SEPTEMBER, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
1023
Conclusions
penetrated because of the opening up of a connecting channel by volume changes. -
Even though the significance of all observed variations in absorption properties may not be completely understood, these properties aid in classifying the results observed in practice and permit a number of interesting generalizations:
These studies in absorption lead to a conclusion that brick nlay have many different sorts of internal structure. Figure 3 illustrates several possible structures all gradations of which probably occur in actual brick. Careful study of an absorp&on curve gives indication of the class of structure to whiih the brick belongs. Thus, structure a would undoubtedly be like brick B26 (Figure 2) ; b like B25; and c, although rarely encountered in practice, is approached by B23. I n the course of this investigation, which has explored only a few phases of brick research, it has become evident that most brick lack homogeneity, not only within each group as determined by pit and manufacture, but within the unit itIt mould Seem that research aimed toward elimination of this condition is highly desirable and would probably contribute much to the fund of information we now possess.
(1) For a given type of clay and manufacture, a high percentage of absorption is found in a brick .rrith a high coefficient of saturation. ( 2 ) A high coefficient of saturation is indicative of interconnecting capillaries or a specific gravity approaching that of the minute clay particles themselves. Such a brick underburned, and coupled v.-ith weathering, is unstable and of poor quality. (3) low coefficient of saturation shows sealed pores and capillaries, and may easily indicate vitrification. (4) A rapid rate of absorption in the early increments of time
+
indicates fine capillary structure, while a high percentage but 62), moderate rate of absorDt,tion,as shown for Brick ~ 2 (pipure indicates an open capiliary structure. absorption curve which has abrupt changes indicates (5) partially sealed capillary planes or voids M hich are suddenly
Rostone Operations Improvements have been made in Rostone, both as to method of manufacture and as to form of product. Rostone reactions have been applied to produce a building block of many desirable properties from easily available raw materials. Some 90 per cent of these raw materials is fly ash, a waste material from the combustion of powdered coal, disposal of which frequently presents a difficult problem.
R. L. HARRISON, P. W. JONES, AND
R. NORRIS SHREVE Rostone, Inc., Lafayette, Ind.
T
HE building material known as Rostone, made from the reaction of naturally occurring aluminosilicates, such as shales and slates, with a n alkaline earth base in the presence of lowpressure steam, has been described.' At the Century of Progress in Chicago there were two houses with exterior walls made of this material. In Indiana, Illinois, and Ohio a number of buildings have also been constructed whose exterior and interior walls are made of this product; numerous other jobs have employed Rostone, such as refronting old buildings, tiling bathrooms, floors, kitchens, etc. By the choice of various fillers and coloring materials, Rostone products may be given unusual and varied appearance and texture a t the command of the designer. Furthermore, the finished indurated product can be made to exact and predetermined dimensions. 1 Peffer, H C , H a r r i s o n , R L , a n d Shreve. R N , 719 (1933)
IVD E U GC H E V ,2 5 ,
RECEIVED May
io, 1935
Over six million people walked down the Rostone stair treads in one of the houses at the Century of Progress during the seasons of 1933 and 1934. The wear was remarkably small-under one-quarter inch a t the edges and less on the main surface. New Rostone Plant
To meet the market requirements, a new manufacturing plant has been established within the past year. The procedures adopted are similar to those previously described which involve the following steps : quarrying and powdering of shale; mixing of shale with fully slaked lime; incorporation of filler and coloring matter, together with the necessary amount of water; compressing of this moist material into requisite shapes; induration of this compressed material by heating in a n autoclave with steam of about 75 pounds per square inch pressure for 2 hours; treating the surface, when necessary, by grinding or by pebbling. The new plant involves efficient handling of the material in a streamline flow. A revolving covered mixer has been found satisfactory for excellent mixing of the materials. Since this reaction involves the combination between solids facilitated by steam, it is readily understood that efficient mixing and compressing are necessary as a prerequisite. Figure 1 shows on the right the storage hoppers from which the prepared moist mixture is dropped into the molds, which are then subjected to compression in the hydraulic press on the left. This press is capable of compressing, to 2500 pounds per square inch, large slabs 25 X 50 inches in size. Experience with this press has shown the advantage resulting from such uniformly even compression, for the particles are brought into intimate contact, thus facilitating reaction during the indurating or steaming stage. Although for several houses large slabs, 18 X 48 X 2 inches in size and weighing about 140 pounds, were used, experience has indicated that smaller slabs, 16 X 24 X 1.25 inches in size, are more advantageous, since one man can place them more easily on the supports. Furthermore, the reduction of thickness from 2 to 11/4inches means that a lighter framework can be used for the support of the slabs. In the earlier work the appearance of the slabs was improved by polishing the outer or exposed surface, but in the last year or two a surface has been produced which has been more pleasing, particularly for exterior work, by roughening the surface by means of an air blast uhing steel shot. Thiq
