I N D U S T R I A L A N D ENGINEERING CHEMISTRY
June, 1925
589
Action of Sodium and Magnesium Sulfates on Constituents of Portland Cement’ By G. R. Shelton CNIVERSITY OF SASKATCHEWAN, SASKATOON, CANA0.A
repeated for 30 days, after which microscopic examinations were made a t longer intervals. RICALCIUAI aluminate (3 Ca0.8l2O3) was made TRICALCIUM ALUMINATE-(a) Sodium Sulfate. The reacfrom specially prepared materials,4 the temperature tion between these substances began almost immediately (1325’ C.) a t which it is formed being low enough to per- with the formation of fine needle-like crystals of tricalcium mit the use of a platinum container. Heating was done in a sulfoaluminate and clear, amorphous grains. These products were found in all the platinum resistance furnace. Tests for free lime made I 1 mixtures (Figure 1). The sulfoaluminate needles were with White’s solution5 on This paper represents the second step in research unextremely fine in the satuthe resulting clinker were dertaken by the Engineering Institute of Canada dealrated sodium sulfate solunegative. ing with the problem of the action of the so-called tion, becoming larger in the By the same method as “alkali” waters on concrete structures.* It describes mixtures containing less sulthat employed by Klein and the preparation, in the pure state, of the major subfate, until they reached a P h i l l i p s , 6 tricalcium (3 stances present in normal Portland cement clinker, maximum size in the 2 per CaO.SiOn) and 8-dicalcium tricalcium aluminate, p-dicalcium silicate, and tricalcent solution. On the secsilicate (8-2CaO.SiO2) were cium silicate, and the effects produced on these constituond day crystals of hydrated prepared from white marble ents by solutions of sodium and magnesium sulfates of t r i c a l c i u m aluminate as and commercial flint. The various concentrations. The solids only were investineedles and hexagonal plates heat treatments were cargated and the changes brought about by the solutions mere noted in the 0.5 per ried out in an oil-fired pot were noted with the aid of the petrographical microscope. cent solution. These infurnace. The analvsis of creased in size, arid in 21 these raw materials showed: days formed masses by ~-------PER CEST-overlapping (Figure 2). In the same solution the sulfoLoib,on aluminate crystals began to disappear, and were entirely gone ignitlon Si02 A I 9 0 3 + Fe:O, CaO 55.19 1.23 0.13 in 14 days. The original grains of tricalcium aluminate Marble 43.41 0.60 0.00 0.23 99.33 Flint never entirely disappeared in any of the mixtures, but remained as clear centers of amorphous particles, even in the No free lime was found in the tricalcium or dicalcium silicate saturated solution, after 4 months. after eight and six heat treatments a t 1700” C., respectively. ( b ) Magnesium Sulfate. The reaction products were sulThe optical properties of the two silicates and of the tricalcium foaluminate crystals, gypsum, and amorphous particles aluminate were identical with the data for these compounds There were two kinds of amorphous grains, one consistgiven by Wright.? ing of large, clear, rounded masses, probably an aluminate, and the other of tiny, irregular fragments of magnesium Table I--Analyses of C o n s t i t u e n t s PER C ~ T hydroxide. The sulfoaluminate crystals were found in the Loss on 0.5 and 2 per cent solutions only. The quantity decreased in ’‘ ignition CaO A1203 Si02 MgO 62.11 37.93 0.00 0.00 the 0.5 per cent solution, disappearing altogether in 14 days, Tricalcium aluminate {::% 62.17 37.79 0.00 0.00 but increased in the 2 per cent solution, so that in 20 days the Tricalcium silicate 0.10 72.39 0.50 26.36 0.69 Dicalcium silicate 0.30 62.57 0.76 34.37 1.47 suspension was too viscous to flow when the tube was inverted. Part of the solid material in the suspension was due to amorCrystalline Constituents and Sodium and Magnesium phous aluminate and magnesium hydroxide. Hexagonal Sulfate Solutions plates of hydrated tricalcium aluminate were found in the To five stoppered test tubes, each containing 0.08 gram of 0.5 per cent magnesium solution. These crystals increased the pure constituent of Portland cement, 5 cc. of the sulfate in quantity and size as the sulfoaluminate crystals disapsolution were added in the following concentrations: 0.5, peared, behaving just like those formed in the same concen2, 5, and 8 per cent, and saturated. The mixtures were then tration of sodium sulfate. Gypsum crystals were formed in vigorously shaken and a drop of the resulting suspension was the 5 and 8 per cent and saturated solutions but not in the removed for microscopic examination. This process was others (Figure 3). The crystalline centers in the amorphous grains were larger in the saturated solution, becoming smaller 1 Received December 23, 1924. as the sulfate content in the solutions became less. They did This work was done under the auspices of a research committee of the Engineering Institute of Canada with the financial support of the Research not disappear in any of the mixtures. Council of Canada, The Canada Cement Co., the Canadian Pacific Railway, TRICALCIUM SILICATE-(a)Sodium Sulfate. The first eviand the three Prairie Provinces of Canada. The first of this series of investigations is reported by Thorvaldson, Harris, and Wolochow, THIS dences of action were the appearance of a layer of amorphous masses around the particles and the formation of gypsum JOURNAL, 17, 467 (1925). a Rankin, THISJOURNAL, 7, 466 (1915). crystals. The amount of gypsum increased with increasing Very pure calcium carbonate and alumina were prepared by David concentration of the sulfate. The crystalline centers of R‘olochow and F. H . I,. Taylor, tricalcium silicate in the amorphous masses quickly disapWhite, Tius JOURNAL, 1, 5 (1909). peared so that none were found after 5 days in the 5 and 8 a Birr. Sfandards, Tech. Paper 43. ‘ A m . J . Scr., 141 39, 7 5 (1915). per cent and saturated solutions. Traces of these crystalline Preparation of Constituents3
T
’
’
-
Gelatino& Parficlrs.
