Concrete Construction Part 30

~Richmond, Ind.~--The first concrete pavement was built in 1896 and since then it has been used extensively, especially for wide alleys and narrow streets where traffic is heavy and concentrated in small s.p.a.ce. The method of construction has varied from time to time but the construction shown by Fig. 120 is fairly representative. Usually a 1-3-5 concrete is used for the base, 5 ins. thick, and a 1-2 mortar for the top coat, 1 ins. thick. In 1904 this pavement cost the city by contract 16 cts. per sq. ft. or $1.54 per sq. yd, with wages and prices as follows: Stone on the work, $1.25 per cu. yd.; gravel and sand, $0.75 per cu. yd.; cement, $2.25 per barrel; common laborers, 16 cts. per hour, and cement finishers, 40 cts. per hour.

[Ill.u.s.tration: Fig. 120.--Concrete Pavement, Richmond, Ind.]

~CONCRETE CURB AND GUTTER.~

Current practice varies materially in constructing concrete curb and gutter. The more common practice is to lay the curb and water table in one piece, or as a monolith, but this is by no means universal practice.

In much work the curb wall and the water table slab are constructed separately, the construction joint being sometimes horizontal where the curb wall sits on the slab and sometimes vertical where the water table b.u.t.ts against the wall. Again it is the common practice to construct curb and gutter in sections, laid either alternately or in succession, separated by sand joints to provide for expansion and contraction, but this is not universal practice, much of such work being constructed as a continuous wall with no provision for temperature movements except the natural breaks at driveways. All of these types of construction appear to have given reasonable satisfaction, but exact data for a final comparison are not available, so that we are forced to reason on general principles. Such a course of reasoning indicates that the best results should be expected where the curb and water table are built in one piece and in sections of reasonable length separated by expansion joints.

[Ill.u.s.tration: Fig. 121.--Box Form for Concrete Curb.]

[Ill.u.s.tration: Fig. 122.--Continuous Form for Concrete Curb.]

~FORM CONSTRUCTION.~--The form construction for curb and gutter work is determined by the general plan of construction followed,--whether monolithic or two-piece construction. In monolithic construction two types of forms are employed, sectional or box forms and continuous forms. A good example of box form is shown by Fig. 121. This form was designed for a curb 14 ins. high at the back, 6 ins. high in front and 24 ins. from face of curb to outer edge of gutter, constructed in sections 7 ft. long. The form, it will be observed, is a complete box, in which alternate sections of curb are molded and after having set are filled between using the same form but dispensing with the end boards which are replaced by the completed sections of curb. A fairly representative example of continuous form is shown by Fig. 122; in this construction a continuous line of plank is set to form the back of the curb and another line to form the face of the gutter slab, both lines being held in place by stakes. When the gutter slab concrete has been placed and surfaced the form for the front of the curb is set as shown and the upper portion of the curb wall concreted behind it. The method in detail of constructing curb and gutter, with this type of form, at Ottawa, Ont., is described in a succeeding section. Here the joints were formed by inserting a part.i.tion of 3/8-in. boiler plate every 12 ft., which was withdrawn just previous to finishing up the surface; the sections between part.i.tions were concreted continuously. Another method is to make the part.i.tions of plank, concrete every other section, then remove the part.i.tion plank and concrete the remaining s.p.a.ces against the previously finished work. A different method of supporting the plank forming the face of the curb wall, is to clamp it to the back form (Fig.

123), s.p.a.cers being inserted to keep the two their proper distances apart. The forms shown by Figs. 121 to 123 are for monolithic curb and gutter. In two-piece construction where the curb wall is constructed on the finished gutter slab practically the same method of construction is employed as is ill.u.s.trated by Fig. 122 except that no attempt is made to concrete the curb wall before the slab concrete has begun to set. The more common and the preferable method of two-piece construction is ill.u.s.trated by Fig. 124; the curb proper is built first using the simple box form shown at the right hand, then the water table is built using the completed curb as the form for the back and a board held by stakes as a form for the front. This board is set with its top edge exactly to the grade of the finished water table so as to serve as a guide for one end of the template, the other end of which rides on the top of the finished curb wall. Forms for curves at street intersections are best constructed by driving stakes to the exact arc of the curve and bending a 3/8-in. steel plate around them or bending and nailing 7/81-in.

strips. Soaking the wood strips thoroughly will make them bend easily.

The cost of form work in constructing curb and gutter is chiefly labor cost in erecting and taking down the forms.

[Ill.u.s.tration: Fig. 123.--Continuous Form for Concrete Curb.]

[Ill.u.s.tration: Fig. 124.--Form for Two-Piece Curb Construction.]

