Self Consolidating Concrete

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1 Self Consolidating Concrete Leslie Struble Civil and Environmental Engineering University of Illinois

2 Scope of talk What is SCC? How is SCC made? How is SCC tested? SCC research at UIUC The Good, the Bad, and the Ugly

3 Definition Benefits A high-performance concrete that flows under its own weight to fill completely the formwork without vibration or mechanical consolidation. place in highly congested formwork place without vibration self-leveling, less need to screed faster construction What is SCC? Flowing into double T beam forms ACI 237 ETS Report

4 How is SCC made? High-range water reducer (polycarboxylate) High paste content Viscosity Modifying Admixture (VMA) Smaller aggregate and optimized gradation

5 Typical SCC mixtures Precast Beam Graded Aggregate Mineral Filler SG UNIT OPC 1 SCC 1 SCC 2 SCC 3 SCC 4 Cement (Type I) 3.15 lb/yd Fly Ash (Class C) 2.65 lb/yd Coarse Aggregate, 3/4" (20mm) 2.70 lb/yd Coarse Aggregate, 3/8" (10mm) 2.70 lb/yd Fine Aggregate (FM = 2.57) 2.64 lb/yd Water 1.00 lb/yd Superplasticizer (CAE) 1.06 fl oz/yd Viscosity Modifying Admixture (VMA) 1.00 fl oz/yd 3 22 Slump flow (standard slump for OPC) in Paste content by Volume % FA/CA ratio w/cm VMA Strong Wall

6 Review of SCC mixes shows departure from normal concrete SCC Database Mixtures studied FA/CA RATIO SCC2 SCC1 SCC4 OPC1 SCC3 Typical non-scc materials, according to ACI mixture proportioning method Higher FA/CA ratio Higher paste content AGGREGATE CONTENT (%)

7 How do SCC strategies affect properties and performance? SCC Strategies high paste content VMA (thickeners) smaller aggregate & controlled gradation HRWR (CAE) mineral fillers & additives Properties flowability stability shrinkage and creep Performance segregation strength and stiffness early age cracking deformation prestress Loss long term durability

8 Fresh SCC properties Flowability: flows easily at suitable speed into formwork Passing ability: passes through reinforcements without blocking Segregation resistance: the distribution of aggregate particles remains homogeneous in both vertical and horizontal directions Static segregation due to gravity, vertical direction Dynamic segregation due to flow, horizontal direction

9 Flowability Slump flow (C1611), also tests dynamic segregation

10 Passing ability L-box test

11 Passing ability J-ring test (C1621)

12 Segregation Column segregation test (C1610). SI = 100(CAB - CAT) / [0.5 (CAB + CAT)]

13 SCC Research at UIUC Rheology Segregation Formwork pressure Creep and shrinkage SCC research group: Prof. D. Lange, myself, Matt D Ambrosia, Ben Birch, Fernando Tejeda, Lin Shen Funded by IDOT

14 Rheology y = x Torque (N.m) y = x Rotational speed (rad/sec) test 1 test 2 Linear (test 2) Linear (test 1) Concrete rheometer measures yield stress and viscosity Yield stress: <100 Pa for SCC, >500 for normal concrete Plastic Viscosity: ~50 Pa.s for SCC, same as normal concrete

15 Segregation Static segregation Dynamic segregation Static segregation mainly controlled by gravity Dynamic segregation depends on flow rate and friction (formwork, floor, etc) Segregation affects strength and stiffness, creep and shrinkage

16 New ways to measure static segregation Visual examination of hardened concrete (visual index) Segregation probe (developed at UIUC)

Visual examination Hardened Visual Stability Index (VSI) rating criteria for concrete cylinder specimens 0 1 2

percentage of coarse aggregate through depth 1: Stable No paste or mortar layer visible at top of cylinder,

or mortar layer visible (<1 ), slight difference in coarse aggregate through depth 3: Unstable Significant

17 Visual examination Hardened Visual Stability Index (VSI) rating criteria for concrete cylinder specimens : Stable No paste or mortar layer visible at top of cylinder, no apparent difference in the size and area percentage of coarse aggregate through depth 1: Stable No paste or mortar layer visible at top of cylinder, slight difference in the size and area percentage of coarse aggregate through depth 2: Unstable Slight paste or mortar layer visible (<1 ), slight difference in coarse aggregate through depth 3: Unstable Significant paste or mortar layer visible (>1 ), obvious difference in the size and area percentage of coarse aggregate through depth

