Concrete Construction Part 3

NOTE.--A, is a "fine gravel" (containing 8% clay) used at Philadelphia. B, Delaware River sand. C, St. Mary's River sand.

D, Green River, Ky., sand, "clean and sharp."

TABLE III.--SHOWING MEASURED VOIDS IN SAND FROM DIFFERENT LOCALITIES.

Percent Locality. Authority. Voids. Remarks.

Ohio River W. M. Hall 31 Washed Sandusky, O. C. E. Sherman 40 Lake Franklin Co., O. C. E. Sherman 40 Bank Sandusky Bay, O. S. B. Newberry 32.3 ......

St. Louis, Mo. H. H. Henby 34.3 Miss. River Sault Ste. Marie H. von Schon 41.7 River Chicago, Ill. H. P. Broadman 34 to 40 ......

Philadelphia, Pa 39 Del. River Ma.s.s. Coast 31 to 34 ......

Boston, Ma.s.s Geo. Kimball 33 Clean Cow Bay, L. I. Myron S. Falk 40 ......

Little Falls, N. J. W. B. Fuller 45.6 ......

Canton, Ill. G. W. Chandler 30 Clean

~Voids in Broken Stone and Gravel.~--The percentage of voids in broken stone varies with the nature of the stone: whether it is broken by hand or by crushers; with the kind of crusher used, and upon whether it is screened or crusher-run product. The voids in broken stone seldom exceed 52 per cent. even when the fragments are of uniform size and the stone is shoveled loose into the measuring box. The following records of actual determinations of voids in broken stone cover a sufficiently wide range of conditions to show about the limits of variation.

The following are results of tests made by Mr. A. N. Johnson, State Engineer of Illinois, to determine the variation in voids in crushed stone due to variation in size and to method of loading into the measuring box. The percentage of voids was determined by weighing the amount of water added to fill the box:

Method of Per cent.

Size. Loading. of Voids.

3 in. 20-ft. drop 41.8 3 in. 15-ft drop 46.8 3 in. 15-ft. drop 47.2 3 in. Shovels 48.7 1 in. 20-ft. drop 42.5 1 in. 15-ft. drop 46.8 1 in. 15-ft. drop 46.8 1 in. Shovels 50.5 in. 20-ft. drop 39.4 in. 15-ft. drop 42.7 in. 15-ft. drop 41.5 in. 15-ft. drop 41.8 in. Shovels 45.2 in. Shovels 44.6 3/8 in. Shovels 41.0 3/8 in. Shovels 40.6 3/8 in. Shovels 41.0

The table shows clearly the effect on voids of compacting the stone by dropping it; it also shows for the -in. and the 3/8-in. stone loaded by shovels how uniformly the percentages of voids run for stone of one size only. Dropping the stone 20 ft. reduced the voids some 12 to 15 per cent. as compared with shoveling.

TABLE IV.--SHOWING DETERMINED PERCENTAGES OF VOIDS IN BROKEN STONE FROM VARIOUS COMMON ROCKS.

--------------------+--------+------------------------------------------------ | Percent| Authority. | Voids.| Remarks.

--------------------+--------+------------------------------------------------ Sabin | 49.0 | Limestone, crusher run after screening out | | 1/8-in. and under.

" | 44.0 | Limsetone (1 part screenings mixed with | | 6 parts broken stone).

Wm. M. Black | 46.5 | Screened and washed, 2-ins. and under.

J. J. R. Croes | 47.5 | Gneiss, after screening out -in. and under.

S. B. Newberry | 47.0 | Chiefly about egg size.

H. P. Broadman |39 to 42| Chicago limestone, crusher run.

" |48 to 52| " " screened into sizes.

Wm. M. Hall | 48.0 | Green River limestone, 2-ins. and smaller | | dust screened out.

" | 50.0 | Hudson River trap, 2-ins. and smaller, | | dust screened out.

Wm. B. Fuller | 47.6 | New Jersey trap, crusher run, 1/6 to 2.1 in.

Geo. A. Kimball | 49.5 | Roxbury conglomerate, to 2 ins.

Myron S. Falk | 48.0 | Limestone, to 3 ins.

