July, 1926
ILVDUSI’RIALA,VD ENGINEERIiVG CHEMISTRY
739
Determination of Uncombined Lime in Portland Cernent 182
By Wm. Lerch and R. H. Bogue NATIONAL BUREAUOF
STANDARDS,
WASHINGTON, D. C.
T
H E production of Portland cements had hardly been The present report is not concerned with the question of developed when the question of the determination of volume constancy or “soundness.” The general problem of the uncombined lime in these products became a prob- “unsoundness” and the relation between this condition and lem of scientific interest. Some of the earliest theories on the the free lime content is reserved for future study. It is thereconstitution of Portland cement assumed the presence of a fore explicitly pointed out that the test for free lime as herein large quantity of uncombined lime. I n an effort to obtain developed may not be construed a t this time as giving any evidence towards the corroboration or the disproof of these direct indication of the volume constancy of the cement. theories a considerable number of methods were proposed Review of the Literature for the determination of the free lime. More recent investigations3 show that a cement clinker It is not within the scope of this report to cite all of the burned a t a sufficiently high temperature will have practically literature on free lime determinations. Asch and Bsch4give‘a all of the lime in chemical Fe203, etc. If, h o w e v e r , e q u i l i b r i u m were a p lications may be mentioned water, acids, limeproached, but not reached, number of methods which have been proposed in some of the CaO would be water, amthe literature for the determination of uncombined monium carbonate, left in an uncombined conor “free” lime in Portland cement have been examined dition. and Ox critically. It has been found that methods involving None of the methods proSeveral additional referthe use of water or dilute acids are to be avoided. In posed for the determination are given by the presence of water or acids, the cement compounds andMeyer*6’‘ithourmore of free lime in Portland are decomposed in such a manner that the results recent kllowledge Of the recement has been accepted obtained are not a true measure of originally free lime. generally as an adequate actions Occurring in cement Two methods involving the use of the microscope a n d c e m e n t compounds, q u a n t i t a t i v e procedure. are of value for the qualitative identification of free The difficulty in determinmany Of these methods aplime. An ammonium acetate titration method is ing this free lime lies in the pear t’ be A well suited for a quantitative determination of free presence, in Portland cefew Of the more important lime. In this method, hydrolysis of the calcium siliment, of various compounds methods a r e des e cates and aluminates does not take place, the process of lime with silica, alumina, is rapid and easily performed, and a satisfactory degree iron oxide, etc., which hyPassow’ has proposed to of accuracy can be attained. drolyze more or less readily determine the freelime in aement by first oonverting the, in aqueous solutions, liberatlime to calcium carbonate ing lime. Consequently, if aqueous solutions are used to dissolve the free lime from the ce- and then determining the increased carbon dioxide content. ment as a procedure preliminary to the making of the test, it The cement and ammonium carbonate are ground together to appears certain that the value obtained in the test will represent a fine powder and heated to 300” C. This heating causes disboth the free lime in the cement and the lime liberated by hy- sociation of the ammonium carbonate. The carbon dioxide drolysis due to the action of the solvent. Only the free lime combines with the free lime while the balance of the reaction present in the cement a t the time the test is made, and not that products volatilize. The operations of adding ammonium which may be liberated during a test, is desired. A method carbonate, grinding and heating are repeated three times. which would determine only the free lime present, in the ceThe use of sugar solutions for the determination of free ment at the time of test would be of considerable value in lime is of especial interest because it has been used by a numstudies on the constitution of cement, and also in the routine ber of investigators during the last half century. Heldt,8 examination of commercial cements. The present study Levoir,g Parsons,lo Zulkowsky,ll RebuffatIt3 Martin,13 and was undertaken, therefore, to examine some of the methods Leduc14 have all used some modification of this method. heretofore proposed and to determine if a method could be The procedure consists essentially in placing the material to devised which would be altogether reliable and specifically be examined in sugar solution for a given time, then titrating applicable to Portland cement. an aliquot of the solution with standard acid. The time of By the term “uncombined lime” or “free lime” the writers contact and strength and quantity of the sugar solutions refer specifically to CaO, together with such amounts of hy4 “The Silicates in Chemistry and Commerce,” 1918, London, p, 330. drated lime, Ca(OH),, as may be present. As pointed out 5 Cement Eng News. 22. 463 (1910) later, however, the proportion of Ca(OH);?present in normal 6 R a u m a f e r d i e n k u n d e . 6 , 141 (1901). 7 Zemenl, 19, 87 (1923). Portland cement is probably very small, and may be negli8 J Prnkl C h m , 94, 129 (1865) gible under ordinary conditions. 9 Rec. Ira% chrm , 6, 59 (1886).
