AUG 8 1961

NBS MONOGRAPH 28

Causes of Variation in Chemical Analyses

and Physical Tests of Portland Cement

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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UNITED STATES DEPARTMENT OF COMMERCE . Luther H. Hodges, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Causes of Variation in Chemical Analyses

and Physical Tests of Portland Cement

B. Leonard Bean and John R. Dise

National Bureau of Standards Monograph 28

Issued April 27, 1961

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, DC. - Price 25 cents

Preface

It is believed that reference to this Monograph will enable a cementtesting laboratory to identify and eliminate many of the more frequently

encountered causes of random or constant errors in test results. In consideration of the fact that some laboratories exhibit a tendency to obtain high values in comparison with computed averages for certain tests, while other laboratories are always low; the reader is cautioned to bear in

mind that the attainment of reproducibility through elimination of one particular source of variation does not, necessarily, indicate that accuracy has

also been attained. It therefore seems advisable for each laboratory to con- duct general inspections of equipment and procedures at regular intervals, and

it is suggested that this compilation would be a helpful reference in these

operations.

m
Contents

Page Preface hi

1. Introduction 1 Part I. Possible causes of error in cement analysis. 1

2. General precautions in chemical analysis 1 2.1. The weighing operation 1 2.2. Ignition procedures.. 2

2.3. Desiccation 3

2.4. Additional precautions 3

3. Silicon dioxide 4

4. Ammonium hydroxide group 4

5. Total iron as ferric oxide 5

6. Aluminum oxide 5

7. Calcium oxide 5

8. Magnesium oxide 6

9. Sulfur trioxide 6

9.1. Turbidimetric method 6

9.2. Gravimetric method 7

10. Sulfide sulfur 7

11. Loss on ignition 7

12. Sodium oxide and potassium oxide 7

13. Phosphorus pentoxide 8

14. Manganic oxide 8

15. Insoluble residue 8 Part II. Possible causes of variation in physical

tests of portland cements 9

16. General considerations in the physical testing

of cements 9

16.1. Laboratory 9

16.2. Treatment of samples 9

16.3. Mixing water 9

16.4. Measurement of mixing water 9

16.5. Standard sands 10

IT

Page

16.6. Weighings 10

16.7. Timing device 10

16.8. Oiling of molds 10

16.9. Specimen storage facilities 10

16.10. Storage period for molded specimens. 10

16.11. Removal of specimens from molds 10

16.12. Marking specimens 11

16.13. Trowels 11

16.14. Care and cleaning of apparatus 11

17. The determination of fineness 11

17.1. Common causes of variations 11

17.2. The turbidimeter fineness test 12

17.3. The air permeability fineness test 13

18. Consistency 14

18.1. Mixing of pastes by hand 15

18.2. The normal consistency determination. 15

18.3. Mechanical mixing of mortars 16

18.4. The flow table test 17

19. The autoclave soundness test 17

20. Time of setting 19

20.1. Common causes of variations 19

20.2. The Vicat time of setting test 19

20.3. The Gillmore time of setting test 19

21. The heat of hydration test 20

22. The determination of the air content of mortar 20

23. Strength of mortars 21

23.1. Common causes of variations 21

23.2. The compressive strength test 22

23.3. The tensile strength test 23

24. References 23
Causes of Variation in Chemical Analyses and Physical Tests of

Portland Cement

B. Leonard Bean and John R. Dise

(June 7, 1960)

Variations in testing that could lead to the rejection of a material fully conforming to

specification requirements, or the acceptance of a material with undesirable chemical or physical properties, are apparent in the results reported by laboratories participating in comparative tests of portland cements. Many of the causes for variation in chemical analyses and physical test results are listed in this discussion, and remedies for some of the more

frequently encountered deficiencies in apparatus and methods are suggested. Particular consideration is given to problems which do not seem to have been covered in sufficient detail

in previous discussions of cement testing procedures. Literature references are given for additional information.

1. Introduction

Man}7 of the organizations engaged in the testing

of portland cements have found it advantageous

to use frequent interlaboratory tests on carefully

prepared samples of the material to evaluate the

performance of the laboratories involved. A re- port on a recent comprehensive effort of this kind was submitted to the American Society for Testing Materials at its 1959 Annual Meeting in Atlantic City, New Jersey [1].*

j All too frequently, variations in testing that

could lead to the rejection of a portland cement

fully conforming to specification requirements, or

the acceptance of one with undesirable properties, are apparent in the results reported by the participants in these programs. This is due in large measure to the fact that many steps are involved

in making the standard chemical analyses and

physical tests, and that the results are sometimes

greatly influenced by seemingly minor variations

in equipment and procedures. Many of these influences have been taken into account in the

preparation of the standard methods of test. However, it is not uncommon to find that inadequate attention has been given to certain important specification requirements because their

significance is not fully understood, or that essential considerations are overlooked simply because

they are not readily apparent. For these reasons

it has been suggested that a discussion of the

causes of variation, in which particular attention

is given to matters not already covered in detail in current publications, might prove helpful to laboratories participating in comparative test programs such as the recently established Cement

Reference Sample Program of NBS.

Part I. Possible Causes of Error in Cement Analysis

B. Leonard Bean

The suggestion was made that this author compile information on analytical techniques,

both from personal experience and from the literature, which might aid analysts in securing

uniform and reliable results. The suggestions which follow, it is hoped, will benefit one who

is seeking some means to bring his own results into line with the average values reported by

all chemists taking part in a co-operative study.

2. General Precautions

2.1. The Weighing Operation

The weights used in interlaboratory analyses

should conform to Class S-l requirements of

NBS Circ. 547. The weights of 1 g and larger

units should preferably be made of stainless steel or other corrosion and abrasion-resistant alloy

not requiring protective coating. These weights

which are used for regular work should frequently

be checked against a reference set of standard

weights which conform to Class S (or Class M)

•Figures in brackets indicate the literature references at the end of this Monograph.

requirements. This reference set should contain

weights from 50 g to 10 mg. The material used

to adjust the weights should have properties of

corrosion and abrasion resistance comparable to the material of the weights. Nickel-chromium

resistance wire is recommended as adjusting

material as it is highly constant and generally

available. If weights have been variable, the

cavities should be cleaned carefully and all old

adjusting material should be removed and drilled out when necessary. Guard against traces of

materials such as oil, corrosion products, or miscellaneous unidentified adjusting material.

Whenever a weight from a working set is known

to have been dropped, it should be cleaned and

1
its weight checked carefully against weights from

a reference set before further use. In such in- stances and whenever the full accuracy of the

weights is required the certified corrections to each individual standard weight should be made

as part of the weighing procedure. When weights

from a reference set which carries NBS certifica- tion are involved in an accident such as being

dropped to the floor, the Bureau calibration of the

weights involved in the accident must be considered to be in doubt. Such weights should be

returned to the Bureau for recalibration.

Balances are now sold with many added features

to speed the weighing process: damping devices,

notched beams to accommodate poises, chains,

projected direct-reading scales, and sets of built-in

weights. These can save weighing time. It must

be recognized, however, that each such added

device may contribute to the error of the weighing.

Tests must be made occasionally to assure freedom

from significant errors. Electrostatic effects must be guarded against in

all weighing operations. Sometimes grounding

the balance is helpful. The claim is made for certain radioactive materials on the market that

they may be placed in the balance to ionize the

air and permit the charge to flow away from

insulating materials. The moisture that may

condense on a dry crucible on a balance pan, due

to humid atmospheres, can be compensated to some extent by placing a tare crucible on the

other balance pan; this expedient cannot be used,

of course, with a balance of the single-arm type

with only one pan.

A balance or set of weights which is suspect may

be returned to the manufacturer for repairs, adjustment, or modernization. There are several persons

who travel through the country specializing in

repairing and adjusting balances and weights.

Although they probably cannot maintain all the

equipment and facilities which a balance or weight

manufacturer has at his disposal, use of their

services does minimize the length of time the

balance or set of weights is out of use in the laboratory. In addition, the balance or weights does not

require transportation after adjustment on the

spot. A balance put into excellent condition by a manufacturer may suffer a mishap while being

returned to its home laboratory, which undoes all the careful adjustment made on it. Excellent information on testing balances and

the terminology used in describing the performance

of balances may be found in Federal Specification

AAA-B-92 [2] ; and articles published in Analytical

Chemistry by the Committee on Balances and

Weights in the Division of Analytical Chemistry

of the American Chemical Society [3], and by

Lashoff and Macurdy [4].

2.2. Ignition Procedures

Where platinum crucibles are used, they should,

in general, be made of pure platinum, that is, not

intentionally alloyed with other platinum metals.

At the temperatures of 1,100 and 1,200 °C used for certain ignitions in cement analysis, other alloying

metals are liable to volatilize slowly and "vitiate the results obtained. Such alloyed crucibles or

lids are sold and used for some purposes because

they are stiffer and do not deform as readily as pure platinum. Some manufacturers have

equipped pure platinum crucibles with alloyed I lids to obviate sticking of crucible and lid. Such ; practice may be permissible at lower temperatures

than those used in cement analysis. Any empty

crucible and lid which consistently loses more than

0.2 mg per hr at 1,200 °C should be suspected [5]. Use of an empty alloyed crucible and correction for

the loss it sustains applied to the crucibles containing precipitates is liable to lead to erroneous

results. The alloying metal covered with precipitate will probably not volatilize at the same rate

as in the empty crucible.

The beginning of the ignition of a precipitate

contained in a wet filter paper should be made at a rate slow enough so that no spattering, popping,

or flaming occurs. After the moisture is expelled

the paper should be "smoked off." Then, when

all danger of flaming is past, the crucible maybe

placed in a muffle furnace which is at the proper

temperature for final ignition.

Some check on the temperatures of the muffle

furnaces is advisable from time to time. Contamination of thermocouples may occur resulting in erroneous temperature readings. A standard thermocouple and portable potentiometer may be

used to check the accuracy of the thermocouples

and temperature-indicating devices ordinarily

used. The National Bureau of Standards issues a copper melting-point standard, No. 45c, which

melts at 1,083.3 °C. Use of pyrometric cones may

be helpful in checking temperatures [6]. E. T. Carlson [7] recommends a modification of

Roberts' technique [8] utilizing the melting point

of potassium sulfate (1,069.1 °C) as a check on

muffle temperatures. Carlson breaks up the

K2S04 with a mortar and pestle and places about

a gram in each of several covered platinum crucibles. These are placed at several points in the

furnace with the indicated temperature somewhat

below 1,069 °C. They are removed and inspected

at about 15 min intervals. The indicated temperature of the muffle is raised by 10 °C intervals.

In this manner the temperature of the various zones in the furnace can be estimated. Almost

invariably the K2S04 in the back of the furnace

will melt first and that at the front last. One must

not be confused by an inversion that takes place

in K2 S04 at about 583 °C, but without melting.

The K2S04 was first crushed to avoid the spattering that takes place on inversion.

When igniting precipitates in a number of

crucibles, six, for example, it is well to reverse the

order of the crucibles when about half the ignition

period has elapsed. Thus crucible No. 1 which

may at first have been at the front of the furnace

in the coolest position will spend the remainder of

2
the time in the back of the furnace which is usually

the hottest zone. (In some furnaces, the middle

portion may be hottest.) It should be borne in

mind also that the temperature shown by the

indicating device is the temperature of the end of

the thermocouple. If the thermocouple is covered

by a protective tube, as is usually the case, the

temperature of any one crucible on or near the

floor of the furnace will probably differ somewhat

from the thermocouple temperature. The position

of the thermocouple is important. It should be

near the middle of the heated zone. If it is accidentally bumped while placing crucibles in the

furnace, it may be so misplaced that it no longer

indicates the average furnace temperature. The

thermocouple position should be checked every

time the muffle furnace is used.

2.3. Desiccation

No absolute rules can be given for desiccation.

The time and technique which will give satis- factory desiccation while the crucibles are cooling

to room temperature so that they can be weighed,

may be a function of many factors: t. Size of the

desiccator, 2. the number of crucibles, their

weight, and the weight of the contents, 3. the

character or composition of the contents, 4. the

material of which the desiccator is constructed,

5. the temperature and relative humidity in the

room, 6. the desiccant used, and 7. the degree to which the lid fits the desiccator. An excellent

discussion of the subject is given by Hillebrand,

Lundell, Bright, and Hoffman [9]. In general,

sulfuric acid or anhydrous magnesium perchlorate

are the preferred desiccants for cement analysis.

Either is satisfactory in glass desiccators; obviously, sulfuric acid should not be used in an aluminum desiccator. The lid should be ground

to fit the desiccator on which it is used. Generally no difficulty is encountered in purchasing glass

desiccators whose lids fit properly. A well- constructed aluminum desiccator has the advantage over glass of speeding the cooling of ignited

precipitates, but, in the writer's experience, the

lids rarely fit properly and require regrinding

before use. It has been claimed that the cost of

such grinding by the manufacturer would be prohibitive. Ordinary silicone stop cock grease (not

High-Vac) is a good sealing and lubricating

material for aluminum desiccators if the lids fit. Petrolatum is satisfactory for glass desiccators.

