1. Presented by Mariah Safritt July 30, 2015
Bond Interface Strength between Ultra High Performance Concrete and Normal Concrete
Presented by Mariah Safritt
July 30, 2015

2. Motivation
Repairing infrastructure is expensive and uses a lot of resources, not efficient or sustainable
UHPC is stronger, so less can be used while obtaining higher strengths
Can UHPC be used as a repair material for existing structures?
Are UHPC and normal concrete (NC) compatible?

3. Introduction to UHPC
Definition: “hydraulic cement-based concrete with a compressive strength at least equal to 22 ksi” (1)
Compare to normal strength concrete 4-8 ksi
UHPC properties compared to NC
Higher compressive strength
Higher tensile strength with ductility (use of fibers)
Increased durability
Higher initial cost but longer life cycle

4. Properties of UHPC Strength, toughness, durability, energy absorption
Impact and fire resistance, freeze-thaw and corrosion resistance, shear and bending resistance
Negligible permeability and conductivity, volume stability (low shrinkage/expansion)
Resistance to chloride penetration

5. Properties of UHPC

6. Experiment Design
2 tests run: Slant Shear Test (compression) and Splitting Tensile Test (indirect tension)
3 UHPC mixes
Mix 1: steel fibers
Mix 2: silica fume and fly ash
Mix 3: fly ash

7. Experiment Design 3 surface preparations Normal Sand blasted
Etched with hydrochloric acid
Digital Image Correlation (DIC) performed on all specimens for future work (strain and deformation analysis)

8. UHPC Mix Design Material Mix 1: Weight (lbs) Mix 2: Weight (lbs)
Portland cement
21.85
16.18
13.82
Fly Ash --
3.93
9.21
Silica Fume
5.57
4.05
Fine sand
10.69
24.27
21.48
Superplasticizer
12 mL
25 mL
Steel Fibers
0.86
Water
8.20
7.25
6.90

9. UHPC Mix Design Cement: Type I/II Sand fineness: 75 μm to 1.2 mm
Sand moisture content: saturated surface dry (SSD) sand for mixes 1 & 3, oven dry sand for mix 2
Superplasticizer (HRWR) used: Glenium 7500

10. UHPC Mix Procedure
Mix all cementitious materials (cement, silica fume, fly ash) dry until well mixed (1-2 min)
Add sand and mix well (1-2 min)
Add HRWR to water first, and then add half of water and mix 2-3 min
Add rest of water and mix 3-4 min
Add any fibers at the very end of mixing procedure and mix until homogeneous

11. Experiment Procedure
1) ASTM standard molds (C39, C882, & C496) - Cylinders: 4x8 in. with dummy section half the size of cylinder, divided along 30° line - Prisms: 4x3x16 in. prisms, with each section 4x1.5x16 in.; use pieces of wood to create dummy section 2) Design and mix normal concrete mix (ACI A4 standard mix) 3) Once cured, roughen surfaces of NC for contact with UHPC - 3 cylinders & 3 prisms sandblasted, 3 cylinders & 3 prisms etched with HCl

12. Experiment Procedure
4) Design UHPC mixes, mix and place UHPC in molds with NC sections 5) Cure in moist curing room; cut prisms into 3 inch long cubes before testing 6) Once fully cured, perform tests on specimens based on ASTM standards - slant shear  direct compression and shear stress - splitting tensile  indirect tension along bond interface - DIC  deformation and strain

13. Results Table 1. UHPC Compressive Strengths Batch 2 Day Strength
6800 psi
9251 psi
10992 psi 2
5238 psi
7179 psi
11289 psi 3
3948 psi
5908 psi
7354 psi
Table 2. Normal Concrete Compressive Strength
Batch
7 Day Strength
Normal A4 Concrete
4668 psi

14. Break Characterization
Results
Table 3. Slant Shear test results
Specimen
Surface Prep
Strength (psi)
Break Characterization 1A
Normal
4200
Bond interface 1B
Sand blasted
7635
Substrate failure 1C
HCl etched
4124 2A
6973 2B
3486 2C
2524 3A
3034 3B
5183 3C
1386

15. Break Characterization
Results
Table 4. Splitting Tensile test results
Specimen
Surface Prep
Strength (psi)
Break Characterization 1J
HCl etched
2013
Bond interface 1K
Sand blasted
2490 1L
Normal
2153 2J
1975
UHPC failure 2K
1519 2L
2841 3J
1734 3K
1724 3L
2129

16. Results

17. Discussion
Strongest overall UHPC mix was Mix 2 with silica fume and fly ash
Best surface preparation (resulted in highest bond strengths) was sand blasting
Most specimens (all but 4) broke along the bond interface; 2 broke in substrate material and 2 broke in the UHPC
All specimens showed higher strengths in slant shear test than splitting tensile test

18. Conclusion
Sand blasted surface preparation creates a stronger bond between UHPC and normal concrete
UHPC Mix 2 (with silica fume and fly ash) was the strongest mix design used since it had the highest overall compressive strength
UHPC Mix 1 was strongest for the slant shear test and UHPC Mix 2 was strongest for the splitting tensile test

19. Questions?

20. Sources
Naaman, Wille; 2012; The Path to Ultra-High Performance Fiber Reinforced Concrete (UHP-FRC): Five Decades of Progress; UHPC International Symposium
Sarkar; 2010; Characterization of the Bond Strength between Ultra High Performance Concrete Bridge Deck Overlays and Concrete Substrates; Michigan Tech thesis
Wille, Naaman, Parra-Montesinos; 2011; Ultra-High Performance Concrete with Compressive Strength Exceeding 150 MPa (22 ksi): A Simpler Way; ACI Materials Journal
Russell, Graybeal; 2013; Ultra-High Performance Concrete: A State-of-the-Art Report for the Bridge Community; Federal Highway Administration
Graybeal; 2013; TECHBRIEF Development of Non-Proprietary Ultra-High Performance Concrete for Use in the Highway Bridge Sector; FHWA

21. Acknowledgments Professor Devin Harris, mentor
Dr. Andrei Ramniceanu, Civil Engineering department lab manager at UVA
Mike Burton, concrete lab manager at VCTIR
Evelina Khakimova, Muhammad Sherif, and Sherif Daghash, grad students at UVA
Ken and Sam and all the other VCTIR employees
Dr. Emily Parkany
Dr. Amir Gheitasi