A
Received March 3, 1926. Paper N o 2 of the Portland Cement Association Fellowship at the Bureau of Standards Published by permission of the Director, National Bureau of Standards 8 Rankin, THISJOURNAL, 7, 446 (191.5). 2
Deuf ToPDer-Ziegler-Zlg , 19, 585 (1888). Tonind - Z f g , 22, 285 (1898) 12 Ibrd , 93, 782 (1899). 1 3 Mon S c i , 13, 173 (1923). 1 4 Z n f r m . Assoc Tesfing Materials, 8 (1901).
10
11
INDUSTRIAL AND ENGIXEERING CHEMISTRY
740
used have varied somewhat with the different workers. Michaelisl5 reported that sugar solutions effected no definite distinction between free lime and lime combined in the form of silicates, but that the amount of lime dissolved was determined by the concentration, volume, temperature, etc., of the sugar solution. Brandenburg16 determined the free lime by a method which depends on the liberation of ammonia from ammonium bromide by the action of the lime. I n order to prevent hydrolysis of the silicates and aluminates, this reaction was carried out in solution of absolute alcohol. The cement and ammonium bromide are placed in a distilling flask with the alcohol, and the ammonia liberated, distilled over, and collected in standard acid. A somewhat similar method has been reported by Hentschel" as a qualitative test. The finely ground cement is shaken with dry potassium carbonate and ammonium chloride. The evolution of ammonia on heating is taken as evidence of free lime in the cement. The potassium carbonate in this case serves as a dehydrating agent to take up any water which would otherwise liberate CaO from the silicates present. Another method has been used by Smith and Hendricks's for determining the free lime in commercial calcium arsenate in the presence of calcium carbonate. This method depends on the reaction of 0.1 N benzoic acid with the lime. An excess of this acid dissolved in 93 per cent alcohol is added to the material to be tested, the mixture vigorously shaken for 6 to 7 minutes, then the excess acid titrated with 0.1 N NaOH. The authors report very good results for this method with no reaction of the acid with the calcium arsenate or calcium carbonate. TrachlerlS evaluates the excess lime in cements which have been properly burned but show a decrease in strength after 6 months. He applies the formulas of Schott and Newberry, X (2.5CaO.Si02) 4- Y (2.5Ca0.R203) X (3CaO.SiOt) Y (2Ca0.Rz03)
+
and
which represent, according to the authors, the maximum amount of CaO present in a sound cement. I n the use of these formulas the MgO is calculated as Mg0.Ca0.Si02, the SO3 as CaSOa, and the NazO as NazSiOs. The sum of these three constituents plus the insoluble SiOz and the S is subtracted from 100, giving the factor to be used in the application of the tables, in which the sum of CaO, SiOz, and R20a is considered 100. Tables are given for use in calculation of the excess lime as well as several examples of their use. A titration method described by EmleyZOwas found applicable for the determination of calcium oxide or hydroxide in the presence of calcium silicates or aluminates. The method was recommended by its author as affording a satisfactory means of attacking problems concerned with sandlime brick and hydrated lime. Experiments were also tried with Portland cement, but in these the results are stated to have been unsatisfactory because the color of the material obscured the end point. The method consists of adding a small amount of the finely powdered material to a solution of 2 cc. of glycerol in 10 cc. of absolute alcohol, bringing to a boil, and titrating while hot with an alcoholic solution of ammonium acetate. Phenolphthalein is used as the indicator. The free lime goes into solution in the alcohol-glycerol and, on the addition of ammonium acetate, the following reaction occurs : Tonind-Ztg., 26, 853 (1901). Chem. Ztg., S3, 880 (1909). 17 Tonid.-Ztg., 34, 34 (1910). 18 THIS JOURNAL, 16, 950 (1921). 18 Tonind.-Ztg., 33, 1334 (1909). 20 Tram. Am. Ceram Sac., 17,720 (1915)
Vol. 18, No. 7
+
+
+
