In 1994, the Erosion Control Technology Council (ECTC), an organization of rolled erosion control product (RECP), hydraulically applied erosion control product (HECP), and sediment retention fiber roll (SRFR) manufacturers commissioned TRI/Environmental to initiate a program to identify and establish a common terminology and to develop standardized index tests for the characterization of RECPs.  In January 1997, a manual of common terminology and recommended index testing standards (ECTC Technical Guidance Manual: TASC 00197) was issued to the industry.

Subsequent to these development efforts, there have been coordinated efforts to work through the ASTM International development process to achieve consensus standardization of RECP index test procedures.

STANDARDS FOR INDEX TESTING AND EVALUATION OF RECPs:

Mass per Unit Area
The mass per unit area, also known as the weight per square yard of a sample, is an important quality control property. ASTM D 5261 was developed for testing this property of geosynthetics and was, until recently, commonly used for RECPs as well. But since sampling and cutting RECPs can be quite challenging, two new standards have been developed by ASTM:

• ASTM D 6566, Standard Test Method for Measuring Mass per Unit Area of Turf Reinforcement Mats (TRMs), which uses ten 8 x 8 specimens at ambient laboratory conditions, and
• ASTM D 6475, Standard Test Method for Measuring Mass per Unit Area of Erosion Control Blankets (ECBs), which uses five larger (typically 12 x 14) specimens that have been dried at 50º overnight.

Thickness
Thickness is another important quality control property. ASTM D 5199 was developed as a geosynthetic test method, but it is commonly applied to RECPs using a modified procedure in order to accommodate the uniquely compressive, three-dimensional nature of RECPs. The modifications typically included replacing the standard 2.22-inch diameter plate with a 6-inch diameter presser foot and testing under a 0.029 psi pressure, rather than the 0.29 standard. ASTM has recently approved a new standard specifically for TRMs that adopts these modifications titled ASTM D 6525, Standard Test Method for Measuring Nominal Thickness of Permanent Rolled Erosion Control Products (RECPs).

Tensile Strength
Tensile strength is the other primary quality control property measured on RECPs. Arguably, tensile strength may also be important if an RECP is subjected to emergency and recreational vehicular traffic and maintenance such as mowing. Originally, ASTM methods D 5035 and D 1682, textile test methods, were used to measure RECP tensile strength. More recently, a new ASTM tensile test method, that uses at least 5 inch-wide grips, has been approved and is titled ASTM D 6818, Standard Test Method for Ultimate Tensile Properties of Turf Reinforcement Mats (TRMs).

Stiffness
The stiffness of an RECP is a measure of how much it will deflect under its own weight. Products with lower test results are more flexible and can more easily conform to the subgrade. Establishing and maintaining intimate contact with the subgrade is paramount to a successful installation. While ASTM D 1388 has historically been used to measure stiffness, appropriate procedures have been incorporated into a new test method that is explicitly applicable to TRMs of any fiber content and any number of components: ASTM D 6575, Standard Test Method for Determining Stiffness of Geosynthetics Used as Turf Reinforcement Mats (TRMs).

Light Penetration
A light box has commonly been used to quantify the openness of textile materials. It illumines a light source inside a box on one side of the specimen. On the other side, a calibrated meter measures the amount of light that is able to pass through the specimen. The Lumite Light Projection test method has been used for years to determine the percent of open area of woven geotextiles. This test method has also been used to measure the amount of light from a 60 watt bulb that penetrates through an RECP. This amount – stated as a percentage of the amount associated with no specimen in place – is the light penetration. The inverse of light penetration is the ground cover. A balance of ground cover and light penetration is important for rapid seedling emergence. The values stated as a percentage are to be regarded as nominal values. A light box procedure that increases the bulb wattage to 150 watts has been standardized by ASTM specifically for TRMs and is titled ASTM D 6567, Standard Test Method for Measuring the Light Penetration of a Turf Reinforcement Mat (TRM).

Compression
Compression is reduction in thickness experienced by the RECP under a standard loading. Five 4.7 x 4.7 specimens are tested at a compressive rate of 10% of thickness per minute. It gives an indication of the RECP’s resistance to flattening. The standard test procedure for TRMs is ASTM D 6454. The same procedures are generally used for geosynthetics.

Resiliency
It is sometimes useful to measure the impact of cyclic loading on the thickness of TRMs. The associated test method establishes the procedures for evaluation of the permanent deformation of a TRM under short-term, repeated compressive loading. It may be relevant to a TRM’s ability to protect newly developing seed from damage during loading. Three 100-psi loads are applied, and the resulting thickness is expressed as a percentage of the original. ASTM D 1777 was originally used to measure thickness before and after loading. The newer thickness measuring procedures of ASTM D 6525 have been incorporated into the TRM-specific ASTM standard titled ASTM D 6524, Standard Test Method for Measuring the Short-Term Compression Behavior of Turf Reinforcement Mats (TRMs).

Ultraviolet Stability
RECPs may need to retain relevant properties when exposed to sunlight. Typically the ultraviolet (UV) portion of the light spectrum is used in accelerated exposure tests. The most common standard accelerated lab test is ASTM D 4355, which uses a Xenon Arc light source. Specimens are exposed to continuous 120-minute cycles of 90 minutes of light only, followed by 30 minutes of water spray and light. Specimens are typically removed after 150, 300, and 500 hours of exposure and tested for residual tensile strength in accordance with ASTM D 6818. The retained strength is reported as the measure of a material’s UV light stability.  (Note: Since accelerated tests have not shown a consistent correlation to outdoor exposures, ASTM’s D 5970, is available to assess an unaccelerated site-specific UV stability via outdoor exposure.)

OTHER NON-STANDARD INDEX TESTS FOR RECPs

The standardization process takes time to build the necessary consensus for a standard to be accepted industry-wide.  While already commonly in use, the following test methods are not ASTM standards:

Porosity - Porosity is the measure of air voids in the material. Porosity is calculated from thickness, mass per unit area, and specific gravity.

Open Volume per Unit Area - Open volume per unit area is the measure of void volume within a material. The value disregards the size of the voids. It is calculated using thickness and porosity.

Water Absorption - Water absorption is a measure of a material’s capacity to absorb water and is generally applicable to organic RECPs. The standard test procedure is ASTM D 1117 and ECTC-TASC 00197.

Swell - Related to water absorption is the swell of an organic RECP resulting from water absorption. The test procedure has been proposed by the ECTC in the ECTC-TASC 00197  using  ASTM D 5199 to measure before and after thicknesses. ASTM D 1777 has also been used for measuring swell.

Specific Gravity - Specific gravity (SG) is a measure of the unit weight of a material as compared to that of water. The standard test procedure is ASTM D 792, Method A.

Smolder Resistance - Smolder resistance is a measure of an organic material’s resistance to ignition by a smoldering cigarette. The test procedure has been proposed by the ECTC in the ECTC-TASC 00197.

Ash Content - The ash content of an RECP is that portion of the material that doesn’t burn when exposed to very high temperatures. It is basically a measure of the amount of inert matter in the product and is determined using test procedure ASTM D 586.

Organic Matter - The organic matter in an RECP is that portion which is likely to biodegrade over time. It can be quantified by measuring the amount of the material that burns when exposed to very high temperatures. The standard test procedure is ASTM D 2974.