Effects of Smoke on
Building Materials Reports and observations show continuation of excessive air pollution and resultant damage to building materials. Effects of tarry matter and sulfur compounds resulting from combustion of fuel are discussed. Complications caused by city smoke in air-conditioning are mentioned. -4ctivities of chemists in the development of materials and protective coatings more resistant to air-borne corrosive agencies are noted. Of equal importance is the necessity for control of deleterious air pollutants not only to extend further the life and maintain the attractiveness of corrosionresistant materials, but to justify the wider use of older, more familiar building materials
.
H. B. SIELLER
AND
L. B. SISSOfi
Mellon Institute of Industrial Research. Pittsburgh, Pa.
D
ISCUSSI O S of the effects of city smoke on architectural materials apparently is being taken up in a spirit of frank inquiry, covering variety and extent of damage as well as preventive and protective measures. Evidence of such a trend \vas given recently by Steel ( I @ , when it headlined: (‘Less Smoke in Cities to Increase Use of Steel” and stated that protection of metal surfaces and their maintenance in an attractive and clean state can be made easy and inexpensive in communities where the best fuel combustion practices are the rule. The director of the Mellon Institute (19) also lent his voice to the movement for cleaner city air when he said that “communities are only temporizing when. . . . . they try to convert outdoor urban air space into an unreliable sewage disposal system.” With leading exponents of industry and research thus joined in sponsoring current efforts to obtain cleaner air, there is no need to indulge in circumlocution when dealing with an atmospheric pollution nuisance which imposes monumental annual losses, estimated a t $30,000,000 in Chicago alone (4).
Air Pollution Damage to Structures The despoiling of structures by bad urban air is very real. There is nothing fanciful about the $3 daily smoke damage 1309
tax paid by the taxpayers of Allegheny County, Pa., on their courthouse and jail over a period of the last fifty years. There is no lack of reality about the fact that some varieties of building stone are in disfavor in Yew York; any traveler on Fifth or Madison Avenues can see ample evidence of the disintegrating power of atmospheric pollutants on dwelling, store, and church. Much the same sort of artificially generated decay is in evidence on the stonework of the Carnegie Library and Museum, not yet thirty years old, in Pittsburgh. There was nothing unreal in the expense incurred by a large Baltimore plant which had the condensing system on its roof destroyed by the smoke stream from a nearby source. Speller (17) recently calculated that the steel production for 1933 was about sufficient for renewals made necessary by corrosion, which is in part caused by air-borne agencies. Visual observations in centers of population and in many commercial, industrial, transportation, and domestic establishments afford evidence that surfaces of structural materials other than steel have sadly deteriorated and thereby exposed the substance of the strength or enclosure members to unchecked attack by chemicalized atmosphere. It is probably correct to say that the destruction of materials by rust and rot is today the greatest ever chronicled. Reliable reports of excess pollution of the air in all large cities and in many of the smaller communities are made continuously. The most notable recent citation of a change for the worse in the corrosive quality of a city’s air is that in 1933 by a committee of the American Society for Testing Materials in Ken. York. In Washington it was found necessary to clean smoke grime from the new Supreme Court Building ahead of occupancy. In Cincinnati the Smoke Abatement League (15)declares its struggle to control smoke has encountered a “serious situation” because the well-to-do have assumed that if the poor are permitted t o burn high volatile fuel (smokily) in homes they, too, should have such privileges. Philadelphia (16) reports 4 per cent tar content in its soot fall. In the absence of any regular measurements of volatile sulfur compounds in American urban air, there can be cited for comparative purpose.. an English document (6) revealing the tar and sulfur content of London air as about unchanged over a two-year period. In the same report there is an interesting item regarding Halifax (England) where the amount of sunlight screened out by qmoke was 20 per cent greater a t the smokiest station than at the less polluted point of observation. This is in line n-ith the findings of the IT. S.Public Health Service (6) in Kew York and Baltimore and with those of the Mellon Institute (11) in Pittsburgh as between “clear” and “smoky” sections. A complete appreciation of the scene from the chemist’s viewpoint might perhaps best be gained by sending him up into the stratosphere from Indianapolis, for example, and equipping him telescopically to sweep the nation from the Rockies to the eastern seaboard. He would count many hundreds of mushroom-shaped smudges, each representing a fuel-burning center of population and each to be regarded as a chemical factory. That the chemicals are not produced for profit but are turned loose in the atmosphere with destructive effect does not alter the essential fact that each city must be realistically dealt with as the creator of a chemicalized atmosphere to which all its property and possessions are exposed.
