Rotational Penetrometer

mobile firmness and stability testing
using an Instrumented Surface Indenter (ISI)

Rotational Penetrometer

mobile firmness and stability testing using an Instrumented Surface Indentor (ISI)

rotational penetrometer (RP)

Beneficial Designs offers surface testing both in the lab and out in the field. The Rotational Penetrometer (RP) allows a single technician to perform mobile surface testing anywhere, providing accurate firmness and stability data of an original surface. Please contact Beneficial Designs today to schedule a test.

The Rotational Penetrometer can also be purchased for unlimited use. For more information, purchasing details, and instructional videos, please click the buttons below.

the need

The US Access Board requires ASTM F1951 testing to measure the objective firmness and stability of playground surfaces. Although this test procedure is the gold standard for laboratory measurements of surface firmness and stability, there are some limitations. First, the ASTM F1951 test procedure must be performed in a lab setting. As a result, there is no way to confirm that a surface installed in the field meets the requirements. Installation variation, differences between manufacturing facilities, weather, and improper installation are some of the factors that may affect surfaces in the field. For this reason, an objective method of testing surface firmness and stability is needed for the field.

portable solution

The Rotational Penetrometer (RP) is an instrumented surface indenter (ISI) that meets the need for a mobile surface testing method. This portable and lightweight device measures objective firmness and stability values by measuring the indentation of a front wheelchair caster wheel into any surface. In combination with the ASTM F1951 laboratory test, the RP enables the verification and validation of the accessibility of the surface installed in the field. This will allow for ongoing testing of a surface and monitoring of the effects of long-term use and weather.

tested & proven

The results of ASTM F1951 surface testing correlate with the results of the Rotational Penetrometer (RP) surface testing on playground surfaces as shown in the peer-reviewed article, “Use of Two Test methods to Ensure Accurate Surface Firmness and Stability Measurements for Accessibility.” Data was collected from ASTM F1951 and Rotational Penetrometer testing performed over the same surface, using a full spectrum of 63 different indoor and outdoor surfaces over a period of 13 years.

Testing showed a strong correlation (R²=0.9006) between the sum of the RP firmness and stability ratings and the sum of the ASTM F1951 straight propulsion and turning results. The study demonstrates that the combination of firmness and stability ratings measured using the Rotational Penetrometer could be used to determine an objective level of firmness and stability required for an accessible surface.

Graph showing sum of ASTM F1951 straight and turning ration on x-axis compared to sum of ISI firmness and stability rating, showing strong correlation.

The figure above shows the correlation of the sum of the ISI (or RP) firmness and stability values versus the sum of the ASTM F1951 straight propulsion and turning results. The vertical line denotes surfaces passing ASTM F1951 straight propulsion and turning for results ≤ 2.0 on the left, for surface versus ramp work ratios less than 2. The horizontal dotted lines denote ISI surface ratings of firm and stable below  ≤ 2.032 cm (0.8 in.) of penetration and moderately firm and stable below  ≤ 3.810 cm (1.5 in.) of penetration.

The surface type acronyms to the right represent the following surfaces:
EWF: Engineered Wood Fibre
LFR: Loose Fill Rubber
NS: Natural Surface
PSM: Paved Surface Material
RS: Solid Rubber

firmness AND stability

The results of the study showed that it is the combination of firmness and stability that creates an accessible surface. The report states, “Lack of stability is often a greater barrier to accessibility than lack of firmness; hence, exceptional stability may compensate for a barely passing or even non-passing firmness value.” A lower ISI firmness and stability sum, including one exceptional value and another low value, may be more accessible than barely passing the firmness and stability values.

RP surface testing

The National Center on Accessibility has used the RP to conduct longitudinal studies of various trail and playground surfacing materials to determine how well those surfaces maintain firmness and stability that meets federal requirements. This means that an agency can now implement a maintenance schedule using the BD Series 100 RP to verify that required firmness and stability is maintained.

For more information on ISI and ASTM F1951 testing, please visit the following sites:

Click: Use of two test methods to ensure accurate surface firmness and stability measurements for accessibility

Click: U.S. Access Board – Accessible Exterior Surfaces Technical Report

convenient mobility

Can’t take your trail, playground, or flooring to the surface testing lab? The only device of its kind, the RP is a reliable, objective, portable instrument for testing all types of indoor and outdoor surfaces on-location.

The Rotational Penetrometer 100 Series is easily transportable, whether by plane, automobile, or even a trail assessment HETAP cart! The fully assembled device weighs only 18 pounds and stands at 28.25 inches tall. When collapsed, the RP may be securely stored in a special carrying case, which measures 26 x 18 x 8 inches. Contrast this with the cost of shipping a crate holding an entire ASTM F1951 instrumented wheelchair, and you will see why many are choosing the RP to perform surface testing.

long-term durability

Constructed of stainless steel and aluminum, along with surface reference plates made of finished marine grade plywood, the RP is designed for durability and long-term outdoor use. The indenter assembly uses a precision spring that presses a caster wheel, as the indenter, into the surface being tested. A precision caliper measures the amount of indentation into the surface. The fully-assembled device can be transported without a carrying case, as is typical for HETAP trail assessments.

0.001 accuracy

reliable accuracy

Research has shown that the Rotational Penetrometer produces repeatable and reproducible results that correlate with the amount of work required to propel a wheelchair across a surface (as measured by ASTM F1951) and the amount of physiological energy required by persons with and without disabilities attempting to negotiate a surface. The RP provides objective and highly accurate firmness and stability readings without the performance of off-site ASTM F1951 testing.

objective surface measurements

The RP provides objective surface measurements which allow individuals to know the exact quality of a surface. Without objectivity, surface descriptions such as firm or soft are empty and meaningless.

Objective surface measurements also provide builders, architects, and site planners with specifications to design and verify they are creating firm and stable, and therefore accessible indoor and outdoor surfaces.

objective firmness

Objective surface firmness measurements are obtained by pressing an indenter into a surface with a precision spring while measuring the exact amount of vertical penetration of the indenter into the surface.

objective stability

Objective surface stability measurements are also obtained by rotating the indenter back and forth on the surface, measuring the total amount of vertical displacement of the indenter after rotation.

measure firmness

While there may be many ways to subjectively test the firmness of a surface, an objective measurement is essential. An objective firmness value of a given surface may be determined by pushing an instrumented surface indenter into the surface with a calibrated spring. Then the amount of indentation into the surface, shown by the vertical displacement of the indenter into the surface can be measured.

measure stability

As defined, stability is the degree to which the surface resists change from a contaminate or force and returns to its original condition. A stable surface will resist change and will not be permanently affected by normal trail use and weather. An unstable surface will shift and change shape when used normally, such as when a foot or tire changes direction or pivots while in contact with the surface. This is what happens when a wheelchair user or an ambulatory person turns or changes direction.

Using an Instrumented Surface Indenter, an objective stability measurement can be obtained by first applying a specified force vertically into the surface, then pivoting the indenter on the surface. The vertical displacement created by the pivoting into the surface can then be measured.