National Buieau of Standards

Librar>', N. % B!dg.

SEP 1 8 1952

Effect of Aging on the Soundness of

Regularly Hydrated Dolomitic Lime Putties

United States Department of Commerce

. National Bureau of Standards

Building Materials and Structures Report 127
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UNITED STATES DEPARTMENT OF COMMERCE • Charles Sawyer, Secretary NATIONAL BUREAU OF STANDARDS . A.V. Astin, Acting Dirictor

Effect of Aging on the Soundness of

Regularly Hydrated Dolomitic Lime Putties

Lansing S. Wells, Walter F. Clarke, and Ernest M. Levin

Building Materials and Structures Report 127

Issued April 25, 1952

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 15 cents
Foreword

The use of regularly hydrated dolomitic lime (type N-normal finishing),

characterized by a high percentage of unhydrated magnesia, has been shown at the Bureau to result in extensive blister-type failures in white-coat plaster.

The failures are caused by expansion in the white coat, accompanying delayed

hydration of the magnesia. The Bureau cooperated in the development of

methods for producing dolomitic limes so highlj^ hydrated that expansion by

further hydration would be negligible, and such limes are now available commercially. Unfortunately, in many instances unsound regularly hydrated

dolomitic lime is still being used in the preparation of white coat. The custom has been to soak regularly hydrated dolomitic finishing lime as a putty for 12 to 24 hours before using, in order to provide a plastic putty. That

such a soaking period is insufficient to provide a sound lime putty, by additional

hydration of MgO, is amply demonstrated by the prevalence of blister-type

failures in white-coat plaster. Some believe, however, that extension of the

soaking period somewhat would be sufficient to provide a sound lime putty.

This report shows that for the regularly hydrated dolomitic limes studied,

the aging period necessary to produce a sound lime putty varied from a minimum of 3 weeks to over 32 weeks, an aging period altogether too long from a

practical standpoint. Suitable alternates are discussed,

A. V. AsTiN, Acting Director.

Contents

Page

Foreword ii

1. Introduction 1 2. Scope 2

3. Materials 2

3.1 Hydrated lime 2

3.2 Cement 3

4. Procedure and apparatus 3

4.1 Preparation and storage of putty 3

4.2 Determination of free water in the putty 3

4.3 Determination of ignition loss of the dried putty 3

4.4 Preparation and testing of autoclave bars 3

5. Calculations 4

5.1 Percentage of magnesia hydrated at start 4

5.2 Percentage of magnesia hydrated at time t 4

5.3 Other equations 5

5.4 Sample data sheet 5

6. Results and discussion 6

7. Summary and conclusions 13

8. References 14

n
Effect of Aging on the Soundness of

Regularly Hydrated Dolomitic Lime Putties

Lansing S. Wells, Walter F. Clarke, and Ernest M. Levin

Regularly hydrated dolomitic limes are potentially unsound because they contain unhydrated magnesia that may hydrate subsequently in the set plaster, causing disruptive expansion. It is important to know the time required to soak these limes as putties so that suffi- cient magnesia will have been hydrated to give a sound putty. The customary soaking

period of 1 day is inadequate, as evidenced by the prevalence of white-coat expansion failures. Consequently, the progressive hydration of magnesia in dolomitic lime putties upon aging

and the attendant decrease in autoclave expansion of cement-lime putty bars were studied

for 18 regularly hydrated dolomitic limes representative of commercial production. The

limes differed markedly in regard both to the time required to reach a given percentage of expansion and to the extent of hydration at the given expansion. The shortest time of aging

required to reduce the expansion to 1 percent (a suggested specification limit for soundness) was 3 weeks, whereas the longest time was in excess of 32 weeks. When the expansion had

been reduced to 1 percent, the proportion of total magnesia hydrated ranged from 83 to more than 97 percent. Inasmuch as long and variable aging periods are impractical, suitable

alternates, including the use of newly developed sound hydrated limes, are discussed.

1. Introduction

Regularly hydrated dolomitic limes have been

used extensively in the preparation of whitecoat plaster. These finishing hydrated limes are

desirable because they yield plastic putties, but

undesirable because they are potentially unsound.

The unsoundness arises from the fact that they

contain magnesia (unhj^drated magnesium oxide)

which may hydrate subsequently (forming magnesium hydroxide) in the set plaster and therej by disruptive expansion may result. Extensive

failures of white-coat plaster caused by this type

: of expansion are described in Building Materials

j and Structures Report 121 [1].^

I Until recently, in the commercial hydration of

1 dolomitic limes, which contain calcium oxide

(CaO) and magnesia (MgO) in nearly equimolar

ratio, the CaO was almost invariably hydrated,

i whereas the MgO was onlv slightly hydrated.

; Wells and Taylor j2] in 1937 developed heat-ofij solution and ignition-loss methods for deter1 mining the degree of hydration of magnesia in

l' hydrated dolomitic limes and putties. They

i showed that for six regularly hydrated dolomitic

limes, as received from the manufacturers, an

average of only 12.5 percent of the total magnesia was hydrated.

More recently, in a study of the expansive

characteristics of hydrated limes and the development of an autoclave test for soundness, Wells,

> Figures in brackets Indicate the literature references at the end of this paper.

Clarke, and Levin [3] showed that for 27 hydrated

limes of this type, an average of 15.7 percent of

the total magnesia was hydrated. Calculations

based on the analyses of 185 regularly hydrated

dolomitic limes submitted to the Bureau for test from 1923 to 1940 indicated that the average was 17.0 percent [1]. Manufacturers of regularly hydrated dolomitic

finishing limes almost invariably recommended

that the putty be used only following a 12- to 24-hour soaking period. An erroneous belief

seemed to be prevalent that such a soaking period was sufficient not only to provide a plastic putty but

at the same time to hydrate the product completely.

However, Wells and Taylor [2] showed that for

six of these hydrated limes the average percentages

of total MgO hj^drated in the putties at the end

of 1, 3, and 7 days were only 19.1, 30.2, and 40.9,

respectively. It is evident that if these values

be representative of the behavior of regularly

hydrated dolomitic lime, then the customary

procedure of soaking the lime as a putty for 1 day

must leave the bulk of the MgO still unhydrated

and the product unsound.

Consequently, the primary purpose of the

present investigation was to determine whether

a potentially unsound regularly hydrated dolomitic

lime can be rendered sound by soaking as a putty

for a reasonable length of time and to point out

to the architect, engineer, plastering contractor,

plasterer, and others concerned with plastering

the types of lime that will give satisfactor}^ per- formance.

1
2. Scope

To procure a fair cross section of the regularly

hydrated dolomitic limes being produced in the

United States, 18 samples were obtained from

separate lime producing centers. The samples were analyzed chemically, and

from the oxide composition the percentages of

hydrated and unhydrated magnesia at the start were calculated.

The limes were then made into putties and

stored under controlled conditions. At definite

time intervals, a sample of each putty was mixed

with Portland cement and cast into a bar. The

autoclave expansion of the hardened bar was

determined subsequently. In this way, it was

possible to ascertain the length of time required

to soak the hydrated dolomitic lime as a putty

in order that the magnesia be sufficiently hydrated so that the autoclave expansion would be no greater than 1 percent. One-percent expansion has been proposed as a specification limit for

soundness of hydrated limes [3]. At the same time intervals, a sample of each

putty was analyzed and the percentages of hydrated and unhydrated magnesia were calculated.

From these data the progress of the hydration was

followed. Equations were derived for making

these calculations.

This information served as a basis for determining the relation between the autoclave ex- pansion values and the percentages of unhydrated oxide in the putty at each time interval.

Studies were also made of the relation between

the autoclave expansion values and the reactivities of the MgO as reflected in the fineness of the

hydrated products.

3. Materials

3.1. Hydrated lime

The 18 regularly hydrated dolomitic limes (also

designed as type N—normal finishing hydrated

lime [4]) were part of the group of hydrated limes

used in the study "Expansive Characteristics of

Hydrated Limes and the Development of an

Autoclave Test for Soundness", RP1917 [3] Thus, for convenience of identification and comparision, the limes in the present paper have been

assigned the same numbers as in RP1917.

