Concrete in Waterworks Construction
The art of concrete construction is not a new art, but dates back into ancient times. We learn that the Romans built their important structures of a concrete mixture composed of lime, sand, stone a and volcanic dust, and the evidences of their activity in this field of engineering are standing today as monuments to their engineering ability.
The modern art of cement making was not discovered, however, until 1813 and it remained a secret until 1824, when its inventor, Joseph Aspdiu, of Leeds, Knglaud. procured patents on Portland cement, socalled because of its resemblance to a ct rtain limestone quarried on the island of Portland, England. Mis process consisted of combining English chalk with river clay, drying the mixed paste and calcining at high temperatures. Many improvements in its method of manufacture have been perfected since that t itm .
Portland cement was first imported into this country in 1805 and the first Portland cement was manufactured here in 1872. During recent years the development of the American Portland cement iudttstrv has been nothing short of marvelous, and its use is now almost universal in the building arts, and this progress has been possible simply because of its merits as a building material.
Portland cement makes an ideal concrete, a a perfect artificial stone. The art of concrete construction has marie rapid advances in every branch of engineering and it is especially adapted to waterworks requirements. Concrete, when properly made, is jdnrahlc, strong, sightly and snnitarv. and its mooctate cost enables it to supplant wo d. brick. tofte and steel in many instances When used in combination with steel for reinf Teed concrete work, concrete m^ikes a perfect preservative of the steel; it prevents its destruction from corrosion, it will withstand exposure to steam, hot water, wet or dry air. seawater. sewer and furnace gases without injury to th encased metal. Reinforced concrete is tire resisting and practically earthquake proof. The steel supplying the element of tensile strength lacking in the concrete itself.
Concercte has many advantages over other types of construction: for instance, it is easily and eonvcnientlv handled and transported, often at a less cost titan stone masonry, and quite frequently the sand and gravel can he found suitable on the site of the work in hand. ith proper supervision. skilled labor is not essential in the usual concrete work, then again the science ot mixing and handling concrete has been so perfected that machines take the place of much of the manual labor incidental to this type of construction Concrete has the additional advantage over stone of being moulded more readily into intricate shapes.
To produce concrete surfaces of a satisfactory smoothness and uniformity it is necessary that the moulds he carefullv and properly built, and also that the concrete be of the proper consistency to flow readily into the prepared moulds and it is also necessarv to thoroughly churn and keep it in motion in the moulds until all air has been removed and every crevice and cavity filled with mortar; properly handled in this manner, it will not le necessary to brush or plaster the work after the removal of the forms, brushing should he used only as a last resort, as it frequently ruins an otherwise gool surface. n honest concrete needs no concealment. Concrete may he placed in moderately’ freezing weather it proper precautions are taken to warm the gravel or stone and sand, to heat the water and to cover the work until initial set takes place.
The problem of preventing ugly eracks forming in concrete is one that has worrier! many engi neers. Plain concrete is more than likely to crack where you least, expect it to. and it has liecomc the practice to provide regular intervals for these cracks toy building short sections in alternate blocks; however, it is the writer’s experience that by the judicious introduction of steel bars in concrete objectionable contraction cracks can be entirely eliminated, and the contraction cracks which do occur are so well distributed as to be either not noticeable at all or if noticeable to be so small as to be insignificant. In the works to be described later these cracks are scarcely wider than a hairsbreadth.
The waterworks engineer or superintendent is particularly interested in the subject of waterproofing concrete. It has been shown that wet concrete is more dense and, consequently, more impervious than dry concrete, and that concrete becomes more or less impervious as the quantity of cement is increased or diminished. A smoothly trowelled surface produces a watertight film or skin, which is very effective. It has also been found that slaked lime added to the concrete mixture helps to make it less permeable. The lime does not injure the cement in any way, although retarding the setting. Hot coal tar, pitch and asphalt mixtures applied on concrete are used with more or less success. A wash composed of 1 lb. of lye, 5 lb. of alum and 2 gal. of water, applied with a brush and well rubbed in, has been used successfully on government fortifications. Again a rich cement mortar plastered over concrete makes a very good waterproofing medium, if the concrete itself is not sufficiently impervious. Proper attention to these details will produce a watertight structure if there is not likely to be contraction cracks, but in works of any magnitude these are hound to occur in variable amount, depending on the exposure to extremes of temperature, and can he best provided against by the introduction of steel bars. It is the writer’s opinion that a rich concrete, properly reinforced with steel bars, coated with plater, and trowelled down smooth makes an ideal waterproof structure.
