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1 NRC Publications Archive Archives des publications du CNRC Thermal properties of fibrereinforced concrete at elevated temperatures Lie, T. T.; Kodur, V. K. R. For the publisher s version, please access the DOI link below./ Pour consulter la version de l éditeur, utilisez le lien DOI cidessous. Publisher s version / Version de l'éditeur: Internal Report (National Research Council Canada. Institute for Research in Construction), NRC Publications Record / Notice d'archives des publications de CNRC: Access and use of this website and the material on it are subject to the Terms and Conditions set forth at READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L accès à ce site Web et l utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at PublicationsArchiveArchivesPublications@nrccnrc.gc.ca. If you wish to the authors directly, please see the first page of the publication for their contact information. Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n arrivez pas à les repérer, communiquez avec nous à PublicationsArchiveArchivesPublications@nrccnrc.gc.ca.

2 Ser I THl I R National Research Council Canada I no. 683 Institute for Research in Construction Conseil national de recherches Canada lnstitut de recherche en construction Thermal Properties of FibreReinforced Concrete at Elevated Temperatures by T.T. Lie and V.K.R. Kodur Internal Report No. 683 Date of issue: April 1995 This is an ~nternal report of the Institute for Research in Construction. Although not intended for general distndutlon. it may be cited as a reference in otner publications.

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4 THERMAL PROPERTIES OF FLBREREINFORCED CONCRETE AT ELEVATED TEMPERATURES ABSTRACT T.T. Lie and V.K.R. Kodur Experimental studies were canied out to determine the thermal properties of fibrereinforced concrete at elevated temperatures. The effect of steelfibres on thermal conductivity, thermal expansion, specific heat and mass loss of fibrereinforced concrete at elevated temperatures was investigated. Test data indicate that the steelfibrereinforced concrete, under elevated temperatures, exhibits thermal properties that are slightly different from those of plain concrete. These studies were canied out as part of a research program aimed at developing methods capable of predicting the fire resistance of fibrereinforced concrete columns. ).# ;j^ 'I: ;' &7 p

5 THERMAL PROPERTIES OF FIBREREINFORCED CONCRETE AT ELEVATED TEMPERATURES INTRODUCTION T.T. Lie and V.K.R. Kodur ~nvesti~ations'~.~ have shown that beneficial effects can be obtained by adding discontinuous discrete steelfibres to plain concrete. The use of fibrereinforced concrete, although limited at the present time, is likely to substantially increase once the construction industry becomes aware of these benefits and has access to proper design guidelines. The use of steelfibres as reinforcement in plain concrete enhances the tensile strength of the composite system, reduces the amount of cracking under serviceability conditions and improves resistance to material deterioration as a result of fatigue, impact, shrinkage and thermal stresses. As a result, fibrereinforced concrete can be used to improve the performance of structural members such as columns, floors on grade and + oavements. and to reduce the section thickness of the members. Fibrereinforced concrete is also used in applications such as slabs in nuclear reactors, gravity dams and large furnace supports where thermal stresses could be significant. In the past, the performance of structural members at elevated temperatures, in paaicular at temperatures encountered in fire, could only be determined by testing. Over the years, however, methods have been developed for the calculation of the fire resistance of various structural These calculation methods are far less costly and time consuming than testing. However, to perform these calculations, knowledge of the thermal properties at elevated temperatures of the materials used to construct the members is required. Previous in~esti~ations'.~ have concentrated on the pryerties of fibrereinforced concrete under ambient conditions, and very little information is available on its thermal properties at elevated temperatures. The present study was undertaken to determine the thermal properties of fibrereinforced concrete under the latter conditions. The study was carried out as part of a research project on the fire resistance performance of concretefilled hollow steel sections, which included the use of fibrereinforced concrete filling. The study was conducted at the National Fire Laboratory (NFL) of the Institute for Research in Construction, National Research Council of Canada, with the support of the Canadian Steel Construction Council and the American Iron and Steel Institute. THERMAL PROPERTIES OF FIBREREINFORCED CONCRETE To be able to predict the fire resistance of a structure, the temperatures in the structure must be determined. For such calculations, knowledge of the thermal properties at elevated temperatures of the materials that comprise the structure is requised. Whereas these properties have been established for various commonlyused concretes, this is not the case with steelfibrereinforced concretes. In the investigations discussed in this report, the relevant thermal properties of various fibrereinforced concretes at elevated temperatures were measured. These properties included thermal conductivity, specific heat, thermal expansion and mass loss of the various concretes at elevated temperatures.

