Experimental analysis of the thermal behavior of concrete Текст научной статьи по специальности «Строительство и архитектура»

» Experimental analysis of the thermal

behavior of concrete

Sara Zatir0, Nacer Rahalb, Houda Beghdadc, £ Abdelaziz Souicid, Halima Aouade, Khaled Benmahdif

a University Tahri Mohamed of Bechar, Architecture and Urban Department, Bechar, People's Democratic Republic of Algeria, e-mail: zatir.sara@univ-bechar.dz, w ORCIDiD: https://orcid.org/0000-0002-6187-3441

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3 b Mustapha Stambouli University, Department of Civil Engineering,

O Mascara, People's Democratic Republic of Algeria;

_j University of Sciences and Technology, Laboratory of Mechanical

< Structure and Construction Stability, Oran,

People's Democratic Republic of Algeria,

x e-mail: n.rahal@univ-mascara.dz, corresponding author,

uj ORCID iD: https://orcid.org/0009-0002-0400-8360

>_ c Mustapha Stambouli University, Department of Civil Engineering,

Mascara, People's Democratic Republic of Algeria, e-mail: houda.beghdad@univ-mascara.dz, ORCID iD: https://orcid.org/0009-0001-3548-5138

d Mustapha Stambouli University, Department of Civil Engineering, Mascaral, People's Democratic Republic of Algeria; ot University of Sciences and Technology, Laboratory of Mechanical

fi Structure and Construction Stability, Oran,

^ People's Democratic Republic of Algeria,

^ e-mail: a.souici@univ-mascara.dz,

ORCIDiD: https://orcid.org/0009-0004-3845-7409 J e Mustapha Stambouli University, Department of Civil Engineering,

Mascara, People's Democratic Republic of Algeria, e-mail: rahnac2002@yahoo.fr

O f Mustapha Stambouli University, Department of Civil Engineering,

Mascara, People's Democratic Republic of Algeria, e-mail: k.benmahdi@univ-mascara.dz, ORCID iD: https://orcid.org/0000-0002-8244-5817

DOI: 10.5937/vojtehg71 -46462; https://doi.org/10.5937/vojtehg71-46462

FIELD: materials, civil engineering ARTICLE TYPE: original scientific paper

Abstract:

Introduction/purpose: When concrete structural members are subjected to fire and then exposed to slow or rapid cooling, there are various changes affecting density, porosity, thermal damage, speed of sound propagation, modulus of elasticity, compressive strength, absorptivity, etc. The heavy use of concrete to build structures on the one hand and the problem of fires on the other require a deep understanding of the effect of fire on the

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structural behavior of concrete, especially after cooling. So far, the two °°

cooling methods used to put out a possible fire have been water and free °

air. Our objective is to experimentally analyze the use of the extinguisher as ®

the third method of cooling concrete exposed to high temperatures. 0

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Methods: To achieve our objective, a series of mechanical and physical tests waw carried out on specimens 40 mm in diameter and 40 mm in height, exposed to high temperatures of 200, 400, and 600 °C. These test g samples were then subjected to three different cooling regimes, namely: free air, water immersion, and extinguisher use. Results: The results clearly show that the use of the extinguisher is more appropriate than the other two cooling methods, namely, natural cooling and immersion in water. heb

Conclusion: The results from this experimental study could be of practical la use when trying to extinguish a possible fire in a concrete structure. m

Key words: concrete, fire, experimental analysis, extinguish, water, free air.

Introduction

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Because of its many advantages over other construction materials, such as simple workmanship, durability, strength, and ease of implementation, concrete has become the primary structural material in the construction of nearly all buildings (Kodur, 2014).

Fire is one of dangerous threats that attack structures. Compared to steel, which has a low thermal conductivity, and to wood, which is rapidly ]o" combustible, concrete construction material is characterized by its good fire resistance; however, it can lose part of its resistance (Annerel & Taerwe, 2009; Ingham, 2009). The type of cement, the nature of the io aggregate, the dimensions of structural elements, the porosity and the moisture content of concrete as well as its thermal properties are all factors which determine the degree of fire resistance (Ak?aozoglu, 2013). The fire resistance is increased with the increase in the dimensions of a concrete element (Tana?an et al, 2009).

During their lifetime, concrete structures can be subjected to high temperatures during fire or near furnaces and reactors. It will then lead to the deterioration of the structural quality of concrete.

