Introduction

This design catalog is intended to give general structural design and mix type selection guidance for some typical Hawai'i HMA pavements. It is organized by general purpose, with each use type being addressed on a different page. These guidelines are intended for use in lieu of other guidance or specification. They are not intended to supercede official guidelines or specifications.

Assumptions

Recommended structural designs use the basic assumptions and classifications discussed below. The limitations and applicability of these assumptions and classifications must be understood before using the recommended structural designs contained in this section.

Traffic

Traffic is classified in a broad sense only. There are many different traffic classification schemes available and traffic can vary widely in both make-up and volume. This design catalog uses the "vehicle manufacturer truck classification", which broadly divides vehicles into the three classes listed in Table 1.

Table 1: Design Catalog Vehicle Classification

Vehicle Category	Gross Vehicle Weight Range	Assumed ESALs per Vehicle	Representative Vehicles
Cars and Light Trucks	0 - 14,000 lbs.	0.0007	cars, SUVs, pickup trucks, ambulances, delivery vehicles
Medium Trucks and Buses	14,001 - 33,000 lbs.	0.25	city cargo van, delivery truck, wrecker, school bus
Heavy Trucks and Buses	over 33,000 lbs.	1.00	semi tractor trailer, concrete mixer, dump truck, garbage truck, fire truck, city bus

Note: This classification is different from the FHWA vehicle classification system

Subgrade

Subgrade soil conditions vary widely across Hawai'i. This design catalog section classifies soils into three broad categories based on strength and stiffness (CBR, , R-value, M_R) as listed in Table 2. These categories are broad and should be used with caution. A subgrade should be categorized based on its strength or stiffness and not its soil type alone. For example, it is not enough to know that a subgrade is primarily classified as an SW in the Unified Soil Classification (USC) system, something must also be known about its strength or stiffness.

A Note on Extremely Adverse Subgrades
The "Poor" classification shown in Table 2 is meant to describe subgrades with low strength and stiffness values and/or high fines content. Extremely adverse subgrade conditions such as water saturated soil, standing water, organic peat and ash provide extremely poor support and do not meet the "poor" classification in Table 2. Paving over extremely adverse subgrades should be avoided if possible. If paving is necessary, a pavement designer and a geotechnical engineer should collaborate to develop a feasible pavement design.

Table 2: Design Catalog Subgrade Classification

Classification	CBR	R-Value	M_R (psi)	Typical Description (by USC)
Good	10 or greater	25 or greater	20,000	Gravels, crushed stone and sandy soils. GW, GP, GM, SW, SP, SM soils are often in this category.
Fair	5 - 9	12 - 24	10,000	Clayey gravel and clayey sand, fine silt soils. GM, GC, SM, SC soils are often in this category.
Poor	3 - 5	5 - 12	5,000	Fine silty sands, clays, silts, organic soils. CL, CH, ML, MH, CM, OL, OH soils are often in this category.

Pavement Structure

All recommended HMA mix designations correspond to standard HDOT mixes (State mixes).
"Aggregate base" refers to crushed aggregate untreated base. The HDOT "aggregate for untreated base" meets the intended definition of "aggregate base".
The minimum recommended crushed aggregate base thickness is 4 inches. Aggregate layers less than 4 inches thick are possible, however (1) they do not add much strength to the overall pavement structure, (2) fines from the underlying subgrade may contaminate a substantial portion of the layer and inhibit drainage, (3) they are difficult to compact, (4) they are frequently subject to quantity overruns and (5) it is difficult to construct and maintain smoothness in aggregate layers thinner than 4 inches.
The minimum recommended HMA layer thickness is 2 inches. Pavement layers thinner than about 2-3 times the nominal maximum aggregate size may be difficult to compact, tear under the screed, and rollers may crush the larger particles during compaction. Because of its smaller nominal maximum aggregate size, State Mix V can be laid in thinner layers (down to about 0.75 inches minimum thickness).
For many of the recommended structural designs presented here traffic is not the controlling factor. For lower volume roads, parking lots and recreational facilities considerations such as HMA aging, constructability and subgrade conditions are primary concerns.

Material Substitutions

ACB can be substituted for crushed aggregate. Structurally, ACB is about three times as strong as an untreated granular base. The ACB page lists important substitution considerations.
0.5 inch Superpave can be substituted for State Mix IV. See Superpave Use for more guidance.
In some situations, ACB can be substituted for a State Mix III or State Mix IV within the middle or bottom of the pavement structure. However, the appropriateness of this substitution depends on many other considerations (e.g., maintaining a thick enough surface course, subsurface drainage, etc.). Therefore, this substitution should only be undertaken after consulting your local HAPI member for further guidance.

Other Information

If a bus route is anticipated on a particular low traffic pavement such as a residential street or collector it will probably control the structural design. Therefore, pavements with bus routes or anticipated bus routes should be designed using an approved design procedure. Otherwise, the heavy bus traffic may cause premature pavement failure.
All recommended designs in this section were checked using the 1993 AASHTO empirical structural design equation using the following values: Reliability = 75%, S_o = 0.50, ΔPSI = 2.0, design life = 20 years.