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tention, which it has in common with the storage battery itself-that of distilled water being added to replace evaporated and decomposed water of the electrolyte. In addition to functioning directly as a rectifier for obtaining continuous current, apparatus built along similar principles may be used for electrolytic condensers and detectors, and possibly lightning arresters. Among other metals which have this property of valve action more or less in common with tantalum are especially magnesium and aluminium. However, owing to the ready susceptibility of both these metals to chemical corrosion, they have not proved very suitable as sources of direct current. Condensers and lightning arresters for high-potential transmission lines are commercially used with aluminium plates.
Concrete in the Construction of Chemical-Manufacturing Facilities
TABLEI-RATING
TYPEOP COLUMN Reinforced concrete
Reinforced concrete
Structural steel
PORTLAND CEMENTASSOCIATION, CHICAGO, ILL.
T
1 Tentative Standard Specifications for Floors of the American Concrete Institute may be had on request from the Portland Cement Association. 2 Copy of full report may be obtained from the Underwriters' Laboratories, the National Fire Protection Association, 70 William St., New York City, or the Bureau of Standards, Washington, D. C.
COLUMNS ON BASISOF FIRETESTS
RATING No. FIREPROOFING Hrs . 1 Limestone or calcareous aggregate with 2-in. covering over reinforcing steel 8 Embedded in limestone or calcareous gravel concrete with a minimum cover of 4 in. on wire mesh 8 3 Same as No. 2 but minimum covering 3 in. 0 Same as No. 2 but minimum covering 2 in. 4 Trap-rock aggregate with 2 in. covering over reinforcing steel 5 Embedded in trap-rock concrete with a minimum covering of 4 in. on wire mesh 5 Same as No. 6 but with minimum covering of 3 in. 4 Same as No. 6 but with minimum covering of 2 in. 3 9 Protected by common brick on side 5 10 Same as No. 9 but with common brick on side and end 1 '11 Embedded in granite sandstone or hard-coal cinder corkrete with &inimum cover of 4 in. on wire mesh 5 12 Same as iVo. 11 but with minimum cover of 3 in. 31/a Same as No. 11 but with minimum cover of 2 in. 2l/z Protected by solid gypsum block 4 in. thick 31/2 Same as No. 14 b u t 3 in. thick 21/2 Same as No. 14 but 2 in. thick 11/2 Partly protected having both the interior of t h e column and the exteior reentrant spaces filled with concrete 2 to 31/2 Embedded in siliceous gravel concrete with a minimum cover of 4 in. over wire mesh 21/a Same as No. 18 but with 2 in. cover 1 Protected b y hollow tile and concrete filling 2 t o 21/2 Protected by portland-cement plaster (10 per cent hydrated lime) on ribbed metal lath 2 Filled and protected by 2-in. thickness of trap rock, granite, or hardcoal cinder concrete or hollow tile and porous semi-fire clay 2 Protected with two layers of portland-cement laster (10 per cent h drated lime? on metal lath each in. thick 1'/n Same as No. 23 b u t with 1 in. layer of plaster a/, Solid section protected by hollow tile 1 to 11/2 Partly protected having exterior reentrant spaces filled with concrete 1/a t o S / r
i2
Structural steel
By A. C. Irwin and Fred W. Ashton
HE USE of concrete in facilities a t chemical-manufacturing plants may be divided into the following general headings-buildings proper, and tanks, containers, etc. BUILDINGS The methods of design of ordinary concrete buildings are matters of more or less common knowledge to structural engineers and a discussion of them would be out of place here. There are, however, some qualities which seem to pertain with especial importance to buildings used for chemical-manufacturing purposes. Among these may be mentioned fireproofness, inherent sanitary qualities, and resistance to wear or attack from chemicals. Floors should be able to resist wear from foot and truck traffic, be easy to clean, and not be disintegrated by chemicals which may come into contact with them. A well-made and cured concrete floor1 will leave little to be desired in its ability to resist wear and the ease with which it may be cleaned, but the question of the action of chemicals on it may need separate attention. I n selecting a floor for a chemical-manufacturing plant, the particular use to which the floor will be subjected should be considered. If the floor is continually wet or alternately wet and dry, material should be chosen which will not be affected by these conditions. Strength needed to carry heavy vats, furnaces, etc., and spans required to give unobstructed space may be decisive as to the type of structure. Ease of cleaning may be of great importance, and certain chemical processes may require special covering or treatment. Reinforced concrete girder spans of over 125 f t . have been used in buildings. Floor loads as high as 2000 lbs. per sq. ft. have been carried by concrete floors. If special floor coverings are necessary, concrete is admirably adapted to form a proper base or surface bond for covering or treatment. The best evidence of the fire-resistive qualities of various building materials or combinations of them was obtained in the extensive fire tests on building columns conducted at the Underwriters' Laboratories, Chicago.
