ASTM F3539 section denoted by this font

The Mark IIIB tribometer measures transitional coefficient of friction (TCOF). TCOF is the point of transition from static COF (SCOF) at slip initiation to dynamic COF (DCOF) when slipping at a constant velocity. 

This procedure is focused on tribometer usage compliant with ASTM F2508-2023 Practice for Validation of Walkway Tribometry Using Research-based Reference Materials, utilizing an 11-groove Vibram® styrene-butadiene rubber (SBR) slider of Shore 38D hardness, in conjunction with a testing contaminant liquid comprising 0.05% sodium lauryl sulfate (SLS) in distilled water. This same SLS solution is also used for cleaning F2508 reference materials and for cleaning the slider if needed.

The Mark IIIB tribometer has previously been Validated to the 2011-2016 versions of ASTM F2508, utilizing a 15-groove Neolite® SBR slider of Shore 92A hardness, in conjunction with a testing contaminant liquid of distilled water for reference materials Tile B, C, and D, and 0.04% Triton® surfactant in distilled water for Tile A. Photos in this procedure show both Vibram® and Neolite® sliders.

In walking surface field testing, the highest relevance to ASTM F2508 Validation will be obtained on nominally planar surfaces with visibly consistent surface texture and without protruding asperities. It is advised to test on the smoothest, flattest locations in the relevant area(s) of interest.

A1.12.1

Test results on walking surfaces with topographical elevation changes of >1.5mm (0.06") within the slider's contact trajectory may be less reliable, due to the reduced points of contact between the slider and surface. If testing across tile grout joints, test at a 10-30 degree bias angle, and if there are elevation differences between tiles across the area of testing, test from the higher tile to the lower tile. Test surfaces should be stable and fixed in location; textiles (mats) and particulate contaminants (sand, broken glass, peanut shells) are inappropriate for testing.

A1.12.2

If pedestrian flow on a walking surface is primarily in one or opposing directions, it is advisable to prioritize testing in those directions.

A1.12.3

Testing on downslopes can be performed as long as the strut is in contact with the strut stop prior to triggering. The mast incline angle (when oriented downslope) must be at least as great as the surface slope. Utilize the slope correction chart at the end of this manual. Choose the row corresponding to the desired level-surface friction goal from the left column of the slope correction chart, then go right to the subject surface's slope to see the measurement value to be obtained. Maximum test slope is 16 degrees.

A1.7.2, A1.8.8, A1.12.5

If it is decided to clean a walkway before testing, consider utilizing a neutral cleaner (e.g., Bona® Hard Surface Floor Cleaner), and consider a rinse with water after using a cleaner.

A1.12.10

SLIDER PREP: Inspect the slider backing plate to ensure it is not bent by sighting down each edge. Ensure that the slider is dry before resurfacing, and if SLS contaminant solution has been used rinse it off with water before drying the slider. After this drying, droplets of water may remain within the slider grooves as long as they do not cause wetting of the sandpaper during sanding. Place 1/3 of the 180grit sandpaper sheet (A1.2.7) on the aluminum sanding plate (A1.2.6). Holding slider as shown, press down with moderate force and pull the slider towards you for 2 strokes. Inspect slider - there should be a uniform appearance with no voids larger than 1.5mm (0.06") across the largest dimension. If the slider contact surface has scratches or a non-uniform appearance, brush off the sandpaper with a synthetic-bristle paintbrush then continue sanding as described above. If during sanding you observe rubber crumbs on the sandpaper and there is less sanding drag, brush off sandpaper every 6 strokes. It is recommended that a dust mask be worn when conducting extended slider sanding. Once sanding is complete, brush off the slider contact surface thoroughly with the synthetic bristle brush, or blow off with dry oil-free compressed air. Once prepared, avoid touching the slider contact surface.

A1.11.2, A1.12.7

If slider has unwanted residues, dip clean scrub brush in SLS solution (A1.2.8) and scrub for 10s, rinse thoroughly with water, dry slider (if necessary) with a clean paper towel or dry oil-free compressed air.

