BEHAVIOR OF REACTIVE POWDER CONCRETE SLABS BEHAVIOR OF REACTIVE POWDER CONCRETE SLABS EXPOSED TO FIRE

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  • http://www.iaeme.com/IJCIET/index.asp 124 editor@iaeme.com

    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

    http://www.iaeme.com/IJCIET/index.asp 125 editor@iaeme.com

    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.

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

    http://www.iaeme.com/IJCIET/index.asp 126 editor@iaeme.com

    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 fibe