applied sciences Article Influence of Cracking on the Durability of Reinforced Concrete with Carbon Nanotubes Jose Alexandre Bogas 1, * , Hawreen Hasan Ahmed 2,3 and Tomás Diniz 3 Citation: Bogas, J.A.; Ahmed, H.H.; Diniz, T. Influence of Cracking on the Durability of Reinforced Concrete with Carbon Nanotubes. Appl. Sci. 2021, 11, 1672. https://doi.org/ 10.3390/app11041672 Academic Editor: Doo-Yeol Yoo Received: 21 January 2021 Accepted: 7 February 2021 Published: 12 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 CERIS, Department of Civil Engineering, Architecture and Georresources, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal 2 Department of Highway & Bridge Engineering, Technical Engineering College, Erbil Polytechnic University, Erbil 44001, Iraq; [email protected] 3 Scientific Research and Development Center, Nawroz University, Duhok 42001, Kurdistan-Region, Iraq; [email protected] * Correspondence: [email protected] Abstract: This study focuses on the influence of natural and artificially induced cracks on the dura- bility of concrete reinforced with carbon nanotubes (CNT). Pre-cracked concrete mixes, unreinforced or reinforced with 0.1% CNT, are characterized in terms of capillary absorption, carbonation, and chloride penetration resistance, and compared to the uncracked reference concrete. The mechanical strength and durability properties were improved in uncracked CNT-reinforced concrete, without significantly affecting its density and workability. The efficiency of CNT was higher when the con- crete was previously subjected to drying conditions. For all tested properties, the incorporation of CNT was effective in reducing the influence of artificial and natural cracks on concrete durability. The main contribution of CNT occurred in the crack surrounding region. Depending on the analyzed property and cracking conditions, the significant reduction of durability in cracked concrete may be 10–30% attenuated when CNT is incorporated. The effect was more pronounced in mechanically induced natural cracks, where CNT may better participate in their vicinity. Keywords: reinforced concrete with carbon nanotubes; artificial cracking; natural cracking; capillary absorption; carbonation; chloride penetration 1. Introduction Concrete is a quasi-brittle material highly prone to crack formation throughout its service life [1,2]. The reasons behind crack appearance in concrete include poor design, mechanical actions, hygrothermal changes, shrinkage, and others [3,4]. Cracks tend to form in concrete when the internal tensile stresses surpass its optimum tensile strength. The newly created paths may increase concrete permeability to water and deleterious agents, negatively affecting its durability. Various investigations have been carried out to study the effect of cracks on the durability behavior of conventional concrete [5–10]. Studies involving pre-cracking via splitting tensile tests indicated that the permeability was significantly affected for crack widths over 0.05 mm [6,8], especially up to 0.2 mm [5,6]. For crack widths wider than 0.2 mm, the permeability increase continued but at a lower rate. In another study [11], considering concrete specimens with natural and artificial cracks, the coefficient of permeability increased parabolically with the crack width (0.1–0.5 mm). Factors affecting the concrete penetrability include orientation, depth, and geometry of the cracks, which makes it difficult to precisely evaluate the cracking influence on the overall concrete durability. In order to overcome this issue, investigators have attempted to estimate threshold crack widths, above which, chloride and carbonation of cracked concrete is significantly increased [7,9,10,12]. Critical crack widths of 0.05–0.08 mm were determined for chloride diffusion in cracked concrete specimens [10,13]. In a study by Schutter et al. [5], the depth of chloride penetration and carbonation of concrete were related to the crack Appl. Sci. 2021, 11, 1672. https://doi.org/10.3390/app11041672 https://www.mdpi.com/journal/applsci
Influence of Cracking on the Durability of Reinforced Concrete with Carbon Nanotubes
May 19, 2023
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