In China, recent statistics show that in 2018 alone, there were 237,000 fires, including almost 107,000 in residential buildings (Bi et al, 2020). Fires can start in tunnels and buildings alike (Annerel & Taerwe, 2009; Khoury, 2000; Du et al, 2018; Tomar & Khurana, 2019; Zhao et al, 2019). This indicates that the occurrence of fire misfortunes is becoming

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more and more common, which affects the safety of structures and leads to significant economic deficits (Hertz, 2005; Aïtcin, 2003; Liu et al, 2019).

Under high temperatures, physical properties change and chemical transformations occur in the cementitious matrix, leading to a deterioration of its mechanical characteristics (Hertz, 2005; Aïtcin, 2003; Liu et al, 2019; Hammoud et al, 2014; ACI, 1989; Khoury et al, 2007; European Commissions, 1992; CEN, 1994; CEN, 2002; CEN, 2004; Bazant & Kaplan, 1996; Phan & Carino, 2000). They also participate in the growth of shrinkage, transient creep, and changes in durability (Pihlajavaara & Kesler, 1972). Mechanical properties such as strength, modulus of elasticity, and volume stability of concrete are significantly reduced during these exposures (Li et al, 2012). Free water in pores and part of chemically bound water in hydrated cement paste are released and a large amount of energy is consumed due to exposure to high temperatures (Su et al, 2014).

This special situation implies the need to assess the safety of concrete structures with regard to possible fires. This analysis is therefore an essential task to ensure the structural safety of concrete structures (Hammoud et al, 2014). In practice, concrete structural elements must fulfill the fire safety requirements defined in the design codes for building structures (ACI, 2007; ACI, 2008; CEB, 2002).

According to the literature, the analysis of the behavior of concrete under high temperatures has been the subject of numerous works, leading to appreciable results (Zhai et al, 2019). We quote:

Wang et al (Wang, 2014) conducted static compression tests and a Split Hopkinson Pressure Bar Impact (SHPB) test on concrete specimens 75 mm in diameter and 55 mm in height. These specimens are heated to high temperatures of 100 to 900 °C and then cooled naturally.

Tao et al (Tao et al, 2011) conducted a compression test on concrete cylinders 50 mm in diameter and 35 mm in height under rapid heating from 200 to 600 °C using microwaves.

Shi et al (Shi et al, 2014) performed SHPB compression-shock tests on cylindrical specimens 98 mm in diameter and 50 mm in height. These concrete blocks are subjected to high temperatures of 200 to 800 °C and are cooled by natural cooling or cold water.

Under different applied loading levels, Jia et al (Jia et al, 2011ab) carried out compression-impact tests on concrete specimens 50 mm in diameter and 35 mm in height. Using microwaves, these concrete specimens were quickly heated to 200-650 °C.

Under various projectile velocities, Li et al (Li et al, 2012) performed an impact compression experiment on a SHPB device and concrete specimens 98 mm in diameter and 48 mm in height heated to 200-800 °C.

Similarly, Su et al (Su et al, 2014) carried out the same tests but on specimens 49 cm high.

SHPB impact compression tests and numerical simulations on concrete blocks 70 mm in diameter and 35 mm in height heated to 200800 °C were developed by Huo et al (Huo et al, 2013).

Previous experimental and numerical research revolves around micromechanics and constitutive models of concrete at high temperature (Huo et al, 2013; Gawin et al, 2011; Ezekiel et al, 2013; Jia et al, 2011 ab; Bangi & Horiguchi, 2012; Noumowe, 2005; Tenchev & Purnell, 2005; Van der Heijden et al, 2007; Wang & Shang, 2014; Lu, 2011; Zhai et al, 2014; Zhang et al, 2013, Carstensen et al, 2013). They analyze the mechanical properties of concrete at high temperature or after high temperature (Ma et al, 2015). However, the analysis of the behavior of concrete cooled after high temperatures has yet to be fully investigated (Zhai et al, 2019).

In turn, Zhai et al (Zhai et al, 2014) conducted impact compression tests on concrete specimens. These test specimens of 35 MPa compressive strength are heated to high temperatures of 200 to 800 °C and are then cooled naturally or in water.

This article is an experimental contribution analyzing the effect of the cooling mode on the thermal behavior of concrete. Until now, the cooling methods used were natural cooling or immersion in water. Through this work, we used natural cooling, water, and a new mode of cooling, powder extinguishers.

To achieve our objective, we carried out mechanical tests on compressive strength, thermal damage, and dynamic modulus of elasticity, and tested physical properties: porosity, density, and speed of sound propagation. These tests were carried out while hot and after cooling. The samples tested were exposed to high temperatures: 200 °C, 400 °C, and 600 °C. After exposure to these temperatures, the samples were then cooled using air, water, and powder extinguishers.

