Road surface friction attenuation rate testing service

Road Surface Friction Attenuation Rate Testing Service – Accredited ISO/IEC 17025 Skid Resistance and Pavement Durability Assessment for the Croatian Market

Road surface friction attenuation rate is a critical safety performance parameter that quantifies the progressive loss of skid resistance of pavement surfaces over time due to traffic polishing, wear, weathering, and environmental factors. This property directly influences road safety, braking distances, accident risk, and the overall service life of road infrastructure. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo mora, prometa i infrastrukture, the Državni inspektorat, the Ministarstvo gospodarstva i održivog razvoja, and the Carinska uprava enforce strict quality, safety, and infrastructure standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of friction attenuation rate is essential for road infrastructure approval, pavement management system implementation, supplier qualification, quality control in construction, and import‑export processes of paving materials. Our laboratory offers a comprehensive road surface friction attenuation rate testing service, applying standardized methods such as EN 13036‑4, EN 13036‑5, ISO 13473, ASTM E274, ASTM E303, ASTM F2493, and HRN EN 13036‑4 to measure initial skid resistance, friction decay curves, polishing rates, and equilibrium friction values under controlled traffic simulation and accelerated polishing conditions. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Road Surface Samples and Pavement Materials We Regularly Test

Our laboratory receives a wide variety of pavement materials, road surface specimens, and core samples for friction attenuation rate testing. Typical samples include:

• Asphalt concrete specimens – from road construction, maintenance, and rehabilitation projects, including wearing course and binder course materials.
• Roller‑compacted and cast‑in‑place concrete specimens – for highway, airport, and industrial pavements.
• Paving blocks and stone sett specimens – for pedestrian areas, cycle paths, and urban streets.
• Surface treatments and seal coats – chip seals, slurry seals, micro‑surfacing, and thin overlays.
• Core samples extracted from field pavements – for condition assessment and friction decay monitoring.
• Prototype and new aggregate blends – submitted by manufacturers for validation of friction performance before series production.
• Polished stone and aggregate specimens – for evaluating the polishing resistance of individual aggregate types.

Initial Skid Resistance Measurement – Baseline Friction Assessment

The initial skid resistance is the starting point for evaluating the friction attenuation rate. Our tests measure the skid resistance of the new pavement surface using standardized friction testers, providing a baseline for the subsequent polishing and attenuation tests. Our procedures follow international standards and the requirements of the Croatian road infrastructure and construction sectors.

• Skid resistance measurement – pendulum method (EN 13036‑4 / HRN EN 13036‑4 / NTC 5700 – for the initial wet friction) – we use a pendulum friction tester (British Pendulum Tester) to measure the initial skid resistance of the pavement surface under wet conditions. The test is performed on the surface of the specimen (or on the field pavement) using a standard rubber slider. The pendulum test value (PTV) or the British Pendulum Number (BPN) is measured. We report the initial PTV/BPN and the test conditions (surface temperature, wetting, and slider type).
• Skid resistance measurement – locked‑wheel method (ASTM E274 / NTC 5701 – for the initial friction coefficient) – we use a locked‑wheel skid trailer (or a portable friction tester) to measure the friction coefficient (μ) of the pavement surface at a specified speed (e.g., 50 km/h, 80 km/h). The test is performed under wet conditions. We report the initial friction coefficient (μ) and the test speed.
• Skid resistance measurement – side‑force method (EN 13036‑5 / NTC 5702 – for the initial side‑force friction) – we use a side‑force friction tester (e.g., a GripTester or a SCRIM) to measure the side‑force friction coefficient (SFCO) of the pavement surface. The test is performed at a specified speed and under wet conditions. We report the initial SFCO and the test speed.
• Macrotexture and microtexture measurement (ISO 13473 / NTC 5703 – for the initial surface texture) – we measure the macrotexture (mean texture depth, MTD) using the sand patch method (EN 13036‑1) and the microtexture using a surface roughness tester. The texture measurements are correlated with the initial skid resistance. We report the MTD (in mm) and the microtexture parameters (Ra, Rz).
• Friction and texture correlation (NTC 5704 – for the baseline performance) – we correlate the measured initial skid resistance (PTV, μ) with the macrotexture (MTD) and microtexture (Ra) to establish the baseline relationship between the texture and the friction. We report the correlation and the baseline performance rating.

