^

3

'

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

421.05 - 4212151 23 May 1966 9323

PROBLEMS IN DEVELOPMENT OF PERFORMANCE STANDARDS

by

Bruce E, Foster

NOT FOR PUBLICATION

Presented at the

Annual Meeting

of the

Society of American Military Engineers

IMPORTANT NOTICE NATIONAL BUREAU OF

j for use within the Governmen

and review. For this reason, whole or in part, is not autl Bureau of Standards, Washin

the Report has been specifica

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

;ress accounting documents intended

is subjected to additional evaluation

ire listing of this Report, either in the Office of the Director, National by the Government agency for which

I copies for its own use.

I). S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PROBLEMS IN DEVELOPMENT OF PERFORMANCE STANDARDS

By

Bruce E. Foster

The performance concept in building has been the subject of a great

deal of discussion and study during the past several years. A Building

Research Advisory Board Committee on this subject has conducted two

National conferences, and other groups are discussing the meaning and

usefulness of the concept. At the National Bureau of Standards, the programs of the Building Research Division now have an emphasis in the direction of development of performance methods.

In the broadest sense, the performance concept is applicable to all

segments of the building process, including determination of the functional

requirements of the user, the design, the fabrication, and the operation

and maintenance. It should be applied to materials, components, construction systems, or whole structures. The performance concept can bring

about an orderly systematic approach to the whole of the building process.

If fully developed, it could furnish also a powerful incentive for innovation, both in acceptance of new materials and the acceptance of new designs

and building methods.

This brief discussion will be concerned only with the narrower field

of performance requirements for materials and components. Performance is

certainly nothing new to specification writers. Except in those cases

where standards are deliberately written in such a manner as to exclude

competitive products, the specification writer, or the test developer,

strives to insure a material or product which will give satisfactory per-
2

formance under the conditions of its intended use. Some specifications

are of the prescription type, and specify composition, proportions, sizes,

and the like, which have been demonstrated by long-time experience to

correlate with satisfactory performance. Often the specification will

consist only partly of prescription- type requirements with the balance

depending on performance-type test procedures such as those which measure

properties like strength or viscosity, or which employ an accelerating aging

process to estimate the long-time performance of the material or product.

As an example, most portland cement specifications have a 5.0% maximum

limit on magnesium oxide, because it is known that some forms of magnesium

oxide which may occur in portland cement can, after several years, cause

a substantial expansion of concrete. The autoclave expansion test, which

subjects cement mortar to steam pressure at 420°F, a condition seldom

approached in the use of concrete, is an accelerated per formance- type

test also included in U. S. cement specifications to give an indication

of the expansion that may develop at later ages due to the presence of

certain forms of magnesium oxide or of other constituents in the cement.

Prescription and per formance- type requirements, such as those just

mentioned, have usually served their purpose well, but with the continual

development of new materials and new uses for these materials, efficient

utilization makes it desirable to develop test procedures which not only

are of the performance type, but also are applicable, with a certain

amount of judgement, to all materials proposed or potentially suitable

for a particular use.
3

Two recent projects in the Building Research Division have been

conducted using the performance concept. They have been concerned

primarily with test methods, leaving the setting of performance levels

to other organizations. In developing performance requirements for

external cladding, and test procedures to evaluate such performance for

any type of proposed material, it was necessary first to decide on the

functional requirements of the cladding. Among other things the cladding must serve to impede the movement of moisture and air. It must

present an acceptable appearance, and one which may be readily maintained. It must satisfactorily resist indentation from objects such as

hailstones or baseballs, and it should remain functional for a long

period of time, usually for the expected life of the house. In drawing

up a list of such properties, the Bureau staff quickly recognized that

the level of performance of the cladding material is certain to be

influenced by the other parts of the wall. The cladding must therefore

be evaluated in combination with the other components with which it will

be used in actual construction. And now other factors, such as rate of

heat transfer, sound transmission, rate of moisture flow into the interior

of the wall with its potential damage, production of smoke and fumes during

a fire, and contribution to the strength of the wall system, also become

of importance and must be tested.

In spite of all of the complicated interactions, it was possible to

make a reasonable list of performance items for which established tests

should be applied, or modified or new methods developed. The one variable
- 4 -

which was not adequately accounted for is time. The measurement of longtime durability under specific anticipated usage and environment is a

particularly elusive, difficult task. Time was not neglected by choice

and indeed some accelerated aging and cycling was included.

Much effort has been expended toward development of accelerated

aging tests for specific materials. The very fact that these tests must

be accelerated tests precludes, in most cases, the direct simulation of

natural exposures, and of course there is no such thing as a standard

natural exposure with which to make a correlation. The development of

an accelerated aging test which would be applicable to all types of

materials is even more difficult, because different materials react to

the various elements of weathering in entirely different fashions. Organic

materials, for example, are generally vulnerable to ultra-violet light

and to elevated temperatures, whereas inorganic materials remain relatively unaffected. The absorption of moisture in inorganic materials,

on the other hand, may bring about one or more destructive actions which

might be totally absent in organic materials.

The second MBS program was directed at bathtubs. Considered in the

study were porcelain-enameled cast-iron tubs, porcelain-enameled steel

tubs, and reinforced plastic tubs and shower assemblies. Again it was

necessary first to list the performance elements of importance in a bathtub. Such items as resistance to static and dynamic loads including sharp

impacts, dimensional stability, the effects of changes in temperature,

resistance to staining and burning, ease of cleaning, resistance to
>

5

cleansing agents and other chemicals which might come in contact with

the fixture, and the overall useful life of an item whose replacement

would, in many cases, create substantial structural problems, need to

be evaluated.

Here again tests developed by others were in some cases adopted

unchanged, and in some cases adopted in a modified form. In others,

new test methods were improvised, and in all cases the test procedures

were applied to representative samples of various types of available

tubs. The program took a great deal of organized thinking, and it

was built upon a great deal of previous thinking by other investigators.

The tests recommended included cycling treatments of temperature, loads,

cleaning, exposure to ultra-violet light, and the like, but again

development of a procedure for estimating the long-time useful life

was not accomplished.

In spite of difficulties, the performance concept is a most useful

tool and a great amount of work should be done in developing test procedures whereby the performance of materials, composites, assemblies,

and more complicated systems can be evaluated in terms of likely results

to be anticipated under specific usage and situations. Many people

prominent in the promotion of the performance concept are fully aware of

the difficulties in developing adequate test methods. Unfortunately

others appear to ignore the variable, time. There is a test method for

measuring the strength of concrete at the age of 28 days. There is no
6

test method for predicting the strength at 28 years. There is an ASTM

laboratory test procedure for measuring the rate of air leakage through

windows. It is recognized that a procedure needs to be developed for

measuring the leakage of the window actually in place in the building,

because of the effects that installation may have on this property, but

no-one knows how to develop a test which will predict the leakage of the

window after it has been in place for ten years and subjected to deterioration of the calking, and the racking brought about by temperature

differentials and wind -loads

.

For some time to come, the per fomance- type tests will have to be

supplemented by technical judgement rendered by experts experienced in

the properties of materials, and the probable interactions as these

materials are put together to form products, composite units, and larger

and more complicated building systems.