US3429094A - Two-phase concrete and steel material - Google Patents

Description

TI'O'HASB CONCRETE MID STEEL MATERIAL Sheet cf 2 Filed July 7, 1965 FIG. i

VALUES FOR NORMALLY REIHFORCED BEAMS )u R. /p .o p w mw m 2 u e. 1 pu p/.im` O 4. O 2 llll. L d 'D ,/Flw M u 2 8 n. O 0./ G Cl 5. O 4. 0. 2. 7 O

JAMES P. QCUALD BY M Feb. 25, 1989 J. |=.R0MUA1 D| TWOPHASE CONCRETE AND STEEL MATERIAL Sheet of 2 Filed July 7, 1965 I l -MU/f AVERAGE WIRE SPACING, INCHES O 5 D O 5 O. 5 O 4. 3. 3 u a l. I o.

0.8 LO AVERAGE WIRE SPACING, INCHES .DI mm. T www wm LP.\Y. m A J B d, m. F

ATTORNEYS United States Patent4 O 3,429,094 TWO-PHASE CONCRETE AND STEEL MATERIAL James P. Romualdi, Pittsburgh, Pa., assignor, by mesne assignments, to The Battelle Development Corporation, Columbus, Ohio, a corporation of Delaware Continuation-impart of application Ser. No. 246,819, Dec. 24, 1962. This application July 7, 1965, Ser, No. 471,505 U.S. Cl. 52-659 Int. Cl. E04c 5/01, 3/20 18 Claims ABSTRACT F THE DISCLOSURE This invention relates to a new concrete material and to a method of preparing it. More particularly, this invention relates to a two-phase material comprising steel wire within concrete, the wires being spaced in a critical fashion. The invention also further contemplates methods of providing such two-phase material. The invention herein described is a continuation-in-part of cop-ending application Ser. No. 246,819 led Dec. 24, 1962, and now abandoned.

For many years, the low tensile strength of concrete has been recognized and has been accepted as an unavoidable limitation to be taken into account in considering applications for concrete. In the past, attempts to compensate for the lack of tensile strength in concrete have usually involved either (a) unstressed reinforcing steel rods, or (b) prestressed reinforcing steel rods. Neither of these procedures really overcomes the low tensile strength limitation, but each merely bypasses it. Thus, concrete reinforced in this conventional manner is characterized' by the fact that cracks form and propagate through regions in tension. Such cracks form at relatively low stresses and they continue until either they reach a -free surface or until they reach a region that is in compression.

Furthermore, the tensile strength exhibited in conventionally reinforced or plain concrete, as determined by standard tests, cannot be relied upon for design purposes since the formation of small incipient cracks due to fatigue, thermal shock or cavities substantially reduces the tensile strength of the concrete. incipient crack formation and subsequent propagation thereof is not alwaysevident, but the conditions favorable for the same cannot be predicted. Even the exercise of exceptional control procedures does not always minimize crack formation and growth. It has, therefore, long been accepted that about one-half of the material in a normally reinforced concrete beam is useless to resist tensile loads. The detrimental effects of tension cracks in reinforced concrete beams are not limi-ted solely to loss of load-resistant area For example, it is apparent that tension cracking severely limits the effectiveness of concrete tanks for containing liquids, Also, the use of reinforced concrete in marine structures is sharply curtailed because of the corrosive effect of salt water on reinforcing steel exposed by tension cracks.

lt is, therefore, an object of this invention to provide a two-phase material comprising concrete and fine steel ICC wires and having tensile strength in the order of two to three times that of conventionally reinforced concrete,

Another object of this invention is to provide a twophase material comprising concrete and tine steel wires 5 and characterized by substantial resistance to propagation of tensile cracks.

Yet another object of this invention is to provide a two-phase material comprising concrete and fine steel wires and possessing attributes of a homogeneous material in that it experiences extensive plastic ow without disintegration.

Still another object of this invention is to provide a resilient and flexible two-phase material comprising concrete and ne steel wires with ability to absorb energy more etiiciently than conventionally reinforced concrete.

A further object of this invention is to provide a twophase material comprising concrete and ne steel wires with enhanced ability to resist the formation and propagation of fatigue cracks as a result of repeated application of tensile stresses.

An additional object of this invention is to provide a two-phase material comprising concrete and ne steel wires with enhanced ability to resist Cracking due to tensile thermal stresses arising from abrupt temperature changes.

Other objects of this invention include a process of preparing a two-phase material characterized by properties set forth above.

Other objects and advantages of this invention will be apparent from the following detailed description thereof, particularly when read in conjunction with the attached drawings wherein:

FIG. l(a) illustrates a material of one embodiment of the present invention and FIG, 1(b) illustrates a beam made from a material of another embodiment;

FIG. 2 is a plot comparing the ultimate bending strength of materials of this invention with conventional materials;

FIG. 3 is a plot showing the critical relationship ofV wire spacing to the properties of the materials of this invention, 4and FIG. 4 is a plot of actual cracking stresses as a function of wire spacing for materials of this invention.

In general, this invention includes within its scope a two-phase material comprising concrete with ne steel wires distributed therein in such a way that the average spacing between wires is not in excess of 0.5 inch, and preferably is less than about 0.3 inch. The steel wires spaced as set forth above provide a crack arrest mechanism that increases cracking strength and provides toughness to a degree heretofore unobtainable in conventional concrete. By virtue of their function to increase cracking strength, the critically spaced wires of the concrete of this invention can be referred to as crack arrestors."

The material is prepared in one embodiment by mixing given proportions of short pieces of wire directly with cement, sand, and water. On the other handmous wires can be placed so as to achieve the critical spacing w ix o concrete is poured around them.

Two embodiments of the invention are illustrated schematically in FIG, 1. In FIG. l(a) a cross-section through a concrete beam l0 in tension is shown with short wire reinforcing elements 12-12 therein.

