1260 INDUSTRIAL A N D ENGINEERING CHEMISTRY Vol. 19, N o . 11

T

The Combination of Lime in Portland Cement Compounds'

Preliminary Investigation By W. C. Hansen and R. H. Bogue

PORTLAND CEMENT h S S O C I A T 1 O N FELLOWSHIP, BUREAU OF ST.ANDAROS, \ vASHINGTON, D. c.

HE researches of Ran- kin,2 BatesJ3 and others have indicated that it

is desirable to have in Port- land cement as large a per- centage of lime as is econom- ically possible to bring into combination with the acidic constituents. The presence of uncombined lime, however, is generally regarded as un- desirable, as it is believed by some to be in part responsi- ble for excessive expansion of mortars and concretes. It is generally believed that the oxides, such as ferric oxide, magnesia, and the alkalies, are not themselves important in forming hydraulic products in Portland ~ e m e n t , ~ but that they make it possible to pro- duce the hydraulic combina- tions of lime, alumina, and

In the process of Partland cement manufacture, lime and other basic oxides combine with silica and other acidic oxides. The completeness with which lime enters into combination can be measured. In this study there is noted the influence of replacements of magnesia, soda, and potash for lime, and of ferric oxide for alumina, on the temperature required for burning and the completeness of combination of the lime. Only one base composition is employed here; others will be reported later.

A continuously operating electric resistance furnace was designed especially for this investigation. Tem- peratures up to 1550" C. are readily obtained under conditions which permit of a control to 10" C., satis- factory duplication of results, freedom from contami- nation of materials, and an output of about 2 pounds of product per day.

The completion of this program will result in an understanding of the influence of the several minor components of Portland cement on the phases pro- duced, the burning temperature required, the extent of combination, and on the cement properties of the products, under a wide range of compositions.

h e a t i n g c h a m b e r , AB, is made of an alundum tube 36 by 1.5 inches (91 by 3.8 cm.) with 0.25-inch (0.6-cm.) walls. The central 24 inches (61 cm.) of this tube are wound with 0.8-mm. platinum-10 per cent rhodium wire, the rhodium being introduced to raise the melting point of the wire. The windings are in three units of 8 inches (20 cm.) each, the first having six to eight turns per inch, the second and third units from eight to ten turns per inch. The wire is cemented onto the tube with alundum cement and this core is placed inside a n o t h e r alundum tube 36 by 3 inches (91 b y 7.6 c m . ) . T h i s i s placed inside a fire-clay cyl- inder 30 bv 11 inches (76

silica in less time and a t lower temperatures than would obtain if they were absent. The extent of their usefulness is not known except in a qualitative way based upon the experience of operators in burning various cement mixes.

A series of investigations has accordingly been undertaken to determine quantitatively the influence of small amounts of magnesia, ferric oxide, alkalies, and other minor compo- nents on the combination of lime attained in various mix- tures a t various temperatures. The present report de- scribes the furnace and materials used, the procedure adopted, and the data obtained on one base composition.

The Furnace

It was first necessary to design and build a furnace which would meet the particular requirements of this study.

I n the rotary kiln, which is the standard equipment for commercial cement manufacture today, the materials ad- vance through the kiln and in so doing are gradually heated to a maximum temperature and then cooled rather rapidly. It was desired to heat mixtures in a similar manner and t o control the time and rate of heating, as well as the maximum temperature to which they were heated. The studies were to be made upon pure materials, and it was therefore neces-

' sary to avoid contamination during the heating process. Also, a capacity of from 1 to 2 pounds of product per day was required, DESCRIPTION-A photograph of the furnace in operation

is shown in Figure 1, and a cross section in Figure 2. The I Received May 25, 1927.

of the National Bureau of Standards. Association Fellowship at the Bureau of Standards.

