Twisted Micro-Rebar Technology
Luke Pinkerton, PE Helix Steel Helix and Infrastructure
• Case Studies, • troubleshooting and problem solving • Cast-in-place operations • Mix designs • Concrete composition • More science/research on concrete mixes Helix for Blast Resistance
Rebar Only With Helix & 50% Less Rebar
Micro-Rebar 12 Years and 30 Countries: Slabs - Complex Structures
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Micro-Rebar Reinforced Concrete Development Length
• R/C is a Two Part System: Concrete fails before rebar works • Rebar Development Length: required to develop full tensile stress. #6 bar (20 mm) is about 2 ft (600 mm) Standard Rebar Design Curves
500 70
60 400 24” (600 mm rebar) 50 300 40 Friction Governs 200 30 Stress (ksi) Stress Stress (MPa) Stress 20 100 Bond Strength 10
0 0 0 0.0015 0.003 0.0045 0.006 Strain
Micro-Rebar Product Description
• Steel wire tensile strength: 270 ksi (1800 MPa) • Electroplated zinc coating: 3 g/m3 • Length: 1.0 inch (25 mm), • Equivalent diameter: 0.020 inch (0.5 mm) • Rectangular Cross Sectional Shape • Each Helix Micro-Rebar has a minimum of one 360- degree twist. • 11,000 parts per pound
Micro-Rebar Helix Micro Rebar Development Length
1/4” (8 mm) Helix Micro Rebar
Untwisting Governs
Bond Strength Micro-Rebar Breaking Laws of Physics Can Plastic Replace Steel?
Modulus'of'Elas+city'(S+ffness)' !35,000.00!! Helix !30,000.00!! • 8 x Stiffer than Concrete !25,000.00!! • 6 x bond of smooth steel !20,000.00!! Synthetic Fibers !15,000.00!! !10,000.00!! • 1/3 the stiffness of Concrete Modulus'of'Elas+city'(ksi)' !5,000.00!! • 1/20 the stiffness of Steel !"!!!! • Acts as void until stretched • No force until 1 mm crack Helix!5"25! Steel!Fiber! and “band is stretched” Grade!60!Rebar! Modified!Olefin! 4000!psi!Concrete! Large crack width testing Copolymer/Polypropylene!! Polypropylene/Polyethylene! Plastic Shrinkage Helix Tensile Resistance ASTM E111 Rebar Test
• ASTM E-111 Test Setup • Hourglass 6” (150 mm) Diameter • 4 inch (100 mm) Gage Length • Machine plots tensile stress vs. strain • ISO/IEC 17025 Laboratory Proactive Reinforcement & Strain Capacity
1.60#
1.40#
1.20#
1.00#
0.80#
0.60# Tensile'Stress'(MPa)'
0.40#
0.20#
0.00# 0# 50# 100# 150# 200# 250# Strain,'x1046' Micro-Rebar Development of a LRFD Tensile Resistance Model
• Load and Resistance Factor Design (LRFD) – J.G. MacGregor, • Required Information • Output Resistance Functions Tensile Resistance Equation (Force & Distribution) (function of dosage and f’c) Variations (Force & Distribution) Resistance Factor Consequence of failure (Classes) Field Test Results (Calibration)
Micro-Rebar Helix Design Classes and Selection
Helix Design Classes Class B Example – Wall
Class Assumptions Applications
A Micro-Cracking 1 Shrinkage and FS 3.7 Temperature Soil Supported Strain Limit 110 με Structures B Micro-Cracking II Soil Supported FS 5 (LRFD) Structures, Arches, Laterally Supported Strain Limit 110 με walls C Multiple Crack III Suspended Cast in FS 8.5 (LRFD) Pace Concrete, Other Structures, Limitation Strain Limit 1000 με Apply
Micro-Rebar Designing with Helix Another Piece of Rebar
• A Familiar Design Process