6 EXPERIMENTAL DETAILS Three types of concrete specimens, namely, NRCl, NRC2 and NRC3, were investigated. The NRCl specimens were made with siliceous aggregate, while the NRC2 and NRC3 specimens were made with carbonate aggregate. The NRCl and NRC3 specimens were reinforced with steelfibres. Three batches of concrete were made for preparing the three types of specimens. The concrete was designed to produce a 28day compressive strength of 35 MPa. In all three batches, general purpose portland cement for construction of concrete structures was used. The concrete mix in Batch 1 was made with siliceous stone aggregate while the mix in Batches 2 and 3 was made with carbonate stone aggregate. The fine aggregate for all three batches consisted of*silicabased sand. In order to improve workability, a superplasticizer (Mifity 150 ) was added to all three batches and a retarding admixture (Mulco TCDA 727 ) to Batch 1. Premixed concrete, including cement, coarse aggregate, sand, water and retarding admixtures, were supplied by Dufferin Concrete, Ottawa. RIBTEC* steelfibres of the XOREX' type1', supplied by Ribbon Technology Coxporation, were used as reinforcement in Batches 1 and 3. XOREX is a mild carbon steel with tensile strength of approximately 960 MPa. A typical XOREX steelfibre is shown in Fig. 1. The cormgated shape of these fibres provides a strong mechanical bond to the concrete. The fibres, which were 50 mm in length with 0.9 mm equivalent diameter, had an aspect ratio of 57. The mass percentage of steelfibres in Batches 1 and 3 was 1.77 and 1.76, respectively. The mix proportions, together with concrete and steel data for the three batches, are given in Table 1. The steelfibres were added to the fresh concrete and mixed for about 2 minutes to ensure uniform dispersion. Vibrators were used to consolidate the concrete. From each batch of concrete, the following specimens were made: 8 cylinders of 150 mm diameter and 300 mm length 3bricksof200mmx100mmx50mm Compression tests on the cylinders were conducted for each of the samples at 28 days after the pouring of the concrete. The 28day cylinder compressive strengths are given in Table 1. The bricks were used for determining the thermal properties of the concretes. The test specimens for the determination of the thermal conductivity and the thermal expansion were prepared by cutting the bricks to appropriate sizes. Specimens for the determination of the specific heat and mass loss were obtained by grinding a portion of the bricks. ' Certain commercial products are identified in this paper in order to adequately specify the experimental procedure. In no case does such identification imply recommendations or endorsement by the National Rescarch Council, nor does it imply lhat the product or material identified is the ben available for the purpose.

7 THERMAL CONDUCTIVITY The thermal,lconductivity of the concretes was measured using a nonsteady state conduction method. In this method, the temperature rise of a heating wire placed between two specimens is measured. The thermal conductivity of the specimen is determined according to the following relation: where: k = the thermal conductivity of the specimen (W/m C) 9 = the heat generated by the wire (Vim) t,, $2 = time since heating switch is on (rnin) TI, T, = temperature of hot wire at times tl and t2 (OC) A schematic diagram of the system is shown in Figure 2(a). In this system, the thermocouple measures the temperature rise of the heating wire. This temperature rise is automatically converted to the thermal conductivity of the specimen according to Eq. (1) and displayed on the meter. A typical arrangement of specimen, heating wire and thermocouple is shown in Fig. 2(b). The fibrereinforced specimens consisted of two bricks of 100 x 200 x 50 mrn in size. For the measurement of the thermal conductivity at elevated temperatures, the specimens were placed in a furnace chamber and exposed to heating until the desired temperature was reached, at which time the heating wire was activated and the thermal conductivity measured. The thermal conductivity of the three concretes was measured at room temperature, 50 C, 75OC, 100 C and, subsequently, at 100 C temperature intervals up to 1000 C. Two tests were conducted for each concrete type, and the average value obtained in these tests was regarded as the representative value of the thermal conductivity of the concrete. The thermal conductivity for the three types of concretes is shown in Fig. 3, where tabulated values and plots of the them1 conductivity of the three concretes are given as a function of temperature. The thermal conductivity for all three concrete types decreases with increase in temperature up to approximately 400 C. Above this temperature, the thermal conductivity was nearly constant. The addition of steelfibres increases the thermal conductivity of concrete at temperatures up to about 700 C, with the maximum increase at room temperature. This increase in thermal conductivity can be attributed to the fact that the thermal conductivity of steel is about 50 times higher than that of concrete. Previous inve~ti~ations'~ have shown that the thermal conductivity of the aggregates pximarily determines the thermal conductivity of the concrete. In the case of fibrereinforced concrete, the steelfibres also contribute to the thermal conductivity. The thermal conductivity of fibrereinforced siliceous concrete is higher than that of the carbonate concrete throughout the temderature range investigated. This is due to the higher clystallinity of the sieceous aggregates as compared to &at of the carbonate aggregate. The higher the cystallinity, the higher the thermal conductivity and the rate of its decrease with temperature*.

