IMPACT OF THE FIRE ON THE BEARING CAPACITY OF THE ORDINARY CONCRETE USED IN REINFORCED CONCRETE STRUCTURES IN BURUNDI. HISTORY AND ARCHITECTURE Текст научной статьи по специальности «Строительство и архитектура»

СТРОИТЕЛЬНОЕ МАТЕРИАЛОВЕДЕНИЕ

НАУЧНАЯ СТАТЬЯ / RESEARCH PAPER УДК 614.841:691.32

DOI: 10.22227/1997-0935.2021.12.1567-1572

Impact of the fire on the bearing capacity of the ordinary concrete used

in reinforced concrete structures in Burundi. History and architecture

Emmanuel Mikerego, Donatien Nduwimana

University of Burundi; Bujumbura, Burundi

ABSTRACT

Introduction. This paper presents the results of an assessment of the impact of fire on the bearing capacity of the ordinary concrete, to be taken into account in the rehabilitation of fire-damaged reinforced concrete structures in Burundi. Materials and methods. Experimental samples of the ordinary concrete made respectively of coarse river aggregates and crushed coarse quarry aggregates were prepared and subjected to different heating temperatures (250, 350, 450, 600 and 900 °C) simulating the fire. After natural cooling, experimental samples were subjected to compression test; and diagrams showing the loss of the load-bearing capacity of the ordinary concrete used in reinforced concrete structures in Burundi were drawn.

Results. Negative impact of the fire on the load-bearing capacity of the ordinary concrete occurs above of 350 °C of heating temperature. Concrete made of crushed coarse quarry aggregates loses 50 and 78 % of its bearing capacity at around 525 and 900 °C of heating temperature, respectively. Similarly, concrete made of coarse river aggregates loses 50 and 70 % of its load-bearing capacity respectively at 600 and 900 °C of heating temperature. An evaluation curve of the after-fire bearing capacity of the concrete used in reinforced concrete structures in Burundi is established.

Conclusions. The negative impact of the fire on the load-bearing capacity of the ordinary concrete occurs above of 350 °C of heating temperature. Concretes made of crushed coarse quarry aggregates and concrete made of coarse river aggregates lose 50 % of its bearing capacity at around 525 and 600 °C of heating temperature respectively. Knowing the heating ^ ® temperature that the fire-damaged reinforced concrete structure has undergone is indispensable in deciding on its demoli- (fl T tion or rehabilitation. 3 j

KEYWORDS: concrete, fire-damaged structures, rehabilitation of structures in Burundi

O

FOR CITATION: Mikerego E., Nduwimana D. Impact of the fire on the bearing capacity of the ordinary concrete used in reinforced concrete structures in Burundi. History and architecture. Vestnik MGSU [Monthly Journal on Construction and • Architecture]. 2021; 16(12):1567-1572. DOI: 10.22227/1997-0935.2021.12.1567-1572

к

о S

Corresponding author: Emmanuel Mikerego, mikeregoemmanuel@hotmail.com. h z

< 1

o 9

Влияние пожара на несущую способность обычного бетона о ¡9 железобетонных конструкций в Бурунди. | (

История и архитектура 11

s <

- US

c M

Эммануэль Микерего, Донатьен Ндувимана

Университет Бурунди; г. Бужумбура, Бурунди ф 3

__0) о

^ —

АННОТАЦИЯ > 6

С о

Введение. Представлены результаты оценки влияния пожара на несущую способность обычного бетона, которая ^ °

будет учитываться при восстановлении поврежденных пожаром железобетонных конструкций в Бурунди. С о

Материалы и методы. Экспериментальные образцы обычного бетона из крупного речного заполнителя и дробле- и =

ного крупного карьерного заполнителя были подготовлены и подвергнуты различным температурам нагрева (250, ф )

350, 450, 600 и 900 °С), имитирующим пожар. После естественного охлаждения экспериментальные образцы испы- ^ .

