- Nhiimg chi djnh ky thudt phai rd rang, mirc kit qua phai dat dugc ciia be tdng tir nhung kiem djnh tieu chuan - Vf du ddi vdi cdc cdt nhd cdng trinh chi sir dung cudng do chiu nen v[r]
(1)DIEN DAN KHOA HOC CONG NGHE
NHffNG CHi TIEU KY THUAT OANH GIA DO B I N CUA BE TONG TRONG CONG TRINH XAY DlTNG
Betong la vat lieu khong hoan thien?
Chung ta thudng dat hang betdng theo cac yeu cdii v l cudng Cudng thi cd the xdc djnh bdng sd, chiing ta cd the dugc
N I U chiing ta yeu edu betdng ed bin 100 nam lam t h i nao de biet vd khang djnh duge?
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P G S T S N G U Y E N VAN C H A N H Trudng Dai Hpc Bach Khoa TP.HCM
Cdc chl tieu ky thuat neu bai ndy nhdm muc dfch giup ky sube tdng vd ky suxdy dung edng trinh:
- Cai tien eae djnh mUe eh! tieu ky thuat de dat duge be tdng vdi chat lugng tdt hon
- Lua chgn nhung dilu kien gidi han thich hap ngodi cdng trudng de ddnh gid ehdt lugng be tdng be tdng Idm viee mdi trudng khae nghiet
- Nhdn bilt vd hieu cdc thf nghiem va ede chl tieu ky thuat ciia thf nghiem dugc sir dung de ddnh gia chdt lugng ciia be tdng
1 Cudng chju nen '*'* Cudng chju nen Id thf nghiem thdng dung nhat
sirdung cho be tdng Mae dii eudng thudng khong phdi Id nhdt mdt chi tieu tdt de ddnh gia bin ciia be tdng, nhung thiet ke ket cau ciia cdng trinh, be tdng d i u phai dat duge mdt mirc t6i thieu v l cudng Khi cdc bd phdn kit cdu cong trinh khdng de cap den ben thi cUdng dp la dieu kien tien quylt de ddnh gid chdt lugng ciia ket cau dd '
ii' Hinh 1: Ciu Phu My va ciu Cin Thd
Hinh 2: Thidt kd ve eddng l<hdng quan tam ddn bdn
Thdng thudng, be tdng thudng thf nghiem eudng nen d 28 ngdy, nhien, nhtmg ngudi thilt ke chuyen nghiep cung cd the linh ddng thay ddi tudi thir cudng nen cua be tdng cho thi'ch hgp vdi cac yeu cdu cua du an Yeu cdu v l be tdng phdt trien nhanh cudng d giai doan ddu cd the thfeh hgp vdi nhufng cdng trinh xdy dung ddi hdi tiln nhanh, nhien dilu cd the ldm cho bin ciia be tdng giam Nlu cdng trinh thiet ke chju tai trgng ddng ve sau thi chl tieu ddnh gia cudng nen cua be tdng
(2)NHffNG CHJ TIEU KY THUAT OANH GIAflOBlN ,
cdn thilt phdi d l cap din eudng d 56 vd 90 ngdy Do b i n
Khi d l cap din dp bin ciia be tdng, ngudi ky su xay dung khdng nen chl dua chu ylu vdo ede chl tieu ky thuat v l cudng nen tdi thieu, ti le N/X tdi da, ham lugng xi mang tdi thieu vd ham lugng bot khf Cd nhirng yeu edu tdt hon de danh gid bin eiia be tdng Do eo ngdt vd thdm thdp Id hai thdng sd ky thuat dae trung eho ben eiia be tdng ket edu lam viec nhtmg dilu kien khac nghiet
Ndi tdm lai, thf nghiem cudng nen eiia be tdng khdng phai la thf nghiem dai dien eho dp ben ciia be tdng Hien nhien la, be tdng ed eudng dp cdng eao thi kha nang khdng nut xdm thuc gay edng tdt, va cd ti le N/X cang thdp Tuy nhien, edn phdi chdc chdn rdng, thdnh phdn cdp phdi eiia hdn hgp be tdng phdi dugc t i l Uu hda de cd the chdng lai duge su xam thue ciia mdi trudng Idm viec ed gdy anh hudng din dp bin eiia be tdng Cu the Id:
- Phai sir dung xi mdng thfeh hgp d l i vdi dilu kien cdu kien betdng mdi trudng sir dung (xi mdng PC, xl mdng it tda nhiet, xi mdng PCB, xi mdng ching lai an mdn sunphat )
- Cdt lieu khdng bj phdn ung kilm
- Cau kien betdng khdng nut eo ngdt vd khdng nirt nhiet
3.06 thdm
