this causes the travel to chip off the edges of the bricks separated by them. Whenever this chipping occurs to any extent, the pavement soon develops a rut or hole. Cracks in a country road, if properly filled when they first open and kept filled afterward, do not injure it appreciably, and it is generally considered that transverse joints in a brick wearing surface, to prevent transverse cracks, are more likely to cause than prevent trouble. Expansion joints are of two types, poured and prepared. The former are made by placing a board filler of the thickness of the joint against the curb and laying the bricks against it. The Maryland rule for the thickness of the joints is as follows: On streets 30 feet or more wide, 11 inches next each curb; on 20 to 30-foot streets, 1 inch next each curb; on 12 to 20-foot streets, inch next each curb; on streets under 12 feet, inch next one curb. In Pennsylvania a 1-inch joint at each curb is specified. On the Illinois brick roads with a sand-cement base a 3-inch joint along one curb is used. The plank filler usually consists of two thin 6-inch boards of a wedge-shape cross-section, dressed on both sides. One of them is laid against the curb with the thin edge on the base, and the other is placed against it with the thick edge downward. The combined thickness of the two is equal to the thickness of the joint. Handles are attached to their upper edges, so they can be lifted out when the grout filler which has been poured has set. The filler for poured expansion joints should meet the requirements for the filler for other joints of this type. With the monolithic and sand-cement cushion types of pavement, the joints should be filled as far as the bricks are laid, each day.

Prepared fillers are now extensively used. They are strips of bituminous material or some kind of felt or fabric impregnated with bituminous material. They are placed against the curb and the bricks laid against them, thus doing away with the board fillers required with poured joints and making it unnecessary to provide heating kettles on pavements with grouted joints.

Experience on the Pennsylvania State highways has shown that a prepared filler extending the full depth of the brick sometimes permitted water to penetrate from the road surface into the cushion, where it froze and heaved the bricks. It is therefore considered advisable on that work to have the prepared filler stop from to 1 inch below the surface of the road and to fill the top of the joint with hot bituminous material.

Where a cement-sand bed is used, a inch prepared expansion joint extending through the entire pavement is recommended by some engineers; it is placed in two strips, the first or bottom strip being placed in the concrete base, and the second strip immediately above it when the bed and bricks are laid.

Small Cubical Bricks

Shortly after small stone blocks were introduced in Europe for constructing pavements having the trade name of "Durax," the county superintendent of Monroe County, N. Y., J. Y. McClintock, employed cubes measuring 2 to 21⁄2 inches on a side for resurfacing old macadam roads to resist motor traffic. In 1916 he stated that vitrified clay cubes had given better results than those of other materials. Those laid in 1916 were 24 inches in each dimension, weighed about 1 pound each, and were laid 225 to the square yard. The only specification for the cubes is that they must not absorb more than 3 per cent. of their weight when immersed in water. They have been laid on a gravel base, broken slag, broken stone and concrete, and the joints are filled with any local fine material. It is considered advisable to make the base several feet wider than the roadway, so that the gravel or broken stone shoulders adjacent to the cubes shall be supported rigidly and the tendency for the border cubes to become displaced will be minimized.

Aspha-Bric

During 1915 and 1916 attention was directed to the possibilities of asphalt impregnated brick. The idea of impregnating brick with bituminous material is not new. In 1893 brick boiled in coal tar were laid in Portland, Ore., and remained in service 17 years. About 1907 nose brick boiled in asphalt were laid along the tracks of the Los Angeles Electric Railway Corporation and 2500 similar brick were laid along tracks in San Francisco about 1912. Brick boiled in bituminous material have also been laid in Nashville and Chattanooga.

The method of treating brick which came into prominence in 1915 is designed to fill completely the pores in the brick. As the porosity of different grades and makes varies considerably, the quantity of impregnating material required will range from about 6 to 15 per cent of the volume of the brick. As a result of the treatment it is claimed that the brick become impervious to moisture, the bituminous jointing material adheres more firmly to the treated than to the untreated brick, and the wearing properties, as indicated by the standard rattler test, are greatly improved. This last advantage is indicated in the accompanying tabulation of tests of untreated and treated "second" brick conducted by Robert W. Hunt & Company. Each test was made with five untreated and five treated brick, 225 pounds of small shot and 75 pounds of large shot, the rattler making 1800 revolutions at the rate of 30 revolutions per minute. The increase in wear due to

Results of tests of untreated and asphalt impregnated brick. Each sample consisted of five untreated and five treated brick

SAMPLE

Weight in pounds:

Before treatment....50.66 48.81 46.50 53.35 45.25 48.65 49.75 47.95 50.03 After treatment.. Asphalt used... Loss in weight, pounds: Untreated. Treated.

56.75 54.01 48.97 55.77 47.49 51.33 54.60 49.94 54.53 6.09 5.20 2.47 2.42 2.24 2.68 4.85 1.99 4.50

Loss in weight, per

cent: Untreated...

27.02 17.39 28.81 17.19 13.93 11.88 19.57 13.63 11.78 8.38 8.96 6.22 10.07 6.51 6.83 7.36 6.46 6.25

53.34 35.63 61.96 32.22 30.79 24.42 39.34 28.43 23.55 14.77 16.59 12.70 18.06 13.71 13.31 13.48 12.94 11.46 0 0 0

Treated.