таны на сжатие. Построены диаграммы, показывающие потерю несущей способности обычного бетона, используе- 1 О

мого в железобетонных конструкциях в Бурунди. с ^

Результаты. Негативное воздействие огня на несущую способность обычного бетона происходит при температуре 3 1

нагрева выше 350 °С. Бетон из крупного дробленого карьерного заполнителя теряет 50 и 78 % своей несущей способ- 1 ®

ности при температуре нагрева около 525 и 900 °С соответственно. Аналогично, бетон из крупного речного заполни- . и теля теряет 50 и 70 % несущей способности соответственно при температуре нагрева 600 и 900 °С. Установлена

г

кривая оценки несущей способности после пожара бетона, используемого в железобетонных конструкциях в Бурунди. д у

Выводы. Установлено, что негативное воздействие огня на несущую способность обычного бетона происходит при е О

температуре нагрева выше 350 °С. Бетон из крупного дробленого карьерного заполнителя и бетон из крупного реч- 1 1

ного заполнителя теряют 50 % их несущей способности при температурах нагрева около 525 и 600 °С соответствен- , ,

но. Знание температуры нагрева, которой подверглась поврежденная огнем железобетонная конструкция, необходи- 2 2 мо для принятия решения о ее сносе или восстановлении.

о о to 10

КЛЮЧЕВЫЕ СЛОВА: бетон, поврежденные огнем конструкции, восстановление конструкций в Бурунди

© Emmanuel Mikerego, Donatien Nduwimana, 2021 1 567

Распространяется на основании Creative Commons Attribution Non-Commercial (CC BY-NC)

ДЛЯ ЦИТИРОВАНИЯ: Микерего Э., Ндувимана Д. Impact of the fire on the bearing capacity of the ordinary concrete used in reinforced concrete structures in Burundi. History and architecture // Вестник МГСУ. 2021. Т. 16. Вып. 12. С. 15671572. DOI: 10.22227/1997-0935.2021.12.1567-1572

Автор, ответственный за переписку: Эммануэль Микерего, mikeregoemmanuel@hotmail.com.

N N

О О

N N

СЧ СЧ

г г

К (V

U 3

> (Л

с и

to <о

<0 <U

и

Ф О)

о ё

<л

(Л

.Е о

dl"

^ с ю о

S !

о ЕЕ

СП ^ т- ^

£

22 J > А

Si

о И

INTRODUCTION

In recent years, repeated fires have partially or entirely damaged reinforced concrete structures in Burundi. For example, the Ngozi market was damaged by fire four times, in 2000, 2006, 2010, and 2011. The central market in the capital Bujumbura was partially damaged by fire in 2012. The Kayogoro market was entirely damaged by fire in 2011. In 2012, the Kirundo and Rushubi markets were also damaged by fire. Recently, in 2021, the Kamenge market was partially damaged by fire. All these cases of fire-damaged structures only reflect instances that have been brought to public attention. Most of these fire-damaged structures have been rehabilitated. Only the central market in the capital Bujumbura will be demolished, and a new structure will be erected instead of rehabilitation.

This rehabilitation of fire-damaged structures is carried out without evaluation studies of the bearing capacity of the concrete post-fire. Meanwhile, foreign literature shows that concrete subjected to high temperatures loses its bearing capacity. Above 350 °C, the compressive strength of the concrete decrease considerably [1-8]. Various studies show that concrete loses more than 80 % of its compressive strength at around 900 °C. It is known that concrete' components influence its behaviour when subjected to high temperatures [9-14]. Different approaches have been used to analyse the properties of concrete subjected to high temperatures [15, 16]. However, the compression test is the most common approach1 [17, 18]. Some assessments on the fire-damaged structures have also been conducted [19, 20].

However, few studies relate the bearing capacity of fire-damaged concrete to the rehabilitation problem of fire-damaged reinforced concrete structures. Thus, the availability of data on the bearing capacity of fire-damaged concrete constitutes an actual need for the problem of rehabilitation of fire-damaged structures in Burundi.

MATERIALS AND METHODS

The first step in this study was to select the materials for making the 10 cm cubic experimental samples. The sand used came from the Mugere River. The sand's bulk density and absolute density are (1550 kg/m3) and (2500 kg/m3), respectively. The fineness modulus is (2.52 %). The compactness, porosity, and sand equivalent are (62 %), (38 %), and (76 %), respectively. The coarse aggregates used to formulate one-half of the experimental samples were aggregates carried out of the Mugere River,

and the second half of the samples were prepared with coarse aggregates from the Gakungwe quarry site (Fig. 1).