The oxide compositions of the selected limes were available from the previous investigation,

but because of aeration caused by frequent

handling and the fact that the storage containers were not completely airtight, it was deemed

advisable to check the limes for additional hydration and carbonation. Inasmuch as the proportions of the different oxides remaining in the

ignited limes could not change with time, only

CO2 and ignition-loss determinations were re- quired as a basis for recalculating the compositions. The chemical analyses, with the exception of the

free-water determination, were made originally

in accordance with Federal Specification SS-L-351

for hydrated lime [5; see also 6]; and the percentages of hydrated and unhydrated oxides were

calculated in accordance with Proposed Amendment 1 [7; see also 6] to this specification.^

The adjusted oxide compositions recalculated on the basis of the new values for the ignition

loss and CO2 are given in table 1, columns 2 to

2 Recently, Levin [8] has presented two nomograms from which the com- pound composition of a hydrated hme can be easily and rapidly determined from the oxide analysis, thus saving time and labor of calculation. Table 1. Chemical a7ialyses and calculated percentages of hydrated magnesia and unhydrated oxide for 18 regularly hydrated

dolomitic limes, together with the ignition losses (after drying) of aged putties made from these limes

Lime

Free water

(volatile at

150° C)

Oxide composition (after drying at 150° 0)

%

23 0. 48

24 .53 27 .45

28 .42

29 .49

30 .46

31 .42 34 .37

35 .25 37 .43

38 .27 40 .42

43 .39 44

45 .48.50

46 .28 47 .48 48 .53

Combined H2O

%

18.34

17. 60 18.68

18. 01

16. 24

18.16

17. 61

36. 65 17.16

18. 30

16. 60 16.84

16. 50

16. 88 16.19

16. 06

16. 03

14. 63

CO2

%

1.64

2.31

0. 56 2.03

5. 81

11.73 1.76

1.61

1. 13

0. 98

1.30

1.31

1. 13 1.45

1.05

0. 80

1.69

SiOj R2O3

1.75 1.07

0. 82 0. 36

.93 .36 .12 .16

.19 .17

.28 .22

. 14 .14

.40 .28

.34 .22

.20 . 18

.20 .10 .20 .12

.18 .16 .79 .53 .10 .12

. 14 .18

1. 42 .46

1.34 .68

CaO

%

45. 21

52. 86

46. 51

46. 82

45. 80

47. 22

47. 01

47. 41

47. 18

46. 68

48. 43

47. 59

47. 85

47. 20

46. 81

48.26

47. 53 48.28

MgO

%

31.85

25. 93 32.94

32. 31.70

32. 37

33.31 33.48

32. 80

33. 41

32. 98

33. 92

34. 00 33.32

35. 23

34.25

33.70

32. 99

Total

Calculated hydrated magnesia

% %

99. 86 10. 05

99. 88

99. 98

3. 50

99. 82

8. 88

8.42

99. 91 8.64

99. 74 8. 06

99. 94 7.19 99.98 4. 79 99.31 6.95

99. 90 8. 43

99. 29 3.22

99. 97 4. 66

100. 00 3. 70

99. 85 4. 87

99. 90 3. 90

99.94 2. 20

99. 94 2. 43

99. 61 " 0.00

Calculated unhydrated

oxide »

%

21. 80

22. 43

24. 06

24. 26

23. 06

24.32

26. 12 2826.85

24. 98

29. 76

29. 26

30. 30

28. 45 31.33

32.06

31.27

0 33. 59

Igni- tion

loss of dry hy- drated lime at

start t

%

19.98

19. 91 19.24

20. 04

22. 05

19. 65 19.34

18. 41 18.77

19.43

17. 58

18. 14

17. 81

18. 01 17.64

17. 11

16. 83 16.32

Ignition loss of putty dried at 150° C after aging for (time in weeks)

%

20. 27 20.36

20. 22 20.03

22. 85

20. 57

20. 03

19. 41

19. 60

20. 28

17. 92

18. 40

18. 44

18.93

18. 84

18. 03

17. 30

17. 12

%

20.98

20. 61 21.10

20. 72

23. 68

21.69

20. 60

20. 74

19. 96 21.92

18. 79

19. 74

19. 28

19. 20 20.31

18. 44

17. 90

16. 99

%

21. 55 21.58

22.37

22. 14

24. 77

22. 82 21.99

22. 51 21.00

23. 41

19. 77 21.17

21.20

20.14

23. 26

19. 78

19. 36

17. 94

%

22.23

22. 76

23. 79

23. 39 25.75

23.92

23. 62

24. 20

22. 13 24.93

20.68

22. 98

23. 55 21.47

25. 58

21.23 21.59

19. 92

%

23. 25

24. 67

26. 21

24. 76

26. 95

25. 29

26. 53

25. 88

23. 38

26. 27

22. 00 25.16

25. 91

23. 68

27. 11

23.42

24. 03 23.35

%

24.69

26.17

26. 43

26. 06

28. 10

26. 57

26. 96

27. 20

25. 01 27.14

23. 94 26.82

27. 49

25. 69

27. 80

25. 72

26. 06

25. 89

19%

25. 51

26. 65

26. 99

26. 60, 28. 43

26. 88

27.34

27. 42

25. 77 27.26

25. 19

27. 14

27. 81

26. 48 27.86

26. 58

26. 68

26. 44

16

20%

26. 06

26. 96 26.94

26. 86

28. 66

27. 10 27.53

27. 62

26. 13

27. 51

25. 72

27. 43

27. 86

26. 91

28. 00

26. 95

26. 72

26. 70

20

%

26. 62

26. 95 28.73

27.17

26.25

25. 97

27.36

27.06

27. 15

26. 751 26. 80

32

%

26.6

26.63

26.47

a Equal to the total MgO (column 8) minus the hydrated MgO (column 10).

•> Equal to the sum of columns 3 and 4.

" Calculations for this lime showed all MgO (column 8) and 0.6% of CaO as imhydrated (column 11). 2
9, inclusive. The recalculated percentages of

hydrated and unhydrated oxides are shown in

columns 10 and 11, respectively.

The arrangement of limes, column 1, follows

the numerical sequence recorded in RP1917, in

which publication the sequence was based on the

order of increasing percentage of calculated unhy

drated oxide. Inspection of column 11 shows some deviations from the percentage sequence.

It is apparent, therefore, that the limes had undergone additional hydration and carbonation of

variable amount.

3.2. Cement

One brand of portland cement was used in this

investiga tion. It conformed to type 1 of Federal

Specification SS-C-192 [9], and was designated

as cement No. 10 in IIP1917. The autoclave

expansion of the cement alone was 0.11 percent.

4. Procedure and apparatus

4,1. Preparation and storage of putty

Approximately 2,250 g of hydrated lime was

weighed into a glass jar. Water was added

slowly with constant stirring until a smooth

plastic mix was obtained. The aim was to approximate an on-the-job mortar-box consistency.

The jar then was sealed with a screw-on cap. The percentages of water in the putties as pre- pared varied from a minimum of 44.4 (for lime

29) to a maximum of 51.1 (for lime 45), with an

average value of 47.5. During the entire investigation, jars were stored in a constant-temperature room maintained at 21° ±1° C (70° ±2° F).

The putties were tested over a maximum period

of 32 weeks, according to the following schedule:

After aging (in weeks) 1/7, 3/7, 1, 2, 4, 8, 12, 16,

20, and 32. At these time intervals, sufficient

putty was removed for the determinations of (1) free water in the putty, (2) ignition loss of the

resultant dried putty, and (3) autoclave expansion

of cement-lime bars made from the putty.

4.2. Determination of free water in the putty

As a putty ages, the proportion of free water

decreases and, conversely, the proportion of

solids increases, because of the reaction MgO-f

H20-^Mg(OH)2. At each test period the per- centage of free water in the putty was determined,

so that in the preparation of all test bars for autoclaving (described subsequently), a constant

amount of hydrated lime on a dry-weight basis

could be used.

The putty was first thoroughly remixed in the

container to uniform consistency in order to re- distribute any water that might have accumulated on the surface. About 2 to 4 g of putty was

withdrawn on the tip of a spatula and spread

thinly around the sides of a tared, 30-ml platinum

crucible. This operation, together with the subsequent weighing of the crucible, was performed

in the shortest possible time. The crucible was

then heated for about 40 minutes in an oven maintained at 150° C, to drive off the free water. No

attempt was made to dry the lime to constant

weight as it was found that additional heatings

usually resulted in slight increases in weight,

which were ascribed to carbonation.

