US2381779A - Protection device against aerial and other bombardment - Google Patents

Description

Aug. 7, 1945. F. s. SCOTT 2,331,779

PROTECTION DEVICE AGAINST AERIAL AND DTHER BOMBARDMENT Filed July 16. 1940 (a) Penetration INVENTOR Patented Aug. 7, 1945' PROTECTION DEVICE AGAINST AER- AL AND OTHER BOREABDMENT Frederick S. Scott, Los Angeles, Calif assigns:-

to Union Oil Company or California, Los Angeles, CaliL, a corporation of California a Application July 16, 1940, Serial No. 345,827

8 Claims.

This invention relates to the safe-guarding of structures and various objects of importance from the destructive effects of aerial or other bombardment. The invention also relates to the composition of materials which are used, and the way in which the materials are integrated to give the best protection.

One of the important factors in defense is the safety of many of the structures which are essential to the continuance of economic life, du ing war as well as peace. Among structures which represent great engineering feats, the preservetlon of which would be a necessity in waging a defensive war, there might be mentioned the Panama Canal locks and numerous dams, such as Boulder Dam. Unfortunately, these edifices were built without anticipating the effectiveness of aerial bombardment, and must now be considered with reference to their vulnerability to attack.

An obiect of the present invention, therefore, is to provide a method whereby not only structures already completed may be rapidly safeguarded, but also the protection of structures yet to be completed, such as forts, etc, of the new defense bases along the coasts of the United Etates and at various points in the Caribbean and Hawaiian Islands.

A further object of my invention is to provide protection of other than stationary objects, since protection against the shattering efiects of bombs on the steel decks of battleships, for instance, may be obtained by using a material having a high degree of protection with reference to its specific gravity.

The effects of bombardment are essentially twotold:

(I) The penetrating efiect due to the kinetic energy possessed by the projectiles, and

(2) The shattering elfect caused by the rapid expansion and production of gases from the explosive contained in the shell.

The importance of the penetration factor varies, being dependent on the speed of the shell, and whether the shell is equipped with a delayed timmg detonator. A deeply imbedded shell is, of course, much more effective than one which explodes on the surface. In constructing any protection against bombardment, therefore, one must cgnsider primarily the two effects enumerated a ove.

My invention resides in the utilization of a covering material composed of layers, each layer being characterized by either its shock-absorbing powers or its resistance to penetration. Such a. structure would include comparatively thin layers of shock resistant material while the penetration resistant layer would be comparatively thick. As shown in the drawing: a is a portion of a concrete dam or fortification, b is composed of a resilient material, while c is penetration resistant material. The number of layers need not be restricted, as

shown.

Furthermore, the shock absorbent layer 1) may be continuous, or it may be honeycombed with air spaces to give a wane-like structure, as long as there is sufhcient material to act as a support for the upper layer. This form has shock absorbent powers not realized in the solid continuous form, since air is an ideal shock absorber. Again, this structure has the advantage of being capable of diffusing the shock waves so that their destructive effect is minimized.

As examples of shock absorbent materials which are resistant to shattering and spelling I wish to list particularly bituminous materials of all ln'nds, including air-blown, steam blown and filled asphalts; mixtures of asphalt with rock, sand and dust which have a high proportion of asphalt, and bituminous saturated roofing felt. However, besides bituminous materials I may use rubber and rubber compounds, cork and, in fact, any similar material which has a minimum capacity of transmitting shock waves. The materials need. not necessarily be resilient, since a shattering or smalling resistance may even be obtained by including a layer of Cellophane between layers of cement, the desired effect here not being due to the Cellophane, but to its producing a discontinuity in the concrete structure, which in turn interrupts the shock waves. A preferred asphalt which has maximum shock absorbing qualities and yet has sufficient supporting strength is one with a melting point of 225 lit-325 F. and a penetration of 77 F. g.5 sec.) of (1-23. The invention need not be limited to the examples of compositions just enumerated, since the essence of the invention is in the use of the two materials having the herein descri' ed characteristics and their use in conjunction we -h one another.