Fig. 1. Coarse aggregates from the Mugere river (a) and coarse quarry aggregates from Gakungwe (b) site in Bujumbura province

For the Mugere river's coarse aggregates, the bulk density and absolute density were (2.12 g/cm3) and (1.50 g/m3), respectively. Furthermore, for the coarse quarry aggregates from the Gakungwe quarry site, the bulk density and absolute density were (2.61 g/cm3) and (1.70 g/m3), respectively. The Los Angeles coefficients were (60 %) and (52 %) respectively, for the coarse aggregate from the Mugere River and the Gakungwe quarry site. The formulated concrete was a standard class concrete [10]. The heating process was carried out in an electrical furnace (Fig. 2).

1 Eurocode 2. Calcul des structures en béton. Partie 1-2: Règles

générales - Calcul du comportement au feu. NF EN 1992; 1-2.

Eyrolles, 2005.

Fig. 2. Electrical furnace with experimental sample with the door open (a) and the electrical furnace with the closed-door (b)

The heating process took 25 minutes for samples to be heated to 250 °C. For samples to be heated to 350 °C, heating took 70 minutes. For samples to be heated to 450 °C, heating took 90 minutes. Finally, heating the samples to 600 and 900 °C took 120 minutes and 180 minutes, respectively. After each heating process, 90 minutes were spent stabilizing the heating furnace. A series of nine (9) experimental samples were prepared for each heating temperature. The mechanical loading of the samples was conducted on a hydraulic

1568

press at the laboratory of materials, university of Burundi (Fig. 3).

Fig. 3. Compression test on heated experimental samples

The collected data from the compression tests were compressive strength. The results were compared to the compressive strength of the unheated experimental samples. Obtained results were also compared to the curve of the bearing capacity of fire-damaged concrete, calcu-

lated by the approach described in the European standard "Eurocode 2"1.

RESULTS AND ANALYSIS OF RESULTS

Obtained results show the significant negative impact of high temperatures on the compressive strength and therefore on the modulus of elasticity also of an ordinary concrete (Fig. 4).

The occurring cracking process, while loading, experimental samples, led to the progressive decrease of the compressive strength of the concrete samples made of the coarse river aggregates under heat (Fig. 5).

The same trend of loss of the bearing capacity was observed for the experimental samples made of crushed coarse quarry aggregates (Fig. 6).

The results obtained show a correlation with the experimental results obtained according to the European standard "Eurocode 2" approach1 and various researches [21] on the estimation of the compressive strength of concrete subjected to high temperatures (Fig. 7).

£

! a

ts i; L.

E

c Li

35 30 25 20 15 10 5 0

/

II if \ \ <

f V \ \ ^ L_1_is;_2

V • 'ft uL *** Nfc 1

.'/J * y r

Concrete with Riueriggngates, T = 20 'C Cone re le willi River aggregates, T= 450 "C Conereit with River aggregates. T= 600 "C Concrete with River aggregates. T ~ 900 "C Cone re It wilh Qwirry aggregates. V - 20 "C Core re le wilh Quarry LLggregalcs, T= 430 "C Co 11creLc with Quarry aggregates, 7"= 600 "C Cone re It with Quarry aggregates. 900 *C

0 I 2 3 4 5 6 7 S 9 10 ! I 12 13 14 IS 16

Time, s

Fig. 4. Some registered diagrams "force-deformation" of samples of an ordinary concrete under axial compression test

< DO

tT

iH

O r

s 2

o </>

§

J CD

U -

r 1

n 0

§ 3 o

n)

<I> '

o

CO CO

§ 3 a 0

§ 6 r 6 o o

o

Fig. 5. Failure (a) and the mean curve of the loss (b) of the bearing capacity of the concrete samples made of the coarse river aggregates

§ )

|!

® 5

a '

O) DO

1 T

s □

S y

c o

(D *

2 2 O O 10 10

1569

Fig. 6. Failure (a) and the mean curve of the loss (b) of the bearing capacity of the concrete samples made of crushed coarse quarry aggregates

N N

o o

N N

ci ci

r r

H (V U 3 > in C M

to <o

<0 0

u

<D <D

o ë

Fig. 7. Correlation between obtained experimental results with these by European standard "Eurocode 2"1 and various researches [21]

M M

.E o

dl"

a

LT> o

s !

o EE

CD ^

T- ^

£

o2 °

A Ü w

Si

0 (A

Fig. 8. Bearing capacity of the ordinary concrete subjected to fire, compared to the compressive strength of the ordinary concrete not subjected to fire

1570

Finally, the results show that the compressive strength of concrete is a function of the heating temperature. The bearing capacity of the concrete of fire-damaged reinforced concrete structure is significantly reduced for heating temperatures above 350 °C (Fig. 8).

