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CONCRETE CONSTRUCTION METHODS AND COST BY

HALBERT P. GILLETTE M. Am. Soc. C. E.; M. Am. Inst. M. E., Managing Editor, Engineering-Contracting AND

CHARLES S. HILL, C. E. Associate Editor, Engineering-Contracting

NEW YORK AND CHICAGO, Copyright 1908 By THE MYRON C. CLARK PUBLISHING CO.



CHAPTER XV.

METHODS AND COST OF CONSTRUCTING SIDEWALKS, PAVEMENTS AND CURB AND GUTTER.

Next to pavement foundations the most extensive use of concrete in street work is for cement walks and concrete curb and gutter. Usually the mixing and placing of the concrete is hand work, practically the only exceptions being where pavement base, curbing and sidewalks are built all at once, using machine mixers. The same objections that have been raised to machine mixers in laying pavement foundation are raised against them for curb and walk construction, and owing to the much smaller yardage per lineal foot of street in walk and curb work these objections carry more force than they do in case of paving work. Another argument against the use of mixers is that both walk and curb and gutter work involve the use of forms and the application of mortar finish, the placing of which are really the limiting factors in the rate of progress permissible, and this rate is too slow to consume an output necessary to make a mixer plant economical as compared with hand mixing where so much transportation is involved. Concrete sidewalk and curb work are essentially hand mixing work; they, therefore, involve a careful study of the economies of hand mixing and wheelbarrow haulage which are fully discussed in Chapter II.

CEMENT SIDEWALKS.

Sidewalk construction consists in molding on a suitably prepared sub-base a concrete slab from 3½ to 7½ ins. thick, depending on practice, and finishing its top surface with a ½ to 1½-in. wearing surface of cement mortar.

GENERAL METHOD OF CONSTRUCTION.—The excavation and preparation of the sub-grade call for little notice beyond the warning that they should never be neglected. The authors have seen many thousands of feet of cement walk laid in the middle West in which the sub-base was placed directly[Pg 308] on the natural sod, often covered with grass and weeds a foot high. Such practice is wholly vicious. The sod should always be removed and the surface soil excavated to a depth depending upon the climate and nature of the ground and the foundation bed well tamped. From 4 to 6 ins. depth of excavation will serve where the soil is reasonably hard and there are no heavy frosts; with opposite conditions a 12-in. excavation is none too deep. The thickness of the broken stone, gravel, cinder or sand sub-base should likewise be varied with the character of the soil, the conditions of natural drainage and the prevalence of frost. In well drained sandy soils 6 to 8 ins. of sub-base are sufficient, but in clayey soils with poor natural drainage the sub-base should be from 10 to 12 ins. thick at least; the local conditions will determine the thickness of sub-base necessary and in places it may be desirable to provide by artificial drainage against the accumulation of water under the concrete. Tile drains are better and cheaper than excessively deep foundations. The thorough tamping of the sub-base is essential to avoid settling and subsequent cracking of the concrete slab. This is a part of sidewalk work which is often neglected.

Portland cement concrete, sand and broken stone or gravel mixtures in the proportions of 1-3-5 and 1-3-6 are used for base slabs. For walks up to 7 ft. wide the slab is made 3½ ins. thick for residence streets and 4½ to 5 ins. thick for business streets; for wider walks the thickness is increased to 7 ins. for 8-ft. width and 7½ ins. for 9 to 10-ft. width. Roughly the thickness of the walk in inches (base and top together) is made about equal to its width in feet. The concrete is deposited in a single layer and tamped thoroughly, either in separate blocks behind suitable forms or in a continuous slab which is while fresh cut through to make separate blocks. For walks up to 8 ft. wide the slab is divided by transverse joints spaced about the width of the walk apart, but for the wider walks the safety of this division depends upon the thickness of the base; an 8-ft. walk with a 5-in. base can safely be laid with joints 8 ft. apart, but if the slab is only 4 ins. thick it had better be laid in 4×4-ft. squares. The mode of procedure in base construction is as follows:[Pg 309]

The sub-base being laid, side forms held by stakes are placed as shown by Fig. 116, with the top edges of the boards exactly to the grade of the top surface of the finished walk. The concrete is then deposited between these side forms and tamped until it is brought up to the level marked by the templet A. If the plan is to deposit the base in sections transverse plates of ⅜ to ¼ in. steel are set across the walk between the side boards at proper intervals and the concrete tamped behind them; sometimes the concreting is done in alternate blocks. When the steel plate is withdrawn an open joint is left for expansion and contraction. Where the plan is to lay the base in one piece which is afterwards cut into blocks, the cutting is done with a spade or cleaver.