Complexity of the Problem Scientists who have been investigating the extent of atmospheric pollution and striving to devise means to protect their products against attack by it are well aware that there are many variables in both the natural conditions and the induced reactivity of city air. Low winds permit concentra-
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AND ENGINEERILYG CHEMISTRY
tions of pollutants. Moisture generally accelerates the rate of attack. Relative humidity may be a powerful factor, especially when high. Temperature ranges are very important. Finally, there is variation in kind and volume of emission of the chemicals as they issue from the chimney and as they enter into combinations. The fact is, no two large centers of industrial population have precisely similar chemical concentrations in their air. Nor will reactions necessarily be exactly alike. Differences in weather are potent agents of modification. Johnson (7) very probably was of this mind with regard to the behavior of materials in various locations when he wrote: “Corrosion is not a single problem but, even for a single metal, comprises a great variety of conditions to which the metal may be exposed.” He calls attention to “great differences in atmosphere from one place to another” and says, “an industrial atmosphere of high average humidity is more corrosive than a relatively dry industrial atmosphere and this, in turn, is worse than dry pure air.” He sees that “the best chance of making real progress is through systematic investigation of films under various conditions of exposure, with the ultimate aim of forming on the metal that f l m which will best protect it from the conditions to which it will be exposed, instead of leaving the formation of the initial f2m to chance as is now commonly done.” His call for ‘‘a systematic investigation to uncover the fundamental facts” regarding atmospheric corrosion might well be supplemented by a survey of the atmosphere of all important cities. Dependable information about the character and the average amount of atmospheric contaminants in any locality would serve as a guide in location, design, and choice of materials for any and all kinds of structures and furnishings. At present, the great majority of owners of property are open t o loss, as Johnson hints, by having to leave too much to chance.
Chemicals in City Atmosphere
CARBONDIOXIDE.Since carbon dioxide as a product of combustion is inescapable in urban air, attention given it will be exercised in the choice of proper materials to be used a t low levels where exhausts from automobiles add to the concentration, and in avoiding use of loosely grained limestone and marbles which would be kept wet by drip water. SULFURCOMPOUNDS.Sulfur compounds constitute the most destructive single chemical agency encountered in the air of urban communities. In the presence of moisture a weak but active solution of sulfuric acid is formed. The sulfur compounds themselves appear to distribute and fall through the air at‘a rate that will give worst ground conditions a t a distance eight to ten times that of the chimney height (IS). Where the sulfur is unaccompanied by oily and tarry soot, by which it is a f i e d and held to structural surfaces, or a t times when it is not mixed with fogs and so held in suspension in the air for considerable periods, its destructiveness is less consequential above ground outdoors. I n cities, however, where smoke haze and grimed walls are proof positive of tar and oil output from fuel combustion, a sulfur content of soot plastered onto both interior and exterior structural surfaces can be assumed. For every pound of sulfur emitted in flue gases, there is the potentiality of 3 pounds of sulfuric acid. This acid will react with its weight in calcareous substances, such as limestone, sandstone with a calcareous cement, marble, or mortar, or it will combine in definite proportions with copper and some other metals to form sulfates. Baines ( I ) , after citing damage to buildings in English cities a t the rate of about $10,000,000annually, reported that the “expansive force developing from the crystallization of these sulfates (calcium and magnesium) along the cleavage planes (of stones) slowly opened up the old sealed vents where they could be attacked by atmospheric acid, and even
VOL. 27. NO. 11
