Evaluation of selected airport pavements in New Mexico

Rehabilitation of poor conditioned airport pavements can be very expensive compared to the rehabilitation of relatively good conditioned airport pavements. Determining the conditions of airport pavements is a first step to determine appropriate rehabilitation method and timing. In this study, the conditions of 10 airport pavements in New Mexico are evaluated. Those airports include a total of 19 runway pavements. The major goal is to rank these airport pavements based on their functional and structural conditions. The functional conditions of the pavements are evaluated based on the field collected surface distress data and skid resistance. Field collected distress data such as rutting, cracking, and shoving are processed using MicroPaver, a commercial pavement management software, to calculate the Pavement Condition Index (PCI). Field collected skid resistance test data are processed to obtain a single value Skid Number (SN). Drilling and field coring are performed to collect samples of asphalt cores, base aggregate, and soils. These samples are then transferred to the Pavement Laboratory at the University of New Mexico for testing. Soil tests include index properties, moisture, and classification tests. Using these laboratory test results, a strength parameter called the California Bearing Ratio (CBR) value of the subgrade soils is determined. Also, the CBR value of base aggregate is determined. These CBR values are used to rank the airport pavements according to the FAA’s Advisory Circular 150/5320 – 6D. Asphalt concrete cores are tested for parameters such as resilient modulus (MR), indirect tensile strength (ITS), void ratio, asphalt content, and aggregate gradation. These parameters are used to determine the structural strength of a pavement in this study. Based on the PCI value, 5 out of 19 runway pavements are found to be in poor condition. These pavements have a PCI value of less than 55. The PCI value is used in pavement rehabilitation design. Based on the SN value, 6 out of 18 runway pavements are found to be in poor condition. Their SN values are below the minimum required value of 50. Low skid resistance can pose a threat to the safe operation of aircrafts on pavements during wet weather conditions. When PCI and SN values are combined to estimate the overall functional condition, 7 runway pavements are shown to be in poor condition, 7 in fair condition, and 4 in good condition. Based on the subgrade CBR value, all the runway pavements look good because they passed the minimum required CBR value of 15 for subgrade. Based on the base course CBR value, all the pavements can be considered to have a fair to good base course. Ranking based on subgrade and base course CBR is important. A subgrade with a poor CBR value may need expensive rehabilitation measures because it requires removing the surface and base course in order to fix the subgrade. CBR value is useful for Aircraft Classification Number – Pavement Classification Number (ACN-PCN) based rating of pavements. Based on the resilient modulus of asphalt concrete (MR), only one runway has shown to have poor performance with a value of 183.6 ksi, 3 runways have fair MR values, and 10 runways have satisfactory MR values. An indirect tension modulus of 300 ksi is considered to be good for existing surface course. The MR value is used in mechanistic design of roadway pavements, however, it has not been adopted in airport pavement design yet. Based on the ITS value, all the pavements are in good condition. A pavement having an ITS value of greater than 100 psi is considered to be in good condition in this study. A pavement with a low ITS value is more likely to develop low temperature cracks during winter seasons. In addition to strength and modulus of asphalt cores, mix design parameters such as asphalt content, air voids, and aggregate gradation of surface course are determined. Five runways have over 7% air voids, 7 runways have between 4-7% air voids, and 2 runways have less than 3% air voids. A high percent of air voids can lead to higher permeability and moisture damage problems. Low air voids can lead to rutting problems. Five runways have more than 7% asphalt content, and nine runways have 5-7% asphalt content. Low asphalt content (2-3%) can be a problem in terms of pavement durability. Based on the structural strength calculated using CBR, MR, and ITS, 1 runway is in poor condition, 9 in satisfactory condition, and 4 in good condition. Overall, based on combined functional and structural strength, 2 runways are in poor condition, 6 runways in fair condition, 4 runways in satisfactory condition, and 2 runways in good condition. It is hoped that this ranking will help design the future alternative rehabilitations when it is time to apply such rehabilitation alternatives.New Mexico Department of Transportation - Aviation DivisionCivil EngineeringMastersUniversity of New Mexico. Dept. of Civil EngineeringTarefder, Rafiqul AlamNg, Tang-TatBrogan, James D