Materials used and sample preparation Cement

The cement used is Portland cement composed of the CPJ CEM II/B-L 32.5 N type, with a minimal resistance of 32.5 MPa at 28 days. Tables 1, 2 and 3 respectively give the chemical, mineralogical, and physical composition of the cement used in this study.

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Table 1 - Chemical composition of cement Таблица 1 - Химический состав цемента Табела 1 - Хемц'ски састав цемента

CaO SiO2 AI2O3 Fe2O3 SO3 K2O Na2O MgO

60.10 18.13 3.25 2.56 2.71 0.26 0.22 1.75

Table 2 - Mineralogical composition of cement according to Bogue Таблица 2 - Минералогический состав цемента (Bogue) Табела 2 - Минералошки састав цемента (Bogue)

Element C3S C2S C3A C4AF

Content (%) 71.976 50.488 4.280 7.790

Table 3 - Physical characteristics of cement Таблица 3 - Физические свойства цемента Табела 3 - Физичка свойства цемента

Characteristics Values

Apparent density (g/cm3) 4000

Absolute density (g/cm3) 1065

Start of setting (minute) 2990

End of setting (minute) 150 ± 30

Normal consistency (%) 230 ± 50

Water composition

For the manufacture of test specimens, we used drinking water distributed by the public service network. The results of the chemical analysis of this water are summarized in Table 4.

Table 4 - Chemical analysis of water composition Таблица 4 - Химический анализ состава воды Табела 4 -Хеми^ска анализа састава воде

Ca Mg Na K Cl SO4 CO3 NO3 Fe pH Organic material

32.86 51.36 38.00 0.00 113.60 65.46 368.44 12.22 0.03 7.88 0.18

Cement Sand 0/4 Gravel 3/8 Water Super-plasticizer E/C

350 616 1143 202 17.5 0.57

Aggregates CO

In this analysis, we used continuous crushed gravel of 3/8 mm in size 5 and quarry sand of 0/4 mm in size.

Preparation of the samples

The dimensions of the specimens used in this study are: the diameter ^ = the height h = 40 mm. For the preparation of the samples, we adopted § the quantities given in Table 5:

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Table 5 - Formulation of micro-concrete Kg/m3 ф

Таблица 5 - Состав микробетона, кг/м3 Табела 5 - Формулацща микробетона kg/m3 Ё

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The specimen heating and cooling

The samples were covered with plastic film to avoid any water exchange with the external environment and were stored in the laboratory at a controlled room temperature of 20 ± 2°C.

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The specimens were classified into four groups (Gi, G2, G3 and G4). m We measured the mass and speed of propagation of sonic waves before ^ exposing the samples to temperatures of 200, 400, and 600 °C.

The three groups of specimens (Gi, G2 and G3) were subjected to maximum temperatures of 200°C, 400°C and 600°C, respectively. «j

The specimens were heated with a constant temperature rise rate equal to 5 °C/min up to the test temperature. Then, to stabilize the thermal field, these specimens were kept at the target temperature for one hour.

The last step was the temperature drop ramp of 1°C/min down to an ambient temperature. On the other hand, the fourth group (G4) was maintained at an ambient laboratory temperature equal to 20°C. For each group, we used a cooling mode for one minute. For 24 hours after the cooling stage, for each specimen, we calculated the mass and the speed of propagation of sonic waves.

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Results and discussion Density

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200 400 600 Temperature (°C)

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Figure 1 - Effect of temperature and the cooling mode on density Рис. 1 - Влияние температуры и режима охлаждения на плотность Слика 1 - Утиu,аj температуре и начина хла^еъа на густину

Table 6 - Effect of temperature and the cooling mode on density (Kg/m3) Таблица 6 -Влияние температуры и режима охлаждения на плотность (кг/м3) Табела 6 -Уmиuаj температуре и начина хла^еъа на густину (kg/m3)

20 °C 600 °C Kg/m3 %

C. Nat 2225 1998 227 10.2

C. Wat 2225 2027 198 8.9

C. Ext 2225 1998 227 10.2

C. Nat: natural cooling C. Wat: water cooling C.Ext : extinguisher cooling

Figure 1 shows the effect of temperature and the cooling mode (air, water, and extinguisher) on density. When the temperature increases, the density of the samples decreases for the three cooling modes. Table 6 shows that the density drop between 20 and 600 ° C is the same, 10.2%,

in both natural and extinguisher cooling. On the other hand, it is a little lower for rapid cooling by immersion in water, at 8.89%.