lifted fragments of stone some tons in weight.” On the Houses of Parliament he found “sulfate-which could only have been derived from the attack upon the stone by atmospheric acid-in cracks and fissures as much as 20 inches from the surface,” and “the increase in the volume of crystallization of from 1 to 4.2 had thrown off great pieces of stone. . . .; over 35 tons were picked off portions of the building by hand without touch of tool or hammer.” The Houses of Parliament are about 90 years old. Into the smoke-rotted mortar between immense stones in the foundation wall of the Pittsburgh jail, now 50 years old, the writers saw a rod thrust two feet by hand power only. Surveys (14) of the sulfur in the air of Pittsburgh (one of the few American cities to be so surveyed) revealed average concentrations for 1927-28, 1931, and 1932 (three surveys a t three different locations) of 0.16, 0.32, and 0.15 part sulfur dioxide per million parts of air with respective maxima of 1.1, 2.5, and 1.1 parts per million. These maximum concentrations occurred during periods of smog (a mixture of smoke and fog) and were accompanied by killing of some greenhouse plants and damage to quantities of displayed merchandise. On one particularly bad day (December 1, 1932) retail authorities in Pittsburgh estimated the cash loss to retail merchants in the city a t $40,000. Concentrations of volatile sulfur compounds comparable to those reported for Pittsburgh may be expected in cities burning equivalent amounts of sulfur-bearing fuel. A fuller discussion of corrosion of building materials through atmospheric agencies may be found in the Architectural Record ( I O ) . With regard to building stones, a chapter by Bowles (8) is recommended. Many cautionary suggestions, most of which are presumably familiar to the chemist, are available in the technical press, but investigations reveal that this information is not yet sufficiently well known or honored to prevent the continuance of obvious mistakes in selection and use of structural materials.
Remedial Measures In the category of remedial measures, one which could be of general application is the reduction to the practical minimum of the amount of sulfur in fuel put into the fire box. Sulfur which does not get into the furnace cannot come out the stack. The problem of caring for the remainder which does go into the furnace would be less difficult than now. A second remedial consideration is to have little or no tar or oily substances leave the chimney in conjunction with sulfur compounds. This favors an expanded use of the lowsulfur and practically tar-free solid smokeless fuels-anthracite and coke-and the further development of equipment and methods to burn higher volatile fuel smokelessly.
Separation of Sulfur Oxides from Flue Gases
d forerunner of possible procedure for large urban fuelburning plants may be found in the major-scale experiments which started a t the Battersea plant, near London, in 1929. Recognition of damage from stack emission led Parliament t o sanction the erection of the first unit of the Battersea electric power station on the condition that “best practicable means would be taken to remove the oxides of sulfur from the flue gases before the latter were emitted to the atmosphere.” Elimination of stack dust was also a factor. The Parliamentary restriction, according to Pearson (15) “was largely and justifiably prompted by consideration of the extensive damage done to the stonework of the Houses of Parliament, and other public buildings, through the acidity of London air.” Pearson adds : “The example set by London has already been followed elsewhere, and will sooner or later be followed by all
NOVEMBER, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
large cities throughout the world.” The specifications for the power stations a t Swansea and Fulham call for approximately 96 per cent sulfur and dust elimination through scrubbing with solutions containing lime or reactivated chalk. I n America considerable work has been done, both in removal of part of the sulfur from coal prior to its use and in development of equipment and processes to separate sulfur from flue gases. The contributions which have been made in this field by the Engineering Experiment Station of the University of Illinois are familiar. I n considering the practicability of sulfur as well as dust separation, it should be kept in mind that a reasonable degree of regulation of such atmospheric pollutants needs to include the smaller plants as well as the comparatively few large plants that can stand the burden of expensive equipment.
