Reed, J.J.; Schofield, J.C.; Watters, W.A.; McIntyre, D.J. 1966 Geological and petrological investigations of wacke aggregates used in Auckland-Hamilton Motorway, Redoubt and Takanini sections. Lower Hutt: New Zealand Geological Survey. Report NZGS 20 1 v.
Abstract: Aggregate used in the Redoubt section of the Auckland-Hamilton Motorway was studied in October 1964 at the request of the Ministry of Works (MOW), and a preliminary report covering examination of Stevenson's Quarry and pit samples from the motorway, was written on 21 Jan 1965. Since that time the investigations have been widened to include pit samples from the Takanini section of the motorway, and a general survey made of wacke quarries in the Auckland district. The purpose of this report is to collate all the geological and petrological data bearing on the failure of the aggregate in the motorway. it is concluded that the wacke used is an argillite of a hardened type, which is characterised by textural and mineralogical variation. The range of variation is the same for the Redoubt, Takanini and recent quarry aggregate, but the Redoubt section contains a higher proportion of weaker, less hardened silt and claywacke which is also partly weathered. The excessive fines found by MOW in the failing sections are produced by breakdown of the argillite. There is no evidence of sub-grade, nor of addition of foreign or deeply weathered material, nor of accelerated weathering. The fundamental cause of the excessive fatigue degradation is considered to be the nature of the unweathered argillite itself. In the case of the Redoubt section, the degradation has been accelerated by the aggregate containing a higher proportion of weaker, partly weathered argillite. (auth/ARC)