US2147195A - Method of constructing pavements - Google Patents

Description

Feb- M W39', s. E. FiNLEY METHOD oF coNsTRUcTlNG PAvEMENTs Filed March 27, 1935 Kul ,..o o, v

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Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE Application March 27,

2 Claims.

My invention relates to a new and improved method of constructing pavements and has to do, more particularly, with an improved method of bonding mineral aggregates to underlying foundations, which foundations may be of chert, gravel, top-soil, shell, sand-clay, macadam, and the like. My present invention has todo with What are commonly termed, in the road building art, as surface treatments, both single and double, when they are practiced in renewing old wearing surfaces, such as sheet asphalt, asphaltic concrete, vitried brick, Portland cement, and the like, and the invention is directed to constructing new bituminous wearing surfaces on clay-gravel, sand-clay, chert, lime rock, waterbound macadam, and the like. Certain features of the method disclosed herein are disclosed and claimed in my pending application, Serial No. 12,478, iiled March 22, 1935, for Method of constructing paved roadways, to which cross-reference is hereby made.

The principal object of my invention is to provide a method by which bituminous pavements, as good as or superior to those built in accordance with present practice, may be constructed at less cost and more quickly. A main object of my present invention is to provide a method which effects a saving of mineral aggregate and time and by which a better coating of the mineral aggregate with bitumen is effected, than was possible in accordance with the prior practices. A further object of my invention is to provide a method of constructing bituminous pavement, or effecting a bituminous surface treatment, which is not subject to the temperature limitations required by prior practice. A further object of my invention is to provide a method of constructing pavements, in which the waste of the aggregate shall be reduced to a minimum.

Further objects, and objects relating to details and economies of operation, will definitely appear from the detailed description to follow. In one instance, I have accomplished the objects of my invention by the devices and means set forth in the following specification. My invention is clearly deiined and pointed out in the appended claims. The application of my invention to the construction of a bituminous pavement is illustrated in the accompanying drawing, forming a part of this specification, in which:-

Figure 1 is a diagrammatic sectional view through a portion of a roadway showing the foundation with a priming coat applied thereto;

Fig. 2 is a similar view showing the application 1935, Serial No. 13,321

course of aggregate to of a portion of the bituminous cement to the aggregate shown in Fig. 2;

Fig. 4 is a similar view showing the application of the balance of the cover co-urse of aggregate;

Fig. 5 is a similar view showing the balance of the bituminous cement applied; and

Fig. 6 is a similar sectional View through the completed pavement.

My present invention will be better understood from a comparison with the standard. practices now in use. In general, present practices call for the application of a coating of bituminous cement over the primed foundation or base and the aggregate is then cast over the bituminous cement. This has the disadvantage that the surface layer is. not securely bonded to the foundation, by reason of which fact the pavements so constructed do not stand up satisfactorily and, in the. course of time, water succeeds in forcing its way into the pavement, with disastrous eifect thereon.

These prior practices are exemplified by the current specifications of the Georgia State High- Way Department which, for double surface treatment, require that, after the prime coat applied to the foundation has properly cured, any excess of sand or objectionable material shall be removed and the surface swept clean before applying the bituminous binding material. There is then applied, over the cured prime coat, a bituminous binder. asphalt of from 180 to 230 penetration at 77 F., Which must be applied at a temperature of from 325 to 375 F., or it may be a tar having a melting point of 149 F., which must be applied at a temperature of not less than 175 or more than 225 F. The quantity cf this bituminous binder directly applied over the prime coat shall range from .4 to .6 of a gallon per square yard. As soon as this hot asphalt, or tar, has been applied, it must be uniformly covered with not less than 50 pounds per square yard of surface (based on an apparent specic gravity of 2.4) of aggregate of size No. 3. 100% of such aggregate must pass a 2 inch ring, 90 to 100% of it must pass a 11/2 inch ring, and not more than 16% of this aggregate may pass a inch ring. These specifications require, further, that no aggregate shall be applied to the bituminous binder when the air temperature is F. or below, in the shade.

