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Article

Anjaly Nair and Osama (Sam) Salem

At elevated temperatures, concrete undergoes changes in its mechanical and thermal properties, which mainly cause degradation of strength and eventually may lead to the…

Abstract

Purpose

At elevated temperatures, concrete undergoes changes in its mechanical and thermal properties, which mainly cause degradation of strength and eventually may lead to the failure of the structure. Retrofitting is a desirable option to rehabilitate fire damaged concrete structures. However, to ensure safe reuse of fire-exposed buildings and to adopt proper retrofitting methods, it is essential to evaluate the residual load-bearing capacity of such fire-damaged reinforced concrete structures. The focus of the experimental study presented in this paper aims to investigate the fire performance of concrete columns exposed to a standard fire, and then evaluate its residual compressive strengths after fire exposure of different durations.

Design/methodology/approach

To effectively study the fire performance of such columns, eight identical 200 × 200 × 1,500-mm high reinforced concrete columns test specimens were subjected to two different fire exposure (1- and 2-h) while being loaded with two different load ratios (20% and 40% of the column ultimate design axial compressive load). In a subsequent stage and after complete cooling down, residual compressive strength capacity tests were performed on each fire exposed column.

Findings

Experimental results revealed that the columns never regain its original capacity after being subjected to a standard fire and that the residual compressive strength capacity dropped to almost 50% and 30% of its ambient temperature capacity for the columns exposed to 1- and 2-h fire durations, respectively. It was also noticed that, for the tested columns, the applied load ratio has much less effect on the column’s residual compressive strength compared to that of the fire duration.

Originality/value

According to the unique outcomes of this experimental study and, as the fire-damaged concrete columns possessed considerable residual compressive strength, in particular those exposed to shorter fire duration, it is anticipated that with proper retrofitting techniques such as fiber-reinforced polymers (FRP) wrapping, the fire-damaged columns can be rehabilitated to regain at least portion of its lost load-bearing capacities. Accordingly, the residual compressive resistance data obtained from this study can be effectively used but not directly to adopt optimal retrofitting strategies for such fire-damaged concrete columns, as well as to be used in validating numerical models that can be usefully used to account for the thermally-induced degradation of the mechanical properties of concrete material and ultimately predict the residual compressive strengths and deformations of concrete columns subjected to different load intensity ratios for various fire durations.

Details

Journal of Structural Fire Engineering, vol. 11 no. 4
Type: Research Article
ISSN: 2040-2317

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Article

Hassan A.M. Mhamoud and Jia Yanmin

This study aims to investigate the effectiveness of different additives (individual effects) in improving the strength of concrete to resist temperatures of up to 60ºC.

Abstract

Purpose

This study aims to investigate the effectiveness of different additives (individual effects) in improving the strength of concrete to resist temperatures of up to 60ºC.

Design/methodology/approach

In all, 13 different mixtures with a constant water/binder ratio of 0.36 and grade M40 were prepared by using ordinary Portland concrete alone, or with partial replacement by fly ash (FA), blast-furnace slag, silica fume (SF) and a combination of all three. After 7 and 28 days under water, their strength and residual strength were measured.

Findings

The results of testing revealed that the addition of 10 per cent SF was found to result in the greatest increase in compressive strength and flexural strength along with decreased the residual strengths. The addition of FA increased the compressive strength and enhanced the residual compressive strength. However, it also decreased the residual flexural strength.

Originality/value

The addition of slag achieved better flexural strength and the best residual compressive strength. The combination of additives also enhanced the compressive strength but was not found to be better than using SF alone.

Details

Journal of Structural Fire Engineering, vol. 9 no. 2
Type: Research Article
ISSN: 2040-2317

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Article

Hassan A.M. Mhamoud and Jia Yanmin

This study aims to focus on the resistance to elevated temperatures of up to 700ºC of high-performance concrete (HPC) compared to ordinary Portland concrete (OPC) with…

Abstract

Purpose

This study aims to focus on the resistance to elevated temperatures of up to 700ºC of high-performance concrete (HPC) compared to ordinary Portland concrete (OPC) with regards to mass loss and residual compressive and flexural strength.

Design/methodology/approach

Two mixtures were developed to test. The first mixture, OPC, was used as the control, and the second mixture was HPC. After 28 days under water (per Chinese standard), the samples were tested for compressive strength and residual strength.

Findings

The test results showed that at elevated temperatures of up to 500ºC, each mixture experienced mass loss. Below this temperature, the strength and the mass loss did not differ greatly.

