Aggregates as a resource : an introductory study of the use and management of aggregates, with emphasis on the south-west region of the North Island

Abstract

Aggregates have not been recognised as an important resource, nor as a resource amenable to procedures for management which are applicable to any finite resource. They are an important commodity to contemporary society, but have a low monetary value in relation to their bulk and weight. They are generally produced close to their point of use and their exploitation has seldom been systematic or planned. Besides research carried out to determine standards and specifications the majority of previous studies have been concentrated on determining the potential regional availability and quality of aggregate resources.

The most important property of aggregates is that of hardness and the rock-types of suitable hardness for aggregates that occur in the study area are: greywacke-argillite, andesite, and hard sedimentary rock. Aggregates are produced from two types of sources - in situ hard rock and unconsolidated sediment formed from the natural breakdown of parent material. Naturally fragmented material is generally preferred as it is easier to extract and less crushing is required. However, aggregates are unevenly distributed throughout the study area; there is a scarcity of suitable sources in parts of Wanganui and Taranaki and indications are that all river s are being depleted.

The total output of aggregates in New Zealand appears to be directly correlated to the level of activity in the economy. Production at a regional level is subject to wide fluctuations which are partly influenced by the population level and the realisation of short-term large scale construction projects use for aggregates. Roading is the most important use for aggregates.

Aggregate recovery is controlled by market conditions and by a variety of local territorial authority and Government by-laws and licenses. At least six parliamentary acts, and in specific circumstances at least another nine acts, may be relevant. In consequence, responsibility for management is often unclear and confusing.

To date aggregate resources have been developed rather than managed. Management involves identifying: 1) sources, including those that are presently uneconomic, 2) their suitability for different uses, and 3) the socio-economic factors involved in their exploitation as aggregates form an integral part of the physical and social environment and exploitation affects not only those directly concerned with the industry, but all sectors of the community. Management policies should be flexible as aggregate resources form part of a dynamic environment with constantly changing variables.