Fast track... the Dynapacs on the job
Favourite Dynapac wins tough chase
01 September 2003
High frequency compaction rollers from Dynapac ensure a UAE contractor meets his commitments in a race against the clock on a highway project.
WHen UAE-based Marwan Contracting Company was called upon to execute the construction of a new 2 km-long highway and a roundabout for the Sharjah Equestrian and Racing Club in a month's time, it had to rely on using equipment that would make the seemingly impossible task possible.
Marwan moved in its fleet of Dynapac high-frequency compaction rollers, rubber-tyred rollers and pavers to do the job of building the new approach road and extended car-park facilities, which were needed to provide improved access and parking for the emirate's first international Arabian horse event.
The contract involved excavating more than 50,000 cu m of sand from the virgin desert using a dozer for fill and cut, and a grader for levelling. To complete the compaction work, the company pressed into service more than 30 Dynapac rollers and pavers including a complete Dynapac paving and high-frequency compaction train.
The compaction was started off with the preparation of a 30-cm sub-base, and was followed up with two asphalt courses and a 60-mm base course and topped with a 40-mm wearing course across the 8.1-m-wide road. Following the use of the Dynapac paver, Marwan used an effective combination of two CC 222 rollers and a CC 422 roller to provide the optimum improved finish and compaction.
Explaining the role played by Dynapac in overcoming the problems associated with compacting the new thinner surfacings, a Marwan spokesman said: 'Traditional low frequency, high amplitude tandem vibrating rollers have been found to be less suitable for compacting the new thinner surfacings of up to 40 mm thickness.
''The combination of low frequency and high amplitude needed to achieve the desired density and depth of compaction of the thicker layers, have a tendency to over-compact thinner layers. It also considerably increased the risk of crushing the larger aggregates used in the new and much thinner stone mastic asphalt surfacings.
'Dynapac's research engineers focused on the combinations of four main parameters to find a practical solution for compacting the new thinner stone mastic asphalt wearing courses. Following exhaustive tests and trials, the team established that the best solution for the successful compaction of thinner asphalt surfacings, while minimizing the risk of crushing the larger aggregate, required a combination of low drum amplitude of about 0.2 mm and high frequency vibration of about 70 Hz to generate sufficient compaction energy. This was a complete reversal of the high amplitude and low frequency required for the compaction of thicker layers.
'In 1996 Dynapac launched the first low amplitude, high frequency hydrostatically driven tandem vibratory rollers, the CC222 and CC232. These rollers were introduced specifically to cater for the thin stone mastic asphalt surfacings. Since then, Dynapac has steadily increased the range of these dual amplitude and dual frequency rollers.
'The company has also been developing a family of tandem vibratory rollers with dual amplitude and dual frequency. These extremely versatile, dual-purpose tandem vibratory rollers, such as the CC422 and CC522 allow contractors to compact traditional thick base and binder courses and thin wearing courses with just one machine.
'The dual-purpose roller can be initially set on a high amplitude and low frequency setting to achieve the required density and depth of compaction in the thicker base and binder layers. The same roller can then be simply switched over to the low amplitude and high frequency setting to complete the compaction of the upper part of the thicker layer and compact the final thin overlaying wearing course. These versatile rollers can also operate as deadweight machines without vibration to perform, if required, a final sealing finishing pass of the wearing course.'
Referring to the completion of the Sharjah project, he said: 'The CC 222 compaction rollers completed an average of four passes - two vibratory and two compaction. The 10-tonne class CC 422 then made a single static pass to achieve the specified 98 per cent degree of compaction. Five Dynapac rubber tyred pneumatic CP 271 rollers completed the 'train' process with six to seven passes ensuring a high quality finish.
'For the 40-mm wearing course, the same train repeated the process but with the Dynapac 7.3-tonne class CC 222 making an additional vibratory pass to achieve a specified 98 to 99 per cent degree of compaction.
''The CC 222 has been designed to pave asphalt up to 1,500 sq m/hr and features a drum width of 1,450 mm. The dual-purpose CC 422 is suitable for high capacity asphalt compaction and is also ideal for sub-base and base courses, sand and gravel. Powered by a Cummins diesel engine it features an operating mass of 10,440 kg and a drum width of 1.68 m.''
Local distributor Inma provides the complete after-sales back-up for Marwan's fleet of Dynapac units. A strong service network and an efficient spare parts distribution have contributed to Inma's continued growth in the market, he adds.
Referring to the Dynapac machines, the spokesman said: 'They are very reliable, with few problems and they guarantee a quality finish. Without the reliability of the machines it would have been extremely difficult and embarrassing to meet the tight contract deadline.'