OF
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Round cast iron
4
75
Structural steel
Table I gives some rating periods assigned to the materials and 'combinations of materials involved in the tests. It will be seen that the columns having the highest rating consist of reinforced concrete columns with 2-in. covering over the steel reinforcement and structural steel columns with 4-in. covering of concrete over the steel. It is also worthy of note that the aggregate used in making the concrete has a decided effect on its fire-resistive ability. Thus, quartz aggregate has a tendency to spa11 off and expose fresh concrete or the reinforcement to the heat. Limestone or calcareous aggregate, on the other hand, calcines on the surface exposed to the heat, but the process of calcination is retarded or wholly inhibited by the protection to the underlying concrete afforded by the surface calcination. This protective coating has a counterpart in the case of many chemicals in contact with concrete. Certain acids form chemical compounds with the cement, which act as protective coatings and inhibit or greatly decrease further chemical action.
CONTAINERS AND TANKS I n general, the hydration of cement results in a number of compounds, among which are hydrated tricalcium aluminate, calcium hydroxide in hexagonal crystals, and noncrystalline (amorphous) hydrated calcium silicate. There are also formed other compounds of magnesia, iron, and alkalies. On contact with air a skin coat of calcium carbonate is formed on the surface of concrete through the action of carbon dioxide on the calcium hydroxide. With these compounds the chem-
June, 1922;
563
ordinary practicing architect or engineer in trying to decide which to use, providing he has been convinced by the arguments of the proponents of these compounds that he cannot get along without them. It is not the purpose of this paper to deny the possibility of virtue in some of these compounds. The arguments advanced to explain their beneficial effect seem reasonable, but those who purchase these materials are deserving of more than theoretical speculation as a justification for investment in them. Nor is the practical experience had with these compounds wholly convincing. The proponents of them, almost without exception, are very careful to specify good workmanship in the manufacture of the concrete itself. Is it, then, illogical to attribute the success achieved to proper handling of the concrete instead of to the inclusion of some foreign substances? Tests are needed-conclusive tests so conducted that each factor influencing the result is carefully segregated so that a proper weight may be assigned to each before accepting the theories of and successful field experience with integral waterproofing compounds. Imperviousness to the passage of ordinary liquids can be obtained by proper attention to the manufacture of concrete. The admixtures so far developed and used may be divided into two general classes-viz., powders, such as hydrated lime, clays, silicates, feldspars, etc., usually mixed with the TABLE 11-C HEMICALS AND INDUSTRIAL LIQUIDSTHATHAVEBEENSTORED dry cement; and liquids and pastes, such as insoluble stearate IN CONCRETE TANKS of lime, sodium and potassium oleate in the form of soluble TREATMENT OF CONTAINER MATERIALc 3NTAINED soap, aluminium stearate, calcium chloride, and oil compounds. Crude oil ) N o treatment in many cases Sodium sihcate, These are usually added to the mixing water. neat cement wash, cement mortar coat, smudgLight oil ing oil, oil-proofing enamel, special varnish and Petroleum 011 PowDmS--Most of the powders are inert, and are supproprietary surface coatings, gunite lining Road oil Menhaden 011 posed to act as void fillers, thus increasing the imperviousLinseed oil No treatment Rosin.oil ness of the concrete. If, however, the admixture is merely Sulfite liquor and cider Surface coating of 1 part gilsonite 2 . 6 parts turpenan inert material, it is reasonable to suppose that by replacing tine, and 5 parts neutral petrofeum oil by weight vinegar Surface coating of gelatin and glycerol applied hot Benzine an equal quantity of cement with inert material the strength Salt brine No treatment Molasses Mostly untreated. Some given inside coating of of the product is reduced. Where a combined mechanical coal-tar pitch, portland cement, and kerosene and chemical action is to be resisted, as when the chemical Coconut oil Bakelite varnish Glycerol Bakelite varnish permeates the concrete and crystallizes into larger volume, Cottonseed oil No treatment Soy-bean oil any decrease in strength is undesirable. Inert material canSodium silicate Fish oil not be held in the pores except through the confining action Peanut oil Ammonia (solution) Coated with tar on inside of the hardened cement, and a t the surface a t least the finely N o treatment Bisulfite of lime No treatment if in dry state Chloride of lime powdered inerts may contribute to weakness where strength Calcium chloride No treatment Electrolyt,e Depends on liquid. Asphalt coating