A look back at HUESKER’s 40 years of experience with asphalt reinforcement

HUESKER was first formed as H. & J. Huesker & Co. in December 1861 in Gescher, Germany. As early as 1958 the company recognised the excellent prospects for the future of synthetic fabrics and started to manufacture filter fabrics and sandbags. Continued expansion of the product range led to the founding of HUESKER Synthetic as an independent company in 1973.

The idea of a reinforcing fabric for road construction first emerged at the end of the 1960s. The initial aim was to develop a product to reinforce asphalt. The embedded geotextile layer was intended to pick up the tensile stresses in the asphalt like steel reinforcement in concrete and prevent cracks from forming. However, it was soon realised that the principle would not work as the developers expected, because of the completely different characteristics of asphalt and concrete. It was found that the product proved excellent at delaying the formation of reflection cracks in resurfaced carriageways.

Even then polyester was the preferred raw material because of the compatibility of its mechanical properties with the stress-strain behaviour of asphalt. Working in close cooperation with a manufacturer of polyester yarns and a weaving mill for technical yarns, Huesker came up with the reinforcement grid HaTelit^® at the start of the 1970s. It was a grid of polyester fibres with a 2.0 cm mesh size.

HaTelit^® was used in several projects during the 1970s. The experience gained from these first practical applications was used in the continuous development of HaTelit^®. Over time it became clear that the bond between the asphalt layers was one of the most important factors in the successful functioning of asphalt reinforcement. The mesh size of the grid was increased from 2.0 cm to 3.0 cm to achieve a better bond and interlock with the asphalt-aggregate matrix.

Many of the influencing factors that are considered self-evident today were completely unknown in those days. There were no comparable products that we could use to orientate ourselves.

A challenging project for HaTelit^® at the end of the 1970s. 

The 45 m wide runway at Brussels Airport was to be refurbished using HaTelit^® 30/13 – a challenging application indeed.

The existing concrete runway was showing damage to such a serious extent that a complete refurbishment was considered essential. In order to delay the propagation of cracks from the expansion joints and the concrete slabs through to the surface, this would be the first time that asphalt reinforcement had been used at the airport. First of all the top centimetre was milled off the runway surface, then any loose concrete slabs were underfilled and a bituminous regulating course was applied. HaTelit^® 30/13 was then installed on top of the regulating course.

As the highest loading from landing aircraft occurs in the centre of the runway, just the central 25 m wide strip of the runway was reinforced. The 10 m wide edge zones remained unreinforced. The whole runway surface was then overlaid with a 5 cm binder course and a 5 cm surface course. The refurbishment works should just preserve the use of the runway for two years.

Three years later in 1983, when the first formal assessment took place, it was found that in the unreinforced zones virtually all the expansion joints between the concrete slabs had propagated through to the blacktop surface. In the HaTelit^®-reinforced zone no individual cracks could be seen. The last assessment took place in 1990 (10 years later). The runway was still in excellent condition. Apart from some minor surface treatment up to then no further measures had been necessary.

The refurbishment of the runway using HaTelit^® 30/13 had been a complete success!

The 1980s saw a rise in demand for asphalt reinforcement in runway refurbishment projects both in Germany and internationally. HUESKER was able to acquire a great deal of experience on many successful projects.

HUESKER's further development of asphalt reinforcement created a large market. Some geosynthetics manufacturers marketed products that had been originally developed for earthworks and foundations and not specifically for asphalt reinforcement.

In addition to great successes, by the end of the 1980s Huesker was also aware of some first occurrences of minor damage. The reason was not always immediately apparent. It took some time until it became clear that the coating of the reinforcement was a decisive factor. Trials with a bituminous surface coating yielded very good results. To improve the bond between the reinforcement and the asphalt even further, HaTelit^® was then manufactured with an applied bituminous coating.

The effect of the reinforcement could be impressively demonstrated but the installation of HaTelit® was not always easy. Sometimes when asphalt lorries ran over the material it tended to lift and stick to their tyres. Many further trials were required over time to optimise the installation technique. Tensioning and nailing the reinforcement in place before overlaying with asphalt produced a definite improvement and prevented the reinforcement from lifting. In order to ensure HaTelit® was properly and smoothly incorporated into the works, the contractor was advised to seek the advice of HUESKER engineers on the best method of installation. This approach to installation paid off.

A few minor product improvements were followed by the development of HaTelit^® C40/17 in the middle 1990s. This represented a completely new product. HaTelit^® C40/17 is a further development of the proven HaTelit^® 30/13 in which an ultralight nonwoven was added to the product to ease installation. To achieve a good bond both the grid and nonwoven were bitumen coated. This installation aid eliminates the need for time-consuming tensioning and nailing of the material as was required with HaTelit^® 30/13. Installing the material in accordance with the HUESKER installation instructions will ensure the operation progresses smoothly and without error. Trials have also shown that the bond can be further improved by increasing the mesh size to 4.0 cm.

Today HUESKER's excellent technical advice and support are still important when installing HaTelit^® for the first time.

The current HaTelit^® C 40/17 product has shown itself to be ideal for asphalt reinforcement. It is tested by independent testing bodies and continuously checked by our in-house ISO 9001 certified laboratory. The raw material polyester still shows best performance as asphalt reinforcement.

Our successes over the years have proven that polyester is the ideal raw material for asphalt reinforcement. Scientific studies have shown that good asphalt reinforcement extends the life of a refurbished carriageway by a factor of 3 to 4. Only after this amount of time it can be clearly appreciated how effective a reinforcement grid actually is. With over 40 years of experience HUESKER has the proof!

In the development of HaTelit^® most emphasis was placed on the acquisition and evaluation of practical experience. Comparative observations of small areas left unreinforced were made in a large number of different projects. The results of these observations confirmed that HaTelit^® provided considerably increased resistance against crack formation in the problem areas.

The claims of some manufacturers of asphalt reinforcement that polyester grids are not recyclable have been disproved by numerous studies.

Trial mixes are frequently carried out using millings from HaTelit^®-reinforced asphalt. A well-documented example is the test length constructed in 2004 at a mixing plant in Schwelm, Germany. Here a bituminous emulsion was applied to an existing length of asphalt roadway, HaTelit^® was then installed and overlaid with approx. 4 cm 0/11 asphalt surfacing. This surfacing was milled off to a depth of 5 cm a few weeks later; i.e. including the HaTelit^® grid. The millings were then added at a rate of 30% by mass to a new batch of bituminous 0/22 CS base material.

All the requirements applicable to the use of asphalt in road bases were fulfilled. There were no negative characteristics with respect to Marshall stability and flow, void content or binder properties.

The frequently quoted argument that polyester grids cannot be milled off was shown to have no basis in fact.

The milling of HaTelit^® reinforced asphalt layers does not normally present any difficulties. The following applies generally to milling: the better the bond, the easier the milling. This is a considerable advantage of HaTelit^®, as the installation aid in combination with the bituminous coating of the grid ensures there is a good bond with the asphalt layers. Only with low output millers the achievable working speed is reduced (down to 80 %).

Research and development for HUESKER Synthetic means translating practical needs into practical products. This task begins with the selection of the appropriate materials, continues with the testing of initial laboratory samples and goes on to include investigating the products’ long-term behaviour in use.

HUESKER is not just a manufacturer, nor just a supplier, nor just a marketing company. HUESKER sees itself as a company that can support the contractor and provide solutions to his problems.

The results are engineering solutions with made-to-measure geosynthetics.