Accelerated Polishing Testing – Simulating the Traffic Polishing Effect

Accelerated polishing testing simulates the progressive polishing of the pavement surface by traffic, using laboratory‑based polishing machines. Our tests measure the friction decay curve (the friction as a function of the polishing time or the number of polishing cycles), providing essential data for the prediction of the long‑term skid resistance.

• Accelerated polishing test – Wehner‑Schulze method (EN 13036‑5 / NTC 5710 – for the polishing resistance of aggregates) – we mount a specimen of the pavement material (or a sample of the aggregate) in a Wehner‑Schulze polishing machine. The specimen is polished using a rotating wheel and a specified abrasive (e.g., emery paper, 60‑grit) under a controlled load and water spray. The specimen is polished for a specified number of cycles (e.g., 100, 300, 1000 cycles), and the skid resistance (PTV) is measured at each interval. The friction decay curve (PTV vs. polishing cycles) is plotted. We report the initial PTV, the PTV after each polishing interval, the polishing rate (the slope of the decay curve), and the equilibrium PTV (the friction at the end of the test).
• Accelerated polishing test – aggregate polishing machine (NTC 5711 – for the polishing resistance of coarse aggregates) – we use an aggregate polishing machine (APM) to polish a sample of the coarse aggregate (the stone) and measure the polished stone value (PSV). The PSV is a measure of the polishing resistance of the aggregate. We report the PSV and the polishing resistance rating.
• Accelerated polishing test – British wheel method (NTC 5712 – for the bituminous mixtures) – we use a British wheel polishing machine to polish a specimen of the asphalt mixture. The friction (PTV) is measured at intervals. We report the friction decay curve and the equilibrium PTV.
• Accelerated polishing test at different temperatures (NTC 5713 – for the thermal effect) – we perform the accelerated polishing test at different temperatures (e.g., 20 °C, 40 °C, 60 °C) to evaluate the effect of temperature on the polishing rate and the equilibrium friction. We report the friction decay curve at each temperature.
• Accelerated polishing test with different abrasives (NTC 5714 – for the traffic simulation) – we use different abrasives (e.g., emery paper, silica sand, or a simulated traffic abrasive) to simulate the effect of different traffic conditions (e.g., heavy traffic, light traffic, or studded tires). We report the friction decay curve for each abrasive.

Friction Attenuation Rate Calculation – Quantifying the Performance Loss

The friction attenuation rate is the rate at which the skid resistance decreases with the traffic load (or the polishing time). Our tests calculate the attenuation rate (the loss of PTV per 100, 1000, or 10,000 polishing cycles) and the equilibrium friction value (the long‑term friction after extensive polishing).

• Friction attenuation rate determination (NTC 5720 – for the performance loss quantification) – we calculate the friction attenuation rate (AR) from the friction decay curve, using the formula: AR = (PTV_initial – PTV_final) / (Number of polishing cycles). We also calculate the polishing rate (the slope of the linear portion of the decay curve). We report the AR (in PTV per 100 cycles or per 1000 cycles) and the polishing rate (in PTV/cycle).
• Equilibrium friction value determination (NTC 5721 – for the long‑term skid resistance) – we determine the equilibrium friction value (PTV_eq) from the friction decay curve, which is the friction value at which the friction no longer decreases significantly with further polishing. The equilibrium friction is a measure of the long‑term skid resistance. We report the PTV_eq and the number of cycles to reach the equilibrium.
• Friction decay curve fitting (NTC 5722 – for the predictive modeling) – we fit the friction decay curve to a mathematical model (e.g., a power law or an exponential model) to predict the friction at any future polishing stage. The model parameters (the decay rate and the equilibrium value) are reported. We report the model equation, the model parameters, and the goodness‑of‑fit.
• Traffic load and life prediction (NTC 5723 – for the pavement life assessment) – we correlate the friction attenuation rate with the traffic load (the number of vehicles) to predict the service life of the pavement (the time to reach the minimum acceptable friction level). The prediction is based on a traffic‑wear model. We report the predicted service life (in years) and the traffic capacity (in vehicles per day).
• Comparison with the specified friction limits (NTC 5724 – for the compliance with the regulations) – we compare the measured initial friction and the equilibrium friction with the minimum skid resistance requirements specified in the Croatian road design standards (based on the HRN EN standards and the Ministarstvo mora, prometa i infrastrukture regulations). We report the compliance and the pass/fail status.

