Be tong- xi mang

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  • 1. Ths.gvc Nguyn Dn 1 TRUNG I HC BCH KHOA NNG KHOA HA - NGNH cnhh & VT LIU Ths.GVC NGUYN DN 2007

2. Ths.gvc Nguyn Dn 2 Chng 1 NH NGHA, PHN LOAI B TNG VA HN HP B TNG XI MNG. B TNG XI MNG CT THEP, B TNG NG SUT TRC. 1.1 nh ngha B tng xi mng la loai vt liu a nhn tao nhn c bng cach khun va lam rn chc lai mt hn hp thch hp bao gm cht kt dnh (cac loai ximng ) nc, ct liu (cat, san, soi, a dm) va phu gia ( nu co). Hn hp cac loai nguyn liu trn ( xi mng, nc, ct liu, phu gia) mi nhao trn ng nht nhng cha rn chc goi la hn hp b tng hay con goi la b tng ti. Trong b tng, ct liu ong vai tro la b khung chu lc, h xi mng ( ximng va nc) bao boc xung quanh cac hat ct liu ong vai tro la cht bi trn ng thi lp y cac khoang trng gia cac hat ct liu. Trong qua trnh ng kt va phat trin cng cua h xi mng, no se gn kt cac hat ct liu thanh mt khi tng i ng nht goi la b tng. B tng xi mng co ct thep goi la b tng xi mng ct thep. Nhng cht phu gia a vao hn hp b tng xi mng nhm muc ch cai thin mt s tnh cht cua hn hp b tng nh tng tnh lu ng cua hn hp b tng, iu chnh thi gian ninh kt, nng cao tnh chng thm cua b tng ... Trong b tng xi mng ct liu thng chim (80 - 85)% con xi mng portland chim (15-20)% khi lng hn hp b tng. B tng xi mng la loai vt liu rt quan trong c s dung rng rai trong xy dng dn dung, cng nghip, thuy li, cu ng... v co cac u im sau: - Co cng nen cao bin i trong pham vi rng t 100, 200 n 900, 1000 daN/cm2 . - Gia thanh tng i ha. Tuy vy no vn co nhc im: nng, cach m, cach nhit kem. 1.2 PHN LOAI B TNG Co nhiu cach phn loai b tng, thng theo 3 cach: 1.2.1. Phn loai theo khi lng th tch. y la cach phn loai thng c dung nht v khi lng ring cua cac thanh phn tao nn b tng gn nh nhau (u la khoang cht v c) nn khi lng th tch cua b tng phan anh c chc cua no. Theo cach phn loai nay co th chia b tng thanh 4 loai: c bit nng: 0 > 2500 kg/m3 , ch tao bng cac ct liu c chc va t cac loai a cha qung. B tng nay ngn c cac tia X va tia . 3. Ths.gvc Nguyn Dn 3 B tng nng: (Con goi la b tng thng) 0 = (1800 - 2500) kg/m3 ch tao t cac loai a c chc va cac loai a cha qung. Loai b tng nay c s dung ph bin trong xy dng c ban va dung san xut cac cu kin chu lc. B tng nhe: 0 = (500 -1800) kg/m3 , gm b tng ch tao t ct liu rng thin nhin, nhn tao va b tng t ong khng ct liu, cha mt lng ln l rng kn. B tng c bit nhe: 0 < 500 kg/m3 co cu tao t ong vi mc rng ln, hoc ch tao t cac loai rng nhe co rng ln (khng cat). 1.2.2. Phn loai theo cht kt dnh. B tng ximng: Cht kt dnh la ximng va chu yu la ximng pooclng va cac loai xi mng khac. B tng silicat: Ch tao t nguyn liu vi cat silc nghin, qua x l chng hp nhit va ap sut cao. B tng thach cao: Cht kt dnh la thach cao hoc ximng thach cao. B tng x: Cht kt dnh la cac loai x lo cao trong cng nghip luyn thep hoc x nhit in, phai qua x l nhit m ap sut thng hay ap sut cao. B tng plime: Cht kt dnh la cht deo (polime) va phu gia v c. 1.2.3. Phn loai theo pham vi s dung. B tng cng trnh: S dung cac kt cu va cng trnh chu lc, yu cu co cng thch hp va tnh chng bin dang. B tng cng trnh cach nhit: Va yu cu chu c tai trong va cach nhit, dung cac kt cu bao che. B tng cach nhit : Bao am yu cu cach nhit cua cac kt cu bao che co day khng ln. B tng thuy cng: Ngoai yu cu chu lc va chng bin dang, cn co chng thm va tnh bn vng trong mi trng.xm thc