05.581~590(11-025).fm

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1 Journal of the Korea Concrete Institute Vol. 23, No. 5, pp. 581~590, October, 2011 GGGGG š p w» j v p 1 Á 2 Á½ 2 Á 1 * 1 š w zy œw 2 w» Characteristics of Early-Age Restrained Shrinkage and Tensile Creep of Ultra-High Performance Cementitious Composites (UHPCC Doo-Yeol Yoo, 1 Jung-Jun Park, 2 Sung-Wook Kim, 2 and Young-Soo Yoon 1 * 1 School of Civil, Environmental and Architectural Engineering, Korea University, Seoul , Korea 2 Structural Engineering & Bridges Research Division, Korea Institute of Construction Technology, Goyang , Korea ABSTRACT Since ultra-high performance cementitious composites (UHPCC not only represents high early age shrinkage strain due to its low water-to-binder ratio (W/B and high fineness admixture usage but also reduces the cross section of structure from the higher mechanical properties, it generally has more shrinkage cracks from the restraints of formwork and reinforcing bars. In this study, free and restrained shrinkage experiments were conducted to evaluate the suitability of incorporating both expansive admixture (EA and shrinkage reducing agent (SRA. The test results indi-cated that approximately 40~44% of free shrinkage strain was decreased. Also, the results showed that 35% and 47% of residual tensile stresses were relieved by synergetic effect of SRA and EA, respectively. Residual tensile stresses from ringtest were relaxed by approximately 61% and 64% of elastic shrinkage stresses due to SRA and EA, respectively, because of the tensile creep effect. Therefore, the creep effect should be considered to precisely estimate the restrained shrinkage behavior of concrete structures. The degree of restraint of UHPCC was approximately in the range of 0.78~0.85. The addition of combined EA and SRA showed minute influence on the degree of restraint. However, the effect decreased when thicker concrete ring was used. Tensile creep strains were measured and compared to the predicted values from 4-parametric prediction model considering time dependent restrained forces. Keywords : ultra-high-performance cementitious composites, residual stress, creep, shrinkage reducing agent, expansive admixture 1. gj p k w ù ùk üš, w ü w. ù û p ùküš q w swwš, w w w» w š š w w š p w (ultra-high performance cementitious composites, UHPCC y w ƒ y w š. 1 UHPCC - w (W/Bƒ ûš w š yy y w w w w» w ü. w»» j w, w x *Corresponding author ysyoon@korea.ac.kr Received February 28, 2011, Revised June 2, 2011, Accepted June 7, X by Korea Concrete Institute k w ³ w ü w k. UHPCC w» w w yw w sƒ, w ƒ w w. gj p j (SRA CSA q (EA ww y w ƒ üá y w š. p 2,3 C 4 A 3 S j f swwš EA» p p(ettringite w y jš v q j, SRA pt ü œ t 4 g jš œ ƒ g wš» k. 5 gj p d wš sƒw ³ w ü ƒ j» w. (»,, x w sƒ, ùkù w v w. gj 581

2 p x j»,, x, w w w. gj p x j v p š w x mw ³ sƒ w ƒ. 6,7 w wš, 1980 z l š gj p w x w w š. ü w ƒ w. p, W/Bƒ û š gj p w x», k»» j ùkùš q» w x ƒ w w. Fig. 1(a w gj p. Hooke's law w k (σ = E c ε sh w w z w w. gj p ³ ƒ w w, j v gj p w jš ³ k. p, Weiss 8 w 30~70%ƒ j v x ùkùš, Fig. 1 Stresses and strains caused by free and restrained shrinkage of concrete sƒw j v w z š w w. Fig. 1(b j v z š w gj p ùkü. (a w» k, (b gj p ùkü. üá w ƒ k x j (σ res. w (c. gj p j v z ƒ wš(d, w x w w (e. (f z š w x ùkü., gj p x x (ε st k x (ε e, j v x (ε cr w ùký. ε sh = ε st ( t + ε e + ε cr EA SRA y UHPCC x -l p ww z sƒw. w, w j v d w,» 4- w w wš x w. 2.1 w 2. x x 1 sp p 0.5 mm w, 96% SiO 2 swwš 2µm, ev(sf, CSA EA, g SRA w. w yw Table 1, x šk e Table 2 w. Table 3 x wt, EA SRA y Mix. A Mix. B w. 2.2 r x 2.2.1» x UHPCC sƒw» w KS L 5111 ³ v x w. (KS F 2405 φ mm x œ w 3,000 kn UTM(universal testing machine w d w, - x» w Fig. 2(a fv l(compressormeter w 120 o 3 LVDT(linear voltage differential transformer ewš x d w. { KS F 2566 w 3 w x ww (1 582 w gj pwz 23«5y (2011