Fig. 116.—Sketch Showing Method of Constructing Cement Walks.Fig. 116.—Sketch Showing Method of Constructing Cement Walks.
Fig. 117.—"Jointer" for Cement Sidewalk Work.Fig. 117.—"Jointer" for Cement Sidewalk Work.

Portland cement mortar mixed 1 to 1½ to 1 to 2 is used for the wearing surface, and is laid from ½ in. to 1½ ins. thick, depending upon the width of the walk and the thickness of the base. As a rule the mortar is mixed rather stiff; it is placed with trowels in one coat usually, but sometimes in two coats, and less often by tamping. The mortar coat is brought up flush with the top edges of the side forms by means of the templet B, and the top finished by floating and troweling.[Pg 310] The wearing coat is next divided into sections corresponding with the sections into which the base is divided, by cutting through it with a trowel guided by a straight edge and then rounding the edges of the cut with a special tool called a jointer and shown by Fig. 117. An edger, Fig. 118, is then run around the outside edges of the block to round them. The laying of the mortar surface must always follow closely the laying of the base so that the two will set together.

Fig. 118.—"Edger" for Cement Sidewalk Work.Fig. 118.—"Edger" for Cement Sidewalk Work.

BONDING OF WEARING SURFACE AND BASE.—Trouble in securing a perfect bond between the wearing surface and the base usually comes from one or more of the following causes: (1) Applying the surface after the base concrete has set. While several means are available for bonding fresh to old concrete as described in Chapter XXIV, the better practice is not to resort to them except in case of necessity but to follow so close with the surfacing that the base will not have had time to take initial set. (2) Poor mixing and tamping of this base concrete. (3) Use of clayey gravel or an accumulation of dirt on the surface. In tamping clayey gravel the water flushes the clay to the surface and prevents the best bond. (4) Poor troweling, that is failure to press and work the mortar coat into the base concrete. Some contractors advocate tamping the mortar coat to obviate this danger. Conversely, to make the surface coat adhere firmly to the base it must be placed before the base concrete has set; the base concrete must be thoroughly cleaned or kept clean from surface dirt; the surface coat must be tamped or troweled forcibly into the base concrete so as to press out all air and the film of water which collects on top of the concrete base.[Pg 311]

PROTECTION OF WORK FROM SUN AND FROST.—Sun and frost cause scaling and hair cracks. For work in freezing weather the water, sand and gravel should be heated or salt used to retard freezing until the walk can be finished; it may then be protected from further action of the frost by covering it first with paper and then with a mattress of sawdust, shavings or sand and covering the whole with a tarpaulin. Methods of heating concrete materials and rules for compounding salt solutions are given in Chapter VII. The danger from sun arises from the too rapid drying out of the surface coating; the task then is to hold the moisture in the work until the mixture has completely hardened. Portable frames composed of tarpaulin stretched over 2×4-in. strips may be laid over the finished walk to protect it from the direct rays of the sun; these frames can be readily removed to permit sprinkling. Practice varies in the matter of sprinkling, but it is the safe practice in hot weather to sprinkle frequently for several days. Moisture is absolutely necessary to the perfect hardening of cement work and a surplus is always better than a scarcity. In California the common practise is to cover the cement walk, as soon as it has hardened, with earth which is left on for several days.

CAUSE AND PREVENTION OF CRACKS.—Cracks in cement walks are of two kinds, fractures caused by any one of several construction faults and which reach through the surface coating or through both surface and base, and hair cracks which are simply skin fractures. Large cracks are the result of constructive faults and one of the most common of these is poor foundation construction; other causes are poor mixing and tamping of the base, too large blocks for thickness of the work, failure to cut joints through work. Hair cracks are the result of flushing the neat cement to the surface by excessive troweling or the use of too wet a mixture. The prevention of cracks obviously lies in seeing that the construction faults cited do not exist. If expansion joints are not provided, a long stretch of cement walk will expand on a hot day and bulge up at some point of weakness breaking the walk.