Experiments . made on large reinforced concrete pipes by the United States Geological Survey. and which were intended to discharge under pressures up to 35 lb. per square inch, demonstrated the permeability of concrete and the practical value of different kinds of plasters, paints and washes. It was found that all of the tests made on washes or paints gave poor and unsatisfactory results, and the conclusion drawn from these experiments was to the effect that the best results could be obtained by giving the inside surface of the pipe or Coat of plaster 54-in. thick, composed of one part cement, parts sand and a small quantity of lime paste thoroughly cooled to retard setting, keeping the pipe well wet ahead of the plastering, and when this coat which is left rough had dried to add another coat about I in. thick of piaster composed of one part cement to one part of sand. This coat should be trowelled to a smooth surface and when dr. the entire inside surface of the pipe should be covered with thick wash of cement and water. In the construction of pipes not subjected to great water pressure no plastering is necessary, if the concrete is sufficiently rich in cement.
Concrete lias found a wide field of usefulness in its application to waterworks, and indeed it would be extremely difficult to imagine a purification works built today in which concrete was not the principal building material, from the foundations to the superstructure. It is particularly adapted to the construction of water conduits and pipe lines, to tanks and basins, to water towers and standpipes, to reservoirs and clear wells and to filters, cither slow or mechanical. Indeed, the present day mechanical filters have been considerably modified by the adoption of concrete construction. The rectangular shape of the concrete mechanical filter irapidly replacing the circular wooden or steel tank, its use resulting in an economy of space.
Little Falls. X J.. was the first filtration plant to adopt the rectangular concrete filter tank and the general use of concrete throughout its purification system. This plant was built in 1901, under the direction of George W. Fuller, consulting engineer. Engineer William Wheeler, in 1895, built the first filters in this country having groined arch covering, at Ashland, Wis. He used brick piers and brick arches, hacked with concrete, and in 1896 built two filters at Somersworth, N H.. with granite piers and brick arches backed with concrete. In 1897. Freeman C. Coffin built a reservoir at Wellesley. Mass., having brick piers and all concrete arches. Charles Hermany, in 1900, at Louisville. Ky.. built his clear of water reservoir with groined arch vaulting of concrete metal, and the piers of concrete 3.4 ft. in diameter, having a span of 22 ft. centre to centre of supports and a rise of 3.8 ft. The columns concrete. About this same time. John W. Hill, were 21 ft. high, and made of Portland cement at Philadelphia, began the construction of its immense filtration system, using concrete exclusively for the filter construction. The use of the concrete groined arch covering’ for reservoirs and filters is now quite general. New Haven, Connecticut, under the direction of George W. Fuller, in 1904, was the first to depart from the groined arch type of cover for its filtration plant, adopting the reinforced concrete flat slab and beam construction with reinforced concrete columns.
It has been the writer’s privilege to be cnnected with the Indianapolis Water company in the development of its purification system, involving pretty generally the use of concrete, and the following descriptions and illustrations of these works are submitted for your consideration, together with several items of cost which are usually interesting to those engaged in this kind of work.
REIN FORCED CONCRETE AQUEDUCT.
The filter plant supplied by a gravity flow from the Indiana ate central canal, which was originally built by the State of Indiana for transportation purposes and was purchased from the State by the waterworks company of Indianapolis and later was acquired by the Indianapolis Water company.