W. H. Henby | 43.0 | " 2-in size.

" | 46.0 | " 1-in size Feret | 53.4 | Stone, 1.6 to 2.4 ins.

" | 51.7 | " 0.8 to 1.6 in.

" | 52.1 | " 0.4 to 0.8 in.

A. W. Dow | 45.3 | Bluestone, 89% being 1 to 2 ins.

" | 45.3 | " 90% being 1/6 to 1 in.

Taylor and Thompson | 54.5 | Trap, hard, 1 to 2 ins.

" | 54.5 | " " to 1 in.

" | 45.0 | " " 0 to 2 in.

" | 51.2 | " soft, to 2 ins.

G. W. Chandler | 40.0 | Canton, Ill.

Emile Low | 39.0 | Buffalo limestone, crusher run, dust in.

C. M. Saville | 46.0 | Crushed cobblestone, screened into sizes.

TABLE V.--SHOWING PERCENTAGES OF VOIDS IN GRAVEL AND BROKEN STONE OF DIFFERENT GRANULOMETRIC COMPOSITIONS.

/--Per cent Voids in-- Pa.s.sing a ring of 2.4" 1.6" 0.8" Round Broken Held by a ring 1.6" 0.8" 0.4" Pebbles. Stone.

Parts 1 0 0 40.0 53.4 " 0 1 0 38.8 51.7 " 0 0 1 41.7 52.1 " 1 1 0 35.8 50.5 " 1 0 1 35.6 47.1 " 0 1 1 37.9 40.5 " 1 1 1 35.5 47.8 " 4 1 1 34.5 49.2 " 1 4 1 36.6 49.4 " 1 1 4 38.1 48.6 " 8 0 2 34.1 ....

Table IV gives the voids in broken stone as determined by various engineers; it requires no explanation. Table V, taken from Feret's tests, shows the effect of changes in granulometric composition on the amount of voids in both broken stone and gravel. Considering the column giving voids in stone it is to be noted first how nearly equal the voids are for stone of uniform size whatever that size be. As was the case with sand a mixture of coa.r.s.e and fine particles gives the fewest voids; for stone an L_{1}M_{0}F_{1} mixture and for gravel an L_{8}M_{0}F_{2} mixture. Tamping reduces the voids in broken stone. Mr. Geo. W. Rafter gives the voids in clean, hand-broken limestone pa.s.sing a 2-in. ring as 43 per cent. after being lightly shaken and 37 per cent. after being rammed. Generally speaking heavy ramming will reduce the voids in loose stone about 20 per cent.

It is rare that gravel has less than 30 per cent. or more than 45 per cent. voids. If the pebbles vary considerably in size so that the small fit in between the large, the voids may be as low as 30 per cent. but if the pebbles are tolerably uniform in size the voids will approach 45 per cent. Table V shows the effect of granulometric composition on the voids in gravel as determined by Feret. Mr. H. Von Schon gives the following granulometric a.n.a.lysis of a gravel having 34.1 per cent. voids:

Retained on 1-in. ring, per cent. 10.70 Retained on 3/8-in. ring, per cent. 23.65 Retained on No. 4 sieve, per cent. 8.70 Retained on No. 10 sieve, per cent. 17.14 Retained on No. 20 sieve, per cent. 21.76 Retained on No. 30 sieve, per cent. 6.49 Retained on No. 40 sieve, per cent. 5.96 Pa.s.sed a No. 40 sieve, per cent. 5.59 Pa.s.sed a 1-in ring, per cent. 100.00

As mixtures of broken stone and gravel are often used the following determinations of voids in such mixtures are given. The following determinations were made by Mr. Wm. M. Hall for mixtures of blue limestone and Ohio River washed gravel:

Per cent. Per cent. Per cent.

Stone. Gravel. Voids in Mix

100 with 0 48 80 " 20 44 70 " 30 41 60 " 40 38 50 " 50 36 0 " 100 35

The dust was screened from the stone all of which pa.s.sed a 2-in. ring; the gravel all pa.s.sed a 1-in. screen. Using the same sizes of gravel and Hudson River trap rock, the results were:

Per cent. Per cent. Per cent.