Macrotexture and Microtexture Evolution – Evaluating the Texture Changes

The friction attenuation is closely related to the changes in the macrotexture and microtexture of the pavement surface during polishing. Our tests measure the texture evolution (the changes in the MTD and the microtexture parameters) during the accelerated polishing test, providing a comprehensive understanding of the friction loss mechanism.

• Macrotexture measurement during polishing (NTC 5730 – for the MTD evolution) – we measure the mean texture depth (MTD) of the pavement specimen at intervals during the accelerated polishing test (using the sand patch method or a laser profilometer). The MTD is plotted against the polishing cycles. We report the MTD evolution curve and the change in the MTD (in mm).
• Microtexture measurement during polishing (NTC 5731 – for the microtexture evolution) – we measure the surface roughness (Ra, Rz) of the pavement specimen at intervals during the polishing test (using a contact or an optical profilometer). The microtexture parameters are plotted against the polishing cycles. We report the microtexture evolution curve and the change in the roughness.
• Texture and friction correlation (NTC 5732 – for the texture‑friction relationship) – we correlate the measured texture parameters (MTD, Ra) with the measured skid resistance (PTV) at each polishing interval. The correlation is used to understand the relative contributions of the macrotexture and the microtexture to the overall friction. We report the correlation and the texture‑friction model.
• Polishing and texture degradation analysis (NTC 5733 – for the wear mechanism) – we use scanning electron microscopy (SEM) to examine the surface of the pavement specimen before and after the polishing test, to identify the wear mechanism (e.g., the polishing of the aggregate, the removal of the binder, or the loss of the macrotexture). We report the SEM images and the wear mechanism.
• Aggregate polishing and binder loss assessment (NTC 5734 – for the material‑specific degradation) – we evaluate the contribution of the aggregate polishing and the binder loss to the overall friction attenuation. The aggregate polishing is assessed by the PSV, and the binder loss is assessed by the change in the macrotexture. We report the aggregate polishing index and the binder loss index.

Environmental and Aging Effects – Evaluating the Long‑Term Friction Stability

The friction attenuation rate can be influenced by environmental factors such as temperature, moisture, and UV radiation. Our environmental and aging tests simulate these conditions and evaluate their effect on the friction attenuation rate, providing a more realistic prediction of the pavement performance in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging and its effect on friction attenuation (ASTM D573 / ISO 188 / NTC 5740 – for the heat‑aged pavements) – we age the pavement specimen in an oven at a specified temperature (e.g., 60 °C, 80 °C) for a specified duration (e.g., 7, 14, or 28 days) and then perform the accelerated polishing test. The effect of the thermal aging on the friction decay curve is evaluated. We report the friction decay curve and the attenuation rate after aging.
• UV and weathering effect (ASTM G154 / NTC 5741 – for the outdoor‑exposed pavements) – we expose the pavement specimen to UV radiation (UVA‑340) and condensation cycles for a specified duration (e.g., 500 hours) and then perform the accelerated polishing test. The effect of the UV exposure on the friction decay curve is reported. We report the friction decay curve and the attenuation rate after UV exposure.
• Water immersion and moisture effect (ASTM D570 / NTC 5742 – for the moisture‑exposed pavements) – we immerse the pavement specimen in water (or a salt solution) for a specified duration (e.g., 7 days) and then perform the accelerated polishing test. The effect of the moisture on the friction decay curve is reported. We report the friction decay curve and the attenuation rate after the moisture exposure.
• Freeze‑thaw effect (NTC 5743 – for the cold‑climate applications) – we subject the pavement specimen to repeated freeze‑thaw cycles (e.g., -20 °C to +20 °C) and then perform the accelerated polishing test. The effect of the freeze‑thaw cycles on the friction decay curve is reported. We report the friction decay curve and the attenuation rate after the freeze‑thaw cycles.
• Chemical exposure effect (NTC 5744 – for the chemically exposed pavements) – we immerse the pavement specimen in various chemicals (e.g., de‑icing salts, oils, or fuels) for a specified duration and then perform the accelerated polishing test. The effect of the chemical exposure on the friction decay curve is reported. We report the friction decay curve and the attenuation rate after the chemical exposure.

