SprayJet versus Conventional Paving with Pre-Spraying of Emulsion

In many countries, paving binder and surface courses with conventional pre-spraying of emulsion is standard practice when rehabilitating roads. Normally, an emulsion of bitumen and water is applied to the milled base by spray bars and the water allowed to evaporate overnight. This is known as “breaking” of the emulsion. A closed-textured bitumen film remains after the process, which is subsequently overlaid with asphalt. The considerable time and equipment required is a disadvantage of this conventional method. A further problem is that the surrounding areas, roads and curbs are fouled with emulsion by job site vehicles. These problems are now a thing of the past thanks to SprayJet technology from VÖGELE. With the SprayJet, the fresh emulsion is directly overlaid with asphalt as soon as it is sprayed.

This saves a great deal of time, since there is no longer any need to bring the work to a halt for some 12 hours while the emulsion breaks. What’s more, the spray nozzles can be set precisely to prevent fouling of the adjacent areas. But is the bond between layers achieved with the SprayJet method just as strong as that produced by conventional pre-spraying? The two paving methods were compared on behalf of the State Office for Mobility, Rhineland-Palatinate (Landesbetrieb Mobilität Rheinland-Pfalz) when a section of the B 49 federal road in Brodenbach near Koblenz, Germany, was rehabilitated. One aspect to be investigated was whether the bond between layers is impaired by the water content of the unbroken bitumen emulsion when the base is sprayed immediately before paving. To this end, drill cores were taken and analysed.

Brodenbach is located in an area of Rhineland-Palatinate known as the “Terassenmosel” (terraced slopes along the river Moselle) in the district of Mayen-Koblenz, about 26km south of Koblenz. The B 49 federal road runs straight through this popular tourist resort. It offers travellers a picturesque view of the river Moselle. However, long years of heavy traffic and patchwork repairs had taken a heavy toll, leaving the road in urgent need of pavement rehabilitation. At the same time, the work had to proceed without unduly impairing tourist traffic; for this reason, only one lane could be closed to traffic at any one time.

A 1,200m-long stretch of this heavily frequented road with a traffic load of over 6,900 vehicles per day was to be rehabilitated. In keeping with the load class Bk 3.2, the roadway was to be given the following structure: bitumen emulsion C60BP1-S, 300g/m2, = 5cm asphalt binder course AC 16 B S, bitumen emulsion C60BP1-S, 200g/m2 and 4cm asphalt surface course AC 11 D S. The existing pavement was removed in several sections, with traffic being diverted over only one half of the road; the same also applied when paving the binder course and surface course. Since the milled surfaces were not homogeneous and unsuitable for use by through-traffic, the work had to proceed in three 400m sections.

The project as a whole was subdivided into four sections in order to permit representative comparison of the methods. SprayJet technology was used in work sections 1 – 3. Binder and surface courses were paved using the conventional method with pre-spraying of emulsion in work section 4.

The bond of layers proves that the SprayJet method produces the same quality

The quality of the bond between layers is one of the most significant criteria for assessing the durability of a road. Shear strength and shearing distance are representative parameters when it comes to forecasting durability. A total of 16 drill cores were taken under official supervision in Brodenbach: four from the section with conventional pre-spraying of emulsion and twelve from the “SprayJet sections”.

Result: both conventional paving and paving with SprayJet technology yielded good results when the bond between layers was analysed.

Conclusion: VÖGELE SprayJet technology is an excellent alternative to conventional paving with pre-spraying of emulsion

As the practical test in Brodenbach showed, a VÖGELE spray paver is also a faster and more cost-efficient option for paving the binder and surface course in the conventional way with pre-spraying. The spray paver saves time because there is no need to wait a long time for the emulsion to “break”. What’s more, there is no danger of the sprayed surface being driven over or fouled by other means; the same also holds for adjacent traffic areas used by the job site vehicles. This eliminates the need for a “big clean-up” afterwards. Most importantly of all, the quality of the bond between layers is also better, as the analysis of the drill cores from Brodenbach proved.

Even when working conventionally and pre-spraying emulsion, the VÖGELE spray pavers really deliver on cost-efficiency and pavement quality. And they also have yet another advantage: these machines are quickly and easily converted to standard pavers without the spraying function. This improves their capacity utilization and profitability still further.

Heribert Müssenich, Group Team Leader, Road Construction Technology in the State Office for Mobility, Rhineland-Palatinate (Landesbetrieb Mobilität Rheinland-Pfalz) who supervised the comparison of methods in Brodenbach, summed it up as follows:

“SprayJet technology has definitely proved its value when paving conventional asphalt mixes.”

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