Civotec Blog

Pavement Is a Structural System

Pavement isn’t just asphalt or concrete laid on the ground. It’s a layered structural system designed to distribute loads from vehicles down into the subgrade soil. The performance of a pavement section depends heavily on the strength of the materials used in each layer, the anticipated traffic loadings, and the characteristics of the native soil.

A typical flexible pavement section (i.e., asphalt pavement) includes:

• Surface course (asphalt)

• Base course (crushed stone or stabilized material)

• Subgrade (existing or prepared native soil)

Rigid pavements, like concrete, act more like slabs and rely less on base thickness, but their design still considers subgrade behavior and load transfer.

Understanding these layers helps architects avoid unintentional issues during early design, such as locating heavy truck zones over unsuitable soils or under-designed pavement sections.

Traffic Loading Drives Design Thickness

Pavement design always begins with understanding the anticipated traffic loads. A driveway to a small office building will require very different pavement than a truck court behind a distribution center. The number, frequency, and type of vehicles—especially heavy trucks and turning movements—drive design decisions.

Engineers use industry-standard methods such as the AASHTO pavement design procedure or TxDOT’s pavement design guidelines to calculate required thicknesses based on:

• Equivalent single axle loads (ESALs)

• Subgrade strength (California Bearing Ratio or resilient modulus)

• Design life (typically 20 years)

• Desired level of reliability and serviceability

As an architect, flagging zones that will experience different traffic intensities—e.g., entry drives, ADA-accessible parking, dumpster pads, fire lanes—early in design allows the engineer to assign appropriate pavement sections and avoid surprises later.

Soils and Subgrade Conditions Matter

The soil beneath the pavement system—the subgrade—plays a pivotal role in how the pavement performs over time. Weak, expansive, or moisture-sensitive soils can lead to cracking, rutting, and long-term failure if not addressed properly.

Pavement design should always be preceded by a geotechnical investigation, which includes:

• Soil classification and strength testing

• Identification of expansive clays or organic materials

• Groundwater depth

• Seasonal moisture variation

Where poor soils are encountered, mitigation options may include overexcavation and replacement, lime or cement stabilization, or the use of geogrids to reinforce the base layer. Architects should coordinate early geotechnical studies in the project schedule, especially for sites with known soil issues or limited grading flexibility.

Concrete vs. Asphalt: Not Just a Visual Choice

While aesthetics often drive initial pavement material discussions, performance and cost factors should guide the final decision between asphalt and concrete. Each has advantages depending on use and budget.

Asphalt is flexible, lower-cost upfront, and easier to repair—but has a shorter lifespan and may rut under heavy loads. Concrete is more durable, resists deformation under trucks, and often requires less maintenance, but comes with higher initial costs and longer cure times.

For high-traffic or heavy-load areas like fire lanes, truck docks, or dumpster pads, concrete is typically recommended. For lighter-use parking areas and access drives, asphalt is usually sufficient. In mixed-use designs, combining both can optimize performance and cost.

ADA Compliance and Surface Drainage

Accessible routes, parking stalls, and curb ramps must comply with the Americans with Disabilities Act (ADA). Pavement slope, smoothness, transitions, and joint detailing are all part of this compliance.

Architects should coordinate with the civil engineer to ensure that:

• Slopes in accessible areas are less than 2% in any direction

• Transitions at ramps or curbs are smooth and meet maximum slope standards

• Surfaces are stable, firm, and slip-resistant

In addition to accessibility, proper surface drainage must be accounted for. Flat pavement areas are prone to ponding, which accelerates deterioration. Slopes of 1.5% to 2% are ideal for most parking areas to promote drainage without creating accessibility issues.

Coordination with Site Grading and Utilities

Pavement design doesn't occur in a vacuum. It must integrate with site grading, utilities, and stormwater infrastructure. Changes to finished floor elevations, retaining wall locations, or utility alignments often ripple into pavement geometry.

Key coordination points include:

• Catch basin and manhole locations in relation to slopes and curb alignments

• Minimum cover requirements for utility trenches under pavement

• Transitions between rigid and flexible pavement at utility crossings

• Pavement tie-ins to sidewalk and building entrances

Bringing the civil engineer into design development early helps prevent grade conflicts and allows for better planning of pavement slopes, joint locations, and storm drain tie-ins.

Life-Cycle Cost and Maintenance Considerations

Initial construction cost often drives decision-making in pavement selection, but architects involved in institutional or public projects should also consider life-cycle costs. A pavement section that requires frequent patching, resurfacing, or reconstruction may ultimately cost more over 20 years than a more robust solution implemented up front.

Concrete pavements, for example, have a higher upfront cost but lower maintenance needs, while asphalt may require overlays or repairs every 8–10 years, depending on traffic and climate. Owners should be made aware of these tradeoffs so they can make informed budget decisions.