KHOA HOC-CONGNGHI
So 3/2017
Anh huong cua cot sai thep phan tan
trong viec tang cirong kha nang chdng nut do co ngot cua be tong xi mang cat
• TS. H 6 ANN CUCfNG - TrUdng Dgi hgc Giao thong van tdi
• ThS. PHAM QUANG KHdl - Trudng Dgi hgc Cong nghe Giao thong van tdi
TOM TAT: Bai bao tnnh bay i n h hudng cda cot sqi thep phan tan den do bdn chong ndt do co ngdt (truong hop co ngot ty do va co ngot kiem che) cua be tong xi mang cat vol ty lg 0 2 % va 5% cot spi theo khoi luong hon hpp be tong. Ket q u i nghien cuu buoc d i u da khing dinh duoc vai tro cot spi thep trong vide hgn chd bidn dang do co ngot, t i m
;ham su hinh thanh va phat tnen vet nut, lam g i i m dd nhay c i m vol hidn tupng nut cOa ket cau be tong do bien dang co ngdt gay ra.
TO K H 6 A : Spi thdp, be tong xi mSng cat, co ngdt ty do, CO ngot kiem che.
ABSTRACT: The paper presents the effect of steel fibers on cracking resistance due to shrinkage (free and restrained shrinkage) of Sand Concrete using a content of fiber is 02%, 5% by weight Preliminary results confirmed that efficiency of using of steel fiber on shnnkage reducing, delay the crack occur and propagation, and limit also the potential for cracking of concrete structures due to shrinkage KEYWORDS: Steel Fibers, sand concrete, freed shrinkage, restrained shrinkage
I . O A T V A N D i
Qua trinh cdng nghidp hda, hidn dai hda hien nay thi eic d u i n ha t i n g ky t h u i t , giao thdng nhu dudng h i m , dudng metro n g i m ; cie d U i n cdng trinh xiy dung d i n dung ngam; cic d u i n i n xiy dung c i u , x i y dung dudng xuydn A. cao tdc Bic - Nam dang dupe tridn Ichai ddng bd... Tuy nhidn, trong q u i trinh khai thie, bd tdng thudng x u i t hidn cic vet nut do t i i trpng hoic do eo ngdt. Cie vet ndt cd xu hudng t i n g d i n vd sd luong, chidu siu, chidu rpng; be m i t bd tdng bj b i o mdn, bong t r d c . l i m g i i m tudi tho edng trinh.Dd khie phuc nhupe didm niy, nhidu g i i i p h i p dupc nghidn cdu, trong do ed vide sd dung cdt spi p h i n t i n . Trong eic loai spi trdn, cic nghidn cUu tren thd gidi cung nhUdVidt Nam [1-5] da nhidu l i n khing djnh bd tdng cdt spi thdp (BTCST) ed
cUdng dd chju keo khi udn eao, t i n g k h i n i n g ehju t i i trpng, t i n g dp ben ddo dai v i d i e biet la t i n g 66 ben chdng ndt do co ngdt - l i eie tfnh c h i t rat ein thiet ehe cic kdt eau edng trinh ha t i n g ky t h u i t .
Tuy nhidn tai Viet Nam, eic nghidn cdu ve BTCST h i u nhu mdi ehi ddng d van d e e o h p e [1-4], ehUa cd nhidu nghidn cdu d i y du vd d i e tinh co ngdt edng (ee ngdt t u do va d i e bidt la eo ngdt kidm chd) cho BTCST ndi chung eung nhu eua bd tdng xi mang eit edt spi thdp (BTCCST) ndi ridng cho kdt c i u cdng trinh ha t i n g ky t h u i t . Bii b i o trinh bay kdt q u i nghidn cdu bUdc d i u vd d i e tfnh co ngdt t u do v i cudng bUc eiia BTCST vdi tJ- Id spi 0%, 02%
v i 5% theo khdi lupng bd tdng.
2. QUA TRlNH THf NGHIDM 2.1. V i t lidu
Soi thep dupe sin xuat t d thdp carbon sin xuit tai Trung Qudc, cudng dp ehju kdo >l,100MPa, md-dun d i n hdi khoing 200GPa, ed chieu dai 30mm, dudng kfnh 0.5mm dupe udn vai bd 2 d i u . Cdt lieu nhd (cit v i n g sdng Ld cd kieh ed 0-^4mm; khdi lupng the tfch 2,62 T/m^), xi m i n g {PCB40, cudng dp chiu nen 28 n g i y Rn >48,5MPa), phu gia mjn (tro bay nhidt dien Phi Lai), phu gia khoing (Silicafume) v i phu gia sidu ddo (Sika).