Corrosion-Resistant Materials The chemist will readily see that the objective is to maintain a city atmosphere in which there will be the smallest amounts of those particular products of fuel combustion which are currently doing the most damage to buildings and contents. Everything that can be done in this clirection will supplement the work of scientists who are striving to improve the corrosion-resistant qualities of their products. There should be progress in air purification to match that being made by the technologists who have, among other products, already given us tiles, porcelains, stainless steel, anodic aluminum finish, and other protective surfacings with which to defy the devils of rust. AVAILABILITY AKD PRICIC.It is not possible, however, to rely upon these newer and more highly corrosion-resistant products to meet all our demands. Some of them are not available in large quantities; nearly all of them represent advances in price above the older materials they are intended to replace. Some of the older materials represent considerable investment in plant and irreplaceable sources of employment and labor, Instead of having familiar building materials forced out of use by reason of their lesser resistance to damage by acidic and tarry smoke deposits, the country would profit more evenly by taking control of its smoke, especially its domestic and commercial smoke, and thereby a t least decelerate the casualty rate of some investments in quarries and mills. PAINTSAND PAINT-LIKE PROTECTIVE COATINGS.An enumeration of the damage done by smoke to such coatings, taken together with a listing of the efforts made to find more durable resistant coverings, mould require a volume. According to a report made in 1913 by master painters to hlellon Institute ( l b ) , ordinary paint such as was then used lasted upward of three years in smoky cities and seven years in rural air. Meantime, much better paints have been involved at increased cost and a t the expense of otherwise serviceable older vehicles and pigments. These proved corrosion-resistant paints average about double m purchase price when compared to ordinary paint but save in labor cost when extra durability of the film, regardless of smoke-smudged appearance, permits postponing of repainting. Where residences or other structures are painted primarily for the sake of appearance, as has generally been found to be the case in most residential and choice commercial sections, the money expended in costlier protective coatings does not keep them from being plastered with smoke deposits containing tarry and oily matter The smoothest paint films could hardly be expected to perform better than the polished stainless steel trim of the Empire State building. This metal lost its refulgent “bloom” after a relatively short bath in New York’s atmospheric haze. Tests revealed that vigorous scrubbing with soap and water was required to remove the asphalt-like accumulation.
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I n the chemists’ fight to defeat corrosion, the sector assigned to paints, lacquers, varnishes, etc., has been the scene of intense activity. In the current period of undermaintenance, protective coatings have been put to hard, practical durability tests. An aluminum priming coat for all wood, under all conditions, has served to keep tar and acid smoke constituents from joining with moisture and reaching the wood. A widely watched experiment is that of adding iron oxide pigment to zinc chromate as a priming coat for both steel and aluminum structural materials used on the Smithfield Street Bridge, under both marine and land smoke, a t Pittsburgh. Two top coats of aluminum paint were applied and these will be studied closely to see if they possess superiority in resisting disintegration under attack of solar ultraviolet radiation. There has been disposition to regard soot as a shield against damage to paint by sunlight. The overlapping flat flakes of aluminum, it may be found, will resist sun penetration and preserve the long-oil varnish or Bakelite type vehicle. This is a highly important point; it bears directly on the preservation of an unbroken, attractive film for exterior metal, as proposed for dwelling houses. AIR-COXDITIONING HAhfPERED. With the advent of airconditioning, a development in which the chemist has played a part, complications have resulted from atmospheric smoke pollution. Metals ordinarily used are reported to have failed under concentrations of sulfuric acid in the washers. Heavily galvanized sheets have been required. Where the smoke burden is especially severe, three to five times t,he ordinary filter space is provided. After examining the air-conditioning installations in seventy-six theaters last year, Kimball (8) cited a list of handicaps that in themselves would have been enough for the promising new industry to carry, without having also to bear up under such troubles as are imposed by smoke. Carter (3) tersely described some of the latter: “I have inspected equipment which has operated satisfactorily for years without any major expense for repairs or any signs of serious deterioration. In the same community I have also seen air-conditioning systems fail in three months, generally on account of local conditions traceable to air pollution by products of combustion. Certainly it is not the fault of the equipment maker. . . . I n the main, corrosion in air-conditioning may be attributed to the presence of a smoke problem, to products of combustion. . . . Scale of corrosion products affects the rate