Cd nhieu quan diem cho rang, de nang cao ben cua be tdng can phai giam thdm be tdng Theo tieu ehuan, ti le N/X rdt quan trpng ddi vdl dp thdm eua be tdng Tuy nhien, thuc t l , nlu chi xem xet mdi yeu td ti le N/X thi cd the gdy dnh hudng den nhung yeu td khdc cua be tdng Ham lugng hd xl mdng (nude + xl mdng) cao thi nhiet hydrat hda se eao, d l nut, modun dan hdi thdp, tU biln cao Ngoai ra, bin hda hge ciia be tdng phu thudc Idn vdo thiet ke thdnh phdn hdn hgp be tdng
Ngdy nay, cimg vdi viec sirdung rdng rai phu gia vd CO hoat tfnh vd phu gia hda hgc tien tiln, chiing ta cd the tdi uu hda cap phdi hdn hgp be tdng theo hdm lugng cd thdm thdp bang nhilu cdch khdc thay yi chi kiem sodt ti je N/X Cd the ddnh gid mUc dp thdm ciia be tdng bdng cdc thf nghiem tieu chuan hien cd ASTM C1202 thf nghiem danh gia
kha nang tham thiu ion cua be tdng thdng qua nhan biet dien thi, thudng dugc ggi Id thf nghiem
thir thdm nhanh ion clo, day Id mdt nhtmg phuong phdp dang duoc sir dung nhilu cdc tieu chuan ky thuat nham ddnh gid dp b i n cua be tdng Theo ASTM C1202, be tdng cd gid trj coulombs Idn hon 4000 duge xem Id cd thdm cap, coulombs 2000 d i n 4000 dugc xem Id cd thdm trung binh, coulombs 1000 d i n 2000 dugc xem Id dp thdm thdp, coulombs nhd hon 1000 dugc xem la dp thdm rdt thdp Ddi vdi hdu hit cdc k i t cdu, be tdng cd gid tri coulombs 2000 d i n 2500 thi dugc xem Id cd thdm du thdp Be tdng cd gid trj coulombs thdp thi se cd kha ndng chdng lai sutham thdu ciia ion clo tdt
4 An mon cdt thep
An mdn edt thep Id mpt qua trinh dien hoa xay edmat cua am vd oxy Qua trinh chuyen hda cdt thep thdnh ri sdt, ri sat ed the tfeh gdp ldn so vdl thep ban ddu Trong Idp be tdng bao ve cd kilm eao hinh thdnh Idp thu ddng xung quanh cdt thep, Idp thu dpng ddng vai trd bao ve edt thep khdng bj an mdn Ldp mang thu dong bj pha hiiy be tdng bao ve tai be mat edt thep bj cacbonat hda Ngodi ra, hdm lugng ion clo tai be mat ciia cdt thep eung gdp phan Idm phd hiiy Idp mang thu dong De bao ve edt thep khdng bi an mdn, can phai tien hdnh nhieu bude Dieu ddu tien, Idp be tdng bao ve phai dil day va ed chat lugng de cd kha nang tri hoan su phdt sinh dn mdn edt thep De tri hoan su phdt sinh an mdn edt thep, cd the sir dung cac bien phdp nhu tang dp ddc sft de gidm dp tham cua be tdng, sir dung epoxy quet len b l mat edt thep, hoac sirdung phu gia Uc che dn mdn qud trinh nhao trpn hdn hgp be tdng DT nhien Id, sir dung loai cdt thep khdng an mdn Id phuong an tdt nhdt v l mat ky thuat, nhien bien phap lai rdt ddt tien
ã 4ô!- ^
Hinh va 4: Thim clorua gay an mon cdt thep
De bao ve cdt thep khdng bj dn mdn xdm thuc eiia nudc bien hodc sutham thdu ion clo, ACI 318 d l nghj sir dung be tdng cd ti le N/X=0,4, eudng dp chju nen tdi thieu Id 350kG/em^ Trong tieu ehuan cung dua gidi han cho hdm lugng ion clo tu ed be tdng, ham lugng tfnh theo phan trdm khdi lugng cua xi mdng, hdm lugng gidi han d mirc 1% ddi vdi be tdng lam viec dilu kien khd rdo, vd 0,06% ddi vdi be tdng irng sudt trudc
(3)ciru, nhien theo cdch hieu thdng thudng thi nhimg v l t nirt nhd (dudi 0,2mm) vudng gdc vdi edt thep thi cd the khdng dnh hudng dang ke din su an mdn cdt thep
Qua trinh carbonat hda ciia be tdng cd ehdt lugng tdt thudng Id mdt qud trinh xay cham vd khdng thuc su ddng lo ngai neu Idp bao ve be tdng du dam bao yeu cau