COST OF CEMENT WALKS.—The cost of cement walks is commonly estimated in cents per square foot, including the necessary excavation and the cinder or gravel foundation.[Pg 312] The excavation usually costs about 13 cts. per cu. yd., and if the earth is loaded into wagons the loading costs another 10 cts. per cu. yd., wages being 15 cts. per hr. The cost of carting depends upon the length of haul, and may be estimated from data given in Chapter III. If the total cost of excavation is 27 cts. per cu. yd., and if the excavation is 12 ins. deep, we have a cost of 1 ct. per sq. ft. for excavation alone. Usually the excavation is not so deep, and often the earth from the excavation can be sold for filling lots.

In estimating the quantity of cement required for walks, it is well to remember that 100 sq. ft. of walk 1 in. thick require practically 0.3 cu. yd. concrete. If the concrete base is 3 ins. thick, we have 0.3 × 3, or 0.9 cu. yd. per 100 sq. ft. of walk. And by using the tables in Chapter II we can estimate the quantity of cement required for any given mixture. In cement walk work the cement is commonly measured loose, so that a barrel can be assumed to hold 4.5 cu. ft. of cement. If the barrel is assumed to hold 4.5 cu. ft., it will take less than 1 bbl. of cement to make 1 cu. yd. of 1-3-6 concrete; hence it will not require more than 0.9 bbl. cement, 0.9 cu. yd. stone, and 0.45 cu. yd. sand per 100 sq. ft. of 3-in. concrete base. The 1-in. wearing coat made of 1-1½ mortar requires about 3 bbls. of cement per cu. yd., if the barrel is assumed to hold 4.5 cu. ft., and since it takes 0.3 cu. yd. per 100 sq. ft., 1 in. thick, we have 0.3 × 3, or 0.9 bbl. cement per 100 sq. ft. for the top coat. This makes a total of 1.8 bbls. per 100 sq. ft., or 1 bbl. makes 55 sq. ft. of 4-in. walk.

As the average of a number of small jobs, the authors' records show the following costs per sq. ft. of 4-in. walk such as just described:

Cts. per sq. ft.
Excavating 8 ins. deep 0.65
Gravel for 4-in. foundation, at $1.00 per cu. yd. 1.20
0.018 bbl. cement, at $2.00 3.60
0.009 cu. yd. broken stone, at $1.50 1.35
0.006 cu. yd. sand, at $1.00 0.60
Labor making walk 1.60
——
    Total cents 9.00

[Pg 313]

This is 9 cts. per sq. ft. of finished walk. The gangs that built the walk were usually two masons at $2.50 each per 10-hr. day with two laborers at $1.50 each. Such a gang averaged 500 sq. ft. of walk per day.

Cost at Toronto, Ont.—Mr. C. H. Rust, City Engineer, Toronto, Ont., gives the following costs of constructing concrete sidewalks by day labor. The sidewalks have a 4-in. foundation of coarse gravel or soft coal cinders, thoroughly consolidated by tamping or rolling, upon which is placed a 3½-in. layer of concrete composed of 1 part Portland cement, 2 parts clean, sharp, coarse sand, and 5 parts of approved furnace slag, broken stone or screened gravel. The wearing surface is 1 in. thick, or 1 part Portland cement, 1 part clean, sharp, coarse sand, and 3 parts screened pea gravel, crushed granite, quartzite or hard limestone. Costs are given of a 6-ft. and a 4-ft. walk as follows:

COST OF 6 FT. SIDEWALK.
Item. Per 100 sq. ft.
Labor $ 5.59
Cement, 1.66 bbls., at $1.54 2.49
Gravel, 2.7 cu. yds., at $0.80 2.21
Sand, 0.46 cu. yd., at $0.80 0.37
Water 0.05
——
Total $10.71
COST OF 4 FT. SIDEWALK.
Item. Per 100 sq. ft.
Labor $ 6.73
Cement, 2.04 bbls., at $1.54 3.15
Gravel, 2.06 cu. yds., at $0.80 1.65
Sand, 0.49 cu. yd., at $0.80 0.39
Water 0.07
——
Total $11.99

