LARIMER COUNTY RURAL AREA ROAD STANDARDS

Chapter 5 – Geotechnical Standards and Pavement DesignSection 5.6 Rigid Pavement DesignTable 5-3Pavement Strength CoefficientsConventional MaterialsPavement StructureComponent*Plant Mix Seal CoatHot Mix Asphalt (Grading SX, S, SG)Existing Bituminous Pavement (age)Aggregate Base CourseExist Aggregate Base CourseGranular Subbase CourseDesign StrengthCoefficients(per inch of material)0.250.440.300.240.110.100.07Limiting TestCriteriaR T 90+9-15 yr> 15 yrR 72+R 69+R 50+Chemically treated Subgrades**(Or Approved Substitute)Cement Treated SubgradeFly Ash Treated SubgradeLime Treated Subgrade0.230.100.14Compressive strength:7 day, 650-1000 psi7 day, 150 psi @ 70°±7 day, 160 psi, PI < 6* The Pavement Structure Component shall be a combination of one or more of the following courses placedon a subgrade to support the traffic load and distribute it to the roadbed. However, the pavement sectionmust be composite in nature.1. Subbase: The layer(s) of specified or selected material of designed thickness placed on a subgrade tosupport a base course, surface course or both.2. Base Course: The layer or layers of specified or selected material of designed thickness placed on asubbase or a subgrade to support a surface course.** Strength coefficient is only acceptable if material is properly mixed and tests correlate with laboratoryresults. When chemical treatment is used for unstable soil mitigation a subsequent reduction in pavementdesign must be approved by the Engineer.6. The Standard Deviation for design of asphalt pavements shall be 0.44.7. The design must reference any mitigation measures required when the subgradecontains swelling soils. Design reports recommending permeable layers in thepavement system must present the measures to be used to ensure adequatedrainage of such layers and to maintain separation of the layers from the swellingsoils.5.6 RIGID PAVEMENT DESIGN5.6.1 DefinitionRigid pavements are those which possess a high bending resistance and distributeloads over a large area of foundation soil. Examples include Portland cement concretepavement or Portland cement concrete surfaced with asphalt.Larimer County Rural Area Road Standards Page 5-7October 22, 2007