4.3. Determination of ignition loss of the

dried putty

The ignition loss of the dried putty was obtained by heating the same sample used for the

free-water determination to constant weight in an

electric furnace maintained at about 1,020° C.

4.4. Preparation and testing of autoclave bars

The reader is referred to RP1917 [3] for a detailed procedure for preparing, curing, autoclaving, and measuring the expansion of test specimens made from dry hydrated lime. In the

summary of that paper it was proposed that

"hydrated limes be tested in the proportion of 1 cement : 1 lime (by weight), that the cement used

have an expansion between 0.05 and 0.15 percent,

that the autoclaving be done at 295-lb/in.^ gage

pressure for 1 hr according to a controlled schedule

. , . " No modification in procedure was neces- sary for the preparation and testing of bars made

from dry hydrated lime and cement, designated

"at start" in tables 2 and 3. However, for the

preparation of bars made from wet aged lime

putty some modification was necessary.

Following the free-water determination, described earlier, a quantity of putty sufficient to contain 150 g of dry solids was weighed into a

1-liter porcelain casserole. Next, 150 g of portland cement was added to the putty. These

quantities were sufficient for the preparation of one test specimen.

For the remainder of the procedure, the operator wore rubber gloves. Immediately after addition

of the cement, the mixture was squeezed and

kneaded for 3 minutes. The mass was then al- lowed to stand undisturbed for 1 minute and

finally vigorously reworked for 1 minute. At this

point a Vicat penetration test for consistency was made according to the procedure given in Federal

Specification SS-C-158b [10], paragraph F-47.

It was found that the Vicat penetration decreased

as the putty aged. In the earlier tests the penetration was greater than 10, but no attempt was made to remove water. In the later tests, whenever the putty had stiffened, water was added to the putty; then the whole mass was mixed to uniformity before the addition of cement. However, the adjustment of the consistency in these

cases was only approximate.

Immediately after the determination of the

Vicat penetration, the cement-lime putty was re- mixed for approximately 15 seconds. This putty

then was molded into autoclave bar molds according to the procedure given in SS-C-158b. para3
graph F-61. The bar molds provided for test specimens having a cross section of 1 in. by 1 in. and a 10-in. effective gage length, SS-C-158b,

paragraph F-43.

Immediately after molding each specimen, the

exposed surface was covered with a strip of waxed

paper pressed down on the mold. This waxed

paper minimized breakage during curing, caused

by shrinkage cracks. The test specimens were

stored in the molds in a moist closet for at least 20 hr, following the requirements of SS-C-158b,

paragraph F-62.

At 23 ±1 hr after making the specimens, they were removed from the molds, measured for

length, and placed in an electrically heated autoclave meeting the requirements of Federal Specification SS-C-158b [6] for an autoclave to be used

in the testing of portland cement. The gage

pressure of the autoclave was raised to 295 Ib/in.^

within 1 to 1% hr, and maintained at 295 ±5

lb/in. ^ for 1 hour. For most of the specimens,

the reduction of the pressure and the subsequent

cooling in water to 21° C were done as required in the procedure of autoclaving as given in Federal

Specification SS-C-158b, paragraphs F-63e and

F-63f, respectively. It was found necessary, however, to cool in air to 21° C those specimens that

exhibited very high expansions (10% or more),

because when cooled in water the greatly expanded

specimens were apt to disintegrate.

For expansions under 2.5 percent, the comparator described in paragraph F-45 of SS-C-158b

was used. For higher expansions, less exact methods, giving values to within a hundredth of an inch, were used.

5. Calculations

5.1. Percentage of magnesia hydrated at start

The method described in Proposed Amendment

1 to SS-L-351 [7] for calculating the percentage

of hydrated MgO in a lime from the oxide analysis

has been well established by Bureau researches

[2,3]. It is based essentially on the premise that CaO

carbonates and hydrates before MgO. In the cal- culations, CO2 is allotted to the molecular equivalent of CaO. The remaining CaO is allotted to an equivalent amount of H2O. The amount of

MgO hydrated is that equivalent to the remaining

combined H2O.

In the following derivation, / designates the

ignition loss in percent and is equal to the sum of

the CO2 and the combined water. The formula for a compound represents also the percentage of that

component present, as determined from the oxide

analysis.

Combined water =/— CO2

CaO equivalent to CO2 =1.274 CO2

CaO remaining = CaO- 1.274 CO2

Combined II2O equivalent =0.3213 (CaO- 1.274 CO2)

to CaO remaining."

» If the calculated value is larger than that of the combined water, un- hydrated CaO is present.

Combined H2O remaining,. =(/- CO2) -0.3213 (CaO1.274 CO2)

Hydrated MgO (%), MgOh,. =2.238 [(/-CO2) -0.3213

(CaO- 1.274 CO2)] (1) Unhydrated MgO =Total MgO-hydrated

MgO (2)

5.2. Percentage of magnesia hydrated at

time t A formula for calculating the percentage of

hydrated MgO in the solids portion of an aged

putty can be derived from the oxide analysis of

the original dr}^ hydrated lime and the ignition

loss of the dried putty at time t. By substituting in the previously derived for- mula for MgOh (eq 1) one can obtain an expression

for the percentage of MgO hydrated at any time f, MgOh(o =2.238 [(/(o-C02(„) ; -0.3213 (CaO(,)-1.274 002(0)]^

(3)

where MgOhco represents the percentage of magnesia hydrated at time t, and the subscript (t) after

/, CO2, and CaO likewise refers to this time.

The oxide composition of a dried lime and its putty on an ignited basis is constant, however,

regardless of aging. Thus the composition of a

dried putty at time t can be expressed in terms of

the analysis at the start (designated as s) and the

ignition losses at times s and t. For example.

CaO(0

(4)

CaO(s) 100-/(,) 100-7(0

CaO,„=CaO„,(i22=|M).

A similar relationship holds for the other nonvolatile oxides. Assuming as negligible any additional carbonation of the lime putties during aging

in the closed jars, the relationsliip given in eq 4 can be applied to the CO2.

Making the appropriate substitution in eq 3

MgO.„,=2.238 |/,„-C0„., (i°oIj|°)

-0.3213 [CaO..,(M^;) ^ (5) _,2HC0.,(M^;)]|

J

Combining terms and simplifying, the final equation is obtamed

MgOh(„=2.238/(o-(100-/(o)

1.3220CO2(.) +0. 7191 CaO (,) 100-/(s)

y (6)

4
When the vahies at the start s are substituted

in eq 6, it reduces to the foUowdng hnear form

Mg0,(„=^/(„-5, (7)

where A and B are constants for a particular Ume.

5.3. Other equations

Several other equations can be derived for cal- culating the percentage of magnesia hydrated at time t, MgOh((), by the application of simple

algebraic principles.

One such equation, involving only the magnesia

hydrated at the start, MgOh(s), and the ignition

losses, is

MgOh(o = /(o(223.8-MgOhw) ^ 100-/w

100 MgOh(,)-223.8/w

(8)

' 100-/(,)

5.4. Sample data sheet

A typical data sheet (for lime 34) is given in

table 2, showing simplification of the formulas,

Table 2. Typical data sheet, including chemical analysis and simplified formulas

Lime 34. Chemical analysis (after drying at 150° C)

Percent Ignition loss 18. 41 CO2 1. 76 CaO 47. 41 MgO 33. 48

Si02 0. 40 R2O3 .28

Total 99. 98 Hydrated MgO, MgOhc,), 4. 79 Unhydrated MgO, MgOuo, 28. 69 Percentage of total MgO hydrated, ^^^XlOO, 14. 31 MgO(8)

Equations

Total MgO at time /:> MgO(o = MgO(.,(^|^^-y^) =33.48(^j^^5_|(|_^^

(1.3220CO2(.)-0.719lCaO(ri) MgO hydrated at time t-J MgOh(o = 2.2387(,)- (100-/(,))- 100-/(,)

9 9^87- nnn T

^ (13220X176-0.7191X47.41) -2.2387(0- (100-/(„) (100-18.41)

= 2.68447(0-44.637-

Calculated ignition loss at 100% hydration: 7 (100%) =27.68% [obtained by equating (a) to (b)].