In general, a rest layer of a resilient shock absorbing substance, such as air-blown asphalt of a high melting point, or mineral rubber, Cellophane, felt containing asphalt, etc., is placed next to the structure to be protected using some suitable thickness which has been determined to suit the properties of the materials used in each of the layers. The second, or penetration resistant layer c, is then applied. As examples of penetration resistant materials which may be used in this layer are Portland cement concrete, steel, brick, sand, rock, hard asphalting concrete and the like, although I prefer to use hard asphaltic concrete, which comprises a mixture of steam blown or airblown asphalt with a suitable quantity of graded sand and/or rock dust.

The advantage of using asphalt compositions in preference to Portland cement mixtures in protection for fortifications and the like, is. evident because of several outstanding reasons.

One of these is that asphalt mastic mixtures reach their final condition of maximum strength as soon as they have cooled, while the overuse Portland cement concrete requires a, twenty-eight day period before approaching its maximum strength. This is important especially in making possible eilective emergency repairs. Freshly poured asphsltic mixtures bond perfectly to old asphaltle mixtures, thus if a portion of the structure is partially destroyed, it can be repaired uickly by merely filling the crater and cracks with a fresh asphaltic mixture. the other hand, it is not feesihlle to obtain a good bond between cured and fresh Portland cement concrete. A damaging shrapnel efieet following explosions is avoided, since an asphalt mixture of good strength can be made without using large proportions of relatively coarse rock. Asphaltic mixtures do not split out large fragments on the surface when a direct hit is made and, furthermore, when an indirect hit is msde the cushioning effect of the rubbery plastic binder in the asphalt mastic is of benefit because the asphalt resists shock relatively'well. Besides these characteristics, certain types of asphaltic mastic compositions resist penetration of high impact missiles to about the same extent as well-cured Portland cement concrete.

In order to test materials for shock absorbent power, the following method can be employed:

A piece of material to be tested is placed on a smooth surface of a leadblock and a half stick of dynamite is then placed on the test material. The depth of the impression produced by detonation of the dynamite serves as a measure of the shock absorbent power of the material Table I gives the materials used as absorbers and the corresponding impression made on lead by the explosion.

Table I Depthof Material description 135? 1m rgfoll,

Air )i 0.100 Plno M (11$ Mineral rubber300 M. P. oxidized as halt. 54 0. 192 Asp zdt mortar-9% steam blown- M 0.27? penetration at 100 g. and soc.) :2 1126 150-200 re der send 0.231 Satuteinted {fit-gigs of Mo" lelt, ssmra 254 a wii. esp 'lilo 54 0.323

The penetration resistance of various composltions is conveniently tested by simply firing rifle bullets at the test substance perpendicular to the surface of this material. The Springfield 30-06 rifle bullet fired point blank at fifty feet using different compositions penetrates as indicated below in Table II.

The asphsltlc concrete 2% inches thick was composed of 48 parts iii-28 mesh gravel, 52 parts to mesh, 10 ports reels larger than 16 mesh, and 29 parts asphalt Bevin: a. penetration of 50-60 at 77' F. (180 8P5 sec). The 8 inches thick sample of asphsltic concrete was prepared usinz 17.1 parts asphalt and 120 parts siliclous concrete send. The asphalt had a penetration value of 150-300 (169 e.-5 sec.) at 17' F., while the send used had the following characteristics: passed 2&3 meals-Lt Darts; 89 to 269 mesh-8.4 parts; 28 to so xneeh--52 parts. 10 to 2-8 mesh- 48 parts; retained on 1G mesh-10.3 parts; clintomaceons earth-4.8 parts, All uant ties given are parts by weight.

The Portland cement concrete was a mi: contraining 1 part of Portland cement, 2 parts sand (104%) mesh) and 4 parts rock (retained on 10 mesh).