Here the results (Fig. 8) show that the concrete material made of crushed coarse quarry aggregates loses 50 % of its bearing capacity at around 525 °C of heating temperature, compared to its strength at a room temperature of 20 °C. Moreover, at a temperature of 900 °C, the same crushed coarse quarry aggregate concrete's bearing capacity is around 22 % of the bearing capacity obtained at a room temperature of 20 °C. Similarly, the results show that the concrete made of the coarse river aggregates loses 50 % of its load-bearing capacity at a temperature of 600 °C, compared to its strength at room temperature. Furthermore, at a temperature of 900 °C, the bearing capacity of the same concrete made of coarse river aggregates is around 30 % of the bearing capacity obtained at room temperature.

CONCLUSIONS

The negative impact of the fire on the load-bearing capacity of the ordinary concrete occurs around 350 °C of heating temperature. Concrete made of crushed coarse quarry aggregates loses 50 and 78 % of its bearing capacity at around 525 and 900 °C of heating temperature, respectively. Similarly, concrete made of coarse river aggregates loses 50 and 70 % of its bearing capacity respectively at 600 and 900 °C of heating temperature. An evaluation curve of the after-fire bearing capacity of the concrete used in reinforced concrete structures in Burundi is established. It is established that the concrete made of coarse rive aggregates is more resistant than the concrete made of coarse quarry aggregates. Knowing the heating temperature that the fire-damaged reinforced concrete structure has undergone is indispensable in deciding on its demolition or rehabilitation.

REFERENCES / СПИСОК ИСТОЧНИКОВ

1. Choinska M., Khelidj A., Dufour F., Pijaudier-Cabot G. Etude expérimentale de l'interaction endom-magement-température-état de contrainte-perméabilité du béton. Revue Européenne de Génie Civil. 2007; 11(6):839-853. DOI: 10.1080/17747120.2007.9692963

2. Bouabdallah M.A. Etude comparative du béton haute performance et un béton ordinaire soumises à un chargement thermomécaniques. Actes des 6ème Journées de Mécanique de l'Ecole Militaire Polytechnique. Avril 2008, Bordj El Bahri, Alger. 2008.

3. Tshimanga M.K. Influence des paramètres de formulation sur le comportement à haute température des bétons. Thèse de Doctorat, Université de Cergy Pon-toise, 2007.

4. Joseph A.A. Residual compressive strength of normal and high strength concrete at elevated temperatures. International Journal of Engineering Research & Technology (IJERT). 2013; 2(6):1744-1751.

5. Kumavat H., Chandak N. Experimental study on behavior of normal strength concrete influenced by elevated temperatures. 2020. Advances in Science and Engineering Technology International Conferences (ASET). 2020. DOI: 10.1109/ASET48392.2020.9118294

6. Bastami M., Aslani F., Omran M.E. High-temperature mechanical properties of concrete. International Journal of Civil Engineering. 2010; 8(4):337-351.

7. Tufail M., Shahzada K., Gencturk B., Wei J. Effect of elevated temperature on mechanical properties of limestone, quartzite and granite concrete. International Journal of Concrete Structures and Materials. 2017; 11(1):17-28. DOI: 10.1007/s40069-016-0175-2

8. Bingol A.F., Gul R. Effect of elevated temperatures and cooling regimes on normal strength concrete.

Fire and Materials. 2009; 33(2):79-88. DOI: 10.1002/ fam.987

9. Hachemi S., Ounis A. L'influence de la nature du sable sur les proprietes physiques et mecaniques du beton soumis a haute temperature. Courrier du Savoir. 2017; 24. URL: www.researchgate.net/publication/318430636

10. Dreux G., Festa J. Nouveau guide du béton et de ses constituants. Eyrolles, Paris, France, 1998.

11. Luccioni B.M., Figueroa M.I., Danesi R.F. Thermo-mechanic model for concrete exposed to elevated temperatures. Engineering Structures. 2003; 25(6):729-742. DOI: 10.1016/S0141-0296(02)00209-2