Published by permission of the Director Paper 10 of the Portland Cement

2 THIS JOURNAL, 7, 466 (1915). Concrete-Cement Age, 3, 3 (1913).

4 Klein and Phillips, Bur. Standards, Tech. Paper 4S (1914).

by 28 cm.) kpported by mag- nesite brick. The ends of the fire-clay cylinder are sealed by disks of transite cemented in with alundum cement. The space between the fire-clay cylinder and the outer alundum tube is filled with low-burned magnesia. Each of the three units is connected, through a 16-ohm rheostat, with a 110- volt current.

Holes are drilled through the core, a t 12, 18, 21.5, and 24 inches (30, 46, 55, and 61 cm.) from end A . Porcelain tubes 6 inches by 0.25 inch (15 by 0.6 cm.) are cemented into these holes with alundum cement. These openings permit the insertion of platinum-platinum rhodium thermo- couples into the heating chamber. They are numbered 1,2, 3, and 4 in Figure 2.

All the platinum used in the furnace was rendered free from iridium, since White6 has shown that a t high tempera- tures iridium distils out of platinum-iridium alloys and that it diffuses into platinum. The diffusion of iridium into a platinum-platinum rhodium thermocouple brings about a continuous change in the e. m. f . developed by the couple, rendering the couple unreliable unless very frequent cali- brations are made.

OPER.4TION-BOatS of 0.125-mm. sheet platinum are employed as containers for the charge. These fit loosely into alundum boats 6 by 1.25 inches (15 by 3.6 cm.) and 0.5 inch (1.3 cm.) deep. The alundum boats are used as supports for the platinum t o avoid unnecessary wearing away of the platinum by abrasion as the boats are passed through the furnace. The boats hold from 25 to 35 grams of mixtures of calcium carbonate, silica, and alumina, and so yield 15 to 20 grams of product per boat. They are entered a t A and advanced in steps of 1 inch (2.5 cm.) every

5 Phys. Rev., 23, 449 (1906).

1262 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 19, No. 11

cidedly more effective than the ferric oxide in J

mixture such as these studied. These factors were con- trolled definitely in this investigation by the use of the specially constructed furnace described above.

Table I-Partial Compositions of Raw Materials (Figures in per cent)

MgC0r.- RAW Mg-

MATERIAL CaCOP Alz03" SiOz" FezOP (0H)z" KzC01b NarCOae

,Mozmum tpmpro/m /JsD .c

Si02 Nil 0.01 99.37 . . . 0.09 0.0031 0.003 AlzOa 0.08 98.48 0.0346 0.07 0.0026 FezOa 0.01 0.002 0.018 99:i5 Fe. 0:Ob FeO Nil . . . . . . CaO 55:+3 kii O:i5 ... 0.06 . . . Ca, o.'OO7 MgO 0.01 . . . . . . ... 36.19 . . . M g , 0.004 Alkalies 0.04 . . . . . . . . . . . . . . . ... HsS metals . . . . . . Xi1

Cl Trace . . . . . . . . . . . . . . . . . . . . . . . . ...

SOa T k e . . . . . . Nil Xi1 . . . . . . . . . ...

Loss on ig-

Hz0 a t nition ... 1.42 0.21 0.93 63.99 . . . . . . 1000 c. . . . . . . 0.02 . . . . . . . . . ...

By H. C. Stecker. b Taken from label on sample as purchased from Baker and Adamson. o Taken from label on sample as purchased from Powers-Weightman-

Rosengarten.

I /M ' I ' /I ' l i /!3 ' ,o f I l ! I l ' i &tmn d statipnlry c b m furnace crpresxd

dh nshca%m A

Figure &Representative Curve of Heating Process Obtained by Maintaining Points 2 and 3 a t a Constant Temperature

Experimental Data

The average composition of Portland cement today is close to the following: CaO, MgO, Na20, and K20, 67 per cent; AlZOs and Fe203, 10 per cent; and SiOa, 23 per cent. The following composition was chosen accordingly as the base composition in this preliminary study: CaO 67, AlzOs 10, and Si02 23 per cent. Various mixtures were then in- vestigated in which a part of the calcium oxide was replaced by magnesia, soda, or potash, and a part of the alumina was replaced by ferric oxide.

