Thickness Design

Thickness design involves the determination of the minimum required CRCP thickness that will produce an acceptable level of stress in the pavement under traffic and environmental loadings. The assumption being that the targeted stress will reduce the potential for punchouts and other structural distresses, while at the same time maintaining an acceptable level of function (e.g., smoothness).

Reduction of stresses in the pavement slab is not only achieved by increasing thickness but by consideration of numerous other factors including:

  • High load transfer efficiency – This can be accomplished by keeping transverse cracks tight with the use of an adequate longitudinal steel content to achieve good aggregate interlock. Selecting large size aggregates that are resistant to abrasion will also improve load transfer at the cracks.
  • Sufficient lateral support – Tied concrete shoulders or widened lanes that extend beyond the wheelpath into the shoulder at least one foot provide improved lateral sup- port over asphalt shoulders, as well as aid in mitigating punchouts.
  • Uniform and stable structural support under the slab – This may be achieved by stabilizing subgrade if swelling is expected and/or by selecting erosion-resistant bases that minimize erosion and pumping of subgrade materials and through accelerated freeze-thaw and wet-dry testing with strength assessment can be demonstrated to have long-term durability.
  • Prevention of subgrade or base saturation – This can be achieved by improving drainage features such as selecting non-erodible or permeable moisture insensitive bases.
  • Improved concrete structural properties – Although excessively high concrete strengths are not desirable, producing concrete with sufficient strength and a low modulus of elasticity will help in reducing stresses due to traffic loading.

Taking the above measures will minimize potential for punchout development at a minimum required thickness, thus resulting in a more cost-effective design.

In the past, it was common practice by some States to design CRCP thickness based on jointed concrete pavement methodology, and then reduce the thickness by as much as 20 percent to account for the effect of increased load transfer efficiency at the cracks.

In some cases, this resulted in an under-design, which in turn required expensive maintenance and rehabilitation. As a result, this practice is no longer recommended.(1)Continuously Reinforced Concrete Pavement (FHWA Technical Advisory T 5080.14) Today, typical CRCP thicknesses vary from 7 to 15 in. (178 to 381 mm) depending on the level of traffic and environmental conditions, although most common practice is between 10 and 12 in. (254 to 305 mm).

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