The different operations in pouring are: 1. The pouring of floor and footings.
2. The pouring of entire wall.
3. The pouring of roof.
In small reservoirs the •wall forms may be supported so that the footings, floor and wall may be poured in one continuous operation. An approved joint or dam must be made between the floor and the wall. When the materials are obtained they should be mixed by a plant of sufficient size and power to carry out each separate pre-arranged operation without danger of delay during the process. The materials should be mixed at least 2 minutes in the mixer, using just enough water to obtain a plastic mix without excess water coming to the surface after concrete is deposited, and a measuring tank should be used so that the amount of water may he kept uniform. The concrete when de posited in forms should be well spaded by at least four competent laborers who are not afraid to use their muscle in compacting the concrete thoroughly and working out the trapped air bubbles. Reinforcement should be of round deformed bars conforming to "Manufacturer's Standard Specifications for Medium Steel." These bars should be bent or curved true to templates carefully placed in their predesigned location and rigidly maintained there by mechanical means. No laps should be less than 40 diameters and no two laps of adjacent rods should be directly opposite each other. The forms should be of a good material, strongly made and braced, or held in place by circumferential bands so that no distortion, allowing displacement of concrete during its initial set, is possible. The surface of the floor should be trowelled smooth as soon as it can be done properly. If all previously named precautions are taken, there should be no -defects in the wall to correct. Concrete mixed 'and' placed as recommended herein is practically oil-tight, but as oils are somewhat detrimental to fresh concrete, it is advisable to put on an interior wash or coating to protect the fresh concrete from the action of the oil for such a time as may be necessary for it to cure and harden sufficiently. Silicate of soda, while not a permanent coating, has been used satisfactorily for this purpose according to this speci fication for oil-proofing. The surface of the floor and the interior surface of the wall are to be coated with silicate of soda of a consistency of 40° B when applied as follows: First coat. One part of silicate of soda and three parts of water, applied with brush and all excess liquid wiped off with cloth before drying. Second coat. One part silicate of soda and two parts water applied as above. Third coat. One part of silicate of soda and one part water, applied with brush and allowed to dry. Fourth coat. Applied same as third. The dome roof is economical to construct where earth covering is not required and where all concentrated loads on walls are eliminated, which might. tend to prodUce unequal settlement with resultant cracks. The inverted dome at the bottom gives additional storage capacity with only increased cost of excavation and lessens height of wall thus re quiring less shoring of banks in loose soils. It allows a better drainage of the reservoir than a flat floor, and better resists up ward exterior pressure. The recommended maximum dimensions for this type of reservoir are as follows: Diameter, 60 feet ; height of wall, 12 feet, rise of roof dome, 1/6th to %th dia ; drop of inverted dome not over 1/10th dia. The floor and roof should be reinforced both circumferentially and radially to vide against temperature and other stresses. There are many details which might be added, but the information given is in tended to cover the principal feattires." Fig. 27 shows a typical reinforced concrete fuel oil reservoir.
The Portland Cement Association in its Bulletin "Concrete Tanks for Industrial Purposes" is authority for the statement that at present there is in the United States concrete tank storage for over 790,000,000 gallons Of oil. Concrete tanks for oil storage are not an experiment, but their use for such purposes has rapidly developed during the past three years because of unusual con ditions during the war. There are examples of concrete oil tanks that have 15 years of service to their credit, thus proving their success in this field. The economy and advantages of the concrete oil tank have established it as a standard 'type of oil storage container, particularly as relates to the needs of industrial plants using fuel oil. Although such tanks can be built above ground, the greatest advantages are derived from placing them underground and covering with two or three feet of earth. Under such conditions the stored oil is maintained at a fairly even temperature, losses from evaporation of the lighter oils are re duced, and greater protection to tank contents is afforded against fire fttom lightning or other causes ; therefore, the insurance on surrounding buildings is not increased because of the presence of stored oil. Insurance on contents of the tank is also less. In addition, there is the advantage that the storage container does not occupy valuable yard space necessary for plant operation or other storage, and the tank may be placed at any convenient loca tion, even under a railroad sidetrack or plant driveway. So far as it has been possible to collect data, the following list, correct to August 1, 1919, shows industrial concerns in the United States and Canada using from 1 to 11 concrete oil storage tanks or reservoirs and the capacity of the storage listed : The France .8z Canada Oil Transport Co., Aransas Pass, Tex., has two 55,000-bbl. cylindrical oil storage tanks of rein forced concrete, 110 ft. inside diameter and 33 ft. deep, which areprobably the first concrete oil tanks of such large size to be built entirely above ground. While in many locations economy would be secured by building the tanks wholly or partly below ground, thus getting the advantage of added insulation as well as the outside earth pressure, these tanks were located on sand foundation not more than 1 ft. above water level and construction above ground was necessary. The nature of the location re quired that the tanks be supported by piling, which would have been equally necessary for steel tanks. Each tank is supported on some 600 piles cut off at water level and capped by a heavy reinforced concrete slab covering the entire area. The walls were built with sliding forms. Because of the intense summer heat in that section of the country and the desire for absolute insurance against temperature cracking, it was decided to make the walls double by constructing an outer shell separated from the main wall by a 5-in, air space. This decision was reached