given t o is needed to resist mechanical action. The addition of cetanks used in electrolytic refining of lead and ment instead of these inerts, or, better still, attention to gradzinc Hydrochloric acid Acid-proof lining ing of aggregates throughout the mass, thorough mixing, Silicate of soda No treatment Fire-brick or acid-proof lining, vitrified tile laid in and the use of just enough water to permit thorough compactSulfuric acid ’ litharge and glycerol ing in the forms will result in dense concrete of great strength, Wood pulp No treatment Stock chests and a t the same time afford a suitable bonding surface for Zinc chloride protective coatings if these are required by the nature of Hemlock liquors Leaching-bark solution Brush-coat neat cement or plasteredzcoat cement the contained chemical. Tanning liquors mortar Quebracho extract Some tests recently completed a t the Structural Materials Coats of neat cement grout Buttermilk Coated with cement mortar Log boiling Research Laboratory, a t Lewis Institute, Chicago, on two Slime settling No treatment well-known admixtures to concrete produced a decrease of No special treatment Gas purifying boxes Caustic soda h-o treatment from 40 to 60 per cent of the strength of normal concrete Corn sirup Acid-proof lining Glucose made of exactly the same materials and consistency, and cured under identical conditions. I n these particular tests PROTECTION AGAINST CHENICAL ACTION no attempt was made t o determine the relative imperviousMethods of protecting concrete against chemical action ness of the treated and untreated samples, but such marked may be divided into two general classes-viz., admixtures reduction in the strength of the concrete is too big a price to to the concrete t,hrough the cement or water or both; and pay for such additional imperviousness as may be obtained by surface coatings-either as a coating only or as a combined using these materials, unless the strength quality of concrete coating and surface-void filler. is unimportant. Moreover, while not a rule of universal and unvarying accuracy, it has been demonstrated that, in ADMIXTURES general, the properties of concrete, such as imperviousness, The question of the value of integral waterproofing com- wear resistance, resistance to acids and alkalies, etc., increase pounds in concrete is a very persistent one. The number of or decrease with the strength of the concrete. Integral these compounds is already so great as to bewilder the compounds, if used a t all, should be selected with a knowledge of the probable chemical reactions involved. With a view t o a See “Concrete Tanks for Industrial Purposes,” Portland Cement Assoassisting those who may bear the responsibility of deciding ciation.
ist may begin to speculate as to what takes place when some other cliernical compound is brought into contact with the concrete. He has also to consider the nature of the aggregate used with the cement in making the concrete. Nor is this all--he is also confronted with the question of the effect on the chemical reactions of variations in the degree of perfection in the proportioning, mixing, placing, and curing of the concrete. Observed differences in the action of chemicals on concrete unquestionably point to the influence of method of concrete manufacture. Imperviousness of .the surface concrete, perfection of the hydrating processes, percentage of the exposed surfacemade up of aggregate, are all factors which affect the *ate of chemical action. It does not always follow that a given chemical reaction involving the compounds in the cement will be harmful-it may be actually beneficial. Thus, if the contained material forms a protective coating, or produces an increase in surface imperviousness, chemical action may cease and the resistance of the concrete to action of other cl-emicals may be greatly increased. While no hard and fast law can bestatpd as to the chemicals which do not injure well-made concrete, it is fairly well established that the chlorides may be regarded as harmless, and some 3f the silicates as beneficial. A partial list of substances for which concrete tanks have been used is gil-en in Table IIS3
1
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 15, KO. 6
just what, if any, admixture to use, a brief outline of the principal ingredients and the action of some of them is presented here. Quicklime was formerly used with concrete as a densifier, but has been discarded. The use of patented compounds, such as insoluble stearates and resinates, was followed by hydrated lime. Most of the secret and patented powders are sold on the basis of their “water-repellent” quality. This property is obtained by adding to the powder some metallic stearate, such as lime soap, which is supposed to a c t as a distributor of the water repellent and as a void filler. Many proprietary compounds are composed mainly of finely ground sand or clay, with or without the addition of hydrated lime or insoluble soaps. The constituents of some of the powdered admixtures to cement are given in Table 111.
