Back in the 1980s Hiway Stabilizers recognised the potential and market for modifying low cost marginal quality aggregates as an alternative to using high cost premium quality aggregates. This has resulted in the development of specialised aggregate stabilisation binders such as KOBM Binder™ and Durabind™. The process is now widely used and accepted.

Pavement Aggregates

Aggregates can basically be categorised as either poor, marginal or premium quality depending on the characteristics of the source material and the processing operation. Generally poor quality aggregates are not suitable for road construction and marginal quality aggregates do not comply with many contract specifications. However by stabilising/modifying a marginal quality aggregate performance properties similar to or better than a premium quality aggregate can be achieved.

Traditionally pavements for roads in New Zealand have been constructed using premium quality aggregates.  With high production costs, limited potential sources and often high transportation costs TNZ M4 specification premium quality aggregates are expensive (often prohibitively).

Many Local Roading Authorities do not have accessible premium quality aggregate sources and have adopted stabilisation/modification for road construction using locally produced aggregate. This enables a sustainable roading program utilising local resources at a much reduced cost to the customer and rate/tax payer.

Stabilisation

Stabilisation of pavements has been practised widely in New Zealand for more than 20 years, however, it has until recent times mainly been confined to subgrade layers or for rehabilitation and maintenance of existing upper aggregate pavement layers.

Following many research and development projects and years of successful application chemically modifying an aggregate of marginal quality is now an accepted process that can produce a material which has structural and performance properties equal to or better than those of premium quality aggregates such as TNZ M4.

Binder Selection

There are many types of aggregates available, each with their own characteristics that will react differently to the different stabilising binders available. To determine the most effective stabilising binder reactivity testing is required. This will also enable cost comparisons to be analysed and the most cost efficient stabilisation treatment to be selected. Hiway Stabilizers has a large database containing reactivity results for many aggregate sources in New Zealand.

Current binders available for aggregate stabilisation/modification are:

• Lime
• Cement
• Cement blends
• KOBM Binder™
• Durabind™

Design

Designing pavements incorporating stabilised/modified aggregate layer(s) is relatively straight forward using the AUSTROADS Pavement Design Guide and its New Zealand Supplement in conjunction with CIRCLY Design Software. The modified layers can be easily modelled and compared until the desired results are achieved.

Following some recent pavement failures on heavily trafficked roads Transit New Zealand are now advocating modifying TNZ M4 AP40 basecourse aggregate to combat its susceptibility to shallow shear failure when under heavy traffic loads.

Constructability

Hiway Stabilizers are experts in constructing stabilise/modified pavement layers and have a fleet of modern equipment capable of high production out puts. The process is relatively straight forward and has many advantages over unmodified pavement construction.

• Aggregate can be placed much quicker with higher volumes per day achievable as compaction and finishing are not critical at this stage.
• The stabilising process is very efficient with up to 1km of two lane road capable of being stabilised/modified in a day by a single experienced stabilising crew.
• Final trimming and surface preparation requires less time and effort and less maintenance prior to surfacing is required as the aggregate particles bind together creating a more durable surface.

Summary

Aggregate stabilisation or modification is a proven pavement construction technique which utilises local aggregates to enable pavement construction at often significantly reduced costs and with out adversely effecting the pavements performance.

No matter what the aggregate type, a stabilisation design using a single binder, binder blend or combination of binders is accessible that will provide significant performance benefits.

Hiway Stabilizers have the experience and expertise to select the most appropriate stabilisation treatment and provide assistance with pavement design. Our stabilisation plant inventory is second to none and is operated by highly skilled and efficient crews capable of high production out puts while maintaining the highest quality standards.