It will be impossible to attempt to discuss in detail here the almost innumerable examples of "Black Base" throughout the country. But in order to indicate what is being done in a few localities, mention will be made of projects which were personally inspected during the course of the past summer; followed by lantern slides made from photographs taken on these inspection trips.

Before proceeding to the consideration of pavements actually examined we must acknowledge the vast yardage of this type in our most western states. This yardage, which is far into the millions, is by no means dormant, but is increasing by added millions of yards each. year. In 1923, California alone had over 2,000,000 square yards of "Black Base" pavement over ten years old. The City of Denver has been building "Black Base" to the tune of about a half million yards per year during the past few seasons. Likewise, in the south and some of the southwestern states there is considerable yardage, including numerous projects with lime-rock asphalt surfaces and also many examples of the same type of rock asphalt employed in the base.

MICHIGAN STATE HIGHWAYS

The State Highway Department of Michigan during the past three construction seasons has been engaged in an extensive program of "Black Base" stone filled sheet asphalt paving over old graveled highways. During the season just passed, the state has operated two railroad plants on this work in addition to some similar construction by contract. In all, about 50 miles of such pavement will be laid on trunk highways during 1926, with a much larger program outlined for next year.

The pavement which has been laid is most excellent both as to design and execution. The old gravel roadways are bladed and roughly trued up and prime-coated with hot bitumen in advance of laying the "Black Base," drainage structures being first provided as on other paving projects. The thickness of "Black Base" varies in accord with the contour of the old roadbed, but has a minimum depth of about 211⁄2 inches and a maximum of about 5 where the old gravel is quite thin and requires reinforcement. The base is laid 20 feet in width and the top 18 feet wide and 21⁄2 inches thick. Bank-run gravel of quite uniform grading is used in the base course which shows the following typical composition:

A. C.

Gravel

5.6% 94.4%

The gravel supply is controlled as to ratio of sand to coarse aggregate, and the appearance of newly laid sections of base, which were inspected, indicate that these proportions are maintained quite satisfactorily.

The top mixture is of the well known stone-filled sheet type of the following typical analysis:

Inspection of all the work laid during the past three seasons shows no defects of any kind. Indeed, one can not refrain from remarking these excellent roads when driving over Michigan's trunk highways.

While we are in Michigan, we mention in passing that the city of Grand Rapids is laying from 50,000 to 100,000 square yards of "Black Base" per year. These pavement employ a 41" "Black Base" with 111⁄2" top and they are costing less than similar wearing surfaces laid on rigid base.

PASSAIC AND PATERSON, NEW JERSEY

In these two cities are to be found numerous examples of "Black Base" pavement from 3 to 5 years old. This type of foundation seems to have developed in Passaic some years ago, due to a desire to speed up construction which was originally intended to be standard 3" sheet asphalt on 6′′ Portland cement concrete base. The contractor (Union Building and Construction Company) suggested substituting 7" "Black Base" and 11⁄2" sheet top in order to permit the use of important thoroughfares several weeks sooner than would have been possible had Portland cement concrete been used, thus making good use of another one of the many advantages of "Black Base. Imagine, if you will, how much valuable time (and time is money these days) can be lost in waiting for Portland cement concrete to cure. In some instances, say in new subdivisions, this might not be such a serious item but in the case of important streets in a big city it becomes a very important consideration.

No doubt the 71" base is somewhat excessive, at least in most cases in these cities, but one can readily understand how it come into use, since the contractor agreed to build for the same price, the same total thickness of an all-asphalt pavement as was provided for usual 6" Portland cement concrete plus 11" of binder and 11⁄2" of sheet topping. All of the work in Passaic and some of that in Paterson has followed this original plan as to total depth of pavement. In Paterson, Madison Avenue between Main Street and the Erie Railroad was laid in 1923 using 4" "Black Base" and 2" of topping, while Ellison Street, adjoining the City Hall and carrying very heavy traffic, was laid the same year, using a 5′′ base and 3" top. Numerous railroad crossings in these cities have been paved with "Black Base" and

sheet top, with the utmost success. There has been no maintenance cost on any of the "Black Base" work; in fact, the City Engineer of Passaic, Mr. Jas. E. Earl, stated that they have been able to forget about these pavements.

Fig. 1-Typical Michigan State Highway work over old gravel roadways. Stone-filled Sheet on Black Base.

Fig. 2-Hennepin County (Minneapolis, Minn.). Widening Portland Cement Concrete with black base and resurfacing with Asphaltic Concrete on binder. Fig. 3-LaPorte, Ind. (Lincoln Highway). Brick pavement on P. C. Concrete base widened with 12" sheet on 5" Black Base. Laid 1924, photo

Fig. 4-Decatur, Ill.

