# Technologies and Principles of Hot Recycling and Investigation of Preheated Reclaimed Asphalt
## 4 Results and Discussion
Standard deviation of kurtosis \(s_{ku}\) was multiplied by 5, which resulted in \(5s_{ku}=0.672\) and \(5s_{ku}=0.617\), respectively. \begin{table}
\begin{tabular}{c c} \hline \hline
**Materials** & **Total Batch Mass of a Paving Mix, \%** \\ \hline Batch aggregate component & \(\pm 1.5\) \\ Mineral filler & \(\pm 0.5\) \\ Bituminous material & \(\pm 0.1\) \\ Zero return (aggregate) & \(\pm 0.5\) \\ Zero return (bituminous material) & \(\pm 0.1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Tolerances of batch masses of AMP batches’ materials according to ASTM D 995-95b. When \(|sk|<3s_{sk}\) and \(|ku|<5s_{ku}\), it could be stated that the hypothesis of normality of the empirical data is confirmed. The normality of sample size data distribution can be verified using more complex methods, such as Kolmogorov and Pearson. Null hypothesis can be verified according to the Bartlett criterion, where the available data is close to normal distribution. Thus, [PERSON]'s criterion was used to compare the variances of various sample sizes according to normal distribution. This criterion is convenient to compare two or more variances of the normal distribution sample sizes when these sample sizes are unequal. If statistics \(B\) is less than \(\chi_{\alpha,\
u}^{2}\), RAP batch mass variation is statistically equal. Therefore, the average calculated value of sample variance \(s_{q}^{-2}=752.52\) kg and general standard deviation \(\overline{s}_{q}=27.43\) kg. Statistics \(B=0.0094\) is less than critical \(\chi_{\alpha,\
u}^{2}=3.84\) with the selected \(\alpha=0.05\) significance level and degrees of freedom \(\
u=l-1\) (where \(l\)--the number of comparable variances (samples). Therefore, it could be concluded that both (with 25% and 50% RAP content) batch mass variation (standard deviation \(s_{q}=27.46\) kg and \(s_{q}=27.40\) kg) are statistically equal. The physical and mechanical properties of a recycled HMA mixture are influenced by RAP percentage content in each mix batch of RHMA mixture. This parameter allows to determine the proportion of RAP in the whole mix batch. When hot fractions, IF and RD batches are weighed in AMP, their mass like that of RAP has a certain variation, which influences the variation of RHMA mixture batch masses (Figure 8). Therefore, the mass of RHMA mixture batches always differs from JMF, i.e., from 3000 kg and is of stochastic type. Average values \(\overline{x}_{RAP}\) of RAP percentage Equation (7) of both sample sizes out of 1324 (with 25% RAP) and 1569 (with 50% RAP) were approximate to JMF (Figure 8). \(\overline{x}_{RAP_{\text{S}}}=24.53\%\), \(\overline{x}_{RAP_{\text{S}}0}=49.45\%\). Standard deviation \(s_{x}\) of RAP percentage content was rather low: in mix batches with 25% of RAP content--0.705%; in mix batches with 50% of RAP content--0.507%, and their variation coefficients were \(vc_{x25}=2.87\%\) and \(vc_{x50}=1.03\%\), respectively. Average values \(\overline{x}_{RAP}\) of RAP percentage content Equation (7) of both sample sizes out of 1324 (with RAP percentage content in RHMA mix batches were approximate to those designed in JMF; however, histograms show that most of the data is grouped below the value of JMF (Figure 8). There was a tendency of lack of RAP content in RHMA mixture. Figure 8: Normal distribution curves and statistical indices of histogram of RAP percentage content in recycled hot mix asphalt (RHMA) mixture, when its content according to JMF had to be: (**a**)—25%; (**b**)—50%. When asphalt pavement is hot-mix in-plant recycled, the sequence of technological operations depends on the structure of an AMP and additional equipment for feeding, transporting, and proportioning or batching of RAP. The model constructed by the authors contains two types of technological operations. First, hot-mix recycling in a batch plant, when RAP is dried and heated up due to the contact with superheated virgin mineral materials, i.e., conductive heat transfer occurs.