Delivering sustainable outcomes through in-situ pavement recycling

Society, industry and government are working together in leading a strong drive towards implementing sustainable outcomes within pavement construction, reconstruction and rehabilitation activities.

This approach is resulting in a conscious decrease of environmental impacts across the pavement industry. However, further consideration should be given to the substantive benefits provided by in-situ pavement recycling.

IN-SITU PAVEMENT RECYCLING

In-situ pavement recycling is the process of reclaiming and/or recycling either naturally occurring soil or pavement material through the use of a reclaimer/stabiliser and often the addition of a small volume of binder.

The obvious benefits of recycling include waste minimisation and minimal use of additional or virgin material. In-situ recycling also has direct sustainable benefits that are not all gained through other means of pavement construction, reconstruction or rehabilitation activities.

These benefits include a broad range of sustainable outcomes, including direct cost, whole of life cycle, environmental and social benefits and are available to all asset owners and their subsequent stakeholders.

SUSTAINABLE OUTCOMES

Key opportunities for sustainable outcomes, with regards to pavement reconstruction and rehabilitation, commonly include the following:
• Direct construction cost and financial whole of life cycle costing savings

• Minimising construction waste, resource extraction impacts, and virgin material use

• Reducing truck movements and the impact on surrounding pavements

• Reduced fuel consumption and CO2 emissions during construction activities

• Reducing construction duration, associated social impacts and loss of amenity.

There have been feel-good stories recently around the use of used printer cartridges in asphalt and concerted attempts to improve other forms of recycled asphalt featuring up to 30 per cent recycled materials.

These are great initiatives to try and improve materials that are not sustainable. However, if there are genuine interests in maximising the opportunity to construct in a sustainable manner then options that utilise around 95 per cent recycled materials should be considered with greater weighting.

Understanding the benefits of maximising recycling opportunities on a road project can easily be evaluated on a case by case scenario by reviewing the input materials, construction processes and transport activities throughout its life cycle.

Evaluation tools such as the Greenhouse Gas Assessment Workbook for Road Projects (Transport Authorities Greenhouse Group, Feb 2013) provide harmonised methods for evaluating greenhouse gas emissions.

HOW TO RECYCLE PAVEMENT IN-SITU

In-situ pavement recycling is essentially the process of mixing the existing pavement material in place and adding water, binder and sometimes additional granular material to rehabilitate the pavement structure.

Determining the scope and design required to recycle a pavement involved the same investigation and sampling process used for other treatments and structural design follows common principals through consideration of traffic and subgrade information.

Understanding in-situ material properties is the key step and enables selection of suitable binder (cement, lime, foamed bitumen etc) to carry out mix design testing.

Mix design is determining which binder and at what application rate and generally involves common testing procedures using either CBR or UCS testing within a NATA- accredited laboratory.

FACILITATING THE PROCESS AND EVALUATING THE OPTIONS

Stabilised Pavements of Australia (SPA) is an industry leader in the field of pavement rehabilitation and stabilisation. Its team of qualified civil engineers works with clients to evaluate potential treatment options and the subsequent budget and sustainability considerations related to all treatment options.

SPA works with clients through the project investigation and design phases to ensure its experience is used to maximise efficiency of the design process and provide confidence in risk management.

SPA offers assistance in evaluating ways to reduce pavement management costs and increase opportunities to utilise the most sustainable construction methods and treatment options.