Strain-rate effects on the tensile behavior of strain-hardening cementitious composites En-Hua Yang a,⇑ , Victor C. Li b a Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore b Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA highlights  Sources responsible for strain-rate effects of strain hardening cementitious composites (SHCC) were discovered.  Rate dependence in component phases, i.e. fiber, matrix, and interface, were experimentally determined.  A dynamic micromechanics-based strain hardening model was developed for SHCC component tailoring and ingredient selection. article info Article history: Received 6 February 2013 Received in revised form 23 October 2013 Accepted 5 November 2013 Available online 30 November 2013 Keywords: Strain-rate effects Strain-hardening cementitious composites SHCC Micromechanics abstract This paper investigated the strain-rate effects on the tensile properties of strain-hardening cementitious composite (SHCC) and explored the underlying micromechanical sources responsible for the rate depen- dence. Experimental studies were carried out to reveal rate dependence in component phases, i.e. fiber, matrix, and fiber/matrix interface. A dynamic micromechanical model relating material microstructure to SHCC tensile strain-hardening under high loading rates was developed. It was found fiber stiffness, fiber strength, matrix toughness and fiber/matrix interface chemical bond strength were loading rate sensitive and they increase with loading rates in a polyvinyl alcohol fiber-reinforced SHCC (PVA-SHCC) system. These changes in component properties result in the reduction of tensile strain capacity of PVA-SHCC as the strain-rate increases from 10 5 to 10 1 s 1 . Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Terrorist attacks and natural hazards highlight the need for assuring human safety in civil infrastructure under extreme load- ing such as projectile impacts and bomb blasts. While concrete has served as an eminently successful construction material for years, reinforced concrete (R/C) infrastructure can be vulnerable under severe dynamic loading [1]. Many catastrophic failures of R/C structures subjected to impact or blast loading (IBL) were asso- ciated with the brittleness of concrete material in tension as sug- gested by Malvar and Ross [2]. Brittle failures, such as cracking, spalling, and fragmentation, of concrete were often observed in R/C structures when subjected to IBL [3], and can lead to severe loss of structural integrity. Apart from that, high speed spalling debris ejected from the backside of the structural elements can cause serious injury to personnel behind the structural elements. There is a need to enhance concrete ductility to enhance the safety of R/C infrastructure under IBL. Strain-hardening cementitious composites (SHCC), a new class of concrete material featuring high ductility and damage tolerance under tensile and shear loading, offers a potential solution to reducing R/C structure vulnerability under IBL. SHCC with tensile strain capacity in excess of 3% under quasi-static uniaxial tensile loading can be attained with only 2% fiber content by volume [4]. However, the success of SHCC as a ductile concrete material under IBL depends on its ability to retain tensile ductility at high strain- rates [5], which requires a systematic investigation. Literatures on strain-rate effects of SHCC were not always con- sistent. For example, the authors reported the tensile strain capac- ity of a polyvinyl alcohol fiber-reinforced SHCC (PVA-SHCC) decreases while the tensile strength increases with increasing strain-rate from 10 5 to 10 1 s 1 as shown in Fig. 1 [5]. Similar re- sults were observed and reported by others [6,7]. This observation implies the brittleness of SHCC increases with loading rate which is unfavorable to the high energy absorption demand when R/SHCC structures are subjected to IBL. Maalej et al. [8], however, reported the tensile strain capacity of a hybrid steel and polyethylene fiber-reinforced SHCC shows negligible strain-rate effects when strain-rate increases from 10 6 to 10 1 s 1 . Boshoff and van Zijl [9] reported similar results with another version of SHCC. These 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.11.013 ⇑ Corresponding author. Address: N1-01b-56, 50 Nanyang Avenue, Singapore 639798, Singapore. Tel.: +65 6790 5291; fax: +65 6791 0676. E-mail address: ehyang@ntu.edu.sg (E.-H. Yang). Construction and Building Materials 52 (2014) 96–104 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat