INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 1, No 4, 2011

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1 The effect of elevated on concrete materials A literature review Anand.N 1, Prince Arulraj.G 2 1 Asst.Professor, School of Civil Engineering, Karunya University, Coimbatore, India 2 Prof & Dean of Civil Engineering, SNS College of Technology, Coimbatore, India anand_1612@rediffmail.com ABSTRACT A review is presented based on experimental studies on the performance concrete when exposed to higher. The compiled data revealed distinct difference in mechanical properties of normal, high strength and self compacting concrete. Shape of (cube, cylinder, beam etc), size of, magnitude of load applied on the, time maintained for, reference on time, rate of, rate of cooling, time taken for hot after curing period, time taken for load after, heat on stressed/unstressed member, type of cooling adopted on heated by natural cooling or cooling by spraying water etc are the parameters that influence the results. To understand the behavior of concrete under elevated, it is necessary that several factors be taken into account for each experiment. Strength of concrete, type of cement, type of aggregate, water cement ratio, density of concrete, percentage of reinforcement, cover to the reinforcement etc are some of the important factors that affect the performance of concrete at elevated. Key words: High strength concrete, Self compacting concrete, Spalling, Coefficient of thermal expansion, Metakaolin 1. Introduction and methods A review of methods used by various investigators for ing concrete at elevated indicates that, the s can be categorized into two types namely cold ing and hot ing. In stressed s, a preload (20 40% of the compressive strength at 27 C) is applied to the prior to and the load is sustained during the period. Heat is applied at a constant rate until a target is reached, and this is maintained for a time until a thermal steady state is achieved. Stress or strain is then increased at a prescribed rate until the fails. In the unstressed, the is heated, without preload at a constant rate to the target, which is maintained until a thermal steady state is achieved. Stress or strain is then applied at a prescribed rate until failure occurs. In unstressed residual strength, the is heated without preload at a prescribed rate to the target, which is maintained until a thermal steady state is reached within the. The is then allowed to cool, following a prescribed rate to room. Load or strain is applied on the at room until the fails. Based on the review of literature, the experimental investigations on strength of concrete at elevated can be broadly classified into three categories as shown in Figure

2 Figure 1: Classification of Moetaz M. ElHawary et al (1996) studied the effect of fire exposure time and the concrete cover thickness on the behaviour of R.C. beams subjected to fire in shear zone and cooled by water. Eight reinforced concrete beams (1800 x 200 x 120 mm) were investigated. The beams were divided into two groups. Group (1) consisted of four beams with a cover thickness of 20 mm and group (2) consisted of four beams with a cover thickness of 40 mm. Each group was subjected to a of 650 C for different periods of time, i.e. 0, 30, min. The compressive strength of the beams were determined nondestructively by using a Schmidt hammer on the next day after exposure to fire. The beams were ed by applying two transverse loads incrementally. Strains and deformations were measured at each load increment. Cracking loads, crack propagation and ultimate loads were recorded for each beam. The behaviour of the beams exposed to fire in the shear zone was found to be highly affected by the fire exposure time and the change of the cover thickness. The salient features of the are shown in Table 1. Table 1: Salient Features of Test Carried out by Moetaz M. ElHawary et al Beam (1.8x0.12 x0.2) 650 C (furnace ) 0, 30min, 60min, 120min Sprayed with water immediately Chan et al (1999) carried out an investigation on the fire resistance of normal strength and highstrength concrete, with compressive strengths of 39, 76, and 94 MPa respectively. After exposure to s upto 1200 C, compressive strength and tensile splitting strength 929

