Calculate asphalt temperature at depth and the modulus adjustment factor using the BELLS model.
The calculator uses the BELLS empirical models to predict the temperature at a specific depth (Td) within an asphalt layer.
Given routine testing (BELLS3) with an IR surface temperature of 35°C, a previous day average air temp of 25°C, at a depth of 50 mm, measured at 2:00 PM (14.0 hours). Using a default slope of -0.021 and reference temp of 21°C:
The Pavement Temperature Calculator is a specialized engineering tool designed for pavement engineers, technicians, and researchers to accurately predict the temperature within an asphalt layer at a specific depth. It also calculates the Asphalt Temperature Adjustment Factor (ATAF), which is crucial for standardizing pavement modulus data. The calculator is based on the well-established BELLS empirical models (BELLS2 and BELLS3), which were developed as part of the Strategic Highway Research Program (SHRP) and the Long-Term Pavement Performance (LTPP) program. These models are the industry standard for estimating in-situ pavement temperatures from easily obtainable surface measurements.
The primary benefit of the Pavement Temperature Calculator is its ability to normalize pavement structural data. The stiffness (or modulus) of asphalt concrete is highly dependent on its temperature—it is stiffer when cold and softer when hot. When conducting tests like the Falling Weight Deflectometer (FWD) to assess a pavement's structural capacity, the measured modulus will vary significantly throughout the day. To make meaningful comparisons of data collected at different times and temperatures, it must be adjusted to a standard reference temperature. This is where the ATAF becomes indispensable. Our Pavement Temperature Calculator computes this factor, allowing for reliable pavement analysis and management.
The tool provides two distinct models. The BELLS2 model is intended for use under LTPP data collection protocols, where the pavement surface is shaded for five to six minutes before the IR temperature is taken. This shading causes some surface cooling. The BELLS3 model, however, is calibrated for more routine testing scenarios where shading is minimal (one minute or less), making it more suitable for typical FWD operations. The formulas incorporate variables for surface temperature, previous day's air temperature, depth, and time of day to capture the complex thermal dynamics of the pavement structure. For more detailed information on the LTPP program, the Federal Highway Administration (FHWA) provides extensive resources. The fundamental principles of asphalt properties are also well-documented on platforms like Wikipedia's article on Asphalt Concrete.
Ultimately, the Pavement Temperature Calculator serves as an essential utility for anyone involved in pavement evaluation. By removing the guesswork from temperature correction, it enhances the accuracy and consistency of structural analysis. This leads to better decision-making in pavement rehabilitation, maintenance, and overall asset management. Using the Pavement Temperature Calculator ensures that your pavement data is comparable and reliable, regardless of the ambient conditions during testing.
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BELLS2 is for LTPP testing where the pavement is shaded for 5-6 minutes before taking an IR temperature reading, causing cooling. BELLS3 is for routine testing (like FWD) with minimal shading (less than 1 minute), which results in a warmer surface temperature reading. Choose the model that matches your field procedure.
Asphalt is a viscoelastic material, meaning its stiffness (modulus) changes significantly with temperature. To compare pavement structural capacity measured on different days or times, the modulus values must be adjusted to a single, standard reference temperature. The ATAF allows for this normalization.
The default value of -0.021 log(MPa)/°C is a widely accepted average based on extensive LTPP research. While using a mix-specific value from laboratory testing is always more accurate, the default value provides a reasonable estimate for most standard asphalt mixes.