Originality/value

When adding a 10 per cent silica fume, 25 per cent fly, 25 per cent slag to HPC, the compressive strength increased by 17 per cent and enhanced the residual compressive strength. A sharp decrease was observed in the residual flexural strength of HPC when compared to OPC after exposure to temperatures of 700ºC.

Details

Journal of Structural Fire Engineering, vol. 8 no. 4
Type: Research Article
ISSN: 2040-2317

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Article

Daniel Paul Thanaraj, Anand N. and Prince Arulraj

The purpose of this study is to investigate the effect of standard fire on the strength and microstructure properties of concrete with different strength grades.

Abstract

Purpose

The purpose of this study is to investigate the effect of standard fire on the strength and microstructure properties of concrete with different strength grades.

Design/methodology/approach

Different strength grades of concrete used for the investigation are M20, M30, M40 and M50. An electrical bogie hearth furnace was developed to simulate the International Standards Organization 834 standard fire curve.Concrete samples were subjected to high temperatures of 925, 1,029, 1,090 and 1,133°C for the duration of 1, 2, 3 and 4 h, respectively, as per standard fire curve. Compressive strength, tensile strength, thermal crack pattern and spalling of heated concrete specimens were evaluated by experimental investigation. Scanning electron microscopy and thermo-gravimetric analysis were performed to investigate the microstructure properties of heated concrete specimens.

Findings

Test results indicated reduction in the strength and changes in the microstructure properties of concrete exposed to elevated temperature. The degree of weight and the strength loss were found to be higher for concrete with higher grades. An empirical relation is proposed to determine the residual strength of concrete with different strength grade using regression analysis.

Social implications

Results of this research will be useful for the design engineers to understand the behavior of concrete exposed to elevated temperature as per standard fire.

Originality/value

When concrete is exposed to elevated temperature, its internal microstructure changes, thereby strength and durability of concrete deteriorates. The performance of concrete with different strength grade exposed to standard fire is well understood. This research’s findings will be useful for the designers to understand more about fire resistance of concrete. A simple relationship is proposed to determine the residual strength of concrete exposed to various durations of heating.

Details

Journal of Structural Fire Engineering, vol. 11 no. 3
Type: Research Article
ISSN: 2040-2317

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Article

Rajkishor , Pradeep Bhargava, Navratan M. Bhandari and Umesh K. Sharma

This paper aims to present a mathematical model of predicting the residual moment capacity of fire-damaged reinforced concrete (RC) elements after cooling to ambient…

Abstract

Purpose

This paper aims to present a mathematical model of predicting the residual moment capacity of fire-damaged reinforced concrete (RC) elements after cooling to ambient temperature which also reflects the role of bond between steel rebar and surrounding concrete.

Design/methodology/approach

The prediction of residual moment capacity of fire-damaged RC element has been carried out for two scenarios: by assuming perfect bond between surrounding concrete and steel rebar after fire exposure and by incorporating a relative slip between surrounding concrete and steel rebar and hence assuming partial bond between them after fire scenario. The predicted results are then compared with the experimental results available in different literatures.

Findings

It is found that on comparison between the predicted results and the experimental results, the proposed mathematical prediction model, when bond-characteristics are considered, shows better agreement with the experimental results as compared with those by conventional method with perfect bond assumption.

Originality/value

The constitutive relationship for thermal residual properties of steel rebar and concrete has been used in the proposed prediction model along with relative slip approach between surrounding concrete and steel rebar after fire scenario and consequently to predict the residual moment capacity of the fire-damaged RC element after cooling.

Details

Journal of Structural Fire Engineering, vol. 8 no. 1
Type: Research Article
ISSN: 2040-2317

Keywords

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Article

Daniel Paul Thanaraj, Anand N. and Prince Arulraj

This paper aims to explain the influence of Standard Fire as per ISO 834 on the strength and microstructure properties of concrete specimens with different strength grade.

Abstract

Purpose

This paper aims to explain the influence of Standard Fire as per ISO 834 on the strength and microstructure properties of concrete specimens with different strength grade.

Design/methodology/approach

The strength grades of concrete considered for the experimental investigation were Fck20, Fck30, Fck40 and Fck50. The specimens were heated up to 1, 2, 3 and 4 h as per standard fire curve. Effect of elevated temperature on compressive and flexural behavior of specimens with various strength grades was examined. Effects of age of concrete, weight loss, surface characteristics and thermal crack pattern were also investigated.

