NDRRA Saturation Damage Foamed Bitumen Rehabilitation Bruce Highway, Qld
The Queensland Department of Transport and Main Roads (DTMR) carried out a major rehabilitation of the Bruce Highway and other major North Queensland roads following the rainfall events of 2008-2009 wet season.
The challenge for DTMR was to adopt rehabilitation solutions along the National Highway that would negate construction risk during wet weather, provide adequate pavement structure for the assigned traffic loading and also ensure that the highway remained serviceable throughout the construction period. The adopted design included a granular overlay, foamed bitumen stabilisation and a PMB seal coat.
SPA, through our strong project delivery performance on previous projects within the region, was able to obtain two of the three projects delivered in 2009 including rehabilitation of 10km of the Bruce Hwy between Ingham and Cardwell.
This particular section of road had been in poor condition for several years and the damage sustained from the aforementioned wet season rendered the section as one of the worst along the entire Bruce Hwy.
The pavement design (Figure 1) for this particular contract included a 100mm Type 2.1 gravel, foamed bitumen stabilisation (3.5% bitumen and 1.5% cement) to a depth of 250 mm followed by a 10mm primer seal and 14mm PMB seal coat.
Points of interest within this design include the following:
⦁ Use of FAB cement as the secondary stabilising agent due to the local cost and logistical restrictions of high volumes of lime. It was essential that the incorporation of the cement was not excessive as this would contribute to developing a rigid pavement and hence reduce the effectiveness of the flexible foamed bitumen basecourse properties
⦁ Use of 100mm granular overlay to improve the pavement depth and hence enable sufficient working platform throughout the construction process and to also improve the formation height and hence reduce the risk of pavement saturation
⦁ The issues encountered by Main Roads with regards to primer seal design and the use of cutter. With the incorporation of 3.5% bitumen, early primer seal coats incorporating cutter were flushing and deteriorating in a number of days in combination with slow moving traffic and high pavement temperatures.
The timing of project delivery resulted in two key challenges for SPA with limited local specialised subcontractors and also a need to ensure that the majority of works were completed prior to the approaching wet season.
In order to ensure a speedy completion to the majority of pavement works, SPA employed the use of a 2m profiler and two Wirtgen foamed bitumen reclaimer / stabilisers to achieve daily productions of up to 1000t import of gravel and the foamed bitumen stabilisation of 5,000m2 of pavement per day.
Whilst efforts to complete the majority of pavement works prior to the wet season were successful, the remainder of works that were to be completed early 2010 did experience the expected high rainfall. The final 20,000m2 of the project was hit by a severe low pressure weather system and was subsequently left under traffic loading and to the elements without primer seal for a 2 week period that produced 200mm of rain.
The pavement showed no signs of deterioration during this period and is a testament to both the resilience of foamed bitumen basecourse to resist moisture ingress and also the astute decision by the Main Roads to adopt the foamed bitumen rehabilitation process. The preservation of other projects within the area with different rehabilitation methods experiencing the same rainfall were not so fortunate.