3 were determined. The pore structure in HSC and in NSC was also investigated. Results indicated that HSC lost its mechanical strength in a manner similar to that of NSC. The between 400 and 800 C was critical to the strength loss. High s had a coarsening effect on the microstructure of both HSC and NSC. On the whole HSC and NSC suffered damage to almost the same degree, although HSC appeared to suffer a greater worsening of the permeabilityrelated durability. The salient features of the are shown in Table 2. Table 2: Salient Features of Test Carried out by Chan (0.1x0.1 x0.1) Up to 1200 C BS (Part 20) Peak maintained for an hour cooling to room ChiSun Poon et al (2003) carried out an experimental investigation to evaluate the performance of metakaolin (MK) concrete at elevated s up to 800 C. Eight normal and high strength concrete (HSC) mixes incorporating 0%, 5%, 10% and 20% MK were prepared. The residual compressive strength, chlorideion penetration, porosity and average pore sizes were measured and compared with silica fume (SF), fly ash (FA) and pure ordinary Portland cement (OPC) concretes. It was found that after an increase in compressive strength at 200 C, the MK concrete suffered a more severe loss of compressive strength and permeability related durability than the corresponding SF, FA and OPC concretes at higher s. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents. The salient features of the are shown in Table 3. Table 3: Salient Features of Test Carried out by ChiSun Poon (0.1x0.1x0.1) (0.1x0.2) Up to 800 C 2.5 C/min cooling & Kumar A and Kumar V (2003) carried out an investigation to find the residual strength of reinforced cement concrete beams exposed to higher for long. Six RCC beams were cast with same reinforcement, length, grade of concrete and clear cover. Four beams were exposed to fire for s of 1 h, 1.5 h, 2 h and 2.5 h. These beams were exposed to fire for 2.5 h and ed at room failed in serviceability criteria. The reduction in stiffness was found to increase with the increase in the of fire exposure. The following conclusions were drawn by the authors from the carried out on RCC beams. RCC beam of grade M20 with 25 mm clear cover was unable to resist a fire exposure 930

4 of about 2.5h as it failed in serviceability criterion. Spalling of concrete was observed at many places, which increased further with the time. Even 2 h fire was found to be critical as the beam was able to take only about 50% load of the companion beam. The behavior of M20 RCC beam exposed to fire of 1 h was found to be satisfactory as its strength was found to be about 83% of the companion beam. The salient features of the are shown in Table 4. Table 4: Salient Features of Test Carried out by Kumar A and Kumar V Beam(3.96x0.2 x0.3) 1hr,1.5hr,2hr, 2.5hr IS air load Min Li et al (2004) investigated on compressive strength, splitting tensile strength and bending strength of normal and highstrength concrete after high. Oil furnace was used in this study for the s. The time was close to the standard, which conforms to Chinese standard GB/T After being heated to s of 200, 400, 600, 800 and 1000 C respectively, the mechanical properties of HSC were found. The influence of, water content, size, strength grade and profiles on mechanical properties of HSC were discussed. They concluded that the larger the size, the lesser the strength loss. The salient features of the are shown in Table 5. Table 5: Salient Features of Test Carried out by Min Li et al Beam(0.415x0.1x0.1) (0.1x0.1x0.1) (0.15x0.15x0.15) 200 to 1000 C Chinese standard (GB/T ) Cooled naturally load Persson (2004) made a comparison between the performance of vibrated concrete and SCC under elevated. s and columns were ed by Compressive loading with high. Polypropylene fibers were used to avoid the spalling of concrete. Hydrocarbon and ISO 384 fire s were used. was maintained at 240 C and 480 C per hour. Specimens were heated in the of 20 to 800 C and s were slowly cooled upto room and ed. It was observed from the results that explosive spalling took place for columns with SCC but not for columns with vibrated concrete, even through the vibrated concrete columns were cured exactly as SCC columns. It was found that fire spalling mainly depended on the stress in the concrete, 931

5 cementpowder ratio and w/c ratio. Lower elastic modulus at fire was observed in SCC than in vibrated concrete. The salient features of the are shown in Table 6. Table 6: Salient Features of Test Carried out by Persson (0.1x0.2) Prestressed column (2x0.2x0.2) 20 to 800 C 2hr & 4hr ISO 384 fire & modified hydro carbon 240 C/hr & 480 C/hr 60 C/hr GaiFei Peng et al (2006) carried out an investigation to explore the relationship between occurrence of explosive spalling and residual mechanical properties of fiber toughened high performance concrete exposed to high s. The residual mechanical properties measured includes compressive strength, tensile splitting strength, and fracture energy. A series of concretes were prepared using ordinary Portland cement and crushed limestone. Steel fiber, polypropylene fiber, and hybrid fiber (polypropylene fiber and steel fiber) were added to enhance fracture energy of the concretes. After exposure to high s d from 200 to 800 C, the residual mechanical properties of fiber toughened highperformance concrete were investigated. For fiber concrete, although residual strength was decreased by exposure to high s over 400 C, residual fracture energy was significantly higher than that before. Incorporating hybrid fiber seems to be a promising way to enhance resistance of concrete to explosive spalling. The salient features of the are shown in Table 7. Table 7: Salient Features of Test Carried out by GaiFei Peng et al (0.1x0.1 x0.1) Beam(0.3x0. 1x0.1) Temperatur e 200 to 800 C duratio n temperatur e temperatur e 10 C/min (Target temperatur e maintained for an hour) cooling to room temperatur e duratio n b/w hot & load 2 days Metin husem (2006) examined the variation of compressive and flexural strengths of ordinary and highperformance microconcrete at high. Compressive and flexural strengths of ordinary and highperformance microconcrete which were exposed to high 932

