# Complex Method of Airfield Pavement Condition Evaluation Based on APCI Index
## 2 PCI Method  
The evaluation of the technical condition of the airfield functional elements pavement can be performed on the basis of several developed and implemented ways. One of the most commonly used methods in the world is a method using the PCI. This is a standard procedure developed and used by the U.S. Army Corps of Engineers, which is based on the inventory of surface damage pavement [29; 30]. During the review, the type of damage is taken into account, as well as their number and harmfulness. PCI is a unitless number from 0 to 100 describing the technical condition of the pavement, where 100 means a pavement in a perfect condition, and 0 a pavement in a fully degraded state, not allocated to any age. The scale of the pavement assessment based on the PCI is shown in Figure 1[6]. The same figure also presents a generalized PCI scale for a coarse assessment of the pavement. The pavement inspection takes place in a strictly defined manner, according to the procedure contained in previously quoted standards. The first stage of work is to divide the airfield pavement for research samples-functional elements of the airport, i.e., on the roadways, taxiways and aprons. Then, each of the elements are divided into a single sample. The division takes place in accordance with the instructions. All surfaces made of cement or asphalt concrete are divided into samples with an area of 5000 \(\pm\) 1000 sq. ft., which corresponds to approx. 460 \(\pm\) 180 m\({}^{2}\). Each of the samples is considered individually. Due to the fact that the examination of all samples is time-consuming, which determines cost of work, it is possible to reduce the number of samples. The advantage of such a solution is to reduce the costs related to inspection, but at the expense of the quality of the results obtained. The minimum number of test samples \(n\) is calculated from Equation (1) [28]:  
\[n= \frac{N\cdot s^{2}}{(e^{2}/4)(N-1)+s^{2}}, \tag{1}\]  
where \(N\) is a total number of samples resulting from the pavement division, \(e\) is acceptable Estimation error of the PCI, and \(s\) is a standard deflection of the indicator value of PCI obtained on individual samples. The next step is to choose samples to evaluate. Samples should be distributed evenly over the entire surface of the element. The easiest way to achieve this is to divide the number of all samples through the minimum number, which will give the interval at which the samples should be selected. For example, if the total number of testing samples is 50, and the minimum 16, the interval will be 50/16, which after rounding down gives the value of 3. Thus, if in the study all samples are numbered from 1 to 50, we should take into account the samples with numbers 1, 4, 7,..., 48. On critical elements of functional airports, as a more frequently used circulation ways or intersection, reasonable from the point of view of ensuring the safety and continuity of air operations is to review all samples. This applies in particular to the runways. The review process itself consists in a list of damage observed on the surface of the pavement, according to the legend contained in the standards. The census of damage is made in tables, noting their type, harmfulness, number and approximate location on the sample. The number of individual damage cases, their harmfulness and density of occurrence are determined for each analyzed sample. Based on the census, the PCI for the individual sample according to the following procedure is determined:  
1. Calculate distress density as a total area of each distress type to total area of the sample ratio. 2. Define the deduct value based on the nomogram for any type of damage and harm corresponding to it (high, medium or low). A typical nomogram is shown in Figure 2 [8]. Figure 1: PCI indicator scale [6]. The maximum allowed number of deducts \(m\) is then determined by dependence (2) [8]. \[m_{i}=1+(9/95)(100-HDV_{i}), \tag{2}\]  
where: \(HDV_{i}\) is the highest, individual deduct value for single sample \(i\). 3.