Table 1 Chemical compositions of material Composition, % (mass Cement (1 Silica fume (SF Expansive admixture (EA CaO 61.33 0.38 13.55 Al 2 O 3 6.40 0.25 18.66 SiO 2 21.01 96.00 3.80 Fe 2 O 3 3.12 0.

98 Note (1 Type I Portland cement Table 2 Properties of steel fiber Type of fiber Density (kg/cm 3 Tensile strength (MPa l f (1 (mm l f / d f (2 (mm/mm Straight fiber 7.

3 Table 1 Chemical compositions of material Composition, % (mass Cement (1 Silica fume (SF Expansive admixture (EA CaO Al 2 O SiO Fe 2 O MgO SO K 2 O F-CaO Specific surface (cm 2 /g 3, ,000 3,117 Density (g/cm Note (1 Type I Portland cement Table 2 Properties of steel fiber Type of fiber Density (kg/cm 3 Tensile strength (MPa l f (1 (mm l f / d f (2 (mm/mm Straight fiber 7.8 2, Note (1 l f : length of fiber, (2 d f : diameter of fiber Fig. 2(b. d UHPCC w w k w z KS F 2436 ³ w (ring-test x x AASHTO PP34-98 w w w r Fig. 3. w q lv p w w gj p wš, üá ew z UHPCC k w. k z 24 z wš g w w., gj p Ì sƒw» w gj p Ì 35 mm(r1, 76 mm(r2 w x ww. w w sƒw» w gj p g w t w w (PS t w w (FS w x ww (Fig. 3(b., e w R1 R2 r w Fig. 2 Test methods for mechanical properties Fig. 3 Restrained ring-test specimens Table 3 Mix proportions (ratio in weight Nomenclature W/B Cement SF Filler Sand Superplasticizer (SP Steel fiber SRA (2 EA Mix. A V f =2% (1 Mix. B Note (1 Volume fraction, (2 Shrinkage reducing agent š p w» j v p 583

4 Fig. 4 Designation system for restrained shrinkage specimens q, gj p v j R1 r t w w x ww. x d w 4 t ü ewš l w x d w, 23 ± 1 o C, 60 ± 5% w w x ww. ww x e Fig x x w» w, mm ƒ x k ƒƒ 35 mm, 76 mm w R1, R2 r w x w. x v x w d w r š jš UHPCC k w. gj p w w» w lv p w x w w w x ww. x gj p k z l l w d w 24 z kx wš r w v (exposed surface area-to-volume ratio, S/V l v w ó w. 7», R1-FS S/V 0, R2-PS , R1-PS x 3.1 UHPCC» p UHPCC» x Table 4. EA SRA y w y ùkû. Mix. B» { Mix. A w w 7 z w ùkü, 7.5% EA 1% SRA y w UHPCC {, v e w w q w. ù ùkü EA y w Mix. B Mix. A w» x ùkû. UHPCC w k (2 w, Table f ck f 1 E c = ε », f ck gj p, f 1 50 µε x w, ε 2 40% w x. Mix. B k Mix. A w j ùkû. w, Mix. A B k 3 ¾ ƒw ƒ z ƒ w w w w. 3.2 Fig. 5 ü x ùk ü. R1-PS Mix. A B ü x µε, 79 µε ùkû. Mix. B EA SRA y z w Mix. A û x, gj p k z 8 z l ƒ w j v w x ùkü. 28 R1-FS x ƒƒ 108 µε, 56 µε ùkû. R1-PS w x ùkù w w». R2-PS 28 x 158 µε, 104 µε R1-PS w 28%, 32% ƒw ùkû. w ü w wš x ƒw gj p Ìƒ ƒw w ƒw» q. B-R2-PS 8 z j v w x B-R1-PS w ƒw, j w gj p w» q. 3.3 S/V x w» w w (2 Table 4 Properties of fresh and hardened concrete Nomenclature Flow I.S. (1 F.S. (2 Compressive strength (MPa Flexural strength (MPa Secant modulus of elasticity (GPa (mm (hr (hr 1 day 3 days 7 days 28 days 1 day 3 days 7 days 28 days 1 day 3 days 7 days 28 days Mix. A Mix. B Note (1 Initial setting (3.5 N/mm 2, (2 Final setting (28 N/mm w gj pwz 23«5y (2011

5 Fig. 5 Measured average strains in the steel ring. w S/V r w. Fig. 6 S/V UHPCC. 28 EA SRA y w 40~44% ùkû, Mix. B EA w gj p k z 0.9 z l vƒ q w w. Mix. A ƒw Mix. B gj p k z 8 z l ƒ w z UHPCC j ùkû. 28 Mix. A B x ƒƒ 770~838 µε, 428~506 µε ùkû S/Vƒ j x ƒw. ƒ w gj p ƒw». ù UHPCC W/Bƒ ûš, ev(sf w» ƒ j ùkû. Fig. 7 S/V ùkü, j ƒw w. S/Vƒ Mix. A 1.07, 1.09, Mix. B 1.13, 1.18 ùkû. Mix. Bƒ Mix. A w ƒ j EA y» p pƒ vƒ q w y pt œ x š w ü» q., w y pt,, d, y Fig. 6 Total free shrinkage with various S/V Fig. 7 Comparison of shrinkage ratios according to various S/V at 28 days w w xk w. Mehta 9 w y w w w w d C- S-H sheets w š 11% w w. gj p w m 5~50 nm j» ü œ w w w,» vq w œ w ƒ jš, 60% wš w w x ww» w ƒ k q. š p w» j v p 585

6 3.4 -l p w sƒ ü x gj p y w» w Fig. 8 j» š w (P i w ƒ v w, (3 d x k,»ww p mw dw. 10 P i 2 2 ( r os r is = E 2 st ε st 2r os», r is, r os ü,, ε st, E st x k ùkü.» gj p j, mw ùký. (3 σ θ 2 r ic 2 r oc P i 2 r ic 2 r oc = r 2», r ic, r oc gj p ü,, r w. gj p gj p üd t wš t r r ic ƒ w (3 (4 w, ü x d mw gj p w w. σ tmax = E st ε st 2 2 ( r os r is r 2 2 ( r ic oc r os ( r oc r ic Fig. 9 Hooke's law w k (5 mw w. k (6 w dw, z 11 Table 5 w. E c a ( t = E FYQ c b t», E c28 28 gj p k, a, b z. Fig. 8 Idealization of the restrained ring specimens 6 (4 (5 (6 Fig. 9 Calculated elastic shrinkage and residual tensile stresses considering creep relaxation Table 5 Non-linear regression coefficient for 28-day secant elastic modulus Nomenclature a b R 2 Mix. A Mix. B Fig. 9 k z w w ùkû. R1-PS, FS r 28 Mix. A B k 61%, 64%ƒ, A, B-R1-PS 28 ƒƒ 14.1 MPa, 9.1 MPa ùkûš, A B-R1-FS 12.4 MPa, 6.6 MPa. Mix. A B ³ w, ü w ƒ j q. (3 ü»w k, x w. x w k ü w w S/V, g j p Ì w (Fig. 10. x, Mix. Aƒ Mix. B w j ùkþ, gj p Ì S/Vƒ j ƒw w. gj p ü xw gj p x w. w, Fig. 5 gj p w ü xw,» x (ε r (t (7 586 w gj pwz 23«5y (2011