As previously pointed out, the values obtained in this study with respect to temperatures and degrees of combi- nation cannot be considered as absolute because of uncon- trollable factors, but those of each series are comparable and the different series are to a considerable degree comparable with each other. This is shorn to be true by the following examples:

Two charges of the same composition-CaO 67, A1203 10, and Si02 23 per cent-were heated during the same run but with two boats between them. The first charge was found, after heating, to contain 6.0 per cent free calcium oxide and the second 5.9 per cent. Two charges of another composition-CaO 63, MgO 3, NazO 1, A1203 10, Si02 23 per cent-were run on different days. The temperatures were the same within * 10" C., and the per- centages of free calcium oxide found were 5.3 and 5.0, respec- tively.

The increase in combination, as shown by the decrease in free-lime content which results through an increase in the temperature of burning, is shown in Table 11. A maximum temperature of about 1500' C. is required to effect complete combination of lime, alumina, and silica, in the composition given, and under the manner of heating used in the present study.

Table 11-Influence of Temperature on Combination of CaO (Composition: CaO 67, AlrOa 10, Si02 23 per cent)

TEMPERATURE OF HEATING THERMOCOUPLES No. 4n No. 3b No. 2b No. 1b FREE CaO

c. e c. c. O C. Ptr cent 1160 1360 1330 1320 8.2 1140 1380 1380 1320 7.6 1160 1410 1410 1360 5.8 1160 1420 1420 1360 3.9 1330 1500 1475 1450 0.0

* 2 0 ° C . b j=lO°C.

Figures 4 to 13, inclusive, show the effects on the combi- nation, as revealed by the free-lime content, resulting from the replacement of magnesia, soda, or potash for calcium oxide, and ferric oxide for alumina, in amounts up to 5 per cent. These effects are shown both singly and in combina- tion. The initial composition is given in each case, so that the exact composition of any point on the curves may easily be ascertained. The maximum temperatures also are given, and the temperatures at each thermocouple for all samples are listed in Table 111. Table 111-Temperatures Measured a t Four Thermocouples of All

Samples Illustrated in Figures 4 to 13 TEMPERATURE OF HEATING THERMOCOUPLES

No. 2b No. 1 b FIGURE KO. 4" KO. 3b c. c. c. c.

4 5

6 and 7 8 9 10 11 12 13A 13B

1160 1160 1200 1160 1200 1000 1080 1090 1160 1140

1330 1410 1425 1315 1400 1270 1290 1300 1410 1400

= + z o o c. a *io0 c. Ejec t of replacing calcium oxide by magnesia (Figure 4) and

alumiitn by ferric oxide (Figure 5). A decrease in free lime is noted. The samples containing magnesia were burned at a lower temperature than those containing ferric oxide. The curves show that small percentages of ferric oxide replacing alumina, and of magnesia replacing lime, aid materially in effecting com- bination of the lime.

will be observed that e about 4 per cent of magnesia replacing lime brings about com-

t 4 plete combination a t 0 / 2 3 4 5 temperature of 1350 Arcvri c+ flfl raplaring CaO.

c.3 while 4 per cent of Figure 4-Effectlon Combination of CaO ferric oxide replacing Due to Replacement of CaO by MgO up alumina brings about t o 5 Per Cent comdete combination only'at the higher tem- perature of 1410' C. Hence it is shown that 4 per cent of ferric ox- ide caused complete combination of lime at a temperature 100' C. . - I . lower than was re- quired for the without ferric oxide, to 4 Per Cent

Figure-&Effect on Combination of CaO Due to Replacement of A1208 by Fez03 up

and 4 per cent mag- nesia effected complete combination a t a temperature 150' C. lower than was required for the sample without magnesia.