8 SPECIFIC HEAT The specific heat, at constant pressure, was measured using a ~ u~ont' Differential Scanning Calorimeter (DSC) for temperatures up to 600 C. The DSC measurements were carried out on the concretes without the steelfibres, which were removed from the samples. The specific heat of the steel was taken inio account by applying the additive theorem", in which the known specific heat of steel was added to that of the concrete. The tests were conducted with a sample size of 3040 mg in a nitrogen atmosphere and a heating rate of 10 C/min. For measuring the specific heat above 600 C, a ~ u~ont' high temperature Differential Thermal Analyzer (DTA) was used. Two runs of specific heat measurements were canied out: one with powdered sapphire (AL03) as the calibration material and one with the sample. The experiments were carried out in a stepwise heating program. In this program, a period of constant material temperature, during which the measurements were made, was followed by a period of temperature rise, and this was followed again by a period of constant material temperature in which measurements were made. This program was maintained in the C temperature range. The heating rate was 10 C/min. The specific heat of the sample, which is proportional to the temperature difference measured by the DTA, was calculated by comparing the temperature difference measured during the test of the samples with that of the powdered sapphire. The specific heat of the three types of concrete is shown in Fig. 4, where tabulated values and plots of the specific heat of the three concretes are given as a function of the temperature. For all three types of concrete, the specific heat shows a peak at temperatures near 100 C and 425 C. The first increase is caused by evagoration of free water and the second by removal of crystal water from the cement paste. In these temperature regions, most of the heat supplied to the concrete is used for the removal of water and only a small amount is available for raising the temperature of the material. As a consequence, the specific heat increases substantially in these temperature regions. The specific heat of concrete is also affected by other physicochemical processes that occur in the cement paste as well as in the aggregates at temperatures above 500 C. The increase in specific heat for the fibrereinforced siliceous aggregate concrete, at about 550 C, can be attributed to the presence of quartz, which transforms in this temperature region. The steep increase in specific heat, for both the plain and the fibrereinforced carbonate concretes, at about 750 C is due to the presence of d~lomite in the aggregate, which disassociates and absorbs heat in this temperature region. The prcscnce of stcel generally decrcascs the specific hcat of the fibrereinforced concrete. cxccnt in the temderature region near 750 C. This can be amibuted to the fact that the specific heat of steil is generay lower than that of the concrete except in the temperatye region near 750 C, where the specific heat of steel peaks and exceeds that of concrete. However, the influence of the steel on the specific heat of the concrete is very small and insignificant in the temperature range examined. The specific heat of fibrereinforced siliceous aggregate concrete is generally higher than that of plain and fibrereinforced carbonate aggregate concrete. THERMAL EXPANSION The thermal expansion of the concretes was measured using a Theta' dilatory apparatus with a computercontrolled heating and data acquisition system. The specimens were approximately 40 mm long and had square cross sections of 10 to 12 mm The specimens were heated at a rate of 10 C/min temperature rise, measured on the surface of I I

