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^ N G H I E N C U t J A N H H U ' A N G C U A H A M LU'OnVG H A T T H O I D E T D E N T I N H C O N G T A C V A C U ' D N G B Q C t f A B E T O N G
I>|ng Vdn Thanh' Nguyen Van Bdc^
TS. Trudng Dgi hgc Ldm nghigp KS. Trucmg Dgi hgc Ldm nghigp TOM TAT
Bang phuong phap thi n ^ i e m trong irfiong xac dinh do sut ciia hon hop be tong va cuong do chiu nen ciia be tong, nghien cuu danh gia sg anh huong cua ham lugng hat thoi det co trong cot lieu lon den tinh cong tac va cuong d$ ciia be tdng. Tir dc loai nguyen, vat lieu dugc lira chon, sii dung phuong p h ^ ly thuySl kit hgp thirc nghiem, t i ^ hanh thifit kfi thanh phan hon hgp be long. Voi ket qua dat dugc, c6 dinh ham lugng cac thanh phan vat lieu (c6t lifiu ldn, c6t lieu nh6, xi mang va nuoc) theo thifit kfi, difiu chinh ham lugng hgtt thoi det co trong cot li^u Ion theo cac muc: 0%, 5%, 10%, 15%, 20% va 2 5 % dfi nhao tron h6n hgp xac dinh do sut va chfi tao cac mau be tdng xac djnh cuong dg chiu nen. Ket qua nhifin ciiu chi ra rang, su anh hucmg ciia ham lugng hsit thoi d?t trong c6t hfiu Ion dfin dg sut va cuong do chiu nen la rat ro ret; dfi xu5t voi cac loai be long tuong ducmg B15, ham lugng hat thoi d^t khong nfin vugt qua 15%.
Tir khoa: Cu&ng d^ bi tong, dg sut, hdm lugng hgt thoi det, kdm lugng tgp chat
I. DAT VAN DE
Trong thiet ke thdnh phdn be tdng thi vide xac dinh cap phoi cot Ii?u va cac tinh chat ky thudt ciia cot lieu Id dac bi^t quan trgng, nd anh hudng rat ldn ddn dac tinh ky thu^t ciia be tdng thiet ke. Tir trudc den nay, cac nghidn cuu ve be tdng xi mang thudng tap trung vao mdt so Imh vuc nhu: dg nen dap va cudng dg cdt lieu ldn (Ai-Qin Shen. 2004, Tian-Yu Liang. 2004, Kai-Wei Song. 2005, A.M Na Wei er. 1983;
dudng kinh danh dinh ldn nhdt (Li-Bin Yu.
2002, Fu zhi. 2012, A.M Na Wei er. 1983, Kai-Wei Song. 2005); ham lugng cdt Udu Idn (Baalbaki va cdng su. 1991, Turan et al. 1997, Alain Denis. 2002)... Cac ket lu$n tir cdc nghidn cuu nay deu dugc dua ra tir kdt qua thi nghi?m cd co sd khoa hgc, tuy nhien sd lugng thi nghidm vd tinh he thdng, tinh toan di?n van cdn ban chd. Ddng thdi, ciing mgt vdn dd nghidn cihi, cimg yeu to dnh hudng nhung kdt qua nghien cuu cung khdng hoan todn gidng
nhau, thdm chi trdi ngugc nhau. Do dd, vdn cdn nhieu van de can phai tiep tuc nghien cuu;
trong do cd mgt so van dd nhu: cac nghien cuu chii ydu tap trung ve be tdng diing trong xdy dung ndi chung, nghien cuu ve be tdng xay dung dudng d td vdn cdn it; ket qua nghien cuu su dnh hudng cua ham lugng hat thoi det (kich thudc cua hat theo cdc phuang chdnh lech nhau qud 3 ldn) trong cdt lieu ldn van chua thdng nhdt va toan dien; cdc nghidn cuu ve anh hudng ciia ham lugng tap chdt trong cdt lieu vdn cdn han chd; cac nghien cuu van chua de cap den vide bd tdng diing cho cac cap dudng, cac viing khi hau khac nhau... Dac bidt d Viet Nam, vdn cdn qua it nghidn cuu vd su dnh hudng ciia dac diem cdt lieu den tinh nang cua bd tdng xi mdng. Bdng phuang phap thuc nghiem trong phdng, nghidn cuu nay phdn tich danh gid sir dnh hudng ciia ham lugng hat thoi det trong cdt Ueu ldn den do sut cua hdn hgp va cudng do be tdng.