The rates of wages and the number of men employed were as follows: 1 foreman, at $3.50 per day; 1 finisher, at 30 cts. per hour; 1 helper, at 22 cts. per hour; 15 laborers, at 20 cts. per hour.[Pg 314]

Cost at Quincy, Mass.—The following costs are given by Mr. C. M. Saville for constructing 695 sq. yds. of granolithic walk around the top of the Forbes Hill Reservoir embankment at Quincy, Mass. This walk was laid on a broken stone foundation 12 ins. thick; the concrete base was 4 ins. thick at the sides and 5 ins. thick at the center; the granolithic finish was 1 in. thick. The walk was 6 ft. wide and was laid in 6-ft. sections, a steel plate being used to keep adjacent sections entirely separate. The average gang was 6 men and a team on the base and 2 masons and 1 tender on the finish. The average length of walk finished per day was 60 ft. The cost was as follows:

  Stone Foundation: Per cu. yd. Per sq. ft.
Broken stone for 12-in. foundation $ 0.40 $0.015
Labor placing at 15 cts. per hour 1.50 0.056
—— ———
    Totals $ 1.90 $0.071
  Concrete Base 4½ ins. Thick:
1.22 bbls. cement per cu. yd. at $1.53 $ 1.87 $0.026
0.50 cu. yd. sand per cu. yd. at $1.02 0.51 0.007
0.84 cu. yd. stone per cu. yd. at $1.57 1.32 0.019
Labor (6 laborers, 1 team) 3.48 0.050
—— ——
    Total for 90 cu. yds. $ 7.18 $0.102
  Granolithic Finish 1 in. Thick:
4 bbls. cement per cu. yd. at $1.53 $ 6.12 $0.019
0.8 cu. yd. sand at $1 0.80 0.002
Lampblack 0.29 0.001
Labor (2 masons, 1 helper) 6.36 0.016
—— ——
    Totals $13.57 $0.038

The two masons received $2.25 per day each and their helper $1.50 per day, and they averaged 360 sq. ft. per day, which made the cost 1⅔ cts. per sq. ft. for labor laying granolithic finish. The cost of placing the foundation stone is very high and the cost of concrete base also runs unusually high, the reasons for these high costs are not evident.

Cost at San Francisco.—Mr. George P. Wetmore, of the contracting firm of Cushing & Wetmore, San Francisco, gives the following figures relating to sidewalk work in that city.[Pg 315] The foundations of cement walks in the residence district of San Francisco are 2½ ins. thick, made of 1-2-6 concrete, the stone not exceeding 1 in. in size. The wearing coat is ½ in. thick, made of 1 part cement to 1 part screened beach gravel. The cement is measured loose, 4.7 cu. ft. per barrel. The foundation is usually laid in sections 10 ft. long; the width of sidewalks is usually 15 ft. The top coat is placed immediately, leveled with a straight edge and gone over with trowels till fairly smooth. After the initial set and first troweling, it is left until quite stiff, when it is troweled again and polished—a process called "hard finishing." The hard finish makes the surface less slippery. The surface is then covered with sand, and watered each day for 8 or 10 days. The contract price is 9 to 10 cts. per sq. ft. for a 3-in. walk; 12 to 14 cts. for a 4-in. walk having a wearing coat ¾ to 1-in. thick. A gang of 3 or 4 men averages 150 to 175 sq. ft. per man per day of 9 hrs. Prices and wages are as follows:

Cement, per bbl. $2.50
Crushed rock, per cu. yd. 1.75
Gravel and sand for foundation, per cu. yd. 1.40
Gravel for top finish, per cu. yd. 1.75
Finisher wages, best, per hr. 0.40
Finisher helper, best, per hr. 0.25
Laborer, best, per hr. 0.20