6 s (200, 400, 600, 800 and 1000 C) and cooled differently (in air and water) were obtained. Compressive and flexural strengths of these concrete samples were compared with each other and then compared with the samples which had not been heated. On the other hand, strength loss s of these concrete samples were compared with the strength loss s given in the codes. Experimental results indicate that concrete strength decreases with increasing, and the decrease in the strength of ordinary concrete is more than that in highperformance concrete. The type of cooling affects the residual compressive and flexural strength, the effect being more pronounced as the increases. Strength loss s obtained from this study agree with strength loss s given in the Finnish Code. The salient features of the are shown in Table 8. Table 8: Salient Features of Test Carried out by Metin husem (0.15X0.3) Beam (0.04x0.04 x0.16) 200 to 1000 C 5.5 C/min Air and water b/w hot After cooling by air/water Noumowe et al (2006) carried out an investigation to understand the behavior of conventional vibrated high strength concrete and self compacting high strength concrete at high. Based on the results they concluded that, the residual mechanical properties of self compacting high strength concretes were similar to that of conventional highstrength concrete. The risk of spalling for selfcompacting highstrength concrete was greater than that of conventional highstrength concrete. The s showed that severe spalling could occur with selfcompacting highstrength concrete even at a rate as low as 0.5 C/min. The salient features of the are shown in Table 9. Table 9: Salient Features of Test Carried out by Noumowe et al (0.16x0.32) Beam(0.4x0.1x0. 1) Temperatur e duratio n 600 C temperatur e ISO 834 (Eurocode) heatin g 0.5 C/ min Simultan eous cooling Stressed hot Chang et al (2006) carried out an investigation to obtain complete compressive stress strain relationship for concrete after to s of C. All concrete s were standard cylinders of diameter 150 mm and height 300 mm, made with siliceous aggregate. The heated s were ed at 1 month after they were cooled to room. From the results of 108 s with two original unheated strengths, a single equation for the complete stress strain s of heated concrete was developed. Through the 933

7 regression analysis, the relationships of the mechanical properties with were proposed to fit the results, including the residual compressive strength, peak strain and elastic modulus. The equation proposed is applicable to unheated and heated concrete s at different s. In addition, the split cylinder s of 54 s were also found and a relationship between splitting tensile strength and was established. The salient features of the are shown in Table 10. Table 10: Salient Features of Test Carried out by Chang et al (0.15x0.3) 100 to 800 C 2hr & 4hr ISO 834 fire 1 to 4.5 C/min cooling 1 month Anagnostopoulos et al (2009) carried out an investigation to determine the influence of different fillers on the properties of SCC of different strength classes when exposed to high s. They reported that explosive spalling occured in both the cases of SCC and NCC when the oven peak of 600 C is maintained. SCC was found to spall more compared to NCC due to lower permeability and higher moisture content. SCC with ladle furnace slag in its composition was found to have higher compressive strength at the age of 28 days due to slag s cementitious behavior, but was more susceptible to spalling effects after fire exposure compared to other mixtures. SCC produced with glass filler had greater rheological characteristics at fresh state condition, but did not perform well after heated at high s. SCC produced with limestone filler was found to have better performance compared to mixtures prepared with different filler materials. The salient features of the are shown in Table 11. Table 11: Salient Features of Test Carried out by Anagnostopoulos et al (0.1x0.1 x0.1) (0.15x0.3) 300 min 600 C@70 min 10 C /min load 24 hours 24 hours Udaya kumar et al (2009) carried out an investigation to generate experimental data on residual flexural strength of heated RCC beams and their strengthening using various repair techniques. A total of 25 RCC beams were cast with similar cross sectional details, length and grade of concrete and clear cover. Twenty beams were ed after fire exposure and the remaining five were used as companion beams. The beams were heated in two stages. In the first stage, two beams were kept at each for 3 h between 100 C and 1000 C, in increments of 100 C. Beams exposed to ranging between 100 and 500 C were 934

