VALUABLE ROADING DATA.

Putaruru Press, Volume VI, Issue 250, 16 August 1928, Page 1

VALUABLE ROADING DATA.

METHODS COMPARED. Differential Treatment Justified. Efficiency With Economy. A very fine and informative report on a tour of inspection of various roads throughout the ■ North Island was presented to the Matamata uounty Council at Tirau on Friday . by its engineer, Mr. M. E. Fitzgerald, i Several kinds of roading treatment and their costs and efficiency were traversed as follow: “ My recent tour of roads embraced the route Tirau, Taupo, Napier, Dannevirke, Palmerston North, Pahiatua, Masterton, Wellington, Foxton, Wanganui, Taranaki, Awakino, Te Kuiti, ICihikihi and Cambridge. The journey was broken at Wellington, where various road works were inspected, in company with the engineer in charge, and again in Taranaki an opportunity was taken to go over most of the important roads in that locality. Some very useful data were obtained from engineers whom I was fortunate enough to meet, and this is being added to my correspondence. I propose referring very briefly to some matters of general interest which have practically no bearing upon the work in this county, and devoting more space to experiences which may assist in solving our own problems. f Premix Work. “ The well-known Hutt road has a surface of the very highest class, and the reports circulated to the effect that the original work was a failure were most misleading. The portion running along the coast was of “ hot mix,” laid on new foundations, and it has never been anything but a complete success since the time of its construction. A portion of the road running through the urban areas north of the harbour broke up owing , to faulty preparation of’ the foundations. Hot mix was also see*i in some very high-class surfaces in and near Hastings, but the work was comparatively cheap owing to the use of high-grade local sands and shingles, which are obtainable at very low cost. The hot mix principle is applied in a somewhat novel manner by j Wanganui city, and as the system • may have some application to places with local supplies of sand I collected full details. The aggregate for the mjx is a hard, clean and small-grained sand which has its various sizes naturally graded to a suitable mixture. The supply is a sand dune in the heart of the city and supplies can be loaded in a condition so dry that artificial drying is j seldom necessary. When mixed with « bitumen the material is used for carpeting old roads and footpaths, where it makes a surface equal in appearance to some of the most expensive city streets. Finished work, with a thickness of about inches, has been done for as low, as 2s 7d per square yard. One may be excused for envying Wanganui her natural advantages which make such results possible. Matamata has very much inferior sands, which would cost more to use, hut the time may arrive when the possibility of their application in a similar manner will be worth serious consideration.” “ A test length near Taupo on the Napier highway is of interest but does not appear to have any direct application to conditions in this county at present. The pumice subgrade was brought to a proper camber and bituminous road oil was mixed with the surface material to a depth of about two inches, over a width of about 14 feet by means of harrowing, spraying and grading. The finished surface contains approximately 21 gallons of oil per square yard. Carting costs were naturally high, and the finished work cost 3s per square yard. The surface relies upon traffic for consolidation, and, except in the two wheel tracks, it is loose. I imagine that maintenance ’ will be costly, but until the experiment has extended over at least 15 months, or perhaps two years, i 1 would be premature to form any verj decided opinion about the system. Grouting. “A good many local authorities ar«

laying down metal surfaces grouted and sealed, anu in some ... s very excellent results na\ c o_ mined, notably between masterton and Greytown, between Waikanae and Levin, near Wanganui and near Opunake. In some cases there was distinct evidence of uitumen being applied too heavily and unevenly. Both prepared tar and light-grade bitumens have been used for grouting, but the general practice has been to use bitumen of 100 penetration; a practice which is justifiable where good, clean metal is available, as was generally the ease. This procedure was adopted in this county for No. 19 main highway south of Putaruru. Sealing. “ Examples Of surface-sealing were encountered in great variety and at many places. Some examples showed the common defects of too heavy a coating or uneven distribution. Some had first-class true surfaces of good shape, whilst others were uneven. Some of the latter are, however, as creditable to those responsible for them as better jobs by reason of the fact that they were laid down many years before present standards were considered necessary, and at a time when the cost of building to present standards was out of the question. The builders of those days were pioneers and their work, carried, out under the usual difficulties experienced in pioneering, Was not only well in advance of other work, but is even to-day the foundation for modern road surfaces to which the old roads can be raised at comparatively little j cost. “ Wanganui county is carrying out on a comprehensive scale what has been termed ‘ three coat work,’ and other local bodies have done smaller amounts on a similar system. We did similar work in small patches incidental to the sealing of the summer before last. The first CQat consists of priming the metal surface with tar or light-grade bitumen (Wanganui used prepared tar). The road is first swept free from loose material. Bad holes are filled with a premix of bitumen and chippings, but miner unevennesses are disregarded. The surface is then in the state of a lightly-seal-ed road of more or less bad shape. It is merely primed to receive a bituminous carpet. Old tarred roads are already in this condition, except perhaps for some necessary widening which may be carried out by grout-

