CONCRETE ROADS.

Manawatu Herald, Volume XLI, Issue 2001, 10 July 1919, Page 3

CONCRETE ROADS.

MR. CRAW’S EXPERIMENT,

The following report was submitted by Messrs H. Toogood and S. Mair, civil engineers, to the -Kairanga County Council at its meeting on Tuesday, on the experimental length of road laid down in concrete on Rangitikei line by Cr. G. Craw: —“The experimental section of road on the Rangitikei line by Mr Craw has been inspected by us. We are favourably impressed with its surface appearance, except for defects caused by driftwood in the river shingle. These pieces of wood were worked up to the surface during the laying of the concrete, and as the covering film has worn away, they have caused pitting. These holes should be filled up with bitumen and stone without delay.- We would point out that the construction adopted is in certain repects novel and apparently is quite satisfactory with the class of traffic that is being carried. It is unfortunate that no attempt has been made to ‘keep an account of the volume of traffic and reduce it to the unit of tons miles. This cmild have been done by taking representative days of maximum and minimum traffic in representative months. The traffic should bo further detailed into the percent ago of iron wheels to rubber tyres. It is just a year since the road in question was opened for traffic, and although the signs'of wear are no greater (ban is uual with this class of road, we are not satisfied to recommend your Council to proceed on (he lines of Mr Craw without a longer experience. CLIMATIC CONDITIONS.

‘‘Two eonrsc work has been abandoned in other parts of the world whore eonerete roads have been standardised, but that is no reason why this method should be eondemned in Now Zealand without fail’ trial. Extreme elimatie variations are the greatest cause of (rouble in concrete roads, and in Xew Zealand they are not subject to such severe conditions in this respect as.elsewhere. In Mr Craw’s work a great saving of cement has been made by using a weak mixture for the base. The novel feature, however, is the use of plums. By using stones as plums (which we understand were about 4 inches in diameter),the base concrete was built up about 5-1 inches of thickness with poor mixture, and surfaced with 1-Vin. thickness of mixture of usual richness. It must be admitted that there is a great element of danger in carrying put such work comprehensively and universally, by reason of the fact that there can be no margin of safety in such construction. While being satisfied that the road in satisfactory under the present traffic, and the climatic conditions through which it has passed, we cannot indicate the result of greater severity in traffic or elimatie conditions. In considering concrete roads, your Council should face the question whether it is going to discourage traction engine traffic or not, and also take into consideration the wheel loads you are prepared to admit to your roads. This is most important having regard to Mr Craw's system of weak mix base. With the elimination of traction engines and reduction of loads to two tons per wheel on suitable tyre width and diameter, we are of the opinion that this class of road would serve equally as well as any other eonerete road for ’ the traffic of the district.

FURTHER REPORT TO BE MADE.

“The time at our disposal has not permitted us to deal with in economic comparison between concrete and tar-treated roads, but we propose to submit a report in detail to you for your next meeting, but we are of the definite opinion that as the aggregate is already showing slight, and to be expected, wear, Mr Craw’s road will have to lie carpeted with bituminous compound in a few years. • This is common to all concrete roods, and in no wise peculiar to Mr Craw’s length. We have gone carefully through the -account, and have made enquiries relative to the ruling prices at the time the work was done, and append herewith our estimate in detail of what we consider the work would have cost if it had been carried out by (he county, taking into consideration all contingencies which from our own personal experience we know to bo necessary in connection with works of (his nature. It is evident to us that Mr Craw lias been able to transmit some of his enthusiasm to the men employed, with the result that lie has been able to submit accounts which could not have been attained by the ordinary countv methods.” STATEMENT OF COSTS.

Messrs Miiir and Toogood attached 1 lie following statement of f-ost as estimated on the conditions laid down by the Council to be adopted by Mr Craw in laying down the experimental length of concrete road; Materials ; Gravel and boulders, loaded and hauled three miles to site, 170 cubic yards at 7s, £59 10s; royalty on the above (170 cubic yards at fid), £4 ss; cement at 5s 7.’[d, less lid, phis 4d, 248 bags at 5s 101 cl, £B3 2s 7d (note, present price of cement £O4 13s 8d); labour, mixing and placing, 150 cubic yards at 6s, £45; excavating and trimming grade, £3 15s; curing, watering (labour only), and replacing cover at haunches, £3 17s 6d; fencing,.£l ss; lighting, £4 7s 4d; hire of mixer, £1; tools, including loss and repairs, £1 10s; joints at Is each, including fixing, 10 at Is, IQs; water for mixing and curing, £2 IQs; side road formation under summer conditions, £2 3.0 s ; total, £42 12s fid jper chainj

grand total, £213 2s sd. (1) It is to be noted that no rolling has been allowed to consolidate the sub-base; this under average conditions is a necessity. (2) The covering, of the haunches is not as complete as it should be; an edging of river shingle should have been provided. cost has been added for maintenance in patching the surface; it is evident that a certain amount has been expended in this direction which docs not appear in the accounts. (4) The above statement does not include any improvements to Mr Craw’s method which we consider essential; these will be covered in a further report. (5) In investigation from the merchants we find the ruling price of cement at the date of construction was 5s 7;fd per bag on trucks, with discounts allowed; the cost of cartage would have been 2d per hag, or Is fid per ton per mile, and 2d for handling and storage; credit is allowed for empty hags at l]d, making a total of 5s 10.1 d per bag, as against 5s 4d less lid charged by Mr Craw,” —St anda rd.