T^P CHI KHOA HQC VA CONG NGHE LAM NGHIEP S 6 2-2015 83
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a VATIiHJ VAHIUtaSGPHAPNGHIENCUtJ Luong San - Hda Bmh - Viet Nam. Cac thdng 2.1. \%X li^u so ky thuat co bdn ciia Ioai xi mdng nay ddu Chat kdt dmh: Dd tai sir dung xi mdng pooc thda mdn quy djnh ciia Tieu chuan Viet Nam Idng PC 30 dugc san xudt tai nha may xi mdng (TCVN 2682: 2009), dugc thd hi?n d bang 01.
Bang 01. Mgt sd chi tieu ky thugt cua ja mdng PC-30
Chi tilu ky thu|t Tri so
Gidi han ben nen:
- Sau 3 ngdy ± 45 phiit -Sau 28 ngay ± 8 gid Thdi gian ddng ket - Bat dau - Kdt thiic
Dp nghien min, xac dinh theo:
- Phin cdn lai tren sang kich thudc l6 0,09mm - Be mat rieng, phuong phap Blaine
> 16 N/mm^
> 30 N/mm^
> 45 phut
< 375 phiit
< 15 %
> 2800 cmVg Cot li^u: su dyng cdt lieu nhd Id Ioai cat
vdng Sdng Hdng, khai thdc tai khu vuc Son Tdy - Hd Ngi - Viet Nam; cdt lieu ldn la lo^i da dam dugc khai thdc vd chd bien tir md da Hda Th^ch - Qudc Oai - Hd Ndi; cdc thdng so ky thudt cua cdt lieu ddu thda man quy dinh
Bang 02. Lua chgn thdnh phdn vgt ligu che tgo be tdng ciia Tieu chuan Yi&t Nam.
Thanh phdn be tdng: Ap dimg phuang phap ly thuyet ket hgp thuc nghidm dd thidt kd thanh phdn bd tdng BIS; kdt qud lya chgn cdc thdnh phan v|t li?u dugc thd hidn d bang 02.
D (kg/mO C (kg/mO X (kg/m^) N (lit)
1140 765 390
2.2. Phuvng phdp nghien cihi
Dya tren ca sd kdt qud thiet kd thanh phdn be tdng xi mang; bdng vide dieu chinh ham lugng h^t thoi d?t trong cdt U?u ldn, tien hanh chd tao mdu vd ldm thi nghi?m xac djnh dg sut ciia hon hgp be tdng vd cudng do chiu nen ciia be tdng; thdng qua cdc ket qua thi nghidm, phdn tich tdng hgp va ddnh gid su anh hudng den dg syt va cudng do.
2.2.1. Thi nghiim xdc dinh dnh htrdng cua hdm lugrng hcit thoi det
De ddnh gid dnh hudng ciia ham lugng hat thoi d^t (hat yeu - ky hi?u: Y) trong cot Ii?u ldn den do syt va cudng do chiu nen, sii d\mg 06 nhdm mdu cot Udu ldn cd hdm lugng hat thoi det ldn lugt Id: 0%; 5%; 10%; 15%; 20%
va 25% dd che tao cac mau hon hgp bd tdng vdi ti 1? thanh phdn v§t Ii?u theo thidt ke. Cu thd v^ thanh phan vdt lieu (Da dam - D, Cat - C, Xi mang - X va Nudc - N) che tao cdc miu hdn hgp dugc thd hidn d bang 03.