1024
INDUSTRIAL AND ENGINEERING CHEMISTRY
roughening of the surface brings out in a very pleasing manner the variation intentionally caused by the use of aggregates of different sizes and colors. I n the construction of a building using synthetic stone 11/4 to 2 inches thick, a distinctly improved method of construction is now utilized. Steel track or angles are fastened to the subframe of the building by means of nails or screws in horizontal rows spaced 16 inches apart. The Rostone is placed on these tracks or angles and held in place by means of small steel dowels which fit into the upper edge of the lower slab and into the lower edge of the upper slab through the steel track (Figures 2 and 3). Between the outer Rostone facing and the interior finished wall insulation is placed to give the modern protection against cold and heat. However, the Itostone wall is an effective insulating agent because of its high resistance to heat and cold. The use of this type of construction permits the rapid erection and mass distribution of standard shapes of synthetic stone. Larger shapes, such as 25 X 50 inches, are finding a wide use in modernization of old buildings and are applied in the usual way that natural stone is attached with copper wire anchors and mortar.
Application to Fly Ash The disposal of the ash from the combustion of powdered coal has always been a source of annoyance and expense. Powdered coal combustion has many advantages, and it has been used generally for a number of the larger power units, but the resulting ash has created a problem of handling huge tonnages of a waste bulky material for which no use has been developed which would consume the quantities obtained. The d a c u l t y and cost of disposing of this ash have had a limiting action on the application of this efficient powdered coal as fuel for power plants. Much time and money have been spent in searching for an economical use of this waste. This ash, commonly termed “fly ash,” is obtained in quan-
VOL. 27, NO. 9
tities ranging from a few hundred tons a weekpp to 500 tons a day. It may be collected from the combustion gases by electrostatic precipitation or wet scrubbing methods, to prevent the nuisance of its deposition on the surrounding neighborhood. Fly ash is not suitable for filling in ground or for the similar uses usually made of the clinker ash from stokerfired boilers. It must be dampened to eliminate dusting even for haulage in open conveyances and is sometimes disposed of by dumping in abandoned quarries or the like. Fly ash, as defined here, is not to be confused with other types of “flying ashes” or coal ash from other types of combustion, since the ash from powdered coal combustion is physically and chemically differentiated in various degrees from these other materials. Various uses for fly ash have been suggested, which include fillers for asphalt, cement, etc. While the various results appear favorable, no application of this nature appears adapted to consume the large tonnages of fly ash obtained even a t the present time. An investigation during the past several years has sought to develop a process for using fly ash as one of the main ingredients in a synthetic stonelike material for building purposes; a marketable product would consume large quantities of fly ash. A product has been obtained by the Rostone procedures utilizing a reaction between fly ash and an alkaline earth base; the fly ash constitutes approximately 90 per cent of the finished product. This product has satisfactory physical characteristics for building purposes and is now in limited use in the form of brick and hollow back-up units for load-bearing walls (Figure 4).
Chemical and Physical Characteristics of Fly Ash Fly ash as received from the combustion gases varies in color usually from light gray to grayish black, although brown fly ash is sometimes obtained, depending upon its
S E F r m l B E l ~ ,1Y35
INDUSTHIAS, AND ENGINEERING CHERlISTKY
.ource. The particle &es i-ary accordingly. as shown by the followiiig t.wo sieve aiialyses frrini two diflerent localities 8 in per cent) ; Srrii'pie .4
Retained OD 100 Emesli Retained on 200 mesli Retained on 325 meah Through 525 mesh
6.26 9.40
7.75 76.00
Sample I3 6.5 0.7 4.6 88.2
The individual particles, when inspected tirider a micro*cope,are generally &dike in appearance aud are soruetimes i n the form small lidlow spheres or Iiuhbles, demonstrating that vitrification has been carried to a high (legree. ..
.
.
.
.
