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Canada's “Rock to Road”
Magazine
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What is Rubbilizing? Rubbilizing is the in-place breaking of an existing concrete pavement by the application of a specific surface impact, thereby converting the pavement’s concrete panels into coarse granular subbase. Its purpose is to eliminate joint problems caused by excess relative movement between adjacent panels or the hinging of larger pieces of concrete. These movements typically result in reflective cracking of the asphalt overlay, particularly at transverse joints and at longitudinal joints in cases where the travel lanes have been widened. The rubbilizing on the Oxford County Road 2 job utilised International Resonant Breaking’s patented PB-4 pavement breaker. This is a self-propelled rubber-tired machine that incorporates a massive 3.8 m long forged steel beam. During operation, rotating eccentric weights induce vibration in the beam which resonates in a similar manner to a tuning fork. This vibrating mass stores energy that is then transmitted to the breaking tool mounted at the front of the machine. The blow delivered to the concrete by the tool has specific characteristics that are designed to optimize the rubbilizing action – a low amplitude of 25.4 mm (1-in), a 907 kg (2000 lb) force, and a frequency of not less than 44 Hz (cycles/second). The PB-4 has an operating weight of 28 123 kg and is 7.2 m long, 2.4 m wide and just over 3 m high. Its outside turning radius is 7 m. During rubbilization, reinforcing steel is mostly debonded from the concrete and left in place, while any pieces that protrude from the surface are removed manually. Quoted production rates for the process are 500 square metres per hour or higher, depending on the condition of the existing slab, subbase conditions and site congestion. After rubbilization, no individual pieces of concrete are said to exceed 250 mm in any dimension, with the majority of the rubbilized material sized between 25 mm to 100 mm. A vibratory roller is then used to settle and seat the rubbilized surface, in preparation for paving. A smooth steel drum roller with a gross weight of not less than 9.1 tonnes is specified for this application. This machine operates in vibratory mode, with high frequency and low amplitude, to optimize the interlock and compaction of the newly created base material. According to IRB, the breaking system on the PB-4 does not create a greater hazard to buried objects than the vibratory roller; the vibrations produced by the resonant breaker are said to be isolated to the areas immediately adjacent to the breaking shoe. Aggregates
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