XPERIMENTAL LENGTH

Evening Post, Volume CXI, Issue 71, 24 March 1926, Page 10

XPERIMENTAL LENGTH

—, —* VARIOUS TYPES OF PAVEMENT

SEALII^ COATS DO NOT WORK OUT

PAVIJFG BETWEEN TRAM TRACKS.

M Eafhcr over a year ago a suggestion was made that the Local and Main Highways Board should co-operate in the laying down of a series of experimental lengths of paving material in an endeavour to ascertain, which process, or processes, promised best under local traffic conditions. The idea was welcomed and as an admirable one and resolutions were passed accordingly which is always very necessary—and thereafter again nothing was done about it. The idea still exists, but the experimetal lengths do not, at any rate in one locality. Nevertheless a considerable number of pavement types have been tried out within the last two or three years, not taking into account the successful woodblocks, now about twenty years old, tar macadams, of various ages and of varying success, and a small area of brick on concrete. There is a theory among some engineers, by the way, that the life of concrete when protected by a surface coat of one kind or another blocks, bricks, or bituminoius or other cushion courses, is about twenty-five years, and' that theory seems to have an application to Wellington's wood-blocked roads, for here and there the heavy concrete foundation is now shewing sighs of old age* and traffic vibration, quite a different thing fvom actual wear and tear. The TopeUa, hot-mix, pavement is no longer an experiment, it is the standard Wellington pavement, but the sheet asphalt, as laid on Thorndon quay, on the Petono Esplanade, in Cuba street, Petone, and in Evans Bay, was an experiment on a large scale and not a particularly successful one. It is not at all likely that any more sheet asphalt will be laid about Wellington, at any rate with the materials available when Thorndon quay was surfaced. THREE SEALING OOAT TRIALS. Another experiment upon a small scale—an experimental scale—was the sealing of the lower end of Tinakori road, between Hobson street and the junction with Thorndon quay, with a skin coat of bitumen. It was sufficient to show that a bitumen sealing coat is at best, upon an ordinary macadam surface, a very temporary surface, for under light traffic, chiefly cars, the skin quickly faded away. ■■■.'' . Another short length of water-bound macadam was. treated with a skin coat of a proprietary bituminous preparation, an emulsified bitumen which was simply spread over the macadam with brooms and then covered with a layer of metal chips or sand. This surface held the dust and carried off the rain in fine style', till it, too, disappeared under light car traffic within a few months. .. ■ '• Still another experiment was carried out, by the Public Works Department, on the second bend of the Mungaroa hill road, where a short length of tarsealing was tried, about five or !>i'x months ago. The Mungaroa hill carries a good deal of traffic, but nothing like that of an average city street; the sealing coat there failed also, and to-day there arc only patches here and there. BETWEEN TRAM TRACKS. There are still other types of pavement going down, a new style of bituminous surfacing, requiring no heat in the mixing, which is being tried oat by the Petone Borough Council, and with which some of the tennis courts at Miramar have recently been laid, and a mixture which the Tramways Department puts down between and on either side of its tram tracks. The success of the cold-mix method under local conditions has yet to be determinod, though those carrying out the work are confident that the claims made for it wilt be substantiated. The success of the method employed by the Tramways Department is no longer in doubt; as compared with the standard bituminous pavement laid down by the City Engineer's Department it is not a success. It rolls out and ridges very., noticeably within a week or two of . the date of laying. Possibly it is cheaper, but it is not tie ideal.