Porosity

Figure 2 - Effect of temperature and the cooling mode on porosity Рис. 2 - Влияние температуры и режима охлаждения на пористость

Слика 2 -Утицаj температуре и начина хла^еъа на порозност

Table 7 - Effect of temperature and the cooling mode on porosity (%) Таблица 7 - Влияние температуры и режима охлаждения на пористость (%) Табела 7 - Утица] температуре и начина хла^еъа на порозност (%)

20 °C 600 °C %

C. Nat 23.45 27.38 14.3

C. Wat 23.45 25.24 7.1

C. Ext 23.45 25.21 7.0

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Figure 2 shows the effect of temperature and the cooling mode (air, water, and extinguisher) on porosity. It was discovered that the porosity value increases in lockstep with increasing temperature from 20 °C to 600 °C.

Table 7 shows that with natural cooling, porosity increases twice as compared to the other two cooling modes.

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Figure 3 - Effect of temperature and the mode of cooling on the speed of sound

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Рис. 3 - Влияние температуры и режима охлаждения на скорость распространения звука Слика 3-Утицаj температуре и начина хла^еъа на брзину ширена звука

Table 8 - Effect of temperature and the mode of cooling on the speed of sound

propagation (m/s)

Таблица 8 - Влияние температуры и режима охлаждения на скорость распространения звука (м/с) Табела 8 - Утица] температуре и начина хла1]еъа на брзину ширена звука (m/s)

20 °C 600 °C m/s %

C. Nat 3769 2206 1563 41.47

C. Wat 3769 2068 1701 45.13

C. Ext 3769 2666 1103 29.27

Figure 3 shows the effect of temperature and the mode of cooling (air, water, and extinguisher) on the speed of sound propagation. It clearly shows that the speed of propagation decreases with increasing temperature. Table 8 shows that with sprinkler cooling, the speed of sound propagation is significantly lower than with the other two cooling methods.

Elasticity dynamic modulus

Figure 4 - Effect of temperature and the mode of cooling on the dynamic modulus of

elasticity

Рис. 4 - Влияние температуры и режима охлаждения на динамический модуль

упругости

Слика 4 -Уmиuаj температуре и начина хла^еъа на динамички модулус

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Table 9 - Effect of temperature and the mode of cooling on the dynamic modulus of

elasticity (GPa)

Таблица 9 - Влияние температуры и режима охлаждения на динамический модуль

упругости (гПа)

Табела 9 - Уmиuаj температуре и начина хла^еъа на динамички модулус

еластичности (GPa)

20 °C 600 °C Gpa %

C. Nat 28.99 8.78 20.21 69.7

C. Wat 28.99 7.82 21.17 73.03

C. Ext 28.99 12.77 16.22 55.95

In Figure 4 we have shown the effect of temperature and the mode of cooling (air, water, and extinguisher) on the dynamic modulus of elasticity. When temperature increases, the dynamic modulus of elasticity of the samples decreases. Table 9 clearly shows that with quench cooling, the

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Compressive strength

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Figure 5 - Effect of temperature and the mode of cooling on compressive strength Рис. 5 - Влияние температуры и режима охлаждения на прочность при сжатии Слика 5 - Утицаj температуре и начина хла^еъа на компресивну снагу

Table 10 - Effect of temperature and the mode of cooling on compressive strength (MPa) Таблица 10 - Влияние температуры и режима охлаждения на прочность при

сжатии (мПа)

Табела 10 - Уmицаj температуре и начина хла^еъа на компресивну снагу (МРа)

20 °C 600 °C Mpa %

C. Nat 23.53 16.12 7.41 31.5

C. Wat 23.53 17.02 6.51 27.7

C. Ext 23.53 16.93 6.6 28.0

Figure 5 shows the effect of temperature and the cooling mode (air, water, and extinguisher) on compressive strength. We notice that resistance decreases with increasing temperature. This loss of resistance can reach 40%.

Table 10 clearly shows that compressive strength is practically the same for all three cooling modes.