The head gates and concrete sluiceways ot this canal are located about 6½ miles above the intake of the filters The canal is carried over Fall creek near the filter plant in an open aqueduct at a height of 18 ft. above said creek. On March 26. 1904. a disastrous flood carried away tlie then existing aqueduct which was built of wood, supported by steel trusses on rubble masonry piers and abutments. The middle pier was undermined and scoured out, crumbling and breaking up and destroying the superstructure.
The aqueduct was immediately rebuilt, but of a different material. It is a reinforced concrete structure 300 ft. long and 41 ft. wide, having four skew segmental arches, each of 60-ft. clear span with a 1.0-ft. rise from the springing line to the soffit, and a crown thickness of 18 in. The heighth from the foundation courses to the tow path is 35 ft. 9 in. The foundation for the piers, abutments and wing walls were carried down 16 ft. below water and rested upon a bed of sand and gravel. The arch ring is reinforced with 8-in. steel beams spaced 2 ft. 6 in. on centres and bent to tb curvature of the arch, and is reinforced transversely with steel bars.
Over the extrados of the main arches and in line with Fall crek were built small transverse arches, the purpose of which was to increase th* discharging capacity of the bridge during fresluT a id to ebminate the possibility of freezing, which might occur with hollow spandrels.
Over these smaller arches was placed the trunk or aqueduct proper this was constructed of a 9-in concrete slab reinforced with steel rods, extending into the side walls, which were 6 ft. high and 2 ft. 6 in. wide with a projection of 2J4 ft. supported by concrete brackets, making a walk or tow path 5 ft. wide on the down stream side and series of notches or weirs on the upstream side to relieve the canal of surplus water.
The trunk is 36 ft. wide in the clear, w’th a depth of water A the channel of 5 ft. These side walls were built n short alternate sections and were connected by sheet lead expansion joints. The lead sheet was about 20 in. wide and 6 ft. long; it was folded lengthwise with a convolution in the centre of the sheet and hoies were punched in the sheet for anchorage in the adjoining sections. This expedient has proven entirely successful, the aqueduct having been in service now for four years, no leaks having ever developed in the trunk, although contractions of the sections are evident during cold weather. This work was done during the winter of 1904-5.
The structure contains 4.500 cu. yd. of concrete mixed 1-2-4, the unit costs being as follows:
The gravel was taken from the bed of the creek.
RE IN FOHCED CONCRETE FILTER COVERS.
The filters built in 1902 are of the slow sand type, covering 4.8 acres; they were originally built open and in three large units. It was found necessary to cover and divide them into six units, approximately 100×350 ft. each.
Cast iron columns were selected for the supports in preference to concrete piers, to save time in the erection of same and to minimize the disturbance of the filter material and pure water drainage system, which had been oompelted and in operation since September, 1904. No provision had been made for covers in the original plans of the filters. The covers consist cf 3-in. slabs, supported by concrete beams H ft. 7 in. long spaced 6 ft. 9 in. on centres; the beams being 8 in. wide and 15 in. deep; these beams are in turn carried by 18-in. L-beams encased in concrete and bolted to the columns, forming a continuous girder 22 in. deep, which is supported on cast iron columns 7 in. in diameter and spaced 20 ft. 3 in on centres. The columns rest on cast _ iron base plates 15 in. sq., laid on short piers. These columns are filled with concrete and are kept painted outside with asphalt paint. The excavation for the columns was accomplished by means of cylindrical sections of steel plate which were easily driven down through the 4 ft. of of filtering material. This plan of carrying on the work resulted in a very material saving of time.
The partition walls are each 350 ft. long, 14 to 17 ft. high and 1 ft. thick, reinforced in both faces vertically and longitudinally with ¼-in. and -in. bars, respectively. The slab reinforcing is 34″⅛. bars spaced 3 in. on centres in the direction of load and 0 in. on centres in the opposite direction. I he beams are continuous over 19 supports and the girders over II supports: The entire slab, covering 70,000 sq. ft. in each double filter, is built monolithic, without any attempt to provide expansion joints. About the four ides there is a parapet wall for retaining a cinder filling, and for closing the spaces between the beams. This wall is kept separate from the main supporting wall by a paraffine joint, the I-beam resting on rollers in the wall. 1 he lubricated joint was provided to allow the cowr to expand and contract freely without into mcing bending into the main walls. These covi rs and walls are watertight for all practical purposes.