8 repaired by applying paint. The beams exposed to ranging between 600 and 1000 C were repaired for spalling. In the second stage, all repaired s were again heated. These s were ed for flexural strength after bringing them to room. The variation of flexural strength of repaired RCC beams with increase in has been studied and the flexural strength of beams before and after the repair was compared. The salient features of the are shown in Table 12. Table 12: Salient Features of Test Carried out by Udaya kumar et al Beam (1.2x0.112x0.24) 100 to 1000 C 3hr ISO 834 fire Cooled naturally load Tayfun Uygunoglu and Ilker Bekir Topcu (2009) Studied the effects of aggregate type on the coefficient of thermal expansion of self consolidating concrete produced with normal (SCC) and lightweight aggregate (SCLC) at elevated. Two types of aggregate namely crushed limestone and pumice were used. Different combinations of water/powder ratio and super plasticizer dosage levels were prepared for the SCC and SCLC mixtures. The total powder content (cement and mineral additives) was constant in the experiments. Thermal was performed to accurately characterize the coefficient of thermal expansion (CTE) of SCC and SCLC aged 28 days using the dilatometer. The CTEs of SCC and SCLC were defined by measuring the linear change in length of concrete s subjected to a of s. Test s were varied from 20 to 1000 C at a rate of 5 C/min. The results, in general, showed that SCC has higher CTE than normal weight concrete and that lightweight aggregate reduced the CTE of SCC due to their porous structure. The aggregate type has significant influence on the thermal expansion of SCC. The salient features of the are shown in Table 13. Table 13: Salient Features of Test Carried out by Tayfun Uygunoglu and Ilker Bekir Topcu (0.07x0.07x0.07) (0.15x0.3) 20 to 1000 C 5 C /min Hanaa Fares et al (2009) carried out an experimental study on the performance of selfconsolidating concrete (SCC) subjected to high. Two SCC mixtures and one vibrated concrete were ed. Mechanical and micro structural properties were studied at ambient and after. Compressive strength, flexural strength, bulk modulus of elasticity, porosity and permeability of these concrete were found. For each, the s were heated at a rate of 1 C/ min upto desired target s (150, 300,

9 and 600 C). In order to ensure a uniform throughout the, the was held constant at the target for 1 h before cooling. In addition, the mass was measured before and after in order to determine the loss of water during the. The salient features of the are shown in Table 14. Table 14: Salient Features of Test Carried out by Hanaa Fares et al ( ) 150 to 600 C Peak maintained for an hour 1 C/ min b/w hot 24hr Jin Tao et al (2010) reported the results of laboratory investigations carried out to study the effects of high s ranging from room to 800 C on the compressive strength of SCC and HSC. It was reported that the hot compressive strength of SCC decreased with increase in. It was found that grade of concrete had an effect on the strength loss of concrete, especially in the below 400 C.Higher grades of SCC resulted in higher loss of strength. But this difference was found to be less in the permanent strength loss stage. Compared with normal strength SCC, high strength SCC was found to possess a larger compressive strength when exposed to high. It was also reported that addition of polypropylene fibers decreased the strength.however the addition reduced the probability of explosive spalling. The salient features of the are shown in Table 15. Table 15: Salient Features of Test Carried out by Jin Tao et al (0.15x0.3) 200 to 800 C 5 C/min & 30 C/min above 500 C Hot load Immediate load application Sivaraja (2010) studied the effect of high on mechanical strength properties of five different selfcompacting concrete mixes. Initially five different SCC mixes such as normal concrete, SCC (Self Compacting Concrete) with Fly ash, SCC with silica fume, SCC with rice husk ash and SCC with 20% quarry sand and were designed. The fresh concrete properties such as filling ability and passing ability were ascertained. Specimens were subjected to high up to 500 C and 1000 C for 1 hour in hot furnace. Mechanical properties such as compressive strength, split tensile strength and modulus of rupture were obtained by conducting respective s as per Indian Standards. Results of s subjected to high were compared with the conventional s. The salient features of the are shown in Table