Findings

Experimental investigation shows that strength grade, duration of exposure and age of concrete are the key parameters affecting the residual strength of concrete. For the beams exposed to 3 and 4 h of heating, the residual flexural strength was found to be so insignificant that the specimens were not able to even sustain their own weight. The loss in compressive and flexural strength of Fck50 concrete specimens heated up to 1 h were found to be 26.41 and 86.03 per cent of the original unheated concrete, respectively. The weight loss was found to be more for higher grade concrete specimens, and it was about 8.38 per cent for Fck50 concrete. Regression analysis was carried out to establish the empirical relation between residual strength and grade of concrete. Scanning electron microscopy and thermogravimetric analysis were carried out to examine the damage level of fire-affected concrete specimens.

Originality/value

Empirical relationship was developed to determine the residual strength of concrete exposed to elevate temperature, and this will be useful for design applications. This database may be useful for identifying member strength of reinforced beams subjected to various durations of heating so that suitable repair technique can be adopted from the available database. It will be useful to identify the proper grade of concrete with regard to fire endurance, in the case of concrete under compression or flexure.

Details

Journal of Engineering, Design and Technology , vol. 17 no. 5
Type: Research Article
ISSN: 1726-0531

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Article

Sachin V. and N. Suresh

Concrete is a widely used construction material which can be prepared using locally available resources (aggregates, cement and water) by following relevant standard…

Abstract

Purpose

Concrete is a widely used construction material which can be prepared using locally available resources (aggregates, cement and water) by following relevant standard guidelines. The residual properties of concrete determined by heating in an electric furnace may not produce a similar effect of fire. The purpose of this paper is to compare the effect of a fire with that coming from the exposure of normal strength concrete to predetermined reference temperatures, for which two sets of specimens were heated in a fire furnace provided with gas burners and an electric furnace.

Design/methodology/approach

The concrete cubes and cylinders were subjected to 200oC, 400oC, 600oC and 800oC temperature in a gas-controlled fire furnace and an electric furnace for 2 h. The physical properties and mechanical properties of concrete were determined after cooling the specimens in air. The quality of concrete specimens was determined using the ultrasonic pulse velocity test, and surface hardness of the heat-exposed cubes was recorded using the Schmidt rebound hammer.

Findings

The fire-exposed specimens were found to have lower residual compressive strength, tensile strength and higher porosity/voids/internal cracks than the specimens heated in an electric furnace at the same temperature. Further, a good agreement with compressive strength and rebound numbers was observed for each of the two heating systems (flames coming from gas burners and electric furnace).

Originality/value

Normal strength concrete specimens exposed to heat in an electric furnace will not give the same effect of fire having the same maximum temperature. Further, it is noticed that concrete subjected to elevated temperature is sensitive to heating modalities, be it the flames of a gas furnace or the radiation of an electric furnace.

Details

Journal of Structural Fire Engineering, vol. 12 no. 1
Type: Research Article
ISSN: 2040-2317

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Article

N. Suresh and Manjunatha M.

The purpose of this paper is to investigate the effect of elevated temperature on mechanical and physical properties of concrete specimens obtained by substituting the…

Abstract

Purpose

The purpose of this paper is to investigate the effect of elevated temperature on mechanical and physical properties of concrete specimens obtained by substituting the river sand with copper slag (CS) at proportions of 25%, 50%, 75% and 100%. The specimens were heated in an electric furnace up to 100, 200, 300, 400, 500 and 600 C and kept at these temperatures for 2 h duration. After the specimens were cooled in the furnace, mass loss, ultrasonic pulse velocity (UPV), compressive strength, split tensile strength (STS), flexural strength (FS) and modulus of elasticity (MOE) values were determined. No spalling occurred in the specimens after subjected to elevated temperature. The surface cracks were observed only in specimens exposed to 600 C. The maximum reduction in compressive strength and STS at 600C is 50.3% and 36.39% for referral mix (NC), 18% and 16% for specimens with 100% CS (MCS4). The reduction in MOE of specimens is observed to be high as copper slag content increases with increasing temperature. Scanning electron microscopy (SEM) studies are carried out to examine the changes in micro-structures of specimens after exposed to elevated temperatures.

Design/methodology/approach

After casting of concrete specimens, it is cured for 28 days. After attainment of 28 days age, the concrete specimens is taken out from the curing tank and allowed to dry for 2 days to remove any moisture content in the specimens to prevent explosive spalling during the time of heating. The prepared concrete specimen is subjected to temperatures of 100°C, 200°C, 300°C, 400°C, 500°C and 600°C up to 2 h duration. The physical test, mechanical test and SEM studies are carried out after cooling of specimens to room temperature (RT). The quality of concrete specimens is measured by conducting UPV test after cooling to RT.

