Ảnh hưởng của phụ gia khoáng hoạt tính silica fume đến các tính chất của bê tông

412 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II<br /> <br /> <br /> <br /> <br /> ANH Hl/d-NG CUA PHU GIA KHOANG HOAT TJNH<br /> SILICA FUME D i N CAC TJNH C H A T CUA BE TONG<br /> TS. Nguyin Thanh Bdng'"<br /> ThS. Phgm Diic Trung"'<br /> <br /> Tom tit:<br /> Bai viet gidi thieu mgt dac tinh cua phu gia khoang hoat tinh sieu mjn Silica fume<br /> va cac kit qua nghien CLPU tren t h i gidi v i anh hudng ciia nd d i n cac tinh chit cua<br /> be tdng.<br /> Summary:<br /> EFFECTS OF MINERAL ADMIXTURE - SILICA FUME<br /> ON CONCRETE QUALITIES<br /> This acticle introduces some properties of mineral admixture - Silica fume and<br /> research results about effects of silica fume on concrete qualities.<br /> <br /> <br /> <br /> I. Dat van d e<br /> Trong tien trinh phat trien va hdi nhap vdi the gidi, ITnh vyc cdng nghe be tdng<br /> ciia ta da va dang tiep can dugc nhirng cdng nghe, vat lieu mdi va tien tien. Ciing vdi<br /> viec phat trien ciia khoa hgc cdng nghe, hien nay tren thj trudng cac san pham phu gia<br /> cho be tdng da trd nen het siic da dang va chat lugng ngay cang cao. Van de ldn nhat<br /> ddi vdi chiing ta la lam the nao de iing dyng hieu qua chiing vao trong thyc trang xay<br /> dyng nudc nha. Bai viet nay tac gia mudn gidi thieu mgt each tdng quan nhiing thdng<br /> tin va cac ket qua nghien ciru tren the gidi ve loai phy gia khoang hoat tinh sieu min<br /> silica fume, mdt sd tinh chat ciia be tdng nhu mgt tai lieu tham khao nham giiip cac nha<br /> nghien ciru, thiet ke cd them tu lieu trong viec nghien ciiu iing dyng hieu qua loai phu<br /> gia nay.<br /> II. Gac dac tru-ng ly hoa cua silica fume<br /> Silica fume la san pham phu ciia cdng nghiep Iuyen kim. Loai hgp kim san xuat<br /> trong Id nung la yeu td co ban quyet dinh tinh chat ciia vat lieu tao thanh d cae dng lpc<br /> (silica fume). Ld nung de san xuat hgp kim sat - silic vdi ham lugng silic cao hon 72%<br /> se cho silica fum© cd chat lugng tdt va thanh phan rat ddng deu. Hai ngung ty tir hgp<br /> kim canxi-silic, sat-silic, mangan-silic cd dac trung vat ly tuong ty nhau, nhung thanh<br /> phan hda hgc khac nhau ea ban.<br /> <br /> ' Vien ThCiy cong. Nguai phan bien: PGS.TS. Hoang Pho Uyen<br /> PHAN II - XAY Dt,JNG VA BAO VE CONG TRINH... 413<br /> <br /> <br /> Cac hat silica fume cd dang hinh ciu, be mat tron phang, kich thudc trung binh<br /> ciia hat silica fume vao khoang 0,1-^0,2 ym, tiic la vao khoang 1:50-^1:100 kich thudc<br /> hat xi mang hoac tro bay, ty dien bl mat hat silica fume vao khoang tir 13000-^25000<br /> m /kg [1]. Bpt silica fume ed khdi lugng don vj d trang thai dd ddng rit nhd, vao<br /> khoang 0,15-^0,2 tan/m^ [2]. Silicafume cd ham lugng dxit silic boat tinh cao vao<br /> khoang 85^98% [2].<br /> <br /> III. Anh hu-ang cua silica fume d§n cac tinh chit cua be tong<br /> /. Tinh deo eda vira bi tdng<br /> Mdt sd thi nghiem da cho thay vdi be tdng 300 kg/m^ xi mang pooelang va dudi<br /> 10% silica fume thi do syt thyc te khdng cd gi thay ddi nhieu so vdi be tdng ddi chimg<br /> cd ciing ham lugng chat ket dinh. Vdi be tdng giau xi mang viec them silica fume ddi<br /> hdi tdn nang lugng hon trong viec do va dam do viira be tdng bj quanh lai. Trong<br /> trudng hgp dd can thiet phai them vao viia be tdng phy gia deo hda.