.(a)

.(b)

.(c)

Tabulation

7(0 100-7(0

MgO(o

MgOh(oUnhydrated MgO(o

MgO^o

MgO(o

Expansion. . .

Time (weeks)

At start 1 2 4 8 12 16

Percent

33. 48

4. 79

28. 69

14. 31

9. 2

Percent

19. 41

80. 59

33. 07

7. 47

25. 60

22. 59

9. 0

Percent

20. 74

79. 26

32. 52

11. 04

21. 48

33. 95

9. 0

Percent

22. 51

77. 49

31. 80

15. 80

16. 00

49. 67

6. 8

Percent

24. 20

75. 80

31. 10

20. 33

10. 77

65. 37

6. 1

Percent

25. 88

74. 12

30. 41

24. 84

5. 57

81. 68

2. 7

Percent

27. 20

72. 80

29. 78

28. 38

1. 49

95. 01

0. 37

Percent

27. 42

72. 58

29. 78

28. 98

0. 80

97. 31

0. 32

Percent

27. 62

72. 38

29. 70

29. 51

0. 19

99. 36

0. 21

' Equation (a) is a variant of eq 4, p. 4.

' Equation (b) is eq 6, p. 4.

5
after substitution of the constants and the A^alues determined. The chemical analysis for this lime, as given in table 1, columns 3 to 11, inclusive, and

the ignition losses, columns 12 to 20, inchisive, are repeated for the purpose of convenience.

The calculated ignition loss at 100-percent

hydration was obtained for this lime by equating

the simplified expression for the MgO hydrated

at time t (eq b) to that for the total MgO present

at time if (eq a) and solving for /(^ (eq c). This

value was of practical importance, since by comparing it with the experimentally determined ignition loss at a given time, one could rapidly note

the approach of the sample to complete hydration.

At complete hydration, the value also served as an approximate check on the accuracy of the

chemical analysis and the calculations, as it was

the theoretical maximum ignition loss that could

be obtained.

6. Results and discussion

Table 1 gives the chemical analysis and the

calculated percentages of hydrated magnesia and

unhydrated oxides for the 18 regularly hydrated

dolomitic limes, together with the ignition losses

(after drying) of aged putties made from these

limes. From these data, the percentage of total magnesia hydrated in each putty at the various

testing periods was calculated, as shown in the

typical data sheet (table 2). The results are re- corded in table 3, together with the corresponding

linear autoclave expansion of cement-lime putty

bars (proportioned 1 to 1 on dry weight basis). It may be noted that all values obtained from

chemical analyses are reported to the nearest 0.01

percent. The calculated hydrated magnesia, un- hydrated oxides, and proportion of magnesia hydrated for all limes and putties also have been

reported to the nearest 0.01 percent. However,

it should be emphasized that the accuracy of

these calculated values is not known to 0.01 percent. The reproducibility of determining per- centage of expansion of cement-lime test specimens

is discussed in RP1917 [3]. Figures 1 and 2 show the effect of time of aging on the percentage of total magnesia hydrated and

on the linear expansion of cement-lime putty bars

(1:1, by dry weight) for the 18 regularly hydrated

dolomitic limes. The limes are arranged according to increasing time required for the expansion

of the cement-lime putty bar to decrease to 1 percent. One percent was chosen as the basis for

comparison because it is the suggested limit of

expansion proposed in a test for determining the

soundness of hydrated limes, described in Bureau

Kesearch Paper RP1917 [3]. Several conclusions are at once apparent from

these figures. Most striking is the correlation

Table 3. Percentages of total magnesia hydrated in 18 regularly hydrated dolomitic limes and in aged -putties made from,

these limes, together with the aidoclave expansions of cement-lime bars made from the hydrates and putties

Calculated proportion of total magnesia hydrated (time in weeks)

At

start ' %

31.55

13. 50 26.96

25.76

27. 26

24. 49

21.59

14. 31

18. 14 25.23

9. 76

13. 74

10. 88

14. 62

10. 85

6. 42

7. 21

0. 00

16.8

%

34. 10

18. 39

35. 25 25.68

34.59

32. 88

27. 37 22.69

25.19

32. 58

12. 15.84

15. 97

22. 25

19. 96

13. 76

10.5.26

22.5

%

40. 45 21.13 42.98

31.64

42. 35

42. 88 32.24

33. 95

27. 74

46. 82

19. 88

26. 89

22. 87

24. 51

31. 58

17. 09

15.87

4. 19

9.2

%

45. 61 31.86

54. 36 44.23

52.76

53.27

44. 41

49. 67

37. 40 60.26

28. 29

39. 10

39. 19

34. 76

50. 21

%

51.89

45. 50 67.53

55. 70

62. 43

63. 67

59. 23

65. 37 47.59

74. 56

36. 29

55. 21

60. 29

44. 22 76.96

28.17 40.58

28.05 47.53 12.12 29.20

41.1 54.7

%

01.51 66.83

81.21

68. 71

74. 61

77. 06

77. 43 81.68

59. 19 87.67

48.22

75.63 82.84

63. 55 91.33

60. 27 70.16

60. 92

71.6

%

75. 48

86. 69

93. 34 81.50

86.63

90. 03

91. 68

95. 01

74. 90

96. 43

66. 49

92. 02

98. 73

84. 04

98. 07

82.18

90. 12

86. 34

87.2

12

%

83. 71 92.80 99.09

86.93

90. 14

93. 21 95.63

97. 31

82. 48

97. 65

78. 79 95.23

100. 08

92. 00

98.63

90.71

96. 43 92.03

92.4

16

%

89. 33

96. 66

98. 56

89. 60

92. 66

95.54

97. 49

99. 36

86. 12

100. 20

84. 15

98. 20

102. 58

96. 40

100. 00

94. 47 96.83

94. 81

95.2

20

%

95. 14

90.52

93. 41

96. 26

'87."34

86. 66

97. 48

97.98

96.48

97.14

96.84

''96.1

32

%

95. 55

91.22

91. 84

96. 60

Linear expansion of cement-lime putty bar (proportioned 1 to 1 on

dry-weigtit basis) (time in weelis)

At

Start » M 1 2 4 8 12 16 20 32

% % % % % % % % % % %

15.2 12.

1

11.7 12.0 12.5 9.1 6.5 4.3 3.6 2.6 2.2

8.6 8.2 7.4 7.0 5.6 2.6 0. 56 0.28 0. 22

9.4 7.3 7.0 6.9 4.0 2.6 .46 .17 .18

12.

1

12.8 11.9 10.6 9.0 7.2 3.7 1.5 .87 "6.' 71 8.8 8.3 7.0 6.0 4.9 3.0 0.59 0.36 .27 .22

7.5 7.4 6.6 6.8 4.7 2.6 0.46 0.27 0. 22 0.18

10.7 11.2 9.5 8.6 6.6 3.6 .60 .31 0. 24 9.2 9.0 9.0 6.8 6.1 2.7 .37 .32 .21 14.9 16.5 15.5 14.7 13.6 11.8 8.1 5.5 4.6 'To" '2.'3" 6.7 6.2 5.3 1.8 1.7 0. 89 0.26 0. 27 0.17

17.7 16.8 71.2 17.2 1.5.2 14.4 9.1 4.8 2.8 1.8 0.66

12.6 (') 11.8 10.7 8.6 4.9 0. 88 0. 35 0. 27 0. 22

11.4 10.9 (') 8.5 6.2 2.9 .27 .19 .17

14.3 13.1 13.1 12.3 9.4 5.9 3.4 1.5 .78 "Vii

9.8 8.0 7.5 5.0 2.8 0. 72 0.17 0. 13 .13

17.3 16.6 17.0 17.4 15.2 11.6 5.1 2.4 1.1 0. 61 13.2 10.5 9.2 8.7 6.7 4.5 0. 91 0.51 0. 31 0. 29

16.0 13.9 14.1 13.5 11.3 7.6 4.0 2.4 1.9 1.6 1.2

12.0 11.0 10.6 9.7 8.0 5.5 2.5 1.4 1.0 ''0.8

» Dried hydrated lime as received; value derived from columns 8 and 10, table 1.

I" Bar made with hydrated lime as received.

« Bar cracked during curing.

<> Average based on all 18 samples, using extrapolated values where no figures are given.