2.2. Che tao hon hop v i t lidu
Nghidn cUu d i chd tao dupe 3 cdng thUc BTCCS thep vdi cac ten gel BTOCS, BT2CS v i BT5CS tUPng dng vdi cac ty Id 0%, 2% va 5% cdt spi theo khdi lupng bd tdng. Cdng thUe BTOCS khdng sU dung cdt spi dung de ddi chdng. Kdt q u i edng thde thanh phan duoe tdng hpp chi tidt d edng 2.;.
Bing 2.1. Thinh phin dp phii vit liiu diing trong thl nghiim
LOAI M A U
BTOCS
BT3CS
BT5CS Nl/lSC lltt/m')
.»
168 I U
X I M A N G (kSfm-l
520
SSI
S70 Ikg/m'l
I25«
i j s e
12Se TRO SAY ( V g t a ' l
312
312
31]
SILICAFUME
S2
i2
ii PKM GIA Ilft/m3)
...
!»
?.fi cSrs^THep lb k h i i
0
2
i (kg/
0 50 I2S
2.3. Cac thf nghidm 2.3.1. Thinghiem co ngdt tudo
59
KHOA H O C - C 6 N G NGHE
Thf nghidm xic dinh dp eo ngdt tdng cdng, co ngdt lien kdt v i ce ngdt khd b i n g cac mau d i m cd kfch thUde 10x1 Ox40cm cho e i 3 loai be tdng 0%, 02% v i 5% cdt scri.
- Co ngdt tong cdng: Dupe de tren mau khdng bpc cho phdp mau cd the ehju t i e ddng qua lai true tidp vdi mdi trudng ben ngoii, nude trong bd tdng cd the t u de thoat ra ngoii.
- Co ngdt lien ket: Dupc do trdn mau bpe nilon, trong sudt thdi gian thee ddi thf nghidm. Bpe nilon se d i m bio, trong sudt qua trinh thuy hda, mau khdng eo t i c dpng qua lai vdi mdi trudng xung quanh. Nude trong mau sd khdng bj bay hai ra ngoai m i tdn tai bdn trong m i u phuc vu q u i trinh thuy hda, ddng r i n bd tdng.
' Co ngdt khd: Se dupe tfnh gian tidp thdng qua hai CO ngdt trdn thdng qua quan hd:
Co ngdt khd = Co ngdt tdng cpng - Co ngdt lidn kdt.
Vdi mdi loai bd tdng, sd dung 3 mau cho mdt loai thf nghidm. Kdt q u i duoc l i y trung binh cua 3 g i i tri ghi.
Cdng t i e ghi sd lieu co ngdt dupe tidn h i n h tUgid thd24 sau khi dd bd tdng.
Dd eo ngdt duoc tfnh theo cdng thdc E, = Dl/L (mm/m) Trong dd:
Al - Chdnh Idch chieu d i i giUa eie ehdt do eua mau tai thdi didm (t) so vdi ban d i u , mm; L - Khoing eieh giOra cic chdt do, m.
Od CO ngdt eda be tdng tai thdi didm (t) sd dupc liy trung binh sd hpc cua ba m i u cung td, chfnh xic tdi 0.01mm. Cin khdi lupng cie m i u ddng thdi vdi ghi sd li^u eo ngdt.
2.3.2. Thl nghiim co ngdt kiim chi
Nhim sing td hieu q u i cua cdt spi thdp trong viee han chd ndt kdt c i u BTCST thdp do bidn dang co ngdt, thf nghidm co ngdt vdng kidm chd duoc thuc hidn theo tidu chuin ASTIW C 1581 -04 [6]. D i y l i phucJng p h i p thf nghidm tupng ddi hidn d^i dupc sU dung phd bidn hien nay trdn thd g\di n h i m d i n h g i i tinh trang ndt trdn kdt c i u be tdng do bidn dang co ngdt g i y ra. Nghidn cdu thue hidn vdi BTOCS v i BTSCS.
Thf nghidm n i y iSuac thue hidn b i n g cich BTCCS thdp duoc dd theo hinh v i n h khuyen xung quanh mpt vdng thdp cUng {Hinh 2.1) dd kidm chd l^i sU co ngdt eCia v i t lidu, trdn vdng thdp cd d i n hai tem didn trd - d i u do (tenzomet-Strain Gages) do bidn dang cua v i n h thep theo thdi gian.
