lin kt ion) to nn lp dinh
(bao quanh ht v dy theo tiin trnh thu ho) lm c S lin kt cc ht Xi
mng vi nhau (lin kt C hc) xo b ranh gii cc ht v ng thi chng Cn lin
kt c hc vi Ct liu nh (ct) to nn cu trc con va xi mng lin kt v to nn
cu trc n nh c tnh cht c li. Nhng phn ng thu ho Vn tip tc xy ra, do
vy trong cu trc Vn tn ti b phn li ht l khi xi mng khan v khng gian
gia cc ht xi mng lin kt l khong rng c cha nc.Cc yu t tham gia vo cu
trc:+ Vai tl' ca ht Ct. Mi nhn c th ngh s tham gia ca ht ct l tha,
nhng n li c vai tr ht Sc quan trng trong phn tng cng n nh khng gian
ca cc ht xi mng lin kt, n c tc dng nh cht hot tnh tng cng` s linh
ng ca cc ht xi mng v phn t nc kch thich qu trnh thu ho, ng thi di
tc ng ca c hc v s linh ng ca bn thn trong dung dch huyn ph (giai on
nc lin kt keo gia cc ht xi mng) lm gim bt s cn tr ca mng lin kt xi
mng nc to cho s thm nhp ca phn t nc vo bn trong ht thu ho tip. Do ,
tc dng cui cng l gim lng l rng trong cu trc, tng d bn, kh nng chu
lc ca cu trc.+ Cc ht xi mng thu h0.' Tuy rng lc dnh kt cc ht xi mng
tu thuc phn ln vo loi xi mng (hm lng cc thnh phn trong xi mng),
nhng mc linh ng ca cc ht xi mng - nc ph V th can bng tm thi lm cho
cc ht xt nhau hon to nn th Cn bng n nh hon v girn cc l rng, lc dnh
cc ht cng cao hon. Thi im v khong thi gian tc ng c hc c nh hng ti
lc dnh ny. Ngoi ra tc , mc phn ng thu ho nh hng ti hm lng ht xi mng
c thu ho, mong mun ht thi gian bo dng b tng hoc thi gian bt du chu
lc th hm lng Xi mng trong li ht xi mng cha c thu ho l nh nht. y cng
l mt yu t tng cng ca xi mng.Mt sidc im ca phn ng thu ho xi mng- L
loi phn ng chm dn v ko di rt lu. Mt S l thuyt cn nu rng y l loi phn
ng rt kh kt thc (diu ny l gii phn no cng ca b tng tng dn theo thi
gian tt nhin l khng xt ti nh hng ca mi trng, iu kin chu lc).40
40. - Thng thng theo thi nghim thy rng hm lng xi mng cha thu ho
sau 28 ngy khong di 2% hm lng ton b ht.- y l loi phn ng c Sinh nhit
(ch yu l do thnh phn CgA, C,S thu ho Sinh ra). Nu b qua tc ng ca bn
ngoi tng lng nhit ph thuc vo loi xi mng v lng Xi mng.Tc v mc d ca
phn ng thu ho ph thuc vo yu t Sau: mn ca ht xi mng, nhit ni ti
trong hn hp, tc ng c hc (tuy nhin nu thi gian dm m ln li gim tc thu
ho), ph gia tc ng, tc d to nhit.+ Cc l rng trong cit trc.' L rng
lun tn ti trong cu trc.va xi mng v nh hng rt ln ti tinh bn ca ,cu
trc ny. Phi tm Cch gim ti da hm lng l rng. Nguyn nhn to ra l rng:-
Do tnh khng th Xt c ca cc ht xi mng khi lin kt.- Do lng nc t do
(lng cn li Sau phn ng thu ho v lng nc t do ny thng chim 10 - 20%
tng lng nc S dng, tu theo loi b tng). _- Do hm lng bt kh to ra
trong qu trnh trn. Nh vy, nguyn tc gim rng (tng d cht) l:- Gim ti a
c th lng nc khng cn cho thu ho- To linh ng cho Cc ht xi mng khi thu
ho.- Tc dng co hc hp l gim tr lc ca lin kt xi mng nc lc u gip cc ht
