Dec., 1916
T H E J O U R N A L OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
SOME SLOW VOLUME CHANGES IN PORTLAND CEMENT EDWARD D. CAMPBEI.L Received August 3, 1916
By
Engineers have realized for many years t h a t free lime a n d magnesia m a y cause dangerous expansion i n P o r t l a n d cement a n d have sought b y specifications covering chemical c o m p o s ~ t ~ o nand physical tests t o eliminate trouble f r o m these t w o sources. Free lime c a n b e readily detected and its deleterious effect prevented by proper ageing Of cement before Free magnesia. on t h e o t h e r h a n d , c a n n o t b e as readily detected a n d t h e expansion d u e t o t h e presence of free magnesia does n o t manifest itself t o a n y great ext e n t i n t h e length of t i m e or u n d e r t h e conditions usually employed i n testing Portland cement. It is for this latter that engineers who consider the safety of structures as t h e first requisite, usually specify a maximum allowable per centof magnesia, low enough, so t h a t u n d e r no conditions of o r d i n a r y practice a n d m a n u f a c t u r e the a m o u n t of free magnesia could b e large enough to produce serious results. ~f the total magnesia is k e p t u n d e r 3 Per cent n o t r o u b l e will arise from t h i s cause u n d e r a n y circumstances. On account of very extensive deposits of limestone t o o high i n magnesia t o permit i t s use i n t h e manufact u r e of P o r t l a n d cement if t h e allowable per cent of magnesia is kept down by specifications t o 3 Or 4 per c e n t , efforts have been made t o produce f r o m these magnesian limestones Portland cementswhich would Satisfactorily Pass all t h e Physical t e s t s t o which these cements a r e usually subjected. Cements containing 7 . j or even 9 per cent magnesia have been prepared which h a v e Stood t h e o r d i n a r y physical t e s t s a n d showed no abnormal expansion after intervals of 6 or even mo. immersion in water. A~~~~~ not familiar with t h e Slow r a t e Of h y d r a t i o n Of magnesium oxide would n a t u r a l l y conclude t h a t a cement which g a v e no abnormal expansion after mo. immersion might b e t r u s t e d i n a n y work. It is because of t h i s mist a k e that we a r e s u b m i t t i n g some measurements which have been carried On in ‘Ontinuation Of work described b y t h e a u t h o r i n conjunction with Alfred H. White some ten years ago. In t h i s article, “Some Conditions Influencing Constancy of Volume i n P o r t l a n d Cements,”l the preparation and testing of a n u m b e r of samples of
cement Of different degrees of basicity, Some containi n g free lime, others free a n d combined magnesia, was described. T h e expansion measured by means of a special micrometer o n b a r s 100 m m . i n length was expressed i n per cent, t h e measurements being made at increasing intervals of time. The time intervals selected were 7, 14, 2 1 a n d 28 d a y s ; 2 , 3, 4, 6, 9, 1 2 a n d 18 mo.; a n d b y intervals of I y e a r each a f t e r t h e second year, t h e longest t i m e recorded being 5 years from t h e t i m e a given b a r was made. T h e influence of chemical composition a n d ageing of t h e cement or clinker on t h e volume changes was studied a n d t h e conclusions in p a r t summarized as follows: “Free lime in Portland cement will not only not be slaked during the mixing and setting- of the cement but will not become I
J . A m . Chem. SOL.,98 (1905), 1273-1303.
I IO1
completely hydrated even when the cement is immersed in water, until about 14 days have elapsed. The result of this gradual slaking is to produce abnormal expansion of the cement. Any evil effects due to the presence of free lime in cements kept under water will be manifested within 2 mo. I n case free lime is present in cement used in structures above ground or where it is usually dry, the expansion due to hydration of the cement will be more gradual but several times greater in volume than when the material is under water. The expansion due to free lime slaking in the air may become so great after several months a? to cause complete disintegration. “The deleterious effects of free lime may be completely removed by aging the ground cement or storing the clinker to weather until the pat will stand a perfect boiling test. Weathering the clinker for 3 mo. is usually sufficient. It is difficult to state the length of time necessary properly to age ground Cement to eliminate free lime. It will not ordinarily be less than one month and may be much longer according to the conditions under which it is stored. “Cement which passes a perfect boiling test may safely be assumed to contain no free lime. The expansion of a bar of neat cement containing no free lime when kept in cold water for 7 days is usually under 0.040 per cent, but occasionally it may go as high as 0.060 per cent. A cement with 2.8 per cent free lime showed an expansion of 0 . 2 2 0 per cent in the same period. “The effect of magnesia, like that of lime, depends less upon its total amount than upon the form in which it exists. Combined magnesia like combined lime has no injurious effect in Portland cement. Magnesia combined with silica and alumina forms a hydraulic cement which is safe, but as compared with Portland cement is too weak to be of any commercial value. Free magnesia has no appreciable effect in cement used above ground where it is continuously dry. If the cement is wet for a part or whole of the time, the free magnesia will very slowly hydrate and cause expansion. Even where the cement is continuously immersed in water the expansion due to free magnesia is not appreciable until after 2 mo. and becomes distinctly evident only after a year. The hydration Seems to be well under headway only at the end of the first year and expansion continues a t an increasingly rapid rate for a t least s yrs. and probably longer, Ageing does not seem to diminish the deleterious effect of free magnesia in cement. This is to be expected, since the rate of hydration of hard-burned magnesia in air is almost imperceptiblyslow. “The boiling test for 24 hrs. does not detect free magnesia as it does free lime. Cement containing as high as 4 per cent of free magnesia has passed a perfect boiling test, yet the last measurement of this cement a t the end of 5 yrs. in cold water showed a total expansion of over I per cent, nearly half of which occurred during the fifth year after making. “This slow hydration of free magnesia with its accompanying expansion seems to be the probable cause of the expansion, frequently accompanied by more or less complete disintegration, SO often noted in sidewalks, occurring several years after the walk has been laid. “One per cent or less of free magnesia in cements kept under water causes little noticeable expansion even in neat cement, probably simply filling up the voids. Increased percentages of free magnesia cause cumulatively greater expansion until with 3 per cent of free magnesia the expansion is too great to be at all safe. “In the manufacture of cement from raw materials containing magnesium carbonate, some portion of the magnesia Will remain in the free state. This amount will increase with coarseness of raw materials, increasing percentage of lime and increasing percentage of magnesia. If the total magnesia does not exceed 3 per cent it is not likely that well-made cement will carry enough of this magnesia in the free form to cause injurious expansion under any conditions of service. If the percentage of total magnesia rises above 3 per cent there will be increasing probabiliqy of enough magnesia remaining in the free form to cause injurious expansion.” Since t h e publication of t h e work summarized above, measurements of t h e b a r s k e p t i n water have been continued, some of t h e periods being extended u p t o 13 and 14 years. As t h e purpose of t h e present p a p e r is t o call a t t e n t i o n t o t h e slow volume change, no measurements of expansion for a period of less than one year a r e given i n T a b l e I, i n which a r e shown t h e long-time measurements Of expansion. If the short-time measurements a r e desired, reference m a y
I102
T H E J O C R S A L OF IAVDL7STRI.4L A N D ENGINEERI-VG C H E M I S T R Y
Vol. 8 , No. 1 2
EXPT.
