# Technologies and Principles of Hot Recycling and Investigation of Preheated Reclaimed Asphalt
## 4 Results and Discussion  
The aim of the study was to identify how accurately and precisely RAP is batched when producing an asphalt mixture. The experiment data show that when producing RHMA mixture AC 16 PD (with 25% RAP) for pavement single ply surface course, the batched quantity of RAP into an AMP mixer was on average \(\overline{q}_{RAP}~{}=738.63\) kg. According to Equation (8), batching accuracy \(\Delta q_{RAP}=\frac{738.63-750}{750}\times 100=-1.52\%\). RAP batch mass varied from 643 kg to 845 kg. Range \(R=q_{max}-q_{min}=202\) kg (Figure 6a). Standard deviation showing batch mass variation was \(s_{q_{RAP}}=27.46\) kg and coefficient of variation was \(V_{q}=3.72\%\). The specifications do not regulate AMP batching tolerances of bitumen, hot and cold mineral materials. They are specified in ASTM Standard Specification for mixing plants for hot-mixed, hot-laid bituminous paving mixture. According to the Specifications above, the automatic proportioning system shall be capable of consistently delivering materials within the full range of a batch size of the following tolerances (Table 4). The electric circuits for the above delivery tolerances of each cut-off interlock shall be capable of providing the total span for the full allowable tolerance for maximum batch size. Tolerance controls shall be automatically or manually adjustable to provide spans that are suitable for less than full-size batches. The automatic controls and interlock cut-off circuits shall be capable of being consistently coordinated with the batching scale or meter within an accuracy of 0.2% of the nominal capacity of the said scale or meter throughout the full range of the batch sizes according to ASTM D995-95b. Having investigated all 1569 asphalt mix batches of grade AC 22 PS RHMA mixture (with 50% RAP content) produced in 12 days for the base course, it was identified that RAP is batched rather accurately. When the mean of RAP of all the batches is \(\overline{q}_{RAP}=1483.27\) kg, and \(q_{RAP,JMF}~{}=~{}1500\) kg, then according to the mean RAP is batched rather accurately: \(\Delta q_{RAP}=\frac{1483.27-1500}{1500}~{}\times 100=-1.11\%\) and error is less than 1.5%, i.e., lower than tolerances. The value of batching preciseness is standard deviation \(s_{q_{RAP}}=27.40\) kg, and variation coefficient \(V_{q}=1.85\%\).The maximum mass of a RAP batch is 1631 kg and the minimum mass is 1380 kg. Range \(R~{}=~{}q_{max}-~{}q_{min}=251\) kg (Figure 6b). Taking into consideration the specification that not only RAP batch mass mean is \(\overline{q}_{RAP}\), but its weighed batch mass \(q_{RAP}\) differed from rated value \(q_{RAP,JMF}~{}\)does not exceed the permitted tolerances (\(\pm 1.5\%\)), when \(q_{RAP,JMF}~{}=~{}750\) kg, the amount of weighed RAP shall be not less than 738.75 kg and not more than 761.25 kg. When \(q_{RAP,JMF}~{}=~{}1500\) kg, the minimum permitted batch mass of RAP may be 1477.5 kg, and the maximum batch mass 1522.5 kg. In fact, the diagrams (Figure 7) above show that the mass of quite a lot of RAP separate batches does not meet tolerance specifications. Only 29% of them (392 out of 1324) are within the range of permitted tolerances, when the estimated \(q_{RAP,JMF}~{}=~{}750\) kg and 51% (803 out of 1569) when it was \(q_{RAP,JMF}~{}=~{}1500\) kg. The normality of data distribution was verified according to skewness and kurtosis. Empirical coefficient of skewness of RAP batch masses \(sk\) were 0.007 and 0.013, and the coefficient of kurtosis \(ku\) were 0.122 and 0.488, respectively (Figure 7). They were compared to the critical values which depend only on sample size \(n\). When RAP batch sample sizes \(n\) were 1324 and 1569, standard deviations of skewness and kurtosis were calculated as follows: \(s_{sk}=0.067\), \(s_{sk}=0.062\) and \(s_{ku}=0.134\), \(s_{ku}=0.123\) (AC 16 PD and AC 22 PS mixtures, respectively). The estimated \(s_{sk}\) values were multiplied by 3, which resulted in \(3s_{sk}=0.202\) and \(3s_{sk}=0.185\), respectively.