The Butler Manufacturing Company, Kansas City, made the following quotations as of July 1, 1920, for storage tanks, f. o. b. Kansas City : It is only recently that concrete has been considered a suit able material for making containers for fuel oil. The knowledge of the desirability of concrete for oil storage tanks was acquired during the war through the practical elimination of steel plates.
Mr. H. P. Andrews, in a paper read before the American Concrete Institute, states that reinforced concrete has proved to be satisfactory in many ways, if intelligently handled. As it is necessary to install most fuel oil reservoirs underground, steel tanks rust if not protected. Concrete can be designed better to resist exterior stresses, as hydrostatic Or earth pressures. It has the dead weight to better resist upward hydrostatic pressure in soils which often are filled with water. It does not attract light ning like steel, nor if properly constructed is it affected by elec trolysis. It is a non-conductor of heat and cold, thus retarding evaporation of oil in summer, and also retarding the lowering of the temperature of the oil in winter, an advantage in pumping. In case of a conflagration the oil is much safer in a concrete con tainer than in steel. But, as previously stated, oil reservoirs of concrete must be designed correctly, the concrete proportioned correctly and mixed and placed correctly in order to get satis factory results. And by satisfactory results it is meant that there shall be no leakage or seepage when built or, thereafter, to cause fire hazards or financial loss. When these necessities have been provided for, reinforced concrete reservoirs will contain fuel oil of a consistency up to 40° B., and practically all fuel oils are below this, the Mexican oils having a specific gravity as low as 16° B. For the lighter oils, including kerosene, gasoline or benzine, some provision should be made for a lining of special material, and the writer understands that the U. S. Shipping Board has been making some extended experiments along this line. The design and the location of a fuel oil reservoir may be considered from various standpoints. (1) Location. The reservoir should be located a safe distance from inflammable structures as far as pos sible consistent with pumping requirements, covered with at least 18 in. of earth, if near buildings, to decrease fire hazards and also to minimize oil evaporation. If distant from buildings it should be at least half underground, and if possible, the excavated ma terial be used in banking up around it. (2) Size. The reservoir should be limited in size for two reasons: First, the necessity of a day's working limit in the operation of pouring concrete so that joints between operations may be eliminated ; and secondly, so that of an accident or fire in any reservoir, that too much oil in storage will not be involved. This size limit should not be over 300,000 gallons under most conditions, and the majority of contractors have not the facilities to construct properly a reservoir of this capacity. (3) Shape. The reservoir should be circular in shape, the better and more directly to take care of involved stresses and to avert danger of tensile or temperature cracks. (4) It should be so proportioned and designed as to limit the number of pouring operations of concrete, so as to avoid joints between these operations. (5) Care should be taken to provide for all exterior stresses, such as hydrostatic pressure from ground water, earth pressure on walls, and roof if reservoir is buried, and also to avoid as far as possible concentration of loads on walls or footings. Where joints are absolutely necessary they should be so protected that there will be no leakage through them. Regarding hydrostatic pressure, while engineers have found from tests that this pressure in soils is only about 50 per cent of the full head of water, it is not safe to design for stresses less than the full head, as any deflection in the concrete admitting a film of water between the earth and the concrete will produce the full hydrostatic pressure. (6) To so design the reservoir, piping and vents as to comply with municipal regulations and insurance requirements. (7) To
protect temporarily or permanently concrete surfaces so that oil will not come in immediate contact with them if concrete is less than six weeks old. (8) To so design the false work for holding concrete temporarily in place that it will not fail or be distorted while placing concrete. It is especially necessary to provide for the firm holding of wall forms, as the pressure of several feet of concrete poured quickly as a monolith is intense, and any give of the forms after the concrete has obtained its initial set breaks up the crystals already formed, allows expansion of the concrete mass, with resultant porosity and loss of strength. (9) To design the concrete so that it will resist all exterior stresses to which it is subjected and so that it will be oil-proof. And one of the principal features of this design is to make the walls of circular reservoirs in tension, sufficiently thick so that the ultimate strength of the concrete in tension will not be ex ceeded. It is not meant, of course, to leave out the steel rein forcement so that the stress will theoretically be borne by the concrete, but, nevertheless it will actually be borne by it unless some unforeseen weakening of the concrete should throw it upon the steel. An extended investigation by the writer on high circular concrete standpipes for water showed that if the concrete in the wall was stressed beyond its elastic limit or ultimate strength, which is practically identical, vertical hair cracks will appear of sufficient width to admit water into the body of the concrete. This ultimate tensile strength in a 1 :3 concrete from tests made for the writer at the Watertown Arsenal was 203 lbs. per square inch. Where the concrete is in large sectional areas and reinforced,. this tensile strength probably will be some what higher. If a stress not exceeding 150 lbs. per square inch is allowed in tension there will be no danger of these vertical cracks appearing. (10) To design the reinforcement so that it will take care of all interior and exterior stresses and with fittings to hold it rigidly in place while concrete is being poured. Steel in tension in walls should not be stressed over 10,000 lbs. per square inch to conform with insurance companies' requirements. Personally, the writer does not think that it is necessary to figure the stress as low as this, under usual conditions, having satis factorily constructed many reservoirs using a stress of 14,000 pounds, but of course, the lower stress is an additional safeguard against inferior workmanship by inexperienced contractors and against any decrease in bond strength due to oil penetration of concrete. It is probably unwise to depart radically from in surance companies' recommendations. For other parts of the reservoir the recommendations of the Joint Committee on Con crete, Plain and Reinforced, should be followed. All reinforcing rods in concrete exposed to oil should be of a deformed section for better bending value. To carry out these requirements neces sitates the employment of competent engineers, experienced in the work, to make the design and specifications and to superintend construction. The concrete should be no leaner than a mix com posed of 1 part of cement, PA parts of sand and 3 parts broken stcne or gravel. To this mix should be added a "densifier." Hy drated lime has been found econcmical and satisfactory for this purpose, using ten lbs. of dry lime to each bag of cement. The stone must be hard and clean, trap rock, granite or gravel being the best material. The sand must be free from any deleterious matter ; and should be well graded. Cement should be of an established quality. The concrete should be deposited contin uously in concentric layers not over 12 ins. deep in any one place. No break in time of over thirty minutes is permissible in de positing concrete during any one operation, and if. any delay occurs, the previous surface must be chopped up thoroughly with spades before the next layer of concrete is deposited.