In the removal of forms, front ten days to two weeks were allowed to elapse after placing the concrete. The work was done with a cable tramway spanning 450 ft., suspended from movable towers mounted on tracks, the concrete being handled from the mixer to the cableway by means of a shuttle car on a narrow guage track, propelled by a stationary engine and cable. In this way 80 cu. yd. was an average day’s work, covering 5.000 sq. ft. of surface.
COST OK COVERS.
KKINFORCED CONCRETE-PURE WATER RESERVOIR.
During the summer of 1907 the Indianapolis Water company built a pure water reservoir having a maximum capacity of 5,500,000 gal.
The reservoir is built near Fall creek on a gravel foundation at the ordinary ground water level. The groined arch bottom was designed to resist the upward thrust of extraordinary high ground water at such times that the reservoir is empty. The earth fill, 2 ft. deep on the cover, and the weight of the structure itself would overbalance any upward pressure that might occur. The inverted groined arch construction also distributes this load uniformly over the bottom. The lower section of the arches is reinforced with 2-in. twisted bars spaced 10 in. on centres in either direction, to bind the sections together and to prevent contraction cracks. And the joints were brushed with cement grout in addition. No other waterproofing material was used, as under the low head of water carried, the amount of percolation through the concrete itself would be inconsiderable if cracks could be prevented. The walls were 1 ft. thick, securely anchored to the floor and cover, and were reinforced against side thrust in both faces and against longitudinal temperature stresses by bars as showm. The wall was built monolithic about the four sides of the reservoir, the corners being rounded by curves. Nothing worse than a fewfine hair cracks showed up and these did not occur at the corners as is usually the case. I lie roof slab is 5 iti. thick, reinforced with ffj-in. thick rods as shown, with variable spacing; this slab is supported by concrete beams 8 in. wide and 16 in. deep, which are carried by plain concrete columns 42 in. square, spaced 10 ft. on centres.
The costs, as follows, do not include superintendence or office expenses:
Cost per 1.000 gal. stored, $9.33.
The concrete was mixed with a batch mixer using a cableway for distributing same and a shuttle car to convoy the concrete from the mixer to the cableway. The gravel was taken from the excavation and was used unscreened and unwashed in the proportions of one part of cement to six of gravel.
The quantities involved were: Concrete, 5,195 cu. yd.; steel. 283 tons; cement. 6,300 bbl.; gravel, 7,700 cu. yd.; lumber, 210,000 ft.; excavation, 26.000 cu. yd.; refill, 10,000 cu. yd.
PER CUBIC YARDS OF CONCRETE.
Cement, 1.21 bbl.; gravel 1.10 cu. yd.; steel, 1.09 lb.; lumber. 40 board ft.
The greatest amount of concrete placed in one dav of ten hours was 134 cu. yd., while the average amount for the concreting period was 70 cu. vd. The cableway was used in distributing the till on the cover, a special scraper being constructed for that purpose.
REINFORCED CONCRETE PIPE LINE.
This pipe line was built during the winter of 1907-8. Tt is 840 ft. long and is used for the purpose of conveying raw water to the precipitation basins.
It is laid 11 ft. below the hydraulic gradient. The inside diameter is 66 in. and the concrete shell is 6 in. thick. It is reinforced with ½-tn. twisted bars spaced 8 in. on centre in either direction. The pipe was built in three general operations alter the ditch had been dug to dimensions corresponding to the outer circumference of the pipe. _ A
A concrete cradle 30 in. wide was first laid to grade holding the lower circumferential rods, the rods being held in position by curb boards notched out to receive them and also by the lower longitudinal rods. These lower circular rods were heated and bent in the field to the required shape and thev were left long enough to project into the upper ring about 12 in. Semi-circular metal forms then placed on this cradle and fastened down bv limbers laid across the tops and staked into the side of the trench to prevent the forms from floating. Hie concrete was mixed in the porportion of one of cement, two of sand and four of gravel, and was poured into the space between the side of the ditch and the metal form, this operation completing the lower half of the pipe; the metal forms were then inverted and supported on wooden roller bearings and wooden track. The upper rods were then fastened to the lower projecting rods and curved wooden forms were braced into position for moulding the upper ring, leaving a space 18 in. wide open along the top for placing the concrete. It was kept well churned and produced a smooth and perfect piece of work.
