Design of CRCP for Airports
PDF courtesy of the American Concrete Pavement Association’s (ACPA’s) technical resources archives.
Continuously reinforced concrete pavement (CRCP) may be defined as a concrete pavement in which the longitudinal reinforcing steel is continuous throughout its length and has no transverse joints other than construction joints. In actual practice, the continuity is interrupted by expansion joints at structures, but except for these, there is technically no limit to the length of CRCP.
Transverse contraction joints were long considered essential to prevent pavement damage due to volume change stresses. Unfortunately, the major distress associated with concrete pavement was found to be at the joints. Thus, over the years, various joint spacings have been used. In order to increase joint spacing beyond 15-25 feet, reinforcing steel was introduced to control cracks that occur from volume change stresses. The concept of controlling cracks with reinforcing steel and limitations of the joint raised the question of eliminating transverse joints altogether. It was this challenge that led to research initiatives by the U.S. Bureau of Public Roads and construction of the first CRCP. In 1938, Indiana constructed a pavement with varying joint spacing. On some of these pavements, the joints were placed at very large spacings since high percentages of longitudinal steel were used, i.e., 0.5 to 1.0%. It was found that between joints these pavements performed as a continuous unit. From this, the concept of CRCP was developed. After World War II, various state highway departments in Illinois, Texas, California, Mississippi, New Jersey, Michigan, Maryland, and Pennsylvania constructed similar CRC pavements that have provided excellent service for a number of years. With the advent of the Interstate Highway Building Program, CRCP was used extensively throughout the United States. (Refs. 1 – 5)
The successful use of CRCP for highway pavements led to their implementation for airport pavements. In the late 1960’s, CRCP runways were constructed at USAF Plant 42 in Palmdale California and at O’Hare International Airport (Chicago, Illinois). The Palmdale installation was an unbonded CRCP overlay of an existing jointed pavement, and has since provided a maintenance free pavement for over 20 years. The initial pavement constructed at O’Hare on Runway 9-27 was only 12 inches thick and has required an intermediate overlay due to heavy traffic. Subsequent runways constructed at major U.S. airports have provided excellent performance. Thus, CRC pavements arc a sound choice for airport runways, taxiways and aprons. They have been found to minimize maintenance costs, aircraft delays, and operating costs. (Ref. 6)
The development of CRCP has now progressed to where a pavement for an airport may be successfully designed and constructed that will provide excellent service over an extended time period, i.e., 25 – 35 years. The excellent service is reflected in the following significant features for the airport owner, operator, and user:
- Minimal maintenance during the life of the pavement.
- Continuous availability to aircraft operations.
- Minimal cost for maintenance and rehabilitation.
- Smooth riding pavement for the aircraft that maximizes comfort for the passenger and minimizes detrimental induced dynamic loads to the aircraft and pavement.
The construction industry’s experience has now evolved to the stage when the initial cost of CRCP may only be slightly larger than alternative concrete pavements. Thus, any type of systematic cost evaluation over a long analysis period (20-40 years) will demonstrate CRCP is the most cost effective pavement for runways, taxiways, and aprons with large volumes of aircraft movements.
Author: B. Frank McCullough, PhD