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This is a repository copy of The influence of frequency normalisation of FWD pavement measurements on backcalculated values of stiffness moduli.

IntroductionThe pavement engineering and related technologies must mainly take into account the influence of multiple sources: extreme temperatures, time-related variable properties of the used materials, snow, rain, the properties of pavement subgrade, traffic load, and maintenance policy. These issues were discussed very systematically in the paper [24] and although its contents refer to the pavements localized in the areas with the cool climate, many of the elements included there can be applied to any type of pavement and varied climatic zones. In any case, these are just some factors that demonstrate the range of the pavement degradation phenomenon and, above all, their stochastic nature. The most complex observations of pavement degradation in time domain are probably ensured by the measurements results analysis of pavement sections in natural conditions. Among them, the most relevant are those that relate to the full-scale accelerated pavement testing [2,20]. The paper [10], on the basis of pavement deflection measurements values tested both in singleload and multilevel-load tests in the range from 17 kN to 70 kN, describes a method of prediction of the rutting depth. There were confirmed a satisfactory compatibility between these quantities for a wide range of road pavement structures. It is worth noting here that it might provide a basis for the development of small-scale accelerated pavement testing approach. The accelerated test series, using the FWD-type unit, were also initiated during the preparation of the report [4]. It was noticed there that the deflection ratio obtained from multi-load level deflections may predict the type and quality of the base/subgrade materials. At the same time, the true hypothesis says that the difference in the multi-load deflections small yield information related to the future performance of pavements. The characteristic feature of construction materials fatigue phenomenon assessment is their randomness [17]. At the basis of the description of cyclic phenomena (fatigue phenomena) lies the theory of cracks initiation. And the most appropriate mathematical description of the fatigue phenomenon are the theories of stochastic processes [17]. The microscopic initiation of cracks in the pavement layers bonded with any binder is subject to considerable uncertainty, both in relation to the speed of the cracks development and its

The thermal properties of pavement layers made of concrete with varying bulk densities are a particularly interesting topic in the context of development road technologies. If a hybrid layer system is used as a starting point, with thin asphalt layers (from 1 cm to 4 cm) laid on top of a foam concrete layer, thermal properties begin to play a crucial role. The main research problem was to create a test method enabling the assessment of the influence of solar heating on the thermal parameters of the building material, especially cement concrete. For this reason, this paper is concerned specifically with the assessment of a new methodology for testing and calculating the value of the thermal diffusivity coefficient of samples made of concrete varying bulk densities. In this case, using the proprietary concept the authors built a solar simulator using a multi-source lighting system. The analysis of the results of laboratory tests and numerical analyses allowed the authors to observe that there is a strong correlation between the bulk density of samples heated and the thermal diffusivity parameter, which appears in the unidirectional heat transfer equation. The strength of this relationship has been expressed with the coefficient of determination and amounts to 99%. The calculated values of the coefficient of thermal diffusivity for samples made of foam concrete range from 0.16×10−6m2s to 0.52×10−6m2s and are lower (from 2.5 to 8 times) than the value determined for samples made of typical cement concrete.

Although the complex modulus is one of the most basic properties used in pavement analysis and design, its accurate measurement for existing pavement layers has always been a challenging task. When samples cut out from the pavement asphalt layers are used for the HMA complex modulus tests, they are performed separately for each layer. This paper describes an original method for determining the complex moduli of individual asphalt layers. The new idea is tested by applying uniaxial loading-unloading cycle tests to the HMA specimens combined of multiple layers. It was observed that changing the thickness ratios in samples' layers, allows obtaining the sets of load and displacement values (F,u), which effectively enlarge the database needed for the back analysis. For now, the conducted analysis presented in the paper focused on numerical modelling of HMA specimens. The simulated numerical testing conditions were based on viscoelastic parameters of asphalt concrete samples whose values were determined in real laboratory tests. In the case of noisy results of laboratory test simulations with a stochastic Gaussian process, by applying multiple cuts and changing sample's height, the determined values of stiffness moduli of the individual layers do not vary from the reference values by more than 10%.