of heat transfer markedly and may result in actual failure of the equipment or in costly repair or cleaning bills. ” In one of the largest cleaning and dyeing establishments in the country, the extra-size air filter was overwhelmed during a smog period and heavy damage was done to valuable cleaned garments. Where the air pollution cannot be lessened, an alternative solution is to add corrosion-inhibiting chemicals to the water and maintain hydrogen-ion concentration within the range pH 8.0 to 9.0. This method is also cited by Kirnberley and Scribner (9) after they had investigated damage done to library contents by atmospheric contaminants and recommended air cleaning for every room in which important papers, books, and documents are permanently kept. They caution: “In localities where a high degree of atmospheric pollution is encountered, the metal parts of air-conditioning systems corrode so rapidly, if preventive measures are not taken, that complete replacement has in certain cases become necessary after less than a year of operation.” Carter (3) found an instance of hydrogen sulfide from an industrial source in city air which caused him to replace the copper portion of an air-conditioning system with aluminum. Separation of solids from stack gases has not been considered here, inasmuch as this is a physical problem. It must be understood, however, that any attack on air pollu-
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INDUSTRIAL ATD ENGINEERING CHEMISTRY
(9) Kimberley, A. E., and Scribner, B. K., Natl. Bur. Standards, Miscellaneous Pub. 144 (1934). (10) Meller, H. B., and Sisson, L. B., Architectural Record, 75, 378-93 (1934). (11) Meller, H. B., and Warga, hl. E., Am. J . Pub. Health, 23, 217-34 (1933). (12) O’Connor, J. J., Mellon Inst. Ind. Research, BulZ. 4 (1913). (13) Pearson, J. L., Nonhebel, G., and Ulander, P. H. N., J . Inst. Fuel, 8 , 119-52 (1935). (14) Schade. C., J. I n d . Hyg., 15, 3 (May, 1933). (15) Smoke Abatement League (Cincinnati), Annual Rept., 1934. (16) Smyth, H. F., Rept. on CWA Air Pollution Study, Philadelphia, 1934. (17) Speller, F. N., Iron Age, 133, 28-31 (1934). (18) Steel, 95, 17, 39 (Oct. 22, 1934). (19) Weidlein, E. R., Am. City, 50, 2, 61 (Feb., 1935).
tion resulting from the combustion of fuels will include this important phase.
Literature Cited (1) Baines, F., “Examination into Effects of Air Pollution on (2) (3) (4) (5) (6) (7) (8)
Building Stones, etc.,” Manchester, England, Natl. Smoke Abatement SOC., 1934. Bowles, O., “The Stone Industries,” Chap. 15 (1934). Carter, W. H., Chem. &: Met. Eng., 41, 140-2 (1934). CWA Survey, Dept. of Smoke Inspection, Special Rept., Chicago, 1934. Engineering, 137, 631-2 (1934). Ives, J. E., U . S. Pub. Health Bull. 197 (1930). Johnson, J., IND.ENG.CHEY.,26, 1238-44 (1934). Kimball, D. D., Heating, Piping, A i r Conditioning, 6,497 (1934). 0
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Compounds in Portland Cement Revealed by High-Temperature Research upon Cement Components
R. H. BOGUE National Bureau of Standards, Washington, D. C.
P
ORTLAND cement is not a material of great antiquity. It was discovered only a little over a century aqo and quite by accident. It had been the custom in the manufacture of hydraulic limes to heat argillaceous limestones to temperatures not greatly above that a t which the carbon dioxide would be liberated, but this process was carried out in a stack furnace under conditions such that some parts of the material were heated to temperatures which produced sintering. These hard lumps of sintered material were discarded because they were so much more difficult to grind than the unsintered material. However, in 1824 dspdin (I) ground some of these hard lump5 and, in confirmation of a report of T’icat, found that they produced a cementing material far superior to any of those formerly produced by the old process. To this the name “Portland cement” was given because of a similarity in appearance, when made into concrete, to a natural rock quarried on the Isle of Portland in England. For half a century the amounts of this new material produced Jvere very small, and even up to the beginning of the twentieth century there was only a suggestion of the tremendous industrial importance which Portland cement was detined to attain in building construction.
Microscopical and X-Ray ;Methods
A TRANSCEXDENT EX.4MPLE OF ARTISTRYIN CONCRETE, THE BAHA’I TEMPLE IN CHICAGO
illthough LeChatelier (IO)learned something of the chemical combinations of Portland cement by a n application of microscopical technic, it remained for high-temperature research on the cement components to produce an adequate picture of the compound constitution of Portland cement. More than 90 per cent of this material is made up of lime, silica, and alumina in some form of chemical combination. An understanding of the nature of that combination can be reached thoroughly only by an intensive physico-chemical research on the phase relationships of the compounds formed and their regions of stability. The studies of Rankin and Wright ( l a ) , and co-workers a t the Geophysical Laboratory, on these three components have established the equilibrium compositions within the system, with all possible mixtures of those oxides. Figure 1 gives the conventional concentration diagram for the ternary system lime-alumina-silica. The diagram is so constructed that the composition of any point within the triangle is defined by its location. The binary compounds are indicated by points on the sides, and the ternary compounds
