Concrete Construction Part 49

Item. Per day.

8 men handling materials, at $1.75 $14.00 5 men operating molds, at 1 ct. per block 15.00 1 man mixing facing mortar, at $1.75 1.75 2 men loading blocks onto trucks, at $1.75 3.50 2 men unloading blocks from trucks, at $1.75 3.50 3 men sprinkling blocks, at $1.75 5.25 ------ Total, 21 men molding and curing blocks $43.00

The average daily run was 1,500 blocks, or 300 blocks per machine.

This output was easily maintained after the gang got broken in; sometimes it ran higher and sometimes lower, but the average was as given. The men operating the block machines thus earned $3 each per day.

The labor cost of molding and curing per block was thus 2.87 cts. As the blocks had about 25 per cent. hollow s.p.a.ce, each block 8816 ins.

contained 0.45 cu. ft. of concrete; a cubic yard of concrete, therefore, made 60 blocks, so that the labor cost of making the blocks was 60 2.87 cts. = $1.72 per cubic yard. This cost does not include foreman's time, materials, interest, depreciation or general expenses. It was estimated by the owners that the blocks cost them 9 cts. apiece cured, or about $5.40 per cubic yard of concrete. This 9 cts. evidently includes materials and labor alone.

Upon removal from the molds the blocks were loaded onto cars, taken to a large shed and there unloaded onto shelving arranged to hold five rows of blocks one above the other, two blocks opposite each other on each shelf. The blocks were left in the shed 24 to 48 hours to get the preliminary set, then they were loaded on small cars and taken to the yard, where they were removed from the cars and stacked. They were sprinkled every day for six days, being kept covered meanwhile with oiled cotton cloth. The labor costs given above include molding, sprinkling and handling the blocks up to this point.

To lay the blocks they were again loaded on cars and run to an elevator in a wooden tower outside the building. The elevator lifted the car to the floor on which the blocks were to be used, where it was run off onto a track reaching the full length of the building. The blocks were unloaded directly behind the masons. Where the walls were high enough for scaffolding the blocks were unloaded directly onto the first scaffold and, when necessary, handed up to the scaffolds above. The masons employed were regular stone masons receiving the regular scale of wages of $3.50 per day. The number of blocks laid by each mason was 125 per day in building pilasters and 200 per day in building plain wall.

Sometimes 250 blocks per day per man were laid in plain wall work. The cost per block of laying above was thus 2.8 cts. pilasters and 1.75 cts.

in plain wall. This cost does not include transporting the blocks from yard or of handling them to the scaffold behind the masons, nor does it include the cost of materials and labor for mixing and delivering mortar.

One of the features of this work was the method of transporting the blocks by cars. A complete system of tracks was provided covering the block plant and yard, the building sites and the several floors of the buildings themselves. All blocks and other materials were transported by cars running on these tracks, both cars and tracks being of the type made by the Chase Foundry & Manufacturing Co. of Columbus, Ohio.

~Residence, Quogue, N. Y.~--The following record of methods and cost of constructing a concrete block residence is furnished by Mr. Noyes F.

Palmer: A mixture of sand and pebbles was had on the site; screening was necessary merely to sort out the odd size stones. A mixture of 1 cement and 5 sand was really a 1-2-3 mixture, the 2 being the finest grades of sand and the 3 being various gravel sizes--none too large, none too small--so that the proportion was 2/5 fine sand and 3/5 gravel.

The concrete was hand mixed, and as the gravel had always just been excavated it contained moisture and did not have to be wetted. The sand and gravel were mixed and turned three or four times and spread out thin, and the cement was carefully spread over them in a uniform layer.

The ma.s.s was then turned three or four times until the eye could detect no difference in color; that is, each grain large enough for the eye to discern seemed to be coated with cement. After this dry mixing, water was added in a fine spray--not a deluge from a pail--but only enough to moisten the mixture. The ma.s.s was then turned three or four times. The mixture was then shoveled into the mold, no special face mixture being used, so as to about half fill it, and was then tamped by two men, one standing on each side of the machine. Altogether three layers of material were so placed and tamped and then a shovelful of sand and cement mixture was spread over the top to permit an even "strike-off."