~CONCRETE MIXTURES AND CONCRETING.~--The curb body is usually made of a 1-3-5 or 6 concrete and the curb finish of a 1-2 mortar. Portland cement is employed almost exclusively. The concrete mixture commonly used is of such consistency that thorough ramming is necessary to flush the cement to the surface. The cubical contents of combined curb and gutter of the forms ill.u.s.trated will run from 3 to 5 cu. yds. per 100 ft., and about one-eighth of this will be facing mortar 1 in. thick; thus a curb running 5 cu. yds. per 100 ft. will contain per 100 ft. about 0.83 cu.

yd. of mortar and 4.17 cu. yds. of concrete. The usual method of concreting is to erect the forms for the back of the curb wall and the front of the gutter slab and concrete to the height of the water table clear across; then shape the exposed top of the water table to section and place the mortar finish, and then erect the face form for the gutter wall, bring the concrete backing and vertical face finish up together and, finally, finish the top. The finish coat is placed by troweling on the horizontal surfaces; on the vertical face of the curb wall it may be placed in any one of several ways. Frequently the mortar coat is simply plastered against the face board and filled behind with concrete.

Another method is to lay a 1-in. board against the inside of the form, concrete behind it, then withdraw the board, fill the s.p.a.ce with mortar and tamp concrete and mortar to a thorough bond. The special face forms shown in Chapter VIII may be used in place of the board. The securing of a good bond between the backing concrete and the mortar facing is governed by the same conditions that govern sidewalk work.

~COST OF CURB AND GUTTER.~--The cost of concrete curb and gutter is commonly estimated in cents per lineal foot. The cost of excavating, loading and carting will run about the same per cubic yard as for sidewalks. Excavating the trench and preparing the sub-grade usually runs from ct. to 2 cts. per foot of curb, but sometimes it amounts to 3 cts. Placing the sub-base will cost for placing and tamping 1 ct. per ft., to which is to be added the cost of materials; a 6-in. sub-base 30 ins. wide contains 4.7 cu. yds., tamped measure, of materials per 100 ft. The amount of materials per foot depends upon the cross-section of the curb; it equals in cubic yards the area of cross-section in square feet divided by 27, and of this volume about one-eighth will be 1-2 mortar and seven-eighths 1-3-6 concrete. The tables in Chapter II give the amounts of materials per cubic yard of these mixtures; the product of these quant.i.ties and the cost of the materials on the ground gives the cost. The labor cost of mixing and placing, including the form work, will run from 10 to 14 cts. per foot. In round figures curb and gutter of the section shown in the accompanying ill.u.s.trations may be estimated to cost in the neighborhood of 40 cts. per lineal foot. The following sections give records of cost of individual jobs of curb and gutter construction.

~Cost at Ottawa, Canada.~--The method and cost of constructing 1,326 ft.

of concrete curb and gutter at Ottawa, Ont., are given in some detail by Mr. G. H. Richardson, a.s.sistant City Engineer, in the annual report of the City Engineer for 1905. We have remodeled the description and rearranged the figures of cost in the following paragraphs.

The concrete curb was built before doing any work on the roadway, and the first task was the excavation of a trench 2 ft. wide and averaging 1 ft. 8 ins. in depth through light red sand. On the bottom of this trench there was placed a foundation of stone spalls 8 ins. thick; in width this foundation reached from 3 ins. back of the curb to 6 ins.

beyond the front of the water table. The curb was made 5 ins. thick and ran from 10 ins. to 5 ins. in height, and the water table was 14 ins.

wide and 4 ins. thick, with a fall of 1 ins. from front to back. The concrete used was a mixture of 1 Portland cement, 3 sand, 3 5/8-in.

screened limestone, and 4 2-in. stone. It was deposited in forms and tamped to bring the water to the face and then smoothed with a light troweling of stiff mortar.

The forms were constructed by first setting pickets and nailing to them a back board 2 ins. thick and 12 ins. wide and a front board 2 ins.

thick and 6 ins. wide. The concrete for the water table was deposited in this form in sections and brought to surface by straight edge riding on wooden strips nailed across the form and properly set to slope, etc.

After the water table had been troweled down and brushed a 110-in.

board was set to mold the front face of the curb. This board was sustained by small "knee frames" made of three pieces of 12-in. stuff, one conforming to the slope of the water table and long enough to extend beyond the front of the 26-in. front board, a second standing plumb and bearing against the 110-in. face board, and the third forming a small corner brace between the two former to hold them in their proper relative positions. The 110-in. face board, etc., was separated from the 212-in. back board by a 5-in. block at each end, and then braced by the knee frames every 3 or 4 ft. In this way it was possible to bring this 110-in. board into perfect line by moving the knee braces in or out, and when correct nailing them to the 26-in. front board. The 110-in. face board being in position and braced and lined, the curb material was thoroughly tamped in, and when ready was troweled and brushed on the top, a small round being worked onto the top front corner with the trowel.

Expansion joints were provided for by building into the curb every 12 ft., a piece of 3/8-in. boiler plate, which was afterward withdrawn and the joint filled with sand and faced over. As soon as the concrete had set sufficiently the face board was taken down and face of curb finished and brushed, the fillet between curb and water table being finished to 2 ins. radius. Circular curb and gutter of same construction was built at each corner, -in. ba.s.swood being used for forms, instead of 21-in.

lumber.