drated lime as an inert void filler. The stearates of soda and potash (ordinary soap) are readily soluble in water, but when in solution in the presence of cement, less soluble lime soaps are formed and precipitated. When used as a surface coating, it is doubtful whether sufficient lime soap is formed and precipitated to act as a protective coating before the soluble soaps are dissolved and washed off. Experience indicates that, in general, surface coatings of soap solutions do not produce lasting results. Several proprietary cements used as waterproofers have been analyzed by the Bureau of Standards with the results shown in Table V.
TABLEIII-/iN.4LYSI% O F I N E R T FILLERS4 (Clays, sands, feldspar, and hydrated lime) N . Y. Mo. Clav Clav Feldspar Sand 58,iO 72.91 64.02 89,50 Silica 2.36 16,85 15.01 19.38 Alumina 2.58 6.41 2.79 0.70 Ferric oxide 0 . 0 3 Trace 0 .12 0 . 0 6 Mancanese oxide 1.37 4.22 0.59 0.87 Lime 0.57 2.92 0.85 0.33 Magnesia 0.21 0.12 0.12 0.10 Sulfuric anhydride (503) 0.26 2.52 0.72 0.80 Sodium oxide 0.70 11.76 2.71 2.12 Potassium oxide 0.06 0.60 0.20 1.12 Water (105’ C.) 2.35 7.00 3.81 0.54 Ignition loss 99.96 100.28 100.22 100.15 TOTAL
Silica. . . . . . . . . . . . . . . . . . . . Alumina. . . . . . . . . . . . . . . . . Iron oxide., . . . . . . . . . . . . . . Lime. .................... Magnesia, . . . . . . . . . . . . . . . . Sulfuric anhydride (SOs) , . . Sodium oxide.. . . . . . . . . . . . Potassium oxide. . . . . . . . . . . Ignition loss, . . . . . . . . . . . . .
........
7
7
-
HYdrated lime 1.34 0.45 0.13
.....
46.90 32.19 4.02 15.05
..... ..... .....
100.08
The hydrated lime may be partly carbonated, especially on the surface; the i‘eldspar may decompose by the leaching out of the alkalies; the sand will change but very little, if composed of a high-grade quartz sand; the clay will be very inert, although some theories have been brought forward which.assume a very important role for clay when mixed with concrete. This is to the effect that the colloids of the clay protect the calcium compounds from quick hydration, and consequently prevent increase in volume due to chemical action.
The following analysis of a chemically active filler is fairly typical of its class: TABLE ?Vd Silica Alumina Iron oxide Lime Magnesia Sulfuric anhydride (503) Soda Potassium oxide Ignition loss (organic matter)
................
TOTAL....
Per cent 46.66 16.71 0.93 11.97 0.72 2.73 0.34 1.44 18.64 100.14
This compound was a white powder with a strong aromatic It was, in fact, partly a resinate of potash, which would be decomposed by the lime present to the corresponding lime resinate, which is comparatively insoluble. The greater part of the compound is entirely inert, being china clay and hydrated lime.
‘ odor of kauri resin.
Some proprietary cements are mixtures of portland cement and stearates of lime, or soda and potash with sand and other materials, treated to produce a water-repellent cement, Again, some waterproof cements are made by mixing about 5 per cent (by weight) of a lime-oil compound in clinker form, with portland cement clinker. Fish oil, boiled with hydrochloric acidpnd mixed with burnt lime while slaking, is also used. The resulting product is a paste which hardens as clinker. Another compound in the ’form of mortar consists of 1 part by weight of copal gum, 1 part hydrated lime and fine clay, and 1 part portland cement. The lime-oil cement compounds depend for their impervious tendencies upon the formation of insoluble stearates of lime in the mass and surface of the concrete which act as barricades, and on hy4
Bur. Standards, Tech. Paper 8 .
TABLE V-ANALYSES OF PROPR€ETARYCEMENTS USED
TOTAL .................
Carbon dioxide.. . . . . . . . . . . Organic (fatty acid) b . Water. . . . . . . . . . . . . . . . . . .
..... TOTAL. ................
