Roading Problem Study

Press, Volume CIII, Issue 30560, 1 October 1964, Page 3

Roading Problem Study

(N.Z. Press Association) WELLINGTON, September 30. The D.S.I.R. will join with the Ministry of Works in an accelerated study of the problem of greywacke which has been used in thousands of miles of roading throughout New Zealand.

The Minister of Works (Mr Allen) said today that the problem had arisen on a length of the Auckland southern motorway. He said 12.9 miles of this motorway was now in use

and of this 5.9 miles were constructed on a base course of greywacke. “Three miles of this type of construction have shown signs of damage in the form of cracking of the asphalt surface.

“The cracking is showing over a strip up to six feet in width at the outer edge of the outside lane and nearly all is in the northbound lane,” Mr Allen said. Mr Allen said the section showing damage had been under traffic for nine years. Greywacke was by far the most abundant mineral available for road construction in New Zealand. “We have used it successfully in thousands of

miles of road and we must find ways and means of using it under the increasing loadings of modern traffic,” he said.

In recent years engineers had become aware that greywacke could break down due to chemical action after it was placed in the roadway. The evidence of this breakdown had shown up more obviously under “really heavy traffic and perhaps.” Mr Allen said, “we have been lulled into a sense of false security by the previously good performance under more moderate loadings.” When the first signs of trouble occurred on other greywacke base courses, not the motorway, these were usually pavements 15 to 20 years old and there was a tendency to think the original materials had been carelessly chosen. “The Auckland motorway job, however, was most carefully controlled and has been very well documented. Thus it has been possible to check back on the materials in particular positions, and to compare their quality at the time of laying with their present condition in the road.” Mr Allen said the technical problem and the commercial use of greywacke were both so important that he had agreed with the Commissioner of Works that a special re search effort should be put into study of this material.