BEHAVIOR OF REACTIVE POWDER CONCRETE SLABS …BEHAVIOR OF REACTIVE POWDER CONCRETE SLABS EXPOSED TO FIRE FLAME Prof. Samir A. Al-Mashhadi and Farah Alaa Alwash Department of Civil

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International Journal of Civil Engineering and Technology (IJCIET) Volume 6, Issue 11, Nov 2015, pp. 124-135, Article ID: IJCIET_06_11_013 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication ___________________________________________________________________________

BEHAVIOR OF REACTIVE POWDER

CONCRETE SLABS EXPOSED TO FIRE

FLAME

Prof. Samir A. Al-Mashhadi and Farah Alaa Alwash

Department of Civil Engineering, Engineering college, Babylon University, Iraq

ABSTRACT

This work is devoted to study the behavior as well as the mechanical

properties of reactive powder concrete (RPC) slabs subjected to fire flame.

The experimental program includes investigation the effect of burning

temperature and duration on some important mechanical properties of RPC

compared with normal strength concrete (NSC) such as compressive strength,

modulus of rupture, splitting tensile strength and modulus of elasticity.

Additional tests are also conducted to study the effect of temperature,

duration, existence of steel reinforcement and slab thickness on the flexural or

punching shear behavior of simply supported RPC slabs having dimensions of

(520×520×50mm) under concentrated load at the center of the slab. The test

results showed that the performance of RPC specimens at fire were worse than

that of conventional concrete due to increased spalling. All RPC samples were

spalled and loss their mechanical properties under burning at (600ºC) for (60

mins.) duration. Slab thickness of (50 mm) was enough to resist fire exposure

at high temperature level without spalling of the upper surface of concrete. .

Key words: Reactive Powder Concrete (RPC); Spalling; Punching Shear; Mechanical Properties.

Cite this Article: Prof. Samir A. Al-Mashhadi and Farah Alaa Alwash, Behavior of Reactive Powder Concrete Slabs Exposed To Fire Flame. International Journal of Civil Engineering and Technology, 6(11), 2015, pp. 124-135. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11

1. INTRODUCTION

Exposure to elevated temperatures, which is mainly caused by accidental fires, represents one of the more severe exposure conditions of buildings and structures. The fire resistance and post heat exposure behavior of structural members depend on thermal and mechanical properties of the materials composing these members (Muhaned and Sallal, 2007).

Behavior of Reactive Powder Concrete Slabs Exposed To Fire Flame


1.1. Fire Effect on Mechanical Properties of RPC

Tai, et al., (2011)studied the stress-strain relation of RPC in quasi-static loading after

an elevated temperature. The cylinder specimens of RPC with 50mm×100mm are

examined at the room temperature and after 200–800°C. He indicated that the residual compressive strength of RPC after heating from 200–300°C increases more than that at room temperature, but, significantly decreases when the temperature exceeds 300°C. The residual peak strains of RPC also initially increase up to 400–500°C, then decrease gradually beyond 500°C. Meanwhile, Young’s modulus diminishes with an increasing temperature.

Sana, (2013) conducted the effect of elevated temperatures on mechanical properties of reactive powder concrete (RPC), mainly on compressive strength, flexural strength and splitting tensile strength. RPC was prepared using cement, silica fume, fine sand and steel fibers to cast and test 128 specimens (cubes, cylinders and prisms) with various steel fibers ratios of (0, 1, 2 and 3)% at temperatures of (20, 200, 400 and 600)°C. Results generally showed that the decrease in compressive strength, flexural strength and splitting tensile strength became larger when temperature exceeded 400°C. At 600°C the decreasing ratios were 17.8%, 38.87% and 58.58% for compressive strength, flexural strength and splitting tensile strength, respectively. Explosive spalling of RPC at elevated temperatures was also observed and discussed.

