# Application of Data Mining Techniques to Predict Luminance of Pavement Aggregate
## 2 Materials and Methods
### Test Stand  
According to the requirements contained in Polish standards WT-2 [41] and PN-EN 1436 [42], the measurement of the luminance coefficient should be made at an angle of 2.29\({}^{\circ}\) (equivalent to viewing the road from a distance of 30 m from the position of a driver of a passenger vehicle). The measurement field should be a rectangle of 185 mm \(\times\) 50 mm, with an angular span of observation of \(\pm\)0.17\({}^{\circ}\). This requirement was met by the LTL-X Mark II device used to perform the tests. The device allows the determination two parameters, Qd and RL, with the ability to import the results into a database. The device and test stands are presented in Figure 2.  
The test is performed in fixed diffused light. The sample is illuminated with a D65 standard light source of constant luminance, as specified in ISO/CIE 10526 using the aforementioned LTL-X Mark II device (Figure 2a). The measurements are performed while the ambient temperature is between 0 and 30 \({}^{\circ}\)C, and the temperature of the test sample/surface is between 5 and 40 \({}^{\circ}\)C.  
The test form met the recommendations of WT-2/2014 [41], according to which the stable test area should be 700 mm \(\times\) 700 mm (Figure 2c,d). Meanwhile, the empty space that is not subject to measurement should be filled with any rigid material (Figure 2c). The working area in which the aggregate was placed was sized to match the retroreflectometer's working area, i.e., 320 mm \(\times\) 235 mm (Figure 2d). Each aggregate sample was tested 5 times, at different locations in the working area. Subsequently, another sample was taken from another location in the aggregate stockpile (series). Each aggregate was evaluated on the basis of a dataset of 5 series. Thus, every luminescence coefficient of aggregate was measured on subsamples taken from 5 different locations of stockpile in 5 places for each subsample. As a result, to determine coefficients Qd and RL, 25 measurements for each grain size and aggregate type were performed. Such an amount of data was required in order to obtain a robust DM model. The number of aggregate datasets, as well as test repeatability (including reproducibility in the validation stage), should be big enough to cover the spectrum of potential cases in order to predict using a potential model.  
The research plan included conditions of sample surface preparations by taking into account the compaction of the sample. Therefore, in some cases, a vibrating table was used (Figure 2b). Test conditions are presented and explained in Section 3.1. Adequate repeatability, adopted as >10% (results range) [41], was obtained at a compaction time of 3 min and an amplitude of 3 mm. The use of vibrations in the mold of the sample preparation reduced the results of Qd variability up to 3 mcd\(\cdot\)m\({}^{-2}\cdot\)k\({}^{-1}\) for all aggregates. Summarizing the effect of compaction on variability of the Qd is presented in Figure 3.  
Figure 3: The influence of compaction on variability of Qd results.  
Figure 2: The measuring instrument and test stand for luminance coefficient testing: (**a**) LTL-X Mark II road retroreflectometer; (**b**) laboratory compactor; (**c**) mold with test sample; (**d**) scheme test stand.  
Observing results in Figure 3, it should be noted that compaction had a slight but significant influence on decreasing the dispersion of Qd results for each aggregate type. Thereby, compaction was included as a factor in the DM model.