The aspheltic mixture compositions may be further improved to give them more resistivity to penetration, mainly by varying the type of filler used. In the case of the Portland cement concrete, the spell crster was very large or about 5-10 times greater in diameter than that produced in the asphalt composition having the penetration resistance given in the examples described herein. As the resistance to penetration is increased in the asphaltic concrete, 1. e., up to a value equal to that characteristic of :1 Portland cement concrete, the brittleness increase and the smile from a rifle bullet shot being thrown several feet. These two opposed qualities of low spelling and low penetration resistance may be compromised by varying the composition at will. The compositions may be varied considerably by using nsphalts having wide ranges of properties and by using different kinds of sand and rock. For instance, the shock resistant layer may contain 845% asphalt having a normal" penetration at 77 F. (180 g. at 5 sec.) of Iii-3&9 and the penetration resistant layer may contain 345% asphalt having approximately the same specifications.

Tests were also carried out to demonstrate the greatly improved resistance of 9. Portland cement concrete structure to explosives when it is protected using the method herein described.

Two blocks, each 5 ft. x 5 it. x 3% ft., were employed in the test. Qne block was protected in any way, while the second one was covered with asphalt saturated paper followed by a 12 inch layer of 9% asphalt concrete. The asphalt concrete was composed of about our parts 10-80 mesh decomposed granite, four parts less than No. 10 mesh decomposed granite, one part greater than mesh decomposed granite and limestone dust, and $4; part asphalt. This asphalt had the specifications: Melting point of -105 F4 penetration at, 77 F. g.-5 sec.) of -200.

To simulate a hit by an aerial bomb, the blocks were subjected to repeated blastlngs using three sticks of Hercules straight 60% nitroglycerin dynamite at a time. The sticks weighed 6 ounces apiece, and the bundle was placed each time in the crater produced by the preceding explosion. After five charges. no shattering of the asphalt bloc; had warned, while after four charges, long cracks were produced in the Portland cement concrete block. After sever. blastings the Portland cement block was seriously cracked all over the top and down the sides, the top foot of the block having no supporting value at all. Al though seven blasts finally had split the asphalt covering into four segments, the Portland cement 2M0 mesh sand, 4 parts rock dust finer than 7 concrete block beneath was undamaged.

This experiment also presented an opportunity to show clearly the reduced spelling which occurs in the asphalt mastics as compared to the Portland cement concrete. At the end of the sixth blasting, the crater in the Portland cement concrete block measured 34 x 29 inches at the surface of the block and was 8% inches deep, while the crater in the protective covering of asphalt mastic at the end of the sixth blasting measured only 13 x 13 inches at the surface and was Eli-Q inches deep. The reduction in spalling of the asphalt compositions in comparison to the Portland cement mixtures is shown in Table II. where riiie fire was the method of testing employed.

It is understood that the above description is merely illustrative of preferred embodiments of my invention of which many variations may be made within the scope of the following claims without departing from the spir t thereof.

I claim:

1. An article comprising a structure having thereon a coating comprising a relatively thin internal layer of shock resistant material and a relatively thick external layer of penetrationresistant hard asphaltic concrete.

2; An article according to claim 1 in which the shock resistant material is about {a inch to about /2 inch in thickness, and the penetration resistant material is at least 6 inches thick.

3. An article according to claim 1 in which the shock resistant material is felt saturated with asphalt.

4. An article according to claim 1 in which the shock resistant material is pine.

5. An article aCCOIdlng to claim 1 in which the shock resistant material is an asphalt having a melting point of 225 F. to 325 F. and a penetration at 77 F. (100 g.--5 sec.) of to 20.

6. An article according to claim 1 in which the shock resistant material is honeycombed with air pockets.

7. An article according: to claim 1 in which the penetration resistant 1.-iaterial contains about 3% to 15% of asphalt having a penetration at 77 F. (100 g. at sec.) of to 300.

8. An article comprising a structure having thereon a coating comprising a. continuous inner layer about inch to 2; inch thick, made of asphalt of about 225 to 325 F. melting point and about 0 to penetration at 77 F. g.-- 5 sec), and a continuous outer layer of at least six inches thick, made of a hard asphalt concrete, containing about 3% to 15% of asphalt having a penetration at 77 F. (100 g. at 5 sec.) of 1G to 300 together with a mineral aggregate.

FREDERICK S. SCOTT.

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