18 Segregation probe Quick and easy Set on top of concrete and measure settlement Correlates well with HVSI Segregation Probe results 1/8 ¼ 2½ 2¼ 2 HVSI

19 Robustness Robust mix resists segregation due to small changes in w/cm Segregation probe allows us to characterize robustness Robustness measured as margin in w/cm between target and maximum allowable penetration

20 Dynamic segregation Flowing SCC may segregate during placement May be sufficient to impact hardened concrete performance - shrinkage, elastic modulus, creep

21 UIUC strong wall Cast 2004 Used SCC to achieve consolidation with congested formwork

Dynamic segregation in 80% 60% A 0 B 20 C 29 strong wall D 36 6 E 44 Total Aggregate - estimate F G 53 56 63.6% Pump location Aggregate Content 40% Coarse Aggregate 33.

22 Dynamic segregation in 80% 60% A 0 B 20 C 29 strong wall D 36 6 E 44 Total Aggregate - estimate F G % Pump location Aggregate Content 40% Coarse Aggregate 33.7% 20% 0% Distance Traveled (ft) G F E D In strong wall, segregation occurred abruptly at 45 of flow Static segregation tests did not predict dynamic segregation C B A 0

23 Measuring dynamic segregation Visual inspection of slump flow Loss of aggregate during flow in trough (developed at UIUC)

24 Modeling dynamic segregation Dynamic segregation depends on flow velocity and aggregate properties Model using forces on aggregate: drag from paste (depends on paste velocity, rheology), friction from formwork (depends on aggregate size, density)

25 Evaluating creep and shrinkage Restrained stress test machine Sealed for 24 h, then dried at 50% RH, 23 o C Companion specimen tested for free shrinkage 3 in (76 mm) LVDT Extensometer 3 in (76 mm) Load cell Actuator Feedback Control

26 Creep and shrinkage results Early age tensile stress was greater in SCC than in most previous concretes tested If aggregate content low, creep and shrinkage high Shrinkage Stress (psi) SCC, w/cm = 0.34, 36% paste Age (days) Low w/cm also produces autogeneous shrinkage High paste and low w/c a dangerous combination

27 Microcracking Stress-Strength Ratio OPC1, w/c = SCC1, w/c = 0.39 SCC2, w/c = SCC3, w/c = SCC4, w/c = Age (d) Specific Creep (x10-6 m/m/psi) OPC1, w/c = 0.40 SCC1, w/c = SCC2, w/c = 0.33 SCC3, w/c = 0.41 SCC4, w/c = Age (days) Occurs one or two days after drying Induced by high stress-strength ratio Intensified by lack of creep relaxation

28 Cracking Surface cracks in UIUC strong wall due to early age shrinkage, probably caused by segregation (0.4 mm)

29 Evaluating formwork pressure Using pressure transducers to study formwork pressure

30 2 Formwork pressure results FW pressure/hs pressure bucket truck pumper time (min) Pressure decreases as cement flocculates and hydrates Concrete stays at full hydrostatic pressure only during rapid placement or with continuous shearing

31 The Good, the Bad, and the Ugly The Good: high flowability The Bad: segregation, high formwork pressure The Ugly: shrinkage cracking Presentation by D. Lange

32 Summary SCC is an exciting new concrete technology Recommendations for SCC mix proportioning: Design to prevent static segregation Set limits on flow length to prevent dynamic segregation Set limits on paste contents to avoid shrinkage Avoid low w/cm ratios to reduce shrinkage Set limits on placement to reduce formwork pressure Challenges remain: New tests to measure properties New models to predict performance New strategies to control segregation, cracking, formwork pressure

INSPECTION MANUAL FOR SELF-CONSOLIDATING CONCRETE IN PRECAST MEMBERS

INSPECTION MANUAL FOR SELF-CONSOLIDATING CONCRETE IN PRECAST MEMBERS Product 0-5134-P1 TxDOT Project 0-5134: Self-Consolidating Concrete for Precast Structural Applications By Eric P. Koehler and David