cao. B tng lam ng: Dung lam tm lat mt ng, ng lam bng sn bay... loai b tng nay cn co cng cao, tnh chng mai mon ln va chu c s bin i ln v nhit va m. B tng n nh hoa hoc: Ngoai yu cu thoa man cac ch tiu k thut khac, cn chu c tac dung xm thc cua cac dung dch mui, axt, kim va hi cua cac cht nay ma khng b pha hoai hay giam tui tho cng trnh. B tng chu la: Chu c tac dung lu dai cua nhit cao khi s dung. 4. Ths.gvc Nguyn Dn 4 B tng trang tr: Dung trang tr b mt cng trnh, co mau sc yu cu va chu c tac dung thng xuyn cua thi tit. B tng nng chu bc xa: Dung cac cng trnh c bit, ngn c bc xa cua tia hay bc xa ntrn. 1.3. KHAI NIM V B TNG CT THEP. 1.3.1 Khai nim. B tng la loai vt liu don, cng chu nen ln, nhng kha nng chu keo va chu un thp ch bng 1/10 n 1/15 cng chu nen. y la nhc im c ban cua b tng xi mng. Qua nghin cu va thc t s dung s phi hp gia vt liu b tng va ct thep tao nn b tng ct thep se khc phuc nhc im noi trn. S d co c tnh u vit noi trn la do 3 ly do sau: - Lc bam dnh gia b tng va ct thep rt ln (xem 3.4.3 chng 3). - B tng bao v thep khng r. - dan n nhit hai loai vt liu nay xp x nhau. 100 o C h s dan n nhit cua b tng la 10.10-6 con ct thep 12.10- 6 . 1.3.2 Phn loa cu kin b tng ct thep. Cn c vao cach t ct thep, loai b tng a dung, trong lng, cu truc va cng dung cua cu kin, ngi ta chia lam 4 loai: Theo cach t ct thep: Cu kin co hoc khng co ct thep. Nu co ct thep co th la ng sut trc hoc khng. Theo loai b tng: B tng nng hoc b tng nhe. Theo cu truc, trong lng: Cu kin c hoc rng, nng hoc nhe. Theo cng dung gm co: - Nhom cu kin dung cho nha va cng trnh cng cng. - Nhom cu kin dung cho nha cng nghip. - Nhom cu kin dung cng trnh thuy li. - Nhom cu kin dung cho cng trnh giao thng. 1.3.3 Qui trnh san xut cu kin b tng xi mng ct thep. 1.3.3.1 Cac phng phap tao hnh. Qua trnh san xut b tng xi mng ct thep thng co 3 cng oan: Ch tao hn hp b tng, gia cng ct thep, chun b ct thep - tao hnh - dng h va trang tr b mt cu kin. Co 3 phng phap tao hnh cu kin: Phng phap khun c nh. Phng phap khun di ng. Phng phap dy chuyn lin tuc ( phng phap can). Mi phng phap co u nhc im ring. 5. Ths.gvc Nguyn Dn 5 Tao hnh theo phng phap khun c nh thun li nht cho vic uc cac cu kin co kch thc ln va nng, v cac cu kin o di chuyn trong qua trnh ch tao se gy kho khn va tn cng sc. Do vy phng phap nay giam tiu hao cng sc, thit b n gian, vn u t thp nn c s dung rng rai trong cac nha may cung nh cng trng. Song phng phap nay cung co nhc im mc c kh hoa thp. Tao hnh theo phng phap khun di ng trn xe co li v mc c kh hoa cao trong moi khu, nhng co nhc im vn u t trang thit b cao va kem linh hoat khi chuyn sang san xut cac cu kin mi. Tao hnh theo phng phap khun di ng theo nhom may th ngc lai. Tao hnh theo phng phap dy chuyn lin tuc co nng sut cao nht, nhng co nhc im ch san xut cac cu kin co kch thc han ch va tng i tn xi mng v ch dung c loai b tng hat mn. 1.3.3.2 Vt liu ch tao b tng xi mng ct thep. Hn hp b tng xi mng ( trnh bay cac chng sau). Ct thep: gm co cac loai thep: Thep tron, thep si, thep can nong co g, li thep, thep cap, thep can bep trang thai ngui. Yu cu ct thep co gii han chay cao, b mt sach, khng co vy st hay b r. Bang 1.1 Cac loai thep thng dung va cac c trng c ban cua chung Cac loai thep ng knh (mm) Gii han chay (KG/cm2 ) Gii han bn ( KG/cm2 ) dan dai tng i (%) Pham vi s dung Thep tron CT3 6-40 2.400 3.800 25 Ch tao ct