Beam 10 can be prepared by rst mixing sand, cement, and water in a mixer and subsequently adding wire thereto. Because individual wires have a tendency to ball-up, it is sometimes desirable to project the same into the rotary drum by means of a suitable blowing mechanism.

Following wire addition, additional water may be added as required. Care should be 'exercised in adjusting the water-cement ratio. Where the mixture is either too wet or too dry, there is a tendency for knitting of wires into 3 balls. The correct water/cement ratio is determined by i visual observation of the mass undergoing mixing. It has also been observed, that at higher ratios of length of wire ito diameter, there is a greater tendency for knitting of individual wire elements during mixing. In addition to cement, sand,` and water, the concrete mix may also in- Vclude coarse aggregate. The coarse aggregate may contsist of pieces of aggregate with largest dimension greater than 0.3 inch and also greater than 0.5 inch. When coarse M 'aggregate is used, the volume percent of wire added (t should be such that the average spacing between the wires 'j in the sand, cement, and water portion occupying the interstices between the coarse aggregate is not in excess of i0.5 inch, and preferably less than 0.3 inch.

. A similar concrete beam with reinforcing elements l 14-14 arranged in parallel relation is illustrated in FIG. l(b). In the second embodiment, the material is t prepared by placing long continuous wire strands, or wire i mesh, in the forms and then pouring a very huid sand and cement mixture in the forms.

It is postulated that the surprising improvement in i cracking strength provided by the two-phase concrete mat'terial according to this invention results from a two phase ibehavior at the critical wire spacings. To better undertstand this behavior, it is necessary to consider the bellhavior of concrete subjected to tensile stress. As concrete is subjected to tensile stress, one of the many flaws in- ;hcrent in the material will enlarge to a crack which will propagate throughout the tensile zone, thus resulting in 'failure of the member. It is believed that at the critical wire spacings described herein, displacements developing i in the material ahead of the crack edge are reacted on by the steel thereby producing a force on the matrix sui- `cient to prevent stretching of the Concrete in the immediate vicinity of the aw. An individual wire element can only extend a small lamount, if at all, to prevent relief .i of resisting forces holding the aw together. Crimped 4lwires or wavy configurations used to reinforce concrete structures of the prior art are not essential to the practice of this invention and would be considerably less eis cient than the straight wires described herein. This is be- `itcause the wires would not be aligned in a direction pertpendicular to the crack front. Similarly, a wire element having a modulus of elasticity less than that of steel (e.g., ibout 27 to 32 million psi.) would not be effective. The crack arrestor must have considerably greater stiffness Ythan the matrix. Because the strength of concrete is re- ,lated to the size of internal aws inherent therein, the smaller the wire spacing and consequently the smaller the Iallowable aw, the greater the tensile strength that can be g 'achieved. i In characterizing the material of this invention, it is f emphasized that a Wholly new concrete material is pro- ?vided. The nature of this new material and the unique two-phase behavior resulting therein at critical spacings of wire can `best be understood by comparison with "conventional reinforced concrete wherein a variety of sizes and shapes of reinforcement have been provided in the prior art. The distinctive properties of the former ma- ,"tcrial results from the wholly different functions periformed lby the metallic elements in each case. In convenltional reinforced concrete, regardless of the size and t shape of the reinforcement, the ultimate load bearing icapacity of the structure may be improved. This means lthat the structure will hold together after the first crack, but the first crack still appears at about the same bending tmoment as in a plain concrete beam of the same dimenisions. Heavy steel reinforcing bars act to carry the tensile 'load in conventionally reinforced concrete following cracking. Short wavy or otherwise irregular configurations lof the prior art may be provided to hold together cracked lconcrete by virtue of their configuration. In the present inivention, substantially straight steel wires or crack arresftors are added to concrete in a manner so as to provide a critical maximum spacing of added wire below which there is an increase in the tensile strength or cracking resistance of the concrete. Thus, the full tensile strength of concrete can be relied on for design purposes and the influence of corrosive environments in practice are minimized. Following formation of the first visible crack in the material of this invention (at the tensile strength), its behavior further deviates from that of reinforced concrete. In the latter, brittle behavior prevails and cracks propagate freely with little resistance until there is pull out of the reinforcement (at the ultimate strength). In the present material, a large amount of energy is needed to propagate a crack from wire to wire and the material is stable in the presence of cracks as in a ductile material. Both materials have a higher ultimate strength than unreinforced concrete. The outstanding characteristic of conventionally reinforced concrete lies in this higher ultimate strength. The cracking strength of the aforementioned reinforced concrete does not differ from that or plain unreinforced concrete and it also remains brittle. The uniqueness of the present concrete lies in its ability to demonstrate a much greater cracking strength than conventionally reinforced concrete together with ductility.

Although wires may be placed in a variety of positions, the essential element in the practice of this invention is the provision of the critical spacing. The only difference between the use of short, randomly dispersed wires and the use of long wires arranged parallel to the direction of principal tensile stress is that a greater volume of steel must be used in the former case. This is because certain of the random wires will be ineffectively oriented and correction must be made based on the ratio of the average of the projected lengths in one direction to the total lengths of the wire. In the case of a truly random distribution, only about 40 percent of the wires will be effective. Because it is the average spacing between the centroids of these wires that controls the behavior of the material, about 21/2 to 3 times more steel must be used for randomly spaced wire elements. When reference is made to a random distribution of short wires, the term short refers to a length sufficient to insure a random distribution of wires in a concrete article of given dimensions. To maintain a random distribution, the length .of the wires should be less than the short dimension of the concrete article. Where greater lengths are used the distribution is no longer random, and the volume percent of wire needed decreases from that required for a random distribution. This is because more wires are distributed in the direction of principal tensile stress. Similarly, when wires of any length are purposely placed in the direction of principal tensile stress, the amount needed is less than that required for a random distribution. In any event, it has been discovered that a vastly improved concrete material having exceptional cracking strength is provided when spacing of reinforcing wire is such that maximum spacing between wires is less than 0.5 inch. This latter spacing appears to be a threshold value and it has been found that the aforementioned increases of cracking strength become especially evident when maximum spacing between wires is reduced to below 0.3 inch.