When the lid of a desiccator fits and is lubricated

properly, air will be heard to rush in when the

cooling period (usually 30 to 60 min) is over and

the lid is opened slightly by cautiously sliding or by opening a valve, if the desiccator is so equipped. If this sound is not heard one is always uncertain as to how much moisture-laden room air may have entered the desiccator during

the cooling period. Care must be exercised to avoid blowing precipitates out of the crucibles by

this inrushing air. If a desiccator has been found

not to have been kept tightly closed overnight, it

is good practice to recharge with fresh desiccant.

Hot crucibles should never be placed in a desic- cator at quitting time and then weighed in the

morning. Such weights will seldom agree with

those obtained after the usual cooling period.

Weighings made just prior to quitting time should

be viewed with suspicion if there has been any

tendency to shorten the usual desiccating period

in favor of leaving at a given hour. Crucibles

and contents which appear to gain weight on the

balance during weighing may have been left in

the desiccator for too short a period. Slightly

warm crucibles cause convection currents in the

balance and affect it in other ways which generally

result in a weight which is too low and somewhat

unstable during the weighing period. This latter phenomenon may be superimposed on the uncertainty involved in weighing hygroscopic materials which have been properly cooled for a suffi- cient length of time in a good desiccator.

Ignited silica, ammonium hydroxide group

(R2 03), and calcium oxide should be treated as hygroscopic materials, or potentially so, and kept

tightly covered in the crucible during desiccation

and weighing. Calcium oxide should be desiccated over magnesium perchlorate or preferably, phosphorus pentoxide and weighed as rapidly as

possible.

It is not easy to know when a desiccator should

be recharged with fresh desiccant. G. Boehm

[9, p. 33, note 22] describes a technique 1 for checking the effectiveness of sulfuric acid as a drying agent, by using acid containing 18 g of

BaS04 dissolved in each liter. Some analysts

have found it useful to mix a few pieces of indicating Drierite with magnesium perchlorate in a

desiccator; when the blue color changes to pink

the desiccant should be discarded. In fact, it probably should have been discarded prior to

that. Most laboratories do not have the vacuum

equipment required to reactivate magnesium

perchlorate and prefer to discard the used material

and recharge the desiccator with fresh material.

2.4. Additional Precautions

Filter paper should be visually inspected before

folding and, of course, discarded if evidence of a weak spot or a hole is detected.

A piece of glass broken from a wash bottle tip

is an occasional cause of high results. Failure to decompose the sample of cement

completely in the initial hydrochloric acid treat- ment can lead to erroneous results for almost all subsequent determinations.

Silicone stopcock grease is not recommended for use in burettes. It may tend partially to water1 ". . .no precipitate will form in sulfuric acid containing 18 g of dissolved barium sulfate per liter until enough water has been taken up to reduce the concentration of acid to about 93 percent. Between 93 and 84 percent, needlelike crystals of BaS0)-2H2 S04-H20 separate freely. On further dilution by

absorbed water, the needlelike crystals change to fine crystals of BaS04, at which point the acid is no longer effective as a drying agent."

3
proof the inner surface of the burette. Silicone

grease can be removed from a burette by use of

fuming sulfuric acid. Extreme caution must be

exercised in using fuming sulfuric to avoid injury.

Individual Determinations

Many of the statements which follow are in- tended to apply to comparative analyses in which,

presumably, the utmost in accuracy is sought.

Less rigorous techniques may be satisfactory for routine analyses, where conformance to specification requirements is not in doubt.

3. Silicon Dioxide

High Results. For the determination of silica,

ignition temperature of 1,200°C for at least one hour is recommended, with subsequent heating

periods of 30 min at the same temperature until

constant weight within 0.2 mg has been established

[10, also 9, p. 679].

Recovery of residual silica from the ignited

ammonium hydroxide precipitate together with a

correction for the silica recovered from a reagent

blank can lead to high results. This is discussed on page 682 of [9], where the importance is stressed

of adding as much iron and alumina to the reagent

blank as is contained in the sample being analyzed.

This is time-consuming and makes necessary the

use of two blanks, if silica is to be recovered: one containing nothing but reagents in order to correct the R203 for filter paper ash; the other

with added iron and alumina to carry down silica from the reagents and glassware. The present

ASTM method [11] does not take this into account. The present Federal method [10, Method 1101,

pars. 3.1.1 and 3.1.2] does not require the recovery

of sdica from the R2 03 because the amount in- volved is likely to be almost insignificant, the

probable errors of recovery high, and the time

required excessive.

Low Results. In careful work, the HF residue can generally be kept below 1 mg in cement analysis. If the referee (double dehydration) method

is used this residue should seldom be more than

half a milligram. Whenever the HF residue is much higher than these values, uncertainty in

results for silica exists, usually tending to give low

silica values. (Subsequent determinations of other

constituents may also be affected.) Impurities

may be weighed as chlorides during the ignition

of the crude silica and as sulfates or oxides after treatment with HF and H2 S04

. The error can be

minimized by following the usual dilute HC1

(1:99) and water washings of the precipitated

silica with one or two washings with dilute H2S04 (1:4) or by moistening the combined papers

containing the silica with a few drops of dilute

sulfuric acid before drying and igniting [12, also 9, p. 863]. Thorough washing of silica to remove

contaminants is the best insurance against high

HF residues. The higher the HF residue the more

error can be introduced if the contaminants are not present in the same form before and after

treatment with HF and H2S04 [9, p. 681]. Special

precautions need to be taken in washing when

the optional ammonium-chloride method of silica separation is used. The bulk of the gelatinous

silicic acid should be transferred to the funnel

without dilution with water and the small volume

of concentrated acid solution allowed to drain

through. Thorough washing with hot HC1 (1:99)

and then hot water follow. It is useful to tear

off small pieces of filter paper and use them to- gether with a rubber policeman to scrub the inside

of the beaker thoroughly in order to remove all adhering silica. This use of filter paper should be

delayed until no more ferric chloride color can be

seen. If the scraps of filter paper are added to the funnel too soon, their presence impedes the

washing procedure and causes high HF residue.

Low results for silica can be caused by baking

the second dehydration at temperatures over

110 °C or for longer than 1 hr. Such treatment

can cause recombination of silica and magnesia,

resulting in formation of an acid soluble silicate

[9, p. 678].

4. Ammonium Hydroxide Group (R203) High Results. In the determination of the

ammonium hydroxide group ignition of R203 at 1,100 °C for one hour is recommended, followed

by subsequent 30-min ignition periods until con- stancy of weight within 0.2 mg is indicated.

If 10 to 15 ml of HC1 is not present before

neutralization with NH4OH, coprecipitation of some magnesium Irydroxide with the R203 may

occur. The presence of that quantity of HC1

insures the formation of a sufficient amount of

NH4C1 so that the ionization of NH4OH is depressed to a point where insufficient hydroxyl ion

is present to exceed the solubility product of

Mg(OH)2

. Ammonium chloride also tends to keep magnesium in solution by formation of an ammonia complex, assists in buffering the solution, and aids in coagulation of the precipitate.

Use of ammonium hydroxide which contains

carbon dioxide can cause coprecipitation of calcium

and magnesium carbonates. Reagent ammonium

hydroxide bottles should be kept stoppered to prevent contamination. Digestion of the ammonical solution and precipitate should not be

prolonged beyond 10 min. Otherwise C02 may

be absorbed from the air. The results for R2 03 may be affected by the

completeness of recovery of silica in the previous

step. Any silica which has escaped the double

dehydration or ammonium-chloride separation

will cause high results for R2 03 unless a careful

recovery of residual sdica is made with due regard

for a properly determined blank. In addition, a reagent blank correction must be made to correct

for the impurities in the reagents and for the filter paper ash. This blank will generally amount to about 0.5 mg.

Low Results. Failure to neutralize with ammonia to the exact end point will cause low results.

4
Stopping short of the methyl-red end point will

leave some hydroxides unprecipitated. Going

past the end point of methyl red by more than the one drop of 1:1 NH4OH prescribed, will redissolve

alumina and cause low results. The presence of

any iron in the ferrous condition will cause results to be low because ferrous hydroxide is not quantitatively precipitated at this pH. Whenever fer- rous iron is suspected, such as by a blackened

precipitate, redissolve with hydrochloric acid, add

four or five drops of concentrated nitric acid, and

boil for a few minutes to oxidize all the iron. Then

precipitate with NH4OH as before. It may be

necessary to add more methyl-red indicator from

time to time because of the effect of the nitric

acid on the indicator. In the event the first precipitation of R2 03 has

been completed at the end of the working day,

the filter paper together with its precipitate

should not be treated with acid, pulped up, and

allowed to stand overnight in this condition. It may even be better not to do this over a lunch

hour. In a strongly acidic environment organic

matter from the filter paper pulp tends to complex some of the aluminum and prevent completeness

of precipitation on subsequent treatment with

NH4OH [9, pp. 66 and 98]. In this respect filter paper may act a little like tartaric or citric acid.

Use of filter paper for this separation which is less retentive than Whatman #40 is not recom- mended because some Fe(OH)3 might pass

through.

5. Total Iron as Ferric Oxide

In the determination of iron, the reduction

process with stannous chloride is critical. If less than the required amount is added, results will be low. An excess of one drop after the yellow

color of ferric ions disappears, will give satisfactory

results provided the specified concentration of stannous chloride is used. This solution has a tendency to become more concentrated on standing in the presence of metallic tin. After cooling

to room temperature and adding the mercuric

chloride solution, a small amount of white silky

precipitate should be in evidence. If none appears, insufficient stannous chloride was used

and the determination should be repeated. The

presence of much mercurous chloride is also objectionable because it may become oxidized.

If the precipitate is gray, it indicates the presence

of finely divided elemental mercury because too much stannous chloride had been used. In the

latter event, also repeat the determination because

the results will be high [12, pp. 573 and 580].

After reduction with stannous chloride, the

solution should be cooled in a cool water bath and

the remainder of the determination completed

immediately thereafter. The reduced solution

should not be allowed to stand overnight before

titrating; air oxidation could cause low results.

6. Aluminum Oxide

Alumina is not actually determined in cement

but is calculated by difference. The ammonium

hydroxide precipitate in cement is assumed to consist of AI2O3, Fe2 03 , Ti02 , P205 , and residual

Si02 , together with possible traces of Zr02 , V2 03 , and Cr203 . If, as is usually done, only the per- centage of Fe203 is subtracted in the calculation,

the results for A12 03 will always be expected to be high by the amount of the other undetermined

oxides. Any error in the R2 03 or Fe2 03 determinations will cause corresponding errors in the

A1203 percentage reported. Note the suggestions

given in the two preceding sections.

7. Calcium Oxide

High Results. In the determination of calcium

oxide high results can be caused by failure to remove manganese, or to separate iron or alumina

completely. When the optional method is used,

the results obtained may be either high or low

depending on the degree of washing with hot water. The suggestion in the specification method to use about 75 ml of hot water in washing will generally

be satisfactory. However, variations in size of

wash bottle tips, lung power of individual chemists,

and the degree to which the precipitated calcium

oxalate is churned up during washing, will cause

variations in the result. It is suggested that

each analyst occasionally analyze a sample of NBS Standard No. 177 and vary his operations

throughout the analysis, particularly his washing

technique, until he is able to get CaO values close to the certificate value for that cement. If the

final titration in the presence of the added filter paper is prolonged unduly some of the paper

will be oxidized. The one-hour standing period

for precipitation of the oxalate is critical and

should not be prolonged lest coprecipitation of magnesium result. It is difficult to ignite CaO to constant weight

for the referee determination. Ignition at 1,200

°C for at least one hour is recommended, followed

by heating at the same temperature for 30-min

periods until constancy of weight within 0.2 mg is indicated. The crucibles should have well fitting- covers. Magnesium perchlorate is preferable to

sulfuric acid for desiccating CaO. Phosphorus

pentoxide is definitely superior to either. The

second weighing of CaO should be made in reverse order from the first weighing to detect any errors due to standing in a desiccator already opened.

It is especially necessary to rotate the crucibles

in the furnace for the CaO ignition.

Low results. The presence of C02 during the

precipitation of the ammonium hydroxide group

can cause some of the calcium to precipitate there

instead of later as the oxalate. This was dis- cussed more fully under the R2 03 precipitation.

Failure to wash the R203 precipitate adequately

may leave calcium absorbed on the gelatinous

precipitate.

582426—61 2 5
8. Magnesium Oxide

There are many precautions to be heeded in

order to obtain correct results for the gravimetric

determination of magnesium. The subject is covered thoroughly in authoritative discussions

by Hoffman and Lundell [13], Kolthoff and Sandell

[12, p. 352-62], and Hillebrand, Lundell, Bright,

and Hoffman [9, p. 636-40]. It is impossible in a paper of this type to list more than a few pre- cautions to be observed in the determination of

magnesium by either the phosphate or oxyquinolate method.

High Results. If manganese has not been re- moved—and it is not mandatory—high values for magnesium may be obtained by the oxyquinolate

(optional) method.