10 Table 16: Salient Features of Test Carried out by Sivaraja (0.15x0.15 x0.15) (0.15X0.3) Beam (0.5x0.1x0.1) 500 and 1000 C Peak for hour 5 C /min cooling & After natural cooling 2. Conclusions From the literature review, concrete s subjected to fire load can be broadly classified into three types namely Stressed, Unstressed, Unstressed residual strength s. It is reported in the literature that behaviour of Normal strength concrete, high strength concrete and self compacting concrete were different when exposed to high. Many parameters influence the results and affect the performance of concrete s exposed to high. Analytical modeling of concrete elements exposed to thermal loads was the missing phenomenon in the review of literature. Since the methods were costly and difficult to carry out, it is necessary to develop analytical modeling. Special attention has to be paid to the material properties for analysis and evaluation of the residual strength of structural elements exposed to accidental fire loading. Further examinations are needed in order to document material properties for design purposes and for the evaluation of residual strength of structural elements exposed to fire. Literature reveals that researchers adopt different procedures for the application of heat load as well as for ing the s. Hence there is a need to carry out an extensive investigation to find out the effect of the variations in the ing procedures. 3. References 1. ElHawary. M.M., Ragab. A.M., Abd ElAzim. A and Elibiari. S., Effect of fire on shear behaviour of R.C beams, Computers & Strucrures 65(2), pp , Chan Y. N., Peng, G. F and Anson M., Residual strength and pore structure of highstrength concrete and normal strength concrete after exposure to high s, Cement and Concrete Composites, pp 2327, ChiSun Poon, Salman Azhar, Mike Anson and YukLung Wong., Performance of metakaolin concrete at elevated s, Cement and Concrete Composites, pp 8389, Kumar.A and Kumar.V. Behaviour of RCC beams after exposure to elevated s, IE(I) Journal CV, 84, November 2003, pp

11 5. Min Li, Chun Xiang Qian and Wei Sun., Mechanical properties of highstrength concrete after fire Cement and Concrete Research, pp , Persson. B., Fire resistance of selfcompacting concrete, SCC, Materials and Structures, 37, November 2004, pp GaiFei Peng, WenWu Yang, Jie Zhao, YeFeng Liu, SongHua Bian and LiHong Explosive spalling and residual mechanical properties of fibertoughened highperformance concrete subjected to high s, Cement and Concrete Research, pp , Metin husem., The effects of high on compressive and flexural strengths of ordinary and highperformance concrete, Fire safety journal, pp , Noumowe. A., Carre. H., Daoud. A and Toutanji. H., HighStrength Selfcompacting concrete exposed to fire Test, Journal of Materials in Civil Engineering November/December 2006, pp Chang Y.F., Chen Y.H., Sheu. M.S and Yao. G.C., Residual stress strain relationship for concrete after exposure to high s, Cement and Concrete Research, May 2006, pp Anagnostopoulos. N., Sideris. K.K and Georgiadis. A Mechanical characteristics of selfcompacting concretes with different filler materials exposed to elevated s, Materials and Structures, pp , P. M. V. Udaya Kumar, M. Potha Raju and K. Srinivasa Rao Performance of repaired fire affected RC beams, Current science, 96(3), 10 February 2009, pp Tayfun Uygunog lu and Ilker Bekir Topcu Thermal expansion of selfconsolidating normal and lightweight aggregate concrete at elevated, Construction and Muilding Materials, pp , Hanaa Fares, Albert Noumowe and Sébastien Remond., Selfconsolidating concrete subjected to high Mechanical and physicochemical properties, Cement and Concrete Research, pp , Jin Tao., Yong Yuan and Luc Taerwe., Compressive Strength of Selfcompacting concrete during high exposure, Journal of Materials in Civil Engineering, October 2010, pp Sivaraja.M., Self compacting concrete under elevated, International J. of Engg. Research & Indu. Appls. (IJERIA). ISSN , 3(II) (May 2010), pp