ROAD PAYING.

Press, Volume LXIV, Issue 19312, 17 May 1928, Page 11

ROAD PAYING.

METHOD TO REPLACE "HOT-MIX." CHRISTCHURCH CHEMIST'S CLAIM. Mr P. W. Saxton, of Christclmrch, claims to have made a chemical discovery which will give the country districts city roads, permit road-making all the year round, instead of only in .the dry months as at present, and cost one-twentieth of the capital outlay on a complete h ox-mix unit. He outlined 1 ■ his discovery to a representative of The Press last evening, in the laboratory of Mr A. E. Oldridge, where the last stages of his researches have been carried out. Mr Oldridge agrees with Mr Saxton that the discovery will be a valuable one in the forming of roads in New Zealand. , Mr Saxton, chief chemist for a wellknown paving firm, was formerly chemist to the Wellington City Council and made a special study of paving work. He states that his researches have extended over a number of years, resulting in his discovery. One of the great advantages which it possesses, he says, is that the equipment and plant required is much simpler than that used at present, is cheaper, and is portable to any part of the country. It can offer no very great reduction in cost, but can achieve results with much greater expedition. It can be used where hotmix is not practicable and will save about twelve per cent, per square yard of road treated.

Discovery Explained. - "Hot-mix is the most effective form of paving that has yet been evolve' 3 but hot-mix is open to one or two serious drawbacks," said Mr Saxton. "These relate to the process of construction, as the road must be manipulated and compacted while hot. The engineer is restricted by the distance from the central plant—generally about 15 miles. Also,. as hot-mix is dependent on temperature, there are several months in the year —during the winter —when the hot-mix cannot be laid, and the work must cease. Many attempts have been made to achieve results'by a coldmix and there have been two processes on the market. One is the emulsion process which relies on coating t|ie cold aggregate by finely subdividing the bitumen in the form of an emulsion. It has been demonstrated that the prolonged action of water on bitumen is detrimental, and as the surface exposed by the bitumen in emulsion is relatively enormous, the detrimental effect is accelerated. The other process also relies on finely subdividing the bitumen. In. this case it is very hard bitumen, capable of being pulverised. A solvent is used to render this fluid for. coating purposes. If the solvent be not volatile the road will never harden, and if it be volatile the road, finally, will be left bound together by the original bitumen which was too hard and brittle for paving purposes. "I have evolved a process that also relies on bitumen in a finely subdivided state, to coat the cold aggregate. But I have managed to overcome the objections to both previous processes in an entirely novel method," said Mr Saxton, in explanation. "I rely on atomisation to produce the fine subdivision, and the aggregates, rotated in a concrete mixer, have imparted to them, a thin, uniform film of bitumen of the correct consistency, identically in the same condition as in the case of the hot-mix, with the exception that the aggregate is cold. For raking, and compaction, the bitumeu film is softened, temporarily, by the use of a small quantity of volatile solvent. After raking and compaction, which proceeds exactly as in the case of hot-mix, it has been found that the solvent evaporates, leaving the pavement quite hard and suitable for traffic within 16 hours the same time as in the case of hotmix. The aggregates used are proportioned in exactly the same way, and consist of stone, sand, filler, and bitumen, and the final result is indistinguishable from the hot-mix. This process, therefore, combines all the advantages of the existing cold-mix. with those of the hot-mix, without the disadvantages of either, and, when developed, it is fully expected to supersede hot-mix as a means of permanent paving. "The Public Works Department in Wellington has offered a stretch of road upon which to make a trial, and the next step will be to avail myself of their offer, and lay the stretch, which will demonstrate, publicly, the correctness oi' my claims."