Cost in Iowa.—Mr. L. L. Bingham sent out letters to a large number of sidewalk contractors in Iowa asking for data of cost. The following was the average cost per square foot as given in the replies:

Cts. per sq. ft.
Cement, at $2 per bbl. 3.6
Sand and gravel 1.5
Labor, at $2.30 per day (average) 2.2
Incidentals, estimated 0.7
    Total per sq. ft 8.0

This applies to a walk 4 ins. thick, and includes grading in some cases, while in other cases it does not. Mr. Bingham writes that in this respect the replies were unsatisfactory. He also says that the average wages paid were $2.30 per man per day. It will be noted that a barrel of cement makes 55½ sq.[Pg 316] ft. of walk, or it takes 1.8 bbls. per 100 sq. ft. The average contract price for a 4-in. walk was 11½ cts. per sq. ft.

CONCRETE PAVEMENT.

Concrete pavement is constructed in all essential respects like cement sidewalk. The sub-soil is crowned and rolled hard, then drains are placed under the curbs; if necessary to secure good drainage a sub-base of gravel, cinders or broken stone 4 to 8 ins. thick is laid and compacted by rolling. The foundation being thus prepared a base of concrete 4 to 5 ins. thick is laid and on this a wearing surface 2 to 3 ins. thick. As showing specific practice we give the construction in two cities which have used concrete pavement extensively.

Windsor, Ontario.—The street is first excavated to the proper grade and crown and rolled with a 15-ton roller. Tile drains are then placed directly under the curb line and a 6×16-in. curb is constructed, vising 1-2-4 concrete faced with 1-2 mortar. Including the 3-in. tile drain this curb costs the city by contract 38 cts. per lin. ft. The pavement is then constructed between finished curbs, as shown by Fig. 119.

Fig. 119.—Concrete Pavement. Windsor, Canada.Fig. 119.—Concrete Pavement. Windsor, Canada.

The fine profile of the sub-grade is obtained by stretching strings from curb to curb, measuring down the required depth and trimming off the excess material. The concrete base is then laid 4 ins. thick. A 1-3-7 Portland cement concrete is used, the broken stone ranging from ¼ in. to 3 ins. in size, and it is well tamped. This concrete is mixed by hand and as each batch is placed the wearing surface is put on and finished. The two layers are placed within 10 minutes of each other, the purpose being to secure a monolithic or one-piece slab. The top layer consists of 2 ins. of 1-2-4 Portland cement and screened gravel, ¼ in. to 1 in., concrete. This layer is put on rather wet, floated with a wooden float and troweled with a[Pg 317] steel trowel while still wet. Some 20,500 sq. yds. of this construction have been used and cost the city by contract:

Per sq. yd.
Bottom 4-in. layer 1-3-7 concrete $0.57
Top 2-in. layer 1-2-4 concrete 0.32
Excavation 0.10
——
    Total $0.99

This construction was varied on other streets for the purpose of experiment. In one case a 4-in. base of 1-3-7 stone concrete was covered with 2 ins. of 1-2-2 gravel concrete. In other cases the construction was: 4-in. base of 1-3-7 stone concrete; 1½-in. middle layer of 1-2-4 gravel concrete, and ½-in. top layer of 1-2 sand mortar. All these constructions have been satisfactory; the pavement is not slippery. The cost to the city by contract for the three-layer construction has in two cases been as follows:

  Church St., 8,000 sq. yds.: Per sq. yd.
4-in. base 1-3-7 concrete $0.57
1½-in. 1-2-4 and ½-in 1-2 mixture 0.32
Excavation 0.10
——
    Total $0.99
 
  Albert and Wyandotte Sts., 400 sq. yds.: Per sq. yd.
4-in. base 1-3-7 concrete $0.66
1½-in. 1-2-4 and ½-in. 1-2 mixture 0.39
Excavation 0.10
——
    Total $1.15

The cost of materials and rates of wages were about as follows:

Portland cement f. o. b. cars Windsor, per bbl. $2.05
River sand, per cu. yd. 1.15
River gravel, screened, per cu. yd. 1.25
Crushed limestone, ¼ to 3 ins., per ton 1.15
Labor, per day 1.75 to 2.00

At these prevailing prices the contractor got a fair profit at the contract price of $1.15; at 99 cts., any profit is questionable, according to City Engineer George S. Hanes, who gives[Pg 318] us the above records. Expansion joints are located from 20 to 80 ft. apart and are filled with tar.