To facilitate the setting as this work was done during the cold weather, gasoline torches were burned inside the completed portion until the whole was completed and the narrow exposed strip on top was protected by canvas. About 100 ft. of completed work a day was the usual progress, the metal forms being moved ahead in ll0-ft. sections without disjointing. No cracks of any kind were discernable at the completion of the work and the pipe is watertight, although no plastering or brushing was done.
The unit costs were as follows:
llie pipe contained altogether 300 cu, yd. of concrete and the total cost was $12.46 per cu. yd. The concrete was mixed in a batch mixer and wheeled an average distance of 500 ft Bids received on 60-in. light steel pipe proposed for this purpose on board cars Indianapolis ran trom $6.70 to $7 per foot. One bid, contemplating furnishing and laying into the ditch prepared by the company, for $8.25 per foot Sixty-inch light weight cast iron pipe would have cost $15.50 JHT foot f.o.b. Indianapolis, to which must be added the cost of lead and laying to make the costs Comparative. The cost of the concrete pipe did not include excavation, which would have been the same in either case, nor the cost of the gravel which would add about 27 cents per foot; so that the reinforced concrete pipe cost about one-half as much as steel and about one fourth as much as cast iron; in addition, it was 6 in. greater in diameter than eith r, besides having die advantage over steel of greater durability.
REINFORCED CONCRETE VENTURI METER.
With the installation of the preliminary treating plant, it became necessary to know bow much raw water was being treated with chemical, and at the same time have the apparatus for recording and indicating these amounts at a convenient location to the operating headquarters. Accordingly a Venturi meter of reinforced concrete. 42 in. in diameter, having a throat diameter of 21 in., was built in tin 42-in. raw water conduit, which is also of concrete, anti the indicating apparatus was placed in the laboratory building. The throat section was of cast iron and brass and was furnished together with the recording apparatus by the Builders Iron Foundry, of Providence, R. 1. The Conical forms were made up by a planing mill and worked to perfect lines and dimensions, sand papered and coated with a thin layer of asphalt paint. The forms were then suspended and braced into perfect alignment. The concrete was mixed in the proportions of one of cement, one and one-half of sand and three of gravel, producing uniformly smooth inner surfaces. The meter was built in the fall of 1908 and has been in service now for several months, and is in every respect satisfactory.
The purification work of the Indianapolis V ater company may be termed a modified slow sand filtration plant, the ordinary operation of filtration being mollified by preliminary treatment to coagulation and sedimentation.
During about one-fourth of the year the waters of White river, which furnish the supply, carry large amount of finely divided day and other suspended matter, producing an average turbidity of about lit parts per 1,000,000 and reaching at times 1,200 to 1,500 parts per 1,000,000. This muddy water going directly to the filters made the operation at such times very difficult. Acting on the advice of Mr. George YV. Fuller, consulting engineer, the company, during 1007 and 1908, built these large precipitation basins and chemical treating station.
The basins cover an area of 15½ acres of water surface, the average depth being about 10 ft. They are operated on the displacement plan, by a gravity flow from the canal and through the filters. The embankments are of earth, with inner slopes of two on one and outer slopes of one and a half on one. That portion of the basin nearest the inlet and covering about 5 acres is lined with concrete and divided into three channels, eaeli about 7o ft. wide. The dividing walls are of reinforced concrete 15 in. wide and 12 ft. high, the base of which is 5 ft. wide and 1 ft. high. The base is reinforced with -Vs-in. and ¾ in. square bars, spaced 24 in. apart. The vertical bars and ¾-in. square and spaced 4 ft. on centres, horizontal reinforcing bars and ⅝ in. square, spaced i ft. apart, with three bars in the top of the wall.
