Abstract
There has been a tendency to design ever slender building construction using high strength concrete in recent years. Application of HSC is also growing in tunnel construction. One of the most important challenges is to control explosive spalling of concrete and the method recommended by Eurocode 2 (EN 1992-1-2:2008/NA:2010P) is addition of polypropylene fibres to the mix. The purpose of the research described in this paper was to evaluate the changes of mechanical properties of HSC exposed to the effect of high temperature. The tests were carried out on three types of high strength concrete: air-entrained concrete, polypropylene fibre-reinforced concrete and reference concrete having constant water/cement ratio. The properties of hardened concrete including compressive strength, tensile splitting strength, flexural strength and E-modulus were studied. The latter tests were carried out on both on concrete cured at 20 °C and concrete subjected to high-temperature conditions at 300 °C, 450 °C and 600 °C. The results enabled us to evaluate the effect of high-temperature conditions on the properties of high-performance concrete and compare the effectiveness of the two methods designed to improve the high-temperature performance of the concrete: addition of polypropylene fibres and entrainment of air.
Highlights
In terms of fire resistance concrete outperforms by a wide margin the other most popular building materials i.e. wood and steel
Heating at 300 °C increased the compressive strength in relation to the initial value determined at 20 °C in the case of air-entrained and fibre-reinforced concretes
Heating at 300 °C increases the compressive strength of high-performance concrete in relation to the initial strength determined at 20 °C, which was observed on all tested types of high-performance concrete: air-entrained, fibre-reinforced and reference specimens
Summary
In terms of fire resistance concrete outperforms by a wide margin the other most popular building materials i.e. wood and steel. With generally accepted 28day curing time (Husem 2006; Biolzi et al 2008; Saad et al 1996) such tests were carried out on very young concrete even one day after moulding (Chen et al 2009) Another variable in the high temperature exposure tests is the moisture content of concrete at the time when it is subjected to the elevated temperature simulating fire conditions. According to Eurocode 2 (EN 1992-1-2:2008/NA:2010P) and Kowalski (2008) the compressive strength of concrete decreases with the increase of the exposure temperature This tendency has been confirmed by the result of various research projects (Neville 2012; Drzymała, Bednarek 2011b; Xiao, König 2004). Note that the decrease of elasticity is much greater in the case of high-performance concrete as compared to regular concrete (Xiao, König 2004)
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