Compound Used zs Direct Cement Per cent 23.75 5.96 1.97 64.44 0.91 1.21 0.11 0.73 1.07 100.15 0.52 0.10 0.45
FOR
WATI$RPROOFINGb
Compound Used as Coating‘ (Cement Content) Per cent 22.40 7.98 3.63 59.34 1.85 1.15
.... .... ....
2.16 0.32 0.93 99.76
a This compound consists of portland cement (27.73 per cent) a n d sand (72.27 per cent). The sand (all passing one-eighth sieve) is mixed with t h e cement, and is composed of quartzite and dolomite, with a trace of f a t t y acids. b The organic material is fatty acids with a melting point of 52’ F., and present as a lime soap.
INTEGRAL LIQUIDSAND PASTES-The liquids are mainly composed of metallic salts, such as chloride of lime; they also consist of oil emulsions and soap solutions, and solutions of paraffin in benzipe or benzene. The paraffin solutions are applied to masonry surfaces. The waterproofing properties of these liquids depend upon the formation of gelatinous coatings around the smallest particles of the constituents of the masonry. The following discussion of integral liquids and pastes is taken largely from ‘Waterproofing Engineering,” by Ross :
Of course, this would tend to decrease the strength of the concrete, and often does. There is also a coal-tar product used as an integral waterproofing, from which the volatile oils have been almost entirely removed, and the remaining materials tend to bind together the particles of cement and fill the voids in the concrete. Some other compounds are composed of fish oil and water glass (sodium silicate). The fish oil, which is semidrying, is slowly saponified by the lime of the cement, and the water glass forms a lime silicate, both actions, however, being incomplete, due to the insufficiency of lime present in the cement for such action. Analyses of a fish-oil compound and one of calcium chloride follow: FISHOIL Soap Oil., . . . . . . . . . . . . Ash water glass.. Volatile (water).
............
...
Per cent 1.05 47.29 11.64 40.02
CALCIUM CHLORIDE Per cent Silica ....................... Trace 0.25 Alumina and iron oxide.. Calcium chloride.. 27.19 Magnesium.. ................ 0.04 Water (and iron resinate, 15 per cent) ...................... 72.52
...... ............
Most pastes are soluble mixtures of secret ingredients which depend for their waterproofing qualities upon precipitation of insoluble materials in the voids of the concrete. Sometimes pastes are made by mixing a powder, such as alum, to the cement, and a soap solution to the tempering water. In making the concrete this paste is added, and the two constituents combine to form a stearate of aluminium, which is a stable, water-insoluble, void-filling compound. Before specifying integral pastes or any integral compounds, it is advisable first to investigate the results accomplished on previous work. Analyses should be made by a qualified
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chemist to determine the effect on the strength of the concrete, waterproofing properties when subjected to extreme ranges of temperature, effect of common acids and alkalies on them, and effect on steel reinforcement-i. e., if productive or preventive of corrosion, etc. SURFACE COATJXGS Concrete tanks and containers for liquid chemicals that mill attack well-made concrete can be protected with greater certainty of success by the use of impregnative and surface coatings or by membranes than by the use of integral compounds designed to change the action of the liquid on the concrete. The absorptive property of concrete, held in common with practically all nonrusting materials used for the construction of tanks, renders it well adapted to forming a bond with surface coatings. Some of these coatings have already been mentioned, but there are scores of patented arid secret compounds of paraffin, tar, elaterite, gilsonite and asphalts, mixtures of alkalies with soap and alum, paints containing suet, asphalts dissolved i n naphtha or benzine or mixed with oil and other hydrocarbons, oil-tar pitch, graphite, and several cold-water paints which have portland cement as an ingredient. There are so-called, but not true, enamels, consisting of linseed oil and rosin, solutions of Bakelite. etc. There are the iron oxide coatings consisting of pulverized iron mixed with an active oxidizing agent such as sal-ammoniac. The silicates and fluosilicates are used both as integral compounds and as surface coatings or “hardeners.” Combinations of portland cement with stearates, calcium chloride, and hydrated lime, combinations of oils partially “rubberized” and dissolved in a mixture of volatile hydrocarbons and turpentine distillates are all used. Lime has been used with cement both as quicklime and in its hydrated condition. At present hydrated lime is used exclusively, either alone or in combination with other materials. The theory of its beneficial effect is based on the voidfilling property of fine inert powders and a lubrication of the particles of the mass facilitating compacting of the concrete. Tests6 indicate a reduction in strength of concrete due to addition of hydrated lime and the presence of excess lime in