These specifications require that this covering of coarse aggregate shall next be rolled, after This may be an which the road surface is opened to traic but, at a suitable time thereafter, this coarse aggregate foundation must be thoroughly cleaned by sweeping it free of all loose material, which loose material is mainly composed of the mineral aggregate cast over the bituminous binder and not absorbed thereby. Then, a second coating or a seal coat is applied, consisting of from .21 to .3 of a gallon per square yard of bituminous binder, of the character above described, and this is covered with a coating or dusting of ne aggregate.

These specifications contain `the further requirement that no bituminous material shall be applied between November first and March first. It is apparent, therefore, that,.in view of the foregoing requirement and the requirement that no aggregate shall be applied when the temperature is below 70 F., there are practically five months of each calendar year when the construction of road surfacing in accordance with these specifications is prohibited. Thus, the activities of road builders are greatly limited. Moreover, there is a further loss of time, and delay in finishing the roadway, because of the time that must elapse between the application and rolling of the coarse aggregate and the application of the seal coat. Furthermore, in allowing traffic to travel over the coarse aggregate for the purpose of embedding it in, or causing it to be absorbed by, the bituminous binder directly applied over the prime coat, a considerable economic waste results, in that from 10 to 20% of the coarse aggregate is swept off under traffic and entirely wasted.

The method of my present invention overcomes all of these difficulties, saves aggregate and time, and is not limited to any season or period in which the work has to be performed, it being only necessary vthat the foundation and the `aggregate vbe dry and the temperature not lower than 50 F.

In accordance with my invention, I proceed as follows to effect a single-surface treatment: The roadway or foundation is first suitably primed with liquid bitumen, as illustrated in Fig. 1, in which the foundation is indicated at III and the priming coat of liquid bitumen at II. VI next spread from50 to 60% of the aggregate or cover material required under present practices directly upon this primed foundation. The aggregate is preferably applied to, and partly embedded in, the foundation before the priming coat has dried, in accordance with the invention disclosed and claimed in my said pending application, Serial No. 12,478, whereby certain advantageous results will be attained as described in said applicati-on. In Fig. 2, I have shown this portion I2 of the aggregate applied to the primedfoundation I0. More specically, I apply to this primed foundation from 25 to 30 pounds per square yard of aggregate of size No. 3. To this layer of aggregate, or cover material, I then apply approximately half of the bituminous cement required by thepresent practice, Aas indicated by the specifications quoted above; that is to say, I would applyfrom .25 to .3 of a gallon per square yard of bituminous cement of the character described in the above-mentioned specifications. This application of bituminous cement would coat the layer of mineral aggregate uniformly, as indicated in Fig. 3, in which the bituminous cement I3 is shown applied to the aggregate I2.

I next cast over the previously coated aggregate lying on the foundation or base the balance of the cover material required in vaccordance with present practice; that is to say, having reference to the 5abovementioned specifications, I would now cast over the coated aggregate, as shown in Fig. 3, from 20 to 25 pounds per square yard of aggregate of size No. 3, and this is then rolled lightly. In this way, I not only form a mechanical bond between the aggregates, but the uncoated aggregates falling in between the previously coated ones receive at their sides and upon their under portions a coating, from the first application of bituminous cement, by friction and pressure. This application of the balance of the cover material is illustrated in Fig. 4, the uncoated aggregates last applied being indicated at I4.

I next apply the balance of the bituminous cement required by present practice; that is to say, I `apply from .25 to .3 of a gallon per square yard of bituminous cement of the character set forth in the above-mentioned specifications, with the result that all of the coarse aggregates have been uniformly coated with bituminous cement and are Well coated and bonded to the foundation. This stage of theoperation is illustrated in Fig. 5, in which the second application of bituminous cement is indicated at I5. The surface is then rolled and may be immediately sealed by applying a cover of fine aggregate, as indicated as I6, in Fig. 6, which fine aggregate may be sand, stone screenings, or the like, which may be uncoated or pre-coated with a small percentage of liquid bitumen. The roadway is then ready for traiiic.