6
Figure 1. Effect of time of aging lime putties at 21° C {70° F) on the increase in magnesia hydrated and on the decrease in autoclave linear expansion of cement-lime -putty bars. The twelve regularly hydrated limes used are arranged according to increasing time required for expansions of cement-lime putty bars (1:1 by dry weight)

to be reduced to one percent when autoclaved for 1 hour at a gage pressure of 295 Ib/in^. 0> Magnesia hydrated. •, Linear expansion (autoclave)

.

7
7 14 21 2a 35 42 49 56 6 12 16 20 24 28 -32 TIME, DAYS TIME, WKS.

0 7 W 21 28 35 42 49 56 8 12 16 20 24 28 32 TIME, DAYS TIME,WnS.

/4 21 28 35 42 49 56 8 12 15 20 24 23 32 T)ME, DAYS TIME, WKS. Figure 2. Efect of time of aging lime putties at 21° C {70° F) on the increase in magnesia hydrated and on the decrease in autoclave linear expansion of cement-lime putty bars. The six regularly hydrated limes used are arranged according to increasing time required for expansions of cement-lime putty bars (1:1 by dry weight) to be

reduced to one percent when autoclaved for 1 hour at a gage pressure of 295 Ib/in^. O, Magnesia hydrated. Linear expansion (autoclave)

between percentage of magnesia hydrated in lime

putty during aging and autoclave expansion of

cement-lime bars made from the putty. For any

one lime, as the percentage of magnesia hydrated

increases, the percentage of linear expansion decreases; thus, as the hydration of the magnesia

approaches 100 percent, the linear expansion approaches 0.2 to 0.3 percent.

In comparing the behavior of different limes

with respect to the effect of aging on hydration

characteristics of the putties and on expansion, it appears that a slow rate of hydration is attended

by a slow decrease in expansion. The effect is particularly apparent by comparing extreme dif- ferences, as shown in figures 1 and 2, for example,

lime 37 with lime 35. Table 4 gives the times of aging of lime putties at which the expansions of cement-lime putty

bars were 1 percent ; the corresponding percentages

of total MgO hydrated in the putties; the expansions of cement-lime bars prepared from the dry

hydrated limes (as received) ; and the corresponding percentages of unhydrated oxide in the dry

lime. These expansion and hydration values at the 1-percent point for the different limes were

obtained from figures 1 and 2. It can be seen that the shortest time of aging

required to reduce the expansion to 1 percent was

3 weeks (lime 37) ; the next shortest time was 4

weeks (lime 45), followed by nine others, or half

the total number, distributed over a period of 6

to 8 weeks. The remaining seven limes required

much longer periods, and three (48, 23, and 35)

gave expansions in excess of 1 percent, even after

32 weeks of aging.

It is also apparent from table 4 that at least 83

percent of the total MgO was hydrated before the

expansion was reduced to 1 percent; and in two

cases over 97-percent hydration was required.

The figures and table 4 reveal the fact that the

limes differed markedly from one another, both in

regard to the time required to reach a given percentage of expansion and to the extent of hydration at the given expansion.

Table 4. —Times of aging of lime putties required to reduce

the autoclave linear expansions of cement-lime putty bars

to 1 percent and the corresponding percentages of total MgO hydrated in the putties, together with the expansions

of cement-lime bars prepared from the dry hydrated limes "as received" and the corresponding percentages of unhydrated MgO in the dry lime

Lime

Time

required

to reach

1 percent expansion

MgO hydrated at

1 percent expansion

Expansion

of bar made

.with dry hydrated

lime "as received" »

Unhydrated

MgO in dry

hydrated

lime "as received" •>

Weeks Percent Percent Percent

37. 3 83 6.7 24.98

45- 4 92 9.8 31.33

43 6 95 11.4 30. 30 24 6.5 83 8.5 22.43

31 - 7 91 10.7 26. 12

34 7 93 9.2 28. 69 30 7 88 7.5 24. 32

27 7 91 9.4 24.05

29 7 85 8.8 23. 06 47—- - 8 90 13.2 31.27

40 8 92 12.6 29.26

44 14 94 14.3 28.45

28__ 16 90 12.1 24.26 46 16 95 17.3 32.05

38_ 26 91 17.7 29. 76

48 Over 32 « Over 97 16.0 33. 59

23.... Over 32 d Over 96 15.2 21.80 35 Over 32 ' Over 91 14.9 26. 85

» From table 3, column 13.

i> From table 1, column 11.

" 1.2-percent expansion at 32 weeks.

^ 2.2-percent expansion at 32 weeks.

• 2.3-percent expansion at 32 weeks.

8
A factor of prime importance in explaining the

variability exhibited by the different limes is the

reactivity of the constituent MgO. The reactivity of the MgO is closely connected with the

phenomenon of overburning in the lime kiln during the conversion of the limestone to quicldime.

The extent of overburning with the resultant decrease in reactivity of the oxides to water is in- creased with temperature as well as with the time

of bm'ning. As MgCOs decomposes at a much

lower temperature than CaCOs and as MgO is sus- ceptible to overburning, it follows that dolomitic

quicklimes contain overbm-ned MgO the reactivity of which varies greatly depending on the

conditions of burning.^ Variation in the reactivity of the MgO is manifested by (1) the extent

to which MgO is converted to Mg(0H)2 in the

production of the hydrate from the quicklime

(table 3, column 2) ; (2) the rates of hydration of

the MgO when the lime is hydrated further as a putty (table 3 and figs. 1, 2); and (3) the different

values of autoclave expansions of cement-lime

bars attending the hydration, within the autoclave, of equal quantities of MgO.

The third case is clearly evident in figure 3, where the percentages of unhydrated oxide in all the times and putties at each test period are plotted against the corresponding percentages of

linear expansion of the autoclaved cement-lime

putty bars. The percentage of unhydrated oxide

for each lime at a given period was calculated

from the data in table 1, according to the method

illustrated in table 2. From figure 3 it can be

seen that although there is a strong trend for inO o

— o

, OP

5 o

o o

I I L

5 10 15 20 Z5 30 UNHYDRATED OXIDES REMAINING IN THE UME, PERCENT

35

Figure 3. Relation between percentage autoclave linear ex- pansion of cement-lime putty bars {1:1 by dry weight) ^and

unhydrated oxide (MgO) in putties at the various test periods.

3 A more complete discussion of overburning is given in BMS121 [11.

creased unhydrated oxide to be associated with

increased expansion, nevertheless, the points are spread fan-shaped from the origin and that, in

general, the expansions vary for a given percentage

of unhydrated oxide.

The same conclusions are reached from figure 4, which has been reproduced from a previous publication [3, fig. 8]. Figures 3 and 4 are compar0 5 10 15 20 25 30 35 UNHYDRATED OXIDES IN HYDRATED LIME , PERCENT Figure 4. Linear expansion of cement-lime bars prepared

with hydrated limes containing various amounts of unhydrated oxides, in the proportion of 1 cement to 1 lime {by

weight) and subsequently autoclaved for 3 hours at a gage

pressure of 295 Ib/in^.

See figure 8 of RP1917 [3]. The specimens were prepared with a cement, which, without addition of hydrated lime, had a linear autoclave expansion of O.ll percent. X, High-calcium; 9, regularly hydrated dolomitic; Oi highly hydrated

dolomitic; A, magnesian.

able, but it is interesting to note that in figm-e 4,

variations in unhydrated oxide were obtained es- sentially by using many limes of different types

rather than by aging putties of a selected few

regularly hydrated dolomitic limes, as for figm*e 3. By testing high-calcium, magnesian, highly hydrated dolomitic, and regularly hydrated dolomitic

limes, it was possible to cover the range of unhydrated oxide from 0 to 34 percent, in figure 4. A careful comparison of figures 3 and 4 reveals an apparent discrepancy between the two. It can

be seen that the spread of expansion values asso- ciated with unhydrated oxide of under 5 percent

is difi^erent in the two figm-es. In figm'e 4, all but one of the limes (actually 37 out of 38) show ex- pansions of less than 1 percent when the unhydrated oxide is undei' 5 percent, whereas in figure 3, only about two-thirds of the expansion values

(actually 44 out of 63) are less than 1 percent for the same range of unhydrated oxide. However,

the distribution of the 19 exceptions is not apparent from figme 3. Actually, all of the exceptions occurred among the seven limes requiring

9
aging periods of 14 weeks or longer before expansions were reduced to 1 percent (table 4, limes 44,

28, 46, 38, 48, 23, 35); furthermore, 12 of the ex- ceptions occurred among the 3 limes requiring more than 32 weeks (table 4, limes 48, 23, 35). It is a significant fact that the lime putties re- quiring the longest aging periods to effect a reduction in expansion to 1 percent yield the highest

expansions for a given percentage of unhydrated

MgO. This again may be explained by the process of overburning. It should be borne in mind

that in the commercial production of lime the

degree to which the MgO is overburned is not

likely to be uniform for the whole mass of MgO,

because in the calcining process the dolomite is added in lumps and consequently a temperature

gradient exists between the surface of the lump

and the core. However, the bulk of the MgO is sufficiently overburned so that little is hydrated

in the normal process of producing a hydrated

lime. During the aging of a lime as a putty,

apparently the less overburned MgO, being more

reactive, hydrates first, leaving behind the more

overburned, less reactive, MgO. However, re- gardless of the state of overburning, all of the

MgO hydrates under the temperature conditions

of the autoclave test. But the highly overburned

MgO gives rise to the largest expansions in the

autoclave.

