DOMINION ROADS

Poverty Bay Herald, Volume LXIII, Issue 18975, 27 March 1936, Page 14

DOMINION ROADS

CONCRETE OR BITUMEN COMPARISON OF TYPES LETTER FROM MINISTER -The. relative merits of concrete and bitumen roads, from the aspects of original cost, durability, maintenance costs and comfort, are discussed by the Hon. R. Semple, Minister of Public Works, in a letter received by. an inquirer'who wrote to the. Minister asking for an opinion on the matter. The Minister also makes reference to the general policy followed in the past in New Zealand* "The matter of concrete versus bitumen roads concerns principally the work on main highways, and I have, therefore, referred the points raised by you to the acting-chairman of the board," the Minister states in his letter. "It is pointed out that those who have not had the opportunity of careful study of road economics usually make the following assumptions :--(!) Concrete roads do not wear out; <2j concrete roads require no maintenance; (o) concrete roads are 100 per cent, local production; (4) .-that it is not necessary to correlate road types to traffic intensity. For loan purposes the life of a concrete road is lixed at 2b years, and an ordinary scaled road, at'eight to 10 years. No doubt many concrete roads have given more than 25 years' service—many have not. ■ COMPARISON QUOTED

many of the original tarsealed roads in tnis country have been in existence for over 20 years and are still giving service. In fact, if a scaled road is placed on a sufficient base and is top-dressed, say, every five .years, there is no reason why it should not last indefinitely, so long "as traffic intensities in the. meantime do not increase to the extent that" a higher class pavement is'warranted. Even so, the flexible type of road is eminently, suited for stage construction.

"Concrete roads do wear out. Already in this country one of our concrete roads is .showing signs of stress after about-eight years' service, biit the average life • botit of concrete and bituminous roadsi is somewhat indefinite. It might" be argued that there are fewer failures in concrete roads-than in bitumen roads, and if we consider that concrete roads cost, in most cases, 2£ to seven times us much as bituminous roads, it would say very little for the concrete.road if maintenance costs were the same in easch case. "Maintenance costs to be really comparable' should be taken out over a long period of years —much longer than the board has been in existence—but for what it is worth it might be mentioned that the maintenance for the last year for 12 miles seven chains of the concrete road south of Auckland, from Otahiihu to Eapakura, cost £909, or, say, £75 a mile,' and 54 miles of the bitumen road composing all types between" Waitara and Hawera cost £5030, or £93 a mile. USE. OF IMPORTED MATERIALS • "It is significant that a concrete road cannot be repaired with concrete. It is necessary to have recourse to some form of bituminous patching. One of the lightest, class bituminous pavements at present'being 'constructed' is 'the' Ngahia ; Wahia-Hamiltou. section,, eight, miles, .78 chains, which is costing £3130 a mile for the remetaMng" 'diUV surfacing. The cost of the imported material is £266 a mile. The last 2| miles of the concrete road-south of Pupakura cost £7470 lor the concrete pavement only, and contained some £370 a mile of imported material. "The imported materials required tor concrete-road construction are:- (a) The marginal reinforcing steel; (b) the longitudinal joint;; (c) the cement bags; (d) bituminous transverse joint filler, it is understood that a concrete pavement requires some 9000 cement bags at a cost of 2£d each. If this is so the bags cost more than the bitumen in a two-coat seal where tar is used for the first coat and bitumen for the. second coat. In general the cost of the bituminous surfacing ranges from the figure abovementioned down to £IOOO a mile. "The policy, therefore, has been to spread the benefits from motor taxation as much as possible,, by giving long lengths of a cheaper form of dustless surfacing in keeping with traffic intensities, rather than short lengths of concrete with tho balance of the highways indifferent. If the cost of cement were brought down from, say, £4 a ton to £2 5s a ton, the saving in a mile of concrete road would be from £BOO to £9OO « mile. INTENSITY OF TRAFFIC "Again, for riding comfort, some of the latest cut-back bitumen roads arc giving roughome'ter readings of under 10 units a mile, against about £0 units a mile on the best concrete roads. The main concern is to correlate road types to traffic intensity. In this country it is considered that a concrete road is not justified for fewer than £OOO vehicles per diemrVery few of our rural roads carry more than £CO vehicles. It is considered that a two-coat seal is capable of carrying Up - to 10CO vehicles per diem and alfows at least a ICQ per cent, margin for future development. If in isolated sections the increase is more rapid, then, as already pointed out, this type admits ol construction to meet any abnormal increase'that might take place. "Now with regard to the employment that might be produced by a larger use of cement, it appears to me that when one'sees.the raw materials being fed into one end of the mill and the finished material coming out at the other with practically no handling, little in the way of extra employment can be obtained by working the mills longer hours. Obviously there would be some more quarry' men and coal-miners employed, but it i* doubtful whether the employment so produced "would measure up with the expenditure involved. In other words, the problem so far as Whangarei is concerned might defuiitely be solved, but 1 am afraid it might leave the rest of New Zealand verv short. With regard to the price of cement. I will go further into the matt, ol '-"