74
75 7i 78 79
80 82 81
83
85
be made t o t h e above-mentioned paper. A s t u d y of t h e figures given in t h e accompanying table seems t o sustain fully t h e conclusions drawn from t h e results published I O yrs. ago. T h e continued expansion due t o free magnesia long after 5 years is very clearly brought o u t , as well as t h e fact t h a t i; magnesium oxide is in t h e combined form it will produce little or no volume change. In view of t h e fact t h a t efforts are being made t o utilize, as a source of raw material for Portland cement, limestones too high in magnesia t o enable t h e production of a cement low enough in this constituent t o be safe under a n y conditions of manufacture, attention should be called t o t h e results of t h e l o n g - t h e measurements on Expts. 74 and j 9 . Both of these cements contain about 7 per cent total magnesia, h u t E x p t . 74 contains 0.53 per’ cent less silica and 0 . 6 7 per cent more calcium oxide t h a n E x p t . 79. T h e CaO ratio of E x p t . 74 is 2 8 0 . 2 while t h a t of E x p t . 79 is 2 7 0 . 7 t o I O O molecules of Sios. I n addition t o t h e difference in basicity t h e raw material used in E x p t . 74 was not quite as finely divided as t h a t used in E x p t . 79. Although in E x p t . 79 b y keeping t h e basic ratio low a n d having t h e material very finely ground, a cement was produced with a total magnesium oxide per cent of 7 . 2 , a n d which would pass all t h e ordinary tests t o which cements would be subjected and which even after 13 or 14 yrs. immersion h a d not expanded t o a n y extent which would probably be dangerous, yet a relatively slight increase in t h e basic ratio a n d coarseness of ran- materia! has shown in E x p t . 74 Very nearly double t h e amount of expansion taking place after t h e first year, this increased expansion being due t o the increased proportion of free magnesia. I t is this liability of having a dangerous amount of free magnesia in cements made from raw materials much higher i n magnesia t h a n is usually considered permissible for t h e best quality t h a t should make manufacturers very cautious about adopting high magnesia raw material and if t h e y do employ such
material t h e y should realize t h a t much greater care in manufacturing mill be required t o produce a reliable cement t h a n if t h e purer raw material were used. UXIVERSITY OF MICHIGAN, A N N ARBOR .
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THE EFFECT OF TEMPERATURE AND THE TIME FACTOR IN THE FORMATION OF GASOLINE 1N THE GAS PHASE AT CONSTANT PRESSURE By GUSTAV EGLOPF, THOMAS J. T W O M E Y
AXD ROBERT
J. h I O O R B
Received September 6 , 1916
I n a recent communication’ t h e formation of gasoline from catalysis in t h e gas, liquid a n d solid phase system was studied. T h e present paper deals with t h e production of gasoline by t h e gas phase system a t constant pressure and varying temperatures a n d rates of oil flow or time factor.2 SCOPE O F T H E I S V E S T I G A T I O N
I n t h e present investigation a series of experiments were conducted with a view t o ascertaining t h e value of a Pennsylvania crude petroleum oil, after removal of t h e gasoline present in t h e oil, for cracking purposes in t h e production of “cracked gasoline,” this cracking t o t a k e place without t h e removal of waxes, gas, fuel and lubricating oil or other constituents of a like value, present in t h e residue from t h e crude oil; in short, t o convert t h e residue into gasoline a t constant pressure of ~ j lbs., o temperatures of 600, 650 and 7 0 0 ° C., a n d rates of oil f l o x ~of r 7 , 2 3 , 30, 3 6 , 4 j a n d 6; gal. per h r . E X P E RI LIE STA L
PR 0C E D U RE
T h e experimental work was carried on in a n 8-in. diameter steel t u b e , gas-heated, a n d the temperaturc control maintained b y means of a base metal thermocouple. T h e pressure in t h e system was built up t o 1 5 0 lbs. b y means of a n air compressor with natural Egloff and Moore, M e t . and Ciicm. Eng., 14 (1916), 67. Egloff and Twomey, “The Time Factor in the Formation of Aromatic Hydrocarbons from a Paraffin Base Oil,” I b i d . , 15 (19161, 2 4 5 . 1 ?
