CHEAPER HIGHWAYS

Sun (Auckland), Volume IV, Issue 1078, 16 September 1930, Page 7

CHEAPER HIGHWAYS

CONCRETE PENETRATION METHOD PROVED ALBANY TEST RESULTS cheaper concrete roads are now Within the bounds of possibility, and tie smaller local bodies and the counts will have at their disposal a method of reconstructing their main roads in permament materials. This is the opinion of Mr. A. Murray, engineer to the Waitemata County Council, who has succeeded in directing official notice to the practicability of using the “penetration" method of building concrete roads. He is carrying out a pioneering strip of road work tnder agreenv. nt with the Main Highways Board. The experimental section has been laid down on the Birkenhead-Albany portion of the Auckland-Maungaturoto main highway, and the work has already be<?n inspected by representatives of local authorities in Gisborne, Wanganui, Auckland, Mijunt Albert, Takapuna. Devonport, Northcote, Birkenhead, Glen Eden. Henderson, Helensville and the counties of Raglan, Waikato, Manukau, Mangonui, Wliangaroa, Rodney and Whangarei. The Auckland City Engineer. Mr. J. Tyler, has also made a special visit of inspection. Auckland City introduced to _\ew Zealand the idea of concrete roads and is anxious to follow new developments. Mr. Murray states that he has been notified that other interested bodies will accept tile Waitemata County's invitation to study the work as it actually progresses. highways board convinced The original plans, prepared four years ago. for the reforming of the Birkenhead-Albany Road, provided for bituminous surfacing of a speciallyprepared blue metal road. Some miles have been laid according to that plan at a cost of 9s 4d a square yard. Bituminous road work has not found favour round Auckland, largely because the communities have bad before them the example of hard surface concrete roads. The Main Highways Board, however, lias sought to induce local bodies to adopt bituminous surfacing for roads on the score of lower first cost, but the Waitemata County, on the advice of its engineer, was so positive that concrete penetration methods not only would give low maintenance, but relatively low first costs that a deputation went tb Wellington and finally convinced the Highways Board that a properly directed experiment was worth while, and. further, that the county was willing to conduct it. Mr. A. Tyndall, the Highways Board engineer, was loath to admit the value of the method and, just prior to his recent departure for America, came to Auckland to make a personal inspection of the work near Albany. Previously it had been demonstrated that the mortar in the new work was harder than that in the roads put down by a neighbouring local body, and much harder than that in the portion of the TakapunaNorthcote road, laid in ordinary concrete to Mr. Tyndall's own specifications. The workmen on the road relate that Mr. Tyndall tried, with a hammer, to dislodge a piece of blue metal he found adhering on the surface of the new road work; his iirs-t effort merely broke a piece off the stone: the second broke the hammer handle.

The factors to be weighed in any scheme for road reconstruction are first .cost, maintenance costs and permanency. The latter factor includes the question of whether any specified roading material will meet climatic conditions, and withstand the effects o! heavy traffic, and it takes in also the ease of repair in case of accidental damage or positive wear. Mr. Murray has the balance of expert opinion with him when he claims that the experience of Auckland shows that concrete i 3 the best material for withstanding climatic conditions and the effects of heavy traffic. It can also be repaired successfully. QUESTION OF COST The question of whether it should he recommended for county roads turned on the whole issue of the first cost. A cost that might be borne without difficulty by rich municipalities could not be entertained by counties or roa.d boards. Any system of road reconstruction about Auckland means ripping up the existing mud and metal roads and starting anew, a heavy addition to costs. Certain that concrete was the material to be used, Mr. Murray was concerned with reducing first costs of building roads with it. He knew that in Victoria. Ireland and Plngland the penetration method 'of construction had been used as successfully with cement as it had been with bitumen.

He claims the experiment has more than justified his beliefs. Calculating on the same unit costs for blue metal, sand and cement, he finds that while concrete laid by the pre-mix method averages on recent jobs about Auckland £3 a cubic yard; the same work by penetration process works out at £1 l"s 3d, or roughly £2 a cubic yard. This means a saving of one-third in first costs, °r. alternatively, practically one-third more road mileage for the same money. Every observer of the work bas asked; Does the liquid cement reach the bottom of the metal? After Wrsonal inspection, the observers uave been convinced. Tests at the Auckland University School of Engineering have shown that seven days concrete from the Albany road work had an average compression resistance of 2.4081 b a square inch. At days the resistance had risen to •j.3301b. The fracturing of the test cubes showed that penetration was Perfect. In some cases the blue metal had yielded before the interocking mortar. Beam tests with the oncrete have also given very satistlctory results. The mixture on tulysis was shown to he metal, sand unq cement in the ratio of Si, 24 and

CONDITIONS OF EXPERIMENT U' le Albany experiment has not conducted under the most favhali V le conditions. The foundations bee n put in 14ft wide fur a road. The concrete slab is ■ t wide, as the engineer contended was the minimum width. It ah" 1 ’ howe ver. that a strip of the ii'o ‘ wide on either side, had to considered. The engineer u«w thick, while the thickHin ° n the crown of (he road is chao j Ttle blue n »etal used was pur,o*l originally for the bitumen ta . w prk, too. and this has neeessibe «h the use of chips that have to with ken into Place by rolling first roll heavy roller and then by a light PouT i T lle concrete liquid is then e< l into the compacted metal, ef-

fectively locking it, the usual transverse and longitudinal joints being provided The fact that the slab is only 16ft wide has precluded the laying of the work in two long strips although Mr Murray believes that this should be done. Unlike the ordinary premix work it is possible to run a light roller over the freshly concreted road. A two-ton roller is used to compact the mass, which is then covered with bags to cure it tor three weeks. Blue metal has cost 23s a cubic yard and sand 17s at Albany. These items have increased the cost of roading in the district. At Howick, for instance, the metal costs from Ss 6d to 10s 6d a yard, and sand l-.s. The work has been carried out by ' mv/marray says that more efficient plant would reduce costs.