-It is obvious that for the case of long, continuous wires, spacing is easily controlled and thus readily defined. Similarly, in any purposeful arrangement of wire elements, spacing is readily controlled. Where a random distribution of wires within a concrete body is desired, the average spacing of wires operating to benefit cracking strength is more difficult to define. As previously mentioned herein, a higher volume percent of randomly oriented wires must be added because not all wires will be oriented to act in the direction of principal tensile stress. For the case of randomly oriented wires, mathematical derivation can be made to describe the spatial relationship of randomly oriented wires. Although numerous manners of calculation may be employed to describe these relationships, it has been found that a rule of thumb calculation to determine the volume rcent of wire needed to. achieve a particular average wire spacing of short wirestis provided by the formula:

S=average spacing in a uniform distribution of short wires, in. d=wire diameter, in.

. P=percent of steel by volume.

Por example, to attain an average spacing between wires of not greater than 0.5 inch, .027 volume percent of wire having a diameter of .006 inch or .07 volume percent of wire having a diameter of .010 inch would be required. For the -more favorable average spacing of 0.3 inch, .08 volume percent of wire having a diameter of .006 inch or .21 volume percent of wire having a diameter of .010 inch would be required.

From the above, it is apparent the smaller diameter wires, characterized by a diameter of at most about 0.3 inch are more favorable to achieve the spacing of crack arrestors according to this invention within practical limits of volume percent of wire. Generally it has been found that for a given volume percent of wire higher ratios of length to diameter provide somewhat better cracking strength and improved -ultimate strength. For a given diameter and volume percent of wire, greater length (e.g. ll/z inches v. l/2 inch in a 2 x 2 x 12 inch beam) gives a less random distribution of wire or favors the vwire loadings, in percent by volume', of

about 1.9, 2.7, and `3.?. (as illustrated by Example 1) and 3A, ll/z, and 2 (as illustrated by Example 5) for short wire segments distributed randomly;

and wire loadings, in percent by volume, of

about 0.7, 1.5, and 1.6 (as illustrated by Example 2) for continuous wire strands.

. Example 1 To determine the effectiveness of the present invention in providing a material of greatly improved properties, a series of tensile studies was made on two-phase materials comprising concrete and short pieces of steel wire. Measurements of tensile strength were made in accordance with an indirect tension test for brittle materials, as described in an article entitled Tension Test for Concrete" by N. B. Mitchell, J r., Material Research and Standards, October 1961, pages 780-788. In this test, the specimen is in the form of a cylinder loaded in compression along two diametrically opposed edges. Ihe usefulness of the test lies in the fact that the stress in the direction perpendicular to load application is tension and is constant along the diameter of the specimen that lies along the line of load application. The magnitude of the stress is a function of the specimen size and of the total load. Table I below summarizes conditions and results of tests performed:

TABLE I Wire Tension Stress (p.s.i.) Cylinder No. Water-Cement Sand-Cement Age (days) A verage Ratio Ratio Length Percent by Spacing (inch) rack Full (inches) Volume Initiation Crack 1:2. 67 1:2.00 12 None 410 410 1:2. 67 1:2.00 l2 1.125 3.16 0.0" 925 1,090 1:4. 00 1:2. 15 21 0. 750 2. 70 0. 070 1, 035 1, 210' 1:2. 67 1:2. 00 9 1.000 1. 91 0. 083 885 945 N OTE-All cylinders 3% inch diameter. All wires 34 gage (diameter=0.0104 inch).

Wires having diameters of Inches: As illustrated by Exampleand short wire segments of lengths of l/z in. and in. (as illustrated by Example 6) and 1% in., l in., and 11/2 in. (as illustrated by Example l) distributed randomly;

continuous wire strands of lengths of 6 ft. 6 in. (as illustrated by Example 2) distributed parallel; length to diameter ratios for short wire segments of about 67, 96, and 118 (as illustrated by Example 1),

and about 83, and 104 (as illustrated by Example 6);

These test results indicate a substantial improvement in tensile strength for the closely spaced, short-wire concrete. The unreinforced concrete cracked in the ex.-` pected range at a value of 410 pounds per square inch.

The closely spaced, short-wire specimens resisted tension stresses in excess of twice this amount. Furthermore, the closely spaced, short-wire material did not exhibit the disintegration normally associated with conventionally reinforced concrete at post-cracking load, `but de` formed as a homogeneous plastic material with litmwidening of the cracks.

Example 2 Tests were made with wire mesh to establish the operability of the embodiment of the invention related to the use of critically spaced long continuous wires.

The wire used was a bright lfinish grade of high strength steel. The gages and properties are summarized below STEEL WIRE SIZES AND PROPERTIES Wire Diameter Yield Ultimate Modulus of Gage (inches) Strength Strength Elasticity (p.s.i.) (psi.)

16; 0. 0625 92, 000 104. 000 215x104 20 0. 0350 110,000 14T. 000 32X10' With two exceptions, to be described below, the wire reinforcement was woven into a mesh to facilitate placing in the forms. Detailsf thehniesh are described below.

( WIRE MESH DIMENSIOY1 Mesh Center Designation, to Center Wire Gage Number ot Spacing Wires/Linear of Wires Inch (inches) 2 x 2 0. 500 3 x il 0. 311,3 6 x 6 O. 167

Test 7 e The mesh was woven so that the wires in one di- Jrcction were straight and the transverse wires were ,crimped In all cases the straight wires were oriented parallel to the longitudinal axis of the beams.