12. Oyelade A.O., Odegbaro D.O., Fapohun-da C.A. Effect of elevated temperature on the com-pressive strength of concrete produced with pulverized steel mill scale. Nigerian Journal of Technology. 2018; 36(4):1030. DOI: 10.4314/njt.v36i4.6

13. Abdulkareem O.M., Ahmad A.H. Effect of high temperature on mechanical properties of concrete containing admixtures. Al-Rafidain Engineering. 2010; 18(4):43-54. DOI: 10.33899/rengj.2010.31523

14. Short N.R., Purkiss J.A., Guise S.E. Assessment of fire damaged concrete using colour image analysis. Construction and Building Materials. 2001; 15(1):9-15. DOI: 10.1016/S0950-0618(00)00065-9

15. Short N.R., Purkiss J.A., Guise S.E. Assessment of fire-damaged concrete using crack density measurements. Structural Concrete. 2002; 3(3):137-143. DOI: 10.1680/stco.3.3.137.38957

16. Khoury G.A. Compressive strength of concrete at high temperatures: a reassessment. Magazine of Concrete Research. 1992; 44(161):291-309. DOI: 10.1680/ macr.1992.44.161.291

< П

tT

iH *к

О Г s 2

0 со n со

1 <

< -»

J CD

U -

r i

n 0

< 3 o

oî

O n

со

CO

l\J со

0

1

CO CO о о

< )

I!

ф ®

л *

ai п

I т s □

s У

с о ф *

II

M 2 О О 10 10

1571

17. Shang X., Lu Z. Impact of high temperature on the compressive strength of ECC. Advances in Materials Science and Engineering. 2014; 2014:1-7. DOI: 10.1155/2014/919078

18. Albrektsson J., Flansbjer M., Lindqvist J.E., Jansson R. Assessment of concrete structures after fire. SP report 2011:19. 2011.

19. Engin R.M., Mata L.A, Dilek U. An analytical model for estimating load-test deflections in fire-damaged

precast, prestressed concrete members. Pci Journal. 2009; 54(3):129-142. DOI: 10.15554/pcij.06012009.129.142

20. Kodur V.K.R. Tenue au feu des éléments de structure en béton haute résistance. Institut de recherche en construction IRC. Canada, 1999.

21. Abrams M. Compressive strength of concrete at temperatures to 1600F. Michigan, American Concrete Insitute (ACI) SP 25, 1971. DOI: 10.14359/17331

Received November 9, 2021.

Adopted in revised form on December 21, 2021.

Approved for publication on December 21, 2021.

B io n о t e s : Emmanuel Mikerego — Candidate of Technical Sciences, Lecturer of the Faculty of Engineering Sciences; University of Burundi; B.P 2700, Bujumbura, Burundi; ORCID: 0000-0002-5743-6476; mikeregoemmanuel@ hotmail.com;

Donatien Nduwimana — master student; University of Burundi; B.P 2700, Bujumbura, Burundi; nduwdon@ gmail.com.

Contribution of the authors:

E. Mikerego — conceptualization, methodology, data processing, writing of the article, scientific editing of the

text.

D. Nduwimana — methodology, data gathering and processing. N N The authors declare no conflict of interest.

СЧ СЧ

^ ^ Поступила в редакцию 9 ноября 2021 г. jj ® Принята в доработанном виде 21 декабря 2021 г. Одобрена для публикации 21 декабря 2021 г.

> (Л

с и> to со

. г

(О

ш

Об авторах : Эммануэль Микерего — кандидат технических наук, преподаватель факультета инже-Е нерных наук; Университет Бурунди; В.Р 2700, г. Бужумбура, Бурунди; ОЯСГО: 0000-0002-5743-6476;

О mikeregoemmanuel@hotmail.com;

Донатьен Ндувимана — студент магистратуры; Университет Бурунди; В.Р 2700, г. Бужумбура, Бурунди; nduwdon@gmail.com.

Вклад авторов:

Э. Микерего — концептуализация, методология, обработка данных, написание статьи, научноередакти-

ч*

Ф О)

11

—■

о

О £ со > со 5-

^ с рование текста.

о Œ

с^ с Д. Ндувимана — методология, сбор и обработка данных.

от|

от Е —

^ (Л

.Е §

CL U

• с ю О

^ я

Авторы заявляют об отсутствии конфликта интересов.

§ h fe о

СП ^

£

ОТ О

I

Si

О (Я

1572