Journal of Building Engineering 32 (2020) 101724 Available online 28 August 2020 2352-7102/© 2020 Elsevier Ltd. All rights reserved. Effects of different kinds of carbon black nanoparticles on the piezoresistive and mechanical properties of cement-based composites Gustavo Henrique Nalon a, * , Jos´ e Carlos Lopes Ribeiro a , Eduardo Nery Duarte de Araújo b , Leonardo Gonçalves Pedroti a , Jos´ e Maria Franco de Carvalho a , Rodrigo Felipe Santos a , Alex Aparecido-Ferreira c a Department of Civil Engineering, Federal University of Viçosa, Av. Peter Henry Rolfs, Campus UFV, Viçosa, Minas Gerais, Zip Code: 36.570-900, Brazil b Department of Physics, Federal University of Viçosa, Av. Peter Henry Rolfs, Campus UFV, Viçosa, Minas Gerais, Zip Code: 36.570-900, Brazil c Department of Physics, Federal University of Parana, R. Cel. Francisco Her´ aclito Dos Santos, 100, Jardim Das Am´ ericas, Curitiba, Paran´ a, Zip Code: 81.531-980, Brazil A R T I C L E INFO Keywords: Structural Health Monitoring Carbon black nanoparticles Smart cement-based composites Mechanical properties Piezoresistivity ABSTRACT Carbon black nanoparticles (CBN) of different sizes, morphologies, microstructures and surface areas can be used to develop cement-based materials for strain monitoring and damage detection of concrete structures. There is a lack of systematic comparisons between mechanical and electrical properties of smart mortars fabricated with CBN of different characteristics. In this study, (4 × 4 x 7.5) cm prismatic composites containing CBN of distinct dibutyl phthalate (DBP) absorption number, conductivity and surface area were produced and subjected to direct current (DC), biphasic DC, piezoresistive and compression tests. Results show that CBN aggregates with the lowest structure (DBP of 125 cm 3 /100 g) and the highest resistivity provided high values of gauge factor, stress sensitivity and compressive strength, while CBN aggregates with very high structure (174 cm 3 /100 g) and low resistivity provided low internal capacitance and high electrical conductivity. The experimental data indicated that increases in structure and surface area improved the conductive network and reduced the internal capac- itance, but decreased both compressive strength and piezoresistive response, due to reductions of variations of tunneling resistance between nanofllers. 1. Introduction Concrete structures are exposed during their service life to hazards that may affect their integrity and structural performance. Structural Health Monitoring (SHM) systems have been used to continuously monitor strains and damage of concrete elements, identify any unde- sirable structural behavior in the early stages, and prevent the failure of the structures and loss of lives. Nanomodifed cement-based composites with intrinsic self-sensing and damage detection properties have been developed to work as structural elements with sensing and health monitoring abilities. These smart cementitious materials are produced with conductive nano-admixtures that improve their electrical conduc- tivity. Then, they can be used as embedded sensors in concrete elements, since mechanical deformation and damage in the cementitious matrix cause changes in the internal electrical resistivity and impedance of the composite [1–5]. Carbon black nanoparticles (CBN) are examples of conductive nano-admixtures that can be used to fabricate smart cement-based materials. Carbon black is the generic name of a family of small particles of carbon which are formed during the thermal decomposition process of hydrocarbons. During the combustion of fuel oils, oil drops or gaseous hydrocarbons are incompletely burned, due to the gradient of temper- ature caused by various oxygen depletions. CBN are smaller than 300 nm. During the production process, they fuse to form aggregates, while clusters of aggregates may form agglomerates. In general, the degree of aggregate branching is known as the “structure” of carbon blacks. High structure blacks present extensive interlinking between primary parti- cles, while low structure ones exhibit a small number of primary parti- cles per aggregate [6–10]. The formation of CBN aggregates depends on different factors, such as type of fuel, maximum temperature and duration of combustion. Then, their size, morphology, microstructure and surface area are ex- pected to vary signifcantly. In fact, there are many kinds of * Corresponding author. E-mail addresses: gustavo.nalon@ufv.br (G.H. Nalon), jcarlos.ribeiro@ufv.br (J.C.L. Ribeiro), eduardonery.fsica@gmail.com (E.N.D. Araújo), lpedroti@gmail. com (L.G. Pedroti), josemaria.carvalho@ufv.br (J.M.F. Carvalho), rodrigo.felipe@ufv.br (R.F. Santos), alex@fsica.ufpr.br (A. Aparecido-Ferreira). Contents lists available at ScienceDirect Journal of Building Engineering journal homepage: http://www.elsevier.com/locate/jobe https://doi.org/10.1016/j.jobe.2020.101724 Received 26 May 2020; Received in revised form 19 August 2020; Accepted 25 August 2020