Rheology vs. slump and washout. First encounter with rheology

Transcription

1 ACI Fall 9 Convention Relationship between Rheology and Flowable Concrete Workability Kamal Henri Khayat Things you Need to Know about Workability of Concrete - 9 Fall Convention Relationship between Rheology and Flowable Concrete Workability Rheology vs. washout resistance Rheology vs. workability of SCC Rheology vs. workability test methods Workability of fiber-reinforced SCC Effect of mix design on rheology of SCC Rheology vs. hardening properties - form pressure - interlayer bond of green SCC - top-bar effect First encounter with rheology Rheology vs. slump and washout Rio.. what..? Rheology affects ease of mixing, pumping, flow, segregation, washout, formwork pressure, surface finish, microstructure development Oh, I see! Binder W/CM CM (kg/m ) Sand / agg. % cement & % silica fume Slump (mm) 9 7 SCC UWC Welan gum (% cwt),.,., and. Cell. (ml/ kg CM), 9, and Rheology of Underwater Concrete Washout loss test (CRD C) Slump = ± mm Washout loss (%) % C % SF No AWA ml Cell.% cwt WG Khayat and Assaad, w / cm

2 ACI Fall 9 Convention Washout not a function of slump Slump (mm) Khayat and Assaad, W/C =.7 W/C =. Washout loss (%) W/C =.7 W/C =.7 SCC MK-III Rheometer gtorque (Nm) 7 N Time h T = g + h N... Speed (rev/s). Effect AWA + HRWRA on g and h Torque (N m) S= +mm W/CM=.7 %SF AWA + SP g (N m) % C % SF WG Cell. W/CM =.7 W/CM =. W/CM =.7 W/CM =.7 SCC... Speed (Rev/s). No AWA. Khayat and Assaad, Washout loss (%) Workability box for washout loss h (N m. s) % C % SF WG Cell. W/CM =.7 W/CM =. W/CM =.7 W/CM =.7 SCC g (Nm) 7 Washout = f (g, h) % < wash. < % % < wash. < 7% Khayat and Assaad, Washout loss (%) 7% < wash. < % washout > % h (Nm.s) Khayat and Assaad,

3 ACI Fall 9 Convention Relationship between Rheology and Flowable Concrete Workability Rheology vs. washout resistance Rheology vs. workability of SCC Rheology vs. workability test methods Workability of fiber-reinforced SCC Effect of mix design on rheology of SCC Rheology vs. hardening properties - form pressure - interlayer bond of green SCC - top-bar effect Flow behavior of SCC is complex and must be optimized to secure adequate performance low resistance to flow (low τ ) high stability (moderate visc.) high passing ability (low τ + mod. visc.) Conventional concrete Rheology of matrix must be controlled to avoid particle segregation low yield value and viscosity Lack of static stability after casting Laboratory & field test methods to assess SCC workability τ y / g (ρ p ρ m ) MSA T vs. h V-funnel flow vs. h Slump flow time T (sec) Cement content = kg/m³ Cement content = kg/m³ V-funnel flow time (sec) Cement content = kg/m³ Cement content = kg/m³ h (N.m.s) Khayat et al. h (N.m.s) Khayat et al.

4 ACI Fall 9 Convention Increase of L-box and U-box flow times with h L-box flow time (sec) L-box test; R² =. U-box test; R² =.7 U-box test h (N.m.s) Khayat et al. U-box flow time (sec) Correlate workability characteristics to intrinsic rheological properties T (sec) T V-funnel V-funnel (R =.) N= T (R² =.7) N = NCHRP, (φ = ± mm) µp (Pa.s) V-funnel flow time (sec) Relative error, % T 7 V- funnel µ p L-Box blocking ratio, h/h Viscosity vs. passing ability MSA C/ in. MSA C/ in. MSA C/ in. MSA G/ in. (R =.) N = (φ = ± mm). NCHRP, µp (Pa.s) Viscosity vs. static stability τ controls onset of segregation µpl affects rate of segregation Seggregation index (%) 7 τ y / g (ρ p ρ m ) MSA (φ = 7 ± mm) MSA ¾ in. MSA /, ½ in. NCHRP, µ p (Pa.s) Surface settlement Surface settlement vs. µp. (φ = 7 ± mm). No VEA Surface settlement (%)... Conv concrete..9 No VEA. No VEA Plastic viscosity (Pa.s) Elapsed time (h) NCHRP, Maximum settlement (%)

5 ACI Fall 9 Convention Slump flow (mm) 7 7 % no fibers.% steel fibers % steel fibers Slump flow filling capacity 7 9 Filling capacity (%) Khayat and Roussel, Filling capacity (%) h (Nm.s) Vf Vca S/P Khayat and Roussel, Yield stress (Nm) Filling capacity of FR-SCC can be related to rheological parameters 9 Volume of steel fibers..% % Vca = S/P = Filling capacity % - 7% 7% Plastic viscosity (Nm.s) Khayat and Roussel, Relationship between Rheology and Flowable Concrete Workability Rheology vs. washout resistance Rheology vs. workability of SCC Rheology vs. workability test methods Workability of fiber-reinforced SCC Effect of mix design on rheology of SCC Rheology vs. hardening properties - form pressure - interlayer bond of green SCC - top-bar effect Height of concrete (m) Variations in lateral pressure envelope. Slump flow = mm. R = m/hr. at casting.. ρgh. ~ % after hr. 7 Lateral pressure (kpa) K at hrs (%) Loss in slump flowis not sufficient to evaluate decay in lateral pressure 9 7 Khayat et al., Around 7 SCC mixtures Loss in slump flow after hrs of rest (mm)

