MODERN ROAD-MAKING.

New Zealand Herald, Volume LVI, Issue 17294, 18 October 1919, Page 15

MODERN ROAD-MAKING.

TAft MACADAM V. CONCRETE. COMPARISON OF COSTS. Mr VV. Lopdell, engineer to the M°anuta.u County Council, writes : — I did not ntend to take any further part in the :ontroversy in regard to reading systems, Hit Mr. Gibbs' remarks call tor some re;ly, especially those in which my state-nent-s and figures are challenged. I a sell to say at the outset that 1 am not in opponent of cement concrete roads. 1 relieve that uiider__ certain conditions as 0 price of materials and locality, a :eruent concrete foundation is preieiable .c any lorm of foundation, but generally iPtaKing, on country roads, tins lorm of instruction is unnecessarily uign, and a ..urOen on the ratepayers that can be avoided by the adoption of another form )i road construction as lasting, and not learly so expensive. Instead of quoting American experience, would it not be setter lor Mr. Gibbs and Mr. Shannon to jot down the costs and confirm these ' .ousts by reference to New Zealand engineers who have put down concrete roads. 1 challenge these gentlemen to produce details, of any stretch of concrete road, say, 7in thick of proper mix (for instance,l- -11—3) that lias been put down for Jess than 10s per superficial yard. In the cost must be charged labour, wear and tear of plant, expansive punt material, water supply, cement, sand, stone, preparation of foundation, boxing, and all other details connected with the job. A_mile uf road 20 feet wide contains 11.1*02 square sards, "which at 10s per square yard represents £5866. Vet Mr. Gibbs says '' the figures mentioned bv Mr. Shannon, viz.. £2500 to £3000 per' mile : re quite correct, and applicable to most 0 1 onr districts within reasonable access of the supply of good materials." , Do these gentlemen realise that their quoted cost is 5s Id per square yard v The bare material will cost more than this. Mr. <Jibbs asks further: " Can I place the .necessary amount of materials on a 20ft road to produce a foundation equal to concrete in his tar-road nig system for an equal total annual cost of maintenance, interest, and sinking fund, interest and depreciation on plant!"" My reply is that properly constructed tar macadam of a less depth will make as lasting a foundation as cement concrete, and will cost considerably less per mile. Further, the cost of maintenance of the wearing surface after the first two years will be identically equal, except that in the case of concrete there might be trouble in getting the tar or bituminous carpet to adhere, whereas there would be no trouble with the tar macadam. Tar grouting and tar •sealing are cheaper forms of road construction, but a properly grouted road on a foundation equal to that provided for cement concrete will carry any country load traffic and cost no more to maintain tl.an the carpet on a cement foundationOr to put it another way. for every pound spent on an expensive concrete road the ratepayers are burying 10s which could be utilised in constructing twice the mileage of a permanent road, which would cary the same maintenance charge as the cement road. Mr. 0-fbbs says '"the amount of funds required to maintain a tar macadam roan over a term of 36£ years would construct a permanent concrete road alongside of it. Would Mr. Gibbs take it another way? "The saving in interest and sinking fund on the difference of cost of a concrete road and a tar macadam road would enable the ratepayers (with the tome expenditure) to enjoy three miles of good road to every one undei the expensive system, and yet pay m more per mile in maintenance. The" £1C per mile maintenance over 36j years oi concrete roads is an illusion dispelled long ago. Even the cement trade jour nals. from which we get so much information these (Jays, admit this. I quite agree with Mr. Gibbs that th« concrete road work recently carried out bv the Auckland city "stands as a moiiU' ! merit tt> the far-seeing intelligence of tin 1 engineer, hut would Mr. Gibbs dare ad ! vise his council to construct similar road: I admittedly suitable for city traffic al I similar cost in the Piako County? There arc quite a number of concrete road; down in various parts of the Dominion and the cost should be accessible, anc Mr. Gibbs could' by inquiry confirm o; otherwise his estimate of cost. In conclusion I would repeat that it i; very dangerous for engineers to dogma Use. We are all striving after the bes M'c can get •with the funds at our dis rxisal. Each county has its own problen and the local conditions to a great exten determines the class of road" most suit able for the particular localitv.