<br /> Silica fume lam tang tinh dn dinh ciia vira be tdng, nd lam giam phan tang, tach<br /> nudc cho viia be tdng. Trong viia be tdng giau chat ket dinh nd cd the gay nen hien<br /> tugng mit do co ngdt. Cho nen ddi vdi cac viing thdi tiet nang ndng va gid nhu tai<br /> Viet Nam thi can thiet phai cd bien phap bao dudng that can than.<br /> 2. Swphdt triin cw&ng dp eda bi tdng<br /> Ciing gidng nhu cac vat lieu puzalan, silica fume tham gia phan iing vdi Ca(0H)2<br /> trong be tdng tao ra san pham cd kha nang ket dinh. Silica fume cang tinh khiet, cang<br /> min thi hieu qua ciia phan ung cang cao va nhanh. Ciing vdi sy kliuech tan ciia minh<br /> cac hat silica fume lap day vao khoang giira eac san pham thiiy hda ciia xi mang, lam<br /> chat ciu triic da xi mang va lam tang kha nang ket dinh giiia da xi mang va cac hat cdt<br /> lieu. Do hoat tinh ciia silica fume phu thudc vao kha nang phan irng ciia Si02 vdi<br /> Ca(0H)2.<br /> Vdi silica fume cho phep san xuit dugc be tdng cd cudng dp cao hon nhieu so<br /> vdi be tdng thdng thudng. Vdi viec sir dung cdt lieu thien nhien cd the che tao dugc<br /> be tdng cd cudng do len tdi tren 150 N/mm^, vdi cac loai cdt lieu dac biet thi cd the che<br /> tao dugc be tdng cd cudng do len tdi 300 N/mm [1].<br /> Tdc do phat triin cudng do ciia be tdng cd sir dyng silica fume hai khac so vdi<br /> be tdng thudng. Trong diiu kien tieu chuin, sau 7 ngay cudng do ciia nd chi dat dugc<br /> tir 55-^65% cudng do d tudi 28 ngay [1]. Hoat tinh ciia silica fume diin ra ehii yeu<br /> trong giai doan tir 7 din 20 ngay. Silica fume thudng hay sir dung ket hgp vdi tro bay<br /> hoac xi Id cao d l dat duge toc do phat trien cudng dp cao hon.<br /> Cac thi nghiem gin day d mpt sd nudc cho thay, 1kg silica fume cd the thay the<br /> tir 3-^5 kg xi mang pooelang thdng thudng ma khdng lam thay ddi ve cudng dp ciia<br /> be tdng, tuy nhien mirc dp thay the chi trong mot chirng myc nhat dinh.<br /> 414 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II<br /> <br /> Vdi viec cho vao trong be tdng lugng silica fume tdi 30% va cd sir dyng ket hgp<br /> vdi phu gia sieu deo cd the che tao dugc vira be tdng cd ty le N/CKD nhd hon 0,3. Loai<br /> be tdng nay cd cudng do rat cao trong dieu kien giii am tdt. Trong nhiing mdi trudng co<br /> dp im khdng cao cd the dan den nhirng hau qua khdng nhu mong mudn nhu co, niirt v.v...<br /> Tac ddng ciia nhiet dp den kha nang phan iing ciia silica fume manh hon so vdi<br /> xi mang pooelang thdng thudng. Vdi nhiet dp thap phan img xay ra cham, nhiet dp cao<br /> phan img xay ra nhanh hon.<br /> 3. Dp kiim ciia be tdng<br /> Nhirng nghien ciiu cua cac nha khoa hpc tren the gidi da chirng minh rang, silica<br /> fume cd anh hudng dang ke den dp kiem ciia nudc trong cac Id rdng cua gel ximang.<br /> Phan irng ciia silica fume vdi Ca(0H)2 dan den sy hinh thanh cac gel cd ham lugng<br /> Si02 trong lien ket cao ciing vdi ham lugng nudc lien ket ldn. Do pH trong cac Id rdng<br /> ciia be tdng thdng thudng vao khoang 14, trong trudng hgp cd sir dung silica fume vdi<br /> lieu lugng vira phai chi sd pH nhanh chdng giam xudng 13. Vdi viec sit dung 15%<br /> silica furhe trj sd pH giam xudng 12,5. Khi lieu lugng diing len tdi 2 5 % thi silica fume<br /> trung hda gan nhu hoan toan vdi ty do trong be tdng, liic dd chi sd pH giam den miic<br /> cd anh hudng tieu cyc den tinh tro ciia cdt thep dudi tac ddng ciia mdi trudng an mdn.