X Ill0
x
100
centers wcre found in tlir ;iin~~rpli~,us iiiatrri:il i n 0.5 a i d 2 pi'r ccnt sulfate solutions after 2 months. The amorphous particles werc acded lipon by tlir 8 per lent and saturated solut,ionn, hcing broken up into very small fragments. Sdjofe. Owing to the fnrmation of magnesirmi hgdroxidc the superiiat.ant liquid became quite milky in all tlic tubes $1few hours after mixing. Gypsum crystals and amorphous layers around t.he silicate grains were produced rapidly. The crystalline ccnt,ers in the amorphous particles disappeared very soon, only slight anrouiits being found on the fift,h day in the saturated soliition. In 3 weeks it, xras difficult to find even traces in any of the 8olutions. The amorplious silicate particles were broken up into tiny grains hy the action of the satura,tcd solution, as in the i;at,iirated sodium siilfltte solution. Uic.41r:rn~ SII,ICATE--(U)Sodiuni Sulfufe. In some preliminary exprriments the reaction iif thcse two substances proi:ecded SO slowly that the tests with 0.5 per cent siiIfaIe sol~tiimwerc omitted. No change was noted in aiiy of the mixtures until after 4 days, when a small quantity of gypsum was found in the 8 per cent and saturated solutions. In 2 weeks a layer of gel covered the silicate grains in the 5 and 8 per cent mturated solutions, and a small quantity of gypsiim was noted in them. Apparently, the action then ceased, for after 2 months there was no decrease in the crystalline cmters or increase in the quantity of gypsum. ( b ) Magnesium, SdJate. Gypsum crystals and amorphous magnesium hydroxide were noted immediately iii all the mixtures of the dicalcium silicate with sodium sulfate, hiit the quantit.ies were small. The action proceeded in the same manlier as in the tests with sodium sulSate. However, the crystalline centers were smaller in the saturatcd solutioii a t the end of 2 months. Hydrated Constituents and Sodium and Magnesium Sulfate Solutions
The constituent was hydrated by shaking 2.5 g r a m of i t with 30 cc. wat.er until a microscopic examination showed that hydration was complete. Immediately after shaking the resuliiiig suspension, 1 ce. was withdrawn by means of a pipet and placed in a test tube with 5 cc. of the sulfate solutioii. The tube was then stoppered with a paraflined cork and shaken vigorously. The sulfate solutions were in the following percentage concentrations: 0.5, 1, 2, 3, 4, 5, 6, 7, 8, and saturated. Microscopic examinations were made daily after the mixtures had been thoroughly shaken.
