Available online at www.CivileJournal.org Civil Engineering Journal (E-ISSN: 2476-3055; ISSN: 2676-6957) Vol. 9, No. 07, July, 2023 1737 Effect of Cooling Conditions, Retrofitting on Strength of Concrete Subjected to Elevated Temperature Swapnil B. Kharmale 1* , Pramod S. Sathe 2 , Yashwant A. Kolekar 2 1 Department of Civil Engineering, Government College of Engineering and Research, Savitribai Phule Pune University, Awasari 412405, India. 2 Department of Civil Engineering, COEP Technological University, Pune 411005, India. Received 24 March 2023; Revised 06 June 2023; Accepted 17 June 2023; Published 01 July 2023 Abstract Concrete has a high degree of fire resistance at moderate temperatures. High temperatures, however, cause concrete to lose its stiffness and strength. The effects of cooling techniques and retrofitting on the strength of concrete exposed to high temperatures have not been synchronized in previous studies. This experimental research aims to evaluate the effect of cooling conditions and the effectiveness of retrofitting concrete subjected to elevated temperatures. Four types of concrete: M 20 normal concrete (NC); M 20 metakaolin concrete (MC); M 40 standard concrete (SC); and M 40 self-compacting concrete (SCC) are considered in this study. A total of 864 samples consisting of cube, beam, and cylinder specimens are subjected to sustained elevated temperatures of 400 o C, 600 o C, and 800 o C for 2 hours rating. The weight and strength of half of the heat-damaged samples are assessed following natural air cooling (NAC) and water jet cooling (WJC). The remaining 50% of samples retrofitted with carbon fiber reinforced polymer (CFRP) are tested to evaluate the upgraded strength. The experimental findings demonstrate that water jet cooling (WJC) causes more strength degradation, and CFRP proves to be effective in restoring the strength of heat-deteriorated specimens. Overall, self-compacting concrete (SCC) has shown high resistance to elevated temperatures. Keywords: Fire Resistance; Natural Air Cooling (NAC); Water Jet Cooling (WJC); Carbon Fiber Reinforced Polymer (CFRP). 1. Introduction Fire is one of the hazards for which structural systems often require retrofitting and rehabilitation. After devastating fire events such as the 9/11 World Trade Center [WTC] attack in New York, USA; 2011 AMRI Hospital fire in Kolkata, India, the research is focused on the evaluation of the mechanical properties of construction materials at elevated temperatures, fire-induced damages, and retrofitting techniques. Cement concrete, a widely used construction material, is considered fire-resistant as well as non-combustible material due to its low thermal conductivity [1–3]. Concrete is a heterogeneous material consisting of cement, water, fine aggregates, and coarse aggregates. When concrete is subjected to elevated temperatures, alteration of pore pressure, and an increase in porosity, thermal expansion, thermal cracking, and thermal creep take place. These physical and mechanical changes damage the micro- and mesostructure of concrete, leading to its spalling and strength degradation [4]. Research on Effect of Elevated Temperature on Properties of Normal Strength Concrete: Researchers have studied the effects of high temperatures on the physical and mechanical characteristics of various normal-strength concrete mixes, and their findings indicate that as the temperature rises, there is a significant loss in * Corresponding author: sbkharmale.civil@gcoeara.ac.in http://dx.doi.org/10.28991/CEJ-2023-09-07-013 © 2023 by the authors. Licensee C.E.J, Tehran, Iran. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).