All concrete was made from a slag -base cement. The mixes were very fluid to facilitate pouring through the :mesh and a densicr agent was used to retard set and #reduce shrinkage. The only aggregate -used was a good `quality sand. The water cement ratio was kept at 0.45

it and the sand cement ratio at 2.50. Compression cylinders fwere obtained from each mix.

Nineteen beams were made and tested. The beams were i3 inches wide, 5 inches deep and 6 feet and 6 inches long. The clear span during testing was 6 feet and the i-beams were loaded at the third points. This provided ia section between load points that was in pure bending. ,i Two of the beams were reinforced with two :Va inch Vround deformed structural grade bars, two beams were reinforced with long continuous wires, and 15 beams .fwere Cast with m 1 The mesh was prepared for the forms #by stacking strips of mesh in la ers separated by short glengrlIs-D'ftfsl'd'em''tl-Tesrate layers. This retsults in a three-dimensional mesh that is easy to handle. iT he mesh was place in t e wooden forms. The two beams provded with long continuous wires were made in a `similar form, but the separate wires were strung through templates at the ends of the forms and fastened after :being pulled hand taut. In these, the mesh was placed ronly in the end portions for shear reinforcement.

The beams were tested to destruction and data on de- Jtlection, strain and load were taken at frequent intergvals. Table Il summarizes essential details of each beam sand lists the ultimate bending moments. The dimensionless `tratio M/fcbd2 was also computed, where 'Muzultimate moment f=compressive strength of concrete ;b=beam width td=depth to centroid of beam.

`1The wire reinforced beams failed in a sudden manner ratio M/,"cbnl2 is plotted as a fnnciton of the ratio p/ pu. In this plot, p lrepresents the percentage of reinforcement by volume pu is given by 0.4 fc/fy. The results, when plotted as in FIG. 2 show the increased strength of beams made according to the present invention, but the criticality of wire spacing is not apparent in FIG. 2. However, when the ratio Mu/fcbd2 is plotted as a functionof the average spacing of the wires, the criticality of spacing (7U) becomes apparent. This .has been done in FIG. 3. In the -gures (as in FIG. 2), the Solid lines represent the ultimate strength of conventional beams as computed from the empirical equation (See Report of ASCE-ACI Joint Committee on Ultimate Strength Design, Proc. American Society of Civil Engineers, Vol. 81, Paper No. 809, October 1955.) An average yield strength of 101,000 p.s.i. was used inasmuch as the yield strength of the mes-h varied from 92,000 to 110,000 p.s.i. The plot in FIG. 3 shows a clear relationship between ultimate strength and wire spacing. A significant rise in strength occurs at a spacing of about 0.5 inch and becomes marked at 0.3 inch. At an average of 0.2 inch, the increase in strength is about percent and the data indicate that a percent increase in strength could be expected at an average spacing of 0.1 inch.

No attempt was made to locate and measure cracks accurately during these studies. It was noted by careful visual inspection, however, that hairline cracks appeared late in the life of the beams provided with continuous wire or wire mesh and hereinbefore described in Table II. Furthermore, the cracks were widely dispersed and limited to the lower extremities of the tension zone and they did not penetrate to the region of the neutral axis until failure was imminent.

Example 3 The test results of Example 2 and represented in FIGS.

l2 and 3 are reported in terms of ultimate bending moment which is enhanced as tensile resistance of the concrete is improved. Tests were also performed on a series of beam specimens with direct measurement of tensile cracking strength. The beams were reinforced with short pieces of uniformly dispersed wires. The results are plotted in FIG. 4 in terms of the ratio of the tensile strength of closely spaced wire reinforced concrete to plain concrete mixed at the same time. The pronounced effect of wire spacing on the tensile strength is evident. The plain concrete had a low tensile strength characteristic of a ma- TABLE II.SUMMARY OF BEAM DETAILS AND TEST DATA Steel P, per- Spacing, in. Mn, [y fs M l N o. Wire Area cent by in.lbs. .sfi. .s i. d in. 2 it in. volume Horiz. Vert. p p l M p/p in' 2/-inch diameter r0ds 0.22 1. 47 48,000 40,000 7,150 4. 67 0.104 0.21 g. 3 x 3 0. 22 1. 47 0. 33 0. 50 63, 000 92, 000 7, 700 3. 25 0. 256 0. 44 0. 41

0. 22 1. 47 0. 16 0. 25 84, 000 110, 000 7, 700 3. 25 0. 341 0. 52 0. 20 0. 24 1. 60 0. 50 0. 25 59, 600 92, 000 7, 700 3. 37 0. 22S 0. 48 0. 37 0. 11 0. 73 0. 50 0. 50 32, 400 92, 000 6, 000 3. 44 0. 132 0. 24 0. 50 0. 22 1. 47 0. 50 0. 19 67, 200 92, 000 6, 900 3. 78 0. 227 0. 49 0. 34 D. 11 0. 73 0. 33 1. 00 3l, 200 92, 000 6, 900 3. 14 0.153 0. 24 0. 66 0. l1 0. 73 0. 17 0. 62 42, 000 110, 000 6, 900 3. 44 0. 172 0. 29 0. 39 0. 22 1. 47 0. 33 0. 19 7S, 000 110, 000 6, 000 3. 91 0. 246 0. 59 0. 26 0, 22 1. 47 44, O00 40, 000 5, 900 4. 67 0. 114. 0. 25 0. 22 1. 47 0. 33 D. 25 72, 000 02, 000 5, 900 4. 00 0. 254 0. 57 0. 20 0. 22 1. 47 0. 17 0. 19 86, 500 110, 000 5, 900 3. 97 0. 310 0. 69 0. 18 0. 13 0. 87 0. 50 0. 54 2S, S00 92, 000 5, 650 3. 31 0. 155 0. 35 0. 52 0. 22 1. 47 0. 17 0. 16 74, 200 110,000 5, 650 3. 87 0. '290 0. 71 0 16 0. 22 1. 4Z 0. 33 0. 41 2, 200 2, 000 5, 650 3. 50 0. 250 0. 60 0 37 0. 22 1. 4i 0. 33 0. 43 48, 000 92, 000 5, 650 3. 37 0. 250 0. 40 0. 38 0. 22 1` 47 0.17 0.16 71, 000 110, 000 5, 650 3. S1 0. 290 0. 71 0. 16 y 0. 22 1. 47 0. 33 0. 32 74, 500 S2, 000 6, 620 3. 75 0. 270 0. 50 0. 32 tl.) 0 0. 22 1. 47 0.17 0. 17 105, 500 110, 000 6, 250 3. 87 0. 350 0. 65 0. 17

