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Concrete Construction - Methods and Costs
by Halbert P. Gillette
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CIRCULAR RESERVOIR, BLOOMINGTON, ILL.—An open circular reinforced concrete reservoir was constructed in 1905-6 for the water-works of Bloomington, Ill. This reservoir is 300 ft. in diameter, 15 ft. deep at the circular wall and 25 ft. deep at the center of the spherical bottom. The wall construction is shown clearly by Fig. 278, and the floor is a 6-in. spherical slab reinforced by a mat of -in. round rods placed 6 ins. on centers in both directions. The wall reinforcement is corrugated bars. Neither the wall nor the bottom has expansion joints.

Concrete.—The specifications required not less than 1 part Portland cement to 2 parts sand and 5 parts clean gravel, and stipulated that there should always be more than enough cement to fill the voids in the sand more than enough mortar to fill the voids in the gravel. The proportions were varied, depending on the character of the available material and on the location the concrete was to occupy. The stipulations regarding the minimum quantities of cement and mortar were, however, always at least fulfilled. A 1-3-4 mixture of cement, broken stone and gravel was largely used in the footing and wall. The gravel was fine and contained 40 to 50% of sand; the broken stone was the crusher-run, with the dust screened out, and the maximum-sized pieces not larger than those which would pass a 2-in. screen. The mortar facing on the front face of the wall was made of 1 part cement to 4 parts fine gravel, containing sand. Some gravel from the excavation was used in the concrete for the floor. This gravel was so fine that about one-quarter of it was replaced with broken stone and the mixture made 1-6. Both faces of the wall were painted with a 1-1 mixture of cement and sand; the inner face was also painted with a 1-1 mixture of waterproof Star Stettin Portland cement and sand. The sidewalk finish on the surface of the floor consisted of 1-1 mortar.

Mixing and Handling.—The concrete mixing plant was set up outside of the site of the reservoir along a side track from the railroad. The concrete materials were delivered on the side track, except some gravel from the excavation that was used. A Foote portable continuous mixer was used in making the concrete for the wall footings and the wall. It was mounted so it could discharge into dump cars on a service track laid on the ground. A double hopper was built up over the mixer, one compartment for sand and one for broken stone. The end of a service track leading from the side track was laid on an inclined trestle up to a floor level with the top of this double hopper, the materials being hauled in dump cars from the side track to the hopper. The service track from the mixer extended entirely around the wall, and 10 ft. from it, on the embankment made there with earth from the trench for the wall-footing. The concrete was dumped from the cars on the service track to portable shoveling platforms near the point where work on the wall was in progress. It was shoveled by hand from these platforms to place in the forms as the presence of the reinforcement bars in the narrow forms precluded dumping in large quantities. The footing was built without forms up to the right-angle joint between it and the base of the wall at the front, and to the top of the 45 slope on its rear face. A layer of concrete 2.5 in. thick was first placed in the completed trench. The reinforcement bars near the bottom were then laid on this green concrete, the vertical bars near the front face of the wall usually being erected at the same time. The concrete in the toe of the footing and in the footing proper up to the top layer of reinforcement was then laid. After the top layer of reinforcing bars had been laid, the footing was completed, except for a top layer about 2 ins. thick at the base of the front face of the wall and 15 ins. thick at the toe of the footing. This left a strip of surface about 6 ft. wide, sloping at about 1 in 6 from the wall toward the center of the reservoir, and furnished the widest and best possible bond for the joint which had to be made when floor was laid.

Location and Construction of Forms and Wall.—The design of the wall of the reservoir, although simple in itself, required unusually accurate work in the location and construction of the forms for it. The location was made with very little difficulty, however, by an arrangement devised by the contractor which enabled the foreman, without the aid of an engineer, to set the necessary grade and reference stakes. A post, 10 ins. in diameter, was set very accurately and firmly in the ground at the center of the reservoir. This post was sawed off squarely on top so that the line of collimation of an engineer's transit set on it without a tripod would be exactly at the grade of the top of the completed wall of the reservoir. A 200-ft. steel tape was used to measure the radial distance from a nail in the center post to the posts of the back, or outside forms for the wall. In the form for the back face of the wall 26-in. posts, spaced one one-hundredth of the circumference apart, were set considerably in advance of any concrete work, and were made the basis of all measurement in building the forms. The forms as originally planned are shown in Fig. 278.

The wall, when started, was built continuously in both directions from the starting point. The back forms consisted of planks for lagging nailed to vertical posts, which were accurately set and firmly braced. The front forms were made in lengths equal to one one-hundredth of the circumference of the reservoir, and when set up were fastened to the back forms. Twenty-one of these front form sections were built and all set up at once. Concrete was filled in between the front and back forms, starting at the central form, and was rammed in inclined layers, sloping, at about 1 on 6, both ways towards the end forms. This method was adopted in order that the concrete might be laid continuously and without joints. The lagging of 1-in. boards on the vertical portion of the sections was nailed to the vertical posts, and was carried up just ahead of the concrete filling.

When the concrete had reached the top of the central one of the 21 sections of the forms, and the concrete in that section had set sufficiently, the section was broken up and removed, leaving two sets of 10 sections of the forms. Subsequently the other forms could be removed in turn as desired without being broken up. As the filling-in proceeded between the two sets of 10 forms each, the form in each set nearest the starting point was removed, carried forward, and put in place at the other end of its set of forms. Twelve men were required to take down and transport one of the front form sections.

In setting up a front form, its inner toe was firmly supported by a stake driven into the ground and by the horizontal board, nailed transversely under the bottom 44-in. horizontal stringers, which rested on the ground. The upper part of the form was then securely fastened to the 26-in. posts of the back forms by temporary wooden connecting strips, which were removed as the concrete filling was carried up. The sections of the front forms were also securely tied to each other.

A facing of gravel concrete, rich in cement and with no pebbles larger than -in. was placed on the front face of the wall, extending from the back edges of the vertical reinforcing bars to the surface. A sheet-iron plate, about 8 ins. wide by 5 ft. long, was placed vertically just back of those bars. The concrete was shoveled in loose to the top of these iron plates, and then the mortar was poured in between the latter and the front face forms from buckets. The iron plates were next drawn by handles attached to them, and the mortar and concrete tamped together before either had set. In making joints, the old concrete surfaces were always brushed and wet down, and, if necessary slushed with a grout of neat cement before new concrete was laid on them.

Construction of Floor.—The excavation over the site of the reservoir floor was brought accurately to grade 6 ins. below the surface of the finished concrete by hand after the scoop-bucket excavator had passed over. In making the excavation the levels were given on radial lines drawn from the ends of the 10-ft. sections of the wall to the center. A rod, on which the elevations of the sub-grade at every 10 ft. from the wall to the center of the reservoir were clearly marked, was used in connection with a transit on the center post in locating the elevations of different points in the reservoir floor. By using this method the elevations required were easily found by the foreman in charge without the assistance of an engineer. When the work approached the center, the post was removed and the transit was placed on a portable pedestal which was set on points of known elevation on the finished concrete.

The slanting surface left on the top of the footing inside the wall formed, together with the projecting reinforcement rods, an excellent bond between the concrete of the wall and that of the floor, when the latter was laid. A circular strip of the floor, 16 ft. wide, was put down next to the wall first, and the remainder of the floor was laid according to the progress of the excavation. The lower 3 ins, of the concrete was usually first spread out over an area 12 or 16 ft. square, then the reinforcement was placed, and after that the top 2 ins. of concrete and a -in. sidewalk finish surface were laid.



The -in. rods in the bottom are 6-ins. on centers in both directions. They were in 12 and 16-ft. lengths and were partly woven together in mats before being placed. The rods in one direction were all laid out and woven with four or five of those in the other direction, the joints being tied with small wire. The remaining cross rods were laid after the mat had been placed. The mats were overlapped 1 ft. This method of placing proved economical and efficient, giving at the same time something permanent on which to lay the remaining concrete.

STANDPIPE AT ATTLEBOROUGH, MASS.—The stand pipe was 50 ft. in diameter and 106 ft. high inside, with walls 18 ins. thick at the bottom and 8 ins. thick at the top. Figure 279 shows the general arrangement of the reinforcement. Round bars of 0.4 carbon steel were used; the bars came in 56-ft. lengths, so that three lengths with laps of 30 ins., made a complete ring around the tank. The concrete was a 1-2-4 mixture of to 1-in. broken stone with screenings used as portion of sand.

The floor was built first, and on it was erected a tower to a height of 60 ft. and a derrick with a 40-ft. boom was set on its top. The derrick was operated by an engine on the ground which also had a revolving gear attached. When the work had reached the top of this tower, the tower was raised to 110 ft. in height and the derrick shifted to the new elevation. The forms were convex and concave sections 7 ft. high and about 11 ft. long. The concave or outside forms were made in 16 panels, with horizontal ribs and vertical lagging; two complete rings of panels were used. The panels were joined into a ring by clamps across the joints, this clamping action and the friction of the concrete holding them in place. The inside forms consisted of vertical ribs carrying horizontal lagging put in place a piece at a time as the filling proceeded. They were supported by staging from the derrick tower. The remaining plant comprised a Sturtevant roll jaw crusher feeding to screens which discharged fines below -in. into one bin, medium stone into another bin and coarse stone into a third bin. These bins fed to the measuring hopper of a Smith mixer, which discharged into the derrick bucket.

The mode of procedure was as follows: The reinforcing rings were erected to a height of 7 ft. The bars were bent by being pulled through a tire binder and around a curved templet by a steam engine. The bending gave some trouble, due, it was thought, to the stiffness of the high carbon steel. Vertical channels 4 ins. deep were set with webs in radial planes or across wall at four points in the circumference. The flanges of these channels were punched exactly to the vertical spacing of the reinforcing rings. Through the punched holes were passed short bars on the opposite ends of which the reinforcing rings were supported and wired. The three sections of rod of which each ring was composed, were lapped 30 ins. and connected by Crosby clips. Considerable difficulty was had in holding the reinforcing rings in line by the method employed; it is stated by the engineer that a greater number than four channels would have been much better.

The reinforcement being in place, an inside and an outside ring of forms was erected. Concreting was then carried on simultaneously from four points on the circumference and a ring 7 ft. high was concreted in one operation. Several facts were brought out in the concreting; careful and conscientious spading was necessary to get a smooth dense surface; a too wet mixture allowed the stone to settle and segregate; care was necessary in this thin wall containing two rings of bars to keep the stone from wedging among and around the bars and thus causing voids. The engineer states that for this reason the substitution of mortar for concrete in tank walls is worth considering. He estimates that in this work, costing $35,000, that the use of a 1-2 mortar in place of the 1-2-4 concrete would have increased the cost by $2,300, a 1-2 mortar by $1,500, and a 1-3 mortar by $750. It was also found that there was danger from a movement of the reinforcement in the concrete and of the forms in placing the concrete.

When a ring of wall 7 ft. high had been concreted, the reinforcement was placed as before described for another ring. The two rings of forms below those just filled were removed from the wall, hoisted up and set in place on top. These two operations of placing reinforcement and setting forms for another ring of wall took three days, so that the top surface of the wall to which new concrete was to be added, had become hard. This hard surface was very thoroughly washed and then coated with neat cement immediately before depositing the fresh concrete. Water was admitted to the tank as the work progressed, being kept about 20 ft. below the work in progress. Numerous small leaks developed, but only two were large enough for the water to squirt beyond the face of the wall. These leaks appeared to grow smaller as time went on. To do away with them entirely, the inside wall was plastered. The first coat of plaster was not successful in stopping the leaks, so the standpipe was emptied and replastered, five coats being used in the lower 20 ft. This did not serve so resort was had to a Sylvester wash. A boiling hot solution of 12 ozs. to the gallon of water of pure olive oil castile soap was applied to the dry wall. In 24 hours this was followed with a 2 ozs. to the gallon solution of alum applied at normal temperature. Four coats of each solution were applied, which reduced the leakage to a small amount. To do away with all leakage another four-coat application of Sylvester wash was used.

Details of the cost of the work are not available. There were 770 cu. yds. of concrete in the walls and 185 tons of steel bars. Altogether 3,000 Crosby clips, costing $1,100 were used. The cost of the concrete in place was about as follows:

Cement, per cu. yd. of concrete $ 4.80 Sand and stone, per cu. yd. of concrete 3.90 Mixing, per cu. yd. of concrete 0.40 Placing, per cu. yd. of concrete 2.20 Forms, per cu. yd. of concrete 2.65 ——— Total per cu. yd. of concrete $13.95

GAS HOLDER TANK, DES MOINES, IOWA.—The tank was 84 ft. in diameter and 21 ft. 5 ins. deep. It had a horizontal floor 16 ins. thick 5 ft. below ground level and a wall 21 ft. high, 18 ins. thick at base and 12 ins. thick at top under coping and with alternate pilasters and piers around the outside. The concrete for the floor was a 1-2-5 2-in. stone mixture and the concrete for the walls was a 1-2-4 1-in. stone mixture. The floor was constructed first, with a circular channel for the wall footing, and then the wall was constructed.

Piles were driven in the bottom and their heads cut to level and filled around with tamped cinders. Two circumferential rows of posts were driven around the edge so that a pair of posts, one inner and one outer, came on each radius through a wall pilaster or pier. These posts served primarily to carry the frames for the wall forms and secondarily for holding the forms for the circular wall footing channel as shown by the sketch Fig. 280. The floor concrete was put in in diamond-shaped panels between forms, whose top edges were set to floor level. Each form was designed to make a groove in the edge of the slab so that adjacent slabs would bond with it. The concrete was wheeled to place in barrows, thoroughly tamped, roughly floated to surface and finally given a trowel finish.



To construct the walls, the posts before mentioned, were cut off to exact level 6 ins. above the finished floor. A bent for the wall forms was then erected on each radial pair as shown by Fig. 281. The bents were erected by hand and carefully plumbed and lined up, both radially and circumferentially. The pier and pilaster forms were then erected across wall opposite each bent as shown by Fig. 281. The forms for the wall between pilasters and piers consisted of panels 4 ft. high.



A panel for the inner face of the wall is shown by Fig. 282, the panel for the outer face was similar in construction but was, of course, concave instead of convex. Enough panels of each kind were made to reach entirely around the tank. The inside panels were bolted at the ends to the uprights of the bents; the outside panels were similarly lag screwed to the uprights of the pier and pilaster forms; Fig. 281 shows the holes for bolts and lag screws. The spaces between ends of inside panels in front of the bents was closed by a 6-in. steel plate the full height of the wall; this plate was bolted to the bents and had anchor bolts every 3 ft., reaching into the wall. This anchoring of the plate to the wall permitted the diagonal bracing of the bents to be removed to allow runways to be laid on the cross-pieces, since the plate held firmly the bent post to which it was bolted as indicated by Fig. 283. A complete circle of inside and outside forms was erected and filled, then the forms were raised 3 ft. by block and tackle from cross timbers across wall between bent and pilaster form, and this depth concreted and the forms raised again. The forms were oiled on the faces coming against the concrete. It took about half a day to raise and set a complete circle of forms. The concrete was mixed outside the tank and was wheeled up inclines and dumped onto runways laid on the cross pieces of the bents and then loaded and wheeled to place. The runway was raised to successive horizontals as the work progressed.



Only a few general cost figures are available. The labor for mixing and placing concrete was as follows:

For floor, per cu. yd. 3.4 hrs. For walls, per cu. yd. 5.2 hrs. For cornice, per cu. yd. 5.4 hrs.

The cost of unloading the reinforcing steel from cars and placing it in the structure was $7 per ton, or 0.35 ct. per lb. The cost of form lumber, framing, erecting and taking down forms was 9 cts. per square foot of wall covered.

GAS HOLDER TANK, NEW YORK CITY.—The tank for the Central Union Gas Co.'s gas holder at 136th St. and Locust Ave. has an interior diameter of 189 ft. and a depth of 41 ft. 6 ins. The exterior wall is 42 ft. 6 ins. deep, 5 ft. 6 ins. thick at the base and 4 ft. 6 ins. thick at the top; concentric with it and 11 ft. 6 in. away is the interior wall 166 ft. in external diameter and 16 ft. 6 ins. high with a uniform thickness of 2 ft. 6 ins. The bottom of the tank enclosed by the interior wall is a truncated cone whose base is at the level of the wall top. Fig. 284 shows the arrangement.

It was specified that the diameter of this tank should not vary more than 2 ins. and that the exterior wall should not vary more than 1 in. from the vertical. The main form was a circular drum whose exterior face formed the inner face of the main wall. Its framework consisted of 40 vertical trusses or radial frames 6 ft. deep and 42 ft. high set equidistant around the tank, these trusses being braced together on both edges by circumferential timbers. Radial horizontal pieces nailed across the radial frames and projecting beyond their faces carried vertical iron guide strips against which the movable panels of lagging were seated. These panels were cylindrical segments 5 ft. high and long enough to span between two radial frames or 14 ft. 11-5/8 ins. The panels were adjusted radially by wedges to give 1/8 in. clearance in respect to inner face of wall; enough of them were made to form a complete circle and they were set with 1-in. clearance between vertical edges of adjacent panels to allow for swelling when wetted.



The concrete bottom of the annular space between walls was first constructed. On this floor were set 66-in.8-ft. sills for the radial frames; these were located accurately by transit. The radial frames were then set on the sills by a derrick, adjusted to exact radial position by a measuring wire swiveled to the center point of the tank and plumbed by transit. A complete circle of lagging panels was then adjusted to the frames at the bottom of the trench. For concreting, the wall was divided circumferentially into three sections. These sections were separately concreted to the top of the lagging panels, that is to a height of 5 ft. After the concrete had set 48 hours the panels were hoisted 4 ft., so that their lower edges still overlapped the concrete 12 ins., and another ring of wall was concreted. This procedure was repeated until the wall was completed. The back of the wall was formed against the side of the trench where possible and in other places against rough board lagging held in position in any convenient way.

For handling the concrete, four equidistant panels of the form framework were converted into double compartment elevator shafts providing for two balanced cars controlled by a sheave provided with a friction brake. Three mixers supplied concrete to these elevators. Considering a single elevator, two barrows of concrete were wheeled from the mixer onto the car at the top of the elevator frame, the friction brake was released and the loaded car descended to the work hoisting at the same time its twin car loaded with two empty barrows. The elevators distributed to wheeling platforms cantilevered out from the outer face of the framework and located successively 5 ft., 15 ft., 20 ft., etc., above the bottom of the trench. On these platforms the concrete was distributed as required, the maximum wheeling distance being never over one-eighth the circumference of the tank. The concrete was mixed very wet and deposited in 6-in. layers.

The inner and outer surfaces of the wall were both painted with two coats of stiff cement grout neat, and in addition the inner surface was rubbed smooth by carborundum brick. Regarding this finishing work Mr. Howard Bruce, Engineer of Construction, writes:

"The scouring was done on each section of the wall immediately after the forms supporting these sections had been removed. The object was to rub this interior surface with carborundum before the surface of the concrete had taken its final set. By rubbing the concrete at this stage and at the same time applying with a brush a coating of neat cement grout, we believe the face of the concrete was made more or less impermeable, as examination shows the pores of the concrete are very largely filled up. We have no accurate figures as to the cost per square yard of this treatment, but one can readily see that this cost would be insignificant as compared with the possible improvement of the work. The carborundum brick was selected on account of its hardness. I believe practically any stone would answer the same purpose. In addition to filling the pores of the concrete, this treatment gives the surface a good smooth finish."

LINING A RESERVOIR, QUINCY, MASS.—The following methods and costs are given by Mr. C. M. Saville, M. Am. Soc. C. E., for lining the Forbes Hill Reservoir at Quincy, Mass. This reservoir is 100280 ft. on the floor, with side slopes of 1 on 1.75, and was built by contract in 1900-1901.



Figure 285 is a section of the concrete lining; the bottom layer for the floor was a 1-2-5 natural cement concrete, and for the sides a 1-2-6 Portland cement concrete; the top layer on both floor and sides was a 1-2-4 Portland cement concrete; 2-in. stone was the maximum size allowed in any concrete and 1-in. the maximum allowed in the top layer. Smaller stone was used for special surface work, as noted further on. The stone was cobbles turned up in the excavation work and had to be gathered from scattered piles and washed before crushing. A 915 Farrel crusher, operated by a 12 HP. engine did the crushing; it was rated at 125 tons a day, but averaged only about 40 tons. The fine dust was screened out and the remainder discharged into a 30-cu. yd., three-compartment bin, one compartment for stone less than 1 ins., another for 1 to 2-in. stone and a third for returns. The stone had 46 per cent. voids and weighed 95 lbs. per cu. ft. The sand was of excellent quality. Atlas and Beach's Portland and Hoffman natural cement were used.

All concrete was mixed and placed by hand, the concrete gang consisting generally of 1 sub-foreman, 2 men measuring materials, 2 men mixing mortar, 3 men turning concrete three times, 3 men wheeling concrete, 1 man placing concrete and 2 men ramming concrete. Two gangs were ordinarily employed, each mixing and placing about 20 cu. yds. per day, or 1.43 cu. yds. per man per day. The materials (sand and stone) were measured in bottomless boxes, the following sizes being used:

—Sand Box— —Stone Box—

Prop. of Mix. Size. Vol. cu. ft. Size. Vol. cu. ft.

1-2-4[H] 2'9"2'1'8" 9.25 5'4'5" 14.8 1-3-6[H] 2'9"2'2' 11.1 5'6'8" 22.2 1-2-5 2'9"2'1'4" 7.4 5'6'6-5/8" 18.5 1-2-6 2'9"2'1'8" 9.25 5'7'2" 24.05

[Footnote H: These mixtures were used for gate house and standpipe foundation work.]

The bottom layer was placed in a continuous sheet; the top layer was laid in 10-ft. squares on the floor and in 810-ft. squares on the sides; these squares alternated in both directions, one-half being first laid and allowed to set. In laying the sides the surface was left 1 in. low and then before the concrete had set was brought to plane by a 1-in. layer of 1-2-4 mixture using stone and stone dust less than 3/8 in. The concrete for the floor was mixed rather wet and rammed until it quaked; on the sides a drier mixture was necessary to prevent flow. The cost of the lining concrete was as follows:

Bottom Layer on Floor: 1-2-5 Mixture: 1.25 bbls. natural cement at $1.08 $1.350 0.34 cu. yd. sand at $1.02 0.347 0.86 cu. yd. stone at $1.57 1.350 4 ft. B. M. lumber at $20 per M. 0.090 Labor, on forms 0.100 Labor mixing and placing 1.170 Labor general expenses 0.080 ——— Total $4.487

Bottom Layer on Sides: 1-2-6 Mixture: 1.08 bbl. Portland cement at $1.53 $1.652 0.37 cu. yd. sand at $1.02 0.377 0.96 cu. yd. stone at $1.57 1.507 Lumber for forms (about 1 ft. B. M.) at $20 0.016 Labor, on forms. 0.121 Labor, mixing and placing 1.213 Labor, general expenses 0.177 ——— Total $5.063

Top Layer on Floor and Sides: 1-2-4 Mixture: 1.37 bbls. Portland cement at $1.53 $2.09 0.47 cu. yd. sand at $1.02 0.48 0.75 cu. yd. stone at $1.57 1.17 12 ft. B. M. form lumber at $20 per M. 0.25 Labor, on forms 0.26 Labor, mixing and placing 1.530 Labor, general expenses 0.150 ——— Total $5.93

The side finish with 1-2-4 concrete of 3/8-in. stone cost $0.154 per sq. yd. 1 in. thick. This work was done by a gang of 3 plasterers and 3 helpers.

The layer of plaster between the concrete layers was put down on 4-ft. strips and finished similarly to the surface of a granolithic walk. This layer consisted of 1-2 mortar finished with a 4-1 mortar. To keep the plaster from cracking it was covered with strips of coarse burlap soaked in water; this precaution was not entirely successful, some cracks appeared and had to be grouted. Three gangs, each consisting of 1 plasterer and 1 helper, did the plastering, each gang laying about 700 sq. yds. per day. The cost of the plaster layer was as follows:

Item. Per 100 sq. ft. Per sq. yd. Per cu. yd. Cement at $1.53 $1.15 $0.103 $7.42 Sand at $1.02 0.13 0.012 0.86 Burlap 0.02 0.002 0.14 Labor 0.92 0.083 6.00 ——- ——— ——— Totals $2.22 $0.200 $14.42

It will be noted that it took over 5 bbls. of cement per cubic yard, and that the labor cost was $6 per cubic yard.

RELINING A RESERVOIR, CHELSEA, MASS.—The following account of relining the Powder Horn Hill Reservoir at Chelsea, Mass., is taken from a paper by Mr. C. M. Saville. This reservoir which holds about 1,000,000 gallons is oval in shape, 98175 ft. at the top, 68148 ft. at the bottom and 15 ft. deep, with side slopes about 1 on 1. The work was done by day labor. For sake of completeness the costs of excavation and back-filling are given here as well as the concrete costs.

The top of the bank was too narrow to allow the use of carts and an 18-in. gage railroad was decided upon as most convenient for handling materials. A 65-ft. boom derrick with a 70-ft. mast was used for removing the excavated material and for depositing concrete. The derrick was operated by a 15-h.p. double drum hoisting engine, was held in place by six wire guy ropes, and had a reach such that only one moving was necessary after it was placed. The engine and derrick were set up on the floor of the reservoir, and the work of excavation was begun at about the middle of the south side. In order to facilitate the work, a platform supported on A frames was set up. These frames were spaced about 15 ft. apart and rested on the bottom and slope of the reservoir, being held in place by bolts driven into the floor.

The paving blocks on the top of the slope were removed and piled up to be taken away. The old lining and the material excavated from the bank were shoveled into the scale pan of the derrick, hoisted to the cars on the top of the bank, and then run by gravity to a dump a short distance down the hillside. Here the cars were run out on a rough trestle, the load dumped, and the empties hauled back to the work by a rope carried through pulleys to the winch head on the hoisting drum of the engine.

For the storage of some of the materials, two small portable storehouses were set up—one 8107 ft., the other 1116 x 7 ft. The bulky portions, such as cement, sand, and stone, were delivered as necessary, a few days' supply only being kept on hand. A branch from the railroad was so arranged that it passed the storehouses and stone piles, while the sand was piled close to the concrete mixing board. The intention on the work was to do nothing by hand that could possibly be done by steam, except that all of the concrete was mixed by hand. As great a proportion of water was used as could be done without causing the material to slide when rammed in place.

The lower layer of concrete was of the proportion by volume of 1 cement, 2 sand, and 6 crushed stone (sizes from to 1 ins.). This was rather a lean mixture, and as it could not be rammed enough to flush all over, the surface was finished where necessary by a thick mortar made in the proportion of 1 cement to 6 sand, and applied with heavy brushes. Before placing any of the concrete, the bank back of the old concrete left in place was thoroughly rammed with iron railroad tampers, and the edge of the old concrete was scrubbed with water and a stiff brush and then coated with 1 to 4 grout, which was allowed to fill in the angle between the concrete and the slope. Just before placing the concrete the earth bank was well wet in order that moisture might not be drawn from the concrete while it was soft.

In order to make the new lining as waterproof as possible, a layer of asphalt was placed on top of the lower layer of concrete and brought up on the exposed edge of the old layer at the bottom of the new work. This, it was expected would make an elastic and watertight joint between the new and the old work.

Venezuela asphalt, "Crystal Brand," was used, being poured upon the top of the concrete layer and allowed to run down the slope, care being taken that the concrete was entirely and perfectly covered. After the first layer of asphalt was cool, a second layer was similarly applied, and the resulting sheet was about in. thick. Any inclination to crawl down the slope when exposed to the sun was readily stopped by throwing on a pailful of cold water. A most particular part of this work was to get the asphalt as hot and liquid as possible and yet not burn it. All of the concrete was protected from the sun and kept damp by being covered with strips of burlap, which were moistened by sprinkling.

The upper layer of concrete was composed of a much richer mixture of concrete than that used in the bottom layer, the proportions by volume being 1 cement, 1 sand, 1 stone dust, and 4 broken stone of the sizes mentioned above. On account of the steep slope it was possible to do only a little ramming, and the material was laid as wet as possible. To make this layer more impervious and also to obtain a smooth surface, the concrete was left about an inch below and a finish coat applied by expert granolithic finishers. This coating was applied as soon as it was possible to do so after the main layer was in place, but on account of the steepness and the liability of the wet concrete to flow, care had to be taken not to begin work too soon.

The top finishing coat was made in the proportion of 1 part cement, 1-2/3 part sand, and 3-1/3 parts stone dust. In order to help in bonding, the last ramming on the concrete was done with rammers studded with pieces of iron about 1 in. long and in. deep.

The finishing was done in three operations: The material was spread on the concrete and thoroughly worked into it by the finishers, using rough wooden floats; after this it was gone over and partially smoothed down with a thin steel float; and finally it was worked to give the finished appearance and an impervious surface.

The under layer of concrete was placed in a continuous sheet. The upper layer was put down in alternate strips, 10 ft, long (the whole length of the layer) and 5 ft. wide. These blocks were built up in forms, which were not removed until the concrete had set. Finally, the back or edge of the block toward the bank was well wet and thoroughly plastered, to prevent, as far as possible, the infiltration of any water. The plaster was mixed in the proportion of 1 part cement to 4 parts sand. When the forms were wholly removed, the space between the concrete and the bank was refilled, to within about 6 ins. of the top, with a clayey material previously excavated, and the space was filled and graded to the top of the bank with loam. During the work two holidays intervened; the men were also transported to and from the work. Charges were made for these items, amounting to $209.77, and this sum, together with the cost of installing the plant ($716.03) are proportionally charged against the work as follows:

Per cent. Total. Per cu. yd. Excavation 70.3 $651 $2.17 Lower concrete 12 111 1.16 Upper concrete 15.4 143 1.11 Back fill 2.3 21 .28

The detailed cost of repairing the reservoir lining is given in the following tabulations:

Excavation.

Rate. Per cu. yd. Foreman 9 5/9 days $4.00 $0.13 Engineman 12 3/9 days 3.00 .12 Carpenter 2 days 2.67 .02 Laborers 9 6/9 days 2.25 .07 Laborers 110 2/9 days 2.00 .73 Laborers 46 5/9 days 1.75 .27 Derrick 12 3/9 days 3.75 .15 Rails and cars 11 2/9 days 0.40 .02 Stove coal 3.05 tons 6.50 .07 Egg coal .95 tons 6.25 .02 —— Total, 300 cu. yds. 1.60

Estimated proportionate charge for plant installation and holidays 2.17 —— Grand total 3.77

Lower Layer Concrete. Rate. Per cu. yd. Foreman 3-7/9 days $4.00 $0.16 Engineer 2-3/9 days 3.00 0.07 Carpenters 7 days 2.67 0.20 Laborers 1-7/9 days 2.25 0.06 Laborers 89 days 2.00 1.87 Laborers 4 days 1.75 0.07 Derrick and engine 2-3/9 days 3.75 0.08 Rails and cars 2-2/9 days 0.40 0.01 Cement 106-3/8 bbls. 1.35 1.50 Sand 37.4 cu. yds. 1.10 0.43 Broken stone 117.9 tons 1.35 1.67 Egg coal .41 tons 6.25 0.03 Lumber 1.3 M. ft. 21.00 0.28 —— Total, 95.5 cu. yds. $6.43

Estimated proportionate charge for plant installation and holidays 1.16 —— Grand total $7.59

Upper Layer Concrete. Rate. Per cu. yd. Foreman 6-7/9 days $4.00 $0.21 Engineer 1-8/9 days 3.00 0.04 Carpenter 18-5/9 days 2.67 0.38 Laborers 1-7/9 days 2.25 0.03 Laborers 119-5/9 days 2.00 1.85 Derrick and engine 1-8/9 days 3.75 0.05 Rails and cars 8-3/9 days 0.40 0.03 Cement 176 bbls. 1.35 1.86 Sand 30.2 cu. yds. 1.10 0.26 Stone dust 41.6 tons 1.50 0.48 Broken stone 122.8 tons 1.35 1.28 Egg coal .2 tons 6.25 0.00 Lumber 4 M. ft. 21.00 0.65 Burlap 300 yds. 0.04 0.10 Nails 170 lbs. 0.05 0.03 ——

Total, 129.2 cu. yds. $7.25 Estimated proportionate charge for plant installation and holidays 1.11 —— Grand total $8.36

Back Plaster. Rate. Per cu. yd. Plasterer 3-8/9 days $5.40 $0.08 Plasterer 8/9 days 6.00 0.02 Plasterer 5-5/9 days 4.50 0.09 Laborers 9-3/9 days 2.25 0.08 Laborers 3/9 days 2.00 0.00 Cement 6 bbls. 1.35 0.03 Sand 3.3 cu. yds. 1.10 0.01 —— Total, 262 sq. yds. 0.32

Surfacing. Rate. Per cu. yd. Plasterer 7-6/9 days $5.40 $0.09 Plasterer 2-1/9 days 6.00 0.03 Plasterer 9-4/9 days 4.50 0.09 Laborers 12-8/9 days 2.25 0.06 Laborers 2-4/9 days 2.00 0.01 Cement 22 bbls. 1.35 0.06 Sand 5.07 cu. yds. 1.10 0.02 Stone dust 14 tons 1.50 0.04 —— Total, 460 sq. yds. $0.40

Asphalt. Rate. Per cu. yd. Foreman 1/9 day $4.00 $0.00 Asphalt man 11 days 2.00 0.05 Laborers 6 days 2.00 0.02 Asphalt kettle 11 days 1.50 0.03 Asphalt 3.9 tons 30.00 0.25 Asphalt mops 3.00 0.01 —— Total, 464 sq. yds. $0.37

Back Filling.

Rate. Per cu. yd. Foreman 1-3/9 days $4.00 $0.07 Laborers 23-3/9 days 2.00 0.62 Laborers 9 days 1.75 0.21 Rails and cars. 2-2/9 days 0.40 0.02 Loam 27-5/9 cu. yds. 1.25 0.46 ——- Total, 75 cu. yds. $1.38

Estimated proportionate charge for installing plant and holidays $0.28 ——- Grand total $1.66

Installing Plant.

Total. Foreman 15-4/9 days $4.00 $61.78 Sub-foreman 1 day 3.00 3.00 Engineer 8-4/9 days 3.00 25.33 Carpenter 3 days 2.67 8.00 Watchman 42 days 2.00 84.00 Laborers 17-4/9 days 2.25 38.36 Laborers 149-8/9 days 2.00 299.78 Double team 10 days 5.00 52.50 Single team 6 days 2.00 12.00 Single team 1 day 3.50 3.50 Teaming (total) 53.00 Derrick and engine. 11-4/9 days 3.75 49.92 Rails and cars 8-2/9 days 0.40 3.29 Broken stone 7.05 tons 1.35 9.52 Egg coal .6 ton 6.25 3.75 Kerosene 30 gal. 0.11 3.30 Oil 4 gal. 0.25 1.00 Spikes 220 lbs. 0.05 11.00 ———- Total $723.03

The cost of the concrete work in the lower and upper layers can be still further detailed as shown below:

Lower Layer Concrete. 95.5 cu. yds., 1-2-6 concrete.

Materials: Rate. Per cu. yd. Atlas cement 1.11 bbl. $1.35 $1.50 Sand .39 cu. yd. 1.10 0.43 Broken stone (.97 cu. yd.) 1.23 tons 1.35 1.66 Miscellaneous, plant, coal, etc. 1.28

Labor: Mixing and placing $2.09 Carpenter work on forms at $24.00 per M. .34 ——- Total per cu. yd. in place $7.30

Upper Layer Concrete. 129.2 cu. yds., 1-1-1-4 concrete.

Materials: Rate. Per cu. yd. Atlas cement 1.37 bbl. $1.35 $1.85 Sand .24 cu. yd. 1.10 0.26 Stone dust (.25 cu. yd.) .32 ton 1.50 0.48 Broken stone (.75 cu. yd.) .96 ton 1.35 1.30 Lumber 0.31 M. ft. 21.00 0.65 Miscellaneous, plant, etc. 1.32

Labor: Mixing and placing 1.85 Carpenter work on forms at $21.00 per M. 0.66 ——- Total per cu. yd. in place $8.37

The following approximate labor costs are also given: Transporting, erecting and removing derrick, $260.85. Equivalent time: Foreman, 6 days; engineer, 4 days; laborer, 85 days.

Transporting, laying and removing track, $125.03. Equivalent time: Foreman, 4 days; laborer, 40 days.

Caring for dump and disposing of surplus by rough grading, $70.28. Equivalent time: Foreman, 1 day; laborer, 33 days.

The total cost of the work was $3,503.66, divided up as follows:

Excavation $ 480.79 Lower layer concrete 614.15 Upper layer concrete 937.94 Back plaster 84.73 Surfacing 186.04 Asphalting 170.94 Back filling 103.27 Installing plant 716.03 Transportation and holidays 209.77 ————- Grand total $3,503.66

LINING JEROME PARK RESERVOIR.—The bottom of the reservoir that was lined covered 250 acres, and the concrete lining was 6 ins. thick. The lining was laid in alternate strips 16 ft. wide between forms set to grade. The concrete was mixed in 18 Ransome mixers provided with charging hoppers and mounted on trucks without boilers. Steam was supplied to the mixer engines from the boilers of the contractor's locomotives. One locomotive supplied steam for three or four mixers. Tracks were laid in parallel lines across the reservoir bottom from 150 to 200 ft. apart. Sand and stone were hauled in on these tracks. The sand was dumped in stock piles at intervals; the stone was shoveled from the cars directly into the charging hopper and the sand was delivered by wheelbarrows to the same hopper. Four men shoveled the stone for each mixer. To deliver the concrete from the mixer to the work required six men with wheelbarrows. Two men leveled off the concrete discharged by the barrows and two other men floated the surface by means of a straight-edge spanning the 16-ft. strips and riding on the forms. By using a wet but not sloppy concrete and moving the straight-edge back and forth a good surface was secured. The gang mixing and placing consisted of 20 men for each mixer and 18 gangs laid approximately 1 acres per 10-hour day. The gang organization and wages were as follows:

Item. Per 10 hours. 4 men shoveling stone at $1.50 $ 6.00 2 men wheeling sand at $1.50 3.00 2 men delivering cement at $1.50 3.00 1 man dumping mixer at $1.50 1.50 1 man tending engine and water at $1.50 1.50 6 men wheeling concrete at $1.50 9.00 2 men spreading concrete at $1.50 3.00 2 men leveling concrete at $1.50 3.00 1 foreman 3.00 ——— Total per day $33.00

These costs do not include the fraction of a day's labor for fireman or the cost of fuel.

RESERVOIR FLOOR, CANTON, ILL.—The following costs are given by Mr. G. W. Chandler for lining the bottom of a 16080-ft. reservoir with corners of 20-ft. radius and vertical brick sidewalls. A 1-3-7 crushed stone concrete was used; it was mixed by hand in batches of 2.7 cu. ft. cement, 9 cu. ft. sand and 20 cu. ft. stone. The sand and stone were measured separately, the sand and cement mixed dry, then shoveled into a pile with the rock, well wetted, shoveled over again and then shoveled into wheelbarrows. The stone had 40 per cent. voids and the sand 30 per cent. voids. The lining was 10 ins. thick including a -in. coat of 1-2 mortar spread and worked smooth with a trowel. The cost per cubic yard of the lining in place was as follows:

0.856 bbl. cement at $2.50 $2.14 10.1 bu. sand (100 lbs. per bu.) at 5 cts 0.58 0.857 cu-yd-stone at $2.17 1.86 Labor, mixing and placing at 19 cts. per hr. 0.80 ——- Total $5.38

RESERVOIR FLOOR, PITTSBURG, PA.—The following methods and costs of laying a reservoir floor are given by Mr. Emile Low, M. Am. Soc. C. E., for the Hiland Reservoir constructed at Pittsburg, Pa., in 1884, by contract. There were 7,681 cu. yds. of concrete in the floor which was 5 ins. thick and laid on a clay puddle foundation.

Natural cement costing $1.35 per barrel was used. The broken stone varied in weight from 147 to 152 lbs. per cu. ft.; it was quarried and hauled 20 miles by rail and then unloaded into small cars and hauled mile to the reservoir. The cost of the stone per cubic yard delivered was:

Quarrying, per cu. yd. $0.45 Breaking, per cu. yd. 0.35 Transporting, per cu. yd. 0.50

Total $1.30

The sand was obtained on the site at the cost of excavation, or 1 cts. per bushel.

The method of proportioning and mixing the concrete was as follows: Platforms 1016 ft. of 2-in. plank were laid on the puddle foundation and by these were set 541-ft. boxes on legs. Into these boxes 1 bbl. of cement and 2 bbls. of sand were emptied and thoroughly mixed dry, then mixed with water to a thin grout. Five barrels of stone were placed on the platform and thoroughly wetted; the grout was then emptied over the stone and the two turned over three times with shovels. The concrete was rammed until the mortar flushed to the surface. The following costs cover various periods as follows:

Two Days Work (101 cu. yds.): Total. Per cu. yd. 27 laborers, 2 days, at $1.25 $72.90 $0.7217 1 foreman, 2 days, at $2.50 5.00 0.0495 ——— ———- Total $77.90 $0.7712

One Month's Work (1,302 cu. yds.): 642 days, laborers, at $1.35 $ 866.70 $0.6649 17 days, water boy, at $0.60 10.20 0.0078 22 days, foreman, at $2.50 55.00 0.0421 ——— ———- Total $931.90 $0.7148

Two Days Work (101 cu. yds.): Total. Per cu. yd. 27 laborers, 2 days, at $1.25 $72.90 $0.7217 1 foreman, 2 days, at $2.50 5.00 0.0495 ——— ———- Total $77.90 $0.7712

One Month's Work (1,302 cu. yds.): 642 days, laborers, at $1.35 $ 866.70 $0.6649 17 days, water boy, at $0.60 10.20 0.0078 22 days, foreman, at $2.50 55.00 0.0421 ——— ———- Total $931.90 $0.7148

Total Work (7,861 cu. yds.):

Quarrying stone $0.45 Transporting stone 0.50 Breaking stone 0.35 1-1/3 bbl. natural cement 1.80 8 bu. sand 0.10 Water 0.05 Labor mixing and laying at $1.25 0.75 Incidentals 0.05 ——- Total $4.05

The contract price was $6 per cu. yd.



CONSTRUCTING A SILO.—The form construction shown in Fig. 286 was employed in building a silo 28 ft. high, 22 ft. 3 ins. interior diameter, and having 6-in. walls. The bottom of the silo was made 9 ins. thick and set 2 ft. below the surface. The reinforcement consisted of ten 23/16-in. rings spaced equally in the lower half and of woven wire fencing in the upper half. The iron rings were hoops removed from an old wooden silo. The concrete was a 1-6 mixture of Portland cement and sandy gravel. Figure 286 is a section through the forms. There were twenty T-shaped posts, which extended perpendicularly from the ground to a height of 28 ft., being secured at top and bottom by a system of guy ropes and posts. The rings, of which there are four, two inside and two outside, were built of weather boards with their edges reversed. Four thicknesses of board were used in each ring. The curbing consisted of 28-in. sticks 4 ft. long. Wedges driven between the vertical posts and the rings held the latter in place. When the forms were to be removed the wedges were knocked out and the rings sprung enough to permit the removal of the curbing. The rings were then pushed up and fastened in place for another section. The average rate of progress was one 4-ft. section per day. The forms were filled in the afternoon and moved up the following forenoon. Five-foot sections could have been built just as readily.

The work was all done by farm laborers hired by the month and 100 man-days of such labor were required, excluding seven days work of a mason brushing and troweling the surface. The cost of the work, not including the old hoop iron or the old lumber used in forms, was as follows:

Item. Total. Per cu. yd. Cement $100.00 $2.62 Gravel and sand 35.00 0.92 1 20-rod roll of fencing 5.20 0.01 New lumber 18.00 0.47 100 days labor at $1.75 175.00 4.60 7 days mason troweling at $3.50 24.50 0.64 ———- ——- Total, 38.2 cu. yds. $357.70 $9.26

The external area of the silo is 1,950 sq. ft., which makes the cost of brushing and troweling 1 cts. per sq. ft. There were about 2,300 ft. B. M. of lumber used in the forms, or about 61 ft. B. M. per cu. yd. of concrete.

GROINED ARCH RESERVOIR ROOF.—The following data are given by Mr. Allen Hazen and Mr. William B. Fuller, in Trans. Am. Soc. C. E. 1904. The concrete was mixed in 5-ft. cubical mixers in batches of 1.6 cu. yds. at the rate of 200 cu. yds. per mixer day. One barrel of cement, 380 lbs. net, assumed to be 3.8 cu. ft., was mixed with three volumes of sand weighing 90 lbs. per cu. ft., and five volumes of gravel weighing 100 lbs. per cu. ft. and having 40 per cent voids. On the average 1.26 bbls. of cement were required per cu. yd. The conveying plant consisted of two trestles (each 900 ft. long) 730 ft. apart, supporting four cableways. The cables were attached to carriages, which ran on I-beams on the top of the trestles. Rope drives were used to shift the cableways along the trestle. Three-ton loads were handled in each skip. The installation of this plant was slow, and its carrying capacity was less than expected. It was found best to deliver the skips of concrete to the cableway on small railway track, although the original plan had been to move the cableways horizontally along the trestle at the same time that the skip was traveling.

The cost of mixing and placing the concrete was as follows:

Per cu. yd. Measuring, mixing and loading $0.20 Transporting by rail and cables 0.12 Laying and tamping floors and walls including setting forms 0.22 ——- Total $0.54

The cost of laying and tamping the concrete on the vaulting was 14 cts. per cu. yd. The vaulting is a groined arch 6 ins. thick at the crown and 2 ft. thick at the piers.

The lumber of the centering for the vaulting was spruce for the ribs and posts, and 1-in. hemlock for the lagging. The centering was all cut by machinery, the ribs put together to a template, and the lagging sawed to proper bevels and lengths. The centers were made so that they could be taken down in sections and used again. The cost of centering was as follows:

Labor on centers covering 62,560 sq. ft.

Foreman, 435 hrs. at 35 cts. $ 152.25 Carpenters, 4,873 hrs. at 22 cts. 1,096.42 Laborers, 3,447 hrs. at 15 cts. 517.05 Painters, 577 hrs. at 15 cts. 86.55 Teaming, 324 hrs. at 40 cts. 121.60 ————- Total labor building centers, 313 M. at $6.37 $1,973.87

Materials for centers covering 62,560 sq. ft.

313,000 ft. B. M. lumber, at $18.20 $5,700.00 3,700 lbs. nails, at 3 cts. 111.00 8 bbls. tar, at $3 24.00 ————- Total $5,835.00

These centers covered two filters, each having an area of 121-1/3258 ft. There were six more filters of the same size, for which the same centers were used. The cost of taking down, moving and putting up these centers (313 M.) three times was as follows:

Foreman, 2,359 hrs. at 35 cts. $ 825.65 Carpenters, 12,766 hrs. at 22 cts. 2,872.35 Laborers, 24,062 hrs. at 15 cts. 3,609.30 Team, 430 hrs. at 40 cts. 172.00 3,000 ft. B. M. lumber, at $20 60.00 3,000 lbs. nails, at 3 cts. 90.00 ————-

Total cost of moving centers to cover 196,660 sq. ft. $7,629.30



The cost of moving the centers each time was $8.10 per M., showing that they were practically rebuilt; for the first building of the centers, as above shown, cost only $6.37 per M. In other words, the centers were not designed so as to be moved in sections as they should have been. Although the centers were used four times in all, the lumber was in fit condition for further use. The cost of the labor and lumber for the building and moving of these centers for the 8 filter beds, having a total area of 259,220 sq. ft., was $15,438, or 6 cts. per sq. ft.

GRAIN ELEVATOR BINS.—In constructing cylindrical bins 30 ft. in diameter and 90 ft. high for a grain elevator the forms shown by Fig. 287 were used. For the inside wall a complete ring of lagging 4 ft. high nailed to circular horizontal ribs of 28-in. planks was used. For the outside wall two, three or four segments fitting the clear spaces between adjoining tanks were used, these panel segments being also 4 ft. high. The inside and outside rings were held together by yokes constructed as shown, and bolted to the inner and outer ribs. A staging built up inside the tank carried jack screws, on which were seated the inner legs of the yokes.



CHAPTER XXIII.

METHODS AND COST OF CONSTRUCTING ORNAMENTAL WORK.

The safest rule for ornamental work is to leave its construction to those who make a specialty of such work. This is perfectly practicable in most concrete structures having ornament. Bridge railings can be and usually are made up of separately molded posts, balusters, bases and rail. Ornamental columns in building work, keystones, medallions, brackets, dentils, rosettes, and cornice courses can be similarly molded and placed in the structure as the monolithic work reaches the proper points. The general constructor, therefore, can readily delegate these special parts of his concrete bridge or building to specialists at frequently less cost to himself and nearly always with greater certainty of good results than if he installed molds and organized a trained gang for doing the work.

Good concrete ornament is not alone a matter of good design. It is also a matter of skilled construction. Nearly anyone can mold an ornament, but few can mold an ornament which is durable. To produce clean, sharp lines and arises which will endure, the molder must have special knowledge and familiarity with the action of cement and of concrete mixtures, both in molding and on exposure to the elements. This is knowledge that the general concrete worker rarely possesses but which the ornament molder does possess if he knows his business. Special work is always best left to the specialist.

While the more intricate ornamental work is best done by sub-contract, so far at least as the actual molding of the ornaments is concerned, there is a large amount of simple paneling and molding which the general practitioner not only can do but must do. Knowledge of the best methods of doing such work is essential and it is also essential that the constructor should know in a general way of the special methods of molding intricate ornaments.

SEPARATELY MOLDED ORNAMENTS.—The cement for ornamental work must be strong and absolutely sound. Where an especially light color is wished a light colored cement is desirable. So called white cements are now being manufactured. Lafarge cement, a light colored, non-staining cement made in France, gives excellent results. Of American cements, Vulcanite cement has a light color, and next to it in this respect comes Whitehall cement. A light colored ornament can, however, be secured with any cement by using white sand or marble or other white stone screenings. Some authorities advocate this method of securing light colored blocks as always cheaper and usually superior to the use of special cements. The choice between the two methods will be governed by the results sought; where as nearly as possible a pure white is desired it stands to reason that a white or nearly white cement will give the better results.

In the matter of sand and aggregate for ornamental work, the kinds used will ordinarily be the kinds that are available. They must conform in quality to the standard requirements of such materials for concrete work. Where special colors or tints are wanted they can be secured by using for sand and aggregate screenings from stones of the required color. This is in all respects the best method of securing colored blocks, as the color will not fade and the concrete is not weakened. A great variety of pigments are made for coloring concrete; these colors all fade in time, and with few exceptions they all weaken the concrete. The mixtures used in ornamental work will depend upon the detail of the ornament and upon whether color is or is not required. Generally a rich mixture of cement and sand or fine stone screenings will be used for the surface and will be backed with the ordinary concrete mixture. A surface mixture of fine material is necessary where clear, sharp lines and edges or corners are demanded.

The molds used for ornament are wooden molds, iron molds, sand molds and plaster of Paris and special molds. Each kind has its field of usefulness, and its advantages over the others. They will be considered briefly in the order named.

Wooden Molds.—Wooden molds are perhaps the best for general work where plain shapes and not too delicate ornamentation are wanted. They give the best results only with a quite dry and rather coarse grained surface mixture. If a wet mixture is used such water as flushes to the surface cannot escape and small pits and holes are formed, which necessitates grout or other finishing. The following are examples of wooden mold work:

In constructing a five-span reinforced concrete arch bridge at Grand Rapids, Mich., in 1904, the railings and ornamental parts of the bridge, such as keystones, brackets, consols, dentiles and panels, were cast in molds and set in place much as cut stone would be. Special molds were employed for each of these different shapes. These molds were plastered with an earth damp mortar composed of 1 part cement and 2 parts fine sand, which was followed up with a backing of wet concrete composed of 1 part cement, 2 parts sand and 3 parts broken stone passing a -in. ring. The facing mortar was made 1 ins. thick. The castings cannot be told from dressed stone at a few feet distance.

The part elevation and sections in the drawings of Fig. 288 show the arrangement of the various castings to form the completed railing, coping, etc. To specify, A is the arch ring, B the brackets, C the coping, and D, E, F, respectively, the base, balusters and rail of the bridge railing. The blocks G and H show the keystone and railing post. The forms or molds for each of these parts are shown by the other drawings of Fig. 288. A description of each of these forms follows:

The keystones were molded in wooden forms, consisting of one piece, a, forming the top and front; of two side pieces, f, of a bottom consisting of two parts, b and c; and of a back piece, g. The back and side pieces are stiffened with 23-in. pieces, and the front, sides and back are held together by yokes or clamps. The front of the mold was the only portion calling for particular work, and this was made of boards laminated together.

The bracket molds consisted of two side pieces provided with grooves for receiving the front and back pieces, and with slots for tie rods clamping the whole mold together. It will be noted also that the side pieces had nailed to them inside a beveled strip to form a groove in each side of the cast block. The purpose of this groove was to provide a bond to hold the bracket more firmly in the adjoining concrete of the wall. The bottom of the mold was formed by a 2-in. plank, and when the concrete had been tamped in place the forms were removed, and the bracket was left on the bottom to set. It may be noted here that a goodly number of the brackets showed a crack at the joint marked x caused by tamping at the point y. In construction the bracket castings were set at proper intervals on the spandrel walls, which had been completed up to the level of the line X Y. The coping course was then built up around the bracket blocks to the level of the bottom of the railing base.



The mold or form for the coping course was designed to build the coping in successive sections, and was built up around the bracket blocks, and supported from the centers as shown by the drawings. To form the expansion joints in the coping course there were inserted across the mold at proper intervals a short iron plate in. thick, cut to fit. The cutting of this plate was found to be a slow operation.

The forms for the base of the railing (Section D) consisted of 1-in. stock for the sides, and -in. stock for the slopes. They extended across the arch, and were held together by a very simple though very efficient clamp. This consisted of two 2333-in. pieces nailed to a 2317-in. piece by means of galvanized iron strips. About half-way down the long pieces, a -in. rod was run through, and secured up against blocks, h, placed about 56 ins. apart. These blocks were removed as the concrete was put in place. It will be noticed from the cross-section of the railing that the balusters are set into sockets formed in the top of the base course. These sockets were formed by means of the mold shown at W and Z.

In casting the balusters, Section (E), a 3/8-in. cast iron mold, consisting of four iron sides and an iron top, was used. Originally there were two end plates of iron, but it was found more convenient to have the bottom one of wood and allow the cast spindle to stand and set. The mold was held together by -in. bolts. It would have been more practical to have had the side casting composed of two parts.

The form for the railing is built up around the tops of the spindles. The bottom piece is 19 ins., to which 4-in. ogee molding is nailed. The sides are of 1-in. stock, and are clamped together. The top is finished off with a trowel.

The mold for the posts is made in four parts, which fit together at the top and bottom by a bevel joint, as shown in the one-fourth section. The broad sides rest against the narrow ones, and are held against the same by means of -in. rods running through 23-in. stock: 2-in. projections of the broad sides facilitate the removal of the form from the completed post.



In constructing a concrete facade for a plate girder bridge at St. Louis. Mo., the railing above the base was constructed of separately molded blocks as follows: The balusters were cast in plaster molds. To make these molds a box square in plan and the height of the baluster was constructed of wood and cut vertically into three sections. The inside lateral dimensions of this box were made 6 ins. greater than the largest dimension of the baluster. A full size wooden pattern of the baluster was set up and the three sections of the box were set around it. Sheets of thin galvanized metal, with their inner edges cut to conform to the curves of the baluster, were inserted in the joints of the assembled box so as to divide the vacant space between the pattern and the box into vertical sections.



A mixture of 1 part Portland cement and 1 part plaster of Paris, made wet, was then poured around the pattern until the box was filled. When this mixture had become hard, the box was taken down, leaving a plaster and cement casing separated into three parts by the sheets of galvanized metal. This casing was separated from the pattern and given a coat of shellac on the inside. Four or five molds of this description were cast. To cast a baluster, the sections were assembled and a -in. corrugated bar was set vertically in the center. A mixture of 1 part Portland cement and 3 parts sand was then poured into the mold and allowed to harden. The molds for the urns on the railing post and the balls on the end posts were made in exactly the same manner as the baluster molds. The construction of the railing posts is shown by the drawings of Fig. 289. Referring first to the end posts, it will be seen that they were molded in place in seven sections marked A, B, C, E, F, and G. The construction of the mold for each section is shown by the correspondingly lettered detail. The intermediate posts were built up of the separately molded pieces I, K and H. The costs of molding the several parts were: Balusters, 60 cts. each; hand rail, 40 cts. per lin. ft. The six intermediate posts cost $12 each, and the four end or newel posts cost $75 each.



In constructing the 72-ft. span-ribbed arch bridge over Deer Park Gorge, near La Salle, Ill., a hand railing of the design shown by Fig. 290, was used. In constructing this railing, the posts were molded in place, but the open work panels between posts and the hand rail proper were molded separately and set in place between the posts as indicated. For molding the panels a number of boxes constructed as shown by Fig. 291, were used. These were simple rectangular boxes on the bottom boards of which were nailed blocks of the proper shape and in the proper position to form the openings in the railing. The bottom of the form was first plastered with mortar, then the concrete was filled in and plastered on top. As soon as the concrete had begun to set the blocks were removed so that final setting could take place without danger of cracking. When the concrete had set so that the panel could be safely handled, it was removed from the form and stored until wanted. The hand rail for each side was molded in two pieces in forms constructed as shown by Fig. 292. The total cost of the railing in place was about $2 per lineal foot. The concrete was a 1-2-4 mixture of screenings and 7/8-in. broken stone.

Iron Molds.—Iron molds have the same disadvantages as wooden molds in the use of wet mixtures. They can be made to mold more intricate ornaments, and in the matter of durability, are, of course, far superior to wood. Iron molds can be ordered cast to pattern in any well equipped foundry. Many firms making block machines also make standard column, baluster, ball and base, cornice, and base molds of various sizes and patterns. These molds are made in two, three or more sections which can be quickly locked together and taken apart. A column mold, for example, will consist of a mold for the base, another for the shaft, and a third for the capitol, each in collapsible sections. Where the pattern of the shaft changes in its height, two shaft molds are commonly used, one for each pattern. Prices of iron molds are subject to variation, but the following are representative figures: Plain baluster molds 14 to 18 ins. high, $7.50 to $10 each; fluted square balusters, 14 to 18 ins. high, $10, each; ball and base, 10 to 18-in. balls, $15 to $25 each; fluted Grecian column, base, capitol and one shaft molds, $30; Renaissance column, base, capitol and two shaft molds, $45.

Sand Molding.—Molding concrete ornaments in sand is in all respects like molding iron castings in a foundry. Sand molding gives perhaps the handsomest ornament of any kind of molding process, the surface texture and detail of the block being especially fine. It is, however, a more expensive process than molding in wooden or iron molds, since a separate mold must be made for each piece molded. The process was first employed and patented in 1899, by Mr. C. W. Stevens, of Harvey, Ill., and for this reason it is often called the Stevens process. Sand molded ornaments and blocks are made by a number of firms to order to any pattern. The process as employed at the works of the Roman Stone Co., of Toronto, Ont., is as follows: The stone employed for aggregate, is a hard, coarse, crystalline limestone of a light grey color, being practically 97 per cent. calcium carbonate, with a small percentage of iron, aluminia and magnesia. Nothing but carefully selected quarry clippings are used and these are crushed and ground at the factory and carefully screened into three sizes, the largest about the size of a kernel of corn. Daily granulometric tests are made of the crusher output to regulate the amount of each size got from the machines. It has been found that next in importance to properly graded aggregates is the gaging of the amount of water used in the mixture. This is done by an automatically filled tank into which lead both hot and cold water and in which is fixed a thermometer to properly regulate the temperature. In gaging the mix about 20% of water is used, but of course when the cast is made the surplus is immediately drawn off into the sand, where it is retained and serves as a wet blanket to protect the cast and supply it with the proper amount of water during crystallization. Experiments seem to indicate that about 15% by weight gives the greatest amount of strength of mortar at the age of six months, while, giving less strength at shorter time tests than mortar gaged with a smaller percentage of water.

The method of handling the mix and casting is quite simple and almost identical with the practice in iron foundries. The mixture is made in a batch mixer to about the same consistency as molasses, from which it is poured into a mechanical agitator and carried about the foundry by a traveling crane. This agitator is so constructed that it keeps the materials in motion constantly and prevents their segregation. In each cast is inserted the proper reinforcing rods, lifting hooks and tie rods, and the casts are allowed to remain for a proper period in the wet sand after they are poured; they are then taken to the seasoning room which is kept at as constant a temperature as it is practical to maintain. Each cast is marked with the number which determines its location in the building and the date it was cast, and it is then kept in the storage shed a fixed time before shipping.

Records are kept of each cast made and the company is able to get, as in mills rolling structural steel, the exact number and location of all casts made from the same mix. Careful records are always kept of the tests of cement and material, and test cubes are made from each consignment of cement so tested; in this way all danger of defective stone through inferior cement is eliminated. The patterns used in making the molds and the method of molding are quite similar to ordinary iron foundry practice except that the sand used is of special nature. The finish of the stone is generally tooled finish molded in the sand, the different textures of natural stone being produced by the veneering of the pattern with thin strips of wood which are run through a machine producing the different finishes. Each stone is provided with setting hooks cast in the blocks which take the place of the ordinary lewis holes used in cut stone.

Plaster Molds.—Plaster of Paris molds are made from clay, gelatin or other patterns in the usual manner adopted by sculptors. They are particularly adapted to fine line and under cut ornaments. The concrete is poured into the plaster mold and after the cement has become hard, the plaster is broken or chiseled away, leaving the concrete exposed. Two examples of excellent work in intricate concrete ornaments are furnished by the power house for the Sanitary District of Chicago, and by the State Normal School building, at Kearney, Neb. In the power house, the ornamental work consisted of molded courses, cornice work; and particularly of heavy capitals for pilasters. These capitals were very heavy, being 7 ft. long and of the Ionic design. These were made from plaster molds; made so as to be taken apart or knocked down and to release in this way, perfectly. There were also scrolls, keystones and arches in curved design over all of the 40 windows. None of this ornament was true under cut work. In building the Normal School building, Corinthian capitals, in quarters, halves, corners and full rounds were made in plaster molds. There were some 30 of these capitols. They were made in solid plaster molds; the molds having been cast in gelatine molds, one for each capitol. Into these, the concrete was tamped, made very wet, and after the concrete had hardened, the plaster cast was chiseled away. This was very easily accomplished. These capitols were true Corinthians, having all the floriation and under-cut usually seen in such capitols.

ORNAMENTS MOLDED IN PLACE.—Molding ornaments in place is usually, and generally should be, confined to belt courses, cornices, copings and plain panels. Relief work, like keystones, scrolls or rosettes, can be molded in place if desired, by setting plaster molds in the wooden forms at the proper points. This method is often advantageous in bridge work, where comparatively few ornaments are required, such as keystones.



The construction of forms for ornamental work in place is best described by taking specific examples. Figure 293, shows the face form for the arch ring, spandrel wall and cornice or coping course of the Big Muddy River Bridge on the Illinois Central R. R. The section is taken near the crown of the arch. The lagging only is shown; this was, of course, backed with studding. The point to be noted in this form is the avoidance of any approach to under cut work; there are, in fact, very few straight cut details. This brings up a point that must be carefully watched if trouble is to be avoided, namely, the construction of the form work in sections which can be removed without fracturing the ornament. To illustrate by an assumed example, supposing it is required to mold the wall and cornice shown by Fig. 294. It is clear that if the backing studs are in single pieces, notched as shown, the forms cannot be removed without fracturing at least the corner A. If the studs and lagging be constructed in two parts, separated along the line a b, the form is possible of removal if great care is used without damage to the concrete. The construction shown by this sketch does not greatly exaggerate matters. Figure 295 shows a wall form that has been given several times as a presumably good example in which, as will be seen it is impossible to remove the board a, without breaking the concrete even if the narrow face were not broken by the swelling of the lumber before ever it became time to take down the forms.



This matter of making provision for the swelling of the forms is another point to be watched. Referring again to Fig. 294 it will be seen that the swelling of the lagging, even if the cornice instead of being under cut at A were straight cut on the line c d, is liable so to crowd the lagging into the corner A and B that the concrete is cracked along the lines e f or g h. A suggested remedy for this danger is shown by Fig. 296. At a distance of every 3 or 4 ft. insert a narrow piece of lagging a and behind these lagging strips cut notches b in the studs. When the concrete has got its initial set pull back the lagging strip a into the notches b, leaving an open joint to provide for expansion due to swelling.



In constructing a concrete facade for a plate girder bridge at St. Louis, Mo., the form shown by Fig. 297 was used. The completed facade is shown by Fig. 298. The ceiling slab was first built and allowed to set and then the forms were erected for the frieze and coping. After these were molded the forms were continued upward as shown for the base of the railing. Above this point the several parts were separately molded as shown by Fig. 285 previously described. Molded in this manner the ceiling cost 25 cts. per sq. ft.; the frieze and coping cost $2 per lin. ft., and the railing base cost 45 cts. per lin. ft. In constructing the concrete abutments of this same structure use was made of the forms shown by Fig. 299. These abutments had curved wing walls and for molding these girts cut to the radii of the curves were fastened to the studs and vertical lagging was nailed to the girts. All the lagging was tongue and groove stuff.



In constructing an open spandrel arch bridge at St. Paul, Minn., the cornice form shown by Fig. 300, supported as shown by Fig. 301, was used. The particular feature of this form was the use of a lath and plaster lining to the lagging. This lining was used for all exposed surfaces of the bridge. So called patent lath consisting of boards with parallel dovetail grooves and ridges was used. This was plastered with cement mortar and the concrete was deposited directly against the plaster after smearing the plaster surface with boiled linseed oil. This lining is stated to have given an excellent surface finish to the concrete. It cost 55 cts. per sq. ft. for materials and labor. A section of the balustrade and cornice is shown by Fig. 302. The posts, balusters and railing were molded separately. The balusters were molded in zinc molds. At first some trouble was had in getting good casts on account of air pockets. This was largely done away with by filling the mold as compactly as possible and then driving a -in. iron rod through the center vertically; this rod crowded the concrete into all parts of the mold and also served to strengthen the baluster. The baluster molds were made in two parts; this proved a mistake—three parts would have been better.



CHAPTER XXIV.

MISCELLANEOUS DATA ON MATERIALS, MACHINES AND COSTS.