Use of filter paper that is too coarse for filtration of R2 03 may allow iron to run through and increase

the subsequent MgO values. A green precipitate

of what is supposed to be magnesium oxyquinolate

is evidence of contamination by iron. This may

also be caused by failure to keep all the iron in

the ferric state during its precipitation and washing. The magnesium oxyquinolate precipitate

should be yellow.

Berman found [14] that this method gave high

results even after manganese removal in the case

of cements containing over 2 percent MgO.

When the phosphate (referee) method is used,

any mechanical loss of calcium by creeping over

or passing through the filter paper, will produce

high results for magnesium because of coprecipitation of calcium phosphate.

If the ignition of magnesium ammonium phosphate in the presence of filter paper is carried out

too rapidly, incorrect results, either high or low,

may be obtained. The carbon may become partially fireproofed, rendering it impossible to burn

it out [9, p. 637]. Or, the pyrophosphate may be

slowly reduced and phosphorus volatilized. This

latter action can ruin a platinum crucible. It is probably safer to ignite such precipitates in porcelain. The final ignition temperature should be

1,100 °C. At 1,200 °C, as permitted in some

specification methods, the pyrophosphate slowly

loses weight [12, p. 359].

Low Results. Absence of sufficient NH4 C1 during the R203 precipitation will cause some of the

magnesium to precipitate there and subsequent

values for MgO will be low.

During the calcium precipitation, if the oxalate

is added to an ammoniacal solution, or if the solution and precipitate are boiled, some coprecipitation of magnesium will result [12, pp. 347-8]. Older

specification methods recommended such procedure and some laboratories may still be using

this technique, causing low magnesium results. Berman [14] reported low results for MgO by

the optional oxyquinolate method at levels less than 1 percent MgO.

In the phosphate (referee) method, supersaturated solutions of magnesium ammonium phosphate sometimes prevent complete precipitation

in the case of low magnesia contents. This can be remedied by longer standing before filtration. It is generally advisable not to discard the filtrate from the phosphate separation for at least one day so that in the event postprecipitation does

occur, the additional precipitate may be filtered

off and added to the main precipitate. The blank

should be treated in the same manner. The amounts of ammonium oxalate called for in the specification methods for precipitation of

calcium, generally do not leave enough excess to interfere with the magnesium determination ac- cording to Kolthoff and Sandell [12, p. 360]. In

a few instances, in the author's experience, re- moval of oxalate and ammonium salts by evaporation with 75 ml of nitric acid [9, p. 133] and [12, p. 370] has increased the amount of magnesium

ammonium phosphate that could be precipitated

from certain cements. For very careful work, the

additional time consumed may be warranted.

9. Sulfur Trioxide

9.1. Turbidimetric Method

' I li.i & | When the optional, turbidimetric, method is used for the determination of sulfur trioxide, it is recommended that the operator study Rudy's

paper [15] upon which the specification method

was based. It contains many excellent suggestions and precautions to be observed: necessity

for close control of temperature, changes of variables which require preparation of a new calibration curve, and necessity for maintaining fairly

uniform BaCl2 -2H2 0 crystal size. In connection

with the latter point, a further precaution might

be in order. It is usual to separate a rather large

supply of the BaCl2 -2H2 0 that will pass a No. 40

sieve and be retained on a No. 80 sieve, because a new calibration curve must be prepared every

time a new batch is sieved. If, however, the

operator should fall into the habit of shaking the

bottle before taking out each scoop of crystals in

the mistaken idea that mixing is desirable, he will actually change the crystal size by such shaking

and obtain incorrect results. If four or five months have elapsed since the supply of crystals was sieved, it is advisable to resieve the BaCl2

- 2H2 0 and prepare a new calibration curve anyway. The crystal size may have changed just by

standing.

Molded glass sedimentation tanks should be

used for S03 determinations because hydrochloric acid solutions are liable to dissolve the

material used to hold the glass together in forming

the other type of tank.

Many of the suggestions given under 17.2 in Part

II of this Monograph will be helpful in maintaining

the turbidimeter in proper operating condition.

6
9.2. Gravimetric Method

From a study of the discussions on the determination of sulfur as barium sulfate in wellknown textbooks such as those by Kolthoff and

Sandell [12, pp. 322-335] and Hillebrand, Lundell,

Bright, and Hoffman [9, pp. 711-722], one almost

reaches the conclusion that it should be impossible

to obtain the correct result by precipitating

BaS04 in the presence of all the constituents of

Portland cement. Evidently, the reasonably good

results generally obtained are because compensating errors just about balance each other. It will be noted in the certificate of analysis of NBS

Standard Sample 177 that J. R. Spann, of our

laboratory, reported a value of 1.59 percent S03 found in that cement. His method of determination included reduction of iron with hydroxylamine, addition of BaCl2 solution rapidly and

treatment of the ignited BaS04 with HF to remove silica [12, pp. 329, 330, 332]. In comparison with this value of 1.59 percent by a refined

method, Spann obtained values of 1.56 percent

and 1.63 percent S03 for the same cement by the

ASTM and Federal referee specification method.

Failure to wash out all the occluded BaCl2 , or

to burn off all the carbon of the filter paper, are probably the two most common causes of high

results. A digestion time much shorter than 12 hr

generally leads to low results. After filtration,

the precipitated BaS04 should be washed thoroughly with hot water, as stated in the specification method. The temptation to use dilute HC1

solution for washing in order to remove iron stains

must be avoided. Any Fe2 (S04) 3 present already

has a lower molecular weight than its equivalent

amount of BaS04 and will probably lose its S03 during ignition. Washing out the Fe2 (S04 ) 3 with

acid will make the results still lower. The silica occluded possibly compensates for the lower

weight caused bv some of the sulfate coming down

as Fe2 (S04) 3 . Slow ignition with good access of air will avoid

reduction of BaS04 .

10. Sulfide Sulfur

The evolution method for sulfide sulfur [16] is not regarded as being the most accurate available.

However, it is fairly rapid, and even though all the assumptions upon which it is based may not

hold rigidly, it is widely used throughout industry.

11. Loss on Ignition

High Results for Portland Cement. If the ignition temperature is too high, approaching 1,200

°C, S03 will be lost and some alkali volatilized.

This will not only cause high results but will make

it difficult to attain constant weight. A muffle

furnace with an accurate temperature control is much to be preferred to ignition over a gas burner

where the temperature can only be estimated.

A 1 g sample of hot cement takes a long time to

cool in a desiccator. If it is weighed slightly

warm, low weights can be obtained which cause high results. Generally, at least 1 hr in the

desiccator is required.

Sulfide-Containing Cements. Recent work of

several investigators has shown that the regular

ignition loss procedure used in the analysis of Portland cement is not applicable to cements containing sulfide constituents. ASTM and Federal

methods have been recently revised to include

suitable corrections, based on an additional sulfate

determination performed on the ignited material

together with suitable calculations.

Chaiken [17] indicated that a direct ignition

method utilizing a helium atmosphere gave satis- factory results for blast-furnace slag cements.

12. Sodium Oxide and Potassium Oxide

No attempt will be made to discuss the gravimetric determination of sodium oxide and potassium oxide in cement because it has been rather

extensively covered in standard texts [9, pp. 925-

930] and is now seldom used because of the greater

ease of using flame photometry for the purpose.

In general, the flame photometric determination

of potassium is rather straighforward and not

subject to many sources of error within the ac- curacy generally required in cement analysis. The

same cannot be said for the sodium determination.

Errors, if present, generally tend to give slightly

low results. The calcium present emits light in

the same wave length region, 589 m/x, at which

sodium is measured. Silica, present in varying

amounts in cement, inhibits the emission of calcium. Because the standard solutions used do

not normally contain silica, this leads to somewhat

low results for sodium (by a few hundredths of a percent) unless the silica is removed [18]. In fact, one or two cements manufactured domestically

contain such a low content of Na20 that some

flame photometers indicate a slight negative Na2 0

content if silica is not removed. It is rather embarrassing to try to report a negative Na2 0 content for a sample of cement. Flame photometers

equipped with adjustable-width slits can be made

to minimize this effect by using a rather nairow

slit. Some older flame photometers of the motordriven chopper type tend to give low results if the motor mountings become loose.

If the standard solutions are stored in glass

bottles for several months, a small amount of sodium may be leached from the glass. This

makes the actual sodium content of the solution

higher than its nominal value. This can cause

results reported for sodium oxide to be low by a few hundredths of a percent. An exchange between constitutents of the glass and the solution

may occur under some conditions. The best

remedy is to store the standard solutions in polyethylene bottles. These have the added advantage

of not supplying any chips of glass to plug up

the atomizer.

7
13. Phosphorus Pentoxide

The only referee specification method described

for the determination of phosphorus pentoxide in

cement is the ASTM method [11, pp. 77-78] in

which the phosphorus is first isolated as ammonium

phosphomolybdate and finally precipitated as magnesium ammonium phosphate, ignited, and

weighed as magnesium pyrophosphate. This is a

classical method. The majority of portland

cements in this country probably contain not over one tenth of a percent P2 Os. Results obtained are

liable to be low because of the tendency of magnesium ammonium phosphate to form supersaturated solutions when the phosphorus content

is low. It is not unusual for one to find that the

blank weighs slightly more than the pyrophosphate

obtained from one of the samples. Filtrates from

the magnesium ammonium phosphate precipitation should not be discarded for several days. If any evidence of postprecipitation occurs, it should

be filtered off, ignited, and the weight so obtained

added to that already found. The blank should

be treated in the same manner. The addition of

the same measured volume of a standard solution

of a phosphate to each sample as well as to the

blank is one means of dealing with this difficulty.

By this procedure there is less tendency for the

formation of supersaturated solutions. The author

would like to suggest that the respective ASTM

and Federal committees give consideration to incorporation of a spectrophotometric method for

determining the small amounts of phosphorus

pentoxide in portland cements.

14. Manganic Oxide

The bismuthate method for determining manganic oxide [11, pp. 78-79 and 9, pp. 443-446] is fairly straightforward. A few precautions might

be emphasized. It is important that the 1:33

HN03 added after oxidation with NaBi03 , be

completely freed of HN02 by boiling. In the

titration it may take practice to recognize the end

point. This is the point at which no further color

change can be noted on further addition of sodium

arsenite. The end point of the solution should be

observed in a strong light and against a white

background. Here, again, it is suggested that a spectrophotometric method for determining manganic oxide in portland cement would be a welcome

addition to the specification methods.

15. Insoluble Residue

Halstead and Chaiken made a thorough study

of the various factors affecting results obtained

for the insoluble residue determination. Their

published [19] recommendations have been used as the basis for recent revisions in ASTM and Federal

specification methods. These modifications be- came necessary largely because the previous

specification methods were not giving reproducible

results for slag cements. These investigators

recommended more specific requirements for heating equipment, dilution and digestion techniques, and thorough washing.

Concluding Remarks

It is generally recognized that analytical chemistry still is a mixture of science and art. As long

as this situation prevails there will be differences

in results obtained by different analysts for the same sample of material. The suggestions given

in this paper are presented with the hope that

they may be of some assistance in minimizing

these differences in the analysis of cement.

The author acknowledges advice and assistance

from the Mass and Scale Section of NBS on material pertaining to weighing and weighing equipment.

8
II. Possible Causes of Variation in Physical Tests of

Portland Cements

(John R. Dise)

The physical properties of portland cement for which specification requirements and

standard methods of test have been developed are Fineness. Soundness, Time of Setting, Heat

of Hydration, Air Content of Mortar, Compressive Strength, and Tensile Strength. Fineness tests are made on the cement itself ; soundness, time of setting, and heat of hydration tests are made on pastes consisting of cement and water; and the air content, compressive strength,

and tensile strength tests are made on mortars consisting of cement, water, and a natural silica sand. In the following discussion of the possible causes of variation in these tests, particular at- tention is given to matters not already covered in detail in current publications. A limited amount of background information, including the year in which each method was first published by the American Society for Testing Materials, has been incorpoiated in the belief that it will foster greater appreciation for the efforts that have been expended in the development of the details of the tests. A brief description of each method has also been included in order that the discussion might have more meaning for a casual reader.

16. General Considerations in the

Physical Testing of Cements

Important considerations which are generally

applicable to several or all test procedures are discussed herein. It is intended that the pertinent parts of this section be considered an integral part of all subsequent sections.

16.1. Laboratory

(a) Temperature and relative humidity. The

atmosphere of a laboratory can have a significant

effect upon the behavior of mixes and test specimens, and for this reason the standard methods of

test for cements require that the relative humidity

be maintained at not less than 50 percent, and the

temperature between 20.0 and 27.5 °C. In nearly

all instances, automatically controlled conditioning

equipment must be used in order to accomplish this. Drafts of air as well as low relative humidity can

cause rapid evaporation of water from both mixes

and specimens, and therefore mixing slabs and test- ing apparatus should be shielded from excessive

drafts from air conditioner duct outlets, and also from direct sunlight and local sources of heat such

as radiators, steam pipes, hot plates, autoclaves,

and ovens.