<br /> <br /> 4. Tinh thdm eda bi tdng<br /> Hieu qua tir viec lap day cac Id rdng bang cac hat silica fume rat mjn la lam giam<br /> kich thudc cac Id rdng mao quan, tang kha nang chdng tham cho be tdng. Tren thyc te<br /> ngudi ta da che tao dugc be tdng khdng tham vdi lieu lugng silica fume vira phai va<br /> ham lugng xi mang pooelang khdng cao. Hieu qua anh hudng ciia silica fiime den kha<br /> nang chdng tham ciia be tdng tdt hon la den cudng do [1]. Be tdng cd sit dyng silica<br /> fume cd kha nang chdng tham cao hon nhieu so vdi be tdng thudng tuang duong. Dieu<br /> nay cd y nghia dac biet ddi vdi eac cdng trinh thuy lgi, thuy dien cd yeu eau chdng<br /> tham cao.<br /> <br /> 5. Khd ndng bdo vi cdt thep<br /> Ve ly thuyet do kiem trong be tdng cdt thep giam se lam giam do ben cua nd dudi<br /> tac dpng cua cabonat hda va clo. Tuy nhien nhirng nghien cim d Na Uy va Thyy Dien<br /> ddi vdi cac ket cau be tdng cdt thep trong vdng 12 nam cho thay, dp bin ciia be tdng<br /> cdt thep chat lugng cao cd sir dung silica fume dudi tac ddng cua cacbonat hda khdng<br /> thap hon be tdng sir dung ximang pooelang thdng thudng cd cudng do tuang duang,<br /> ngoai ra be tdng cd sir dung silica fume cd kha nang ngan ngira thim clo tir nudc bien<br /> ldn han nhieu so vdi be tdng thudng. Tuy nhien niu sy bao duong be tdng cd sit dung<br /> silica fume khdng tdt thi sy hu hdng ciia kit ciu lai Idn han so vdi be tdng thudng.<br /> Mpt sd cac thi nghiem nghien ciiu an mdn cdt thep cua mdt sd nudc cho thiy<br /> trong dieu kien bao dudng tdt kha nang bao ve cdt thep cua be tdng cd sit dung silica<br /> fume khdng khac so vdi be tdng thdng thudng cd ciing cudng do.<br /> PHAN II - X A Y DLJNG vA B A O VE CONG TRINH... 415<br /> <br /> <br /> 6. Be tdng co sir dung silicafume dw&i tdc dpng hoa hgc (sunphdt)<br /> Chiing ta biet rang, kha nang chdng tham cao va ham lugng vdi ty do it lam tang<br /> dp ben ciia be tdng chdng lai mpt sd chat xam thyc hda hpc. Be tdng cd sir dyng silica<br /> fume cd dp ben rat tdt vdi hang loat cac chat xam thyc. Cac thi nghiem trong mot thdi<br /> gian dai va toan dien d Na Uy da cho thay dp ben ciia be tdng cd sir dyng silica fume<br /> trong mdi trudng sunphat tuong duong vdi dp ben ciia be tdng sir dung xi mang<br /> pooelang ben sunphat [1].<br /> <br /> IV. Kit luan<br /> Silica fume vdi nhung tinh nang uu viet cua minh da cai bien mpt each rat hieu<br /> qua mpt sd tinh chit co ban ciia be tdng nhu da neu tren. Hien nay viec nghien cim va<br /> sit dung nd d nudc ta chua phd bien, dac biet la trong nganh Thuy lgi, can phai dugc<br /> tiip tye nghien ciiu va irng dyng sau rdng hon niia nham dap img yeu cau ngay cang<br /> cao cua cdng nghe xay dyng trong nudc.<br /> <br /> TAI LIEU THAM KHAO<br /> [1].^. JT^tc. Haph'ep - BexoH c co/iep>KaHneM MHKpoKpeMHeseMa - 2006. (Be tdng cd sir<br /> dung phu gia khoang hoat tinh silicafume - 2006).<br /> [2]. Ba^KenoB K). M. - TexHOJiorna dexona - 2002. (I.M. Bazhehov. - Cdng nghe<br /> be tdng - 2002).<br /> [3]. Rachel J. Detwiler and P. Kumar Mehta - Chemical and Physical Effects of Silica<br /> Fume on the Mechanical Behavior of Concrete, Materials Joumal - 1989. (Rachel<br /> J. Detwiler va P. Kumar Mehta - Hieu irng ly hoa ciia silica fume den tinh chat ca<br /> hpc ciia be tdng. Tap chi Vat lieu xay dyng - 1999).<br /> [4]. Ziad Bayasi and Jing Zhou - Properties of Silica Fume Concrete and Mortar,<br /> Materials Joumal - 1993. (Ziad Bayasi va Jing Zhou - Cac tinh chit ciia be tdng va<br /> vira cd diing silica fume. Tap chi Vat lieu xay dyng - 1993).<br />