Broken brick:

Untreated..

Treated....

1 0

0

33

0 0

0 0

impregnation will, it is stated, enable manufacturers to stop their burning at a lower temperature than is now customary, thus materially reducing the number of poor brick in a kiln, and to obtain the necessary strength by impregnating the brick. It is also claimed that grades of brick unsuitable for pavements may be made into satisfactory pavers by impregnation. For example, impregnating clay building brick with 11.3 per cent of asphalt gave a product showing 9.3 per cent loss in the standard rattler test, although untreated brick showed 100 per cent loss after 500 revolutions. Shale building brick which showed 42.4 per cent loss in the rattler test before they were treated, lost only 17 per cent after treatment. Sand-lime brick which showed 100 per cent loss after 400 revolutions lost only 23 per cent after being impregnated with 10 per cent of asphalt. Impregnating clay and shale building brick with 8 per cent of asphalt reduced the loss in the rattler test from 40.9 to 14.2 per cent. The impregnation of the brick also reduces their absorption of water to practically nothing.

The asphalt-impregnating process begins when the brick are removed from the kilns or dryers. They are loaded on small cars which are run into a cylinder. There they are heated to about 300°F., which expands them, and a vacuum is produced in the cylinder to remove all moisture from the brick and leave their pores open. The cylinder is then filled with a special grade of asphalt at a temperature of 350°F. and the cylinder put under heavy pressure until the gauges show that impregnation is complete. The asphalt is drained off and pressure again applied until the brick have cooled. During cooling they contract somewhat, causing the asphalt to become sealed in the pores.

A BRICK PAVEMENT ON A ONE-INCH CONCRETE BASE1

A brick pavement was laid in 1917 in Stockland township, Iroquois County, Illinois, on a one-inch concrete base. This pavement is 9 feet wide, and the contract is for about 6 miles, of which about 3 miles has been constructed. The contract price for this work is approximately $8700 a mile, of which about $300 is for bridges and culverts and about $450 for grading. The price for the slab alone is $1.50 per square yard.

This pavement is being laid on an old gravel road for a foundation and, in order to secure the full benefit of this old material, the gradient of the new pavement varies but slightly from that of the present road. By not disturbing the old gravel, it has been possible to secure a very firm subgrade and we have no doubt but the pavement will prove very satisfactory. The concrete base is composed of 1 part cement to 2 parts fine aggregate and 4 parts coarse aggregate. The fine aggregate consists of sand all of which passes a 1-inch mesh. The coarse aggregate consists of material which would be retained on a 4-inch mesh and passes a -inch mesh. As a matter of fact, there is very little of this material which will not pass a inch mesh and it is the same type of gravel that is commonly used for roofing purposes.

I have no doubt but this pavement would be practically as good as if the brick had been laid directly on the old gravel road, but in a construction of this kind, it is necessary to have some sort of a concrete base in order to secure a perfectly smooth and uniform surface on which to lay the bricks.

The subgrade was thoroughly rolled and all soft places, of which there were very few, were removed and the subgrade brought up to a true plane by the addition of fresh material which was thoroughly compacted. Before concrete was placed, the subgrade was well wet; after the concrete was placed, it was struck off by means of a template and the bricks were laid directly on the green concrete.

Two brick setters were used on this job and by having a brick hammer on each side of the road, the setters not only started but finished the courses, as on a pavement of this width no bats, except

1 By Rodney L. Bell, Division Engineer, Illinois State Highway Department.

one half-sized brick, are required in starting and finishing the courses. Bricks were carried on to the pavement in such a way that the good side of the bricks was always placed up and the lugs all in one direction. By requiring the brick carriers to use some care, a large amount of the culling which ordinarily takes place on a brick road was eliminated. Just as soon as the bricks were culled, the pavement was swept and the rolling started.

One man did nothing but keep the roller moving the entire time. It was a small hand roller about 30 inches in length and 24 inches in diameter and when filled with water weighed about 700 pounds. This weight was sufficient to secure a good surface over the entire length of the pavement. The first rolling was begun at the outer edge and the pavement was rolled parallel to the center line of the pavement. After the entire surface had been covered in this way, the pavement was cross-rolled in opposite directions, the roller making an angle of about 45 degrees with the center line of the pavement.

In order to allow plenty of time to secure a thorough job of rolling, the grouting machine was kept about 100 feet behind the brick layer. The grout mixture consisted of one part cement and 1 part of sand mixed in a machine designed for this purpose. It was the intention to practically fill the joints at the first application so that after the grout had had a chance to settle, it would leave from to inch to be filled with subsequent applications.

The second application of the grout was mixed slightly thicker than the first, and was wheeled back over the pavement from the mixing machine rather than bother with moving the machine back over the pavement a second time. This application was worked into the joints by use of a squeegee and on the final going over, the squeegees were pulled at an angle of about 45 degrees with the joints in order to secure a better surface and to keep the grout from being dragged out from between the brick.

After the grout had set sufficiently, the pavement was covered with 1 inch of loose dirt, which was kept wet for one week. The pavement was opened to traffic after it had been down three weeks.

This work is being paid for by a bond issue which has been voted by Stockland township, Iroquois County, and is under the general supervision of Benj. Jordan, county superintendent of highways of Iroquois County.