Preliminary experiments with cement-MgO bars

prepared with MgO of different reactivity have

verified the conclusion that it is the less reactive

MgO which gives rise to the greater expansions in

the autoclave. The MgO was prepared by completely hydrating reagent quality MgO in an autoclave at 295 lb/in. ^ and subsequently heating portions of the Mg(pH)2 at 500°, 1,000°, and 1,300° C.

The corresponding percentages of expansion of the

cement-MgO bars, containing in each case 5 percent of MgO, were 0.12, 0.27, and 5.0. The ex- pansion of the neat cement bar was 0.11 percent.

Table 4 reveals the interesting fact that the

group of 7 limes whose putties required aging

periods of 14 weeks or longer to effect a re- duction in expansion to 1 percent had the greatest

autoclave expansions when tested on the "as re- ceived" basis. The average expansion value at the start for these seven limes was 15.4 percent

as compared to an average of 9.8 percent for the

other 11 limes. However, the average value for

the unhydrated oxide of the seven limes was 28.1

percent as compared to an average of 26.9 percent

for the remaining limes. The small average dif- ference of 1.2 in the percentage of unhydrated

oxide in the two groups is not statistically significant and does not adequately account for the

large difference in autoclave expansion of 5.6 percent.

It may be added that the seven limes whose

putties required aging periods of 14 weeks or longer to effect a reduction in autoclave expansion

to 1 percent when tested in the proportion of 1 cement to 1 lime had the greatest expansions when

tested on the "as received" basis not only for that

proportion but also for the 2 cement to 1 lime and

1 cement to 2 lime proportions.^

Thus there is added evidence that the degree of

overburning is of prime importance and that the

autoclave expansion of a bar is the resultant effect of two fundamental factors: (1) the total quantity

of unhydrated MgO present; and (2) the reactivity of the MgO, which is a measure of the

degree to which the lime has been overburned during the calcining process, which, in turn, is a function of stone size and time and temperature of

calcining. It is obvious that the autoclave test in addition to serving as a soundness criterion for hydrated lime also shows promise as a possible

control method for determining the degree of over- burning.

It is known that increasing the temperature

and/or time of calcining increases the degree of

overburning of a lime. Also, as the degree of over- burning increases the, bulk densities of the CaO

and MgO increase, indicating a consolidation of

the molecules and a reduction in surface area. Staley and Greenfeld [11], in a study of the surface areas of high-calcium quicldimes by the nitrogen

adsorption method, have found that the surface area of CaO decreases appreciably both with in- creased temperature and time of burning. More

recently, Murray, Fischer, and Sabean [12], in a study of the effect of time and temperature of

burning on the properties of quickline prepared

from calcite, have shown that the porosity, surface

area, and activity of the quicklime are closely

related, and that high values of porosity are asso- ciated with high values of surface area and with

high values of activity with water. The surface area of MgO should be decreased even more than in the case of CaO, because MgO

is more susceptible to overburning than CaO.

Inasmuch as about one-quarter to one-third of

regularly hydrated dolomitic lime consists of over- burned MgO, extent of overburning may be re- flected in the surface area. Consequently, surface areas of the 18 hydrated

limes were determined by the nitrogen adsorption

method. Samples were sealed in glass adsorption

cells and evacuated at 100° C overnight to a pres- sure of approximately 1X10"^ mm of Hg. The

quantity of space of each sample holder not

occupied by the solid adsorbent was determined

with helium. Adsorption tests were made using

purified nitrogen gas with samples in a bath of

liquid nitrogen. The quantities of nitrogen adsorbed were determined at four to six partial

pressures in the range of 0.05 to 0.30 mm of Hg

for each sample. Surface areas of all samples were

evaluated by means of the Brunauer-EmmettTeller equation [13], assuming that the nitrogen

molecule occupies an area of 16.2 square angstroms. Table 5 gives the results of the determinations

' The autoclave expansion values for the bars proportioned 2 cement to

1 lime and 1 cement to 2 lime are given in table 1 and figures 7, 9, and 10 of RP1917 [3]. 10
of surface areas expressed as square meters per

gram. For convenience of comparison, the linear

expansion of cement-lime bars prepared from the

dry hydrated limes (as received), and the corres- ponding percentage of unhydrated MgO in the

dry lime are also included. The limes are arranged

in the order of increasing expansion. Inspection

of the table indicates a tendency of the surface

areas to decrease with an increase in the autoclave

expansions of the hydrated limes "as received."

Table 5. Surface areas available to nitrogen for 18 regularly hydrated dolomitic limes arranged in order of in- creasing autoclave linear expansions of cenient-lime bars prepared from the dry hydrated liynes "as received'', and

the corresponding percentages of unhydrated MgO in the dry lime

Lime

Expansion

of bar made

with dry

hydrated

lime "as received""

Unhydrated

MgO in dry hydrated

lime

"as

received" i>

Surface

area

available

to nitro- gen

Percent Percent

37 6.7 24. 98 12.9

30 7.5 24. 32 12.7

24 8.5 22.43 10.0

29 8.8 23.06 12.6

34 9.2 28. 69 11.8

27 9.4 24. 06 12.7

45 9.8 31.33 11.0

31 10.7 26. 12 11.6

43 11.4 30. 30 11.3

28 12.1 24.26 11.7

40 12.6 29.26 8.2

47 13.2 31.29 9.1 44 14.3 28. 45 12.8

35 14.9 26. 85 9.9

23 15.2 21.80 10.5

48 16.0 33. 59 7.5

46 17.3 32. 05 9.4

38 17.7 29. 76 8.0

» From table 3. column 13. •> From table 1, column 11.

Figure 5 is a scatter diagram of the linear expansion and surface area. The line fitting these data,

determined by the method of least squares, is 7=26.3—1.33 X, where Fis the value of the

linear expansion and A' the value of the

surface area. The coefficient of correlation between the linear expansion and

surface area is r=-0.7, where r=XXY/^^JP^^

Hence, there is a significant correlation between

the linear expansion of cement-lime bars prepared

from regularly hydrated dolomitic limes and the

surface area of these hydrates.

In considering these data it should be mentioned

that the samples were obtained from several

widely separated lime-producing centers. Dolomitic limestone differs from one area to another,

and the characteristics of a quicklime are related

to the limestone from which it is made. Likewise,

the properties of a hydrated lime, such as fineness

and plasticity, are largely determined by those of

the quicklime. It should be emphasized that

about two-thirds to three-quarters, by weight, of

regularly hydrated dolomitic lime, is composed of

16

16

li 10

6

' 1 o

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1 6 8 10 12 14 SURFACE AREA,M2/e

Figure 5. Relation between autoclave linear expansion of cement-lime bars in the proportion of 1 cement to 1 lime

(by weight), table 3, column IS, and surface area of 18

regularly hydrated dolomitic limes

materials other than MgO, primarily Ca(0H)2

and smaller amounts of Mg(0H)2. The presence

of these hydrates tends to mask differences in

surface area attributed to the MgO. All of these

factors contribute to the scattering of the points

in figure 5. In addition, the quantity of unhydrated MgO is not a constant. These factors also

tend to mask differences in sm'face areas of MgO

resulting from differences in degree of overburning.