(b) Lighting. The laboratory should be well

illuminated with both natural and artificial light so that operators will have no difficulty in reading

instruments and gages or dials on test apparatus.

(c) Arrangement of equipment. Equipment

should be so located that all items are readily

accessible to laboratory personnel. Piling and

jamming of apparatus is to be avoided because

these conditions promote carelessness in testing

and create safety problems.

16.2. Treatment of Samples

Aeration of cement markedly affects its physical characteristics. For this reason, samples

should be kept in air-tight, moisture-proof containers from the time they are taken until all tests

are completed. Before testing, each sample should

be passed through a No. 20 sieve in order to mix

the sample, break up lumps, and remove foreign

materials. Foreign materials and hardened lumps

that do not break up on sieving or brushing should

be discarded. An unusual amount of lumpy material may be an indication that moisture is present

in the sample.

16.3. Mixing Water

In general, water fit for drinking is considered

to be satisfactory for use in the testing of cement

if it does not contain abnormal concentrations of a particular mineral or minerals. In instances

where the suitability of the mixing water is questioned, it may be helpful to compare results

obtained with that which is customarily used to

results obtained with distilled water. Water from

specimen storage tanks should not be used in the

preparation of mixes.

It is required that the temperature of mixing

water be maintained between 21.3 and 24.7 °C.

Since the temperature in outside pipes will vary

over a broad range in any 12-month period, it is usually necessary to make special provisions for bringing the temperature of tap water within the

specified range prior to use. With respect to time of setting and strength

tests, it may be helpful to bear in mind that warm

water hastens the hardening of cement and cold

water retards it.

16.4. Measurement of Mixing Water

Mixing water should be measured in a clean

glass graduate of the capacity and type specified

in the applicable test method. In no case should

the capacity be more than twice the volume re- quired in the mix. A graduate which is not clean

will not deliver the indicated amount of water,

and for that reason frequent cleaning with dilute

HC1, or a suitable glassware cleaning solution, is recommended.

9
Significant errors can sometimes be attributed

to bad practices in reading graduates. A technique which avoids a number of possible variations consists of permitting the filled graduate to come to rest in a vertical position while it is held

lightly at the top between the tips of two fingers; after which the elevation of the hand is adjusted

to bring the bottom of the meniscus into a horizontal plane with the line of sight. The readingis made using the bottom of the meniscus.

The degree of uniformity being attained in these

measurements should be checked periodically by

weighing a series of measured volumes of the same

magnitude on a mix balance. In this check, the

graduate may be used as both the weighing container and the measuring device. It may be of

interest to compare the weights thus obtained

with the theoretical weight of a given volume of

water, at the temperature involved, as derived

from a standard volumetric table.

16.5. Standard Sands

The two gradations of natural silica sand from

Ottawa, Illinois, used in making mortars for test purposes are customarily referred to as Standard

Sand and Graded Standard Sand. Because a number of other gradations are also prepared by

the processing plants, it is advisable for a laboratory to check each new shipment to ascertain

that the proper sand has been received.

Contamination of the sand with an agent ca- pable of entraining air in mortars sometimes occurs during processing, shipment, or storage. In many

instances, the first evidence of an accident is a

substantial mcrease in the air content, or a noticeable decrease in the strength, of test mortars.

The test method for air-entrainment of standard

Ottawa sand developed by DeFore and Corah [20] provides a convenient way in which to determine

whether or not a given lot of sand is contaminated.

Another is to run parallel check tests with sand

which is considered to be uncontaminated.

16.6. Weighings

(a) Mix balance. The balance should be

mounted on a plane, nonskid surface, on a vibration-free table with a rigid top. It should be

shielded from direct sunlight and from stray cur- rents of air. The permissible variation on balances

at loads from 1 to 2 kg should be ± 1 g. (b) Mix weights. A common mistake in weighings is the use of mix weights which do not conform

to the accuracy requirements of the various cement

test methods. The difficulty can usually be at- tributed to the loss of slugs from a "two-piece"

weight, or surface wear on the bottom of a solid

weight. Because of the wear problem, it is most

desirable that weights be lifted rather than skidded

from one location to another, and that they be

stored in a suitable wooden block when not in use. Every laboratory should be equipped with a spare

set of new mix weights which can be used for periodic checking of the weights in daily use.

16.7. Timing Device

One or more timing devices, preferably those

equipped with sweep second hands, should be so located that operators oan conveniently observe

the time from any point in the laboratory. In

general, stop watches and pocket watches are less suitable than devices such as wall clocks and

bench-type timers with large faces.

16.8. Oiling of Molds

Several of the test procedures require that the

surfaces of molds be thinly covered with mineral

oil. Nondetergent oil is preferable. Animal fats or vegetable oils should not be used in lieu of

mineral oils.

16.9. Specimen Storage Facilities

Well made specimen storage facilities are essential. Some of the important considerations are as

follows:

(a) Temperature. It is required that the temperature of the air in a moist cabinet or moist

room, and the temperature of the water in a stor- age tank, be maintained between 21.3 and 24.7 °C.

Many cement testing laboratories have found it necessary to install automatic controls in order to maintain storage temperatures within these limits.

(b) Relative humidity. It is required that the

moist closet or moist room, be so constructed as to provide storage facilities for test specimens at a

relative humidity of not less than 90 percent.

Specimens in storage should both look moist and

feel moist.

(c) Storage of filled molds. It is intended that

molds containing specimens be so stored that the

upper surfaces are freely and uniformly exposed

to the atmosphere of the moist storage unit.

Molds should not be piled one upon the other in

such a way that the plates of the upper molds

exclude ah from the specimens beneath. When

sprays are used to humidify the moist storage unit,

precautions should be taken to prevent water from

falling upon the surfaces of freshly molded speci- mens.

16.10. Storage Period for Molded Specimens

Molded specimens are to be stored in a moist

atmosphere until they have attained the age of

24 hr, at which time they are either tested or placed in water storage. In no case should speci- mens be removed from the molds until they are at

least 20 hr old. If removed before 24 hr have

elapsed, they should be placed on the shelves of the

moist storage unit until the expiration of the 24-

hr period.

16.11. Removal of Specimens from Molds

Specimens which are damaged during mold

stripping operations should be discarded even though the damage may be considered to be slight.

10
Damage to test specimens, and also to molds, can

be minimized if a rawhide hammer is used to apply the gentle taps usually needed to break the

bond between mold and specimen. When stripping is completed, care should be taken to insure

that mold parts are not inadvertently interchanged. In many instances, the dimensions of

molds will not conform to specification requirements after an interchange of parts.

16.12. Marking Specimens

Reliable identification marks, preferably numerals, must be made on each test specimen if errors due to mistaken identity are to be avoided.

The marks should be made on paste specimens,

such as the Gillmore pat and the autoclave bar,

immediately after they are formed. Identification tags should be used for freshl}7 molded mortar

specimens such as briquets and cubes. Under no

circumstances should identification of a specimen

depend upon its position on a shelf or table, or its proximity to a marked specimen. When mortar

specimens, such as briquets and cubes, are removed

from moist storage, the identification should be

marked on the bottom surfaces with a soft crayon

after the plates have been removed, but while the

specimens are still in the molds. A graphite

crayon will make very distinct and durable markings. Colored crayons should not be used because

their marks may fade very quickly after specimens

are placed in a water storage tank. The practice

of using a sharp tool to scratch marks in the sur- faces of mortar specimens is objectionable.

16.13. Trowels

The specifications require that the trowels used

in making specimens have steel blades, 4 to 6 in. in

length, with straight edges. Many operators have

found that a slightly curved blade is of great

assistance in making briquets. Such trowels are not to be used for other purposes. Damaged,

blunt, or badly worn implements should not be

used in any operation.

Excessive troweling of the paste in a Vicat ring

or an autoclave bar mold often occurs after the

surface of the material is torn in the process of

slicing off that which projects above the top edge

of the mold. Torn and uneven surfaces will be

encountered frequently when an implement with

blunt edges is employed, and therefore, it is advantageous to reserve a trowel with specially sharpened

edges for use in the preparation of paste specimens.

16.14. Care and Cleaning of Apparatus

It is usually difficult, if not impossible, to obtain

satisfactory test results with testing apparatus

which is not clean, and for this reason much

helpful information on cleaning has been incorporated in the various cement testing standards.

Particular attention is invited to the fact that

power-driven wire brushes and brushes with steel

bristles are not suitable for use in cleaning molds.

Numerous situations arise wherein the laboratory

finds it necessary to adjust the weight of test apparatus. A common mistake on these occasions

is the failure to clean the apparatus prior to starting

the adjustment. Another is the use of an inaccurate balance or weight for checking the work.

These mistakes may have a very significant effect in tests employing a Vicat apparatus, the Gillmore

needles, or a 400-ml measure.

17. The Determination of Fineness

The literature advises that fineness has long

been recognized as one of the important physical

properties of a cement. Early tests were based on

the use of sieves and it was not until 1933 that a

satisfactory replacement, the Turbidimeter Fineness Method, was introduced. Another new test, the Air Permeability Fineness Method, was introduced in 1943. Currently, both of these procedures

are used as standard tests of cement.

17.1. Common Causes of Variations

Although the two fineness tests are distinctly

different in technique and theory, there are a number of considerations which are of importance

in either procedure. Some of these are presented

herewith.

(1) Problems with the standard fineness sample.

Although great care is taken in the blending and

packaging of standard fineness samples, an occasional vial is found to be unsuitable for calibration

purposes. It therefore is advisable to check the

calibration of an instrument with a freshly opened

sample whenever an unexpected difficulty is en- countered. The risk of contaminating fresh samples with glass chips when the containers are opened

may be reduced if opening is accomplished by

inverting the vial and pressing the sides in the

empty section against a thin, curved, high-resist- ance wire mounted between the terminals of a

small transformer.

(2) Exposure of apparatus to a source of variable

heat. The location of a turbidimeter or an air permeability apparatus above, or near, a source

of variable heat such as a radiator, hot plate, oven,

or autoclave, may cause considerable variation in

test results.

(3) Errors in calculations. Among the common

errors in calculations are the following: (a) Mistakes in the use of arithmetic, algebra, or logarithms, (b) Errors in the transcription of figures,

(c) Mistakes in the use of slide rules and other

calculating devices, (d) Selection of the wrong

equation for a basic calculation.

(4) Conversion of one test value to another by means of afactor. Since the air permeability value

is frequently about 1.7 times greater than the

turbidimeter value, this factor is sometimes used

in converting from one test value to the other.

The practice is unsound because the results in

these tests may be affected by such unpredictable

11
influences as differences in the ignition loss of a cement from day to day, or differences in the

particle size distribution caused by variations in

grinding, and values obtained in this manner may

be seriously in error.

17.2. The Turbidimeter Fineness Test

The method of test for fineness of portland

cement by the turbidimeter was introduced in a paper presented by L. A. Wagner in 1933 [21], and adopted as a standard test for cement in 1934.

The procedure provides for the determination of

specific surfaces by measurement of the turbidities

of cements in liquid suspensions. Essentially,

the turbidimeter consists of a source of light of

constant intensity adjusted so that approximately

parallel rays of light pass through a suspension of

cement in clear white kerosene and impinge upon

the sensitive plate of a photoelectric cell. The

current generated by the cell is measured with a microammeter and the indicated reading is a measure of the turbidity of the suspension. The

turbidity is in turn a measure of the surface area

of the suspended cement.

An attractive feature of the test is that it provides a means for determining the particle size distribution as well as the specific surface of portland cements. This advantage has been nullified to a certain extent, however, by the difficulties a laboratory encounters in maintaining all of the

various elements of the apparatus in satisfactory

operating condition, and in teaching new operators

to make the determination. It is important to bear in mind that the test is not intended for use

in determining the fineness of materials other than

Portland cement.

17.2.1. Causes of Variations

A. Apparatus

(1) Apparatus improperly mounted. Vibration

of the wall, or other object, to which the shelf supporting the sedimentation tank has been

fastened may disturb the suspension and thereby

affect test results. The shelf should be so located

that the indicator on the scale on the side of the

case reads zero when the center of the slot in the

photoelectric cell is at the same elevation as the

surface of the liquid in the tank.

(2) Water cell in poor condition. When the

cell is not completely filled with water, a difference

in transmission of light may be encountered

above and below the water line. Also, a wavering

film of matter inside the cell, or dirt and sedimentation lines on the glass ends of the cell, may

influence the transmission of light. Keeping the

cell completely filled with distilled water helps

to avoid these problems.

(3) Sedimentation tank in poor condition.

Scratches on the faces of the sedimentation tank

may affect the transmission of light.

(4) Reflection of light from bright surfaces inside

turbidimeter case. It is required that the interior

of the case, and the exterior surfaces of the shelf,

parabolic reflector, water cell, shield, and photoelectric cell hood be painted with a dull, optical

black paint. In addition, the cabinet should be

free of light reflecting dust, light-colored wiring,

and shiny pieces of metal, and the gaskets used

to seal the end of the water cell should be black.