Bashandy, (2013)investigated the effects of elevated temperatures of 200, 300 and 500°C in 2 and 4 hours heating durations on the main mechanical properties of economical type of reactive powder concrete. The residual strength of RPC decreased as the exposure temperature increased. Increasing heating time decreased the residual concrete strength. Increasing cement content increased the initial strength of RPC but decreases the residual strength values after heating as the temperature and heating times increased. The steel fibers enhance the mechanical properties of RPC at room temperature up to 150°C. Increasing the temperature decrease the residual strength. RPC samples with cement content up to 750kg/m� behave nearly the same as normal strength concrete (residual strength increased up to 200°C then drops up to target temperature). Increasing cement content up to 800kg/m� decreases the residual strength after exposure to elevated temperature. Finally, RPC can be used as pre-cast concrete elements in elevated temperatures up to 300°C taking into consideration the loss of strength by values up to about 55%. Over that degree, RPC is not recommended to use.

1.2. Fire Induced Spalling

Peng, et al., (2012) investigated the fire resistance of reactive powder concrete. The residual mechanical properties measured include compressive strength, tensile splitting strength, and fracture energy. RPC was prepared using cement, sand, silica fume, steel fiber, and polypropylene fiber. High temperatures can be divided into two ranges in terms of strength loss in RPC, namely, 200-400C and 400-600C, RPC lost their original strength considerably. Under high moisture contents, RPC fully spalled and broke into small pieces, while, under low moisture contents, RPC only partially spalled or experienced no spalling as shown in table (2-1). As a whole, RPC had much higher fracture energy than that of plain concrete. Moreover, fracture energy of RPC after exposure to 600C was still quite high. The reason may be that the bonding force of hardened cement paste in RPC was so high that a more pronounced fiber pullout process can take place during fracture of RPC after heating.



Kodur V., (2014) studied the properties of concrete at elevated temperatures. He discussed the various properties that influence fire resistance performance, together with the role of these properties on fire resistance and the variation of thermal, mechanical, deformation, and spalling properties with temperature for different types of concrete. Concrete, at elevated temperatures, undergoes significant physicochemical changes. These changes caused properties to deteriorate at elevated temperatures and introduced additional complexities, such as spalling in HSC. Thus, thermal, mechanical, and deformation properties of concrete changed substantially within the temperature range associated with building fires. Furthermore, many of these properties are temperature dependent and sensitive to testing (method) parameters such as heating rate, strain rate, temperature gradient, and so on. High temperature properties of concrete are crucial for modeling fire response of reinforced concrete structures. A good amount of data existed on high temperature thermal, mechanical, and deformation properties of NSCand HSC, plate (2-8) shows a comparison in HSC and NSC spalling.

2. EXPERIMENTAL WORK

2.1. Introduction

The experimental work was carried out to decide upon the temperature range and duration of burning. It was decided to limit the maximum exposure to fire to about 400 °C and 600 °C with duration of exposure to fire flame of 30 and 60 mins which cover the range of situation in the majority of elevated temperature test.

2.2. Material and Mixture properties

In this investigation, the cement used was Ordinary Portland Cement (O.P.C) (type Ι)produced in Iraq of (ALMAS). This cement complied with the Iraqi specification No.5 (1984).Very fine sand with maximum size 600µm was used. This sand was separated by sieving (zone 4) sand (specific gravity of 2.7).For normal concrete slabs, rounded gravel with a maximum size of 10mmwas used.

Two mixes were investigated, mix 1 consisted 900 kg/m³ of cement and 25% of silica fume (as replacement of cement with water to cementitious ratio 0.17 by weight, and a dosage (3% by weight of cementitious) of super plasticizer was used to obtain workable concrete mixture. Mix 2 for normal concrete slabs with a mix proportion of {1(cement): 1.4 (sand): 2.5(gravel)} and water to cement ratio of 0.35 by weight with (0.5% by weight of cement) of super plasticizer.

2.3. Mixing Procedure

Concrete was mixed in a horizontal rotary mixer with a capacity of 0.09m3. The micro silica fume powder was mixed in dry state with the required quantity of cement for 5 minutes to ensure uniform dispersion of the reactive powder particles throughout the cement particles. Then, fine sand was loaded into the mixer and mixed for 5 minutes. The required amount of tap water was added to the rotary mixer within 1 minute. Then all the super plasticizer was added and mixed for an additional 5 minutes. When ultra-fine (micro) steel fibers were used, they were introduced, and dispersed uniformly. These were added slowly to the rotary mixer after the rest of the materials had been properly mixed and the concrete had a wet appearance and mixed for an additional 2 minutes. This procedure (mixing steps) is similar to the method used by



(Wille et al., 2011) which was used successfully to produce RPC with compressive strength exceeding 150 MPa without using heat curing.