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TT I 2 3 4 5 6
Y(%) 0 5 10 15 20 25
Bang 03. n a n * D (kg/m')
1140 1140 1140 1140 1140 1140
phdn vat lieu che tao C(kg/in')
765 765 765 765 765 765
cdc nhom mdu X (kg/m')
390 390 390 390 390 390
N(l/m') 195 195 195 195 195 195
2.2.2. Thi nghiem xdc dinh dp sut vd cirdng dp chiu nen
Do syt ciia hon hgp vd cudng do chiu nen cua be tong dugc xac djnh theo Tieu chudn VietNam (TCVN 3106: 1993 va TCVN 3118:
1993).
m . KET QUANGHIEN C U t VATHAO LUAN 3.1 Su- anh hud^g ciia ham luwng bat thoi dft den dg sut
Kdt qud do syt cua cdc mdu hon hgp bd tdng dugc xac dinh ngay sau khi nhao trgn (Si) va sau 30 phiit (S30) dugc thd hidn d bdng 04.
Bdng 04. Ket qud thi ngkigm dp sut TT
1 2 3 i 5 6
Y(%)
0 5 10 15 20 25
Lan 1
s,
65 62 58 50 40 28
S30
46 44 42 32 25 15
D$ sut sau
Sl 68 64 56 46 42 30
ban dau
^an 2
S30
45 43 40 34 23 16
vasau
SI 70 62 58 46 40 31
30 phut (mm) Lan 3
S30
48 45 40 33 22 16
Trung binli Sl Sjo 68 46 63 44 57 41 47 33 41 23 30 16 Tu ket qua thi nghiem, xay dung quan he dugc the hi^n qua dd thi dhinh 01.
giua ham lugng h?t yeu vd dg syt cua hdn hgp,
k . ^ - -0.025V=- 0.SS9Y+ fi"."S
^ ^ ^ - ^ - . . . ^ R ' = 0S96
—•—Bail iliwi
P t ^ . i B a u d a B ) Polv. (Sun JO pbdt)
Sn = -e.OS-IV- - 9.545-i- + - l i . M ^ B s ^ \ . R ; - •.993- ^ ^ ^ s .
liani luong hat yeu, */«
Hinh 01 Quan hg hdm lugng kgt yeu vd dp sut
T ^ CHI KHOA HQC VA CONG NGHE LAM NGHIEP S 6 2-2015 85
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Tvr ket qua thi nghiem dg syt d bang 04 va ddng nghia vdi tong didn tich be mat cdc hat hinh 01 cho thdy: do sut ciia hdn hgp bd tdng tang, Iam ydu cdu lugng hd xi mdng tang (ydu giam ddn khi hdm lugng hat yeu tang. Dieu cdu lugng nudc tang), trong khi lugng nudc ndy la do cdc hat dai nhgn, det dd Iam thay doi nhao trgn khdng doi, tat yeu dan tdi dg syt sy ddng ddu trong thdnh phdn va lam xudt hien gidm. Dg syt ciia hon hgp gidm theo thdi gjan cac hidn tugng phdn tdch, phan tdng; cac hat la do tu khi dua nudc vao nhao trgn, xi mdng thoi det cd di?n tich bd mat ldn, lam cho tdng se thiiy hda, qua trinh ddng cung vd hinh thdnh di?n tich tiep xiic giua cot Ueu vd hd xi mang cudng dg xdy ra, lam hon hgp kem Unh dgng tdng, din den yeu cdu ve lugng nudc nhdo trdn theo thdi gian.
ydu cau tang. Liic nay, ndu diing lugng nudc Quan h? giua hdm lugng h?t yeu (Y) vd dp nhdo trdn khdng doi sd Idm gidm dg sut ciia syt ban d^u (Sj), do syt sau 30 phiit (S30) ciia hon hgp. hon hgp be tdng xi mdng nghidn cuu cd the Khi hdm lugng h^t yeu vugt qua 15%, dg dung cac phuang trinh (I) va (2) dd danh gia- syt ciia hon hgp be tdng giam vdi toe do qua g, = _ o,025Y^ - 0,889Y + 67,78 (1) nhanh (28,78 - 66,19%); ddng didi sau nua gid, ^^^ = .o,0371Y^ -0,3457Y + 46,667 (2) d0 syt cung gidm di rdt nhidu (29,07 - 47,19%).