concrete used in connection with chemical processes may be highly objectionable. High-magnesium or high-calcium lime is used practically without distinction for waterproofing purposes. Casein mixtures with quicklime, borax, or strong solutions of sodium silicate are also used, Their beneficial effects are supposed to result from insoluble precipitates filling the pores of the concrete. They are used both in surface coatings and integrally. Caustic potash is used with alum as a surface coating, and with various bhemicals in secret waterproofing compounds. The Sylvester process, in which soap and alum are used as a surface coating, consists in the application of a hot solution of about 3/.1 lb. of castile soap in 1 gal. of water to a dry, clean masonry surface, followed one day later by a coating of ‘/p lb. of common alum dissolved in 4 gal. of lukewarm water. Both coatings are applied with a flat, brush and repeated alternately, if necessary. The theory of the beneficial action of the soap and alum treatment is the formation of an insoluble stearate of aluminium in the pores of the concrete. A more concentrated treatment of green concrete is the applicalion of a solution of about lb. of concentrated lye and 2 l / 2 lbs. of alum in 1 gal. of water. Soap and alum are also used as an integral waterproofing compound in the pro5 “Effect of Hydrated Lime and Other Powdered Admixtures in Concrete,” Structural Materials Research Laboratory, Bull. 8.
565
portion of 1 part of aluminium sulfate to 3 parts soap by weight. Aluminium soaps are used in many proprietary integral-waterproofing compounds as void fillers and water repellents. Powdered iron in combination with sulfur, sal-ammoniac, and even with cement is sold under a number of trade names for both integral mixtures and surface coatings. The theory of the beneficial effect of powdered iron is based on the increase in volume occurring on oxidation of the iron, thus filling the pores and forming barricades to the passage of liquids. Resin, or rosin, in combination with various gums is used in a great number of surface-coating compounds. The resin is dissolved in ether, alcohol, or a solvent oil, and used as surface filler. The elastic properties are supposed to be given to the coating by the inclusion of gums in the compound with a suitable solvent such as benzine or benzene. Calcium compounds, as calcium sulfate or calcium carbonate, combined with cement and aluminium compounds are used in many secret “waterproofers.” Stearin and its derivatives in the form of stearic acid, stearate, and stearin pitch are included in a multitude of commercially exploited surface-coating and integral compounds. The integral compounds usually employ ammonia or lime. Ammonium. stearate, formed by adding stearic acid to excess of dilute ammonium hydroxide, in the presence of cement forms an insoluble lime or aluminium stearate which is water-repellent. Stearate and asphalt are used as a joint-filling compound, and chemically treated suet as an integral waterproofer for mass concrete. The hydrocarbons and derivatives are so numerous and the method of their use so well known that they need not be discussed here. Specifications for tests and use of various asphaltic and coal-tar coatings have been published by the Bureau of Standards. Asphalts, such as elaterite combined with petroleum oils, linseed oil, gilsonite, and even castor oil, have been given trade names, such as “mineral rubber,” and sold as surface coatings. A simple and yet very effective waterproofing surface coating consists of paraffin dissolved in a suitable volatile: solvent. The solvent carries the paraffin into the concrete, where it remains as a complete seal against the passage of moisture. Paraffin is also applied to a concrete surface by melting it and heating the surface to which the paraffin is applied. By skilful use of a blow torch the paraffin may be caused to penetrate some distance into the concrete.
COKCLUSION I n closing this paper the authors desire to emphasize the importance of following implicitly those methods and practices in the manufacture of concrete which have been found in both laboratory and field to result in a product of the highest quality. Integral compounds, surface hardeners, and surface coatings will not in general compensate for careless manipulation of materials. I n any investigation, therefore, having for its object the protection of concrete from the action of a chemical which will be in contact with it, the first step should be the preparation of experimental samples of concrete to determine whether or not the particular substance in question will really be detrimental to concrete of the highest quality. If the result of this investigation indicates the need of protection, the most promising procedure will be to study the efficacy of surface coatings for the purpose in hand, rather than the inclusion of compounds in the body of the,conCrete. With a knowledge of the substances in contact with the concrete the problem for the chemist will then be to find some surface coating which will be unaffected by the substance.