(5) Trouble in the electrical system. Among the

possible causes of difficulty are the following:

(a) Corrosion of electrical contacts and of the

wires in the rheostats.

(b) Broken or loose connecting wires.

(c) A weak storage battery.

(d) Deterioration of the photoelectric cell. Photoelectric cells tend to have different fatigue

characteristics, and therefore the cell always

constitutes a potential source of difficulty even though it may have been in use for only a relatively

short time.

(e) Looseness of the light bulb in its socket.

(f) Looseness of the reflector in its holder.

(g) Improper focusing of the light beam.

(h) Changes in the color, or intensity, of light

emitted by a bulb after prolonged usage.

(i) Malfunctioning of voltage regulator. In

laboratories where storage batteries have been

replaced with a voltage regulator, malfunctioning

of the regulator may constitute a problem.

(6) Trouble with the microammeter. Among the

possible difficulties with the microammeter are the

following:

(a) Damage in usage. A bent tip on the indicating hand may be an indication that the instrument has been overloaded.

(b) Internal corrosion of parts while instrument

is in storage. A microammeter that has not been

used for some time may have to be "exercised"

before it will give uniform readings.

(c) Static charges on the instrument, or on the

person using it. In some instances, it has been

found necessar}^ to ground both the microammeter

and the operator.

(d) Location of the microammeter on a table

containing magnetic material, or near some strong

external magnetic field. (7) Variations in the character of the suspension.

Among the causes of variations in the suspension

are the following:

(a) Appreciable variations in room temperatures.

(b) Use of a suspending medium other than

clear, white kerosene.

(c) Traces of water in the kerosene. Water

may cause foaming inside the tank during agitation

of the suspension.

(d) Changes which often occur in oleic acid or

linseed oil with age or exposure to heat and light.

When difficulties are encountered in calibrating

the apparatus, one of the first corrective actions

should be to obtain fresh supplies of dispersing

agent and kerosene. In general, technical grade

12
oleic acid does not make a suitable dispersing

agent.

(8) Trouble with the timing buret. Lint in the

capillary of the buret, even though practically

invisible, can slow down the flow of kerosene and

thereby cause an appreciable variation in test

results. Accordingly, utmost precautions should

be taken to keep lint out of the buret, and the

kerosene. As a safeguard, a filter made of No. 325

sieve cloth should be placed across the top of the

buret whenever kerosene is being added, and the

top opening should always be covered when the

buret is not in use. Use of an improperly made,

or a broken timing buret is to be avoided.

(9) Trouble with the wet sieving apparatus.

Variations may occur as the result of plugging of

holes in the spray nozzle, fluctuations in the pres- sure of the water passing through the spray

nozzle, or errors in setting the water pressure. The latter difficulty may be caused by the use of an inaccurate pressure gage, a badly marked gage, or a gage of unsuitable capacity. Fluctuations in

water pressure may be controlled by installing a

pressure regulator in the water line back of the

gage. A gas gage is not suitable for use with

water unless it has been modified for such usage.

B. Test Procedure

(1) Improper cleaning of tank prior to starting

test. If an oily film has accumulated on the

interior faces of a tank, it should be removed with

a "lint-free" wiper before a test is started. A

"squeegee" of synthetic rubber makes a good

wiping device. Wiping of a dry tank with a dry

cloth is to be avoided because this may create

static charges on the tank.

(2) Variations in the agitation oj suspensions.

Variations in the agitation process include allowing

the cement to slide along the inner faces of the

tank during rotation, and loss of a part of the

suspension during alternate inversions. A number of laboratories have found that the use of a

rotatable tank holder helps to promote uniformity

in agitation operations. Customarily, this holder

is provided with an adjustable screw in the center

of the top to hold the glass lid of the tank in

place, and so designed that it can be mounted to a

wall by a pivot arrangement at its center, and

rotated through 180° by means of a handle located near one end.

(3) Fouling of tank faces during handling of the tank. Care must be taken, especially during the

agitation process, to avoid getting liquid or finger

prints on the faces of the tank Avhich are to be

placed in the path of the light. If it becomes

necessary to clean the tank after agitation, the

possibility that a static charge may be created on

the faces of the tank as a result of wiping must be

considered.

(4) Variations in the viet seiving operation. Precautions should be taken to avoid loss of cement

due to splashing at the beginning of the wet

sieving operation.

(5) Errors in calculation. A common source of error is the failure to use standard procedures in

the calculation and application of correction

factors for No. 325 sieves.

17.3. The Air Permeability Fineness Test

The method of test for fineness of portland

cement by the air permeability apparatus was

introduced in a paper presented by R. L. Blaine in

1943 [22], and adopted as a standard test for

cement in 1946. The procedure provides for the

determination of specific surfaces by measurement

of the rates of air flow through prepared beds of

cements of definite porosities. Essentially, the air permeability apparatus consists of a permeability

cell and a U-tube manometer filled to about the

midpoint with a suitable liquid. The test is accomplished by attaching the cell, containing a

carefully measured amount of cement, to the

manometer and evacuating the air in one arm

thereof until the liquid rises to a point just beneath

the cell, after which the liquid is released and the

time required for the meniscus to fall through a

distance of approximately 5.5 cm recorded. The

specific surface is then calculated from this timeof-flow determination.

The procedure is favored by many investigators

because it is economical to perform, and because

it can be used to determine the fineness of materials

other than portland cements. It is to be noted

that the test is not suitable for determining the

specific surface of materials finer than 7,000 cm2 per g, or the specific surface of porous materials

such as diatomaceous earth and fly ashes containing porous cinders. Also, that in testing materials

other than portland cement, it is generally neces- sary to use a specific gravity other than that (3.15)

which is customarily assigned to portland cement.

Air permeability fineness determinations are sometimes influenced by factors which are peculiar

to tests in a single laboratory, or to those in a small group of laboratories, and it is not uncommon

to find that a modification of the standard procedure has been made in an effort to compensate

for such influences. It is very probable that some

of the variations in comparative test results can be attributed to the fact that values reported by

several laboratories were obtained by a modified

procedure rather than the standard procedure

because the operators concerned were not aware

of the difference in techniques.

17.3.1. Causes of Variations

A. Apparatus

(1) Nonconformance of permeability cell with specification requirements. Variations in the volume

of the test bed may result from wearing or damaging of the cell and plunger, or nonplaneness of the

perforated disk. When a unit is being used

regularly, the dimensions of the component parts

should be checked at least once in every six months

13
with particular attention being given to the

clearance between the plunger and cell, and the

volume of the compacted bed should be checked

at least once in every twenty-four months. If the disk is warped, it should be marked so that it can be placed in the apparatus in the same position

for every test. (2) Uneven edges of disks of filter paper. It is often difficult to seat disks of filter paper properly

inside the cell if the edges are torn or uneven. The use of manufactured disks in preference to homemade disks will usually solve such problems.

(3) Unsatisfactory stopcock lubricant. Stopcock

lubricants sometimes foul the upper part of the

manometer to the extent that droplets of manometer fluid will cling to the inner surfaces after the

liquid has receded. When this occurs, the inside

of the manometer should be cleaned, and a check

made to insure that petrolatum, or a petrolatum

base stopcock lubricant, is available for future use. One way in which a manometer tube may be

cleaned is, under the supervision of an expert

chemist, to fill it with an organic solvent to remove

all traces of manometer fluid, rinse out the solvent

with water, allow the interior to dry, fill it with a

20-percent solution of fuming sulfuric acid which

is then aUowed to stand for a period of from 2 to 12 hours, and finally rinse with water to remove

the acid.

(4) Incorrect amount of fluid in the manometer.

The specifications require that the manometer be

filled with fluid to the midpoint. Since the

calculated midpoint often falls either above or below the lower mark, in the interest of uniformity,

it is customary to consider that the lower mark is at the midpoint of the tube. When this feature is checked, it should be remembered that the level of the liquid will often be 2 to 3 mm below the

normal level immediately after a test. (5) Changes in viscosity of manometerfluid. Use

of a liquid whose viscosity may vary appreciably

with changes in temperature is undesirable.

B. Test Procedure

(1) Errors in calibration of apparatus. Among

the common errors in calibration are the following

(a) Incorrect porosity of bed. A loosely compacted test bed is highly sensitive to slight bumps

whereas a tightly compacted bed may spring back

when the plunger is released. Since the porosity of

bed has an important relationship to these problems, it is essential that a suitable value be selected. In general, a value greater than 0.500 should be

used for materials finer than Type I cement, and a value less than 0.500 should be used for coarser

materials.

(b) Failure to fluff the standard fineness sample

prior to use.

(2) Cement not at room temperature at time of test. (3) Variations in the volume of the test bed. Variations in the volume of the bed may be

caused by the following:

(a) Failure to seat filter papers properly. It is required that a rod slightly smaller than the cell diameter be used to press the edges of the bottom

piece of filter paper against the metal disk.

(b) Failure to level the surface of the bed prior

to compaction. It is required that the side of the

cell be tapped lightly in order to level the bed of

cement. Too much tapping is undesirable, particularly when coarse cements are being tested.

(c) Loss of cement around sides of rapidly

descending plunger.

(d) Improper compaction techniques. Among

these is rotation of the plunger after it comes in

contact with the top piece of filter paper.

(4) Errors in timing. Such errors are frequently

encountered where the operator fails to use the

bottom of the meniscus of the manometer liquid

in gaging when to start and stop his timer.

(5) Leakage of air around outside of cell during

test.(6) Theoretical errors. A common mistake is the failure of an individual operator to calibrate

himself by determining his own Ts for the standard

fineness sample, or a suitable reference sample.

Another is the selection of the wrong equation for calculation of fineness. The latter problem may

be avoided by using the following composite

equation for all calculations:

q_Ss Vr es ) Jns Ve3

where

S=specific surface in sq cm per g of the test sample,

specific surface in sq cm per g of the standard sample used in calibration of the

apparatus,

2=measured time interval in seconds of manometer drop for test sample,

Ts =measured time interval in seconds of manometer drop for standard sample used in

calibration of the apparatus,

n=viscosity of air in poises at the temperature

of test of the test sample, ns =viscosity of air in poises at the temperature

of test of the standard sample used in

calibration of the apparatus,

e=porosity of prepared bed of test sample,

es =porosity of prepared bed of standard sample

used in calibration of apparatus,

p=specific gravity of test sample (for portland

cement a value of 3.15 shall be used), and

ps =specific gravity of standard sample used in

calibration of apparatus (assumed to be

3.15).

18. Consistency

Both hand mixing and mechanical mixing

procedures are used in the preparation of mortars

and pastes of the consistency required for the

standard tests of portland cement. Standard 1 :3 14
mortars for tensile strength specimens are mixed

by hand using a calculated amount of water. All

other mortars are mixed with a mechanical mixer,

and their consistencies are measured with the 10-in. flow table. With the exception of those used in

heat of hydration tests, it is generally the practice

to mix pastes by hand and to measure their consistencies with the Vicat apparatus. Pastes for heat of hydration tests are first mixed by hand

with a spatula, and then with an electric stirrer,

using the amount of water indicated in the test method.

18.1. Mixing of Pastes by Hand

The hand mixing procedure begins with the

addition of water to the cement, and mixing

begins at the point where normal portland cements

will have absorbed an appreciable percentage of

the water. The operation consists of continuous

and vigorous mixing, squeezing, and kneading of

the paste with the hands for 1% min. It has long

been recognized that the plasticity of a mass of

cement paste is affected by the amount of work

used in the mixing operation, and that it is often

possible to attribute a large portion of the variations in results for tests employing pastes to this one factor.

A. Causes of Variations

Among the common sources of variations in

hand mixing operations are the following:

(1) Use of wrong amount of cement or mixing

water.

(2) Use of equipment coated with oil or other contaminants.

(3) Unsatisfactory work gloves. Rubber gloves

must be pliable and snug-fitting so that they will

not prevent uniform and vigorous movement of

the fingers throughout the mixing period.

(4) Use of gloves, trowels, or mixing slabs vAich

have not been permitted to dry.

(5) Loss of mixing water due to evaporation. Use

of too large an area on the mixing slab during hand

mixing promotes evaporation of water.

(6) Inadequate mixing of paste. Lack of vigor

in mixing is a principal factor.

(7) Retempering to obtain paste of the desired

consistency.

18.2. The Normal Consistency Determination

The amount of water to be used in preparing

pastes for time of setting and autoclave expansion

tests, and in preparing mortars for tensile strength

tests, is established by the normal consistency

determination. The apparatus for this determination was developed out of equipment used in about

1818 by L. J. Vicat, Chief Engineer of Bridges and

Roads in France [23], and the test had been in use

for many years in both the United States and

Europe prior to its adoption as a standard cement

testing procedure in 1904. The method provides

for the determination of the consistency of handmixed paste by observation of the depth to which

the 1-cm-diam plunger of a Vicat apparatus

penetrates a ring-confined sample during a 30-sec

period, and the paste is considered to be of normal

consistency when the penetration is between 9 and

11 mm. Among the more important variables

in this procedure are improper preparation of the

paste, and failure to observe the specified time

limits on the various operations.