2.4. Burning and Cooling

The concrete specimens were burnt with direct fire flame from a net of methane burners as shown in plate (1) inside a brick stove with dimensions of (1×1×0.8 m) (length× width× height)respectively. The bare flame was intended simulate the heating condition in actual fire. The measurement devices and burning process are shown in plates (2) and (3). After burning, the concrete slab specimens were allowed to cool to the laboratory temperature which is in the range of 25°C.

Plate (1) Net methane burners

Plate (2) Temperature measurement devices.

Four variables were investigated to study the behavior of RPC slabs as follows:

• Temperature of fire flame during burning.

• Duration of burning by fire flame.

• Existence of flexural steel reinforcement (with or without).

• Thickness of the slab.

According to these variables, ultimate loads, crack patterns as well as modes of failure were different from one another. So, these slabs were divided in to five groups as shown in Table (1). Plate (4) shows slab testing setup.



Plate (3) Burning process of the slab specimens.

Plate (4) Details of Slabs Testing Setup.

3. RESULTS AND DISCUSSION

3.1. Concrete mechanical properties

The test results of RPC compared with NSC cubes, cylinders and prisms are shown in Figures (1) to (4) in which it was clear that increasing the fire temperature level to (400 and 600ºC) decreased all the mechanical properties. The reduction in the properties(compressive, flexural, splitting strength and modulus of elasticity)of RPC when they exposed to burning in temperature level around (400ºC), was about (17.6

and 32.9%),(19.6 and 29.2%), (9.2 and 32.8%), and (15.6% and 31.4%) for (30 and

60 min) respectively. In this range of temperature, the absorbed and pore water was directed gradually to be lost. The decarbonation of calcium carbonate and dehydration for C-S-H produced a weak structure. Additionally, the loss of water increased the number of pores in tested samples structures (Zainab, 2014). On the other hand, the reduction was about (41.9%), (38.5%), (30.7%) and (42.8%) when burning at (600ºC) for (30 mins) duration. This was due to the further dehydration of the cement paste due to decomposition of calcium hydroxide, while there was no measured value at (60 min) duration because that all samples failed by spalling.



Table (1) Details of All Test Slabs of the Present Investigation.

Group

No. Slab

No.

Temperature of

fire flame

(ºC)

Duration of

burning

(min)

Flexural steel

reinforcement

Steel

fibers

% by

volume

Slab

thickness

(mm)

Group One

(G1)

( without

flexural

reinforcem

ent)

R1 25 -

Without

2 50

R2 400 30 2 50

R3 600 30 2 50

R4 400 60 2 50

R5 600 60 2 50

Group

Two(G2)

(with

flexural

reinforcem

ent)

R6 25 -

Ø 5mm @ 75mm c/c

2 50

R7 400 30 2 50

R8 600 30 2 50

R9 400 60 2 50

R10 600 60 2 50

Group

Three(G3)

(with 30

mm

thickness)

R11 25 -

Without

2 30

R12 600 30 2 30

R13 600 60 2 30

Group

Four (G4)

(with 70

mm

thickness)

R14 25 -

Without

2 70

R15 600 30 2 70

R16 600 60 2 70

Group Five

(G5)

(Normal

concrete as

a reference

slabs )

N1 25 -

Ø 5mm @ 75mm c/c

0 50

N2 400 30 0 50

N3 600 30 0 50

N4 400 60 0 50

N5 600 60 0 50

.

Prof. Samir A. Al

http://www.iaeme.com/IJCIET/index.asp

3.2. Load-Deflection Characteristics of the slab specimens

In this study, 21 slabs were tested. These slabs are identical in size, different in existence of flexural steel reinforcement, slab thickness, temperature and duration of fire flame. All results are

Figure (1)

Figure (2)

Figure (3) Effect of fire exposure on


ET/index.asp 130 [email protected]

Deflection Characteristics of the slab specimens

this study, 21 slabs were tested. These slabs are identical in size, different in existence of flexural steel reinforcement, slab thickness, temperature and duration of

Figure (1) Effect of fire exposure on compressive strength.

