Rehabilitation of Airport PCC Pavements using HMA Overlays
The rehabilitation of airport Portland Cement Concrete (PCC) pavements is a critical aspect of maintaining safe and efficient airfield operations. Over time, these pavements can deteriorate due to factors such as heavy aircraft traffic, weather conditions, and normal wear and tear. One effective method of rehabilitating PCC pavements at airports is through the use of Hot Mix Asphalt (HMA) overlays.
Things to consider before starting rehabilitation
Before considering pavement reconstruction at PCC airport, start by identifying if the problem is functional or structural. After this has been determined, think about the initial construction cost, life cycle cost, operational downtime, local competencies and the reliability of the chosen method. Possible methods include mill and fill, break and seat, perpetual pavement, rubblisation, overlay, recycling, or rehabilitation.
Assess the airport pavement’s serviceability
The pavement's serviceability, which is represented by PCI, is used to assess the state of the pavement segment. As a pavement's serviceability declines over time, and below a critical PCI level (65 for principal airports and 55 for lesser airports), rehabilitation will be needed. If the state of the pavement warrants rehabilitation, an investigation has to be carried out to identify the root of the failure and to choose the most effective rehabilitation option. The investigation may incorporate information taken from existing databases, a visual condition assessment, non-destructive testing, traffic and pavement analysis, pavement coring and boring, plus drainage analysis.
Select an option for rehabilitation
When it comes to rehabilitating a PCC airport pavement using HMA, there are two options available. The first method involves placing a HMA overlay on top of the existing PCC pavement, which may involve saw cutting and sealing the joints or including a crack relief layer. The second option is to apply a HMA overlay on top of a PCC pavement that has been fractured or rubblised. It is also worth noting that the break and seat process is considered to be more costly and more effective compared to the rubblisation process.
Figure 1: Rehabilitation of Airport Concrete Pavements using HMA Overlays
Option #1 HMA overlay over existing PCC pavement
For years, PCC overlays of existing rigid pavements have been used to restore the structural capacity of the pavements. This process involves fixing the pre-existing concrete slabs, adding edge drains, laying a crack relief layer, providing a HMA levelling course, and applying on a HMA surface course.
Crack/break and seat is a rehabilitation method that’s used to reduce or slow down reflection cracking through limiting the movements in the underlying PCC slab that cause stress in the overlay.
The crack/break and seat approach involves the removal of the HMA overlay (if present), fixing drainage issues, breaking or cracking concrete into pieces at controlled and predetermined intervals, reseating the cracked pieces, removing and patching soft areas, sweeping pavement surfaces, applying a tack coat and installing a HMA levelling and surface course. Concrete that is cracked, shattered, or seated may have a modulus of 500 to 800 ksi.
The crack and seat method is applicable to jointed plain concrete, and has been shown to have an excellent performance history (AAPTP). However, it is not recommended for use on reinforced pavements (A.M. Schutzbach). For reinforced pavements, it is best to use the break and seat method (Asphalt Institute).
Option #2 HMA overlay over fractured or rubblised PCC pavement
Rubblisation is a process that fractures PCC (Portland Cement Concrete) slabs to create a superior quality aggregate base. This technique removes several distresses in the slabs, including reflective cracking, d-cracking, ASR (Alkali-Silica Reaction), slab rocking, pumping, curling, and other forms of slab action. Additionally, it breaks the bond between the concrete and any steel present, transforming a failed rigid system into a new system with improved flexibility (Asphalt Institute).
Rubblisation involves several steps: 1) removing any existing HMA overlay, 2) addressing drainage issues, 3) breaking up a portion of the PCC pavement (typically the upper half or two-thirds), 4) compacting the broken concrete, and 5) applying HMA leveling and overlay layers. The modulus of the resulting rubblised concrete can vary between 200 and 500 ksi.
Other rehabilitation methods for airport PCC pavements
Aside from HMA overlays, you may have to consider other alternative strategies. There are a range of concrete maintenance and rehabilitation strategies, which is discussed in our blog on 7 Maintenance and Rehabilitation Strategies for Concrete Pavements.
Conclusion
When rehabilitating a PCC airport pavement using HMA, it is important to consider the available options and choose the one that best suits your needs. Whether it is the crack relief layer, crack/break and seat approach, or rubblisation process, each option has its own unique advantages and disadvantages.
Consult a pavement engineer to ensure that you are making the right decision that will enhance the longevity and safety of your airport pavement. We offer customised service package to suit your requirements. Click here to find the best service options for your airport pavement.
References
1. AAPTP (2008) ‘Project 04-01: Development of Guidelines for Rubblization Final Report. Available: <https://www.eng.auburn.edu/research/centers/ncat/files/aaptp/Report.Final.04-01.pdf >
2. AAPTP (2009) ‘Final Report 05-04 Techniques for Mitigation of Reflective Cracks’. Available: <https://www.eng.auburn.edu/research/centers/ncat/files/aaptp/Report.Final.05-04.pdf >
3. A.M. Schutzbach (Year N.A) ‘Crack and Seat Method of Pavement Rehabilitation’. Available: <https://onlinepubs.trb.org/Onlinepubs/trr/1989/1215/1215-022.pdf >
4. American Concrete Pavement Association (1998) ‘Rubblizing of Concrete Pavements: A Discussion of its Use’. Available: <http://overlays.acpa.org/Downloads/Rubblization.pdf >
5. Asphalt Institute (2018) ‘Rehabilitation of PCC Airfield Pavement’. Available: <https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=4222&context=roadschool >