9 the specimen. Two tests were performed on each concrete type and the average of the thermal expansions, measured in these tests, was taken as the thermal expansion of the concrete. In Fig. 5, the thermal expansions for the three concrete types are shown as a function of the concrete temperature. For the fibrereinforced siliceous aggregate concrete, the thermal expansion increases with temperature up to about 600 C and then remains constant. The considerable enhancement of the thermal expansion near 550 C can be attributed to transformation of quartz in the siliceous aggregate. A comparison of the thermal expansion of fibrereinforced siliceous concrete with that of plain siliceous concrete15 indicates that the steelfibres somewhat increase the thermal expansion. The plain and the fibrereinforced carbonate concrete have similar thermal expansions up to a temperature of about 850 C. Above 850 C, the thermal expansion of the plain concrete declines somewhat, due to further dehydration and shrinkage of the concrete", whereas the expansion of fibrereinforced carbonate concrete increases steeply with temperature. This steep increase with temperature can be attributed to the presence of the steelfibres, which continue to expand at an increasing rate. MASS LOSS The mass loss for the three concrete types was measured by means of a ~ u~ont' 9900 Thermomavimetric Analvzer (TGA). The mass loss measurements were carried out on the concreres without the &elfibres, which were removed from the concrete. The mass of the steel was taken into account by adding the known mass of the steel to that of the concrete. The specimens, which had a mass between 30 and 60 mg, were placed in a nitrogcn atmosphcrc and hcatcd at a rate of 10 C/min. The test data from the TGA are presented in Fig. 6 in the form of thermogravime+t curves for the three types of concretes examined in this study. Previous studies have indicated that the type of aggregate has strong influence on the mass loss and, therefore, on the density of the concrete at elevated temperatures. The mass loss for all three concrete types is vely small until about 600 C, where it is about 3% of the original mass. Between 600 C and 800 C, the mass of plain and fibrereinforced carbonate aggregate concrete drops considerably with the temperature. Above 800 C, the mass loss again decreases slowly with temperature. The curves and the tabulated values in the figure show that the influence of the steelfibres on the mass loss is vely small and insignificant in the whole temperature range examined. In the case of fibrereinforced siliceous aggregate concrete, the mass loss remains insignificant even after 600 C. SUMMARY AND CONCLUSIONS Experimental and theoretical studies were carried out to investigate the influence of steelfibre reinforcement on the thermal behaviour of concrete at elevated temperatures. Two types of fibrereinforced concrete, namely, a siliceous and a carbonate aggregate concrete were studied, and the thermal behaviour of these concretes was compared to each other and to that of a plain carbonate aggregate concrete. The results and conclusions can be summarized as follows: 1. The thermal conductivity of steelfibrereinforced concrete decreases with increasing temperature. For carbonate aggregate concrete, it is higher than that of plain concrete. The difference in thermal conductivity between these concretes decreases

10 with increasing temperature up to approximately 700 C. At this temperature, the thermal conductivity of the plain concrete exceeds that of the fibrereinforced carbonate concrete. However, above 1500 C, the differences are about 10% or less and not significant. 2. The specific heat of steelfibrereinforced carbonate concrete is slightly less than that of plain concrete in the temperature range C, except for the temperature region near 750 C, where the specific heat of fibrereinforced carbonate aggregate concrete slightly exceeds the plain concrete. The influence of steelfibre reinforcement on the specific heat of the concrete is very small, however, and negligible in the whole temperature range investigated. The specific heat of siliceous aggregate concrete is higher than that of carbonate aggregate concrete up to a temperature of approximately 750 C, where the specific heat of the carbonate aggregate concrete increases steeply, and considerably exceeds that of the siliceous aggregate concrete. 3. The thermal expansion of concrete is not significantly affected by the presence of steelfibre reinforcement at temperatures up to approximately 800 C. Above this temperature, the thermal expansion of the fibrereinforced concrete increases considerably above that of the plain concrete. 4. The mass loss of concrete is not significantly affected by the presence of steelfibre reinforcement in the investigated temperature range of C. 5. Overall, steelfibrereinforced concrete, at elevated temperatures, exhibits thermal properties that are similar to those of plain concrete.