18.2.1. Causes of Variations

A. Apparatus

(1) Incorrect plunger weight. Incorrect plunger

weight may result from loss of shot from the barrel

of the plunger, reduction of weight due to loss of

metal in a machining operation, accumulation of

dirt on the plunger, or replacement of the 1-mm

needle. The weight may be adjusted by var}ong

the amount of shot in the barrel (when construction

of the apparatus permits) ; or by filing material

away from, or adding solder to, the customary

knurled knob on the needle assembly. When

solder is added, it must be determined that the

adjustment is permanent.

(2) Incorrect plunger diameter. The diameter

of the plunger may be incorrect due to errors in

machining or damage in usage. Also, a substantial

reduction in diameter of the end of the plunger

may occur over a period of time from polishing

the sides with emery cloth.

(3) End of plunger in poor condition. The

condition of the end should always be checked

after an uncontrolled drop, or after it has come in forcible contact with a hard object.

(4) Frictional resistance to fall of plunger.

Among the conditions which tend to retard the fall of the plunger are the following:

(a) Use of viscous oil or grease on plunger.

The plunger should be oiled at the contact point

with the frame. Only light oils are suitable for

this purpose.

(b) Hardened cement or rust on the sides of the

plunger.

(c) Accumulation of dirt at point where plunger

contacts frame. Dirt will accumulate rapidly on

the portion of the plunger that slides through the

frame of the Vicat apparatus unless the operator

develops the habit of holding the lower end while

making adjustments of the zero setting.

(5) Vicat apparatus in poor condition. The

apparatus is in poor condition if the indicator is bent or twisted in such fashion that it does not

point to comparable lines on both scales; or if the

scale is tarnished and difficult to read.

B. Test Procedure

(1) Failure to completely fill the Vicat mold with

paste. Such failures may be minimized if the ball of paste is gently shaken into an ellipsoidal shape

15
while resting in the palm of the hand prior to insertion of the mass into the larger end of the

mold.

(2) Failure to make the proper zero setting. It

is a common practice to make the zero setting by

adjusting the indicator to read zero when the

bottom of the plunger is resting on the top of the

side of the mold, which in turn is resting on the

glass plate used with the mold. It is to be noted

that this is only an approximation of the place

where the surface of the paste will actually be. Individuals wearing bifocal glasses sometimes find

it difficult to make an accurate setting.

(3) Improper release oj the plunger. The manipulation of the set-screw holding the plunger must

be such that the plunger will be released gently,

quickly, and completely.

(4) Failure to release the plunger exactly 30 sec

after mixing. The time that elapses between

completion of mixing and release of the plunger

has an important bearing on test results, particularly when cement with false setting characteristics, or highly plastic cements such as Type III

or Masonry Cements, are under test. In many

instances, it will be found desirable to time the

operation of filling the mold in such fashion that

the plunger can be released as soon as the mold is placed in the testing position.

(5) Vibration of work table while penetration

tests are in progress.

18.3. Mechanical Mixing of Mortars

Interest in the use of mechanical mixing in the

preparation of pastes and mortars had existed for many years prior to 1953 when the current procedure for mixing certain kinds of mortars was

adopted as a standard test method. A method

for mechanical mixing of pastes has also been

developed, but use of this newer procedure is being

postponed pending the possible development of some new parts for the mixing apparatus. One

of the more important difficulties with the mixer

at present is inadequate mixing of mortar materials as a result of excessive clearance between

the end of the paddle and the bottom of the bowl.

18.3.1. Causes of Variations

A. Apparatus

(1) Nonconformance of mixer design with specification requirements. It is required that the mixer

be of the epicyclic type and have a mechanical

speed control device, that the mixing bowl have a nominal capacity of 5 quarts, and that the paddle

and bowl be made of stainless steel. The Model

N-50 Mixer, made by the Hobart Manufacturing

Co., is considered to conform with these requirements. However, it is to be noted that the bowl

and paddle often supplied as original equipment

are not made of stainless steel, and therefore must

be replaced if the mixer is to be used in the test- ing of cement. Mixers which do not conform with

specification requirements should not be used.

Paddles equipped with wipers should not be used

unless authorized.

(2) Failure to provide correct current for mixer

motor. Mixer motors are customarily designed to operate on 115 v, 60 cycle, alternating current. Speed control problems will be encountered when

efforts are made to operate the conventional motor

with a different kind of current.

(3) Failure to maintain correct paddle to bowl

clearances. Incorrect clearance between the end

of the paddle and the bottom of the bowl is a fre- quent problem in mechanical mixing procedures.

When the clearance is too great, materials accu- mulate around the bottom of the bowl with the

result that the mixture obtained is not of the ex- pected consistency. When the clearance is too

small, the paddle grinds up a portion of the standard sand, thereby changing the consistency of the

mix and often causing excessive wear of both the

paddle and the bowl.

(a) Adjustment of clearances. Small adjustments can often be made simply by bending the

lugs on the side of the bowl. (Note: In general,

the use of washers beneath the lugs to raise the

bowl is unsatisfactory.) Major adjustments can be made by raising or lowering the motor housing,

or by having a competent machinist rework a given

paddle to fit a given bowl. Recently, it has been

found that a homemade adjustment bracket can

be used to good advantage.

(b) Marking of bowls and paddles. Since they

are seldom, if ever, identical in every small detail,

paddles and bowls, in most instances, cannot be

interchanged at random after clearances have been

adjusted for a given mixer-paddle-bowl combination. Therefore, if equipment is carefully adjusted in such manner that two paddle-bowl sets can be used with a single mixer, each set must be

match-marked so that the proper combination can

be easily recognized. Where more than one mixer

is in use, each mixer-paddle-bowl set must be

match-marked.

(4) Bowl damage. Bowls may be accidentally

damaged by dropping of the bowl, dropping of the

paddle into the bowl, or by raising the bowl into

the mixing position before it is properly seated

in the frame. Careless or nonprofessional efforts to repair a dent may result in a change in the

form of the bowl which renders it unsatisfactory

for use.

(5) Failure to provide a lid for the bowl. A cover

is needed to prevent evaporation losses during

pauses in the mixing operation. This lid should

be made of material not attacked by the cement,

and should be sufficiently rigid that it will lie flat across the top of the bowl. Rags should not

be used in lieu of a lid. (6) Leakage of oil from gear housing into mixing

bowl. A change in the consistency of the mix may

occur if oil falls into the bowl from the gear housing

16
during a mixing operation. ^Yhen a mixer has not

been used for some time, the bowl should be

checked for oil, and cleaned if necessary, prior

to starting a test.

B. Test Procedure

(1) Failure to remove all moisture from paddle

and bowl before use.

(2) Failure to introduce materials into the bowl

in the prescribed sequence.

(3) Loss of materials as they are being introduced

into the bowl. Accidental losses can be minimized

by the use of a funnel-shaped hopper.

(4) Failure to follow the prescribed mixing

procedure.

18.4. The Flow Table Test

A comprehensive specification for the 10-in. flow table, based on the knowledge gained during more than 30 years of experimentation with and

use of this device for measuring the consistency

of mortars, was adopted in 1949. The apparatus

consists essentially of a 10-in. diam rigid table, with

a perpendicular shaft, mounted on an integrally

cast rigid iron frame fastened to the top of a 300-lb concrete pedestal. Accessory items are a mold in the shape of the frustrum of a cone, and

a specially marked caliper. The test is accomplished by leaving the amount of mortar required

to fill the mold on the table while it is raised and

dropped a specified number of times by means

of an electrically-driven cam fastened to the

frame. The flow is the resulting increase in diameter of the mortar mass expressed as a per- centage of the original base diameter.

18.4.1. Causes of Variations

All of the important requirements for the table are covered in detail in the specification, and

a lengthy check list for use in trouble shooting is available [24]. Since so much information has

already been printed, only a few causes of variations other than those taken into account in sec- tion 16 are presented herewith.

A. Apparatus

(1) Nonconformance of apparatus with specification requirements. This is a common problem

with brand new and old apparatus alike. New

apparatus which does not conform to specification

requirements should not be accepted. Old apparatus should be repaired or replaced whenever

the following signs of wear or damage are noted

(a) Damage to contact surfaces.

(b) Excessive clearances between bore and

shaft.

(c) Leakage of water from beneath flow mold

due to damage to bottom edge.

(d) Inaccurate flow measurements due to wearing of caliper.

(e) Curvature in straightedge of trowel used in

striking excess material from the flow mold.

(f) Improper alinement of cam with table shaft

due to bending of the threaded end of the cam

shaft.

(2) Failure to provide correct current for flow

table motor.

B. Test Procedure

(1) Failure to dry and clean the table top prior

to use.

(2) Variations in filling the flow mold. Variations in the amount of material contained within

the mold may be caused by variations in compacting mortars into the mold, including the

failure to use the prescribed 20 tamping pressures. The practice of throwing mortar into the mold

also constitutes a variable. The mold should be

held firmly against the table top during the filling

operation in order to reduce seepage under the

bottom edge.

(3) Failure to dry and clean the table top after

iilling the mold. Any water that may have seeped

from beneath the mold, and all spilled mortar, should

be wiped away prior to proceeding with the test. A circular shield approximate^ 10 in. in diam,

with a center opening approximately 4 in. in diam,

should be used while the mold is being filled to prevent spillages from reaching the table top.

(4) Errors in reading the flow caliper.

(5) Adjustment of flows by application of correc- tion factors. A mixture of ground silica and

mineral oil has been used for a number of years

as a means of gaging flow table performance.

Some laboratories have attempted to correct mortar flow values by adding or subtracting the

difference between assigned flow values and actual

values obtained with the silica-oil mixture. Test

results are not reliable when adjusted in this manner.

19. The Autoclave Soundness Test

Soundness tests have been used for many years

to detect those qualities of a cement which tend

to destroy its strength and durability, and at least four procedures employing artificial conditions

which would hasten the development of such

defects were either being used or studied in the

early 1900's. An autoclave test was among these,

and ultimately, in 1940, it was adopted as a standard test for cement. The method of test

for autoclave expansion of portland cement

provides for the exposure of a prism (1 by 1 by

10 in.) of hardened cement paste to a steam pres- sure of 295 psi within a speciallv designed autoclave for a period of 3 hours. Changes in length

of the prism are measured by means of a suitable

length comparator.

17
19.1. Causes of Variations

A. Apparatus

(1) Use of multicompartmented molds. Single or double compartment molds are preferred

because they make it possible to put bars in moist

storage soon after molding is completed.

(2) Thin end plates in bar molds. Thin end

plates may permit the gage studs to become so deeply imbedded in the ends of bars that an

accurate measurement of length cannot be

obtained.

(3) Operational problems with the autoclave. The rate at which an autoclave reaches test pres- sure is an important factor in some soundness

tests. Since operational problems often affect the rate of heating, all of the following items

should receive special consideration.

(a) Leakage of steam through joint between lid and chamber. In a number of instances this difficulty has been eliminated by replacing the

old-style asbestos gaskets with lead, or metal and

asbestos, gaskets.

(b) Leakage of steam through safety valve.

Use of a pressure release device which employs a platinum rupture disk may help to solve problems

associated with defective safety valves.

(c) Low line voltage.

(d) Deterioration of heating elements. The

failure of an autoclave to heat at the specified

rate, or its failure to maintain the specified test pressure, can often be corrected by replacing the

heating elements.

(e) Errors in indication of pressure. In numerous instances, gages have been reset by laboratory

personnel so that the indicated steam pressure

would be in agreement with the temperature

within the chamber as indicated by a total immersion thermometer. Such adjustments are usually in error because the thermometer well of an autoclave is designed for the use of a partial

immersion thermometer. For this and other

reasons, the accuracy of indication of the pressure

gage should be verified periodically on a gage

tester.

(f) Improper manipulation of heater controls.

The initial heating rate is significantly affected

by the number of bars in the chamber, and therefore it must be controlled by manipulating the

heater controls in a sequence previously found to be satisfactory for the number of bars under test. Only one sequence is required if vacancies in the

rack are filled with previously tested bars so that

the number in the chamber will be the same for

everjr run. Use of a voltage regulator may also prove helpful.

(g) Use of too much water in the chamber. A

measured quantity of water, which is 7 to 10 per- cent the volume of the chamber, should be added

prior to the start of each test. Use of an amount

greater than 10 percent may cause an appreciable

change in the heating characteristics of an auto18

clave. Any water remaining in the chamber at the

j end of a test should be removed with a siphon and

the walls wiped dry with a sponge to prevent

rusting.

(h) Improper adjustment of automatic pressure r controls.

(i) Plugging of connecting pipes. The gradual

accumulation of material in the connecting pipes

may prevent the pressure regulator, the pressure

gage, or the safety device from performing in a

satisfactory manner.

(4) Errors in measurements due to comparator.

The graduations on some dials are very difficult to read, and in some instances the physical condition

of the dial face is such that accurate readings may

be difficult to obtain. Dials in these categories i should be replaced. The use of a small cup on the

end of the dial stem to receive the gage stud, and

another on the comparator base, helps to prevent ' mistakes in measurement.