Figure (2) Effect of fire exposure on flexural strength.

Effect of fire exposure on splitting tensile strength.

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this study, 21 slabs were tested. These slabs are identical in size, different in existence of flexural steel reinforcement, slab thickness, temperature and duration of

splitting tensile strength.



Figure (4) Effect of fire exposure on modulus of elasticity

shown in Tables (2). From figures (5) to (9), it can be seen that under a certain load, the deflection increased with increasing the burning temperature. This can be attributed to the fact that fire caused a reduction in slab stiffness which was essentially due to the reduction in the modulus of elasticity of concrete and the effective moment of inertia of the specimens. Similar behavior was observed by (Muna, 2005).

It can be seen from Tables (2), that the deflection of slabs in group one was higher than those in group two for the same lead. This behavior can be attributed to the existence of flexural steel reinforcement in the slabs of group two, which helped in restraining the deflection with delaying the propagation of cracks and controlling their growth in the slab.

The small slab thickness (30mm) showed aggressive spalling on the exposed surface and the spalling continued to move to the unexposed surface while the spalling was only in the exposed surface for (50 and 70mm) slab thicknesses.

Table (2) Load - Deflection Characteristics of Test Slabs.

Group

No.

Slab

No.

Temp.

ºC

Dur.

min

First

Visible

crack

load (kN)

(1)

Ultimate

load (kN)

(2)

(1)/(2)

%

Mid-span

deflection

at first

visible

crack

(mm)

Mid-span

deflection

at ultimate

load (mm)

Mode

of failure

(G1)

R1 25 - 54.4 112.3 48.4 2.45 9.65

Flexure

R2 400 30 48.6 103.8 46.8 2.82 9.91

R3 600 30 43.1 97.9 44.0 3.30 10.3

R4 400 60 44.2 100.2 44.1 3.77 10.02

R5 600 60 - 89.6 - - 12.42

(G2)

R6 25 - 56.7 143.1 39.6 2.56 10.81 Punching



Group

No.

Slab

No.

Temp.

ºC

Dur.

min

First

Visible

crack

load (kN)

(1)

Ultimate

load (kN)

(2)

(1)/(2)

%

Mid-span

deflection

at first

visible

crack

(mm)

Mid-span

deflection

at ultimate

load (mm)

Mode

of failure

R7 400 30 49.5 130.3 38.0 2.86 11.04

R8 600 30 43.8 122.2 35.8 3.47 11.15

R9 400 60 44.5 124.9 35.6 3.81 11.33

R10 600 60 - 111.6 - - 13.26

(G3)

R11 25 - 32.4 72.7 44.6 3.2 12.55 Flexure

R12 600 30 - 43.2 - - 14.22 Irregular

R13 600 60 - 19.5 - - 16.61 Irregular

(G4)

R14 25 - 68.0 151.3 44.9 1.82 7.14

Flexure R15 600 30 60.2 142.1 42.4 2.70 9.32

R16 600 60 - 127.2 - - 10.93

(G5)

N1 25 - 23.2 56.1 41.4 0.25 3.9

Punching

N2 400 30 21.0 54.6 38.5 0.78 4.1

N3 600 30 18.1 50.2 36.1 1.4 6.6

N4 400 60 18.5 50.6 36.6 1.8 7.4

N5 600 60 15.3 46.5 32.9 2.2 8.89

.

The deflection of slabs in group one was higher than those in group two for the same lead. This behavior can be attributed to the existence of flexural steel reinforcement in the slabs of group two, which helped in restraining the deflection with delaying the propagation of cracks and controlling their growth in the slab, same behavior was obtained by(Salah, 2013).



Figure (5) Load-deflection of slabs in group one.

Figure (6) Load-deflection of slabs in group two.

Figure (7) Load-deflection of slabs in group three.

Figure (8) Load-deflection of slabs in group four.



Figure (9) Load-deflection of slabs in group five.