11 REFERENCES 1. Karneda Y., Koizumi, H., Akiham, S., Suenga, T. and Banno, T., Studies and applications of steel fiber reinforced concrete, Report No. 31. Kajima Institute of Construction Technology, Tokyo, Japan, October 1979,46 pp. 2. Swarny, R.N. and Lankard, D.R,. Some practical applications of steelfibrereinforced concrete, Institution of Civil Engineers, Proceedings, Part 1, Vol. 56, Au~. 1974, pp Craig, R.J., Structural applications of reinforced fibrous concrete, Concrete International, Dec. 1984, pp Lie, T.T., Editor, Structural Fire Protection: Manual of Practice, ASCE Manual and Reports on Engineering Practice No. 78, American Society of Civil Engineers, New York, NY, 1992,241 pp. 5. Friedman, R., An international survey of computer models for fire and smoke, Journal of Fire Protection Engineering, Vol. 4, No. 1, 1992, pp Sullivan, P.J.E., Terro, M.J. and Moms, W.A., Critical review of firededicated thermal and structural computer programs, Journal of Applied Fire Science, Vol. 3, NO. 2, , pp Cook, D.J. and Uher, C., The thermal conductivity of fibrereinforced concrete, Cement and Concrete Research, Pergomon Press, Vol. 4, No. 4, 1974, pp Testing and test methods of fibre cement composites, RILEM Symposium 1978 Proceedings, The Construction Press, Lancaster, UK, 545 pp. 9. Schneider, U., Editor, Properties of materials at high temperatures concrete, REEM, Deparhnent of Civil Engineering, Kassel University, Kassel, Germany, 1985, 108 pp. 10. Carbon steelfibres for concrete reinforcement, Ribbon Technology Corporation, Gahanna, OH, 6 pp. 11. Thermal conductivity meter (TC31), Instruction Manual, Kyoto Electronics Manufacturing Co. Ltd., Tokyo, Japan, 21 pp. 12. Harmathy, T.Z., Thermal properties of concrete at elevated temperatures, ASTM Journal of Materials, Vol. 5, No. 1, Mar. 1970, pp Lie, T.T., Fire and Buildings, Applied Science Publishers Ltd., London, 1972, 276 pp. 14. Lie, T.T. and Allen, D.E., Calculation of the fire resistance of reinforced concrete columns, National Research Council of Canada, Division of Building Research, NRCC 14047, Ottawa, 1972,44 pp. 15. Hu, X.F., Lie, T.T., Polomark, G.M. and MacLaurin, J.W., Thennal properties of building materials at elevated temperatures, Internal Report No. 643, Institute for Research in Construction, National Research Council of Canada, Ontario, 1993, 54 PP. 16. Harmathy, T.Z. and Allen, L.W., Thermal properties of concrete of selected masonry unit concretes, ACI Journal, Vol. 70, No. 2, Feb. 1973, pp

12 Table 1. Batch quantities and properties of steelfibrereinforced concrete mix 8

13 UNIQUE CRESCENT CROSS ON Figure 1. Typical XOREX steelfibre reinforcement used in the concrete mix

14 i I I Power aourca tor (a) Block diagram for measuring Thermal Conductivity (b) Arrangement of sample. heating wire. and thermocouple Figure 2. Schematic diagram and sample arrangement for thermal conductivity test

15 I I 1 I I I I I I Fibre reinforced siliceous concrete... Fibre reinforced carbonate concrete... Plain carbonate concrete.....*......:: T I I 1 I I 1 1 I 1 Temperature ("C) Figure 3. Thermal conductivity for various concrete types as a function of temperature

16 I I I I I I I...*..*... Fibre reinforced carbonate concrete Plain carbonate concrete Fibre reinforced siliceous concrete I I I 1 I I 1 I Temperature PC) Figure 4. Specific heat for various concrete types as a function of temperature

17 I I I t 1 I I I I..*..*... Fibre reinforced siliceous concrete Fibre reinforced carbonate concrete Plain carbonate concrete /".. /+.(......, I I I 1 I I I 1 I Temperature ("C) Figure 5. Thermal expansion for various concrete types as a function of temperature

18 I I I I I I 1 I I..a.. *.:a Temperature ("C) :. :\. :\ Fibre reinforced siliceous concrete Fibre reinforced carbonate concrete :\... :. Plain carbonate concrete _..._. I 1 I I I I Figure 6. Mass loss for various concrete types as a function of temperature