Thermal damage

Figure 6 - Variation in thermal damage as a function of temperature and the cooling

mode

Рис. 6 - Изменение термического повреждения в зависимости от температуры

и режима охлаждения Слика 6 - Варц'ацц'а термалног оштеПеъа у зависности од температуре и

начина хла^еъа

Table 11 - Variation in thermal damage as a function of temperature and the cooling

mode (%)

Таблица 11 - Изменение термического повреждения в зависимости от температуры и режима охлаждения (%) Табела 11 - Варц'ацц'а термалног оштеПеъа у зависности од температуре и

начина хла^еъа (%)

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20 °C 600 °C %

C. Nat 12.301 66.42 81.5

C. Wat 12.301 69.15 82.2

C. Ext 12.301 53.42 77.0

In Figure 6, we show the effect of temperature and the mode of cooling (air, water, and extinguisher) on the variation of thermal damage. We note, for the three cooling modes, that damage increases with the increase in temperature. It is clear the thermal damage is a little lower with the use of the extinguisher as a means of cooling.

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Figure 7 - Effect of temperature and the mode of cooling on initial water absorption Рис. 7 - Влияние температуры и режима охлаждения на начальное

водопоглощение

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Table 12 - Effect of temperature and the mode of cooling on initial water absorption

(g/cm2)

Таблица 12 - Влияние температуры и режима охлаждения на начальное водопоглощение (г/см2) Табела 12 - Утица] температуре и начина хла^еъа на иницц'алну апсорпциу

воде (g/cm2)

20 °C 600 °C g/cm2 %

C. Nat 0.23854 0.6773 0.43876 64.8

C. Wat 0.23854 0.5933 0.35476 59.8

C. Ext 0.23854 0.4633 0.22476 48.5

Figure 7 shows the effect of temperature and the cooling mode (air, water, and extinguisher) on initial water absorption. It is observed that water absorption increases with increasing temperature, particularly at 600 °C. In addition, it is found that water absorption under cooling with the extinguisher is always lower compared to the other two cooling modes. We notice in Table 12 that the use of the extinguisher to put out fire has less absorptivity compared to the two other cooling methods.

Conclusion

The primary goal of this paper is to provide an experimental contribution to the study of the effect of a mode on the behavior of micro-concretes exposed to high temperatures. In this study, the temperatures used are those tested in the majority of previous studies; they are 200, 400, and 600 °C.

Until now, two cooling modes have been used to extinguish fire: one slow, which is natural cooling; and the second fast, which is water cooling. Through this research attempt, we have examined a third mode of cooling; it is the extinguisher. This cooling process practically constitutes an intermediate mode between a slow one and a fast one. For better compression, we carried out mechanical tests concerning compressive strength, thermal damage, modulus of elasticity, and other physical properties: porosity, density, and speed of sound propagation. These tests were carried out hot and after cooling on specimens previously exposed to temperatures of 20°C, 200°C, 400°C, and 600°C.

According to the results obtained (Figures 1 to 7 and Tables 6 to 12), it can be concluded that cooling by the extinguisher presents the most suitable mode for extinguishing a fire of up to 600 °C.

Overall, the analysis of the parameters analyzed (Figures 1 to 7 and Tables 6 to 12) leads us to suggest using the powder extinguisher in the process of extinguishing fire in concrete structures exposed to temperatures up to 600 °C.

In a future study, we will try to analyze the effect of cooling time on the thermal behavior of ordinary concrete as well as to extend this study to other existing concrete types.

References

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https://www.concrete.org/portals/0/files/pdf/previews/216107_bkstore_view.pdf [Accessed: 05 September 2023].

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Экспериментальное исследование тепловых свойств бетона

Сара Затара, Наср Рахал6, корреспондент, Худа Багденв, Абдулайзиз Суайсии6, Халима Туауадв, Халид Ебммахдив

а Университет Тахри Мохаммед Бешар, департамент архитектуры и ° урбанизма, г. Бешар, Алжирская Народная Демократическая Республика

б Университет Туши Мустафы Стамбули, строительный факультет, г. Маскара, Алжирская Народная Демократическая Республика; Университет естественных наук и технологий, лаборатория

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° Маскара, Алжирская Народная Демократическая Республика <

° РУБРИКА ГРНТИ: 67.09.33 Бетоны. Железобетон. Строительные

1 растворы, смеси, составы ^ ВИД СТАТЬИ: оригинальная научная статья

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^ Введение/цель: При воздействии огня, а также при быстром или

медленном охлаждении частей бетонного сооружения происходят различные изменения плотности, пористости, скорости распространения звука, модуля упругости, прочности и на сжатие, водопоглощения и пр. Эти процессы также могут

^ вызвать термическое повреждение. Широкое использование

бетона в строительстве, с одной стороны, и проблемы, и вызванные воздействием огня, с другой, требуют углубленного

понимания влияния огня на поведение бетонной конструкции, ш особенно после охлаждения. До сих пор для тушения пожара

о использовались два метода охлаждения: водой и свободным

потоком воздуха. Цель данной статьи — экспериментально ^ исследовать использование огнетушителя как третьего

0 способа охлаждения бетона, подвергающегося воздействию

высоких температур.