1fYDRATlGD TI~ICAL~IGM A L l I ~ i l . h A i ~ E - - : \ I i e r ~ ~ d B O ~CSaIlii)ic rmtion OS the suspension showed hexagonal plates and needles of hydrated triciileium aluiniiiate, but no smorplious matter. Hydrat,ion was complete in 24 lioiirs, and t,lie suspension had a peculiar silky appcarancc. (a) Sodium 8uZJnte. Sulfoalumiiinte cryatols grew very Is being extrenialy rapidly in all these mixtures, t.lic cr line in t.he saturated sulfate solutions mil becoming larggcr as tlie sulfate content became Icss, until in the 2 per cent and 3 per cent solutioiis thcy were veys limg. Iii the latter sohtions they formed spherulites arid in 20 days these suspensions liecame too viscous to flow (Figure 4). Masses of amorplious matter which may have been aluminiimi hydroxido, were found in all the mixtures; no gypsurn mas noted. The hydrated tricalcium aluminate crystals disappeared very slowly, requiring over 3 months in the saturated solutions, and being found for a much longer time in the ot,her solutions. All the suspensions became.viscous. (b) Mapneslum Sulfate. Gypsum was Sormed immediately in mixtures containing more than 3 per rent magnesium sulfate with the hydrated aluminate, and magnesium liyclroxide was produced in all mixtures. The crystals of hydrated tricalciiini aluminate were qiickly used up, not being found after 4 days in any of the mixtures containing inore than 2 per cent sulfate. The amoqhous matter was fine-grained and wit.h the gypsum rrystals caused the suspension t o thicken, resembling starch paste. HYDRATED TRICALCIUM SiLicATE-After having heen shaken for 28 days and standing for 3 months, the hydration of tricaleiuin silicate mas still incomplete. Crystals of calcium hydroxide and rounded particles of clear gel containing traces of unhydrated silicate grains were found. (a) So&am SdJate. Gypsum crystals were formed rapidly in all the mixtures of the hydrated material made with solutions rontaining over 1 p r cent sodium sulfate. The crystals of hydrated lime mere attacked and at the same time amorphous grainy masses were deposited around them (Eliyres 5 and 6). The unhydrated silicat,e grains in the silicate gel were rapidly rieted upon by the solutions, none being found in any of the mixtures after 4 days. The calcium hydroxido crystals1disappeared after 10 days. Small crystals, which proved to be gypsum, were found in the gel, There was no disintegration of these amorphous grains, which rct,ained their shape for several months. (6) Magnesium Suljate. Gypsum crystals a8 long, slender needles, and also amorphous magnesium hydroxide, were
noted inirnediati:ly. The rrirliydrated grains of silicntc rap- deerensnl in sist: slowly, untii at the end of a rnoiith there were idly disappcarcd in t,he amorphous particles. The ca1i:iurn none in the solutions above 1 per cent. The amount of g y p hydroxide CTyStak wcrc thickly coated with amorphous sum increased as tho i:oncentrxtioii of the magnesium sulfate increascd. The action apparently stopped, since nu uiri needles (Figure 7). The pr~:seur:c crystals could be dctiictcrl betvrcco furthrr chairges were noted. rwsrcd Xiails and also by the general hexagoiral shapc of the Discussion and Conclusions After a m r k tlwre were no crystals of hydrated with the crystnllinc corrstitucirt,~of l'ortlaud any of the solutions mnbaining more than 3 pcr rent, magixsinm sulfate, mid in 2 weeks only traces were found cement are irrrportant since unhydrat,ed ccurent Irns been found in tire most dilute solutioii. The silirnte gel mas lrft iii very in conrrite that has been immersed in water for several m a l l , elcar fragments. years.R JUSOin hydrating the silicates for this investigation, a HYDRATED DIC.~:.,CI~M SILICATE-~II solne prc?liruinary trace of crystalline tricalcium silicate was noted in t.he reexperiments the dicalcium silicate hydrated very slowly. sulting gel, and large quantities of crystalline particlcs reTo hasten hydration the material that had passed through the mained unaffected in the hydrated dicalcium silicate. 200-mesh sieve was reground. Tvo grams of this finely powdered compound wcre shaken with 30 cc. of water for 3 weeks and then allowed to stand.with an occasional shaking for 4 weeks longer. Cnder the microscope the grains showed ineomplete hydration, having a small, elear, amorphous layer around each grain, t,lre core being composed of the original crystalline dicalcium silicate. A few of the smaller particles consisted of the gelatinous amorphous matter only. There were no crystals of hydrated lime. (a) Sodium Sulfate. One day after mixing with the su1fat.e solutions t,herc was only a slight thickening in the amorphous layer around the grains in the saturnkd solution. No crystals were present except the unhydrated centers in the dicalcium siiicatc. In 5 days gypsum crystals were 7-Hydrated Tricalcium silicate noted in the mixtures with saturated so- inFi*ure 9 Per cent Magnesium Sulfate. Uark Hera(Lona1Areas Are Cryetals of Calcium dium sulfate, but they were not found in Hydroxide Covered by Amorphous Grains any of the other mixtures. The amor- and Gypsum Needles. Amorphous Silif a t e Grains Appear a8 Small, Clasr, phous layers around t.he grains in the Rounded Particles. x 100 solutions above 5 oer cent were thicker and there were no further visible clianges, even after screral However, tests on the hydrated constituelrt,s would receive the most atteution in any practical application to cement and conmonths. (a) Magnesium Sulfate. After the first day gypsum crys- crete work in alkaline soils, since the hydration products are tals were found in all the mixtures, being most abundant in abundant in concrete. The reactions of tricalcium aluminate, hoth crystalline and the solutions having sulfate concentrations above 5 per cent (Figure 8). Fine amorphous grains of magnesium hydroxide hydrated, with sulfate solutions are more complicated than were present in all the mixtures. The erystailine centers s johnson, zng. Reiord, TI, NO. 11, 320 (1815).