At intervals of 100 ft. a tin. pipe is built into the wall, having 2½ in hose connections on either sidt. These pipes are supplied by an 8-in. pressuri pipe laid in the centre channel. The purpos of these pipes and hose connections is to facilitate the Hushing or cleaning out of the basins whenever necessary. The slopes are lined with concrete l in. thick and reinforced with $4-in. liars spaced 4 ft. apart in either direction. A coping wall 2 ft. 6 in. high is built round the top of tlu slopes and is reinforced similarly to the dividing walls. In the centre of each channel is constructed open ditches all leading to a 24-in. drain pipe discharging into Fall creek, for the purpose of carrying off the sludge at cleaning periods These ditches are about 2 ft. wide and have a uniform slope 2-10 per cent. The floor slab in each channel is 4 in. thick and slopes uniformly t ft. in 34 from the dividing walls to the ditches
The concrete was mixed in the proportions of 1-3-5 and was distributed from a central mixing station conveniently located. A track was laid along the top of the north embankment and a specially built hopper-shaped car was drawn to and from the mixer by means of a cable attached to a stationary upright reversible engine. When it became necessary to round the curves in the embankment a home made locomotive was improvised, which served the purpose well. Twowheeled harrows, holding 5 cu. ft., were used to convey the concrete from the hopper to the work in hand. remarkable spell of dry weather prevailed during the construction of these basins as only one hour was lost because of rain. The gravel for this work was produced by a Guffin excavator spanning Fall creek.
The dredge is operated by a carriage mounted on a cable supported by “A” frames on either bank, and is operated by an ordinary hoisting engine, discharging bv means of a hook suspended from tlu carriage. centrifugal pump furnishes the water for washing the gravel through the various screens, making it suitable for concrete work This machine we found to operate much more economical and satisfactory than the ordinary sand pump.
REINFORCED CONCRETE CHEMICAL HOUSE.
In connection with the precipitation basins and for the purpose ot treating the raw water at seasons of excessive turbidity, there was built a chemical treatinghouse, of reinforced concrete.
The lower part of the building is formed principally by the lime saturating tanks, over which are built the smaller tanks for the storage of iron and alum solutions. These tanks are of concrete reinforced with steel bars as are also the orifice measuring boxes. The columns, floors, walls, stairways and roof are of reinforced concrete throughout. The floors are designed to store dry chemical, packed in bags, and uniformly distributed 4 or 5 ft. deep. The building is veneered with pressed brick and limestone trimmings to correspond with the present laboratory building which it adjoins.
In connection with the iron solution tanks, it was observed that any tendency for water to percolate through the concrete, usually at the tie wires, was promptly checked as soon as the sulphate of iron solution was introduced. All tanks were built monolithic as open boxes, in one operation and independent of each other. The sulphate of iron is put into solution and transported to the storage tanks by means of an hydraulic ejector similar to a sand ejector, and is diverted to the various tanks on the floor above by means of valves, as shown. The ejector being operated by water from the city mains at a presswri of about 60 lb. per square inch.
These examples of concrete construction are given merely as an indication of how valuable this material has become and illustrate in part the usefulness to which concrete can be put in the development of waterworks generally; its use as a building material is no longer an experiment ; but is irmly established on sound engineering principles ; and in all probability its fleldd of application to engineering generally and to waterworks in particular, will continue to expand indefinitely.
And now, in conclusion, let me acknowledge the part taken by the man, who, by his constructive ability and progressive nature, has made possible the works described; a man of Stirling character, and great business ability, a man who has always taken an active part in the transactions of this association, and one worthy of your greatest respect and esteem, the late president of the Indianapolis Water company, and past president of the American Waterwworks company, and past president of the American Water Works Association, tion last met in convention.