1 mg. Upon tne primed suriace is ; sprayed a fairly heavy coat of bitumen. This is immediately covered with coarse chippings to an average depth of one inch or more as may be necessary. The surface is carefullyraked to good shape with rakes and brooms to rectify the errors in the I original surface. A limited amount i of rolling then takes place. This is followed by the third spray, fine chips or sand and rolling. Although this , class of work has not had an opporj tunity of standing the test of time it I appears to have some very intimate relationship to many problems confronting present-day builders of bitu-minous-surfaced metal roads. The slight additional cost represented by additional quantities of materials used would frequently be warranted. It meets the case of the new . | road which intensive motor traffic , | knocks out of shape before the su-. I . jl face has ripened for sealing, and , c where the heavy cost of refacing and j | grouting is not warranted. The metal . surface is not scarified as is the case with refacing and whatever solidity ; the metal surface has acquired from t its use by traffic is preserved undisb turbed. It points to the possibilitiy 3 of utilising a road of sealed sand, - once the same has compressed to a - permanent shape, as a foundation fur - a bituminous carpet of good shape, a It proves that any bituminous road, a provided it is free from foundation f defects causing springyness, ouch as e found over swamps or a wet clay sub- ;- soil, need not be torn up and reshape ed hut can, at far less cost, be trued y up by the addition of a further cars pet. is “ In Taranaki generally the old :- narrow surfaces were being widened ls by the addition of strips of new :e grouted metal. In the best work this I- new width was being carpeted right 2 across. Some places which had not it been widened. were badly broken at y the edges, hut this is largely due to Ithe complete absence of graders for keeping the haunches up to the metal. “ Near Paekakariki the Public

Works Department is making a success of double-sealing surfaces of inferior greywacke rock. A good deal of expenditure is devoted to feeding the surface beforehand with small metal and keeping it graded to shape. Then when the season is favourable the loose material is swept off, but caked grit is not removed. Material used for the first spray is a mixture of 100 and 200 grades bitumen. Although I examined the surfaces carefully for signs of the carpet lifting I could find no such defects. Egmont county is also using a light-grade material in the same way with marked success. Similar conations through the Manawatu Gorge were successfully met by the use of prepared tar such as Matamata county has used. The severest conditions for coping with a dirty surface are met with near Mt. Messenger, where the metal used is shell rock, a soft limestone, and here several materials, including prepared tar, are used fothe first coat.

“ Although opinions differed about the best material to use in the first or priming coat, there is a universal adoption of No. 100 bitumen for subsequent sprays. V Sand Sealing.

“ The scaling of inferior local sands as carried our at Cambridge is of particular interest to this county, where roads are carried On well-drained subsoils and reasonably good sand is applied to the surface at low cost. “ From the point or view of loan expenditure I regard the Cambridge work as demonstrating the fact that a sealed sand road under proper conditions of subsoil drainage may prove an economical substitute for foundations of expensive crushed metal. The sand may be expected to. compress unevenly and the sealed surface will probably tebd to get appreciably -cut of shape under tne stress ol traffic, but it should be possible to straighten up the surface with a bituminous carpet. To obtain a lasting surface it is desirable to have bitumen with its superior weathering qualities on the exposed face, and the top should have an aggregate of hard stone to resist wear, lne euges of work would tend to break away oauiy unless a kerb were formeu with grouted crushed metal or other substantial material. As work along these lines would have a considerable element of novelty it is essential to try it out in a small way before deciding upon its application on a large scale.

“ The trial lengths of tar laid at Tirau last summer are furnishing useful information. One coat only was sprayed on to unswept sand surfaces. On the main road the sand was well caked and comparatively free from loose material, and, with the exception of a few small pot holes, the surface has stood well. The side road carries very little traffic, and had a loose surface, and its condition indicates that two coats would be necessary to prime such a surface before adding a carpet. It is proposed to continue trial work along these lines next summer. Costs. “ In very few instances did I find that the costs of work were recorded with sufficient detail to permit of a useful analysis, out such information as was available showed that variations in the cost of the finished work depended mainly upon the cost of raw materials and the quantities used per square yard. After allowing for variations, based upon these two factors, there was evidence that the cost of Matamata county work will compare favourably with costs anywhere. “ In some districts there is an absence of effort to make the less costly work of sealing meet requirements and the more costly systems such as renietal and grout are the rule. Personally, I am firmly convinced that differential treatment of each road is fully justified. Of those roads which have been built up by the cheaper methods some, if not all, will prove to have had the treatment they require, whilst those which fall short of the required standard can still be improved without undoing what has been done, and any cost s# added will not result in so high an expenditure as would have been needed to give all roads the more expensive treatment in the first instance.

“ I am now preparing suggestions for next season’s policy in this

county. They will, more or less, follow on from the foregoing observations, and will be accompanied by the usual statement of costs and estimates for consideration by the council at its next meeting.” The report was received with marked attention, and was considered to be a valuable survey of roading problems in general, and of effective application to some degree in Matamata county.