592
INDUSTRIAL A N D ENGINEERI,%-G CHE;MISTRY
those of the silicates with the same solutions. The products of the aluminate with sulfates depend on the concentration of the sulfate, whereas with the silicates the products are the Same regardless of the sulfate concentration. The extreme fineness of the sulfoaluminate crystals formed with concentrated sulfate solutions and tricalcium aluminate indicates that these crystals were formed very rapidly. The crystalline aluminate grains last longer in the more concentrated sulfate solutions, a layer of clear gel surrounding them. In the 2 per cent sulfate solution the sulfoaluminate crystals grew to the largest size, forming in the case of the hydrated aluminate extremely long needles, the felting of which caused the suspension to become semisolid in 20 days. Further experimental work is being done on mixtures of crystalline tricalcium aluminate and very dilute solutions of sodium sulfate. In these mixtures sulfoaluminate crystals are first formed, then disappear and crystals of hydrated tricalcium aluminate grow to a large size. Both gypsum and sulfoaluminate crystals were formed in mixtures of magnesium sulfate with crystalline and also with hydrated tricalcium aluminate. Sulfoaluminate appeared in the dilute (0.5,2 and 0.5, 1, 2 per cent) and gypsum in the other solutions. Sulfate solutions act on crystalline tricalcium silicate in somewhat the same manner as water alone, since a gelatinous coating is formed on the grains, the centers of which gradually grow smaller and finally disappear. However, this change proceeds a t a more rapid rate with sulfate solutions and goes to completion in a short time, no crystalline particles being left. An important difference in the two reactions is the formation of gypsum crystals in the sulfate solutions, thus removing the free calcium hydroxide that is formed during hydration of the silicate in water alone. No explanation can be given for the breaking up of the amorphous silicate grains into very small particles in the saturated solution. It may have been due to the formation of minute gypsum crystals in the gel, but such crystals were noted in only one case. On the whole, solutions of magnesium sulfate had a more destructive effect on the constituents, especially in the hydrated forms, than those of sodium sulfate. Two exceptions were very pronounced. I n one case, grains of crystalline tricalcium aluminate in magnesium sulfate solutions were covered with a gelatinous layer, which protected the centers from further action of the solution. The largest centers were in the 8 per cent and saturated solutions. In the other case, in the hydrated tricalcium silicate mixture with magnesium sulfate, crystals of lime were covered with a layer of amorphous magnesium hydroxide, which caused these lime crystals to persist for a much longer time than they did in the solutions of sodium sulfate. The reactipns with dicalcium silicate are characterized by the slowness with which they proceed. In an attempt to hydrate the dicalcium silicate completely, a sample was ground very fine, shaken with water, and the coarser grains were allowed to settle. The suspension of fine grains was poured off and shaken for about 3 weeks, with the result that all the solid adhered to the walls of the flask and the liquid was clear. Some of the solid was scraped off and on examination showed clear grains of gel with no crystalline centers.
Vol. 17, No. 6
Automatic Buret and Flask for Standard Alkali Solutions' By H. R. McMillin h.ISAT I N S P S C T I O N LABORATORY,
BUREAU OF ANIMAL INDUSTRY, c.
~ r A S H I N O T O N ,D.
The Pyrex glass flask is far superior to a flask with a coating of ceresin
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to a collar made of wire placed somewhat below the neck of the flask. The Peligot tube contains a solution of potassium h y d r o x i d e , c which, in connection the chlo- '1-3-liter flat-bottom Pyrex glass 6ask ride tube, which con- B-Subedte ring, 17 cm. outside diameter C-Peligot tube 13 cm. tains soda lime, D-Calcium chlbride tube, 13 cm. to keep out carbon E-3-way glass stopcock, 50 cc. buret F-Spiral wire springs (two not shown) to dioxide and to remove hold suberite ring to flask this gas from the in- &Lead disk weighing abo3t 1000 grams that fits inside the suberite ring to prevent flask from tipping when only a small coming air when the amount of solution is in the 6ask alkali is drawn into the buret. The potassium hydroxide solution in the Peligot tube prevents evaporation of the standard alkali. As the apparatus is free from attachment to the wall or any fixture, it can be shaken and the condensation which Acknowledgment collects on the inside walls of the flask can be mixed with the standard solution, thereby preventing alteration in its strength. The author acknowledges his indebtedness to T. Thor- The three-way buret allows any solution not used to be revaldion for the suggestion of the problem and for helpful dis- turned to the flask and saved. The buret may then be cussions as the work progressed. He also expresses thanks washed with distilled water and damage, due to alkali left in to W. G. Worcester for the use of equipment and materials it, prevented. in the Department of Ceramic Engineering, and to S. Baster1 Received April 10, 1925 field for criticism of the paper.
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