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The concrete material in structures is likely to be exposed to elevated temperatures during fires. In this paper, an experimental investigation is carried out to study the effect of different exposure temperatures and times on the mechanical properties of ordinary concrete. Cylinders with a diameter of 100 mm and a height of 200 mm were used as concrete specimens, which were tested at the three elevated temperatures of 200, 400 and 600°C for various times from 1 to 6 h. It was found from the experimental results that the temperature of exposure is the main contributor to the decrease in the weight and compressive strength of concrete and the exposure time has little effect. Although the effect of exposure time on weight loss is greater at lower temperatures than that at higher temperatures, after 3 h of exposure time, the difference becomes negligible. In addition, it was found that the relative compressive strength of concrete remains unchanged for exposure times exceeding 3 h. The numerical simulations were conducted using Abaqus. The predicted temperature distributions agree well with the experimental results.
Zhu J and Wu Y (2016) Effect of exposure time and elevated temperature on ordinary concrete Emerging Materials Research, http://dx.doi.org/10.1680/jemmr.16.00091 ice | science Emerging Materials Research Research Article Received 20/04/2016 Accepted 12/12/2016 Keywords: material characterisation/mechanical properties/simulation ICE Publishing: All rights reserved Effect of exposure time and elevated temperature on ordinary concrete Jianing Zhu PhD Yaopeng Wu PhD* School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an, People’s Republic of China School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an, People’s Republic of China The concrete material in structures is likely to be exposed to elevated temperatures during fires In this paper, an experimental investigation is carried out to study the effect of different exposure temperatures and times on the mechanical properties of ordinary concrete Cylinders with a diameter of 100 mm and a height of 200 mm were used as concrete specimens, which were tested at the three elevated temperatures of 200, 400 and 600°C for various times from to h It was found from the experimental results that the temperature of exposure is the main contributor to the decrease in the weight and compressive strength of concrete and the exposure time has little effect Although the effect of exposure time on weight loss is greater at lower temperatures than that at higher temperatures, after h of exposure time, the difference becomes negligible In addition, it was found that the relative compressive strength of concrete remains unchanged for exposure times exceeding h The numerical simulations were conducted using Abaqus The predicted temperature distributions agree well with the experimental results Notation c E fc fT M0 MT T T0 t l r heat capacity exposure time initial compressive strength of the material at room temperature residual compressive strength of the material at elevated temperature weight of the specimen at room temperature weight of the specimen at elevated temperature exposure temperature initial temperature heating-up time thermal conductivity density when it is exposed to different heating treatments with target temperatures of 250, 500 and 750°C and a holding time of 2·5 h Demirel and Keleştemur,5 Akca and Zihnioğlu,6 Tanyildizi7 and Bastami et al.8 investigated the properties of concrete subjected to high temperatures with exposure time of h Moreover, Kizilkanat et al.,9 Lo Monte and Gambarova10 and Rashad11 investigated the performance of concrete by using a heating method with an exposure time of h A standard exposure time of h has been used by many researchers.12–19 In addition, both heating parameters of the peak temperature and the exposure time were simultaneously considered For example, peak temperatures of 400, 500, 550 and 600°C and exposure times of 0, and h were used in the experiment by Yang et al.,20 and specimens were exposed to temperatures of 100 and 200°C for a period of 1, or h by Al-Salloum et al.21 Introduction Fire is one of the biggest threats to buildings Since concrete has become a primary construction material, studies on the material properties of concrete after exposure to elevated temperatures have gained great attention Many studies were carried out on the influence on the properties of concrete on heating rate, exposure temperature, exposure time and so on.1,2 Ergün et al assessed the effects of elevated temperatures and cement dosages on the mechanical properties of concrete In their tests, six-test series were conducted with each series consisting of six different temperatures of 20, 100, 200, 400, 600 and 800°C The samples tested at 20°C were considered the baseline specimens Once the targeted temperature was reached, this temperature was maintained for 45 to achieve a thermal steady state Biolzi et al.4 described the consequences of progressive damage in architectural high-performance concrete In this 102 +5·986 × 102 +5·984 × 102 +5·982 × 102 +5·981 × 102 +5·979 × 102 +5·977 × 102 (b) (a) NT11 NT11 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +5·999 × 102 +5·999 × 102 +5·999 × 102 +5·999 × 102 +5·999 × 102 +5·998 × 102 +5·998 × 102 +5·998 × 102 +5·998 × 102 +5·998 × 102 (c) NT11 (d) NT11 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 +6·000 × 102 (f) (e) Figure Temperature distributions after exposure at 600°C for (a) 1, (b) 2, (c) 3, (d) 4, (e) and (f) h 600°C As the exposure time is increased from to h, the weight ratio decreases at each exposure temperature After over h of exposure time, however, the weight ratio is kept at a relatively constant value, indicating no further weight loss Furthermore, the effect of exposure time on weight loss is greater at lower heating temperatures (such as 200°C) than that at higher heating temperatures (such as 600°C) The results in Figure demonstrate that the weight loss of the concrete specimen occurs mainly at the early stage of hightemperature exposure and almost no further weight loss occurs after h of exposure Therefore, h of exposure time at an elevated temperature is sufficient in the study of the effect of the temperature effect on the behaviour of the ordinary concrete 4.2 Compressive strength Shown in Figure are the relative compressive strengths of concrete after the specimen was subjected to different exposure temperatures with different exposure times, in which the data are the average data from three replicate tests The relative strength is defined as the ratio of the residual compressive strength at the elevated temperature to the initial compressive strength at room temperature It can be concluded from Figure that the decrease in the compressive strength of the specimen results mainly from the exposure temperature and the exposure time has no significant effect on the residual strength in the specimen It is also seen from Figure that at an exposure temperature of 200°C, the relative compressive strength of concrete decreases only slightly when compared to the original strength and is almost independent of the exposure time Downloaded by [ Swinburne University] on [11/01/17] Copyright © ICE Publishing, all rights reserved Emerging Materials Research Effect of exposure time and elevated temperature on ordinary concrete Zhu and Wu 1·00 1·10 0·99 200ºC 0·98 400ºC 1·00 600ºC 0·90 0·80 0·96 0·95 fT/fc MT/M0 0·97 0·94 0·60 0·93 0·92 0·50 0·91 0·40 0·90 Exposure time: h 0·30 Figure Relation of the weight ratio of the specimen with the exposure time at different exposure temperatures When the exposure temperature rises to 400 and 600°C, the relative compressive strength of concrete decreases significantly as the exposure temperature increases, and at 600°C less than 60% of the original compressive strength is maintained At high exposure temperatures of 400 and 600°C, the relative compressive strength of concrete slightly decreases as the exposure time is increased from to h and then is almost independent of exposure time after h This implies that exposure time exceeding h cannot further change the relative compressive strength of concrete 0·70 Conclusions The influence of the exposure temperature (200, 400, 600°C) and the exposure time (1–6 h) on the weight loss and the relative compressive strength of concrete was investigated in this study Based on this experimental study and the numerical simulation using Abaqus, the following conclusions can be made ■ The decrease in the weight and compressive strength of concrete results mainly from the exposure temperature, and effect of the exposure time is insignificant ■ The effect of the exposure time on weight loss is greater at a lower exposure temperature (200°C) than that at a higher temperature (600°C) ■ No further weight loss and decrease in the relative compressive strength of concrete occur after h of exposure time ■ Three hours of exposure time is sufficient to reach a stable state for ordinary concrete at elevated temperatures, which is further confirmed by numerical simulation results using Abaqus 400ºC Exposure time: h 600ºC Figure Relation of the compressive strength of the specimen with the exposure time at different exposure temperatures Government of China (CXY1432(4)), Opening Funds of State Key Laboratory of Building Safety and Built Environment (BSBE2016-2) and Innovation Team of Xi’an University of Architecture and Technology The authors are grateful to the financial support provided by all sponsors REFERENCES Ma Q, Guo R, Zhao Z, Lin Z and He 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To discuss this paper, please submit up to 500 words to the journal office at journal@ice.org.uk Your contribution will be forwarded to the author(s) for a reply and, if considered appropriate by the editor-in-chief, it will be published as a discussion in a future issue of the journal ICE Science journals rely entirely on contributions from the field of materials science and engineering Information about how to submit your paper online is available at www.icevirtuallibrary.com/page/authors, where you will also find detailed author guidelines Downloaded by [ Swinburne University] on [11/01/17] Copyright © ICE Publishing, all rights reserved ... Materials Research Effect of exposure time and elevated temperature on ordinary concrete Zhu and Wu 13 Behnood A and Ghandehari M (2009) Comparison of compressive 18 Uysal M, Yilmaz K and Ipek M (2012)... strength of concrete 0·70 Conclusions The influence of the exposure temperature (200, 400, 600°C) and the exposure time (1–6 h) on the weight loss and the relative compressive strength of concrete. .. white concrete subjected to high temperatures Cement and Concrete Composites 39: 73–81 Demirel B and Keleştemur O (2010) Effect of elevated temperature on the mechanical properties of concrete