thep thng CT3 co keo ngui n 2.800KG/cm2 6-22 2.800 3.800 10 Nh trn CT5 10-40 2.800 5.000 19 Nh trn CT5 co keo ngui n 4.500KG/cm2 10-40 4.500 5.000 8 Nh trn 252C 6-40 4.000 6.000 14 Ch tao ct thep .s trc 252C co keo ngui n 5.5000KG/cm2 6-40 5.500 6.000 6 Nh trn 6. Ths.gvc Nguyn Dn 6 30X2C 10-32 6.000 9.000 6 Nh trn 20X2 6-40 6.000 9.000 6 Nh trn 20XCT 6-32 6.000 9.000 6 Nh trn 1.3.3.3 Qui trnh san xut cu kin b tng xi mng ct thep. Co 3 cng oan: Cng oan 1 Ch tao hn hp b tng va gia cng ct thep. Ch tao hn hp b tng se trnh bay phn sau. i vi ct thep cn nn thng, anh sach r va ct ct thep co chiu dai theo yu cu. Sau o dung may han in han thanh khung hoc li thep. Vic cng ct thep ch tao cac kt cu ng sut trc c s dung phng phap c hoc hay phng phap nhit cua dong in. Phng phap c hoc, phng phap nhit: Xem ct thep nh mt in tr, khi cho dong in chay qua thanh thep se b nung nong va dan dai ra, va nu luc o ta c nh 2 u thanh thep b nung nong, khi ngui trong thep se sinh ra ng sut trc. Phng phap nay hiu qua v khng cn thit b keo cng phc tap. Cng oan 2 Tao hnh cu kin. Co th theo cac phng phap khun c nh, phng phap khun di ng, phng phap dy chuyn lin tuc. Cng oan 3 Dng h cu kin Thng dng h nhn tao vi cac cach: - Hp trong phong co nhit 1000 C va ap sut tiu chun. - Hp trong ctclav nhit (175-250)0 C va (8-12) at. - Trong b nc nong, hay bng sc nong cua dong in. Hp trong phong chia lam 2 loai: loai lin tuc lo tunnel, loai gian oan lo phong. Ch hp phu thuc vao yu cu cng b tng, cng ngh ch tao, tnh cht xi mng ...Thng thng ch hp: tng nhit trong (2-3) gi, hp (6-8) gi va lam ngui trong 2 gi. Nh vy qua trnh hp mt (10-13) gi. i vi b tng dung xi mng portland khi hp dung hi nc bao hoa va nhit (85-90)0 C. 1.4 KHAI NIM V B TNG XI MNG CT THEP NG SUT TRC B tng xi mng ct thep co nhc im: Nng lc chu keo qua kem, nn trong cac phn chu keo cua kt cu b tng ct thep ch co tac dung la lp bao v ct thep va khng co kha nng chu lc. dan dai cua thep khi keo xp x vi dan dai cua b tng xi mng b tng khng t v, nn trong b tng ct thep phai dung thep co cng thp, dan dai khi keo be.( dan dai cua b tng 7. Ths.gvc Nguyn Dn 7 (1-2)mm/m, trong khi thep co th dan cng ra gp (5-7) ln so vi b tng). khc phuc cac nhc im trn, ngi ta tm cach tng kha nng chu keo cua b tng bng cach nen trc b tng trong vung chu keo. Phng phap thc hin: keo trc ct thep ri bung ra gy tac dung nen trc trong b tng, tao nn trong b tng ng sut nen trc tc la lam cho b tng tim tang mt th nng chu keo. Khi kt cu chu tac dung cua ngoai lc gy nn lc keo th u tin b tng mt i phn ng sut nen trc a co khi b nen ri mi chu keo. Do o kha nng chu keo cua b tng tng ln ang k co th xp x cng chu nen. Loai b tng co kha nng nh vy ngi ta goi la b tng ng sut trc ( d ng lc). Ct thep s dung trong b tng ng sut trc la thep si co cng cao va c cng trc bng thit b c bit. Co hai phng phap ch tao b tng ng sut trc. 1.4.1 Phng phap keo cng ct thep trc. Keo cng trc ct thep ri mi hn hp b tng sau. Khi hn hp b tng a rn chc th tha kch cng ct thep ra. Ct thep mt lc cng se co lai va do lc bam dnh cua b tng va ct thep, b tng se b nen tao nn ng sut nen trc trong b tng. 1.4.2 Phng phap keo cng ct thep sau. Khi uc b tng t nhng ng nho trong khun cu kin va lun ct thep qua nhng ng nho nay, sau o hn hp b tng lp ln nhng ng nay. Khi hn hp b tng a rn chc ta keo cng ct thep va neo u cac ct thep nay vao ban neo t v