l For Test Nos. 2 to 9 and 11 to 1T, mesh units are number ot wires] ilincarinclr.

t Zt1n=Moment at ultimate load.

The results presented in Table II clearly show an increased ultimate strength for those beams reinforced with closely spaced wire mesh as compared to conlventionally reinforced beams. This is further illustrated f'= Concrete ultimate strength.

d= Depth from top of beam to center ot steel. )\=Average of vertical and horizontal spacing ol reinforcement.

terial subjected to conditions enhancing the formation of small incipient cracks during. thereafter.

The addition of wires such as to provide progressively iin FlG. 2 of the drawings wherein the dimensionless 75 closer spacing of the same minimized the effect of the curing or at sommintorval.

incipient cracks. It is to be understood, that if the concrete had been produced under conditions where incipient crack formation did not occur, a higher base strength might have been achieved with a consequently lower ratio value. It should be emphasized that because of the Repeated load tests were performed on samples of closely spaced short-wire and closely spaced continuous wire reinforced concrete. The spacings were selected to yield tensile cracking stresses on the order of 900 pounds per square inch. The specimens withstood up to l million repetitions of load to stresses on the order of 800 pounds per square inch without causing the formation or propagaton of cracks.

Example A series of experiments was made to determine the ability of concrete with and without additions of randomly spaced wires according to this invention to withcontents of wire and allowed to cure while measurements of shrinkage were made on the specimens. Shrinkage of stand tensile stresses arising -from curing under conditions but must be provided with many joints. A special rectangular specimen of concrete was used having dimensions of 1% inch x 11/2 inch x l2 inches confining longitudinally a steel plate of equal height and a width of 1/2 inch and a the unrestrained specimen proceeded in a relatively uniform manner until a value of about 0.110 percent was measured at the end of thirty-iive days. The restrained specimen showed a shrinkage of 0.020 percent at thirteen days which increased to,0.023 percent after thirty days. At the end of this period, the full concrete portion was sawed ofi to release the restraint. The released portion immediately contracted 0.024 percent and continued to shrink at a rate comparable to that observed for the unrestrained specimen just after it was made. The modulus of elasticity of the wire reinforced mix for these experiments was about three million pounds per square inch. The elastic contraction of 0.024 percent which occurred just Aafter release of the constraint would indicate a tensile stress of 720 p.s.i. in the concrete immediately before re. lease.

From the above, it is evident that the effect of the reinforcing wires has been found to occur early enough in the curing process to keep ahead of the stresses set up by shrinkage occurring during curing. The absence of shrinkage cracks, and complete development of tensile stresses when shrinkage contraction is prevented, is a property of wide structural application.

Example 6 Further tests were made to study the fatigue strength of the material according to this invention. A total of 69 beam specimens having dimensions of 2% inch x 3 inch x 38 inches were cast in four series (Series A, B, C, and D). The preparation of these beams is described in more detail below:

l Allegheny river sand, gmtn size 0.038 inch.

2 Type III high early strength.

3 308,000 p.s.i. yield strength, brass coated.

4 Portion of water adsorbed by surface ot wires.

length of 101/2 inches. The steel plate acts to effectively restrain shrinkage of concrete cast around its longitudinal ends.

Specimens having water cement ratios of 0.57 and 0.67 were prepared with the following contents of randomly spaced wire segments:

percent of steel wire respectively did not crack during the curing period.

Additional tests were made with concrete mixes containing 2.5 volume percent of 0.50 inch lengthst'of 0.006' inch diameter wire. A restrained specimen and an unrestrained specimen weremade with the above-mentioned A dynamic testing apparatus was designed to fit a constant load Sonntag universal fatigue machine (Model SF-l-U) to approximate closely the same simply supported center point loading conditions of the static test. The machine applied a repeated sinusoidal load from near zero to a preselected maximum at a speed of 188 c.p.m. A minimum load, always about l0 percent of the maximum load, was maintained lto eliminate whip-lash at the supports. The maximum load was chosen by selecting a certain percentage of the virgin cracking stress as previously determined in static bend tests on samples cast under the same conditions as those being tested. The ratio of the maximum dynamic stress to the' virgin tensile strength is the dynamic stress ratio. The approximate dynamic stress ratio at the endurance limit (dened for 2 106 cycles) was established by first adjusting the maximum dynamic iicxural stress to percent of the static iexural strength. The two beams so tested failed within the iirst 1000 cycles..The dynamic stress ratio was then successively lowered until no failure was observed after 11 2)(10G cycles of repeated stress. Results are shown in the compilation below:

