Investigation on electrically conductive aggregates produced by incorporating carbon fiber and carbon black Binmeng Chen a , Bo Li b,⇑ , Yan Gao a , Tung-Chai Ling c , Zeyu Lu a , Zongjin Li a a Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China b Department of Civil Engineering, The University of Nottingham Ningbo China, 199 Taikang East Road, Ningbo, China c College of Civil Engineering, Hunan University, Changsha, China highlights  Electrically conductive aggregates (ECAs) are fabricated by pelletization technique.  Carbon fiber and/or carbon black are well dispersed by semi-dry mixing method.  The threshold percolation of carbon fiber and carbon black are identified for ECAs.  ECAs exhibit excellent resistivity, acceptable strength and water absorption. article info Article history: Received 24 October 2016 Received in revised form 10 March 2017 Accepted 18 March 2017 Keywords: Conductive aggregate Carbon fiber Carbon black Pelletization Electrical resistivity abstract This paper reports on an investigation of newly developed electrically conductive aggregates (ECAs) through the semi-dry mixing method and the pelletization technique. Carbon fiber and carbon black were incorporated into the aggregates as conductive fillers, while ordinary Portland cement and fly ash were used as matrix materials. The effects of carbon fiber and/or carbon black dosages on the electrical resis- tivity, water absorption and crushing strength of ECAs were studied. For ECAs with carbon fiber only, the threshold percolation of carbon fiber was identified to be 1.0% by volume. The ECAs with 1.0% carbon fiber exhibited 3.4 Om electrical resistivity, 13.08% water absorption and 1.57 MPa crushing strength. Moreover, the effect of carbon black content was investigated when the content of carbon fiber was kept at 0.5 vol.%. The threshold percolation of carbon black for ECAs with 0.5 vol.% carbon fiber was 2.0% by weight. These ECAs possessed 7.34 Om resistivity, 24.41% water absorption and 0.95 MPa crushing strength. Scanning electron microscope was employed to study the conductive network formed by two conductive components, which helped to illustrate the conductive mechanism of carbon fiber and carbon black inside the ECAs. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Electrically conductive concrete is a cement-based composite that contains electronically conductive components to achieve a stable and relatively low electrical resistivity [1]. It is a relatively new type of functional material which has drawn much attention due to its good performance in electrical conductivity and mechan- ical properties [2,3]. With the function of electrical conductivity, electrically conductive concrete has been proposed for the applica- tions of deicing, antistatic flooring, electromagnetic shielding, cathodic protection of steel reinforcement in concrete structure and health monitoring of buildings [3–6]. Since the electrical conductivity of normal concrete is very low due to the very limited conductivity of C-S-H and the highly tortuous pore structure [7,8], electrically conductive concrete is normally developed through adding a certain portion of conductive fillers, including steel slag, stainless steel fiber, graphite, carbon fiber, carbon black, etc. Sev- eral studies have already focused on the optimization of conduc- tive fillers to reduce the electrical resistivity of concrete [9–18]. Conduction of electricity in the hardened concrete mainly depends on the movement of electrons, which requires a good con- tact between conductive components. Monteiro et al. [9] prepared a cement-based composite for structural monitoring through add- ing carbon black particles. Test results showed that the resistivity could be significantly decreased as the increase of the carbon black dosage, which enhanced the accuracy of resistivity monitoring. However, the authors also reported that the carbon black was http://dx.doi.org/10.1016/j.conbuildmat.2017.03.168 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: bo.li@nottingham.edu.cn (B. Li). Construction and Building Materials 144 (2017) 106–114 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat