Concrete Construction Part 60

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

[Ill.u.s.tration: Fig. 287.--Forms for Constructing Grain Elevator Bins.]

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 s.p.a.ces 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, bal.u.s.ters, 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 pract.i.tioner 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 coa.r.s.e 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 finis.h.i.+ng. 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 pa.s.sing 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, bal.u.s.ters 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.

[Ill.u.s.tration: Fig. 288.--Molds for Railings and Ornaments for Concrete Arch Bridge.]

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 bal.u.s.ters 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 bal.u.s.ters, 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.

[Ill.u.s.tration: Fig. 289.--Molds for Ornamental Railing Posts for Concrete Facade for Bridge.]

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 bal.u.s.ters were cast in plaster molds. To make these molds a box square in plan and the height of the bal.u.s.ter 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 bal.u.s.ter. A full size wooden pattern of the bal.u.s.ter 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 bal.u.s.ter, were inserted in the joints of the a.s.sembled box so as to divide the vacant s.p.a.ce between the pattern and the box into vertical sections.

[Ill.u.s.tration: Fig. 290.--Railing for Arch Bridge.]

[Ill.u.s.tration: Fig. 291.--Form for Lattice Panels Shown by Fig. 290.]

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 sh.e.l.lac on the inside. Four or five molds of this description were cast.

To cast a bal.u.s.ter, the sections were a.s.sembled 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 b.a.l.l.s on the end posts were made in exactly the same manner as the bal.u.s.ter 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: Bal.u.s.ters, 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.

[Ill.u.s.tration: Fig. 292.--Form for Hand Rail Shown by Fig. 290.]