7 Fig. 10 Calculated maximum interface pressures x ùký. = = ε e t ε r ε sh ε st ( t ( + ε cr (ψ x x ù w. ψ ε r ε st ( t = = ( t ε sh ε sh Fig. 11 (8 w w UHPCC ùkü. R1-PS R1-FS EA SRA y w, R2-PS 0.78~0.81 R1 r w w ùkû. gj p Ìƒ ƒw ƒ w ƒ ƒ w ü x j w». R1 r Mix. B» w w ùkû, gj p k z 8 z l Mix. A w w l p w UHPCC j v gj p t, w gj p w w, (7 (8 w, x, w w š j v x w. w w w w j v x w, w w d w j v x w gj p ³ sƒw. 7 w w w j v dw w. 12 Bažant Mabrouk w 13 Multi chain š, w mw k, k, x, z j v z tx w 4- w w j v w wš, x 15 w. 14 Burgers w 4- Fig. 12 Maxwell chain Kelvin chain š, sx, w, mw ùký. = = = σ σ E0 σ η0, ε ε E0 ε η0 σ = σ E1 + σ η1, ε = ε E1 = ε η1 σ E = Eε E, σ η = ηε η»» w x w x 1, (10 (11 ùký. σ σ ε = E 1 η 1 E 0 ε ε = η σ η 1 (9 (10 (11 x w wš w x ww w.», -l p mw d w j v k x s ww š ƒ wš, k x w j v x š w. + = ε cr = ε c ( t ε e 1 t σ τ η 0 0 ( dr + 1 t σ( τe E 1 t τ η 1 0 ( / η 1 dτ + C (12 w (13 28 sww w tx, w z x Table 6 ùkü. ( = σ 28 1 e at σ t ( (13 Fig. 11 Degree of restraint», σ 28 28, a z, t š p w» j v p 587

8 Fig. 12 Basic 4-parametric rheological model (day. (13 σ(t (12 wš w w w š w j v x tx.», w j v x w ε cr (0 = 0 š, C 0. t ε cr ( = 1 e at σ 28 t η 0 a σ e E 1 / η 1 ( at + ( 1 e at E E 1 ( aη E 1 ( t [ ] (14 Table 6 Non-linear regression coefficient for 28-day restrained stress Nomenclature a R 2 Mix. A Mix. B Fig. 13 Comparison of measured tensile creep strains and predicted values j v x w v sp k (E (η x z mw e w w Table 7 ùkü. gj p j v, w w,, w w, S/V ƒ j v y š w» w a S/V (14 w w. z A, B-R1-PS a S/V ƒƒ , ùkû. Fig. 13 -l p mw R1 r j v x d. x R1-FS r mw d w» j v x R1-PS j v 98% w ùkü. Mix. B j v x Mix. A w 39% w ùkû, EA SRA z w w gj p j w» q. Table 7 Elastic and viscosity coefficients of UHPCC Nomenclature η 0 E 1 η 1 Mix. A Mix. B Fig. 14 Tensile creep strain to shrinkage ratios of R1 specimen (14 y e sƒw» w (error coefficient, M w. 16 M 1 = S ave ( t, t 0 S 0 ( t, t 0 S p t, [ ( t ] n 1 (15», S 0 (t, t 0 S p (t, t 0 j v x d, d, S ave (t, t 0 d s³ x, n l. R1-FS r Mix. A B ƒƒ , , 16 R1-PS , ùk û. Mazloom w ƒ 0.15 w d ùkü q w, Mix. A 4- mw z j v d ƒ w ƒ. 588 w gj pwz 23«5y (2011