As each block was molded it was carried on the working plate and set down on skids properly s.p.a.ced to fit the marks on the plate. This is an important detail and Mr. Palmer comments on it as follows: "The writer saw inexperienced men careless about it and who would break the backs of many blocks by not having the skids properly placed. After the blocks have been at rest for half an hour commence to spray them with a revolving garden sprinkler or by carefully wetting with a sprinkling pot on the center of the block only. The blocks should not be allowed to dry out for at least ten days after removal from the working plate. The removal from the working plate can be done the morning after molding and should never be done before even if the block was made in the morning.

In removing the green block from the skids let there be cones of sand between the rows of blocks and up-end each working plate so as to let the end of the block come upon the sand cushion. Don't twist and turn the block, and to remove the working plate pa.s.s a stick through the core holes in both block and plate so that the plate will not fall when loosened. A slight rap on the center of the plate will loosen it. As soon as the blocks are up-ended commence the spraying and soak the sand underneath the block. It may seem unnecessary to dwell on these points so long, but barrels of cement and barrels of money have been wasted by neglecting to supply the hardening block with water. Curing is just as important as molding in making concrete blocks."

The block construction had been detailed by the architect from cellar to roof, so that it was known beforehand how many blocks of given size were to be made. The unit of length was 32 ins.; this afforded fractional parts of 8 ins., 16 ins. and 24 ins., therefore all openings were in multiples of 8 ins. Odd sizes were made, by inserting "blanks" in the mold box, to inches or fractions of an inch if desired. This unit length was less mortar joints, while the unit of height was 9 ins., or the same as four ordinary bricks with joints. The floor levels were calculated in multiples of 9 ins., so that the wall could be finished all around where the beams were to be seated. This beam course was made of solid blocks; that is, no cores were used in molding them. With the machine used no change was required to mold these solid blocks except to remove the cores. The core holes in the working plate were simply covered with pieces of tin. The shape of the block was the same and the same materials were used.

The best record in making blocks for this work was 30 blocks, 8932 ins., in one hour, working six men, three mixing and three on the machine, and using one barrel of cement for 16 blocks. This was a record run, however, a fair average being 20 blocks per hour, or 200 per ten hours, which was the day worked. We have then the cost of making blocks as follows:

1 foreman, at $2.50 $ 2.50 5 helpers, at $2 10.00 13 barrels cement, at $2 26.00 10 cu. yds. sand and gravel, at $1 10.00 Interest and depreciation on machine 2.00 ------ Total for 200 blocks $50.50

This gives a cost per block of $50.50 200 = 25 cts. The displacement in the wall of each block is 1.75 cu. ft., or the same as 30 bricks.

The cost of laying blocks is the most uncertain item in the whole industry. Mr. Palmer states that he has known of instances where it cost only 5 cts. per block and of other instances where, because of the difficulty of getting help and its inexperience, it cost 15 cts. per block. In this particular building one mason and three helpers laid 100 blocks per day. The building had no long walls, but it did have many turns. The cost of laying, then, was as follows:

1 mason, at $4 $ 4.00 3 helpers, at $2 6.00 ----- Total for 100 blocks $10.00

This gives a cost for laying of 10 cts. per block. We have, then:

Making 2,000 blocks $505 Laying 2,000 blocks 200 ---- Total $705

This gives a cost of 35 cts. per block for making and laying.

The use of a derrick for laying the blocks proved a considerable item of economy in this work. This derrick cost $50 and two men could mount and move it on the floor beams. It had a boom reaching out over the wall and was operated by a windla.s.s. A plug and feather to fit the center 6-in.

hole in the block was used for hoisting the blocks. By this means blocks only seven days old were laid without trouble. It may be noted that the walls were kept drenched with water to make sure that the blocks did not dry out until they were at least 28 days old. In laying the blocks a thin lath was used to keep the mortar back about one inch from the face.

