**3. Results**

The obtained results can be divided into several focus sections.

### *3.1. Assessment of UGM Mixtures*

A commonly used parameter for the evaluation of the bearing capacity is the deflection line parallel to the direction of traffic flow. This, however, might not provide ideal information about the bearing capacity of the entire pavement structure area. When evaluating the properties of the test sections, significant differences have been observed in the bearing capacity of the pavement. When considering the bearing capacity, the pavement structure is non-homogeneous in the transversal direction. For this reason, attention was paid to the development and modification of the test device. The deflectometer was upgraded by an auxiliary cross frame capable of measuring deflection also in the transversal direction from the measuring point. The following tables (Tables 2 and 3) describe the test results of functional tests, i.e., the cyclic triaxial test and CBR test. A comparison of Mr,CTT was performed in relation to the changes in moisture of the unbound mixture tested (see Figure 5) since a variable moisture state was expected across the pavement width. Tables 2 and 3 therefore show the Mr,CTT determined at various moisture contents. It was possible to make specific comparisons of the calculated and measured values of the elasticity moduli of the GMs. The results show that the proposed Mr,CTT testing for unbound mixtures in base layers and the control of the non-destructive testing by impact load test with determination of Mr,FWD are the most optimal systems for the assessment of suitability of used GMs.

**Figure 5.** Specimens for CTT: GM 0/22 (**left**); GM 0/32 (**right**).


**Table 2.** Average Mr,CTT values and approximate values of CBR for subbase layers of the monitored road sections.

1 Determined at optimal moisture content (wopt = 4–5%) in accordance with the EN 13286-2 (Proctor modified). 2 Determinations of bearing ratio CBR in accordance with the EN 13286-47 was performed for the comparison of materials used in pavement subgrades. 3 Test samples for determination of Mr,CTT disintegrated after compaction during manipulation.

**Table 3.** Average Mr,CTT values and approximate values of CBR for base layers of the monitored road sections.


1 Determined at optimal moisture content (wopt = 5–7%) in accordance with the EN 13286-2. (Proctor modified). 2 Determinations of bearing ratio CBR in accordance with the EN 13286-47 was performed for the comparison of materials used in pavement subgrades. 3 Test samples for determination of Mr,CTT disintegrated after compaction during manipulation. 4 Values of elasticity moduli for GM at test Section 3 are only approximate because the gradation had to be adjusted for test purposes from 0/63 to 0/31.5 mm.

### *3.2. Relationship between Mr,CTT and Mr,FWD*

The relationship between Mr,CTT and Mr,FWD is given in Table 4 and Figure 6 at the current natural moisture content, sampled from the edge of the pavement where higher moisture content can be expected.

**Figure 6.** Relationship between Mr,CTT and Mr,FWD of materials from the base and subbase layer.


**Table 4.** Determined elasticity moduli of layers at the monitored sections at natural material humidity during the time of measurement.

The average Mr,CTT value for GM A was 350 MPa. The measured values varied from 315 to 403 MPa. The bearing capacity of GM A was especially affected by the gradation of the mixture with the fine particle content. The average elasticity modulus of GMB was 200 MPa. Some values, however, were below 100 MPa. The reason for this rapid decrease in bearing capacity of GMB was typically the increase in moisture content. Another reason was most likely the penetration of the lower unbound layer with a fine-grain base, especially in the case of pavements with a current lifespan longer than 5 years.

#### *3.3. The Benefit of the Innovated FWD in Determination of Mr,FWD*

The FWD device used for the determination of bearing capacity is capable of measuring in the axis of the traffic line or in the outer track of the wheels. In some cases of pavement disruptions, especially spatial deformations of pavement edges, the measured values of deflection determined in longitudinal direction do not correspond to the edges of the pavement. In situations where this is due to changes in the pavement structure (gradual historical widening) or changes of the parameters, specifically those of the base layer and subbase layer, there is a significant decrease or fluctuation of the bearing capacity of the structure layers. This phenomenon brings about the non-homogeneity of the pavement base layer or subbase layer characteristics, and this can directly affect the optimum planning of maintenance and rehabilitations or the reconstructions of the entire road section. An auxiliary cross frame added to FWD allows the gathering of information about changes of the parameters in transversal directions, in particular the bearing capacity of the structure layers. This allows for better description of the causes of disruption of pavement edges.

Searching for places with lower bearing capacity of the base layer and surface of a pavement allows, for example, a direct comparison of the measured pavement deflection by a sensor 900 mm away from the roadway center in the longitudinal and transversal directions. When a positive difference is found, the lower parameters of these layers can be expected, and closer attention should be paid in these cases during further diagnostic process (tests and laboratory material analysis) or special rehabilitation actions to be planned for these sections (see Figure 7).

**Figure 7.** Comparison of sensors in distance 900 mm from center in X/Y direction.

Another possible use of the data from such modified FWD is to draw up a detailed analysis of the course of the deflection bowl and surface moduli at selected measuring points. Such data can then be used either to determine the homogeneity or non-homogeneity of the bearing capacity parameters of specific structure layers in the longitudinal and transversal directions or to allow focusing on layers which negatively affect the overall bearing capacity of the pavement (see Figure 8).

**Figure 8.** Deflection bowl and values of surface moduli obtained from innovative FWD device.

### **4. Discussion**

Our results show that it was possible to compare the values of the determined Mr,CTT with the real values of Mr,FWD at selected road sections with a lower traffic load, which often suffer from the problem of low bearing capacity at their edges. Thanks to the use of this new, unique, innovative FWD device consisting of a dual-axis system of moduli measurements, it was always possible to find the spots with lower bearing capacity of the pavement edges. Materials sampled from these spots were then subjected to a cyclic compression test, and, indeed, lower parameters of Mr,CTT were found. During subsequent testing of these samples, a higher level of moisture was also determined, and thus the cause of the pavement edge disruptions was revealed.
