Structural and thermal stresses are the internal forces that result from external loads and temperature changes on rigid pavements. Structural stresses caused by traffic loads, wheel wander, curling, warping, and joint movements.
Thermal stresses caused by daily and seasonal variations in pavement temperature, thermal gradients, and frictional restraint. These stresses can induce cracking, faulting, spalling, and other distresses in rigid pavements.
Rigid pavements respond to loading in a variety of ways that affect performance (both initial and long-term). The three principal responses are:
- Curling stress. Differences in temperature between the top and bottom surfaces of a PCC slab will cause the slab to curl.
- Load stress. Loads on a PCC slab will create both compressive and tensile stresses within the slab and any adjacent one (as long as load transfer efficiency is > 0).
- Shrinkage and expansion. In addition to curling, environmental temperatures will cause PCC slabs to expand (when hot) and contract (when cool), which causes joint movement.
These three principal responses typically determine PCC slab geometry (typically described by slab thickness and joint design). As slabs get longer, wider and thinner, these responses, or a combination of them, will eventually exceed the slab’s capacity and cause failure in the form of slab cracking, joint widening or blowup.
There are a variety of ways to calculate or at least account for these responses in design. The empirical approach uses the AASHO Road Test results to correlate measurable parameters (such as slab depth and PCC modulus of rupture) and derived indices (such as the load transfer coefficient and pavement serviceability index) to pavement performance. The mechanistic-empirical approach relates calculated pavement stresses to empirically derived failure conditions.