Nevertheless, in spite of these variables, the extent of overburning of MgO during the calcining

process, as reflected by increased autoclave expansions of cement-lime bars, is also manifested in

lower surface areas of the partially hydrated limes.

The relation, however, needs further study. An

investigation should be undertaken of the effect of overburning on the autoclave ex-pansion, using

hydrates obtained from quicldimes produced from

dolomitic limestone from a single source and

burned and hydrated under carefully controlled

conditions.

Consideration will now be given to a slight error involved in the rapid method used for determining

the quantity of unhydrated MgO in the putties.

The error arose from the procedure for expelling

the free water from the putties, by drying in an

oven maintained at 150° C. Unquestionably,

hydration of some additional MgO occurred during

11
the brief drying period. An estimate of the extent

of this hydration was ascertained by a simple

experiment.

Putties were made from three of the dry hydrates, and after a 15-minute aging period, they were dried and ignited according to the rapid

method described previously. Calculated from

these data, the unliydrated oxide content of the

lime portion of the putty was compared with the

value determioed for the dry hydrated lime and

based solely on the oxide anal^^sis. The assumptions were made that no additional h^^dration had

occurred during the 15-minute soaking period and

that the only difference between the two methods was reflected in the additional hydration occurring

during drjang in the rapid method. Values for

the unhydrated oxide content obtained by the

rapid method were from 1 to 4 percent higher

than those calculated for the dry lime, and a trend was indicated for the greatest differences to be

associated with the limes whose putties hydrated

most rapidly.

It should be emphasized that in determining

the percentage of unli3^drated oxide in the putty

by the rapid method, the error is greatest in the

early stages of aging when the MgO still contains

the most reactive fractions. As aging proceeds,

however, selective hydration occurs; and as the more reactive fractions hydrate, the error should

decrease. Consequently, it is believed that the

high expansion values obtained in some cases with putties containing a surprisingly low percentage of unhydrated oxide are essentially correct. Figure 6 shows the effect of time of aging on the

percentage of magnesia hydrated for all of the

lime putties, plotted on one set of coordinates.

For the purpose of clarity, values for the per- centage of magnesia hydrated in the dry lime, "as received," are omitted. A heavy black line

is drawn through the arithmetical average for each test period, as given in table 3. The wide variation in percentages of magnesia

hydrated at each test period is evident from the

spread of values. The average values of magnesia hydrated at the start, and at 1, 3, and 7 days are 16.8, 22.5, 29.2, and 41.1 percent, respectively (see also table 3). These figures are in

agreement with those reported in 1937 by Wells

and Taylor [2] for six regularly hydrated dolomitic

lime putties at corresponding ages, namely, 12.5,

19.1, 30.2, and 40.9 percent, respectively. Thus

it is evident that the regularly hydrated dolomitic

lime of the present time is fundamentally the same

as that produced in 1937. In fact, calculations

based on the analyses of 185 regularly hydrated

dolomitic limes submitted to the Bureau for test for compliance with Federal Specification SS-L-3 51

[5] from 1923 to 1940 show that the average per- centage of total magnesia hydrated was 17.0 [1]. Figure 7 shows the efl^ect of time of aging on the

percentage of linear expansion of cement-lime

putty bars (1:1 by dry weight) for all of the lime

putties, plotted on one set of coordinates. As in

TIME. WEEKS FinuHE 6. Ejfed of time aging on the percentage of total magnesia hydrated for all of the putties prepared from the 18 regularly hydrated dolomitic limes. The heavy black line is drawn through the arithmetical average for each

test period, as given in table 3.

TIME. WEEKS FiriURE 7. Effect of time of aging on the percentage of autoclave linear expansion of cement-lime putty bars

(1:1 by dry weight) for all of the lime putties prepared

from the 18 regularly hydrated dolomitic limes. The heavy black line is drawn through the arithmetical average for each

test period, as given in table 3.

figure 6, values for the dry hydrated lime "as

received" have not been included, and a heavy

black line has been drawn through the arithmetical

averages (values given in table 3). The wide variation in percentages of expansion

at each test period is evident. The average linear

expansion at the start, 1, 3, and 7 days is 12.0,

11.0, 10.6, and 9.7 percent, respectively (see table

3). At 16 weeks the average expansion is 1 percent, with 13 of the 18 limes under the 1-percent

value. The average amount of magnesia hydrated

at this time is 95.2 percent (table 3). It can be

clearly seen by comparing figure 5 with 6, that

12
as the percentage of magnesia hydrated in the

putties increases, the percentage of Hnear expansion of the bars decreases.

7. Summary and Conclusions

The progressive hydration of magnesia in dolomitic hme putties upon aging and the attendant

decrease in expansion of cement-Hme putty bars were studied.

Eighteen regularly hydrated dolomitic limes

(also designated as type N—normal finishing

hydrated limes) representative of commercial production were made into putties; and these were

stored in airtight containers and aged in a con- stant-temperature room maintained at 21° ±1°C

(70° ±2°F).

At progressive time periods (in weeks) of K, %,

1,2, 4, 8, 12, 16, 20, and 32, representative samples

of the putties were removed, and determinations were made for free water and ignition loss. From

these determinations and the chemical analysis

of each dry hydrated lime, as received, the per- centages of total magnesia hydrated in the lime

of the putties were calculated. A portion of each

lime putty was then mixed with portland cement

in the proportion of 1 : 1 on a dry-weight basis and

cast into bars. Subsequently, the linear expansions were ascertained after autoclaving the bars

at 295 lb/in.2 for 1 hr. Equations were derived for calculating the per- centage of unhydrated oxide and the percentage

of total magnesia hydrated in a dry lime and in an aged putty.

For any particular lime, as the percentage of

magnesia hydrated in the putty increased, the

percentage of autoclave expansion of the corre- sponding cement-lime putty bar decreased; but

neither the rate of increase of hydi-ation nor the

rate of decrease of expansion was a linear function

of time. As the amount of magnesia hydrated

approached 100 percent, the autoclave expansion

approached 0.2 to 0.3 percent.

The limes differed markedly both in regard to the time required to reach a given percentage of

expansion and to the extent of hydration at the

given expansion. The shortest time of aging

required to reduce the expansion to 1 percent (a

suggested specification limit) was 3 weeks, whereas

the longest time was in excess of 32 weeks. The

quantity of total magnesia hydrated when the

expansion had been reduced to 1 percent ranged

from 83 to more than 97 percent.

In general, the lime putties requiring the longest

aging periods to effect a reduction in expansion

to 1 percent also gave the highest expansions for a given percentage of unhydrated MgO.

The hydrated limes which gave expansion values

of 14 percent or more when tested on the "as received" basis required 14 weeks or more of aging

as a putty before the expansions were reduced to

1 percent.

Variations in rates of hydration and in expansive

characteristics were interpreted as a function of

the quantity and the reactivity of tlie unhydrated

magnesia. The autoclave test was suggested as a possible method for checking the degree to which a dolomtic lime had been ovcrburncd during

the calcining process. The average percentages of total magnesia

hydrated in the putties after aging 1, 3, and 7 days were only 22.5, 29.2, and 41.1, respectively, and

the corresponding average percentages of linear

expansion of the cement-lime putty bars were

11.0, 10.6, and 9.7, which values are far in excess

of the proposed specification limit of 1 percent.

It is evident that the customary soaking of a putty for 1 day on the job hydrates but little MgO in a regularly hydrated dolomitic lime (also

known as type iST—normal finishing hydrated

lime) and leaves the putty still potentially unsound. Even 7 days of soaking is entirely inadequate. In fact, it would be most difficult to specify the time of aging required to reduce the

expansion to 1 percent, because the value might

range from a minimum of 3 weeks to over 32

weeks. If a specification is to include all of the

dolomitic finishing hydrated limes of this type,

there would be required about 7 to 8 months—an

aging period altogether too long from a practical

standpoint.

Considering the fact that the use of regularly

hydrated dolomitic lime has resulted in widespread

white-coat plaster failure [1] and that this lime

cannot be rendered sound within a reasonable

soaking period, the question naturally arises as to what suitable alternates are at hand.

