ACI Materials Journal/July-August 2013 413 Title no. 110-M37 ACI MATERIALS JOURNAL TECHNICAL PAPER ACI Materials Journal, V. 110, No. 4, July-August 2013. MS No. M-2011-351.R1 received November 27, 2012, and reviewed under Institute publication policies. Copyright © 2013, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the May-June 2014 ACI Materials Journal if the discussion is received by February 1, 2014. Composite Properties of High-Strength, High-Ductility Concrete by Ravi Ranade, Victor C. Li, Michael D. Stults, William F. Heard, and Todd S. Rushing ductility in one concrete with limited success. The mechan- ical test results of ultra-high-performance strain-hardening cementitious composites (UHP-SHCC) were reported in Kamal et al. 7 The best performing UHP-SHCC has an average compressive strength of 96 MPa (14 ksi) at 14 days, only half that of VHSC, 2 and a tensile ductility of 3.3% at 14 days after casting (longer age data are not reported in this refer- ence 7 ). The development of another such material—ultra- high-performance fiber-reinforced concrete (UHP-FRC)—is presented in Wille et al. 8 UHP-FRC has a 28-day compres- sive strength of approximately 200 MPa (29 ksi) and a tensile ductility of 0.6%, which is at least five times less than ECC. ECC is an ultra-ductile class of fiber-reinforced cementi- tious composites with moderate compressive strength (f c ′ ≈ 30 to 70 MPa [4.3 to 10.2 ksi]) and tensile ductility ranging from 3 to 6%. 4 Various versions of a commercial UHPC have compressive strengths ranging from 160 to 240 MPa (23 to 35 ksi). However, the maximum tensile ductility of commercial UHPC is only approximately 0.1%, 9 which is an order of magnitude less than ECC. 4 In Fig. 1, the compressive strength is plotted against tensile ductility for the materials mentioned previously, along with the HSHDC presented in this study. None of the previously developed composite materials truly combine the compressive strength of VHSC and tensile ductility of ECC in one material. Researchers at the University of Michigan, Ann Arbor, in collaboration with the U.S. Army Engineer Research and Development Center (ERDC), Vicksburg, MS, have recently developed a new fiber-reinforced cementitious composite called high-strength, high-density concrete (HSHDC). A new fiber-reinforced cementitious composite—high-strength, high-ductility concrete (HSHDC)—has been developed at the University of Michigan, Ann Arbor, in collaboration with the U.S. Army Engineer Research and Development Center, Vicksburg, MS. The micromechanics-based design of HSHDC resulted in a unique combination of ultra-high compressive strength (166 MPa [24 ksi]), tensile ductility (3.4%), and high specific energy absorp- tion under direct tension (greater than 300 kJ/m 3 [6270 lb-ft/ft 3 ]). The material design approach and mechanical property character- ization of HSHDC under direct tension, split tension, third-point flexure, and uniaxial compression loading, along with its density and fresh properties, are reported in this paper. Keywords: engineered cementitious composites; high-ductility concrete; high-performance cementitious composite; high-strength concrete. INTRODUCTION High-performance concretes of the present day can be broadly classified into two categories, depending on their superior mechanical property: high-compressive-strength concretes (for example, very-high-strength concrete [VHSC], ultra-high-performance concrete [UHPC], reactive powder concrete [RPC], macro-defect-free concrete [MDF], and concrete densified with small particles [DSP]) 1,2 ; and high-tensile-ductility concretes (for example, engineered cementitious composite [ECC], strain-hardening cement composites [SHCC], and some high-performance fiber-rein- forced cementitious composites [HPFRCCs]). 3-5 Both types of concrete have their associated advantages in structural applications. High-strength concrete facilitates the design of size-efficient structural members and provides addi- tional strength safety margins (particularly in compression) for strategically critical and protective structures. High- ductility concrete prevents catastrophic structural collapse by absorbing massive amounts of energy during extreme load-displacement events—such as earthquakes, hurricanes, projectile impacts, and blasts—and is particularly effec- tive when the failure mode is tension-related. However, the mechanical advantage of each type of concrete proves to be a limitation for the other. High-strength concretes inher- ently have an extremely brittle matrix. 6 Although this limita- tion is partially alleviated by the use of short fibers, it often results in a tension-softening behavior with decreasing load capacity after the formation of very few cracks. On the other hand, high-ductility concretes have compressive strengths two to four times smaller than the high-strength concretes. A combination of high compressive strength and high tensile ductility in one concrete material is highly desirable to ensure resilience of critical structures under extraordinary loads/displacements, which is the motivation for the devel- opment of high-strength, high-ductility concrete (HSHDC). Recently, a few notable investigations have been conducted on combining high compressive strength and high tensile Fig. 1—Strength-ductility comparison chart.