CONCRETE ROADS.

Press, Volume LXI, Issue 18417, 25 June 1925, Page 4

CONCRETE ROADS.

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

The contractor, no matter how eager he may be' to get an early start, will not be allowed to touch the grade until it is thoroughly dried out, except in tho case of rock work, which may bo carried on right through tho winter. The first operation on the grade will l) 0 scarifying by means of tho plough. No matter whether tho new road may follow an old and well gravelled road or not, it must all be ploughed up to allow for the proper grading and rolling, and thus allow for an even settlement. The rolling to be at least 2ft past the paving line. Strange as it may at firs!; appear, in spite of the great advance in tractors, of all sorts, there aro very few cases where they can successfully be used in road ploughing. Teams of horses havo been found to be tho most efficient and tho most profitable. If tho weather is at all dry, the entire grade must be sprinkled before the roller is used. This is very important for the purpose of consolidation. Where fills are made, tho specification calls for the roller at every foot of fill. The roller must nob be less than fifteen tons. The specification called for a pipe line not loss than 2in diameter pipe, with "T" at every hundred feet to allcw for connexion. If the fills aro very deep, and somewhat doubtful, the concrete will be omitted, and the fill planked over for a year or perhaps two years to allow for settlement.

Bog Country Work. For a distance of half a mile we had to cross a very bad piece of sub-grade: what is known as "muskeg" or bog country. In the pioneer days, I learned, this had beau impassable, until they built a road by laying down largo cedar logs. These logs had been down for about 50 years. They had gradually sunk into tho bog, and the gravol, which had been put on for many years, was now about a foot thick. At some places, however, the plough would hit the logs, and those we chopped down until wo had at least a foot of cushion between the concrete and the logs. To havo romoved the logs would have been disastrous, for thcro appeared to be no bottom to tho bog, and cedar logs thus bedded would last a thousand years. Over this entire area the pavement was reinforced by triangular mesh, and although it has been subjected to heavy logging traffic ever sinco there is not tho slightest sign of a failure. _ The culverts we used were cemont pipe up to 3ft in diameter. Over this size they were all boxed and made of reinforced concrete.

Tho important items on the grade are:—The carrying on of the work in good weather; the continuous rolling and sprinkling; tho using of materials in the fills free from all vegetable matter, and the keeping off of all public traffic. The Bibbon Setter. Following immediately after tho grader will be the ribbon setter or form setter The timber used for the form is usually 2x6 sized, and in length from 16 to 20ft. This is a very important piece of work, and requires considerable experience. To get the curves uniform I usually had a long stretch of forms fastened together by nailing on the back across the joint another piece of one inch, or perhaps two inch, material. This w.->uld cause the timber to bend evenly, and eliminate tho kinks at the joints. Following close on the form setter tho sand and gravel is delivered. We uged throe cubic yard motor trucks. On the long haul, which was about six miles, the trucks went night and day, which was necessary when the mixer was working steady. Most engineers will not allow tho grade' to bo more than a few hundred feet ahead of the gravel, otherwiso the trucks will damago the grade very badly. The gravel and sand must bo dumped at proper distances. A boy is usually kept on tho job to do the spotting of each load, its place being marked by a Btako. If tho material is not properly placed, when the mixpr cornea along there will bo involved a great deal of unnecessary labour and loss of material. If there is a shortage of material, it i 3 very difficult to get it brought up to the mixer. If there is too much, the surplus has to be thrown to the one side and wasted.

The system which I used for placing the cement, which was at tho opposite side of the road from tho gravel, was to place the proper number of sacks of cement at every fifteen feet. _As the mixer moved fifteen feet each time, the piles thorefore came exactly opposite the mixer, and savo a great deal of handling. The cement was placed on planks, and each pile was supplied with a heavy rainproof cover. The mixer we used was a Koohring paving mixer of the boom type. The boom mixer is the only type now allowed for this work. For a number of years a mixer with a spout was used, but there was always the tendency for the larger stones to segregate and leave bad voids. By the use of the boom and dump bucket this danger is entirely eliminated. Before the mixer commences, tho inspector, whose duty is to be constantly at tho machine (not a bucket of concrete must be used unless he -is there), inspects and measures all templates very carefully. A template of wood is used for tho fine grade. This is gauged from the top of the side form, and gives the exact depth for tho concrete, Should there be a hollow placo it is filled in and hand tamped, and if there is a high spot it is taken out by means of light, sharp picks. This fine grading is very important, and requires two good men, as they must at all times work very fast and close up to the mixer, Immediately ahead of the concrete, and if they can't keep the grade ahead the whole work is held up. Loss Through Delay.

Even if it should be only for a few minutes, a delay will soon become a eostly matter, where a crew of twenty men may be involved. This is the time that proves what sort of foreman is in charge of the grading. Some grade foremen can leave the surface so that there is very little work left to do when tho mixer comes along. It is right at this juncture that a thoroughly organised crew is essential to the contractor, and it is here that the

deciding factor lies as to how the contract is to work out.

Our greatest difficulty was getting labourers to wheel tho sand and gravel to tho miser. The job is a very hard one, and when there is other work about it is well nigh impossible to get men to do tho work in spite of a wags inducement. We tried a loading machine, also made by tho Koehring company, which, however, proved to be a failure. The general principles on which tho machine worked wero excellent, but a great deal of time was lost through getting the machine into position each time the mixer moved. I understand that some contractors are now using a Ford truck with a light body, built in such a manner that' tho sand, gravel, and cement sufficient for a batch is dumped straight into "the mixer, thus doing away with all shovelling. This, of course, would require quite a fleet of trucks coming at regular intervals. Not only would this be a great saving of labour, but will always koop the material clean, as it will never touch the ground. It is important that the contractor haß all the necessary templates and various tools in readiness, so that when the mixer starts there will be no hitch or stoppage', with consequent loss of time and labour. Should a stoppage take place, it is practically useless to attempt to turn the mixer crew on to any other job. They may as well be allowed to rest under a shady tree, while as for laying them off for the rest of the day, the chances aro there would be no crew next morning. (To he Concluded Next Week.)