The effect of high temperatures on the mechanical properties of concrete made with different types of aggregates Ivanka Netinger 1 , Ivana Kesegic 1 , Ivica Guljas n University of Osijek, Faculty of Civil Engineering, Crkvena 21, 31000 Osijek, Croatia article info Article history: Received 14 January 2010 Received in revised form 1 July 2011 Accepted 15 July 2011 Available online 6 August 2011 Keywords: Concrete High temperature Slag Crushed brick/tile Diabase abstract The main objective of this paper was to assess the benefits of using materials that were formed at high temperatures as an aggregate for concrete that was exposed to high temperature. The fire resistance of concrete made with some locally available, potential ‘‘fire-resistant’’ aggregates, such as diabase, steel slag, crushed bricks and crushed tiles, was investigated. The specimens of measurements 4  4  16 cm 3 were kept in molds for 24 h and, after demolding, were kept in water at room temperature of about 20 72 1C until testing. At the age of 28 days, the specimens, with moisture content within the limits of 3–5%, were exposed to high temperatures in a previously heated test furnace. The residual mechanical properties (compressive and flexural strengths) of these concretes after natural cooling were compared with the residual mechanical properties of concrete made with commonly used river and dolomite aggregates. The replacement of natural concrete aggregates with brick and steel industry waste materials was justified, not only in terms of increased fire resistance, but also in terms of more responsible waste disposal. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is well known for its capacity to endure high temperatures and fires owing to its low thermal conductivity and high specific heat [1]. However, it does not mean that fire, or high temperatures, do not affect concrete at all. Its color changes, while its compressive strength, modulus of elasticity, concrete density and the appearance of its surface become significantly affected by high temperatures [2–5]. Therefore, many researchers have recently become interested in the possibility of increasing the fire resistance of this material. According to studies, the fire resistance of concrete can be improved in several ways. The replacement of cement with slag or fly ash, for example, is a very efficient measure [6–11], as well as the addition of polypropylene fibers into a concrete mix, which is also found to be useful [12–14]. Since thermal properties of concrete are mainly inter- related with the type of aggregates used [15], this paper is based upon the presumption that all materials formed at high tempera- tures and usable as aggregates can improve the fire resistance of concrete. A special emphasis has been placed on the possibility of using slag as a concrete aggregate, which would not only be a great contribution to fire engineering, but also to waste material handling within the Republic of Croatia. 2. Potential ‘‘fire-resistant’’ aggregates As previously mentioned, it has been assumed in this paper that materials developed at high temperatures are potential ‘‘fire-resistant’’ aggregates. At the same time, it was intended to use those that are widely available within the Republic of Croatia. For this purpose, the potential of domestic steel slag and waste material from local brick and tile industries was researched. In addition to steel slag and crushed bricks/tiles, this study also deals with diabase, a sort of eruptive rock, which is supposed to be fire resistant. 2.1. Waste material from the clay brick and tile industry Waste material from the brick and tile industry is the common name for waste material created by damaged brick and tile elements in the final phase of their production. As pre-fabricated bricks and tiles damaged over tolerance limits cannot be placed into the market, they get crushed at a location near to the factory. This type of waste material is often used as filling material for lower and upper layers of sports terrains. However, worldwide research [15–21] implies the possibility of using crushed brick as a concrete aggregate, which would be a valuable contribution to the solution of the ecological handling problem, as well as an Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/firesaf Fire Safety Journal 0379-7112/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.firesaf.2011.07.002 n Corresponding author. Tel.: þ385 31 540 083; fax: þ385 31 540 071. E-mail addresses: nivanka@gfos.hr (I. Netinger), ivanak@gfos.hr (I. Kesegic), iguljas@gfos.hr (I. Guljas). 1 Tel.: þ385 31 540 082. Fire Safety Journal 46 (2011) 425–430