The backcalculation procedure applied to a mechanical characterization of the road pavement is usually limited to an identification of the elastic modulus of each layer only. The remaining parameters of the model are usually set as known, while performing an inverse analysis. Among assumed parameters are thicknesses of the model layers and frequently considered as constants on a homogeneous section of the road. This is an obvious simplification, because sections in general are inhomogeneous, i.e. the thickness of each layer changes slightly along each road section. Thus the precise and possibly nondestructive estimation of the layers thicknesses is very important and crucial in the inverse procedure. Here, a hybrid form of the optimization algorithm, where the condition of a constant thickness does not need to be fulfilled is described. Further on, the objective function is formed as a discrepancy between reference and computed deflection derivative instead of a deflection curve. In consequence, the values of backcalculated parameters are several per cent more precise compared to a standard procedure. Whenever the thickness of the asphalt layer of the pavement structure cannot be assumed a priori as a constant, the proposed here method appears to be necessary if one does not want to perform costly and destructive in situ drilling tests.

Backcalculation is commonly used for determining stiffness moduli of pavement courses and its subgrade based on in situ deflection tests. However, the in situ test results are dependent on the frequency domain, which in turn has a significant influence on the backcalculation results. In this paper, one of the methods for normalising the frequency of load and displacement functions obtained from a dynamic impulse generated by a falling weight deflectometer (FWD) test is verified. The assessment of the method is carried out based on backcalculation results of pavement deflection tests induced by both the dynamic and static loads and an independent numerical experiment. The analysis carried out in this paper shows that the normalisation of vertical displacements and pavement loads to the values corresponding to the frequency of 0 Hz improves the accuracy of the backcalculation results. It can be concluded that the frequency normalisation procedure is an effective way for standardising the boundary conditions in the backcalculation of flexible pavements.

The control of compaction's degree of the lower pavement layers in Poland usually is done by making use of stiff-plate bearing tests. After the subgrade and/or subbase are constructed, there is no further possibility to check if the proper (designed) Ev2 values were achieved during the construction works. Some possible remedy of this problem can come with a nonstandard use of falling weight deflectometer results analysis. This paper presents potential applications of numerical simulations of plate bearing test based on dynamic deflection data and theoretical model of flexible pavement with high modulus asphalt concrete. Considering the combination of dynamic test results with static numerical or theoretical models used as components of inverse procedure the promising estimates of Ev2 can be achieved within non-destructive test frame. The conducted studies show how much the theoretically evaluated Ev2 secant modulus can be reliably characterized from nonstandard testing data with acceptable engineering accuracy.

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\times {10}^{-6}$$\frac{{\mathrm{m}}^2}{\mathrm{s}}$ to $0.52\times {10}^{-6}$$\frac{{\mathrm{m}}^2}{\mathrm{s}}$ and are lower (from 2.5 to 8 times) than the value determined for samples made of typical cement concrete.

The use of expert systems to determine pavement fatigue life (such as backcalculation) is strongly constrained by empirical assumptions. An important obstacle for the development of this research area is a conflict between the complexity of pavement model and actual limitations of methods used to identify its parameters. This article describes the original concept of device, which combines advantages of different methods of testing the pavement needed to calculate its fatigue life. Combined methods are based on the theory of propagation of both mechanical waves and electromagnetic waves in the layered pavement medium. The proposed hybrid solution is the starting point for the development of an expert system based on semi-invasive and non-invasive methods of obtaining the calculation values for parameters of pavement layers. It is believed that backcalculation results based on such identification are characterized by lower uncertainty comparing to the standard approach. As a consequence, the precision of overlay design for pavements will be increased.