Findings

The post-thermal strength properties of concrete specimens with copper slag contents are higher than referral mix concrete. The reduction of MOE of concrete specimens is more with incremental in copper slag content with increase in temperatures. Furthermore, the quality of concrete specimens is ranging from “good to medium” up to 500C temperatures based on UPV test.

Originality/value

In this research work, the natural sand is fully replaced with copper slag materials in the concrete mixes. The post-thermal strength properties like residual compressive strength, residual STS, residual FS and residual MOE is higher than referral mix after subjected to elevated temperature conditions. Higher density and toughness properties of copper slag materials will contribute to concrete strength. The effect of elevated temperature is more on MOE of concrete specimens having higher copper slag contents when comparing to specimens compressive strength.

Details

Journal of Structural Fire Engineering, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 2040-2317

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Article

Swapnil K. Shirsath and Subhash C. Yaragal

This study reports the performance of thermally deteriorated concrete with and without fibres. Attempts have been made to find the suitable performance of steel…

Abstract

Purpose

This study reports the performance of thermally deteriorated concrete with and without fibres. Attempts have been made to find the suitable performance of steel polypropylene (PP) hybrid fibre combination that could significantly enhance the performance of mechanical properties at elevated temperatures.

Design/methodology/approach

In this experimental investigation, concrete cubes of 100 mm in size of various compositions were cast and water-cured for 28 days, and later exposed to elevated temperatures of either 200 or 400°C or 600 and or 800°C with a retention period of 2 h. The properties like change in colour and percentage weight loss were evaluated. Ultrasonic Pulse Velocity test was used to obtain qualitative information of strength variation. Residual strength of thermally deteriorated concrete specimen was measured by destructive testing.

Findings

Steel fibre volume fraction of 1 per cent improves the compressive strength of concrete in the temperature range of 400 to 800°C. The addition of steel fibre and PP fibre (Mix 3) improves the splitting strength of the concrete at elevated temperature range of 400 to 600°C.

Originality/value

Performance enhancement is observed with hybrid fibres for temperature endurance of concrete.

Details

Journal of Structural Fire Engineering, vol. 8 no. 1
Type: Research Article
ISSN: 2040-2317

Keywords

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Article

Ashok Kumar Sahani, Amiya K. Samanta and Dilip K. Singharoy

Present study focuses on scope of developing sustainable heat resistant concrete by adding steel fibre (Sf) and polypropylene fibre (PPf) along with partially replacement…

Abstract

Purpose

Present study focuses on scope of developing sustainable heat resistant concrete by adding steel fibre (Sf) and polypropylene fibre (PPf) along with partially replacement of ordinary portland cement (OPC) and natural fine aggregate with fly ash (FA) and granular blast furnace slag (GBFS). Replacement percentages of FA and GBFS were 40% and 50%, whereas Sf and PPf for fibre-added mixes were 1% by volume of concrete and 0.25% by weight of cement, respectively.

Design/methodology/approach

An experimental work had been carried out to make comparison between control mix (CM), fibre-added sustainable mix (SCMF) and fibre-added control mix (CMF) with reference to weight loss, mechanical strength (compressive, split and flexure) after exposed to room temperature (27°C) to 1000°C at the interval of 200°C for 4 h of heat curing followed by furnace cooling and then natural cooling. Furthermore, microstructural analysis was executed at 27°C, 400°C and 800°C, respectively.

Findings

Colour change and hair line cracks were started to appear at 600°C. Fibre-added control mix and sustainable mix did not exhibit any significant cracks as compared to control mix even at 1000°C. Major losses were occurred at temperature higher than 600°C, loss in compressive strength was about 70% in control mix, while 60% in fibre-added mixes. SCMF exhibited the highest retention of strength with respect to all cases of mechanical strength.

Research limitations/implications

Present study is based on the slow heating condition followed by longer duration of heat curing at target temperature.

Practical implications

Present work can be helpful for the design engineer for assessing the fire deterioration of concrete structure existing near the fire establishment such as furnace and ovens. Building fire (high temperature for short duration) might be the further scope of work.

Originality/value

Concept of incorporating pozzolanic binder and calcareous fine aggregate was adopted to take the advantage pozzolanacity and fire resistivity. To the best of author’s knowledge, there is a scope for fill the research gap in this area.

Details

Journal of Structural Fire Engineering, vol. 10 no. 4
Type: Research Article
ISSN: 2040-2317

Keywords

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