Bond Interface Strength between Ultra High Performance Concrete and

Normal Concrete

Presented by Mariah Safritt

July 30, 2015

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?

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

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

Properties of UHPC

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

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)

UHPC Mix Design

Material Mix 1: Weight (lbs)

Mix 2: Weight (lbs)

Mix 3: 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 12 mL

Steel Fibers 0.86 -- --

Water 8.20 7.25 6.90

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

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

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

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

Results

Batch 2 Day Strength 7 Day Strength 14 Day Strength

1 6800 psi 9251 psi 10992 psi

2 5238 psi 7179 psi 11289 psi

3 3948 psi 5908 psi 7354 psi

Table 1. UHPC Compressive Strengths

Batch 7 Day Strength

Normal A4 Concrete 4668 psi

Table 2. Normal Concrete Compressive Strength

Results

Specimen Surface Prep Strength (psi) Break Characterization

1A Normal 4200 Bond interface

1B Sand blasted 7635 Substrate failure

1C HCl etched 4124 Bond interface

2A Sand blasted 6973 Substrate failure

2B Normal 3486 Bond interface

2C HCl etched 2524 Bond interface

3A Normal 3034 Bond interface

3B Sand blasted 5183 Bond interface

3C HCl etched 1386 Bond interface

Table 3. Slant Shear test results

Results

Specimen Surface Prep Strength (psi) Break Characterization

1J HCl etched 2013 Bond interface

1K Sand blasted 2490 Bond interface

1L Normal 2153 Bond interface

2J Normal 1975 UHPC failure

2K HCl etched 1519 UHPC failure

2L Sand blasted 2841 Bond interface

3J Normal 1734 Bond interface

3K HCl etched 1724 Bond interface

3L Sand blasted 2129 Bond interface

Table 4. Splitting Tensile test results

Results

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

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

Questions?

Sources1) Naaman, Wille; 2012; The Path to Ultra-High Performance Fiber

Reinforced Concrete (UHP-FRC): Five Decades of Progress; UHPC International Symposium

2) Sarkar; 2010; Characterization of the Bond Strength between Ultra High Performance Concrete Bridge Deck Overlays and Concrete Substrates; Michigan Tech thesis

3) Wille, Naaman, Parra-Montesinos; 2011; Ultra-High Performance Concrete with Compressive Strength Exceeding 150 MPa (22 ksi): A Simpler Way; ACI Materials Journal

4) Russell, Graybeal; 2013; Ultra-High Performance Concrete: A State-of-the-Art Report for the Bridge Community; Federal Highway Administration

5) Graybeal; 2013; TECHBRIEF Development of Non-Proprietary Ultra-High Performance Concrete for Use in the Highway Bridge Sector; FHWA

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