because no former experience was available as a guide for de signing an entirely above ground oil tank of this size. As the result of experience with these tanks, however, the engineers are inclined to believe that the outer wall could be omitted with safety. The tanks were treated on the inside with an oilproof coating, for while they are built to hold a low gravity oil, it was felt that they might be used for very light oils at some future date and it would be wise to provide for this possibility. The tank roof supported by concrete beams and columns is a concrete slab covered with 1 ft. of sand. A gas-tight expansion joint is provided where roof joins the walls. Each tank was surrounded with an earthen dike to conform with insurance requirements and equipped with the usual filling and discharge lines, swing pip.: and other fittings. During the severe Gulf hurricane of Sept. 14, 1919, the tanks were partly filled with.oil, each containing about 30,000 bbls. The engineer who designed and built them stays : "The water rose some 15 ft. accompanied by a 98-mile wind. The storm was Ihe 'most severe ever experienced on the Texas coast, which means much. Our tanks were absolutely unprotected from the full fury of the hurricane. Apparently heavy timbers or possibly parts of the pipe lines were driven against the east tank, and slight damage to the outer wall in one place resulted. So severe was the storm that all of the surrounding sand was washed away, and at places near and even under the tanks, there is now from 10 to 18 ft. of water (See fig. 28). The pipe lines were demolished, valves broken off of the tanks, and the oil was lost but the concrete tanks remained intact. Had these tanks been of any material but concrete they would have been de stroyed." Mr. James B. Brooks,a General Superintendent of Buildings and Construction, for the —Westinghouse Air Brake Company, refers to the company's fuel oil tanks at Wilmerding, Pennsyl vania as follows: "During September, 1917, the Westinghouse Air Brake Co. constructed four concrete fuel oil tanks at Wil merding, Pa., and during July, 1918, it constructed six more. The tanks were 15 ft. wide, 25 ft. long and 9 ft. deep with a capacity of 25,000 gals, each, or a total capacity amounting to 250,000 gals. The company has similar concrete tanks at Swiss vale, Pa., with 300,000 gals. capacity, built like those at Wil merding. The concrete in the tanks was made from one part cement, two parts sand and four parts pea gravel. The following method of construction was adopted. Excavating was done by crane and grab bucket and after squaring up the bottom, the reinforcing bars were placed for the floor slab, with ends of bars bent up 90 deg. so as to enter the wall. These rods were wired together and held in place by being suspended from 2 by 8-in. timbers placed several inches above the floor level. The entire floor slab for one tank was then poured, well tamped and finished rough. No. 16-gage galvanized iron strip, 6 in. wide, riveted and soldered at, joints so as to make a continuous band, was then imbedded in the floor slab to a depth of 3 in. and placed so as to be on the center line of wall and projecting into it 3 in. The outside wall forms were then set up after which the reinforcing rods were placed, wired together and fastened to the form. In the meantime the forms and timbers for suspending rods for floor slab No. 1 were being set up and used for floor slab No. 2, the joint between the slabs being filled with pitch. The inside forms for wall, beams, and top slab were then set up and rein forcing rods placed for beams and top slab. Extreme care was taken in cleaning the slab at bottom of wall form, and, before pouring walls, a mixture of one part cement and one part sand was placed in bottom of form and around galvanized strip so as to make a tight joint. The side walls, beams, top slab and man hole are all cast in one piece, the only joint in the concrete being between the floor and bottom of wall. The inlet- pipe cast into the top slab near the manhole is a 4-in. nipple and the outlet pipe is a 2% in. brass pipe threaded its entire length, offering a rough surface for concrete to adhere to. The forms were re moved in 3 or 4 days and the entire inside of tank was given a coat of plaster Y2-in. thick, made up of one part cement and one part sand, troweled to a very smooth surface. The tanks are placed in a double row with a 3-ft. covered passageway between them, with manholes and ladders giving access to pipe and valves leading from tanks. Owing to the possibility of a slight weaken ing of the concrete due to the action of the oil, the tanks are heavily constructed and reinforced. Allowance was made for a weakening of 10 or 15 per cent. The top of tank is designed for a uniform loading of 400 lbs. per sq. ft., thus allowing this space to be used for the storing of miscellaneous material. The tops of tanks are 18 in. below yard grade and are covered with cinder so as to keep down excessive change in temperature. The tanks are filled from tank cars by gravity and piped so that oil can be directed to all or any one tank. They have given perfect satisfaction to date after continuous service and show no signs of seepage or cracks. Not even discoloration caused by oil pene tration shows on the outside. It is the writer's opinion that it is unnecessary to use waterproofing material in the construction of concrete tanks where it is intended to store heavy fuel oil. The oil penetrates to a depth of 2 or 3 in., fills the pores and stops further penetration ; therefore, the walls should be at least 8 in. thick to allow for this pore filling process whereas a 3 or 4-in. wall may possibly show seepage. Owing to the fact that the light oils, such as gasoline and benzine, are very penetrative and have little or none of the sealing qualities found in the heavy fuel oil, it would be necessary that a water-proofing compound in a paste form mixed with the water for mixing concrete should be used, and the interior of tank should have a coat of plaster made up of one part cement and one part sand mixed with a first-class waterproofing compound upon which may be placed a solution of silica of soda, applied with a brush." The fire hazard created by storage of fuel has generally been over-estimated by the insurance companies and until very recently the regulations for the storage and use of fuel oil in the larger cities have been much more stringent than is necessary for pro tection against fire risk.