July, 1926.

College Road, 1923.

Fig. 5-Quincy, Ill. Twelfth Street, typical of more than 100,000 square yards of 11⁄2" sheet on 42" Black Base laid on native clay and black soil. Fig. 6-Brush College Road, Decatur, Ill., in perfect condition after three years of traffic.

MERCER COUNTY (TRENTON), NEW JERSEY

Mr. H. F. Harris, County Engineer of Mercer County, told us in detail about his "Black Base" work at our Louisville meeting two years ago. In July of this year I had the pleasure of inspecting several miles of these pavements with Mr. Harris, and can vouch for the fact that they are giving service of the highest type. All of these pavements are on heavy traffic arteries either within the city of Trenton or immediately adjacent thereto.

The usual construction is 6" of base laid in two courses of regular binder composition, that is, employing comparatively small coarse aggregate, with regulation sheet asphalt top. Hamilton Avenue is an exception to this procedure as the base was laid 3 to 4 inches in depth over an old macadam roadway.

While we are discussing New Jersey work, mention is also made of quite a yardage of "Black Base" of the penetration type in Rutherford, all of which is giving an excellent account of itself.

RICHMOND, VA.

Two years ago, the Richmond-Seven Pines Road was built under the direction of the Virginia State Highway Department. This pavement consists of 4" of base and 11⁄2" of sheet asphalt top. It would be difficult to imagine any pavement being built under any more adverse conditions. The soil is yellow clay which retains its moisture for extremely long periods. There is practically no side drainage away from the pavement and, to cap the climax, it rained almost constantly during the early part of the construction work. In fact, the soil became so saturated and unstable that the engineers ordered the work stopped for a period of six weeks during its progress. It is doubtful if a poorer location could have been chosen for any kind of paving construction, especially without first correcting the sub-grade troubles.

Despite this poor start, the work looks good. There have been a few areas along the edge which have depressed under traffic in the soft earth and these will require some maintenance. But on the whole, the job looks quite satisfactory considering the extremely poor conditions attending its construction.

The state highway officials realize the disadvantages the road is under and consider that it has made a remarkable showing.

PITTSBURGH, PA.

You will recall the enthusiasm of Mr. J. D. Strain as he told us about Pittsburgh's "Black Base" at Detroit last fall. I can assure you that if you care to visit his work, some of which is nine to ten years old, you will agree that he has ample reason for being a strong advocate of this type of construction. As his guest, I inspected many miles of such pavement this past summer and I confess that I have never seen better. The yardage of such pavement in Pittsburgh runs well into the hundreds of thousands. He tells me that none of it has cost the city a cent of maintenance and cost of this work has been done on heavy traffic streets in the downtown district and on boulevards carrying dense traffic.

Much of the "Black Base" has been laid directly upon the native subgrade, while some such as Beachwood Boulevard was laid over old roadways and hence varies in depth from 4 to 7". In some cases such as Smithfield and Diamond Streets (on earth subgrade) which carry extremely dense, heavy traffic, the base was laid 10 to 12" thick Mr. Strain is justly proud of the fact that the entire block in front of the P. & L. E. Station on Smithfield Street was completed, including excavation, base and top, during the working hours on a certain. Sunday in 1921. Again we see the time element a very important factor. Such a feat could not have been accomplished by any other form of construction.

During the season just closing, several "Black Base" projects have been laid under our own supervision. Mention of those will show a few of the many ways in which "Black Base" may be utilized to advantage in accomplishing a very definite purpose. In Hennepin County, adjacent to the City of Minneapolis, a section of old worn-out Portland cement concrete highway pavement on Minnetonka Boulevard was widened by means of "Black Base" and then the whole covered with a minimum depth of 11" binder, followed by 2′′ of coarse aggregate asphaltic concrete.

At Pohler, Wisconsin, a Portland cement concrete pavement was widened by constructing alongside thereof a strip of "Black Base" 42" thick with a 111⁄2" sheet top.

In St. Joseph County (South Bend), Indiana, the Edwardburg Road, which consisted of a narrow gravel roadway, was widened out last year by means of waterbound macadam and this summer the whole was covered with "Black Base" and sheet asphalt top. In some respects the work was quite similar to that being done in Michigan, especially with respect to laying the base two feet wider than the top, thus providing reinforcement of the edge against possible lateral displacement. This is considered very effective and economical treatment of the edge, which generally requires some sort of special design to take care of the thrust of traffic along the outer edge of narrow pavements (18 feet being classed as narrow in these days of super-highways).