B. Test Procedure

(1) Use of an incorrect amount of cement or mixing

water. The practice of using a fixed water content

for all bars made from a certain type of cement

from a given source is undesirable.

(2) Allowing gage studs to shift during molding of

bars.

(3) Excessive troweling of the surface of bars. Excessive troweling can be avoided if the operator

uses a trowel with sharpened edges, and performs

the smoothing operation by drawing the flat side

of this trowel (with the leading edge slightly

raised), over three-fourths of the length of the

mold, in such fashion that the surface of the paste

behind the trowel will be smoothed while any

excess material will be "crowded" toward the end

of the mold. Toward the end of the stroke, the

leading edge of the trowel should be lowered to

ride along the top edge of the mold, and the extra material then sliced away by the sharp edge of the

trowel. The entire operation of smoothing and

finishing can be completed in this manner in the

course of a few passes along the mold.

(4) Allowing bars to dry after molding is completed. Bars should be put into moist storage immediately after molding is completed, and should

not be disturbed until it is time to strip the mold.

The procedure of smoothing the surface an hour or two after the mold has been filled does not con- form with standard practice.

(5) Autoclaving bars which are less than 24 hours

old.(6) Failure to measure bars immediately after removal from moist storage.

(7) Improper cooling of bars after autoclaving.

It is important that bars be cooled to room temperature prior to measurement. A cylindrical container approximately 8 in. in diam and 16 in. in

height, equipped with a bail, makes a convenient

cooling chamber. In use, this container is filled with water and placed on a hot plate at the end
of the 3-hr autoelaving period. Later, when the

autoclave is opened, the rack and bars as a single

unit may be lifted from the autoclave by means

of a suitable metal hook and immersed in the

near-boiling water in the container. The container may then be transferred to a sink, and cold

water introduced through a rubber tube connected

to a cold water spigot. The rate of cooling may

be controlled by regulation of the flow of cold

water through the tube.

(8) Errors in calculations . Such errors are usually mistakes in arithmetic.

20. Time of Setting

Setting properties have been of interest since

the very earliest days of cement testing and numerous procedures for gaging this important

quality have been developed. Presently, there

are two standard methods of test, namely the

Vicat Time of Setting Test, and the Gillmore Time

of Setting Test.

20.1. Common Causes of Variations

The two tests are similar in many respects, and

therefore, there are a number of considerations

which are of importance in either procedure.

Some of the common causes of variations other

than those taken into account in previous sections

of this discussion are presented herewith.

(1) Error in the determination of the normal consistency. It is generally understood that the more

mixing water used, the slower the set. The

amount of mixing water may be incorrect due to an error in the determination of the normal

consistency.

(2) Inadequate mixing of paste. It has been

illustrated by many investigators that the time of

set varies with the vigor of the mixing used in the

preparation of the paste [25]. For this reason, it

is suggested that when difficulty is encountered in

obtaining suitable reproducibility of test results

the experimental procedure for mechanical mixing

of pastes might be used in evaluating the effective- ness of an operator's hand mixing technique.

When making such comparisons, it must be

remembered that machine mixing will give unsatisfactory results if the mixer does not conform to all requirements of the applicable specifications.

(3) Regaging of paste. Regaging usuaUy tends

to make paste slower setting.

(4) Irregularities in testing. A Vicat apparatus,

or a set of Gillmore needles, should be shielded

from drafts of air and from direct sunlight which

might cause evaporation of moisture from speci- mens while readings are being taken. Also, the

length of time specimens are kept out of moist

storage should be held to a minimum.

(/) Errors in determining time intervals. Where

errors in reading times or in calculating time

intervals are encountered, the use of a "militarytype" clock with a face showing the hours from

0000 to 2400 may prove helpful.

20.2. The Vicat Time of Setting Test

The current method of test for time of setting

of hydraulic cement by the Vicat needle was

developed out of equipment and procedures used

in about 1818 by L. J. Vicat [23]. The evolutionary process began in Europe and had been

under way there and in the United States for

many years before a crude version of the present

procedure was adopted as a standard test for cement in 1904. A number of changes in apparatus and procedures have been made since the

adoption, with a recent change of particular note

being the replacement of the tests for "initial time

of setting" and "final time of setting" with a

single test for the "Vicat time of setting".

The test is accomplished by observing the time

required for hand-mixed paste to harden to the

extent that the 1-mm needle of a Vicat apparatus

will penetrate a ring-confined sample to a depth

of only 25 mm during a 30-sec period. This test

is generally found to be more reproducible than

the Gillmore test because there is greater uniformity among test specimens, and because the

personal judgment factor as to when set occurs is eliminated.

20.2.1. Causes of Variations

A. Apparatus

(1) Vicat apparatus in poor condition. In

general an apparatus that would not be suitable

for use in normal consistency determinations

would not be suitable for use in Vicat time of

setting tests. Otherwise, particular attention

should be given to the straightness of the needle,

the diameter and the condition of its end, and the

possible presence of hardened cement or rust on

its sides. The condition of the needle should

always be checked following a free fall through a mass of paste in a plastic state.

(2) Use of oil on Vicat ring. Use of oil on the

ring to facilitate the removal of hardened paste

is not particularly helpful, and introduces the

possibility that the paste might be contaminated

with oil during the test.

B. Test Procedure

(1) Improper procedure. The paste may not

be suitable for test purposes if it has been used

previously in a normal consistency determination.

(2) Failure to completely fill the Vicat ring with

paste. Small holes in the paste may have a

significant effect on test results.

20.3. The Gillmore Time of Setting Test

The use of weighted wires (needles) was originally proposed as a test for time of setting of

cement by a Committee of the American Society

of Civil Engineers in 1885. The wires were called

19
"Gillmore wires" as a courtesy to General Gill- more, the chairman of the committee, although

they had not been proposed by him, but had been

suggested by others [25]. A test based on that

early method was adopted as a standard test for cement in 1916.

A set of Gillmore needles consists of an initial needle, weighing % lb and equipped with a )i2-in. diam cylindrical tip; and a final needle, weighing

1 lb and equipped with a %4-in. diam cylindrical

tip. Initial and final setting times are determined

by the application of these needles to the flattened

top of a specimen of paste (a pat) 3 in. in diam

at the bottom and % in. thick at the center. The

Gillmore test is preferred by many testing agencies because it is simplier, and therefore more

economical to perform, than the Vicat test. Its chief weaknesses are considered to be the failure to obtain a homogenous mass upon which to make

the determination, the difficulty of applying the

needles at right angles to the surface of the specimen, and the personal equation in determining

when the needles cease to make an appreciable

indentation.

20.3.1. Causes of Variations

A. Apparatus

(1) Incorrect diameters of needle tips. The diameter of a needle tip may be incorrect due to

errors in machining, wear, dropping, or encrustations of hardened cement.

(2) Incorrect needle weights. The weight of a

needle may be incorrect due to the inadvertent

loss of shot from the ball, or the addition of excess

shot.

(3) Failure to provide required frame for needles. The ends of needles stored in wooden blocks, or

in drawers, are frequently found to be damaged.

(4) Bent needle shafts.

B. Test Procedure

(1) Use of an incorrect amount of cement or water. Since the specified batch size makes more

paste than is required to make a pat, smaller samples are sometimes mixed by hand or with a

trowel. These methods usually require more mixing water than that indicated for normal consistency, and therefore the rate of hardening of the

paste is altered. Results obtained in this manner

are only approximations of the time of setting.

(2) Specimens improperly formed. This is fre- quently due to the failure to follow specified

procedures. Among the other contributing factors are the following:

(a) Excessive troweling. If operators seem to be over-troweling specimens, an effort should be

made to form pats with less than 40 troweling

strokes. It is preferred that only one application

of pressure be used in flattening the top of the

pat.

(b) Slanting or uneven surface on top of pat. j The surface of the pat should be smooth, and it | should be parallel to the surface of the glass plate ( on which the specimen is formed. A template jl may be helpful in preparing specimens which ij have smooth, level surfaces, and which are of a uniform height. This template should not be

confused with the so-called "pat mold," a device ! which is not suitable for use in the preparation of

specimens.

(3) Variation in technique of applying needles. ! The needles must always be applied at right J angles to the surface of the pat.

(4) The personal equation in judging indentations. Variations in determining the point at i which the pat will bear, without appreciable

indentation, the Gillmore needle, may be due to inadequate lighting of the test area, and therefore f the installation of special lights to insure that jj surfaces of pats are adequately illuminated may

prove helpful. Use of fluorescent lights is recom- I mended to avoid exposing pats to the "drying

heat" of incandescent lights.

(5) Too frequent checking of specimens.

I 21. The Heat of Hydration Test

The Heat of Hydration Test is customarily 1 listed among the physical tests of cement, and

therefore it has been necessary to make several ' references to it. However, because the procedure 1 has much in common with procedures for chemical

analysis of cement, comments about the related

methods and apparatus have not been included ; in this discussion. For those who wish to pursue '

it, considerable information about the test can be

obtained by reference to a published bibliography | [26].

22. The Determination of the Air

Content of Mortar

The need for a rapid physical test whereby

the air-entrainment characteristics of portland j cements treated with air-entraining agents could j be regulated led to the adoption, in 1944, of the b air content of mortar determination as a standard

test for cement. A number of inadequacies in the

original equipment and procedures were soon

recognized, and these were corrected in extensive

revisions of the method in subsequent years. With these changes, the method of test for air 5 content of hydraulic cement mortar has become i one of the most satisfactory of all the physical tests from the standpoint of reproducibility.

The current procedure provides for the determination of air content of machine-mixed mortar;

consisting of 1 part cement, 4 parts standard sand, s and the amount of water required to obtain a flow

of 80 to 95 percent after 10 drops of the flow table;

by comparing the weight of a 400-ml sample

thereof to the theoretical air-free weight of a

similar volume as calculated by the absolute

20
volume method. In general, the uniformity in

results is found to be better in tests of air-entraining cements than in tests of non-air-entraining

cements.

22.1. Causes of Variations

A. Apparatus

(1) Variations in volume oj J+00-ml measure.

It is required that the volume of the measure be

between 399 and 401 ml. Many of the containers

presently in use do not conform to this requirement, and therefore, as a precaution, the volume

of every new measure should be checked, and

adjusted if necessary, prior to acceptance by the

laboratory.

(2) Balance not suitable for test. It is difficult to obtain the desired accuracy in test results if the capacity of the balance is inadequate.

B. Test Procedure.

(1) Use of an incorrect amount of cement, sand,

or water. If water requirements for all cements seem to be consistently in error, the flow table and

mechanical mixer should be thoroughly checked

for conformance with the requirements of applicable specifications.

(2) Failure to place mortar gently in the measure. The technique of throwing mortar into the measure

does not conform with standard practice.

(3) Failure to observe specified time limits on test operations. The desired accuracy cannot be

obtained if the time limits on various test operations are disregarded.

(4) Improper handling of the J+00-ml measure. Shaking or jolting of the measure during the filling

operation must be avoided.

(5) Failure to use specified equipment in performance of test. Particular attention is invited to the advantages of using the specified spoon, spatula, tapping stick, and straightedge in the filling of the 400-ml measure.

(6) Variations in weighings. In many instances,

bench weights will give more uniform results than

the beam and poise with which many mix balances

are now equipped.

23. Strength of Mortars

The use of mortar strength tests as a criterion

of the quality of cements was recorded in the litera- ture as early as 1772 [23], but it was not until

about 1848 that any real efforts were made to devise standard mortar strength tests for portland

cements [27]. Much improved versions of the

compressive strength and tensile strength tests conducted at that time are presently included

among the standard physical tests for cement.

23.1. Common Causes of Variations

Although there are many actual or theoretical

differences betv/een the two strength tests, the

common use of a mortar specimen ensures that

there will be a number of considerations which

would be of importance in either procedure. Some

of these are presented herewith.

(1) Nonconformance of mold design with specification requirements.

(2) Leakage of water from molds. The loss of

water through the joints of a mold, or the joint

between a mold and its base plate, may permit

specimens to develop strengths which are higher

than average. In this connection, it is important

that mold base plates be of sufficient thickness to preclude bending during molding and handling of specimens.

(3) Failure to provide suitable water storage

facilities.

(4) Improper treatment of specimens after removal

from storage. It is required that all strength speci- mens be placed in moist air storage immediately

after molding. Specimens to be tested at 24

hours are taken directly from the moist air storage

and tested at once. Specimens to be tested at

later ages are transferred to water storage for

additional curing. Air drying of any of these

specimens just before testing can cause an increase

in compressive strengths or a reduction in tensile strengths. For this reason, when several 24-hr

specimens are to be tested at one time, it is recom- mended that they be placed in a pan immediately

upon removal from moist storage, and kept

covered with a moist cloth until ready for test. When two or more specimens, other than 24-hr

specimens, are to be tested at one time, they

should be removed from the water storage tanks,

placed immediately in a pan of water, and kept

there until actually tested. As immersion in water

of an appreciably different temperature than the

tank water just prior to testing can have a significant influence on results, it is recommended that

the water in the pan be obtained from the storage

tank.