6 ACI Fall 9 Convention Thixotropy: variation of viscosity with time at constant shear rate (reversible) Testing protocol of thixotropy Shear stress (Pa) γ = fixed γ =. s- sample at rest N =. rps N =. rps N =.7 rps N =.9 rps Shear stress (Pa) (Breakdown area) Magnitude of thixotropy (J/m³.s) Time (s) Structural build-up (flocculation, coagulation) Khayat et al., Time (sec).... Rotational speed (rps) A b vs. lateral pressure measured initially and after and min P(maximum) / P(hydrostatic) (%) Khayat and Assaad, A b - min. vs. min A b 9 min vs. K at min A b min vs. K at min R² =.9 Breakdown area (J/m³.s) 7 SCC.-m high column R² =. R² =. H =. - m L = 7 m W =.9 m As =.% 7 pressure sensors Field validation Head of concrete (m) Typical formwork pressure diagram Khayat et al., hr hr Slump flow = 7 mm S/A =. Ternary cement = 7 kg/m³ w/cm =. P(max) R =. m/hr ρ.g.h right after casting Pressure developed on formwork (kpa) P(maximum) / P(hydrostatic)..... Actual pressure is less than hydrostatic!. Khayat et al., R =. 9. m/hr Time after casting (min)

7 ACI Fall 9 Convention Structural build-up: Static yield stress at rest (τ rest ) Torque (N.m) τ rest = T max /G. T max... N =. rps. Time (s) K = f(h, R, D min, PVτ rest@min@ti ].f MSA.f WP K (%) H=m m R = m/hr m T = o C m D min = mm m MSA = mm m WP = PVτ rest@min (Pa) Khayat and Omran, 9 7 Homogeneity of bond strength H =. m Surface settlement (%).... NCHRP, 9 SCC mixtures Low τ, µ p, A b J-Ring: mm L-box.7 Filling capacity 9% VSI: Med. µ p, A b High µ p, A b Vibrated HPC Elapsed time (hour) Dist. from bottom (cm) In-situ compressive strength 9 NCHRP, 9 High µ p, A b Low τ, µ p, A b Vibrated HPC 9 9 f' c (core)/f' c (bottom) (%) Med. µ p, A b Dist. from bottom (cm) Top-bar effect Med. Low τ, High µ p, A b Vibrated µ p, A b µ p, A b HPC 9 l Lack of proper consolidation l NCHRP, 9 P P ' ' U / f ( bottom ) / / f ( in situ U ) b c t c 7

8 ACI Fall 9 Convention Recommended values to ensure homogeneous properties Static stability Viscosity Mechanical properties NCHRP, 9 Maximum surface settlement.% Column segregation index (Iseg) % Percent static segregation (S) Plastic viscosity.7 psi.s ( Pa.s) (Modified Tattersall two-point rheometer with vane device) Core-to-cylinder compressive strength 9% (similar curing conditions) Bond strength modification factor. References Assaad, J., Khayat, K.H., Mesbah, H., Assessment of Thixotropy of Flowable and Self- Consolidating Concrete, ACI Materials Jr.,, (),, pp. -. Assaad, J., Khayat, K.H., Daczko, J., Evaluation of Static Stability of Self-Consolidating Concrete, ACI Materials Jr.,, (), pp. 7-. Khayat, K.H., Assaad, J. Relationship Between Washout Resistance and Rheological Properties of High-Performance Underwater Concrete, ACI Materials Jr.,, (),, pp Khayat, K.H., Assaad, J. Use of Rheological Properties of SCC to Predict Formwork Pressure, SCC, Proceedings of the nd North American Conference on the Design and Use of Self- Consolidating Concrete and the th International RILEM Symposium on Self-Compacting Concrete, Evanston, IL, Ed. S.P. Shah, pp Khayat, K.H., Assaad, J., Daczko, J., Comparison of Field-Oriented Test Methods to Assess Dynamic Stability of Self-Consolidating Concrete, ACI Materials Jr.,, (), pp. -7. Khayat, K.H., Omran, A.F., Evaluation of SCC Formwork Pressure, Proceedings of the nd International Symposium on the Design, Performance and Use of Self-Consolidating Concrete (SCC 9), Beijing, China, Ed. C. Shi, Z. Yu, K.H. Khayat, and P. Yan, June -7, 9, pp. -. Khayat, K.H., Roussel, Y., Testing and Performance of Fiber-Reinforced, Self-Consolidating Concrete, RILEM Materials and Structures,, July, pp NCHRP Report, Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements, Khayat, K.H., Mitchell, D., 9. FACULTÉ DE GÉNIE