Aggregate Modification
This proven pavement construction method using specialist binders to modify marginal aggregate and deliver significant cost reductions in pavement construction. Actual binders are subject to specific design requirements and can include lime oxide, cement, Durabind and/or KOBM (or blends thereof).
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. These specialist binders are now marketed by Hiway Stabiizers' binder development company Econ Products.
Pavement Aggregates
Aggregates can be categorised as either poor, marginal or premium quality depending on the properties of the source material, the processing operation and the end resulting engineering characteristics. Generally poor quality aggregates are not suitable for road construction and marginal quality aggregates do not comply with many traditional 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) and are becoming more so.
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 leading to a 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 aggregate layers.
Following many research and development projects and years of successful application to chemically modify 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- Various Cement and Lime/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 evaluated technically until the desired performance results are achieved.
Following some more recent pavement failures on heavily trafficked roads where unbound (unstabilised), premium quality aggregates have been used, NZTA are now advocating the modification of NZTA M4 AP40 basecourse aggregate to combat its susceptibility to shallow shear failure when under heavy traffic loads.
Constructability
Hiway Stabilizers are experts at constructing stabilise/modified pavement layers and have a fleet of modern equipment, capable of high production outputs. Once understood the process is similar to traditional pavement construction but offers many advantages over unbound pavement construction as follows;
- Aggregate can be placed much quicker with higher volumes per day achievable as compaction and finishing are not critical at the aggregate placement phase.
- 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.
- The prepared surface (prior to sealng) is considerably more
durable and requires less maintenance due to
agregate particles being "bound" together.
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 without adversely effecting the pavement's performance.
Generally, no matter what
the aggregate type, a stabilising design using a single binder,
binder blend or combination of binders is available that
will provide 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 outputs while maintaining the highest standards of quality and customer service.