subjected at the particular stress ratio. Column 6 lists a yes or no to indicate failure or no failure. Failure is de- Fatigue Dynamic Number Age Beam .\o. Cracking Stress 1 (psi.) Stress Stress of Failure (days) (psi Ratio 1 Cycles XP-2 1,032 (from A P1) 516 0. 50 500, 000` No 52 d0.. 722 0. 70 100` 000 No 5".. 808 0. S 1, 000 Yes 52 T30 0. 53 2, 000. 000 N o 53 S21 0. 70 1, 000,000 N0 54 856 0. 75 700, 000 Yes 54 A--3 1,104 (from A-l, 2 l, 050 0.05 1, 500,000 r 'o 54 It-4 do 1,050 0. 05 1,500,000 No 54 lt-5.. 1,104 (from A-I, 2) 1, 026 0. 93 500,000 No 54 1 -5 -.-do 1,004 0. 00 1,500,000 No 54 .li-5 1, 476 (from A-3, 4) 1. 328 0. 00 2, 000, 000 54 A-7 l0 1, 40G U. 05 2, 000, 000 56 1 5 1, 445 0 18 57 A-D. 1, 404 0 95 53 P-2.-. 730 (from BP-l) 581 0.80 46 15P-4 730 from BP-l, 3 475 0 65 4G 13-4 084 (from 13-2, 3) 830 0 00 2, 000, 000 46 B--5 0 U43 0 J6 1,870,000 47 B--G 054 (from B-2, 3) 984 1.00 2, 000, 000 43 B--T 1,370 (from B4, 5) 1, 23S 0 01 2,000,000 40 B-S do 1.238 0 91 2,300,000 50 C P-3 480 (from C P-l 2) 302 0A 75 00() 4u (10 324 0. 67 1, 740, 000 l1 S U. 13;. 2, 400, 000 42 1133 0. 71 43 S78 0. 95 4-1 800 0. 114 -15 S40 l). 91 2, 4d S31) 0. 00 2, 4T 2:54 0. 925 4S 830 l). 9U 2. 411 830 0. .)0 2, 5U S 0. 90 2, si 953 1. 03 52 S 0. 01 2, 52 802 0. 93 3, 53 S03 0. 97 2, 54 S74 0. 95 2, 55 S74 0. 95 10, 000, 000 No 50 ])S 1,154 (from D-l, 2,3, 4, 5)., S03 0.73 2.100, 42 D-U do 1, 020 0. 8S 2, 000, 4:5 1, 044 0.01. 6, 400, 1, 109 0. 00 2,000, 47 1` 154 1. 00 10, 0 48 1, 126 0. 00 2, 000, 0 40 1, 154 1. 00 2, 000, 000 50 1,151 1. 00 2, 150, 000 50 1,183 1.02 2, 250, 000 51.

1 Taken as the average ot the cracking stress of the beams indicated in this column.

2 Ratio o( maximum fatigue stress to pre-fatigue cracking stress.

An analysis of the test results is facilitated by a close examination of the summary of the test data in the compilation. The first column lists the individual beam specimen-the letter A, B, C, or D referring to the particular series and the number suffix designating the particular beam within the series. The addition of the letter P immediately following the series designation indicates a plain concrete beam without short wire.

The second column refers to the cracking strength of the beam under static loading. Inasmuch as age is an important factor in concrete strength, a new reference static cracking strength was often introduced as the tcsts progressed. For example, the static crackinu strength of g5 Beam AP-l (1032 psi.) was used as the basis for testing Beam AP-2. However, the tests on Beam AP-4 were referenced to the static cracking strength of 1176 p.s.. obtained from Beam AP-3.

Column 3`lists the peak stress to which the beam was subjected during cyclic loading in the fatigue testing apparatus and column 4 is the stress ratio, or the ratio of the peak cycling stress to the static cracking stress obtained from a similar beam` Column 5 indicates thc number of cycles of repeated load to which the specimen was fined as complete separation in the case of plain Concrete lbeams or the appearance of a crack (as detected by a magnifying optical micrometer) in the case of the wire reinforced beams. Column 7 lists the age of the specimens at the time of testing.

The data for Beam AP-Z indicates no failure after 500,000 cycles of stress at a dynamic stress rate of 0.50 and no failure after an additional 100,000 cycles with the dynamic stress ratio raised to 0.70. When the dynamic stress ratio was raised to 0.80, however, the beam withstood only 1,000 cycles of stress and failed. Beam AP-4 withstood 1,000,000 cycles of stress at a dynamic stress ratio of 0.70 but failed after an additional 700,000 cycles when the dynamic stress ratio was raised to 0.75.

The two plain concrete specimens ofthe B series (BP-2 and BP-4) tested in fatigue failed at dynamic stress ratios as low as 0.65. The plain specimens of the C series failed at a ratio as low as 0.67 but did not fail at a ratio of 0.62 (Beam BP-S). Similarly, the D series revealed failure of plain concrete at :i ratio of 0.64 and no failure at 0.58.

The foregoing description of the results of the faligue tests on plain concrete (mortar) beams, although reprel l t An inspection of the data for the short-wire beams, however, reveals an entirely unique behavior. Beam A-S, for example, exhibited no failure after 1,500,000 cycles of stress at a dynamic stress ratio of 0.93 and an additional 1,500,000 cycles of stress ata ratio of 0.99.

The A series of beams is somewhat unusual in that the static cracking strengths of the plain concrete beams were unusually high (1032 p.s.i. for AP-l and 1176 p.s.i. for .AP-3). Thus, the increase in cracking resistance as a result of the crack arrest mechanism of closely spaced wire was not very evident in the case of Beams A-1 and A-2 which cracked at an average stress of 1104 p.s.i.

The conventional behavior of plain concrete mortar is more evident in the B, C, and D series. The static cracking strengths of Beams BP-l and BIP-3, for example, was 730 p.s.i. and the average of CP-l and CP-Z was only 480 p.s.i. BeamsDP-l, DP2, and DP-3 tested at 713 p.s.i. The static strengths of the wire reinforced beams, however, ranged from 984 to 1370 p.s.i. for the B series, an average of 934 p.s.i. for the C series and an average of 1154 p.s.i. for the D series.

