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Roller-Compacted Concrete (RCC) Thickness Design

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Slab Tensile Stress and Influencing Factors

Although all roller-compacted concrete (RCC) pavements are constructed as plain, unreinforced, and undoweled pavements, their structural behavior is similar to that of conventional concrete pavements. Both pavements types have the same thickness design philosophy: maintaining fatigue damage and flexural stress on the pavement caused by wheel loads within acceptable limits. The slab tensile stress and more importantly, the ratio of this stress to the flexural strength (which is called the stress ratio), is the most important parameter in terms of fatigue damage. This page provides an overview of some RCC thickness design procedures. There have also been RCC thickness design procedures suggested by researchers that are not covered here.

Overview

Previous research has shown that RCC fatigue behavior is similar to that of conventional concrete pavements. Therefore, it has been suggested that conventional concrete pavement design software such as StreetPave or WinPas can be used, with the recommendation that the reliability level be increased by 5%, for designing RCC pavements. The joint performance (i.e. load transfer efficiency) of RCC is crucial to the fatigue performance since RCC relies solely on aggregate interlock at the joints (where stresses are greater than the interior of the slab) to provide load transfer. Thus it is especially important to be aware of the default load transfer assumptions of the design software.

The subgrade, subbase, and/or base design for RCC should have sufficient bearing capacity so that adequate compaction of the RCC layer(s) can be achieved.

Design Procedures

Design examples for each design procedure presented below can be found in the Guide for Roller-Compacted Concrete Pavements[1].

Heavy-Duty Industrial Pavements

Design procedures for heavy-duty industrial RCC pavements such as RCC-PAVE or the U.S. Army Corps of Engineers (USACE) procedure account for heavy wheel loads due to loaders or container haulers. The USACE procedure can be found here. The paper that led to the development of RCC-PAVE can be found here. Design examples for both RCC-PAVE and the USACE procedures can be found in the Guide for Roller-Compacted Concrete Pavements.

RCC-PAVE

The pavement engineer can use the RCC-PAVE software or manually solve for pavement thickness using nomographs and charts developed for RCC-PAVE. RCC-PAVE makes the following design assumptions:

  • If multiple lifts of RCC were paved, the entire thickness is considered monolithic (i.e. there is full bond between layers).
  • The fatigue curve that is used in the analysis is conservative (even more so than the 95% reliability fatigue curve based on flexural fatigue testing).
  • RCC-PAVE was developed for industrial and highway applications with a maximum of 700,000 load repetitions.

RCC-PAVE requires the following parameters as inputs:

  • Supporting strength of the underlying layers (i.e. subgrade and/or subbase) - k-value.
  • Vehicle characteristics: wheel loads, wheel spacing, tire characteristics, load repetitions during pavement life.
  • Flexural strength and elastic modulus of RCC (note: these values are typically assumed via correlations with compressive strength).
RCC Flexural Fatigue Curve Developed by the Portland Cement Association for RCC-PAVE

USACE Procedure

The USACE procedure accounts for traffic in terms of equivalent single axle loads of 18 kips. One design chart is used for all pavement applications (i.e. roads, parking lots, and storage areas) and zero load transfer is conservatively assumed across joints since the only mechanism of load transfer is aggregate interlock. The design procedure has three choices for bond condition (full, partial, or no bond).

Parking Lots

Designing RCC for average parking lots (i.e. not heavy-duty industrial parking lots) can be done using the procedure from Design and Construction of Concrete Parking Lots (ACI 330R-08) with the "no dowel" option. This essentially treats RCC as a conventional concrete pavement without dowels. The default design life using ACI 330R-08 is 20 years.

Streets

There are three design methods that are typically used for thickness design of RCC pavements for streets: Guide for Design of Jointed Concrete Pavements for Streets and Local Roads (ACI 325.12R-02), StreetPave, or WinPAS. ACI 325.12R-02 has a default design life of 30 years and requires the subgrade k-value, RCC flexural strength, traffic classification, and annual average daily truck traffic (ADTT) for design. Care should be taken when determining whether or not the RCC pavement would be considered to have a tied shoulder or curb and gutter.

The main difference between StreetPave and ACI 325.12R-02 is that StreetPave uses a variable design curve that depends on user-selected reliability and percent cracked slabs. It is recommended to increase the reliability by 5% when using StreetPave to design for RCC. The option for undoweled joints should be selected. For thicknesses greater than 8 inches, StreetPave automatically requires dowels and therefore the designer should switch back to ACI 325.12R-02.

Related Pages

References

  1. National Concrete Pavement Technology Center. 2010. Guide for Roller-Compacted Concrete Pavements.