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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
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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?
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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
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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
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Properties of UHPC
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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Results
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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
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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
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Questions?
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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
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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
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