CONCRETE ROADS.

Press, Volume LXI, Issue 18423, 2 July 1925, Page 4

CONCRETE ROADS.

THE BUILDERS' VIEWPOINT The following is tho last of the series Of articles on concrete roads from the builders' point of view, taken from the report supplied by Mr W. Mason, who recently visited Xew Zealand, representing the Elliott Machinery Co., of Canada:—

Date Stamps. It is the customary practice to have a date stamp with the contractor's name adjoined, this to be impressed on the fresh concrete on the first slab laid each day. This is used as a record of dates and progress of tho work day by day. The inspector also keeps careful record of the work done each day, the amount of cement used or wasted, tho nature of the sub grade, and all such details. A copy of this is given to the foreman of the work each day at stopping time. A complete crew for a paving miser Should be about twenty men. The most important men are those behind the machine. The first are the men doing the line grading. Next como the two men who handlo the template- or tamper. Those arc known as "rod men." They have a very heavy job and a great* deal depends on these men as to what kind of finish the pavement is to present. The template is very heavy, and must be worked very quickly, immediately after the spreader has levolled off tho concrete with the shovel. Tho mixture being very strong it takes the initial set vory qu.'ckly in hot weather, hence the reason for handling it so quickly. After the rod men come the finisher and his helper with tho floating board, which doc? the work exactlv as a hand float. The board is made out of a piece of lin x ]2in, and of a, length almost the full Width of the road. Thorc is a handle at each end of sufficient length so that stooping is almost unnecessary. After moving the float over the surface several times, a very light roller about 2ft 6in in length, and a handle of ' sufficient length to allow of it to be I operated the full width of the road, is passed over tho surface for the purpose of displacing the superfluous water. Next to be applied is the steel trowel, which is about 2ft in length, also made with a long handle so that it can be used from one. side of the pavement. It would at first seem as though it would be impossible to do anything like a smooth job by this means, but cement finishers havo got to be very export with these long-handled tools, and the old system of doing all tho floating and trowelling with the ordinary handtools, the operator lying on his kuees, is a.thing of the past. Jointing. ■As already mentioned, the :pavir.g _ is put down in 30ft sections, each section being divided by an expansion joint of! a material known as <<Elastite." This is a tar-felt material about onehalf inch thick projecting about 1-Jiu above the surface of the concrete. It will be readily seen that a little difficulty is hero presented to get the surface" on each side of the Elastite to the same level in the finish so that •when the Elastite is later cut off there will be no indication of a bump at each joint, which becomes very irritating when driving fast. A tool known as "Straddle Trowel" is used to get both sides of the joint to the samo i level. This is simply a trowcll with a ' I part cut out to allow it to pass over the projecting Elastite. In order to get the proper consistency, tho water for the mixer must be ; gauged very carefully. This is arrived at by means of a water glass on which there arc indication marks. A slight difference on tho water gauge will be necessary if the gravel and sand has beeomo wetted by rain over night; also, when working on a steep grade. First when concrete roads were constructed it v/as considered impracticable to pour concrete except by working from the bottom of the grade upwards. They also used to have a nightmare about ■'pavement creeping" on a grade, and to offset this they put in what was known as "anchors." Tho anchors were made by digging a trench about 12in x 12iii the full width of the road, at intervals, thus allowing the concrete to fill in and form an anchor. Experience has shown that these precautious are absolutely unnecessary.

As there will naturally be a great deal of fast motor traffic on' all paved roads, the engineers have given special attention to curves. If the curves are very sharp, tho road may be gradually widened to as much as Ave feet. As njuch as one foot of super-elevation--may be-applied to the outside of tho curve. Tho crown of the road wi!' be gradually diminished and made perfectly flat oii the curve. This makes fast driving quite safe ci'cn when there may. be some frost on the pavement. Much attention is now given to the "curing process." If the sun is very bright it may be necessary to cover the newlyfinished concrete with light canvas sheets well soaked in water. Nearly all specifications call for this, but it is very seldom that it is necessary. Twenty-four hours after the concrete has been finished, thewhole surface is covered with 2in of soil thrown in from the sides. This will be sprinkled down for a period of ten days. No traffic of any kind is allowed to pass over the road until every portion has been down for at least 30 days. After a period of 30 days the contractor will be notified to clear off a given portion. This is usually done by means of a light grader which will clear off tho soil and cut off the projecting portion of the Elastito at the same time. Tho last operation is tho shouldering up and side ditching. A shoulder of 2ft on each side of the pavement is allowed 4 -hcn, sloping at an angle of 45 deg., thus forming a ditch about a foot and a-half wide at tho bottom, and about the same depth. In some districts they leave the side forms in place, but most specifications call for these to be removed and the space filled in with loose gravel.

Water Supply. It -will now be seen, -what importance is attached to tho wator supply;- and the reason for the Sin water pipe to be laid all along tho road during construction. Water must be used continually for sprinkling the grade, for the boiler of the roller, for the mixer, and for the curing process. If the grade is almost level it is customary to bank up the sides of the pavement with earth and form a pool of water on the new concrote. This is probably the best and most economical method ia the curing process, but few grades will allow for it. The matter of keeping the public traffic off tho new pavement is often very troublesome. I have had very heavy barricades built, only to find them all down the next morning, and

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the tracks of many motor-cars loft on tho green concrete. It sometimes becomes necessary to have a policeman on duty, and a few arrests usually holp some. Cattlo always cause considerable trouble, and in some districts it becomes necessary to have a watchman continually on the job. Amoug the many things that the contractor is called upon to perform within the limits of his contract, is tho construction of "detour roads" so that the traffic will not be seriously interfered with. In a mountainous'district this becomes quite a difficult problem, and often causes great expense. The speed at which this type of road can be constructed depends entirely on equipment and organisation. A very wood average is twelve sections per day of eight hours, of sixteen foot roadway, which will be 360 lineal feet of finished pavement. Seventeen sections is a big day's work, but one company has done as much as twenty-four. The laying of twenty-four sections was made possible through excellent equipment and organisation, but chiefly through a j bonus system with the labourers. A ; certain number of sections was taken . as a basic day's work, for a certain j wage, plus an additional sum per man ] for each extra section laid over and above this. This bonus system worked out so well that the same number of men eould supply the ' mixer with material at such a rate that the county inspector had io put a limit on the number of sections laid per day! He also had to time each batch for tho period that it should remain in the mixer.

Spring cleaning at Windsor Castle is a Herculean task. The special dread of the lioya-I spring cleaners is beating tho two-ton carpet which covers the floor of the Waterloo Chamber—tha Eoval dining room during Ascot week, when the King and Queen make Windsor their headquarters. Tt takes 60 men to carry this massive "rug" downstairs to the lawn.?. >ighty feet long and forty feet wide, it is the wonderful carpet which took the prisoners or Agra seven years to weave.