3.2 Su- dnh hudng cua ham lutjng hat thoi Didu ndy Id do, khi ham lugng hat ydu (thoi det)
... , i . i- . . A ,., d e t d e n c u ^ g d f i tang, su lien ket moc noi giia cac hat cot lieu
. . , i , i , , , , 1 - . . , , I Ket qua thi nghiem cudng dd cua cac mdu tra nen chdc chan hon, cac hat kho djch chuyen, ^
i , ,« L .• L 1 i ' • 1.= L be tdng xi mane d 7 ngay tuoi (Rhi) va d 28 xoay dao, lam cho turn luu dong cua hon hgp ^ ^ ^
giam; d6ng thoi, ham lu?ng hat thoi det tang "Say tu& (^2,) duoc thi hien 6 bang 05.
Bang 05. Ket qud thi nghigm cudng dp chju nen
TT
1 2 3 4 5 6
Y(%)
0 5 10 15 20 25
Lan 1 R., 17,3 16,8 16,3 15,1 13,9 12,7
Rb2g
22,2 21,5 20,9 19,4 17,8 16,3
Cud'ng a^ i chiu n^n R7 va Ru Lan 2
Rb7
16,8 16,6 16,1 15,4 14,3 12,8
R b l S
21,5 21,3 20,6 19,7 18,3 16,4
,(MPa) Lan 3
Rb7
16,8 16,4 15,9 15,3 13,7 13,0
Riizg
21,6 21,0 20,4 19,6 17,6 16,7
Trung
Rl,7
17,0 16,6 16,1 15,3 14,0 12,8
binh
Rb28
21,8 21,3 20,6 19,6 17,9 16,5
Tir ket qud thi nghiem, xay dung quan hd chiu nen ciia bd tdng, dugc thd hien qua do thi giii'a ham lugng hat thoi det vd den cudng dg d hinh 02.
86 TAP CHI KHOA HQC VA CONG NGHlf LAM NGHIEP SO 2-2015
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Rt3^-S.M<\'^- 0.05SV+ 2I."6
- M P-- = 0.99- Poly (/ngay)
Poly. (28 ngay)
Rui = -0.0049Y= - 0.(M53Y +16.978 R ' = 0.9972
Ham lumig bat yeu, %
Hmh 02. Quan hi hdm lugng hgt yeu vd cudng dg Tir ket qud thi nghidm cudng do d bdng 05
va hinh 02 cho thdy: cudng do cua be tdng giam rd ret khi hdm lugng hat thoi det tang; khi ham lugng hat thoi det chua vugt qua 15% thi cudng do chiu nen ciia cdc mau giam tuong ddi chdm vd co ban van ddm bdo cudng dg yeu cdu (20MPa); khi ham lugng hat thoi det vugt qua 15% thi cudng do gidm vdi tdc do nhanh hem (17,76 -^24,35%) va cudng do bd tdng khdng dat cudng dg ydu cdu.
Quan he giua ham lugng hat yeu (Y) va cudng do d tudi 7 ngay (R*,?), cudng do d tudi 28 ngay (Rbas) ciia Ioai bd tdng xi mang nghidn cuu cd thd diing cac phucmg trinh (3) va (4) dd danh gia:
Rb28 = - 0,006Y^ - 0,05 8Y + 21,76 (3) Rt2g = - 0,0049Y^ - 0,0453Y + 16,978 (4) IV. KET LUAN
Dg syt ciia hon hgp vd cudng dO cua bd tdng giam dan khi ham lugng hat ydu tang.
