The Department of General Services (DGS) conducts annual GMAX testing on synthetic turf fields in all eight wards to assess where maintenance is required. GMAX testing is a surface hardness impact test and is the most commonly used standard set by the American Society for Testing and Materials (ASTM) International which established a GMAX value of 200 for the maximum allowable limit for safety.
GMAX is a stringent test method which scores 10 high-use areas on each field. A single score of more than 200 at any of the District’s synthetic field locations results in temporary, short-term closure of the field to carry out necessary maintenance. Remediation of fields can range from providing minor infill top-off (2-3 days completion) to providing sectional replacements (2-3 weeks completion).DGS has the field turf protocols developed by the District’s Interagency Working Group on Artificial Turf and Playgrounds. DGS has followed the field turf protocols developed by the District’s Interagency Working Group on Artificial Turf and Playgrounds.
GMAX Test Reports
GMAX testing measures the shock absorption of synthetic turf. The results indicate how much shock an athlete absorbs when impacting the turf. As the GMAX value increases, the field becomes harder, and is less likely to absorb shock. These measurements are a fundamental tool alerting you to critical compaction issues and the possible need of additional infill -- keeping your field safe and limiting injuries.
GMAX values increase with high usage, compaction, and infill segregation. These values can be reduced by grooming or top dressing your field. For synthetic surfaces, American Society for Testing and Materials (ASTM), specifies that the reported GMAX value for all test points on a field should be less than 200 GMAX (as measured in accordance with ASTM procedures F355-A and F1936). If the standard isn’t met, the field is considered in need of maintenance and remediation is required. The shock tests, also called “drops,” are done 3 times in 10 separate locations. The results are recorded in the report.
Understanding the Report
The report provides general information on the location site name, address, date, time, weather, and average test score of all 10 test locations. The individual drops and average scores are used to inform maintenance activities. The report includes a test matrix that depicts the results each of the 3 drops at each of the 10 locations totaling 30 drops. It also records the depth of the field material at each test location. Any one drop that is recorded above ASTM standards will be highlighted and the field is considered in need of maintenance. Finally, there are area images and descriptions of all field test locations.