5 Xam thuc sunphat
Cae ion sunphat duge tim thdy nUde ngdm va ddt Trong hdu het eae trudng hgp, mdt sd mudi sunphat cung phan ung vdi eae phdn hydrat hda ciia xi mang tao thach eao, ket qua Id cung gay sU truong nd the tfch Trong mpt sd trudng hgp, cac san pham hydrat hda eiia xl mang bj pha hoai, tU dd lam mdt di cdc tfnh chat ket dfnh eiia da xi mang De ehdng lai sU xdm thuc sunphat gay ra, edn thilt phai sir dung nhtmg loai xi mdng thfeh hgp, va gidm sutham thau eiia ion sunphat ydo be tdng
NHJTNG CHi TIEU KY THUAT OANH GIA 0 B E N
-cd the khdng hieu qua nlu mdi trudng ben ngoai ed chira kiem
Hinh 5: Tham mudi Sunfat tao khoing ettringit gay ndt be tdng
Trong mdi trudng xdm thuc sunphat trung binh, cd the sir dung xi mdng loai II (theo each phdn loai xi mdng ciia ASTM) Trong mdi trudng xdm thuc sun-phat manh thi sirdung xi mdng loai V Xi mdng loai II ed ham lugng C3A tdi da Id 8%, dd, xi mdng loai V cd hdm lugng C3A tdi da Id 5% Khd ndng bin sunphat cua xl mdng Portland dugc thf nghiem theo tieu chuan ASTM C452 Hdu hit cdc loai phu gia yd CO hoat tfnh nhu tro bay (loai F), xi vd mudi silic diu cd kha ndng Idm tang kha ndng bin sunphat cho xl mang Portland
6 Phan ifng kiim-silic
Trong dilu kien cd dp am, cdc ion kilm tdn tai xi mdng se phdn irng vdi nhung thdnh phdn khodng silic hoat ddng elt lieu, phan irng ndy tao gel kilm-sllic truong nd hdp thu nude, tirdd Idm eho be tdng bj nut De trdnh phan ung kilm-silic, ngudi Idm tieu chuan nen yeu cdu phdi sir dung loai edt lieu khdng cd phdn silic hoat ddng Sir dung loai xi mdng cd ham lugng kilm thdp (ham lugng kilm tfnh tUdng duong theo Hafi nhd hon 0,6% khdi lugng xi mdng) cd the ngan chdn dugc phan iing kilm-silic Tuy nhien, bien phdp cung
Hinh va 7: Tie dung cua kidm vdi cdt lieu gay ndt be tdng
Cdt lieu dugc xem Id khdng gdy phan irng kilm-silic dp dan nd 14 ngdy nhd hdn 0,1% thf nghiem theo ASTM C1260, hodc dan nd nam nhd lion 0,04% theo ASTM 1293 Ngodi ra, ed the sir dung phUdng phdp thach hpc de xdc djnh sd lugng thdnh phdn khodng silic hoat ddng ed edt lieu
Neu nhu cdt lieu dugc thf nghiem theo nhtmg thf nghiem dtren vd cho kit qud Id cd khd ndng sinh phdn irng kilm-silic, thi cdt lieu vdn cd the sirdung be tdng chiing ta sirdung cdc bien phap ho trg Idm gidm phdn ung kiem-silie nhu diing phu gia vd eo hoat tfnh vd phu gia hda hpe gdc lithium
Kit luan
-Yeu cdu tfnh chdt ky thudt ciia be tdng phai dat dugc tijy thudc vdo tdi trgng vd mdi trudng sir dung eua cdu kien be tdng
- Nhiimg chi djnh ky thudt phai rd rang, mirc kit qua phai dat dugc ciia be tdng tir nhung kiem djnh tieu chuan - Vf du ddi vdi cdc cdt nhd cdng trinh chi sir dung cudng chiu nen vi bin khdng quan tdm, nhung tieu chuan ciia cdng trinh cd sd tdng phdi bao gdm R^, R,,, gldl han thdm vd nirt eo ngdt vl be tdng sir dung mdi trudng an mdn khac nghiet
- Phai ehi djnh phUOng phdp thf nghiem va mirc tieu chuan chap nhdn de nghiem thu, cae yeu cdu thi nghiem chdt lugng be tdng trude thi edng va cac thf nghiem hien trudng sau thi cdng
- Nhd thdu vd nha sdn xudt be tdng phai thuc hien phdn tfeh vd thilt ke cap phdi hdn hgp be tdng va phUdng phdp thi cdng thfch hgp ddi vdl hdn hgp be tdng de cdu kien be tdng ddng nhdt dat dugc nhOmg chl tieu ky thudt cd ly vd dp bin quy djnh ciia be tdng.Q