Khi ham lugng hat yeu chua vugt qua 15%. chi tieu do syt va cudng dg chiu nen van dam bdo ydu cdu; khi vugt qud 15% dg syt ciia hdn hgp giam nhanh ban vd cudng dp chiu nen khdng dam bdo yeu cdu.
Vdi cdc Ioai be tdng B15 sii dyng vat Udu chd tao la da ddm, cat vang, xi mang PC 30 va khdng su dpng phy gia, muc do anh hudng giira ham lugng hat thoi det trong cdt lieu ldn cd thd dugc thd hien qua cac phuang trinh da thiet lap vdi muc do tin cay cao.
Tdng hgp phdn tich, kidn nghi: vdi be tdng B15 sii dyng vat Udu chd tao la dd dam, cdt vang, xi mang PC 30 va khdng sii dyng phy gia, ham lugng h^t thoi det trong cdt Ueu Idn khdng ndn vugt qua 15%.
T.\I LIEU THAM KHAO
1. Ai-Qin Shen (2004). Cement and concrete. China Communications Press
2. Tian-Yu Liang (2004). Study on influence of coaise aggregate to concrete compression strength.
ChcBigqing University.
3. Kai-Wei Song (2005). Study on influence of coarse aggregate to concrete breaking strength.
Chongqing University.
4. A.M Na Wei er (1983). Performance of Ctmcrete.
Chinese architecture Press.
5. Fu zhi et al (2012). Construction technique on slii>-fQrm of Cement concrete pavement. China Communications Press.
6. Baalbaki, Walid, et al (1991). Influence of coarse aggregate on elastic properties of High-performance concrete. ACI Material Joumal.
7. Turan, ozturan, cangizhanlecen (1997), Effect of coarse aggregate type on mechanical properties of concrete with different strengths. Cement and Concrete Research, 27 (2): 641-643.
TAP CHI KHOA HQC VA CONG NGHE LAAI NGHIEP SO 2-2015
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8. Alain Denis (2002). Effect of coarse aggregate on hop be tong nang - Phuang p h ^ thu - Phuong phap xac the workability of sanderete. Cement and Concrete dinh do sut. Ha Npi, 1993.
Researeh, 32(5): 701-706. I I . Tieu chuSn Viet Nam TCVN 3118 1993 - Be 9. Tieu chuan Viet Nara TCVN 2682: 2009 - Xi tong nling - Phuong phap thii - Phuong phap xac dinh mang Pooc l a n g - Y e u cau ky thuat. Ha Ngi, 2009. cucmg do nen. Ha Noi, 1 ^ 3 .
10. Tieu chuSn Viet Nam TCVN 3106: 1993 - H5n
RESEARCH ON THE EFFECT OF ELONGATION AND FLAKINESS INDEX TO THE SLUMP AND COMPRESSIVE OF CONRETE
D a n g V a n T h a n h , N g u y e n V a n B a c S U M M A R Y
By applying method in laboratory to determine the slum and compressive strength of concrete, this study evaluates the effect of elongation and flakiness index of coarse aggregate to slum index and compressive strength of concrete mixture. Based on the selected materials for the study, the concrete component was designed by both theoretical and empirical method to create the contents of the concrete to determine slump. With the above resuhs, the rate of large dimension matenals are fixed as designed. Then, the elongation and flakiness index are changed with the level at 0%; 5%, 10%; 15%; 20% and 25% to mixed in order to determine the slum of the concrete and create the concrete samples. Then, the compressive strength are tested. The result of the study shows that, the effects of the elongation and flakiness index in the concrete to slum are singnificant. It is used under 15% of elongation and flakiness index. Ifit exceed this limit, the specification of concrete will not be satisfied.
Keywords: Concrete; Slum, Compressive strength. Elongation and flakiness index. Impurity content.
Ngirdi p h a n b i e n
Ngay nhdn bai Ngay phan bien Ngdy quyet dinh dang
TS. Le Tan Quynh 31/3/2015 22/5/2015 09/6/2015
T ^ CHI KHOA HQC VA CONG NGHE LAM NGHI|:P SO 2-2015
