This paper describes a research project that evaluated the effectiveness of the crack and seat method of pavement rehabilitation. The process involves cracking a portland cement concrete pavement intopieces measuring 1.5 To 2 ft and firmly seating the pieces into thesubgrade prior to overlaying with asphalt concrete. Cracking and seating is designed to reduce or retard reflective cracking by minimizing the movements in the underlying concrete that create stress in the overlay. Six construction sections located throughout the state of illinois were cracked and seated between 1983 and 1987. The majority of the projects were thickened edge pavements constructed 55 to 65 years ago, with longitudinal edge bars for reinforcement. One pavement did contain reinforcing mesh. The pavements were cracked with either a spring arm or a guillotine hammer and then seated with a heavy rubber tire roller. The desired crack pattern consisted of hairline cracks, thereby maintaining aggregate interlock. Overlay thicknesses ranged from 3 to 7.5 In. Of asphalt concrete. After construction, the projects were visually surveyed and tested with a falling weight deflectometer biannually. The crack and seat process was beneficial in reducing reflective cracking in overlays on thickened edge pavements containing only edge bar reinforcement. The crack and seat method of rehabilitation is not recommended for use on reinforced pavements. Cracking and seating is possible through existing overlays provided certain precautions are taken. Guillotine-type hammers are recommended for the cracking process. An overlay thickness design procedure based on mechanistic concepts was developed. This paper appears in transportation research record no. 1215, Pavement management and rehabilitation.
Abstract