Effects of small amounts of polassium oxide (Figure 6 ) and so- d i u m oxide (Figure 7). It is apparent that these oxides have no especial value in increasing the combination of lime in this composition.8 They do, however, increase the amount of liquid present during burning to a very marked degree, as was shown by an examination of the resulting products. There was dis- tinctly increased fusion with increased potash or soda content. The potash and soda contents'of the samples, as given on the abscissas, were the amountsrof'potash or soda contained in the original samples. Some of this is undoubtedly volatilized during

8 A similar conclusion with respect t o the:influence of alkalies was reached by S. B. and W. B. Newberry, J . SOC. Chem. Ind . , 16, 887 (1897).

November, 1927

1 ; \,pq . I 1 1 1

I L l

INDUSTRIAL AND ENGINEERING CHEMISTRY 1263

the burning. It is observed that up to 0.5-1.5 per cent, increas- ing potash and soda, respectively, favor combination of the lime, but above 0.5-1.5 per cent a reversal occurs, indicating that additional alkali above this amount decreases the combination.

The validity of the data on the effect of soda and potash is indicated by work previously reported by Lerch and Bogue.6

temperature 40' C. lower than those containing 3 per cent mag- nesia. The 5 per cent samples contain a greater amount of free lime and would require for complete combination about the same temperature as was used with the 3 per cent samples. It will be observed that the percentage of free lime in both series decreases rapidly as ferric oxide is added, up to about 3 per

cent ferric oxide. There is little change beyond that point. E f e c t of ferric oxide when sample contains 3 per cent

magnesia and no soda (Figure 12). A comparison of this curve with Figure 11 shows that soda has very little in- fluence in increasing the combination of the lime in the presence of magnesia.

Figure 13 shows that soda aids slightly in the combina- tion of lime in the absence of magnesia when small amounts Of ferric oxide are added.

Figure 14 shows the effect of increasing temperature upon the combination of the lime in three different compositions.

Percent of KeO reploch9 C.0 Figure 6-Effect on Combination

of CaO Due to Replacement of CaO by K 2 0 u p to 2 Per Cent

Pwcenr cf Ns,O +my 00

Figure 7-Effect on Combination of CaO Due to Replacement of CaO by NazO up to 2 Per Cent

Figure 8-Effect on Cornbination of CaO Due to Replacement of CaO by MgO in the Presence of NazO

Figure 11-Effect on Combination of CaO Due to Replacement of AlzOa by Fez08 In Presence of MgO and NarO

r- Figure %Effect on Combination of CaO Due to Replacement of AlzOa by Fez08 in Presenceiof Nag0

6 c: !L 5 4

e2 I / I 1 lrT++-&l Percent fe r 4 repbring Alt 4

FpFigure 12-Effect on Combination of CaO Due to Replacement of Ah01 by Fez08 in the Presence of MgO

They showed that the presence of soda in a-synthetic laboratory cement in the amount of 2.29 per cent after burning gave a negative test with the ammonium acetate method for free lime, and also that commercial cements known to contain combined alkalies, but no free lime, reacted negatively. This may be re- garded as evidence that the values for free lime obtained and re- ported herewith are actually a measure of this component, and are not vitiated by the presence of the alkalies combined in the material. However, because of the unusual reversal in direction of these alkali curves, a further test was made. A sample con- taining 2 per cent soda was prepared, burned, and titrated for free lime in the usual way. The free lime content was found by this method to be 3.1 per cent. The solution was then filtered off and the total calcium oxide in the filtrate determined gravi- metrically by precipitation with ammonium oxalate. The con- tent of lime by this method was found to be 3.0 per cent. Since the tn-o values are essentially the same, it is shown that the values obtained by the titration method are essentially correct even in the presence of combined alkalies in the product.

