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Technical Note (National Research Council of Canada. Division of Building Research), 1962-08-01
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Identification of Materials in Fire Endurance Testing
Harmathy, T. Z.
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SUBJECT IDENTIFICATION OF MATERIALS IN FIRE ENDURANCE TESTING
Those who have read fire test reports issued by the Division of Building ｒ･ｳｾｾｲｯｨ of the National Researoh Counoil know that a signifioant portion 'of these deal with the speoifioation of the materials used in the test sample. The sponsors of fire tests generally do not objeot to the
inolusion of this kind of information in the report. They realize that an aoourate speoifioation of the speoimen is
just as important a part of the test report as the 'des-oription of the testing prooedure or the presentation of the results. It is quite understandable, however, that some sponsors, generally those manufaoturing proprietary produots, sometimes prefer the omission of oertain information. As will be pointed out later, even in these oases it is not diffioult ,to find a oonvenient way of aoourately speoifying all oomponents of the test sample without disolosing any oonfidential information.
Sinoe the praotioe of presenting a detailed speoifioation of all oomponents of the speoimen is not general among fire enduranoe testing laboratories, it may be useful to devote this short note to a disoussion of the reasons for this praotioe.
Firstly, the information inoluded in the report should be adequate for the aoourate identifioation of all materials used in the speoimen, from the point of view of
their part played in giving the oonstruotion its oharaoteristio fire-enduring quality. There are three different ways in which the materials oan be identified. The first may be oalled a
,
-
2-"descriptive" or "analytical" identification. If the report gives sufficient details about the source of the materials, their appearance, composition, the manufacturing procedure
(if ｾｰｰｬｩ｣｡｢ｬ･ＩＬ and how they are arranged in the test specimen, it is conceivable that a construction erected
exactly according to this description will have approximately the same fire endurance as the specimen for which a classifi-cation has been issued. An advantage of this kind of identifi-cation is that the information that forms the basis of the
description is directly obtainable from the supplier or from relatively simple laboratory tests. There are, however, several disadvantages of this type of identifioation. For example, it is not always obvious which information is essential from the point of view of fire endurance. A common example of inaccurate identification is to specify a concrete by giving only the amount of portland cement, sand, gravel and water used in the miX, and neglecting to mention the sieve analysis, bulk density of the aggregates and mineralogical composition. It is a well-known fact that, among the characteristics of the aggregates, the
mineralogical composition has a marked effect on the thermal properties of concrete and thus on the fire endurance of the whole construction.
Another major disadvantage of the descriptive
procedure is that it is difficult to use for the identifica-tion of proprietary products. In this case, data concerning the composition of some materials or the manufacturing
procedure, which actually shOUld form the fundamental part of any descriptive identification, cannot be included in the test report.
A more accurate way of identifying the materials is by means of their thermal and mechanical properties. From the point of view of their behaviour in fire, such information as the source of materials, their appearance, and composition is only of secondary importance. What an
engineer is ac"tually interested in is the thermal and
mechanical characteristics of the materials which directly affect the behaviour of the construction in fire. This kind
of identification is superior to the descriptive identifica-tion, and can be used without revealing confidential informa-tion about the composiinforma-tion or manufacturing procedure of
proprietary products.
The only disadvantage of this practice is that special, and sometimes fairly expensive, apparatus and
instruments are needed to measure the thermal and mechanical properties of the materials involved, in the appropriate
temperature intervals. At present very few commercial laboratories have such facilities.
There is a third kind of identification which may
be called "identification by characteristic curves." Certain
experimentally determined curves, such as the differential thermal, thermogravimetric, and dilatometric curves provide excellent ways of identifying materials or mixtures of
materials without revealing too much about their over-all
composition or their manufacturing procedure. These curves
also offer valuable information about some physico-chemical changes taking place at elevated temperatures, e.g. dehydra-tion, crystalline transformation and dissociation.
In the fire test reports issued by the Division of Building Research, these three ways of identification are
used. The sponsors are usually requested to have a reputable
testing laboratory furnish the Fire Research Laboratory with 'all the information that will serve as a basis for the
descriptive identification. In order to avoid receiving
irrelevant data, the Fire Research Laboratory of DBn supplies the sponsors with data sheets which list the information
that is important from the point of view of the fire-enduring
ｱｵ｡ｾｩｴｹ of the various materials.
The most important thermal properties (thermal
conductivity, thermal diffusivity, specific heat and coefficient of thermal expansion) of the basic components of the test
specimen are automatically determined and reported by the
Fire Research Laboratory. At present, the values of these
properties at room temperature only are the subjects of
investigation. It is hoped, however, that as laboratory
facilities develop, complete thermal conductiVity versus temperature, enthalpy versus temperature, and thermal
expan-sion versus temperature curves for the 80 to 18000F range
will be included in the test report.
The Fire Research Laboratory has facilities to test the mechanical properties (stress-strain relation,
modulus of elasticity, creep, etc.) of any building materials
in the 80 to l8000F interval, and to determine differential
thermal, thermogravimetric, and dilatometric curves which may be important for the identification of proprietary products.
The second reason for presenting detailed informa tion on the materials in the test 'report is to supply a basis for the correct interpretation of the test results and, in this way, facilitate the development of improved
constructions. The correct interpretation of the test
results is especially important when the construction fails
to give the expected performance. It may also be important
in such cases when the fire endurance turns out to be much higher than that aimed for, thus indicating that the
con-struction may not be economical.
4
-The availability of certain information may also' prove very useful during the production or installation,
when, for example, the replacement of some material by another material, or changes in the geometry of the product are
contemplated. If the thermal and mechanical properties of the materials involved are known; a decision can be made without performins further full-scale fire tests. The rules given in a paper (1) may often be used when estimating the
roesible effect of such changes on the performance of the .
construction.
On the basis of recent developments in the theory of fire endurance rating, there is good reason to believe that in the not too distant future the Itdesign for fire endurance" will also be p,0ssible. By means of numerical methods (2) the Ittherma1 , fire endurance of any building
element can be calculated if the thermal properties of the materials forming the construction are available. Although such calculations are often too complex for everyday use, steps have already been taken to present the results of such calculations in graphical form or in the form of simple design rules.
In this note, an effort has been made to explain Why the Fire Research Laboratory puts great emphasis on the
inclusion of detailed information on the materials of oon-struction in the fire test reports. This practice is by no means in conflict with the interests of the manufacturers; on the contrary, this practice reduces the number of necessary full-scale fire tests and provides a basis for the design of more economical bUilding elements. In other words, it helps the Canadian bUilding industry to produce better fire-enduring constructions at lower cost.
REFERENCES
1. Harmathy, T. Z. Ten rules of fire endurance rating. (In process).
2. Harmathy, T. Z. A treatise on theoretical fire endurance rating. Amer. Soc. Testing Materials, Symposium on Fire Test Methods. ASTM Special Technical Publication No. 301, p. 10-40, 1961. (Reprinted as NRC 6305).