. . . . .. .
l'he percentage chemical auulysk of fly as11 varies iri ILCwrdance wit11 the particuhr coal from which it is obtained, :~ltiioughthe carbon content of the fly ash depends upon the cffciency of the individual installation and upon the charact w d t,he original coal: Y ~ i i m l oh SiOl .iI*O,
46.9 29.51 11.9
B a i s ~ l aB 44.10 20.44 18.72
cuo hfgo Ti0
C
Sainple A
S a i i i ~ l eM
2.6 0.0
6.85
1.3
0.8
0.IZ
0.71 8.26
petrographic examination discloses tlie presence of consideriiI)le niagnetite in the form of black globules and some hematite, which leads to the present belief that probably little of the iron content is combined witir the glassy particles.
Process for Making Building Materials Except for the quicklime content of some fly ash, and variaticiris in adsorbed film around the individual particles which ,,revent proper wetting, the fly ash can be used directly from the houpers below the precipiiators i n t I1e power plants. When s u f f i c i e n t quicklime is present t o cause later unsoundnessin theprodiict, the fly ashmust be slaked either by a g i n g i t in a dampened condition or by heating the dampened fly ash to accelerate the slaking. Somet i m e s slaking is accomplished during the tempering operat,ion. This tempering operation is to reinox or
1023
displace the adsorbed fiim of gases or nonaqueous substance in orrier to afford proper wetting, which facilitates the desired clrcinical renetion with an alkaline earth base. Temperie of fly ash is accomplished satisfactorily ing of ~ ~ i ivarieties during the mixing operation. Other varieties must be mixed with water under shearing and compacting eonditions, while still others must be mixed intimately with water and then aged for a period of time. It is in the latter operat,ion that slaking can occur simultaneously with tempering. The fly ash, as received or as slaked and tempered, is mixed in a wet pan with tho proper proportion of slaked hydrated lime, and a substance whielr prevents emorescence of tlie final product (as described later). To this mixed mass, wat.er is added in carefully adjusted quantities to form a damp, p r e s ~ b l emixture. A preliminary mixer is sonietin~es preferred for the initial incorporation of ingredicuts before the final mixing takes place in a wet pan. After thorough incorporation of the dairip mass, the material is pressed by about 2500 pounds per square inch pressure or is tamped under pressure into the desired shape. The formed shapes are placed on cars which are pushecl int,o a steam-pressure aritoclave. The ma,t,erialis suhject.ec1to snturated steam for 2 hours at 75 pouiids pressure. During this time the chemical reactiori occurs between the fly ash and hydrated lime to forin a dense, hard, stonelike mass. Upon reirroval from the autoclave the shapes have full strength arid are rendy for application. Larger shapes, such as 8 x 8 X 16 iiich hollow blocks, inay have to be aged for a few days tinder ~ ~ a r zconditions n to release the very slight shrinkage which occurs during tbe drying of the block (less than 0.0003 inch per lineal inch).
Control of Emoresccnce Without special treatment, fly asli products will exhibit nn ext,raordinarily bad white efflorescence aitcr being placed
in a wall and exposed to the mattier, or when subjected to the efRoreseence test. Chemical analysis of the white effloresecnce varies with the particular fly ash in use, but the main constituents are sulfates of calcium aud sodium. Extensive tests were made to wash the fly ash free froui soluble salts by washing and filtering slurries of the material. While the amount of soluble material was reduced by this method, elimination of efilorescence was not obtained. It appeared later that base exchangc occurred during the steaming process to set free the sduble sodium salts, which of course would make the naslring process of no avail. The solution to this problem consisted in adding any one of several organic subt;tances to the mix. This one now in use is pulverised wood rosin. The rosin reacts during the steamine nrocess with t h e s o G b l e salts to form resinates; this r e a c t i o n eliminates e f f l o r e s c e n c e , The pereentageof rosinrequired varies with the p a r t i c u l a r fly ash; hoaever more than one per cent of the final dry weight of the mix is s e l d o m r e quired. Tile typical p r o p o r t i o n s , by weight, are as follows: 100 parts fiy ash, 10 hydrated lime (highc a l c i u m ) , 0.5 wood rosin, and 19 water.
1026
INDUSTRIAL AND ENGINEERING CHEMISTRY
Color and Treatment The color of the fly ash product is practically the same as the fly ash used for making the product, usually ranging from slate gray to grayish black. A change in color can be effected by heating the fly ash under oxidizing conditions from 700" to 1000" F. The carbon is burned out and the magnetite changed. The fly ash so treated becomes light tan in color. Various mineral pigments can be added to burned fly ash during the mixing operation to produce permanent colors. The untreated fly ash can be colored likewise, although the resulting colors are deadened considerably by the dark fly ash.