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 space. 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, 1½ 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, 16½ cts. per hour, and cement finishers, 40 cts. per hour.

Fig. 120.—Concrete Pavement, Richmond, Ind.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 butts 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[Pg 319] curb and water table are built in one piece and in sections of reasonable length separated by expansion joints.

Fig. 121.—Box Form for Concrete Curb.Fig. 121.—Box Form for Concrete Curb.
Fig. 122.—Continuous Form for Concrete Curb.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[Pg 320] joints were formed by inserting a partition of ⅜-in. boiler plate every 12 ft., which was withdrawn just previous to finishing up the surface; the sections between partitions were concreted continuously. Another method is to make the partitions of plank, concrete every other section, then remove the partition plank and concrete the remaining spaces 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), spacers 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 illustrated 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 illustrated 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[Pg 321] 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 ⅜-in. steel plate around them or bending and nailing ⅞×1¼-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.

Fig. 123.—Continuous Form for Concrete Curb.Fig. 123.—Continuous Form for Concrete Curb.
Fig. 124.—Form for Two-Piece Curb Construction.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 illustrated 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 space 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[Pg 322] and preparing the sub-grade usually runs from ½ 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 quantities 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 illustrations 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, Assistant 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 2½ 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 5½ ins. in height, and the water table was 14 ins. wide and 4 ins. thick, with a fall of 1¼ ins. from front to back. The concrete used was a mixture of 1 Portland cement, 3 sand, 3⅝-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[Pg 323] 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 1×10-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 1×2-in. stuff, one conforming to the slope of the water table and long enough to extend beyond the front of the 2×6-in. front board, a second standing plumb and bearing against the 1×10-in. face board, and the third forming a small corner brace between the two former to hold them in their proper relative positions. The 1×10-in. face board, etc., was separated from the 2×12-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 1×10-in. board into perfect line by moving the knee braces in or out, and when correct nailing them to the 2×6-in. front board. The 1×10-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 ⅜-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 2½ ins. radius. Circular curb and gutter of same construction was built at each corner, ½-in. basswood being used for forms, instead of 2×1-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 circumstances, 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.[Pg 324]

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:

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

Total. Per lin. ft. cts.
171.112 tons spalls $102.93 7.76
42 tons 2-in. stone 41.16 3.09
30.8 tons ⅝-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. 2×12 boards charged off $ 9.25
500 ft. B. M. 2×6 boards charged off 4.12
1,000 ft. B. M. 1×10 boards charged off 14.25
½-in. basswood 4.30
½ keg 3-in. nails 1.42
½ keg 4-in. nails 1.43
Pickets 3.25
Tools charged off 3.15
———
    Total $41.17

[Pg 325]

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:

  Item. Total. Per lin. ft. P. C. of 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, homogeneous curb and gutter.

Fig. 125.—Concrete Curb and Gutter at Champaign, Ill.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.[Pg 326]

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 partitions staked into place, were used. The cost of the work was as follows:

  Item. No. of men. Total wages. Cost per 100 ft.
Opening trench, 18×30-in. 2 $3.50 $2.43
Placing and tamping cinders 2 3.50 1.00
  Setting forms:
Boss setter 1 3.00 ...
Assistant 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 ...
Assistant 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.: Quantity. Price.
  Portland cement 8⅓ 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

[Pg 327]

This is the total cost, exclusive of lumber, tools, interest, profits, etc., and it is practically 40 cts. per lin. ft.