Beams B-4 and B-5 did not fail after about 2,000,000 cycles at dynamic stress ratios of 0.90 and 0.96, respectively. The reference cracking stress was 984 p.s.i. (averaged from Beams B-2 and B-3). Beam B-6 withstood 2,000,000 cycles of stress with no failure at a dynamic stress ratio of 1.00.

v For VBeams B-7 and l13-8 the reference static cracking strength was taken as 1370 p.s.i. Even with such a high I reference strength Beams B-7 and B-8 withstood 2,000,-

' of 1.00. Several other fatigue tests, however did not fail at a ratio of 1.00 and one test (D-16) ran 2,150,000 cycles at a ratio of 1.02 with no failure. This test, of course merely indicates that the static cracking strength of Beam D-l6 was higher than the reference strength of 1154 p.s.i. Note, however, that the reference strength was the average of five tests.

Example 7 Wire Average Initial Energy Content, Wire Energy, Absorbed,

Percent Spacing, in. ttf-lb. 1t.lb.

....................... 70 l l. 0 10 70 2 2. 0 0 6 70 l0 The results show that specimens containing reinforcing steel wire absorb measurable amounts of energy.

Example 8 Further impact tests were made in a special machine designed to provide an equivalent energy input of 5000 ft.1b. Specimens having dimensions of 1% inches x 3 inches x 12 inches were prepared from neat cement and mortar containing reinforcing steel wire in increments of V: percent to a total of 2 percent. A concrete specimen free of wire was also tested. Specimens supported on .a 10 inch span were broken through the 3 inch dimension by means of the machine pendulum. The average results for three specimens of each composition are shown below:

Wire Content,l Average Wire Energy Specimen percent by Spacing, in. Absorb r1.2

volume 1t.lb.

Do 2. 0 0. 06 75 Concrete I 0 35 1 6 rail x 14 inch steel coated with brass. 2 Initial Energy Input=9101t.-1b.

i 2.4:1 ratio of sand to cement.

5.311 ratio ot sand to cement.

It can be observed from the energies absorbed that the presence of steel wire critically spaced according to this invention increases the energy requirement generally in proportion to the available volume percent of wire.

Example 9 Specimens of concrete, mortar, and mortar containing steel wire having dimensions of 9 inches x 9 inches x 1% inches were evaluated for resistance to abrasion in a sand blasting apparatus. The spray nozzle was directed at the center of the specimen from a distance of about 8 inches at an angle of 30 from the horizontal plane of the specimen tops. Blasting was done for 15 minutes at four 90 intervals. Sand was replaced for each new specimen. The weight loss suffered by the respective specimens is shown below:

Wire Content Average Wire Wei ht Loss Specimen Type Percent by Spacing, in. pgercent volume Concrete.- 4. 52 Morter. 3. 68 D0-- 3 13 Do 1 95 Example 10 The lire resistance of materials containing steel wire was evaluated by placing 7 x 1l inch specimens'having various wire contents and specimen thicknesses over a top opening in a Globar furnace. A l/2 inch thick plate of steel was placed on the cold face of the specimens. Heating of the hot face proceeded at rate suicient to allow the hot face of the slab to reach 2000 F. within about 3 hours.

It was noted that specimens free of steel wire and having thicknesses of V2, 1 and 2 inches cracked completely or exploded catastrophically within less than l hour after heating was initiated. Specimens containing 1.0 and Y 2.0 volume percent of wire showed no cracks throughoutthe entire heating cycle although a slight amount of surface crazing was evident in the thinner samples. The maximum cold face temperature attained during heating of all samples was about equivalent.

It will be apparent that a wholly new material has been provided. Materials of the present .invention may be characterized as possessing properties as follows:

(a) Tensile strength (first tensioncracking) at least 5 (e) Ability to remain intact after appearance of tension cracks;

(f) Characteristics of homogeneous materials, exhibiting extensive plastic flow before disintegration as Compared to brittleness of conventional reinforced concretes; and

(g) Resilient and flexible with ability to absorb energy more efficiently than conventional reinforced concrete.

The advantages of the present invention are many. They may be summarized to include the following:

(1) Beams reinforced according to the present invention have as much as twice the ultimate ilexure strength of a conventionally reinforced beam of similar dimensions and steel quantity. Cracks do not appear until much higher tensile stresses are reached, and such cracks as do appear are restricted to hairline dimensions throughout the life of the element.

(2) The method and materials of this invention can be used so as to eliminate the hand placing and forming of reinforcement. The problem of placing conventional u steel in the direction of principal tensile stress is elimimaterials of this invention in a complex configuration is not limited as in conventionally reinforced concrete by reo strictions on the placement of the rigid reinforcing steel members.

Materials prepared by the method of this invention have many uses. These includes highways, where the increased tensile strength will permit a saving of the order of 10 to percent in the amount of concrete and where the lack of shrinkage cracks will add to the surface life in areas subjected to freezing and thawing. Another use is in heavy duty runwaysfor airlelds, where thicknesses can be reduced with the materials of this invention and where surface spalling will be eliminated. Other uses include shell roof structures, Prefabricated building elements, sewer and irrigation pipes, railroad ties, sidewalks, building footers and massive foundation mats. The materials will also be useful in shore and harbor installations, since the elimination of crack propagation inhibits salt water corrosion of reinforcing steel.

It will be apparent that new and useful methods and materials have been disclosed. Although several preferred embodiments of the invention have been described, it is apparent that modilications may be made therein by those skilled in the art. For example, arrangements of wire ranging from long continuous purposefully arranged wire to a random distribution of short lengths have been described. Any arrangement between these extremes wherein proper spacing is provided would be satisfactory. Such modifications may be made without departing from the spirit or scope of the invention, as is set forth in the appended claims.

