Roading Aggregates


Supplying quality aggregates in the form of sub-basecourse or basecourse for roading projects is a major part of Holcim Aggregates' business.

Our accumulated skill, experience and access to quality raw material means we are able to supply roading contractors with material that has the consistent grading and suitable physical properties to ensure it knits together effectively when placed.

Our aggregates can therefore be spread and compacted with the minimum number of passes, thus saving time and money. The basalt aggregates available in the Auckland region have a particularly good reputation for their binding properties.

General road layering:

  • Road surfacing - sealing chip or asphalt layer
  • Basecourse
  • Sub-Basecourse
  • Subgrade

Aggregate is placed between the wearing surface of the pavement and the compacted sub-grade. Depending on the type of pavement construction and environmental conditions, aggregates serve a variety of purposes, including reducing the stress applied to the subgrade and as a drainage layer. Properties usually required include resistance to pavement deformation, high permeability (or drainability), and low susceptibility to frost action.

A range of basecourses is available from the tightly specificed products used in highway construction down to the non-specified basecourses suitable for use as site access metal or in general construction.

High quality basecourses produced to rigid specification set by Transit New Zealand include TNZ 40 or 65mm products. The material is used on motorway and highway construction, or sometimes specified for other heavy duty pavement construction such as container handling facilities.

General purpose basecourses for use in light-trafficked roadways, parking areas and prive roads etc include the General All Passing (GAP) 40 and 65. These can be produced to Local Authority or quarry production specifications.

These are lower grade, lesser quality basecourses generally suited for use as temporary metal for building site access and as controlled hardfill material.

The primary use of sub-basecourse is in the lower section of the road where the stress and impact from vehicle loading is less.

Sub-basecourses are usually of a larger maximum size than basecourses, commonly All Passing 65 or 100mm.

This fill material is normally used when the natural foundation is not adequate. Products commonly include AP100

For specific information on products and their applications please contact the technical department at Bombay Quarry.