Certain manufacturers are now producing a more completely hydrated dolomitic lime. In

most instances this has been accomplished by

using autoclaves to hydrate the lime at elevated

temperature and pressure. Specifications have

been formulated which will exclude all hydrated

limes containing an undesirably high percentage

of unhydrated oxides. They state that the total

free calcium oxide (CaO) and magnesium oxide

(MgO) in the hydrated product shall not exceed

8 percent by weight (calculated on the "as re- ceived" basis) [7]. In the specifications of the

American Society for Testing Materials such lime

is designated as type S (special) hj^drated lime

[14]. It is recommended that the consumer insist upon a lime meeting the 8-percent requhement.

The new type of lime is marketed in bags carrying an identifying statement.

An accelerated performance test would be preferable to a limitation of the chemical composition.

An autoclave test for soundness with a limit of

1.0 percent has been proposed [3]. But until this

soundness test or a modification thereof is adopted,

the best safeguard for the cosumer is the 8-percent

limitation on unhydrated oxides.

Although most high-calcium hydrated limes are not higlily plastic, nevertheless, they are used for

plastering and masonry construction. They are characterized by having low percentages of un- hydrated oxides and low percentages of autoclave

13
expansion, and, consequently, are eminently

sound [3]. Another alternate is the use of quicklime be- cause a satisfactory lime putty that is completely

hydrated can be obtained from quicklime. It is recommended that the directions for slaking, as given in Standard specifications for gypsum plastering, issued by the American Standards Association as A42. 1-1950 [15], be followed.

The authors express thanlcs to R. L. Blaine and

H. J. Valis for determining the surface areas of

the 18 hydrated limes by the nitrogen adsorption,

method and also to J. M. Cameron for his statistical analysis of the relation between the surface areas and the linear expansions of cement-lime

bars prepared from these limes.

8. References

[1] Lansing S. Wells, Walter F. Clarke, Edwin S. Newman, and Dana L. Bishop, Investigation of failures of white-coat plaster, NBS Building Materials and

Structures Report 121 (1951).

[2] Lansing S. Wells and Kenneth Taylor, Hydration of magnesia in hydrated limes and putties, J. Research

NBS 19, 215 (1937) RP1022.

[3] Lansing S. Wells, Walter F. Clarke, and Ernest M.

Levin, Expansive characteristics of hydrated limes and the development of an autoclave test for soundness, J. Research NBS 41, 179 (1948) RP1917.

[4] Standard specifications for normal finishing hvdrated

lime, A&TM Designation: C6-49, ASTM Standards,

part 3, 159 (1949).

[5] Federal Specification SS-L-351 for lime; hydrated

(for) structural purposes.

[6] Standard methods of chemical analysis of limestone,

quicklime, and hydrated lime. ASTM Designation: C25-47, ASTM Standards, part 3, 187 (1949).

[7] Proposed amendment to Federal Specification SS-L351 for lime; hydrated (for) structural purposes. Date of amendment, February 2, 1940. See also

[6].

[8] Ernest M. Levin, Nomograms for obtaining the com- pound composition of hydrated limes from the oxide analysis, NBS Miscellaneous Publication 196, issued December 30, 1949. See also ASTM Bulletin 162, 58 (1949) TP227.

[9] Federal Specification SS-C-192 for cements- portland. See also type 1 cement of Standard Specifi- cations for Portland cement. ASTM Designation:

C150-49, ASTM Standards, part 3, 1 (1949).

[101 Federal Specification SS-C-]58b for cements, hydraulic; general specifications (methods for sampling, inspection, and testing) ; as well as Standard

method of test for autoclave expansion of portland

cement, ASTM Designation: Cl 51-49, ASTM

Standards, part 3, 35 (1949).

[11] H. R. Staley and S. H. Greenfeld, Surface areas of quicklimes, Ind. Eng. Chem. 41, 520 (1949).

[12] J. A. Murray, H. C. Fischer, and D. W. Sabean, The

effect of time and temperature of burning on the

properties of quicklime prepared from calcite. Preprint, presented at the annual meeting of the American Society for Testing Materials, at Atlantic

City, N. J., June 1950.

[13] S. Brunauer, The adsorption of gases and vapors,

p. 153. (Princeton University Press, Princeton N. J., 1945.)

[14] Standard specifications for special finishing hvdrated

lime. ASTM Designation: C206-49, ASTM Standards, part 3, 161 (1949).

[15] Standard specifications for gypsum plastering; includ- ing requirements for lathing and furring. Am.

Standards Assn. A42.1-1950. Also, ASTM Designation: C5-26A appendix, ASTM Standards, part 3, 158 (1949). Washington, July 23, 1951.

14 U. S. GOVERNMENT PRINTING OFFICE^ I3S2
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete-Block Wall Construction Sponsored by the National Concrete Masonry

Association 15fS BMS33 Plastic Calking Materials 15^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 15^ BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions With "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co 10^* BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co lOjS BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10^ BMS42 Structural Properties of Wood-Frame Wall and Partition Construction with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation 15f5 BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 15^ BMS44 Surface Treatment of Steel Prior to Painting 10^ BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 20^ BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 15(4 BMS49 Metallic Roofing for Low-Cost House Construction 20^ BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

Tilecrete Co _ 10^ BMS52 Effect of Ceiling Insulation Upon Summer Comfort 15^ BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co lOfS BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 10^ BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 10^ BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS59 Properties of Adhesives for Floor Coverings 15^ BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 30^ BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions.. 10^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association 15^ BMS63 Moisture Condensation in Building Walls 15^ BMS64 Solar Heating of Various Surfaces . lOfS BMS65 Methods of Estimating Loads in Plumbing Systems 15^ BMS66 Plumbing Manual 35^ BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floors, and Roofs, Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 20^ BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10<5 BMS70 Asphalt-Prepared Roll Roofings and Shingles 20^ BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20^ BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame WaU Construction Sponsored by the Homasote Co 10<5 BMS73 Indentation Characteristics of Floor Coverings 10^ BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated SheetSteel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co 20^ BMS75 Survey of Roofing Materials in the North Central States 15<i BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 15^ BMS77 Properties and Performance of Fiber Tile Boards lOji BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 25^5 BMS79 Water-Distributing Systems for Buildings . 20^ BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 15^ BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x 7}^ inches).. 30^

[List continued on cover page iv]
BUILDING MATERIALS AND STRUCTUEES REPORTS

[Continued from cover page iii] BMS82 Water Permeability of Walls Built of Masonry Units. 25^ BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 15^ BMS84 Survey of Roofing Mateiials in the South Central States 15^ BMS85 Dimensional Changes of Floor Coverings With Changes in Relative Humidity and

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Wood-Frame Wall Construction Sponsored by the Homasote Co 15j5 BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 15^ BMS92 Fire-Resistance Classifications of Building Constructions 30^ BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure.. 10^ BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" WaUs 15j5 BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 25^ BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 10^ BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board 10^ BMS98 Physical Properties of Terrazzo Aggregates 16^ BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs 15^ BMSlOO Relative Slipperiness of Floor and Deck Surfaces 10^ BMSlOl Strength and Resistance to Corrosion of Ties for Cavity Walls 10^ BMS102 Painting Steel 10^ BMS103 Measurements of Heat Losses From Slab Floors 15^ BMS104 Structural Properties of Prefabricated Plywood Lightweight Constructions for Walls,

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BMSllO Paints for Exterior Masonry Walls. 15^ BMSlll Performance of a Coal-Fired Boiler Converted to Oil 15^ BMS112 Properties of Some Lightweight-Aggregate Concretes With and Without an Air- entraining Admixture 10(S BMS113 Fire Resistance of Structural Clay Tile Partitions 150 BMS114 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters 250 BMS115 A Study of a Baseboard Convector Heating System in a Test Bungalow 150 BMS116 Preparation and Revision of Building Codes 150 BMS117 Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 200 BMS118 Stack Venting of Plumbing Fixtures 150 BMSllO Wet Venting of Plumbing Fixtures ._ 200 BMS120 Fire Resistance of Walls of Gravel-Aggregate Concrete Masonry Units 150 BMS121 Investigation of Failures of White-Coat Plasters 250 BMS122 Physical Properties of Some Samples of Asbestos-Cement Siding 150 BMS123 Fire Tests of Wood-Framed Walls and Partitions With Asbestos-Cement Facings 150 BMS124 Fire Tests of Steel Columns Protected With Siliceous Aggregate Concrete 150 BMS125 Stone Exposure Test Wall _ 300

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