Physical Characteristics All products made of fly ash have smooth, true surfaces. No warpage or shrinkage occurs after the shapes are formed. Bricks of fly ash have the following physical properties: Compressive strength (2-inch cubes) Modulue of ru ture (standard brick test) Absorption (&r. immersion)
6000-8000 Ib./sq. in. 600-1000 lb./sq. in. 3.5-6.0%
VOL. 27, NO. 9
In order to test the resistance to fire, an oil flame was held against a wall of fly ash blocks, and temperatures were recorded on the hot and cold sides and also in the air space within the wall. The temperature obtained on the hot side was 1900" F. The air space within the block and directly in front of the flame had a maximum temperature of 82.3' F. while on the cool side the wall reached a temperature of 300 O F . This wall Tvas quenched immediately following the fire test with cold water. While some shrinkage cracks occurred in the blocks, these cracks extended into the blocks only oneeighth inch and the remainder was found to be intact.
Practical Application A pilot plant is now in operation in the works of the Detroit Edison Company to a limited extent to produce hollow block for load-bearing walls. Figure 4 shows installations and wall construction. One of the attributes of these blocks is the smooth and regular surfaces. I n one case the blocks were used for the walls of a house. By painting or enameling the inside of these walls, a pleasing effect was secured and the expense of lath and plaster was saved. The use of the fly ash in the Rostone operations is offered as a solution to the utilization of this waste product, and for the production of cheap building material in the cities where such products are wanted. The fly ash can be shipped from power plants to a special factory, but where large tonnages of the fly ash are available, it may be better to make the fly ash into building materials in the power plant itself. The finished products will be much easier to ship than the fly ash, and only about 10 per cent additional m a t e r i a l (lime) will be needed. We can visualize the f u t u r e power plant with a floor immediately under the elect r o s t a t i c separators where the fly ash will b'e f a b r i c a t e d into building materials.
The holIow 8 X 8 X 16 inch load-bearing wall block can be made with 55 per cent core space, weighing approximately 23 pounds per block. The compressive strength of the hollow block over gross area has been as high as 2226 pounds per square inch. Building codes may call for a value from 700 to 1000 pounds per square inch over gross area. Water-tight masonry construction has been receiving considerable attention the past few years. The National Bureau of Standards has investigated this problem and reports that for the best results there is an optimum relation between porosity of building unit and the character of the mortar. The optimum absorption of units, whatever it may be, is not easily obtained in most building unit manufacture. With the fly ash products it is possible to vary the absorption value by varying the amount of resinous material used. SHEDOF FLY ASH ROSTONE BLOCKS FIGURE 4. SMALL
RECEIVED April 2 2 , 1935.
*+.
* Germany Using Illuminating Gas for Automobile Fuel Following its national policy of substituting domestic products for imported materials, Germany is now experimenting with cokeoven gas as a motor fuel, according to a report made public by
the Commerce Department's Chemical Division. With a view t o demonstrating the practicality of utilizing cokeoven gas as a motor fuel, the Ruhrgas, A. G., joint distributing subsidiary of Ruhr coke plants, recently sent a large omnibus from Essen to Konigsberg, in the extreme northeastern part of Germany, powered exclusively with gas from Ruhr coke ovens. The trial was pronounced successful. Gas for the trip was carried in steel cylinders on a separate trailer. The cylinders were recharged en route at the Hanover station, which receives its gas supply by pipe line from Ruhr roke plants, and is said to be the only illuminating-gas motor tank station in the world.
A further development in the use of chemically-produced gas as a substitute for gasoline, was the establishment a few months ago in the Ruhr district of the world's first gas-tank station for supplying motor methane, which is produced by the Hibernia nitrogen plant at Herne, and by two other Ruhr companies. The methane is recovered in these plants from coke-oven gas and stored in tanks under normal pressure. The gas is later compressed in high-pressure storage tanks which serve as filling stations for motor vehicles, making it unnecessary for the vehicles themselves to carry compressors. It is reported that, after some months' operation, this methane gas tank station has given excellent service and that already 200 trucks in the Ruhr basin are using this new motor fuel, and that the number is increasing steadily.