M i u bd tdng sau khi dd ngay l i p tde dupe dua v i o phdng dUdng hd cd nhiet dd 22 ± Ol'C, dd i n i 67 ± 02%
Cie dU lidu dupe t u ddng ghi lai vdi t i n sd 10 phdVlan thdng qua 2 d i u do. Sau 24 gid, hai v i n khudn thdp ngeii duoe dd bd.
Thf nghidm co ngdt kiem chd khdng chf xic (Snh thdi didm xuat hidn vet ndt m i cdn c6 thd x i c djnh dupc u^g suit trong mau bd tdng do co ngdt thdng qua bidn dang nen cua vdng thdp.
Tieu chuan [6] quy djnh c i c h tlnh t e i n di xic ^nh hai chi sd p h i n loai dd nhay c i m cua bd tdng vdi sundt do ce ngdt: (1) Ty- sd dng s u i t trung binh S trong miu thi nghidm tai thdi didm ndt (Mpa/ngiy) - Avarage Stress Rate v i (2) t thdi diem x u i t hidn vdt ndt (ngiy) - net time-to-Craeking nhUBdng2.2.
Bing 2.2. Muc dp nh^y dm vdi strndt theo ASIM Cl 581-04
Hinh 2.1: Sodd thl n^i$m CO ngdt kiem chi (trii) vi miu 3ugc k^t nil vdi thii't bj P3 (phil)
60
T i d i diem nint^
(NgayJ 0 < t „ £7 7 < t „ £ 1 4 1 4 < I ^ £ 2 8 28 < t^.
lysA crng suat trung binh, S (MPa/ngay)
0.34 £ S 0.17 £ S < 0 3 4 0.10£S<0.17 S < 0 . ] 0
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Cao Cao via philt TliSpvCiaphil
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3.1. Co ngdt t u d o
Anh hudng cda edt spi thdp ddn ee ngdt tdng cdna ee ngdt khd v i eo ngdt lidn kdt dupe thd hidn trdn cic Hinh 3.1,3.2 vd 3.3. St; thay del khdi lupng cic m i u khdng boc nilon theo thdi gian dupc bidu didn trdn Hinh 3.4.
Hinh 3.1: Anh hudng dt sgi thip din co ngdt ting cdng tl thiriglan
Hinh 3.2: Anh hudng dt spi thip din co ngdt ttf do llin kit tt.
thdi gian
Hinh 3.3: Anh hudng cotsg, thep din co ngdt khd theo thdi giaa
KHOA HOC-CONG NGHC
36 3/2017
Hinh 3.4: Diin biin thay dii khdt lugng theo tiidi gian cda 3 loai biting
Kdt q u i thi nghidm cho t h i y : Theo thcri gian, nhdng n g i y dau, t d n g i y 1 ddn n g i y 7, co ngdt dien ra manh, dudng quan he thdi gian - ee ngdt ed dp doe Idn. t i d p thee, t d n g i y 8 den n g i y 20, eo ngdt v i n tidp tuc, nhung lue n i y dUdng bleu dien quan he thdi gian - bidn dang thoil, chdng td eo ngdt van tang nhung t i n g ehim.Td ngiy 50 trd di, ta t h i y eo ngdt t i n g r i t ft, dudng bidu didn g i n nhu l i dudng n i m ngang, khdng cd sU thay ddi Idn. Cie g i i trj co ngdt lidn kdt chidm ty Id nhd (khoing 20 - 30%) trong g i i trj co ngdt tdng edng. Chu ydu co ngdt khd g i y ra hidn tupng bidn dang ce ngdt cua eie m i u bd tdng. Vi viy, trong q u i trinh khai thac cae edng trii.h, can ehu y ddn co ngdt khd - ddng vai trd chd ydu trong co ngdt tdng edng cda bd tdng.
M i t khic, trong ba dudng bidu didn quan he thdi gian - eo ngdt, dudng bidu didn eCia BTOCS ludn n i m trdn cung tai mpi thdi didm, chdng td khi khdng cd t h i n h p h i n spi thdp thl eo ngdt ldn; dudng bieu dien cda BTSCS t h i p nhat eho t h i y khi h i m lupng spi thdp eing nhidu thi co ngdt eing g i i m . Tai n g i y thU 200, dd ce ngdt cda BT2CS v i BTSCS chl b i n g 45% v i 12% so vdi m i u BTOCS.
Didn bidn m i t m i t khdi Idpng eda eie loai bd tdng theo thdi gian duoc bidu didn trdn Hinh 3.4 g i i i thfch rd thdm vi sao bd tdng khdng cdt spi 1^1 co ngdt nhieu hOn.
Cic dudng n i m tren eho thiy, hidn tuong trao ddi hoi nude ra mdi trudng xung quanh trong q u i trinh trinh thdy hda cda cic mau 0% v i 02% didn ra manh hon so vdi m i u 5%.