A1.11.1, A1.12.6

Slider surfaces with deep scratches aligned with the grooving may be used if the scratches are no wider or deeper than 1mm (0.04") and no longer than 25mm (1"). Scratches that are not aligned with the grooving may be no more than 0.25mm (0.01") wide and deep; it is better to sand such grooves out. After resurfacing (A1.11.2), the uniform appearance of the surface should extend to the corners of the slider. Poor sanding technique may result in wearing away the corners of the slider, and this is indicative of the slider not being sanded flat - which will affect measurements. If the corners are worn such that a 5mm (.2") long area isn't resurfaced (because it has been worn such that it doesn't contact the sandpaper), careful and repetitious flat sanding on the 180 grit sandpaper will address the problem. Always use the aluminum sanding plate (A1.2.6). Discard the slider if the overall thickness (including the mounting clip) is 6.5mm (0.26") or less.

A1.12.4

Ensure the rubber feet have equal numbers of shim washers and that the screws are snug. Lift the slider pivot plate and inspect the magnetic surface, ensure that no debris is present. Install the slider, it only fits one way. Set the mast angle to 0.0 and place the tribometer on the test surface. Using the aluminum “go/no-go” thickness gauge supplied with the tribometer (part ST27), check the gap between the bottom of the slider and the test surface. This is done by seeing that the thinner end of the gauge can be slipped between the slider and the surface while the thicker end of the gauge will not fit in the same space. If the thinner end of the gauge does not fit, the gap is too small and the three rubber feet on the bottom of the tribometer must each be shimmed using an equal amount of shim washers. If the thicker end of the gauge will fit then the gap is too large and it must be reduced by removing an equal number of shim washers from under each rubber foot. After adjustment, ensure that screws for rubber feet are snug. Do not overtighten. Repositioning/reorientation of the tribometer on non-planar test surfaces will necessitate rechecking of the slider height.

NOTE: When removing the slider from the magnetic surface, first support the strut so that it is not resting against the strut stop. Though the strut stop is special high-strength 7075-T6 aluminum, it can be bent, and if bent, measurements may be affected.

For wet testing, using the tab at the front of the slider, lift the slider and strut and apply SLS solution (A1.5) as necessary to ensure that an unbroken "puddle" of solution is under the entire slider surface and is also ~1.5 inches in front of the slider when at rest. A "puddle" is mirror-reflective on the top surface. Do not unnecessarily flood the tile beyond what is necessary to get a puddle as described. The presence of bubbles on the puddle surface is fine.

A1.11.4, A1.12.11

Lift the top handle to cock the tribometer. Ensure that the mast lock knob is tight before each triggering. If wet testing apply contaminant (A1.11.4).

Ensure that the slider rear edge is contacting the tile. While holding the tribometer steady, trigger the tribometer and hold the trigger paddle against the stop until carriage movement has stopped; do not touch the top handle or other carriage parts when triggering. A test observation has occurred when the slider rapidly slips all the way to its limit of travel. The slider should not creep or stutter during a slip. The slider limits of travel have been reached when the top handle impacts the rubber bumper. If a slip does not occur and the slider does not visibly slide at all upon contact, tilt the mast down by 0.02-0.03, reapplying contaminant as needed (for wet testing) to maintain an adequate puddle of liquid, and retest, continuing until slider movement occurs. Once slider movement begins, tilt the mast down in 0.01 increments until a full-stroke, rapid slip occurs. The scale value at which the full-stroke slip occurred is the test observation. To obtain the next observation, tilt the mast up at least 0.02, verify an adequate contaminant puddle (for wet testing), and trigger. There should be at least 1 no-slip triggering of the tribometer prior to a slip. If the first triggering after tilting the mast up results in a slip, do not record the measurement value; tilt the mast up another 0.02 and retry.

A1.2.9

A test determination is done without repositioning the tribometer and it is the average of the first 3 sequential test observations (A1.2.9) that are within 0.03 of each other. A test result is comprised of 3 test determinations; where feasible and relevant a test result should be comprised of 1 test determination in each of 3 directions at least 45 degrees apart. The test result is the average of the 3 test determinations, i.e., a test result is obtained from a minimum of 9 test observations.