xit nhau hn. L rng c tn ti di hai dng. L rng trong khong khng gia
cc ht v l rng tn ti di dng cc mng li mao dn. Tnh cht cu trc va - xi
mng c biu hin qua lin kt gia cc ht xi mng v hm lng ht Xi mng c thu
ho. L rng trong cu' trc l lun lun tn ti ngay c khi lng nc S dng l
ti thiu (chi cn cho thu ho ton b lng xi mng), lng l rng ny s tng mt
cch tnhin theo mc tng hm lng nc ngoi thu ho v s tng hmlng xi mng
cng nh kchc thc ht xi mng.Cu trc vi m ca va Xi mng ng vai tr quan
trng trong to lp cu trc b tng v trong b tng cng cao tc ng ca n vi
tnh cht cu trc b tng cn hn c tc ng ca cu trc ct liu ln. IMun itng
mnh ca cu trc ny phi tng c linh ng ca bn thn cc ht xi mng, tc ng c
hc hp l tng kh nng xp xt ca cc ht41~
41. xi mng lm gim hm lng l rng t nhin. Gim ti da lng nc tha
khng cn cho thu ho, gim lng bt khi to thnh, kch thch phn ng thu ho
Sao cho hm lung li xi mng khan ca ht l t nht khi hit giai on bo
dng.2.5.3. Cu trc vng tiip gip gia h xi mng v ct liu vng tip gip
gia xi mng v Ct liu tn ti Cc lp va xi mng p St b mt ct liu, cc Vng
Cha nc do S tch nc bn trong ca va xi mng, cc l rng do nc bc hi v cc
ht CaO t o cn li. Vng ny tn ti lc dnh gia xi mng v ct liu. Cu trc
tt nht vng tip gip to ra lc dnh kt l ti a v c l rng l ti thiu. S
thay i m vng ny chnh l nguyn nhn gy ra cc biin dng theothi gian cho
b tng. Loi b tng c thit k vi ti l thp, c trnhp l, c m chc hp l S to
ra Vng tip gip tt nht v to ra lc dnh cao nht. Vng tip gip ny l Vng
quan trng nhtmg yu nht ca cu trc b tng. Vi b tng truyn thng vt ntt
u tin trong b tng xut hin ti y v pht trin trong cu trc h xi mng ng
cng. Vi b tng Cng cao do lng nc S dng t hn v do tc ng ca mui silic,
Cu trc vng tip gip c ci thin ng k, khng c CaO t do, m thp, lc dnh c
nng cao, to ra cht lng mi cho b tng X mng.2.6. CC GIAI ON HNH THNH
CU TRC VI M CA HN HP B TNGC th chiathnh ba giai on Sau:- Giai on
cha hnh thnh Cu trc: Lc ny b tng l hn hp bin ng, c tnh k t thi gian
trn tt c thnh phn ca b tng cho ti khi bt du ninh kt. Tnh do ca hn
hp vn bo ton, hm lng xi mng thu ho trong giai on ny l ln nht. Cc ht
xi mng bt u ninh kt (mi trng tip xc gia Cc ht Xi mng chuyn t dng
huyn ph sang dng keo).Khi lc dnh kt gia cc ht xi mng, vi ht ct v c
lc dinh ca h va xi mng cng cha xut hin.- Giai on hnh thnh cu trc
khng n dnh: Lc ny hn hp bt u pht Sinh lc kt dnh, nhng lc kt dnh kt
tinh cn nh, hnh thnh42
42. cu trc cn bng mi bn Vng hon v lm lc dnh pht trin cao hn.
Trong giai don ny hn hp mt dn tinh do, hnh thnh tinh cht C l. Phn
cui giai don ny tnh do mt, bt u to nn tnh cht tinh th n nh v nu tc
ng C hc S lm ph hoi cu trc tinh th, lc dnh gim nhanh v khng cn pht
trin c na. Giai on ny bt u t khi bt u ninh kt ti khi kt thc ninh
kt.- Giai on cu trc n nh: l dng cu trc tinh th, lc dnh pht trin d
khun, dm chc b tng d dng nht m vn to ra c b tong c cht cn thit. do
ca b tng c xc
