Evaluation of Subbase Friction for Typical Korean Concrete Pavement

The frictional force between concrete slab and subbase is accompanied by horizontal slab movements induced by variation of temperature and moisture in the concrete slabs. The frictional force is exerted in the opposite direction from the horizontal slab movement and causes stress in the slab. Rational evaluation of subbase friction is important in configuring joint sealing, slab thickness, and reinforced steel. Determination of the subbase friction is also required as an input for the recently developed concrete-pavement-construction program HIPERPAV. Lean concrete has been widely used as the typical subbase for jointed concrete pavement in Korea. Generally, polythene sheet is placed between the lean concrete subbase and the concrete pavement slab as a friction reducer. In addition, an asphalt bond breaker may be used as an alternative friction reducer in some cases. Three series of push-off tests were conducted to study the characteristics of subbase friction for this typical Korean jointed concrete pavement system under three different subbase conditions (I, test slab directly cast on lean concrete subbase; II, polythene sheet placed between test slab and lean concrete subbase; and III, 4-cm asphalt bond breaker placed between test slab and lean concrete subbase). For each series, tests were performed under various conditions (rate of movement, slab thickness, number of movement cycles) to investigate the influence of these potential factors on the development of subbase friction.