A1.7.1, A1.11.7, A1.12

For dry testing, there is no "break-in" procedure after slider resurfacing. Before conducting wet testing, install the slider and place the tribometer on the test surface. Set the mast angle to 0.15 - 0.20 above the expected TCOF value of the surface; this should result in full-stroke slips. Saturate the test surface with contaminant. For ASTM F2508 Tile E, set to 0.25, for Tile F, set to 0.45, and for Tile G set to 0.65. Operate the tribometer (A1.2.9) to obtain 2 wet slips.

A1.11.3, A1.12.9

The slider should be resurfaced (A1.11.2) before each test result is obtained under dry conditions. Under wet conditions, up to 3 test results may be obtained without slider resurfacing provided that the sample surface topography is nominally consistent (e.g., a nominally planar tile surface).

A1.12.8

It is advisable to conduct user verification before a new session of testing if the tribometer has been transported beforehand. To establish a baseline for user verification, Slip-Test recommends the user obtain a test determination in one orientation on their own ASTM F2508-2023 reference materials Tile F and Tile G in normal indoor climate controlled conditions as soon as feasible upon completion of an ASTM F2508-2023 Validation, and record the values. The direction of testing on each tile should be marked on the side of the tile. Before field testing, Slip-Test recommends user verification, in which a test determination is obtained in the same orientation on either Tile F or Tile G, and the values recorded for comparison to the post-Validation baseline. The field-obtained value for Tile F should be between 0.25-0.39 and for Tile G between 0.47-0.60, assuming moderate ambient conditions.

A1.8.6

User verification surfaces are the ASTM F2508-2023 adjunct reference materials, Tiles F and G. These can be purchased from ASTM, www.astm.org. For 12 inch tiles, order Adjunct # ADJF2508DAT and ADJF2508CRO; for 6 inch tiles, order Adjunct # ADJF2508DAT6 and ADJF2508CRO6. When not in use, store adjunct tiles with top surfaces protected from contact with abrasive objects. Resurface slider before user verification. Clean tiles before user verification, wipe with paper towel wetted with SLS solution. Position tribometer on tile with testing direction aligned with baseline marking. If on 12" tile, center the tribometer. If on 6" tile position rubber feet as shown, use tile spacer under rear rubber foot, white spacer for Tile F (Slip-Test #ST62), and black spacer for Tiles E & G (Slip-Test #ST63). Spacer can be secured with provided screw as shown, or it can simply rest under the rubber foot. Orient tribometer over 6" tile as shown. Using SLS contaminant, obtain one test determination on the tile.

A1.9.2, A1.9.3, A1.9.4, A1.9.5, A1.9.6, A1.10, A1.10.3, A1.10.3.1, A1.10.3.2, A1.11, A1.11.5, A1.11.6, A1.11.8

After wet testing, dry tribometer with a towel - do not put wet towels or an unsealed container of liquid in a closed Pelican case with the tribometer. If strut pivots begin to squeak, apply a small amount of WD-40 to the 4 pivot points, rotate the strut and slider pivots to work the WD-40 in, and then thoroughly blow the excess WD-40 out using compressed air. Do not lubricate the stainless steel main shafts; if surface corrosion appears on them, send the tribometer to Slip-Test for service. The trigger axle and quick-release knob may be lightly lubricated with WD-40 if squeaky. Always clean off excess lubricant so it doesn't migrate to the surface being tested. Always ensure proper orientation of the tribometer in the case. Set mast to 1.0, tighten the knob, trigger the carriage, and retain the slider pivot as with an elastic band as shown in the image.

A1.8.4

Slip-Test recommends the unit be sent in yearly for maintenance, unless it has been used for less than 50 test observations in a year and is stored in indoor climate-controlled conditions.

A1.8.5

All procedures described in this manual are compliant with ASTM F3539. For further information or clarification, please contact Slip-Test or consult ASTM F3539.