In 100 lin. ft. of curb and gutter there were 4.6 cu. yds. of concrete and mortar facing, 4 cu. yds. of which were concrete; hence the 9 men in the concrete gang laid 14 cu. yds. of concrete per day, whereas the 4 men mixing and placing the mortar finishing laid only 2½ cu. yds. of mortar per day, assuming that the mortar finishing averaged just 1 in. thick. Since these 4 men (2 mixers and 2 finishers) received $10.50 a day, it cost more than $4 per cu. yd. to mix and place the 1-2 mortar, as compared with $1.41 per cu. yd. for mixing and placing the concrete. The concrete was built in alternate sections 7 ft. long. The 3 men placing forms averaged 400 lin. ft. a day, so that the cost of placing the forms was $1 per cu. yd. of concrete. The 2 men placing and tamping cinders averaged 16 cu. yds. of cinders per day, or 8 cu. yds. per man. This curb and gutter was built by contract at 45 cts. per lin. ft.

For several jobs, in which a curb and gutter essentially the same as shown in Fig. 125 was built, our records show a general correspondence with the above given data of Mr. Apple. Our work was done with smaller gangs, 1 mason and 2 laborers being the ordinary gang. Such a gang would lay 80 to 100 lin. ft. of curb and gutter per 10-hr. day, at the following cost:

1 mason at $2.50 $2.50
2 laborers at $1.50 3.00
——
    Total $5.50

This made a cost of 5½ to 7 cts. per lin. ft. for labor, and it did not include the cost of digging a trench to receive the curb and gutter.



CONCRETE CONSTRUCTION METHODS AND COST

CHAPTER I.—METHODS AND COST OF SELECTING AND PREPARING MATERIALS FOR CONCRETE.

CHAPTER II.—THEORY AND PRACTICE OF PROPORTIONING CONCRETE.

CHAPTER III.—METHODS AND COSTS OF MAKING AND PLACING CONCRETE BY HAND.

CHAPTER IV.—METHODS AND COST OF MAKING AND PLACING CONCRETE BY MACHINE.

CHAPTER V.—METHODS AND COST OF DEPOSITING CONCRETE UNDER WATER AND OF SUBAQUEOUS GROUTING.

CHAPTER VI.—METHODS AND COST OF MAKING AND USING RUBBLE AND ASPHALTIC CONCRETE.

CHAPTER VII.—METHODS AND COST OF LAYING CONCRETE IN FREEZING WEATHER.

CHAPTER VIII.—METHODS AND COST OF FINISHING CONCRETE SURFACES.

CHAPTER IX.—METHODS AND COST OF FORM CONSTRUCTION.

CHAPTER X.—METHODS AND COST OF CONCRETE PILE AND PIER CONSTRUCTION.

CHAPTER XI.—METHODS AND COST OF HEAVY CONCRETE WORK IN FORTIFICATIONS, LOCKS, DAMS, BREAKWATERS AND PIERS.

CHAPTER XII.—METHODS AND COST OF CONSTRUCTING BRIDGE PIERS AND ABUTMENTS.

CHAPTER XIII.—METHODS AND COST OF CONSTRUCTING RETAINING WALLS.

CHAPTER XIV.—METHODS AND COST OF CONSTRUCTING CONCRETE FOUNDATIONS FOR PAVEMENT.

CHAPTER XV.—METHODS AND COST OF CONSTRUCTING SIDEWALKS, PAVEMENTS, AND CURB AND GUTTER.

CHAPTER XVI.—METHODS AND COST OF LINING TUNNELS AND SUBWAYS.

CHAPTER XVII.—METHODS AND COST OF CONSTRUCTING ARCH AND GIRDER BRIDGES.

CHAPTER XVIII.—METHODS AND COST OF CULVERT CONSTRUCTION.

CHAPTER XIX.—METHODS AND COST OF REINFORCED CONCRETE BUILDING CONSTRUCTION.

CHAPTER XX.—METHOD AND COST OF BUILDING CONSTRUCTION OF SEPARATELY MOLDED MEMBERS.

CHAPTER XXI.—METHODS AND COST OF AQUEDUCT AND SEWER CONSTRUCTION.

CHAPTER XXII.—METHODS AND COST OF CONSTRUCTING RESERVOIRS AND TANKS.

CHAPTER XXIII.—METHODS AND COST OF CONSTRUCTING ORNAMENTAL WORK.

CHAPTER XXIV.—MISCELLANEOUS METHODS AND COSTS.

CHAPTER XXV.—METHODS AND COST OF WATERPROOFING CONCRETE STRUCTURES.





                                                                



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