Методы: Для достижения цели исследования была проведена серия механических и физических испытаний образцов диаметром 40 мм и высотой 40 мм, подвергнутых воздействию высоких температур 200, 400 и 600 °С. Затем испытуемые образцы были подвергнуты трем различным режимам охлаждения, а именно: свободным потоком воздуха, водой и огнетушителем.

Результаты: Результаты однозначно показывают, что использование огнетушителя целесообразнее, чем два других метода охлаждения, а именно: воздухом и водой.

Выводы: Результаты этого экспериментального исследования °° могут быть полезны на практике при тушении пожара в ° бетонном сооружении.

Ключевые слова: бетон, пожар, экспериментальное исследование, тушение, вода, воздух.

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Абдула]зиз Суа]сииб, Халима Туауадв, Халид Ебммахдив

а Универзитет Тахри Мохамед у Бешару, Оде^е^е за архитектуру и

урбанизам, Бешар, Народна Демократска Република Алжир Е

б Универзитет Мустафа Стамболи, Одсек за гра^евинарство, Маскара, Народна Демократска Република Алжир;

Универзитет природних наука и технологи]е, Лаборатори]а за машинске структуре и стабилност конструкц^е, Оран, Народна Демократска Република Алжир Универзитет Мустафа Стамбоули, Одсек за гра^евинарство, Маскара, Народна Демократска Република Алжир ^

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ВРСТА ЧЛАНкА: оригинални научни рад е

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Увод/цил: Када су делови бетонске структуре изложени де}ству и" ватре, а затим брзом или спором хла^еъу, долази до различитих ф промена у густини, порозности, термичком оштеЯеъу, брзини м ширена звука, модулусу еластичности, компресивно] снази, апсорпци]и, итд. Раширена употреба бетона у гра^евинарству, с N }едне стране, и проблеми настали услед изложености пожару, с друге стране, захтева}у детално разумеваъе утица]а ватре на понашак>е структуре бетона, нарочито после хпа^еъа. До сада су коришЯена два метода хла^еъа за гашеъе ватре - водом и слободним стру]ак>ем ваздуха. У раду }е експериментално анализирано коришЯеъе противпожарног апарата као треЯег начина за хла^еъе бетона изложеног високим температурама. Методе: Извршена }е сери]а механичких и физичких испитиваъа узорака, пречника 40 тт и висине 40 тт, изложених високим температурама од 200, 400 и 600 °С. Затим су тест-епрувете подвргнуте хла^еъу на три различита начина: слободним стру]ак>ем ваздуха, потапаъем у воду и коришЯеъем противпожарног апарата.

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Резултати: Резултати }асно показу]у да ]е коришПеъе противпожарног апарата погодни]е од преостала два метода хла^еъа, т]. природног хпа^еъа на ваздуху и натапаъа водом. Закъучак: Резултати ове експерименталне студи}е могли би да има]у практичну примену при гашеъу евентуалног пожара у неко] бетонско] структури.

Къучне речи: бетон, ватра, експериментална анализа, гашеъе, вода, природно стру]ак>е ваздуха.

Paper received on / Дата получения работы / Датум приема чланка: 10.09.2023. Manuscript corrections submitted on / Дата получения исправленной версии работы / Датум достав^а^а исправки рукописа: 01.12.2023.

Paper accepted for publishing on / Дата окончательного согласования работы / Датум коначног прихвата^а чланка за об]ав^ива^е: 02.12.2023.

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© 2023 Авторы. Опубликовано в «Военно-технический вестник / Vojnotehnicki glasnik / Military Technical Courier» (www.vtg.mod.gov.rs, втг.мо.упр.срб). Данная статья в открытом доступе и распространяется в соответствии с лицензией «Creative Commons» (http://creativecommons.org/licenses/by/3.0/rs/).

© 2023 Аутори. Об]авио Во^отехнички гласник / Vojnotehnicki glasnik / Military Technical Courier (www.vtg.mod.gov.rs, втг.мо.упр.срб). Ово jе чланак отвореног приступа и дистрибуира се у складу са Creative Commons лиценцом (http://creativecommons.org/licenses/by/3.0/rs/).