The following cost data comprise such miscellaneous items as do not properly come in the preceding chapters. They are given not as including all the miscellaneous purposes for which concrete is used but as being such items of costs as were secured in collecting the more important data given in preceding sections.



DRILLING AND BLASTING CONCRETE.—Concrete is exceedingly troublesome material in which to drill deep holes, and this statement is particularly true if the concrete is green. The following mode of procedure proved successful in drilling 1-in. anchor bolt holes 6 ft. and over in depth in green concrete. The apparatus used is shown by Fig. 303, re-drawn from a rough sketch made on the work by one of the authors, and only approximately to scale. The drill is hung on a small pile driver frame, occupying exactly the position the hammer would occupy in a pile driver, and is raised and lowered by a hand windlass. By this arrangement a longer drill could be used than with the ordinary tripod mounting and less changing of drills was necessary. A wide flare bit was used, permitting a small copper pipe to be carried into the hole with the drill; through this pipe water was forced under pressure, carrying off the chips so rapidly that no wedging was possible. By this device drilling which had previously cost over 25 cts. a hole was done at a cost of less than 5 cts. a hole.

In removing an old cable railway track in St. Louis, Mo., holes 8 ins. deep were drilled in the concrete with a No. 2 Little Jap drill, using a 1-in. bit and air at 90 lbs. pressure. A dry hole was drilled, the exhaust air from the hollow drill blowing the dust from the hole keeping it clean. The concrete was about 18 years old and very hard. Two holes across track were drilled, one 10 ins. inside each rail; lengthwise of the track the holes were spaced 24 ins. apart, or four pairs of holes between each pair of yokes.

Common labor was used to run the drills and very little mechanical trouble was experienced. Three cars were fitted up, one for each gang, each car being equipped with a motor-driven air compressor, water for cooling the compressors being obtained from the fire plugs along the route. The air compressors were taken temporarily from those in use in the repair shops, no special machines being bought for the purpose. Electricity for operating the air compressor motors was taken from the trolley wire over the tracks. The car was moved along as the holes were drilled, air being conveyed from the car to the drills through a flexible hose. Two drills were operated normally from each car. One of the air compressors was exceptionally large and at times operated four drills. The total number of holes drilled in the reconstruction of the track was 31,000. The total feet of hole drilled was 20,700 ft.

With the best one of the plants operating two to three drills 30 8-in. holes, or 20.3 ft. of hole, were drilled per hour per drill at a labor cost of 2.7 cts. per foot.

For blasting, a 0.1-lb. charge of 40 per cent. dynamite was used in each hole. A fulminating cap was used to explode the charge, and 12 holes were shot at one time by an electric firing machine. The dynamite was furnished from the factory in 0.1-lb. packages, and all the preparation necessary on the work was to insert the fulminating cap in the dynamite, tamp the charge into the hole and connect the wires to the firing machine. In order to prevent any damage being done by flying rocks at the time of the explosion, each blasting gang was supplied with a cover car, which was merely a flat car with a heavy bottom and side boards. When a charge was to be fired, this car was run over the 12 holes and the side boards let down, so that the charge was entirely covered. This work was remarkably free from accidents. There were no personal accident claims whatever, and the total amount paid out for property damages for the whole six miles of construction was $685. Most of this was for glass broken by the shock of explosion. There was no glass broken by flying particles. The men doing this work, few of whom had ever done blasting before, soon became very skillful in handling the dynamite, and the work advanced rapidly. The report made by the firing of the 12 holes was no greater than that made by giant fire-crackers.

For the drilling and blasting the old rail had been left in place to carry the air compressor car and the cover car. After the blasting, this rail was removed and the concrete, excavated to the required depth. In most cases the cable yokes had been broken by the force of the blast. Where these yokes had not been broken, they were knocked out by blows from pieces of rail. The efficacy of the blasting depended largely upon the proper location of the hole. Where the holes had been drilled close to the middle of the concrete block, so that the dynamite charge was exploded a little below the center of gravity of the section, the concrete was well shattered and could be picked out in large pieces. Where the hole had been located too close to either side of the concrete block, however, the charge would blow out at one side and a large mass of solid concrete would be left intact on the other side. The total estimated quantity of concrete blasted was 6,558 cu. yds., or 0.2 cu. yd. of concrete per lineal foot of track. The cost of the dynamite delivered in 0.1 lb. packages was 13 cts. per pound. The exploders cost $0.0255 each.

The cost of drilling and blasting was as follows:

Item. Per mile. Per lin. ft. Per cu. yd. Labor, drilling $ 89.76 $0.017 $0.085 Blasting labor and materials. 285.12 0.054 0.268 ———- ——— ——— Total drilling and blasting. $374.88 $0.071 $0.353



The cost of blasting with labor and materials, separately itemized, was as follows, per cubic yard:

Dynamite and exploders $0.192 Labor 0.076 ——— Total $0.268

Two cubic yards of concrete were blasted per pound of dynamite.

BENCH MONUMENTS, CHICAGO, ILL.—The standard bench monuments, Fig. 304, used in Chicago, Ill., are mostly placed in the grass plot between the curb and the lot line, so that the top of the iron cover comes just level with the street grade or flush with the surface of the cement walk. The monument consists of a pyramidal base 6 ft. high and 42 ins. square at the bottom, with a -in.2-ft. copper rod embedded, and of a cast iron top and cover constructed as shown by the drawing. Mr. W. H. Hedges, Bench and Street Grade Engineer, Department of Public Works, Chicago, Ill., gives the following data regarding quantities and cost. The materials required for each monument are: 1.78 cu. yd. crushed stone, 0.6 cu. yd. torpedo sand, 1 bbls. cement, 60 ft. B. M. lumber, one 24-in. copper rod, one top and cover. A gang consisting of 1 foreman, 4 laborers and 2 teams construct from one to three monuments per day, the average number being two per 8-hour day. In 1906 the average cost of the monuments was $24.12 each, based on above material and labor charges.



POLE BASE.—Figure 305 shows a concrete base for transmission line poles invented by Mr. M. H. Murray, of Bakersfield, Cal., and used by the Power Transit & Light Co. of that city. These bases are molded and shipped to the work ready for placing. They weigh about 420 lbs. each. One base requires 37 lbs. of 2-in. steel bar, 40 lbs. of Portland cement, 3 cu. ft. of broken stone or gravel and enough sand to fill the form or mold, which is 1010 ins. by 4 ft. Unskilled labor is employed in the molding and two men can mold ten bases per 8-hour day. The cost of molding is as follows per base:

2 men at $2 per day $0.40 Brace irons per set 2.50 1-9 cu. yd. stone at $4.05 0.45 40 lbs. cement at 1 cts. 0.60 Sand 0.15 ——- Total cost $4.10

Two men at $2 per day each set five bases in eight hours, making the cost of setting 80 cts. per base. The bases were sunk to a depth of 3 ft. 3 ins. In many cases they were placed under poles without interrupting service by sawing off the pole, dropping it into the ground, placing the new base and setting the sawed-off pole on it and bolting up the straps.

MILE POST, CHICAGO & EASTERN ILLINOIS R. R.—The dimensions of the post are shown by Fig. 306. Each post weighs 498 lbs. They are made when other concrete work is being done. The form is laid flat, with the molds for the letters on the bottom, and bottom and sides are plastered with mortar, which is backed up with a 1-1-2 stone concrete. The cost of the post is given as follows:

barrel of cement at $2 $0.50 267 lbs. crushed stone 0.01 133 lbs. sand 0.01 1-1/3 hours labor at 15 cts. 0.20 1/3 hour carpenter changing letters at 25 cts. 0.08 Coloring cement 0.02 ——- Total $0.82

BONDING NEW CONCRETE TO OLD.—Concrete which has set hard has a surface skin or glaze to which fresh concrete will not adhere strongly unless special effort is made to perfect the bond. Various ways of doing this are practiced. The most common is to clean the hardened surface from all loose material and give it a thorough wash of cement grout against which the fresh concrete is deposited and rammed before the grout has had time to set. Washing the old surface with a hose or scrubbing it with a brush and water improves the bond, as does also the hard tamping of the concrete immediately over the joint. Mortar may be used in place of grout. The thorough cleansing of the surface is, however, quite as essential as the bonding coat, in fact in the opinion of the authors it is more essential. As a rule, a good enough joint for ordinary purposes can be got by tamping the fresh concrete directly against the old concrete, without grout or mortar coating, if the surface of the latter is thoroughly cleaned by scrubbing and flushing. The secret of securing a good bond between fresh concrete and concrete that has set lies largely in getting rid of the glaze skin and the slime and dust which forms on it. Washing will go far toward doing this. The glaze skin can be removed entirely by acid solutions, but the acid wash must be flushed free from the surface before placing the fresh concrete. Ransomite, made by the Ransome Concrete Machinery Co., Dunellen, N. J., is a prepared acid wash which to the authors' knowledge has given excellent success in a number of cases. The glaze coat can also be removed by picking the hardened surface, but the picking should be followed by washing to remove all loose chips and dust.

DIMENSIONS AND CAPACITIES OF MIXERS.—In planning plant lay-outs it is often desirable to know the sizes, capacities, etc., of various mixers in order to make preliminary estimates. Tables XXII to XXXIII give these data for a number of the more commonly employed machines. The Eureka, the Advanced and the Scheiffler mixers are continuous mixers and the others are batch mixers.

Table XXII—Sizes, Capacities and Weights of Advanced Mixers. Cement Machinery Co., Jackson, Mich.

Height ground to hopper top 3' 6" Width over all 3' 6" Length over all on trucks 10' 6" Capacity per hour, cu. yds. 25 to 75 Horsepower, engine 2 Weight: On trucks, without power, lbs. 1,700 On trucks, steam engine 2,000 On trucks, gas engine 2,200 On trucks, steam engine and boiler 2,500

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