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Buckling of a thin CRC layer (usually less than 60 mm) without edge stiffening may develop whenever the following conditions occur:

 

•Uneven slab thickness due to variable support height and variable densification of the concrete (honeycombing).

•High concrete surface temperatures and relatively high coefficients of thermal expansion.

•Loss of bond between slab and subbase. Once slippage of the pavement starts occurring the bond may approach zero.

•Steep gradients resulting in powering/braking of heavy vehicles.

 

The risk of buckling can be calculated using the following equation:

 

Risk = 0.1[3f(alpha.T-Sh)+0.2Grd2.Lgrd] / [Lbckl(h-1.2hhon-hunev+0.3hedg+5Bnd)2]

where

 

f                   flexural strength of concrete, (MPa)

alpha            coefficient of thermal expansion of concrete (micron)

T                  surface temperature of the concrete, (degrees of Celsius)

Sh               shrinkage strain of the concrete, (micron)

Grd               longitudinal gradient of the pavement, (%)

Lgrd                length of grade, (m)

Lbck             expected length of buckling, (m)

h                  slab thickness, (mm)

hon              depth of honeycombing, (mm)

hunev           reduction in slab thickness due to subbase unevenness, (mm)

hedg             thickness of the slab at the edge (must be at least 300 mm wide), (mm)

Bnd             bond (factor)

 

Note: Value of Risk should not exceed 1.