FIELD EVALUATION OF SUBBASE FRICTION CHARACTERISTICS

An important factor to be considered in the design of prestressed concrete pavements is the friction characteristics of the slab support interface. Due to the slab's length, detrimental tensile stresses may develop as the slab movements caused by temperature variations, moisture changes, concrete shrinkage, and/ or creep are resisted by the friction at the interface. This study investigated the effectiveness of single layer and double layer polyethylene sheeting in reducing the friction at the interface. A spray applied bond breaker consisting of white machine oil cut with 1/3 gasoline was also tested. The maximum coefficient of friction for each of the mediums was determined through three series of pushoff tests carried out on four experimental test slabs. The three series of tests were carried out over a period of a year to help determine the performance of the friction reducing mediums over time and changing seasons. The study shows that the double layer polyethylene sheeting produces the lowest maximum coefficient of friction. However, the use of single layer polyethylene is recommended because it is economical and its maximum coefficient of friction is low enough to prevent development of any detrimental tensile stress in the slab (a).