The explanation of the reversal is not clear, but it seems prob- able that the soda may combine with silica or alumina in a different ratio than does lime. For example, a given weight of soda may combine with a larger amount of silica or alumina than does the same weight of lime. Then, on replacing lime with soda, gram for gram, as was done in these experiments, the material (silica or alumina) available for combination with the lime would be decreased with each portion of soda added and the result would be analogous to the addition of more and more lime to the mixture.

E f e c t of magnesia when sample has 1 per cent l ime replaced by 1 per cent soda (Figure 8 ) and of ferric oxide on same composition (Figure 9) . It is evident again that magnesia is more effective than ferric oxide in this composition. The samples containing magnesia were burned at a temperature 70' C. lower than those containing ferric oxide.

By a comparison of Figures 4 and 8 it would appear that, if we wish to maintain the percentage of lime as high as possible, the presence of soda offers no advantage as the influence of mag- nesia and ferric oxide appears to be as great alone as in the presence of soda.

Effect of ferric oxide when samples contain 5 and 3 per cent, respectively, of magnesia and 1 per cent of soda (Figures 10 and 11). The samples containing 5 per cent magnesia were burned a t a

I 4

pcmnt fi$, replacmy A h 4 Figure 10-Effect on Combination ot'CaO

Due.to Replacement of All03 by Fez&,in thegresence of MgO and Nan0

O ' ' ; ' i ' 3 1 I ? .

Figure 13-Effect on Combination of CaO Due to Replacement of AlnOa by Fez08 "A" in the Absence and "B" in the Presence of NazO

Conclusions

The following conclusions may be drawn from these studies, but may be construed to apply only to the one base composition investigated-Ca0 67, AlzOa 10, Si02 23 per cent.

1-The replacement of lime by small amounts of soda or potash produces very little increase in the combination of lime with silica and alumina.

2-The replacement of alumina by small amounts of ferric oxide or the replacement of lime by small amounts of magnesia aids materially in promoting the combination of lime. The in- fluence of magnesia is greater than that of the ferric oxide.

3-Replacements by ferric oxide and soda or magnesia and soda are not appreciably more effective than are replacements by ferric oxide or magnesia.

1264 INDUSTRIAL AND ENGINEERI-VG CHEMISTRY Vol. 19, No . l l

6-A composition of CaO 67, A1203 10, and Si02 23 per cent It is not the aim of the paper to show that ferric oxide, requires, under the conditions of this study, a temPeratVe of magnesia, or the alkali oddes are desirable or undesirable 1500' C. to effect complete combination.

7 - 4 composition of CaO 63, MgO 3, NazO 1, +?03 7, pezo8 in Portland cement except in that they lower the temperature 3, sioz 23 per cent, which approaches the composition of com- a t which a certain base composition can be burned to com- mercial Portland cement, requires a temperature of about plete combination. This base composition (CaO 67, &OI 1325 c. for complete combination under the conditions of these 10, s ioz 23 per cent) approaches the average composition of experiments. This is a decrease of 175" C. below the tempera- ture required for the base composition. Portland cement when the several components are referred to

8-The common belief that any material that will cause an the oxides of lime, alumina, and silica. Furthermore, these increase in the amount of liquid formed in such a system, at a data indicate nothing a t all with respect to any other base given temperature, will likewise cause an increase in the combina- composition, and it is not permissible to assume similar tion of lime is true in this composition for magnesia and ferric oxide, but to a very limited extent for soda or potash, The effects for other compositions. The entire field of Portland charges containing these latter oxides were distinctly more fused cement is now being explored and the data are being correlated than the ones without them, but no great increase in combination with the properties of the products in service. was effected by their presence. A possible explanation is given.

