Performance of Concrete Pavements with Optimized Slab Geometry

The typical slab dimensions for a concrete pavement are 12 ft wide by 15ft long with slab thicknesses ranging from 6 to 14 inches depending on the level of traffic. The required thickness is primarily dependent on the axle weight and number of load repetitions, concrete strength, slab length, and curling stresses. A new methodology for designing concrete pavements has recently been proposed to optimize the slab dimensions, e.g., 6 ft by 6 ft panel sizes, which concurrently decreases the load and curling induced tensile stresses in the slab. This concomitant reduction in stresses enables a thinner concrete slab and subsequently the economical viability of concrete pavements is improved. It has also been proposed that these pavement systems don’t need any man-made load transfer devices across the transverse contraction joints. This new way of designing concrete pavements has been referred to as “Thin Concrete Pavements (TCP)” or concrete slabs with optimized geometry. Full-scale test sections of this new concrete pavement system have been constructed and tested under accelerated pavement loading conditions. The design and concrete material factors that have been subjected to repeated loading in this research are the following: concrete thickness of 4, 6, and 8 inches; aggregate base or asphalt concrete base; plain concrete or fiber reinforced concrete; and edge versus wheel path loading. The accelerated pavement testing showed that these thinner concrete slabs with reduced slab sizes could sustain a significant number of ESALs before cracking. The 8 inch concrete slabs on granular base did not experience fatigue cracking until 51 million ESALs. The 6 inch concrete slabs on granular began cracking on average at 12 million ESALs. The concrete slabs on asphalt base resisted a significant larger number of ESALs than the same concrete thickness on granular base. The cracking performance of the 3.5 inch concrete slabs varied with the stiffness of the soil. In all cases for the 3.5 inch slab thickness, structural fibers provided a longer fatigue life, extended service life, and high load transfer efficiency across the transverse joint relative to the plain concrete slabs. Trafficking tests indicated that the fibers may also be able to serve as a replacement for the lateral restraint pins. Finally, the shorter slabs sizes maintained a medium to high load transfer efficiency over the accelerated loading period for all slab thicknesses. Measurements indicated these slab systems have higher deflections as expected and therefore the aggregate base layer and subgrade must be designed and specified to reduce the rate of permanent deformation and minimize the possibility of pumping and erosion. Premature concrete slab cracking may result if improper base material and thickness is not utilized, a geotextile separation layer is not used between the base and subgrade, and inadequate drainage of the slab system is not provided.