Trap. Gravel. Voids in Mix.

100 with 0 50 60 " 40 38 50 " 50 36 0 " 100 35

The weight of a cubic foot of loose gravel or stone is not an accurate index of the percentage of voids unless the specific gravity is known.

Pure quartz weighs 165 lbs., per cu. ft., hence broken quartz having 40 per cent. voids weighs 165 .60 = 99 lbs. per cu. ft. Few gravels are entirely quartz, and many contain stone having a greater specific gravity like some traps or a less specific gravity like some shales and sandstone. Tables VI and VII give the specific gravities of common stones and minerals and Table VIII gives the weights corresponding to different percentages of voids for different specific gravities.

TABLE VI.--SPECIFIC GRAVITY OF STONE. (Condensed from Merrill's "Stones for Building.")

Trap, Boston, Ma.s.s. 2.78 " Duluth, Minn. 2.8 to 3.0 " Jersey City, N. J. 3.03 " Staten Island, N. Y. 2.86 Gneiss, Madison Ave., N. Y. 2.92 Granite, New London, Conn. 2.66 " Greenwich, Conn. 2.84 " Vinalhaven, Me. 2.66 " Quincy, Ma.s.s. 2.66 " Barre, Vt. 2.65 Limestone, Joliet, Ill. 2.56 " Quincy, Ill. 2.51 to 2.57 Limestone, (oolitic) Bedford, Ind. 2.25 to 2.45 " Marquette, Mich. 2.34 " Glens Falls, N.Y. 2.70 " Lake Champlain, N. Y. 2.75 Sandstone, Portland, Conn. 2.64 " Haverstraw, N. Y. 2.13 " Medina, N. Y. 2.41 " Potsdam, N. Y. 2.60 " (grit) Berea, O. 2.12

TABLE VII.--SPECIFIC GRAVITY OF COMMON MINERALS AND ROCKS.

Apat.i.te 2.92-3.25 Basalt 3.01 Calcite, CaCO_{3} 2.5-2.73 Ca.s.siterite, SnO_{2} 6.4-7.1 Cerrusite, PbCO_{3} 6.46-6.48 Chalcopyrite, CuFeS_{2} 4.1-4.3 Coal, anthracite 1.3-1.84 Coal, bituminous 1.2-1.5 Diabase 2.6-3.03 Diorite 2.92 Dolomite, CaMg (CO_{3}) 2.8-2.9 Felspar 2.44-2.78 Felsite 2.65 Galena, Pbs 7.25-7.77 Garnet 3.15-4.31 Gneiss 2.62-2.92 Granite 2.55-2.86 Gypsum 2.3-3.28 Halite (salt) NaCl 2.1-2.56 Hemat.i.te, Fe_{2}O_{3} 4.5-5.3 Hornblende 3.05-3.47 Limonite, Fe_{3}O_{4} (OH)^{6} 3.6-4.0 Limestone 2.35-2.87 Magnet.i.te, Fe_{3}O_{4} 4.9-5.2 Marble 2.08-2.85 Mica 2.75-3.1 Mica Schist 2.5-2.9 Olivine 3.33-3.5 Porphyry 2.5-2.6 Pyrite, FeS_{2} 4.83-5.2 Quartz, SiO_{2} 2.5-2.8 Quartzite 2.6-2.7 Sandstone 2.0-2.78 " Medina 2.4 " Ohio 2.2 " Slaty 1.82 Shale 2.4-2.8 Slate 2.5-2.8 Sphalerite, ZnS 3.9-4.2 Stibnite, Sb_{2}S_{3} 4.5-4.6 Syenite 2.27-2.65 Talc 2.56-2.8 Trap 2.6-3.0

TABLE VIII.--SHOWING WEIGHT OF STONE WITH DIFFERENT PERCENTAGES OF VOIDS FOR DIFFERENT SPECIFIC GRAVITIES.

Weight Weight in Lbs. in Lbs. Weight in Lbs. per cu. yd.

Specific per per when Voids are Gravity. cu. ft. cu. yd. 30% 35% 40% 45% 50%