This precaution will prevent much labor in cleaning the walls from mortar s...o...b..r.

~Two-Story Building, Albuquerque, N. M.~--The following record of cost of making 91032-in. hollow blocks in a Palmer machine and of laying 2,000 of them in two-story building walls is given by Mr. J. M. Ackerman. Sand cost 60 cts. per cu. yd., and cement cost $3 per barrel. Lime cost 30 cts. per bushel. One barrel of cement made 20 blocks, using a 1-4 sand mixture. In making 2,000 blocks about 100 blocks, or 5 per cent., were lost by blocks breaking in hauling from yard to building or by cutting blocks to fit the work. The blocks were molded by piece work for 5 cts per block, all materials, tools and plant being supplied to the molders.

Three men with one machine made from 100 to 150 blocks per day. The cost was as follows:

Item. Per block.

Cement, at $3 per bbl. $0.15 Molding, at 5 cts. per block 0.05 Sand, at 60 cts. per cu. yd. 0.03 Carting, yard to building 0.02 Lime and sand for mortar 0.03 Laying in wall 0.10 Loss in making and cutting 0.01 ----- Total $0.39

As each block gave 9 32 = 288 sq. ins., or 2 sq. ft., of wall surface, the cost of the wall per square foot was 19.5 cts. a.s.suming 40 per cent.

hollow s.p.a.ce, each block contained 1 cu. ft. of concrete, which cost 23 cts., or $6.21 per cu. yd., for materials and molding. Blocks in the wall cost $10.55 Per cu. yd. of concrete.

~General Cost Data.~--The following data are given by Prof. Spencer B.

Newberry. The average weights of three sizes of hollow blocks are as follows:

Size, ins. P. C. Hollow s.p.a.ce. Weight, lbs.

8932 33-1/3 120 10932 33-1/3 150 12932 33-1/3 180

Costs of materials are a.s.sumed as follows:

Item. Per 100 lbs.

Cement, at $1.50 per bbl. $0.40 Hydrated lime, at $5 per ton $0.25 Sand, gravel or screenings, at 25 cts. per ton $0.012

Mixed in batches of 750 lbs., sufficient for six 8-in. or four 12-in.

blocks, the cost of materials per batch and per block will be for a 1-4 mixture as follows:

Item. Per Batch. 8-in. Block. 12-in. Block.

150 lbs. cement $0.60 $0.10 $0.15 600 lbs. sand 0.072 0.012 0.018 ------ ------ ------ Total $0.672 $0.112 $0.168

In general a factory producing 600 8-in. blocks per day will require 25 men to operate it. At an average wage of $1.80 per day the following is considered as a fair estimate of cost:

Item. Per Day. Per Block.

Materials for 600 blocks $ 60 $0.10 25 men, at $1.80 45 0.075 Repairs 10 0.017 Office and miscellaneous 20 0.034 ---- ------ Total $135 $0.226

This gives for 8932-in. blocks a cost of about $6.78 per cu. yd. of concrete for materials and molding or of 11.3 cts. per sq. ft. of face.

Mr. L. L. Bingham gives the following as the average cost per square foot of face for 10-in. wall from data collected from a large number of block manufacturers operating in Iowa in 1905:

Cement at $1.60 per bbl. 4.5 cts.

Sand 2.0 cts.

Labor at $1.83 per day 3.8 cts.

--------- Total cost per square foot 10.3 cts.

a.s.suming one-third hollow s.p.a.ce, the cost for materials and molding was $5.05 per cu. yd. of concrete not including interest, depreciation, repairs, superintendence or general expenses.

CHAPTER XXI.

METHODS AND COST OF AQUEDUCT AND SEWER CONSTRUCTION.

Aqueducts and sewers in concrete are of three kinds: (1) Continuous monolithic conduits, (2) conduits laid up with molded concrete blocks, and (3) conduits made up of sections of molded pipe. Block conduits and conduits of molded pipe are rare in America compared with monolithic construction; examples of each are, however, given in succeeding sections, where forms, methods of molding, etc., are described. The following discussion refers to monolithic construction alone.