Product Description:

These are needle punched products - a process in which barbed needles are punched through a mat of fibres to create a coherent fabric by the process of entanglement. The fibres are made by melting polyester crystals and extruding the liquid through a nozzle containing thousands of tiny holes. After extrusion, the fibres are strengthened whilst cooling, by stretching them - a process called 'drawing'. As the yarn is stretched, so its diameter decreases and the molecules become longitudinally orientated. The tensile strength increases and the breaking strain decreases accordingly. The weight of an individual fibre is traditionally described in units called "tex". A thread of 1 tex has a weight of 1 gram at a fixed length of 1 km. Consequently, as the fibre becomes finer, so the tex becomes less. Fibres of different tex values are chosen for needle punching, depending upon the required geotextile type and function. Fibres can be pre-treated before needle punching, for example they can be cut in certain ways or made in angular cross sections. This can create increased fibre-to-fibre friction. By varying the type of fibre, the degree of needle punching, or the use of heating to generate fibre-to-fibre fusion, the manufacturer can create a nearly-endless permutation of nonwoven geotextiles with different characteristics.

Applications:

Nonwoven polyester geotextiles are particularly useful for use in high temperature applications such as laying within hot asphalt as a reflective cracking inhibitor. Polyester fibres are generally resistant to temperatures up to about 240 degrees C. In this application, not only is the high temperature resistance advantageous, but the three-dimensional structure of the textile absorbs cut-back bitumen and similar, very effectively, thus promoting the 'waterproofing' of the repaired surface beneath. 

Filtration criteria:

If possible, although not critical, the textile should be chosen for filtration with O90 < 4.D90

Permeability criteria: K geotextile > 10.K soi

Strength Criteria:

There are no design equations for strength in permanent road structures because the textile does not perform a strength function. It is only in access roads that subgrade deformation utilizes a geotextile’s strength.

Performance principle:

The main functions of the geotextile on the subgrade are to prevent the mixing of granular sub-base with the soft cohesive subgrade beneath. Also to permit the effective vibro-compaction of the sub-base and preventing sub-base and subgrade mixing.