Influence of Neutral Salts on the Plumping of Hides'

By R. 0. Page and A. W. Page

~ ' O o L s T O S TAYNERIEs , R'OOLSTON, N E W ZEALAND

Data showing the influence on the plumping of cowhide of the chloride and sulfate of sodium and of calcium chlo- ride in concentrations up to 4 normal, and a t the four pH values of 2,5,8, and 11, are given in detail. The pH of the solutions employed greatly affects the result of the addition of neutral salts. I n acid solutions, addition of the three salts studied reduces the plumping to a minimum value of 0.8 a t a concentration of 0.75 normal. A t greater concen- trations than this the plumping increases again, this in- crease being most marked with calcium chloride, sodium sulfate giving results similar to those given by sodium chloride.

A t the pH values 5 and 8, the three salts give widely differ- ing results. Sodium sulfate gives in both cases a rather flat plumping curve with .a minimum a t a concentration of 0.75 normal, while sodium chloride gives a maximum a t about the same concentration, this maximum being less pronounced a t pH 8 than a t pH 5. Increasing con- centration of calcium chloride increases the plumping a t both these pH values, rapidly a t first, then more slowly a t concentrations between 1 and 3 normal, and finally more rapidly up to 4 normal. The plumping is more marked a t pH 8 than a t pH 5. Hide pieces plumped in the more

concentrated solutions lose calcium chloride rapidly and completely on washing, but lose their plumping much more slowly, hide plumped in a 4-normal solution retain- ing its plumping even after soaking for a week in distilled water.

In alkaline solutions increasing concentration of sodium chloride depresses the plumping, but much less than in acid solution. The least plumping (1.27) occurs a t t he maximum concentration studied. Sodium sulfate, on the other hand, depresses the plumping much more rapidly to a minimum of 0.84 a t 1.5-normal concentration, the plump- ing increasing again slightly in more concentrated solu- tions. Hide plumped in sodium hydroxide solutions of pH 12.5 reaches apparent equilibrium a t the end of a week, but in a calcium hydroxide solution of the same pH the plumping increases in the second week. In neither case does the hide fall to its initial thickness on restoring t o its original pH value, but on bating in both cases it falls further but not to its original substance. There appears to be a close connection between the nitrogen dissolved from cowhide by solutions of neutral salts and the plump- ing in such solutions.

. . . . . . . . . . . . . . ECENT researches have indicated that as far as col- lagen and gelatin are concerned specific-ion effects, R corresponding to the Hofmeister series, have real

significance and cannot always be attributed, as LoebZ has done, to error of experimental method arising from neglect to control the pH values of the salt solutions employed.

Stiasny* and his collaborators found that, in regard to the influence of salts upon both the dispersity of gelatin and the action of enzymes on hide substance, while the Donnan equilibrium is not applicable, the anion action is in accordance with the Hofmeister series. Ostwald, Kuhn, and Bohme4 found that the swelling of gelatin a t constant pH reveals the

1 Received June 16, 1927. Presented before the Division of Leather and Gelatin Chemistry at the 74th Meeting of the American Chemical Society, Detroit, Mich., September 5 to 10, 1927.

9 "Proteins and the Theory of Colloidal Behavior," 1st ed., Chap. V. 8 Collegium, 1S26, 13, 23, 67. 1 Kolloidchem. Beihefte, PO, 412 (1926).

existence of a specific-ion series; while Thomas and Fosters showed that in the destructive action of neutral salts on hide powder over a narrow pH range around the isoelectric point of collagen, once more a specific-ion effect is apparent corresponding to the Hofmeister series. Gustavson6 re- viewed the literature, a t the same time suggesting an ex- planation of the action in question, and later' showed the important influence of previous treatment with neutral salts on the behavior of hide powder during tanning. McLaughlin and Theis,8 on the other hand, while confirming the finding of Thomas and Foster that sodium chloride dissolves hide powder more readily than does sodium sulfate, discovered that in the case of untreated hide the sulfate dissolves as much as the chloride.

8 Tms JOURNAL, 17, 1162 (1925). e J . A m . Leather Chem. Assocn., 21, 206 (1926). 7 Ib id . , 21, 366 (1926). a Cdtegium, 481 (1926).