However, if a seal coat of bituminous binder is desired, I would apply to the surface, as shown in Fig. 6, approximately 10 pounds per square yard (based on an apparent specific vgravity of 2.4) of aggregate of size No. 5, all of which must pass a 5A; inch circular opening, not more than 10% of which may pass a 1/4 inch circular opening, `and none of which shall pass a 10 mesh screen. lI would then apply from .l5 to .3 of a gallon per square yard of the asphalt or tar specified in the above-mentioned Georgia specifications, after which I would .deposit 10 pounds per square yard of aggregate of size No. 6 and roll thoroughly. The roadway is ,then ready for traffic.

On single-surface treatments over the prepared and cured foundation, the standard specifications of .the .State Highway Department of Georgia call for the `application of between .3 and .5 offa gallon for each surface square yard, of bituminous cement, either the asphalt or the tar heretofore mentioned in the said specifications, and for the covering of this bituminous cement with aggregate of size No. 4-D, 95 to 100% of which must pass a 1 inch ring, 90 to 100 of which must passa 3/4 inch ring, and not more than 10% of which may pass a inch ring.

For a corresponding treatment in accordance with my present invention, I would first spread approximately 2O pounds to each surface square yard of crushed stone, slag or other suitable mineral aggregate of the size above specified, and then coat the saidaggregate with approximately .25 of a gallon vper square yard of bituminous cement of the .grade specified. I would then apply approximately 15 pounds per square yard of the same size mineral aggregate, roll and complete the coating of bituminous cement b y applying approximately .25 of a gallon of the same'to each surface square yard. I would then apply approximately 7 pounds of sand, stone screenings or the like, and thoroughly roll, after which the roadway is ready for traffic.

As stated above, the prior practices have always required the application of a coating of bituminous cement directly over the prime coat and the depositing of the aggregate upon this coating of bituminous cement. A characteristic feature of my present invention, which I believe to be entirely novel, is the application of a portion of the aggregate directly to the prime coat.

From the foregoing description it will be seen that there is no wastage of the covering material applied over the bituminous prime, because all of itis firmly bonded and cemented together with bituminous cement and each particle is thoroughly and completely coated. There is no waste of time because the operations are continuous and I thus accomplish in a few days what, in the present state of the art, may require a number of months, before the entire roadway is completed and ready for permanent traiiic. It will be seen, therefore, that my new method of constructing pavements enables the road builder to build .an excellent bituminous pavement more quickly and economically than is possible with the present practices.

I wish it to be understood, of course, that my invention is not to be limited to bitumen of the particular class above mentioned, and that an asphaltic cement of lower penetration or a tar of higher melting point may and can be successfully used. I am aware that the foregoing method of constructing pavements is susceptible of considerable variation without departing from the spirit of my invention and, therefore, I claim my invention broadly, as indicated by the appended claims.

What I claim is:

1. The method of constructing pavements comprising the application of a priming coat to a foundation, depositing a portion of the aggregate required for the pavement directly upon the primed foundation, applying a portion of the bituminous cement required for the pavement to said portion of aggregate, while such aggregate is in a state of repose, depositing the balance of the aggregate upon the portion coated with said bituminous cement, While such coated aggregate is in said state of repose, and then applying the balance of the bituminous cement thereto.

2. The method of constructing pavements comprislng applying a priming coat to a foundation, depositing directly upon said primed foundation a layer of aggregate consisting predominantly of broken stone to form a rough surface, applying a coating of bituminous cement in a quantity insufficient to ll the indentations in said rough surface, depositing upon said rough surface of coated aggregate a second layer o f aggregate substantially identical with that first applied, smoothing said second layer of aggregate, and then applying additional bituminous cement.

SAM E. FINLEY.

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