4. CONCLUSIONS

• Experimental tests show that increasing burning temperature to (400°C) decreased the mechanical properties (compressive, flexural, splitting strength and modulus of

elasticity) to about (17.6 and 32.9%),(19.6 and 29.2%), (9.2 and 32.8%), and (15.6%

and 31.4%) for (30 and 60 min) respectively.

• The mechanical properties was decreased to about (41.9%), (38.5%), (30.7%) and (42.8%) when reaching temperature level at (600ºC) for (30 mins) duration.

• All RPC samples were spalled and loss their mechanical and physical properties under burning temperature level (600ºC) and for (60 min) fire duration. Partial or total spalling was observed to be occurred. While all NSC samples succeeded after burning.

• It was concluded that the load- deflection relations of slab specimens exposed to fire flame temperatures around 600ºC are flat, representing softer load- deflection behavior than that of the control slab specimens.

• Slab thickness of (50mm) was enough to resist fire exposure at high temperature level without spalling of the upper surface of concrete. While in (30mm) thickness, the fire moved through the concrete and reached its upper surface.

REFERENCES

[1] Bashandy, Alaa A., "Influence of Elevated Temperatures on the Behavior of Economical Reactive Powder Concrete", Journal of Civil Engineering Research, Egypt, pp. 89-97, 2013.

[2] Kodur V.," Properties of Concrete at Elevated Temperatures", Hindawi Publishing Corporation, Michigan State University, USA, pp 1-15 ,2014.

[3] Muhaned A. Shallal and Sallal Rashid Al-Owaisy "Strength and Elasticity of Steel Fiber Reinforced Concrete at High Temperatures" Journal of Engineering and Development, Vol. 11, No. 2, pp 125-133, (2007).

[4] Muna Mohammed Karim, "Investigation of the Behavior and Properties of Reinforced Concrete Slabs Exposed to Fire Flame" A thesis submitted to the college of engineering, university of Babylon in fulfillment of partial requirements for the degree of master of science in civil engineering, pp 1-126, 2005.

[5] Peng, Gai-Fei, Kang Yi-Rong, Huang Yan-Zhu, Liu Xiao-Ping, and Chen Qiang, "Experimental Research on Fire Resistance Reactive Powder Concrete", Hindawi Publishing Corporation, China, pp 1-6, 2012.



[6] Salah Mahdi Harbi, "Influence of Using Ultra Fine Steel Fiber on the Behavior of Reactive Powder Concrete Slabs", A Thesis Submitted to the College of Engineering of the University of Babylon in Partial Fulfillment of the Requirements for the Degree of Master of Science in Civil Engineering, pp. 1-120, 2013.

[7] Sana Taha Abdul-Hussain, "Effect of Elevated Temperatures on Compressive and Tensile Strengths of Reactive Powder Concrete" Journal of Engineering and Development, Vol. (17), No.(4), pp 259-278, 2013.

[8] Tai, Yuh-Shiou, Pan, Huang-Hsing, and Kung, Ying-Nien, "Mechanical Properties of Steel Fiber Reinforced Reactive Powder Concrete Following Exposure to High Temperature Reaching 800ºC", ELSEVIER Nuclear Engineering and Design, Vol.(241), Issue 7, pp. 2416-2424, July 2011.

[9] Wille, K., Naaman, A.E., Parr-Montesinos, G.J., "Ultra-High Performance Concrete with Compressive Strength Exceeding 150MPa (22ksi): A Simpler Way", ACI Materials Journal, Vol. 108, No.1, pp. 46-54, January-February 2011.

[10] Zainab, Sabah, "Effect of Fire Flame Exposure on Some Mechanical Properties of Reactive Powder Concrete", M.Sc. Thesis, College of Engineering, University of Babylon, pp. 1-120, Sep. 2014.

[11] Dr. Samal M. Rashied, Punching Shear Resistance of Flat Slabs with Opening. International Journal of Civil Engineering and Technology, 6(4), 2015, pp. 01-12.

Documents

BEHAVIOR OF REACTIVE POWDER CONCRETE SLABS …BEHAVIOR OF REACTIVE POWDER CONCRETE SLABS EXPOSED TO FIRE FLAME Prof. Samir A. Al-Mashhadi and Farah Alaa Alwash Department of Civil