In addition to the actual construction of curb and gutter the cost given below includes the cleaning up of the street, spreading or removal of all surplus material from excavation, and the extension of all sidewalks out to the curbs at the corners. It was also necessary to maintain a watchman on this work, which duty, under ordinary circ.u.mstances, would be done by the general watchman. The total length built was 1,326 ft., of which 1,209 ft. is straight and 117 ft. curved to a 12-ft. radius.

The rates of wages paid were $2 for horse and cart, $1.65 for watchman, and an average of $1.90 per day for labor, including foreman; all for nine hours' work per day. The working force consisted of foreman, finisher, handy man. four concrete men, and three laborers.

The labor cost of the work was as follows:

Per ft. P. C. of Item. Total. cts. total.

Excavation and setting boards $ 88.90 6.7 30 Laying stone foundation 43.30 3.3 14 Concreting 61.30 4.6 20 Finishing 45.15 3.4 15 Carting 9.85 0.76 3 Watchman 25.00 1.89 8 Clearing up 13.60 1.04 4 Extras (sidewalk extensions) 17.23 1.31 6 ------- ----- -- Total $304.33 23.00 100

The cost of materials for curb and foundation were as follows:

Per lin. ft.

Total. cts.

171.112 tons spalls $102.93 7.76 42 tons 2-in. stone 41.16 3.09 30.8 tons 5/8-in. stone 42.57 3.21 33,000 lbs. cement 161.70 12.19 24 cu. yds. sand 19.20 1.45 ------- ----- Total $367.56 27.70

The cost of supplies and tools was as follows:

1,000 ft. B. M. 212 boards charged off $ 9.25 500 ft. B. M. 26 boards charged off 4.12 1,000 ft. B. M. 110 boards charged off 14.25 -in. ba.s.swood 4.30 keg 3-in. nails 1.42 keg 4-in. nails 1.43 Pickets 3.25 Tools charged off 3.15 ------ Total $41.17

This total, when divided by 1,326 lin. ft. of curb, gives the cost per lineal foot as about 3 cts. We can now summarize as follows:

Per lin. P. C. of Item. Total. ft. total.

Labor $304.33 23 43 Material 367.56 28 51 Supplies 41.17 3 6 ------- ---- --- Total $713.06 $0.54 100

As indicated above, on more extensive work the costs of carting, watchman, cleaning up, and extras would be avoided. They cost on this work 5 cts. and the work could therefore be done for 49 cts. if no such charges were included. On such work also the charge for supplies would be lower per foot and on any future work the labor cost could be materially lowered, this curb having been somewhat of an experiment as to method of construction. It is thought that with no charges for carting, cleaning, watchman, and extras, and with the experience obtained, this curb could be built for about 46 cts. The proportions adopted and the method of construction followed, produce a very strong, dense, h.o.m.ogeneous curb and gutter.

[Ill.u.s.tration: Fig. 125.--Concrete Curb and Gutter at Champaign, Ill.]

~Cost at Champaign, Ill.~--The following costs were recorded by Mr.

Charles Apple, and relate to work done at Champaign, Ill., in 1903. The work was done by contract, at 45 cts. per lin. ft. of the curb and gutter shown in Fig. 125.

The concrete curb and gutter was built in a trench as shown in the cut.

The earth was removed from this trench with pick and shovel at a rate of 1 cu. yd. per man per hour. The concrete work was built in alternate sections, 7 ft. in length. A continuous line of planks was set on edge to form the front and back of the concrete curb and gutter; and wood part.i.tions staked into place, were used. The cost of the work was as follows:

No. of Total Cost per Item. men. wages. 100 ft.

Opening trench, 1830-in. 2 $3.50 $2.43 Placing and tamping cinders 2 3.50 1.00

Setting forms: Boss setter 1 3.00 ...

a.s.sistant setter 1 2.00 ...

Laborer 1 1.75 ...

-- ----- ----- 3 $6.75 $1.69

Mixing and placing concrete: Clamp man 1 $1.75 ...

Wheelers 3 5.25 ...

Mixing concrete 4 7.00 ...

Mixing finishing coat 2 3.50 ...

Tampers 1 1.75 ...

Finishing: Foreman and boss finisher 1 4.00 ...

a.s.sistant finisher 1 3.00 ...

Water boy 1 .50 ...

-- ------ ----- Total making concrete 14 $26.75 $7.64 Total for labor per 100 ft $12.76

Materials for 100 lin. ft.: Quant.i.ty. Price.

Portland cement 8-1/3 bbls. $1.85 $15.42 Cinders 7.5 yds. .50 3.75 Gravel 2.5 yds. 1.00 2.50 Broken stone 2.5 yds. 1.40 3.50 Sand 1.0 1.00 1.00 Total for material per 100 ft $26.17 Total for material and labor per 100 ft. $38.93