9 w Mix. B 0.15 j ùk û, w xk w p gj p k z 1.6 z ùkù w j v x x w w» q.» 8 w j v 30~70%, Fig. 14 UHPCC 28 j v 46~53% ùkû. x m w gj p ³ sƒ j v z š w ƒ. 4. EA SRA y w UHPCC, x mw w. 1 Mix. B EA SRA y w, {, v y w ùkû ù EA w» ù kù w. 2 w, EA SRA y w Mix. B 28 40~44% z, ü x 34~48% w ùkû. 3 -l p mw d w l, j v z w k 61%, 64%ƒ. UHPCC -l p w j ùkû, ³ w. R1, R2 r ƒƒ 0.85, 0.78~0.81 ùkûš, gj p Ìƒ ƒw w w. w, j v x 46~53% ùkû, yw sƒ w j v š w w š q. w»» x UHPC 2007 ( w» w w (No š x 1. ½, k, w, š p w p y xy, gj pwz, 18«, 1y, 2006, pp. 16~ Maltese, C., Pistolesi, C., Lolli, A., Bravo, A., Cerulli, T., and Salvioni, D., Combined Effect of Expansive and Shrinkage Reducing Admixtures to Obtain Stable and Durable Mortars, Cement and Concrete Research, Vol. 35, No. 12, 2005, pp. 2244~ w, ½, š k, w, q w w š gj p» p, gj pwz, 16«, 5y, 2004, pp. 605~ ,, s» w CSA q, gj pwz, 16«, 3y, 2004, pp. 369~ Bentz, D. P., Influence of Shrinkage-Reducing Admixtures on Early-Age Properties of Cement Pastes, Journal of Advanced Concrete Technology, Vol. 4, No. 3, 2006, pp. 423~ , y,,, š gj p sƒ, gj pwz, 22«, 5y, 2010, pp. 641~ See, H. T., Attiogbe, E. K., and Miltenberger, M. A., Shrinkage Cracking Characteristics of Concrete Using Ring Specimens, ACI Materials Journal, Vol. 100, No. 3, 2003, pp. 239~ Weiss, W. J., Prediction of Early-Age Shrinkage Cracking in Concrete, PhD Dissertation, Northwestern University, Evanston, 1999, 277 pp. 9. Mehta, P. K. and Monteiro, P. J. M., Concrete, 3rd edn. Mc Graw Hill, Hossain, A. B. and Weiss, W. J., Assessing Residual Stress Development and Stress Relaxation in Restrained Concrete Ring Specimens, Cement and Concrete Composites, Vol. 26, No. 5, 2004, pp. 531~ , ½»x, ½,,, š gj p y w p, gj pwz, 22«, 3y, 2010, pp. 389~ Bažant, Z. P. and Carol, I., Viscoelasticity with Aging Caused by Solidification of Non-Aging Constituent, Journal of Engineering Mechanics, ASCE, Vol. 119, No. 11, 1993, pp. 2252~ Mabrouk, R., Ishida, T., and Maekawa, K., Solidification Model of Hardening Concrete Composite for Predicting Autogenous and Drying Shrinkage, In: E. Tazawa Ed., Autogenous Shrinkage of Concrete, E&FN Spon, London, 1998, pp. 309~ , ½x, gj p j v x d w x 4-, wm wz, 26 «, 1Ay, 2006, pp. 45~ Burgers, J. M., First Report on Viscosity and Plasticity, Nordemann Publisher, Amsterdam, Mazloom, M., Estimating Long-Term Creep and Shrinkage of High-Strength Concrete, Cement and Concrete Composite, 2007, Vol. 30, No. 4, pp š p w» j v p 589

10 š p w (ultra-high-performance cementitious conposites, UHPCC w ùkü» jš, û - w š yy x w t w ³ ƒ j. UHPCC j» w q ww y wš sƒw w w. x q ww y w 40~44% z, 35% 47% w. w w j v k 61%, 64%ƒ ùkû, sƒw j v z š w w š q. 0.78~0.85 ùkû q y w w w š gj p Ìƒ j w w. w, UHPCC j v x d wš w w w 4- j v d w. w : š p w,, j v,, q 590 w gj pwz 23«5y (2011

14.531~539(08-037).fm

14.531~539(08-037).fm G Journal of the Korea Concrete Institute Vol. 20, No. 4, pp. 531~539, August, 2008 š x y w m š gj p { sƒ z 1) * 1) w w Evaluation of Flexural Strength for Normal and High Strength Concrete with Hooked