CaO 2CH3COONHa-(CH~C00)2Ca 2NH8 HzO The ammonia is volatilized from the hot solution. By the use of the microscope i t is possible to obtain a qualitative identification of lime by two methods. White's21 method is dependent on the reaction of the lime with phenol, as a result of which characteristic crystals are formed. This method is very sensitive and is applicable for the identification of lime, even in very minute quantities. The work of White has been confirmed by Riebling and ReyesZZand the method is generally accepted for the qualitative determination of free lime. I n addition, Rankin and Wrightz3 state that, by the aid of a microscope, free lime may easily be recognized by its appearance as fine isotropic grains, usually rounded in outline, and of very high refractive index (about 1.83). Experimental Procedure
The applicability and adequacy of several of the foregoing methods have been tested in this laboratory as described below. By the microscopic examination of commercial Portland cement, Shepherd, Rankin, and Wrightz4found that it was made up largely (over 90 per cent) of three components: 2CaO.Si02, 3Ca0.SiOz, and 3Ca0.A1203. I n addition i t might contain 5Ca0.3,%&03,CaO, Fez03, MgO, and alkalies in uncertain combinations, as well as CaC03 and added gypsum. The presence of these constituents has been confirmed by Bates2& Some of these constituents are readily decomposed by water or weak acids. I n order to determine their reaction to the reagents used in the several methods, each of the compounds mentioned above was subjected to a number of the tests described. I n addition to these pure compounds, several cements were subjected to the tests. The results obtained from a few of the above described methods are given in Table I. Table [-Percentage
of Free L i m e in Various Materials Obtained b y
Several Methods Smith and Hendricks In Inab- Bran9370 solute denWhite alcohol alcohol burg B 2CaO.SiOa Absent 8.09 2.70 0 . 0 3CaO.SiOa" Large amount 22.15 3.10 10.27 3CaO.AlaOa Absent 1.72 0.95 0 . 2 7 5Ca0.3AlzOa Absent 1.61 0 . 0 0.12 CaCOz Absent 0.0 0.0 Gypsum 0 0 0 0 Cement A Present 11:42 2:90 0:65 Cement B Absent 12.40 1.15 0.17 a Incompletely burned.
....
..
Sugar soh. 15% 2.77 13.96 23.80 11.40 0.0 0 0 7:36 6.60
Ammonium acetate Pas- titration sow 0.45 0.0 7.37 12.15 0.40 0.0 0.23 0.0
..
0:97 0.37
A considerable number of additional samples of compounds and cements made in the laboratory have been examined for free lime by White's test and by the ammonium acetate titration method. Results of some of these tests are given in Table 11. I n this preliminary work the ammonium acetate titration method of Emley was the only procedure to give seemingly satisfactory results. Accordingly, a further special study was made of this method.
EJect of Fineness of Grinding, and of Age A number of cements were examined for free lime by the ammonium acetate titration method and by White's test. I n every case samples which contained free lime by White's test were found to contain varying quantities when treated
16
18
0.0
0.0 0.55 0.0
THISJOURNAL, 1, 5 (19091. Philippine J . Sci., 6, 374 (1910). Am. J. Sci.. 39, 1 (1915i. 2 1 THISJOURNAL. 3, 211 (1911). 25 Concrete-Cement Age (Cement Mill Section), 2, 3 (1913). 21 22
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INDUSTRIAL AND ENGINEERING CHEMISTRY
J ~ i l y ,1926
with the alcohol-glycerol solution and titrated with ammonium acetate. It was found, however, that cements which had been allowed to stand for a long time after grinding were slow to react.. This may be due to the formation of a film of CaC03 around the grains of lime. Also, with finely ground cements, the reaction was found to be completed more quickly than with coarse cements. This may be due to the larger particles of lime being partially or completely surrounded by the other constituents. For these reasons it is recommended that the cements be reground very fine (100 per cent through a 200-mesh sieve) a t the time the test is to be made. T a b l e 11-Percentage of F r e e L i m e in Several M a t e r i a l s O b t a i n e d b y W h i t e ' s T e s t and t h e A m m o n i u m A c e t a t e M e t h o d Titration White's Per cent Sample test freeCaO 3CaO.SiOz (1) Absent 0 Absent 0 (2) Absent 0 3CaO.AIzOz (1) Absent 0 (2) Absent 0 5Ca0.3AhOa CaO.AIz0a Absent 0 3CaO.5A1203 Absent 0 y 2CaO.SiOn Absent 0 ( CaO A1203 Si02 (1) Absent 0 Absent 0 (2) Absent
