https://biointerfaceresearch.com/ 5405 Article Volume 12, Issue 4, 2021, 5405 - 5415 https://doi.org/10.33263/BRIAC124.54055415 Effects of the Variety and Content of Natural Pozzolan Coarse Aggregate on the Thermo-Mechanical Properties of Concrete Abdelilah Bellil 1,* , Ayoub Aziz 1 , Mohammed Achab 1 , Abdelmounji Amine 2 , Hamid El Azhari 3 1 Geomaterials and Geo-Environment Team (GeoM&E), GEOBIO Laboratory, GEOPAC Center, Scientific Institute, Mohammed V University in Rabat, Morocco; bellil.abdelilah@gmail.com (A.B.); ayoubaziz100@gmail.com (A.A.); med.achab70@gmail.com (M.A.); 2 Laboratoire de Géosciences Appliquées à l’Ingénierie de l’Aménagement, Faculty of Sciences, Hassan II University, Casablanca, Morocco; Ab.amine@live.fr (A.A.); 3 Hassan First University of Settat, Faculty of Sciences and Technology, Laboratory Physico-chemistry of Processes and Materials (PCPM), Research Team: Geology of Mining and Energy Resources (GRME), 26002, Settat, Morocco; hamid.elazhari@uhp.ac.ma (H.E.A.); * Correspondence: bellil.abdelilah@gmail.com (A.B.); Scopus Author ID 57202074321 Received: 9.07.2021; Revised: 15.09.2021; Accepted: 18.09.2021; Published: 18.10.2021 Abstract: The present study investigated the effects of the variety and content of three natural pozzolan coarse aggregates on concrete. Natural pozzolan aggregates have been obtained from three volcanoes (Boutagrouine, Timahdite, and Jbel Hebri) located in the Middle Atlas region in Morocco. The three pozzolans studied were characterized, and then a comparison was made by replacing the natural aggregate with the pozzolan aggregate in the concrete in different percentages, namely 25, 50, and 100 % in volume. The results showed that the variety and content of pozzolan aggregate have a significant impact on the properties of concrete, primarily caused by the characterization of pozzolan aggregate. The density of concrete decreases with the addition of pozzolan aggregate, which decreases depending on the type of pozzolan aggregate used. The highest compressive strength was measured in the concrete specimens prepared with aggregate BP while the lowest compressive strength was noted in the concrete specimens prepared with aggregate RP. On the other hand, the substitution of NA at 100% by BP, GP, and RP aggregates leads to a decrease in the thermal conductivity of about 67%, 62%, and 55% respectively Keywords: three varieties of pozzolan; lightweight concrete; mechanical strength; thermal conductivity. © 2021 by the authors. 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. Introduction In the recent construction industry, concrete is the most widely used material in all construction areas due to its usefulness and relatively low cost. In the last decade, many studies have focused on improving certain characteristics of concrete, such as lightness and thermal and sound insulation [1–4]. In this regard, the use of lightweight aggregates (LWAC) in concrete replacing normal aggregates is one of the ways to reduce the weight of a structure and improve its thermal and sound insulation due to the air voids in lightweight aggregates (LWA) [5–10]. Based on a literature review, natural pozzolanic aggregate is chosen as a replacement material for coarse aggregate. Pozzolans are pyroclastic volcanic rocks formed by the