Determination of concrete slab thickness

The procedure for the determination of the thickness of the concrete slab is based on the two distress modes, as mentioned earlier, the flexural fatigue cracking of the slab and the subgrade/sub-base erosion. The two distress modes are expressed by two fatigue equations, provided in the reference manual, from which the allowable load repetitions can be calculated. 

For an assumed slab thickness, the minimum required values are given in Table 14.5 the allowable number of load repetitions is determined in each case and for each axle load group type. Then, the ratio of the expected fatigue repetitions to the allowable load repetitions is calculated and multiplied by 100 to determine the fatigue percentage, for each axle load group type, per type of distress. 

The required minimum characteristic design concrete flexural strength for concrete pavements with a design traffic of 10 HVAG or more is 4.5 MPa at 28 days, except for steel fibre-reinforced concrete, where the requirement is 5.5 MPa. 

The methodology also requires the provision of concrete shoulders. These can be either integral or structural. 

Integral concrete shoulders are made up of the same concrete and are the same thickness as the concrete slab, and they are cast integrally with the slab with a minimum width of 600 mm. The minimum width for integral cast shoulders in the median lane may be reduced to 500 mm. 

---