MODERN ROADMAKING.

New Zealand Herald, Volume LVI, Issue 17275, 26 September 1919, Page 5

MODERN ROADMAKING.

SUITABILITY OF MATERIAL.

CONCRETE OR TARRED MACADAM

MANUKAU ENGINEERS CASE

Mr. W. J. Lopdell, engineer to the Manukau County Council, sends the following reply to the statements of Mr. F. Shannon, engineer to the Mataraata County Council, on the advantages of concrete over tarred macadam for roadmaking : —

Mr. Shannon's letter is practically a copy of his report circulated in June, and his report is a reprint of American Engineering Conferences. The figures quoted by Mr. Shannon are entirely applicable to America, and will not work out in practice, as I will prove, in this country. Mr. Shannon in his report savs the cost of a concrete road per mile is" from £2500 to £3000. Now, I have followed this .lass ot roadmaking very closely, and find the cost per square yard is from 10s 6d to 14s 6d. This, then, works out on a 15ft wide road at £4620 on a 10s 6d basis As we have 27 miles of roads to treat in the Mangere Riding, and assuming this width to be only 15ft wide, whereas the would average over loft, we would require a loan of £124,740 I am very much afraid unless I had the assistance of such an able exponent on .concrete as Mr. Shannon I would have little chance of piloting such a loan to a successful issue.

Mr. Shannon eay s that the tar macadam road ib costly to construct and expensive to maintain, and further states that it is • inly 25 per Cent ' cheaper than concrete. If he had said 75 per cent, cheaper he would hive been nearer the mark. As we have St mile to treat with tar on a £30.000 loan I will leave it to the ratepayers to judge if Mr. Shannon's figures 'can be relied upon. Tar macadam works out at «i 7d per cubic yard; tar grouting at Is 9d; tar sealing at Is 2d, providing for two coats; annupj upkeep at about £60 per mile per annum—not £180, as stated by Mr. Shannon.

Mr. Shannon states that a tarred road, after being down for 12 or 18 months, if picked up will be found to be quite dry and granulous, having no adhesive properties, rendering it no better than the ordinary water-bound macadam. Now let me quote what the Commissioner of Highways in America has to say on thi,? subject. Conference held in Washington, U.S.A., 1917: "A tar macadam road laid down in Washington 44 years ago stands ?•■* a monument to the value of proper treatment of road tars. Recently sections of this road were cut out for the purpose of examination and report. The mineral aggregate was found to be exceedingly well bonded, and the tar binder still quite lively, giving off a strong odour of coal tar." While we have no roads in New Zealand which have been down for 44 years, we have many 12 and 15 years old, and the experiences of those of us who have not a mote in our eye coincide with the commissioner in his report, as stated above. 1 have cut through roads which have been down several years p.nd have seen the tar stick to the nicks. After having had eight years practical experience among t?.r in the Taranaki Province, where I raised a £60.000 loan in the Waimate West County, I have since had the satisfaction of seeing the work carried out within the estimate.

Can Mr. Shannon tell me of one concrete road in the Dominion two years old which has not been treated with some* bituminous top-dressing? I can inform him of many streets and roads that have been so treated after one year. I can go further and refer him to a street in Wanganui once laid down in concrete — to-day we find it lifted and replaced with tar macadam. I do not wish to enlarge further en the merits of tar as against concrete, but will conclude by quoting you from the last three annual reports of the Commissioner of Highways, C. J. Bennett, wherein he says : " I strongly favour concrete as a foundation, but after five years it is suitable for paving blocks or bituminous covering." If Mr. Shannon were to confine his remarks to concrete as a foundation he would have many followers, but when he speaks of it as a suitable road to "outlive a loan of 36£ years I am afraid he must claim to have the field to himself.

What stronger proof can we have of the success of tarred roads in Taranaki and their effect upon the rate, than to note that after 12 years' experience we find to-dav that the Taranaki County is raisins; a £60.000 loan. Egmont Countv a £70,000 loan, and Stratford County a £80,000 loan, to fallow in the same lines as their neighbouring- counties, who have given them a lead?

FIEST COST AND UPKEEP,

EXPERIENCE OF AUCKLAND CITY.

Mr. C. H. Mellsop, Cievedon, writes: — The ratepayers of Manukau County should be grateful to Mr. Shannon "for his timely warning and challenge to Mr. Lopdell on the merits of concrete versus tar macadam for up-to-date roadmaking. At a meeting of ratepayers, held in Clevedon on the 16th inst ; I had the audacity to query Mr. Lopdell's statement that tarsealed roads were the best and most up-to-date, my contention being that the heavy annual cost for upkeep condemned the tar-sealed road, and that, if we intended to be right up-to-date in Manukau County, we should go for concrete, which costs more to lay down, but needed practically no upkeep for many years, and which was being put down more and more extensively each succeeding year in America. Mr. Lopdell flattened" out my contention with a Hood of figures and " reDorts" from America, whichf he. said, showed that the concrete road was not a success in that, after two years' heavy traffic, the surface did not stand and had to be treated with tar, and declared that, m his opinion, the tar-sea!ed or tar macadam road stood the wear best, and was cheapest in the end. Now, it seems to me, we have only to go into Auckland City and see what the engineer is doiiv there to make us, as ratepayers, do some hard thinking before we commit ourselves to tar-sealed rrjadfi, -with the costly upKeen, for all time. There are some good stretches of concrete roads in the city which carry' more traffic in a day than our county roads will carry in a month, and, if they are not standing ur> to it,' why does the city engineer continue to lay down more concrete on the busiest thoroughfares? The Manukau County Council proposes, in the near future to spend £70,000 or £80.000 in tar macadam provided the ratepayers will foot the bill, and I think they would be wise to first snend a couple of hundred pounds in orettins? first-hand information as to the durability or otherwise of concrete, both from America and from Auckland City, and other places where such roads are in use. Tar-sealing is, we know, strongly advocated in Taranaki. It is, in fact Taranaki's pet baby; but has Taranaki ever tried concrete? Mr. Shannon is a man of wide experience, and. I am sure, his opinion must have weight with the ratepayers of this county.