Nhu viy, vide bd sung spi thdp v i e trong be tdng da thay del tfnh chat cda bd tdng d i n g kd: Spi thep han chd hidn tupng bidn dang co ngdt. £>idu n i y sd g i i m cie hidn tupng nUt de ee ngdt trong q u i trinh khai t h i c kdt c i u , n i n g cao tudi thp, g i i m ehi phf duy tu, sda chda, b i o dudng v i x i y dung mdi, gdp p h i n tidt kidm cho ndn kinh t d - x i hpi.
3.2. Co ngdt Icidm che
Trdn Hinh 3.5 thd hidn bidn dang nen eda vdng thdp g i y ra bdi su co ngdt kidm chd cua 2 loai BTOCS v i BTSCS. iviiu 0% nut tai 3.1 n g i y trong khi p h i i den 25.1 ngiy, mdi cd hidn tupng ndt tai mau 5%.
Hon nda, dudng g i n t h i n g dUng cCia m i u 0% spi thdp cho thiy, vdt ndt xuit hidn v i phat tridn nhanh hdt t o i n bd chidu cao v i chidu d i y m i u trong khoing 0.5 ngiy.Treng khi dd, vdi mau 5% spi thep, cd the chia q u i trinh bidn dang cua be tdng n i y t h i n h 3 vung:
- Vung 1, dd ddc ldn - eo ngdt p h i t tridn nhanh;
- Vung 2, dd dde t h o i i hon, ce ngdt p h i t tnen c h i m v i cd thd d i x u i t hidn nhdng vdt nUt vi md khidn lue ndn
Idn v i n h thdp khdng t i n g nhidu n h u v u n g l.Thdi diem niy, vai trd cOa eie spi thdp b i t dau phat huy t i c dung thdng qua vide han che su hinh t h i n h v i l i m cham sU p h i t trien cac vdt ndt vi md, ngan e i n q u i trinh ket ndi mang ludi vi md de khdng tao ndn cie vet ndt vl md.
- Vung 3, vdt ndt vT md d i hinh thanh d n g i y t h d ngay 25.1 .Tuy nhidn, ddn ngay t h d 33 m i m i u v i n chua bj ndt t o i n bd chieu eao va chidu day. Q u i trinh ndt dien ra trong khoing 8 ngay, c h i m han nhidu se vdi m i u 0%
(0.5 n g i y nhu d tren) va dupe the hidn thdng qua dudng bidn dang theo xu hudng ddc tU n g i y 25.1 den n g i y 33.
Oidu n i y cang chdng td, eie spi thep han chd su x u i t hidn eung nhU ein trd dp m d rpng, han chd tdc do p h i t tridn cua vdt nut vf md.
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Hinh 3.5. Anh hudng cua cdl spi thip den bien dang cua vong thip theo thdi gian
Kdt q u i p h i n tfch d trdn che thiy, sau khi bd tdng ndt, eic spi thdp da ddng vai trd truyen lUc qua vdt nUt (bridging), han chd dd md rdng vdt ndt v i d i m b i o tinh lien tuc cua kdt eiu.
Tfnh toan thee hudng dan eCta [6] cho 2 loai BTOCS v i BTSCS, ket q u i dupe thd hidn d Hinh 3.6 v i tdng h c ^ d Bdng 3.1, Hinh 3.6 n h i m xie dinh hd sd bidn d?ng a thdng qua quan he gida bidn dang vdng thdp vdi c i n b i e 2 eda thdi gian (ngiy 0,5) tU thdi didm bd tdng 1 n g i y tudi den khi x u i t hidn vdt ndt. Bdng 3.1 cho t h i y dd nhay c i m eua bd tdng vdi sd nUt eua BTOCS l i "Cao", trong khi nhd su cd m i t eCia cdt spi thdp, dd nhay c i m cua BTSCS l a ' T h i p vda p h i i " - e d nghla bd tdng sddung 5% cdt spi ft cd k h i n i n g nUt hOn so vdi 0%.
Kdt q u i tfnh t o i n mot l i n nda k h i n g djnh hidu q u i cua vide sd dyng cot spi thdp da l i m g i i m mUc dp nhay c i m vdi su ndt - t i n g eudng k h i nang chju ndt cda bd tdng do co ngdt, d i e biet khi cic ket c i u l i m viec trong didu kidn kiem che bien dang.
Oie tinh trdn se phu hpp trong eie dng dung ha t i n g ky t h u i t dang t i m Idn, m i t dUdng, vd cdng trinli ndi, ngam...