Complementary Tests – Aggregate Properties, Binder Properties, and Mix Design for Friction Correlation

To fully understand the friction attenuation performance and to correlate it with the material properties, we perform complementary tests, including aggregate testing, binder testing, and mix design analysis.

• Aggregate polishing resistance (PSV – NTC 5750 – for the aggregate quality) – we measure the polished stone value (PSV) of the coarse aggregate using the aggregate polishing machine. The PSV is a direct measure of the polishing resistance. We report the PSV and the aggregate quality rating.
• Aggregate abrasion and fragmentation (ASTM C131 / NTC 5751 – for the aggregate durability) – we measure the Los Angeles abrasion loss (in %) of the coarse aggregate. The abrasion loss is correlated with the resistance to wear and the texture retention. We report the L.A. abrasion loss and the aggregate durability rating.
• Binder viscosity and stiffness (ASTM D2171 / NTC 5752 – for the binder performance) – we measure the dynamic viscosity (in Pa·s) and the stiffness (in MPa) of the asphalt binder. The binder properties are correlated with the resistance to polishing and the binder loss. We report the viscosity and the stiffness.
• Mix design and gradation analysis (NTC 5753 – for the aggregate gradation) – we perform a sieve analysis of the aggregate blend and determine the gradation curve. The gradation is correlated with the macrotexture and the friction attenuation rate. We report the gradation curve and the mix design parameters.
• Air void content and porosity (ASTM D3203 / NTC 5754 – for the mix compactness) – we measure the air void content (in %) and the porosity of the pavement mix. The air void content is correlated with the durability and the resistance to the binder loss. We report the air void content and the porosity.

Test Report and Recognition in the Croatian Road Infrastructure and Construction Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (friction testers, polishing machines, texture profilers, and analytical instruments) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the pavement sample (project name, mix type, aggregate source, and binder type).
• Detailed description of the test methods applied (EN/ISO/ASTM/HRN EN/NTC standards, test conditions, and polishing parameters).
• Numerical results: initial skid resistance (PTV/BPN), equilibrium skid resistance (PTV_eq), friction attenuation rate (PTV per 100 cycles), polishing rate (PTV/cycle), macrotexture (MTD, mm), microtexture (Ra, μm), PSV, and aggregate abrasion loss (%).
• Graphical data: friction decay curves, texture evolution curves, and texture‑friction correlation plots.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (EN 13036‑4, EN 13036‑5, HRN EN 13036‑4, and the requirements of the HZN, Ministarstvo mora, prometa i infrastrukture, and Državni inspektorat).
• Photographs and micrographs (SEM) of the pavement surface before and after the polishing test, showing the texture degradation and the wear pattern.
• Recommendations for the improvement of the friction performance, the selection of the polishing‑resistant aggregates, and the quality control measures to achieve the required skid resistance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo mora, prometa i infrastrukture for the approval of pavement materials and the design of safe road surfaces, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of paving materials and aggregates. Additionally, we offer consulting services for the selection of friction‑resistant pavement materials, the design of durable road surfaces, and the implementation of pavement management and safety programs, contributing to the safety, durability, and sustainability of road infrastructure in the diverse and growing Croatian market, from the coastal highways to the continental and mountain roads.