BITUMEN-SEALED ROADS

Northern Advocate, 24 May 1928, Page 8

BITUMEN-SEALED ROADS

ADDRESS BY EXPERT,

METHODS DESCRIBED,

An address on the bituminous surfacing' of roads was delivered to members of the Whangarei County Council by Mr Edwards, from England, representing the Shell Company. The chairman, Cr L. Webb, when introducing him, said that Mr Edwards was an expert engineer who had been all over the world, and he was glad that he had agreed to- ad dress the council. Mr Edwards stated that he understood that the council was about to consider undertaking bitumen work on some of the roads. He stated that it was a question of whether it intended to adopt the sealing or penetration methods, and he proceeded to describe both.

Once a proper metal surface had been prepared the bitumen sealing alone would cost from 1/ to 1/2 per yard to put down the two coats which were necessary. Only the top coat was of pure bitumen. The first coat usedby the Public Works Department was (iO per cent, of bitumen, the second being 100 per cent, bitumen. He explained how tar was made, and pointed out that there were two kinds of retorts, vertical and horizontal. If *'■vertical' f tar was used it would bo essential to mix bitumen with it. The “horizontal” tar was not made so much nowadays, but the old tar made by that method could be used alone for a first coat. -Mr Edwards referred to various

oils which were used to mix with reading material, and stressed the point that bitumen had to be heated to 350 degrees, which was considerably more than was required for heating tar. The consensus of opinion was that it was 'better to go in for surfacing with tar and to make the second coat of bitumen. However, a solid base road metal was a primary essential to ensure success. In the making of bitumen roads by the penetration system stones of from 2J to 4 inches were used as a foundation. They were rolled but not heavily, and the bitumen was then put down through the metal which was again rolled. The quantity used was from five to six gallons and ft .cost from 5/ to 5/6 per yard. A road made by such a method would last for about ten years with very little attention. Although adoption of the penetrative system was more •expensive it was more permanent than a

sealed road. The latter method had been much more adopted than the former in this country, but in Mr Edwards' opinion it was better to go in for the penetrative system as it had a good stone basis and was the more permanent.

Mr Edwards gave some information regarding the methods adopted of preparing roads for surfacing, and he also referred to some of the sealing works for which his cohipany had supplied bitumen. In reply, to a question, Mr Edwards said that there was an impression abroad that the material used on the Waipu Road was supplied by His firm, but that was not so. It certainly was in barrels marked with the firm’s name, but they were a secondhand lot, which the firm had sold. Great care, said the speaker, bad to be exercised in preparing bitumen. If, for instance, it was heated too much it would impair its efficiency. In penetrative work about 100 tons of bitumen *per mile was used, costing about £BOO, so that it was of great importance that men should have experience when handling work costing so much. However, in Taranaki a lot of bitumen work had been done, and the engineers there had gained experience. Mr Edwards felt sure that they would be willing to impart information to others.

In course of his reply to further queries, Mr Edwards declared that it was essential that the road should be dry when bitumen was applied, and the speaker emphasised the wisdom of making a start With road-work early in the season. It had been his experience that demands were made by local bodies for supplies too late in the season.

In answer to the chairman, Mr Edwards stated that fid per yard should be spent in putting down a further maintenance dressing of resealing every three years. By adopting the penetrative method the maintenance would .be very low for eight or ten years.

Replying to Mr W. Jones, M.P., the speaker stated clearly that bitumen surfacing would not be successful unless the base was of clean metal. It was also advisable to have as hard metal as possible. If soft only was available, the rolling should be lighter.

Mr Edwards admitted that he was not conversant with the quality of rocks in the district, but any basaltic rock should be useful, while good volcanic stone could also bo used. At the conclusion of the address the chairman moved a vote of thank's to the speaker for the information he had given.

Mr Edwards left for Auckland by the mid-day express.