V
Thin gian (ngSy"-^)-BlOCS-1 -BTOCS-2
61
KHOA H O C - C d N G N G H $
Hinh 3.6: Quan hi giOa bim dang vdng Oiip vScSnbic2 cua thdi gian (ngiy 0,5) td Oidi diem bi tdng 1 ngay turn din khi xuit hien vit ndt (mau BTOCS hinh trai. mSu 8T5CS hinh phii)
Bing 3.1. Anh hudng aia sgi tiiip din muc do nhay dm vdi su nutcuaBTcCS
BTOCS BTSCS
1 Ddu do 1
H f i s S b l i n d i n g , a (m/m/ngSy'') ,
D £ u d o 2 1 D J u d o i D i u d o 2
-4x10-' ! -7)110* - 2 K I 0 '
Tn luyet dOi
ng.iy I Thoi diPm KUi hi^n niH t, IngAyl _
trung bmh S [MPj/ngayj Miirc dd nhay
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4. K S T L U A N
Bai b i o tip trung nghidn cUu i n h hudng eda cdt spi thdp (ty le 0%, 02% v i 5% theo khdi lUpng) ddn ddc tlnh CO ngdt cua BTCCS thdp eung nhu lam rd hidu q u i cua spi thep ddn vide h^n che ndt do co ngdt g i y ra. TU nhdng kdl q u i thu dupc, cd the kdt l u i n nhusau:
- Co ngdt tU do eua BTCCS thep g i i m khi tang ty Id cdt spi (dd CO ngdt cua BT2CS v i BTSCS b i n g 45% va 12% so vdi BTOCS).
-Vtf thf nghidm co ngdt kiem chd: BTOCS ndt d ngay thU 3.1 v i q u i trinh ndt didn ra nhanh (trong 0.5 ngay), cdn BTSCS xuit hidn vet nUt nhd d ngay 25.1 va qua tnnh ndt dien ra cham (khoing 8 ngay).
- Cic thf nghidm co ngdt t u do va kiem che d i iam rd CO chd l i m viec cua soi thep trong be tong. Soi thep han che su xuit hien eic vet nUt vi me, lam c h i m q u i trinh cic vdt nUt vi md hinh thanh nen vet nut vl md, han che dd md rdng vet niJt.
- MUc dd nhay c i m vdi sU nUt dupc xic djnh qua ket q u i tfnh toan ty sd dng suit trung binh trong m i u thf nghidm tai thdi diem xuat hien vet ndt. Vdi mau 0% cdt spi, mdc dd nhay c i m la "Cae", trong khi vdi 5% thi ket q u i l i "Thip vua phii'. Kdt q u i tinh t o i n ehdng minh rd cdt spi thdp lam t i n g k h i n i n g chdng ndt do co ngdt ddi vdi BTCCS thdp •
T i i lieu tham Ithio
[1]. Nguyen Tien Binh (2005), Wg/i/dn cdu c/idfpoW tdng cdf soi sieu mdnh polypropylene dung cho sCfo c/nto cdng trinh trong diiu kien khi hdu ndng dm Viet Nam. l u i n i n Tien sT ky t h u i t , Vien Khoa hpc cdng nghe Xiy d i ^ Ha Ndi.
[2]. Nguyen Trung Hidu (12/2014), H/^u qud sil-d(ff^
cot sgi thip trong viic hgn chenuftkit cdu bi tdng do bi&
dgng co ngot, Tap chf Khoa hpe CNXD, sd 22.
[3]. Nguyen Hoang Giang (6/2015), Nghiin cdu dnh hudng cua sgi thep den khd ndng Idm viic vd khdng n&
cua kit cdu dam bitong.Tap ehi X i y dimg.
[41. Pham Quang Khdi, Hd Anh Cuong (2016), M^t so tinh chdt ca ly cua be tdng xi mdng cdt c6t sgi thip vd khd ndng dp dung trong kit cdu vd cdng trinh ngdm, T?p chl GTVT, sd 5.
[5]. H.A. ivlesbah, F. Buyle-Bodln, Efficiency of polypropylene and metallic fibres on control of shrinkage and cracking of recycled aggregate mortars. Construction and Building Materials 13 _1999.439], 447.
[6]. ASTM C1581- 04, Standard Test Method for Determining Age at Cracking and Induced Tensile Stress Characteristics of Mortar and Concrete under Restrained Shrinkage.
Ngiy nhan b i i : 12/01/2017 Ngiy chap nhin d i n g : S/02/2017 Ngudi phin bidn: TS. Vu PhUdng Thio
PGS.TS. Nguyin HuyThip