(5) Failure to clean specimens prior to testing.

Loose sand grains or incrustations must be

removed from the bearing surfaces of specimens

before they are inserted in the testing machine.

If specimens seem to be excessively coated with a soapy substance, the use of a different mold

lubricant should be considered.

(6) Failure to observe suitable time tolerances on

testing. Every effort should be made to maintain

equal intervals between the preparation and test- ing of strength specimens. Since it may not

always be possible to do this, some tolerances on

time should be observed. The following are suggested: 1-day, within hour; 3-day, within 2 hours;

7-day, within 4 hours; and 28-day, within 8 hours.

(7) Inaccuracy of testing machines. The accu- racy of indication of a testing machine should be

verified following its installation in a laboratory,

and at least once in every three years thereafter. When the accuracy of a machine is questioned,

and it is not convenient to make an immediate

verification, it may prove helpful to compare

21
results obtained with the machine in question

against results obtained with machines in nearby

laboratories. In these instances the comparative

tests should be made on specimens from a single

batch, and checks should be made in two properly

equipped laboratories, rather than in just one.

It may be helpful to remember that the failure to maintain a testing machine in proper operating

condition is one of the common causes of errors in

strength testing.

(8) Failure to load test specimens at specified

rate. Appropriate rates for application of loads to strength specimens have been determined by

careful experimentation. The failure to use the

specified rate may have a significant effect on test

results, particularly in compressive strength determinations.

23.2. The Compressive Strength Test

The procedure whereby the strength characteristics of a cement are evaluated by the compressive

strength of 2-in. mortar cubes; consisting of 1 part cement, 2.75 parts Graded Standard Sand,

and the amount of water required to obtain a flow

of 100 to 115 percent after 25 drops of the flow

table; was adopted as a standard test for cement

in 1934. It is favored by many investigators

because the progressive increase in the strength of

cubes, with age, parallels the increase in strength

of concrete, with age, and because the agreement

between laboratories using correct techniques and

equipment is generally satisfactory. Numerous

refinements in apparatus and procedures have been

made since 1934, i.e., machine mixing has replaced

hand mixing and the instructions for molding of specimens have been expanded, with the result

that the number of laboratories reporting unreasonable compressive strength values has been

substantially reduced.

23.2.1. Causes of Variations

A. Apparatus

(1) Nonplaneness oj interior faces of molds.

(2) Failure to keep corners of molds clean. The

accumulation of hardened cement in the corners of the pockets in a cube mold reduces the overall size of test specimens, and thereby causes reductions

in compressive strengths. Prompt cleaning of the

molds after stripping will help to avoid this

difficulty, and normally most of the residue can be

removed with a damp cloth if cleaning is undertaken before the material has had an opportunity

to harden in air. (3) Excessive use of oil on molds.

(4) Inadequate sealing of molds. Operators

frequently fail to follow the instructions for sealing

of cube molds. In numerous instances, the departure is attributed to difficulty in applying the

specified sealing material. One effective technique is to melt the material in a conventional oil can with a "cut-down" spout, and to apply the

liquid thus obtained to the mold, as one might

apply oil, while holding the hot can in a hand

protected by an asbestos glove.

(5) Problems with spherical blocks in compression \ machines. Among the common problems are the

following

(a) Block frozen in place and therefore unable

to adjust to specimen.

(b) Improper design of block.

(c) Damage to spherical surfaces which prevents

normal movement of the block.

(6) Nonplaneness offaces of compression machine \ bearing blocks. All blocks tend to lose their planeness with usage, and this change may occur rapidly , if the bearing faces have not been properly hardened. Planeness may be checked with a flash- light and a toolmaker's straightedge. If the

planeness is within 0.001 in. as required, very little light, if any, will show between the straightedge

and the surface of the block when the flashlight is held behind the straightedge.

(7) Inadequate maintenance of compression test- ing machine. Every laboratory should be provided with maintenance literature for the

compression machine it uses, and all special maintenance equipment should be available, i.e., the

special wrench and oil gun needed for machines

equipped with a fluid support. The indicating

hands should be checked periodically for freedom

of movement, with particular attention being

given to maximum hands. The level of oil in all oil reservoirs should be checked frequently. In

the event of mechanical failure, the services of a competent repairman should be obtained

promptly.

B. Test Procedure

(1) Use of an incorrect amount of cement, sand,

or water. If the water requirements for all cements seem to be consistently in error, the flow table and

mechanical mixer should be checked thoroughly

for conformance with the requirements of appli-

[ cable specifications.

(2) Mixing of mortars by hand. The mixing of mortars by hand, rather than with the mechanical i mixer as specified, will usually produce lower test i results.

(3) Variations in tamping pressures. Nonuniformity in the tamping pressures used in compacting mortar in the mold pockets is a variable in

j compressive strength determinations.

(4) Improper positioning of specimens on compression machine bearing blocks. It is important

that cubes be centered carefully on the bearing

blocks of the testing machine. The use of a special - centering template may be helpful.

(5) Failure to zero compression machine properly

at start of test. (6) Errors in reporting test results. A confusing I error, particularly where low strengths are con- s cerned, is the failure to divide the load in pounds 1 by four to obtain pounds per square inch.

22
23.3. The Tensile Strength Test

The procedure whereby the strength characteristics of a cement are evaluated by the tensile

strength of 1-in. thick, figure-8 mortar specimens

(briquets); consisting of 1 part cement, 3 parts

Standard Sand, and the amount of water indicated

by the normal consistency determination; was

introduced about 1880 [27], and was adopted as a standard test for cement in 1904. The test has

been favored by many investigators because it is simple, and therefore economical to perform.

The retrogression of strength with age, which is sometimes encountered, is frequently mentioned

as a disadvantage.

23.3.1. Causes of Variations

A. Apparatus

(1) Use of worn test apparatus. When strength

values seem to be consistently in error, all apparatus should be carefully checked for conformance

with the requirements of applicable specifications.

A particular problem in recent years has been the

low strength of specimens produced in molds which

have worn so thin as to no longer comply with

minimum thickness requirements. Another problem has been the leakage of water from molds

which are worn in such fashion that the halves no

longer meet at all points.

(2) Variations in mold design. The molds

presently in use vary from the single pocket to the

six pocket type, and fabrication techniques tend

to vary with the type of mold. It would be

advantageous for all laboratories to use the customary 3-pocket type.

(3) Inadequate maintenance of testing machine.

From time to time, grips are observed wherein the

rollers are no longer free to turn. This and other

important maintenance problems are discussed in detail in existing publications [24].

B. Test Procedure

(1) Use of an incorrect amount of cement, sand,

or water. Consistent errors in the amount of

mixing water used may indicate an error in the

normal consistency determination, or an error in

calculating the amount of water from the normal

consistency. In this latter calculation, the given

i percentage of water is expressed in terms of the

weight of cement and sand, and not in terms of the

weight of the cement alone.

(2) Variations in techniques for filling molds.

' Where two or more molds are being filled from the

' same batch, each phase of the fabrication process

i should be completed on each mold before the next

I phase is started, i.e., compaction of the mortar into

each pocket in each mold should be completed

\ before the heaping and smoothing operation is

- started. The mortar in each pocket should be

flush with the top of the mold when smoothing is completed.

(3) Improper compaction of mortar in the mold

pockets. It is recommended that the thumb pres- sures be applied in groups of two per briquet on

each of six trips along the mold. Care should be

taken that the thumb pressures are applied entirely to the surface of the mortar, and not to the

surface of the mold. The specified thumb pres- sure of between 15 and 20 lb may be measured

by molding the briquets on a platform scale or on other suitable apparatus that will indicate the

pressure exerted.

(4) Variations in techniques of finishing speci- mens. In standard practice the excess material

is removed from the molds with a smoothing

motion rather than a sawing motion. Mastery of

the smoothing operation requires a certain amount

of practice, and therefore many laboratories per- mit inexperienced operators to use the simplier

sawing procedure while learning the test. The

prescribed smoothing technique should be adopted

at the end of the apprenticeship period.

(5) Failure to remove all sand grains from face of

mold. Sand grains between the mold and its base

plate promote the loss of mixing water from

finished specimens as well as an increase in thickness. Either of these conditions is capable of

causing an apparent increase in strength.

The author acknowledges the assistance and

advice received from members of the staff of the

Concreting Materials Section NBS, among whom

were his associates in the Cement and Concrete

Reference Laboratory. Appreciation is expressed

to the American Society for Testing Materials for

its permission to use information copied from the

special compilation entitled " ASTM Standards on Cement (with related information)" in this discussion.

24. References

[1] W. J. Youden, Statistical aspects of the cement testing program, ASTM Proc, 59, 1120, (1959).

J. R. Crandall and R. L. Blaine, Statistical evaluation

of interlaboratory cement tests, Ibid., p. 1129.

[2] Federal Standard Stock Catalog, Section IV (pt. 5), Federal Specification for Balances; Analytical,

AAA-B-92, (May 1949). For sale by the Superintendent of Documents, Washington 25, D.C.

Price, 5 cents.

[3] L. B. Macurdy, H. K. Alber, A. A. Benedetti-Pichler,

Hugh Carmichael, A. H. Corwin, Robert M. Fowler,

E. W. D. Huffman, P. L. Kirk, and T. W.

Lashof, Terminology for describing the performance

of analytical and other precise balances, 1954 Report and Recommendations of the Committee

on Balances and Weights, Anal. Chem., 26, 1190,

(July 1954).

[4] T. W. Lashof and L. B. Macurdy, Testing a quickweighing balance, Anal. Chem., 26, 707, (April

1954).

[5] Leonard Bean and Ethel J. Hackney, A study of some operations involved in cement analysis,

ASTM Bull. 197, 44 (April 1954).

[6] Information concerning pyrometric cones may be

obtained from The Edward Orton Jr., Ceramic

Foundation, 1445 Summit St., Columbus 1, Ohio.

23
[7] Private communication.

[8] H. S. Roberts, Phys. Rev. 23, 386 (1924).

[9] W. F. Hillebrand,- G. E. F. Lundell, H. A. Bright,

and J. I. Hoffman, Applied inorganic analysis, pp. 32-33, 46-51, 503. (Published by John Wiley

and Sons, New York, N.Y., 2d ed., 1953.)

[10] Fed. Test Method Std. No. 158, May 1957: Cements

hydraulic; sampling, inspection, and testing;

method 1001, par. 4.2.

[11] ASTM Standards, pt. 4, pp. 68 and 69, (1958).

[12] I. M. Kolthoff and E. B. Sandell, Textbook of quantitative inorganic analysis, p. 391, (Published by the Macmillan Co., New York, N.Y., 3d ed., 1952).

[13] J. I. Hoffman and G. E. F. Lundell, The precipitation

and ignition of magnesium ammonium phosphate,

BS J. Research 5, 279-93 (1930).

[14] H. A. Berman, An improved 8-hydroxyquinoline

method for the determination of magnesium oxide

in portland cement, ASTM Bull., 237, 53 (April

1959).

[15] R. B. Rudy, Determination of sulfuric anhydride in portland cement by means of the Wagner Turbidimeter, J. Research NBS, 16, 555 Nc. 6, (June

1936).

[16] Harry A. Bright, Determination of sulphur occurring

as sulphide in portland cement, J. Research NBS,

18, 137 No. 2, (Feb. 1937) RP968.

[17] Bernard Chaiken, Determination of ignition loss in portland blast-furnace slag cements, ASTM Bull., No. 238, p. 53, (May 1959).

[18] J. J. Diamond and Leonard Bean, Improvements

in flame photometric determination of sodium in portland cement, Anal. Chem., 25, 1825, (Dec.

1953).

[19] W. J. Halstead and Bernard Chaiken, Insoluble

residue determination in portland and portlandslag cements, ASTM Bull., No. 229, pp. 60-65,

(April 1958).

[20] M. R. DeFore and H. J. Corah, A test method for air-entrainment of standard Ottawa sand, ASTM

Bull. No. 248, (Sept. 1960).

[21] L. A. Wagner, A rapid method for the determination

of the specific surface of portland cement, ASTM

Proc, 33, 553 pt. II, (1933).

[22] R. L. Blaine, A simplified air permeability fineness apparatus, ASTM Bull., No. 123, p. 51, (Aug. 1943).

[23] H. F. Gonnerman, Development of cement performance tests and requirements, P. C. A. Research

Bull., No. 93, (March 1958).

[24] ASTM standards on cement (with related information). Appendix I. Manual of cement testing.

[25] Data Considered by Committee C-l of the American

Society for Testing Materials in Preparing the Standard Specifications and Tests for Portland

Cement (Serial Designation C 9-17).

[26] R. F. Blanks and H. L. Kennedy, The technology of cement and concrete, p. 51, (John Wiley & Sons,

Inc., New York, N.Y.).

[27] M. A. Swayze, The testing of cements for inherent

strength, ASTM Bull., No. 209, (Oct. 1955).

24 U.S. GOVERNMENT PRINTING OFFICE: 1961
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