What is claimed is: 1. A two-phase material comprising concrete and steel wire distributed therein so that the average spacing between wires is not greater than 0.5 inch, said spaced wire characterized by:

(a) a modulus of elasticity within the range of about 27 to 32 million p.s.i.; and

(b) a diameter of at most about 0.3 inch, said twophase material characterized by the ability when subjected to tensile stress of a magnitude capable of rendering cracks visible in conventional concrete materials to resist the appearance of said visible cracks.

2. A two-phase material according to claim 1 wherein the average spacing between wires is less than about 0.3 inch.

3. A two-phase material according to claim 2 characterized by a first-crack tensile strength of at least 1000 16 pounds/in.2 and wherein said steel wire distributed therein be of a diameter of from about 0.006 in. to about 0.0625 in. and be present in an amount of from about 0.7 to about 3.2 percent by volume.

4. Material according to claim 3 further characterized by the ability to remain intact after the appearance of tension cracks and exhibiting plastic flow before disintegration.

5. A two-phase material comprising concrete and closely spaced, short wire segments uniformly distributed randomly therein so that the average spacing between wire segments is not greater than 0.5 inch, said spaced wire characterized by:

(a) a modulus of elasticity within the range of about 27 to 32 million psi.; and

(b) a diameter of at most about 0.3 inch, said twophase material characterized by the ability when subjected to tensile stress of a magnitude capable of rendering cracks visible in conventional concrete materials to resist the appearance of said visible cracks. 6. Material of claim 5 wherein said average spacing is less than about 0.3 inch.

7. Material according to claim 6 characterized by a first-crack tensile strength of at least 1000 pounds/in.2 and wherein said closely spaced, short wire segments uniformly distributed randomly therein be of a diameter of from about 0.006 in. to about 0.0625 in., of a length of from about 1/2 in. to about ll/z in., of a ratio of length to diameter of from about 67 to about 118 and be present in an amount of from about 1% to about 3.2 percent by volume.

S. Material according to claim 7, further characterized by the ability to remain intact after the inception of tension cracks and exhibit plastic flow before disintegration. 9. A two-phase material consisting of concrete and closely spaced, short substantially straight wire segments uniformly distributed randomly therein so that the average spacing between wire segments is less than 0.3 inch, said spaced vwire characterized by:

(a) a modulus of elasticity within the range of about 27 to 32 million p.s.i.', and

(b) a diameter of at most about 0.3 inch, said twophase material characterized by a first crack tensile strength of at least 1000 pounds/in?, and further characterized by the ability to remain intact after the inception of tension cracks and exhibiting plastic flow before disintegration. 10. A two-phase material consisting of concrete and substantially straight continuous wire strands spaced within said concrete so that the average spacing between wires is less than 0.5 inch, said spaced wire characterized by: (a) a modulus of elasticity within the range of about 27 to 32 million p.s.i.; and

(b) a diameter of at most about 0.3 inch, said twophase material characterized by the ability when subjected to tensile stress of a magnitude capable of rendering cracks visible in conventional concrete materials to resist the appearance of said visible cracks.

11. Material according to claim 10 wherein said average spacing is less than about 0.3 inch.

12. 1Material according to claim 10 wherein said continuous wire strands are in the form of wire mesh.

13. MaterialV according to claim 11 wherein said continuous wire strands are in the form of wire mesh.

14.. Material according to claim 13 characterized by a first-crack tensile strength of at least 1000 lbs/in?, further characterized by the ability to remain intact after the inception of tension cracks and exhibiting plastic flow before disintegration, and wherein said substantially straight continuous nire strands be of a diameter of from about 0.006 in. to about 0.0625 in. and be present in an amount of from about 0.7 to about 1.6 percent by volume.

15. A method for providing a two-phase material com- 17 18 prised of concrete and steel wires with substantially inis incorporated as long, continuous wires spaced not more creased cracking strength, which method comprises: than 0.5 inch apart.

(a) preparingaconcrete mix; and 18. A method according to claim 17 wherein said (b) incorporating therein a sufficient quantity of sublong, continuous wires are in the form of mesh. stantially straight steel wires with adjustment of the 5 concrete mix to a water/cement ratio enabling and References Cited providing a distribution of said wires in the resulting UNITED STATES PATENTS mass to a maximum average spacing between wires p of no greater than 0.5 inch; whereby the resulting reismet two-phase material, after curing, is characterized by amm a significant improvement in resistance to formation lo 1624389 4/1927 Betts 52- 659 2,677,955 5/1954 Constantmcsco 52-659 of visible cracks and by a substantially increased rst crack strength as evidenced by an ability to resist the FOREIGN PATENTS appearance of visible cracks when subjected to a 252,975 6/1926 Great Britain tensile stress of a magnitude capable of rendering 15 303,406 1/1929 Great Britain cracks visible in conventional concrete. 515,003 11/1939 Great Britain 16. A method according to claim 15 wherein the wire 799,360 g/195g Great Britain, is incorporated as short-wire segments and in a random l manner by blowing said wires onto the concrete mix. BOBBY R- GAY Prmay Exammer- 17. A method according to claim 15 wherein the wire 20 R. D. KRAUS, Assistant Examiner.

Disclaimer 3,429,094. James P. Romualclz, Pittsburgh, Pa. TVVO-PHASE CONCRETE AND STEEL MATERIAL. Patent dated Feb. 25, 1969. Disclaimer filed Jan. 27, 1972, by the assignee, The Battelle Development Oorporation.

Hereby enters this disclaimer to claims 1, :2, 5, 6, and 10-18, inclusive, of

said patent.

[Ooz'al Gazette March 14, 1.972.]

Images