We set the stage for an ultimate resource that turns NCDOT-oriented specifications into practical choices for projects across the state.

Our aim is to align statewide expectations with the day-to-day work of planning, producing, and placing mix for durable asphalt pavement.

We outline major families—dense-graded, Stone Matrix, and open-graded—so teams can match project goals to the right construction focus.

This section previews key topics: design basics, air voids, density targets, lift thickness, and durability metrics that drive lifecycle results.

We also explain how material selection, aggregate balance, and binder choices affect constructability, long-term value, and safety on urban and rural corridors.

Finally, we preview testing, control strips, and documentation practices that verify compliance and show what success looks like on every project.

NCDOT asphalt pavement standards at a glance

We summarize the core pavement standards that link specification language to measurable field outcomes.

Our focus is on predictable results: smoothness, structural strength under traffic, and user safety. We also highlight the documentation and testing information needed for acceptance. Those records make responsibility traceable among owner, contractor, and plant.

At the construction stage, controls for density, temperature, and lift thickness drive long-term performance. Design choices should reflect expected axle load and turning movements in high-load areas. Weather windows and working conditions govern acceptable temperature ranges and night versus day operations.

Production and field QA require specific submittals that state percent recycled or used mix content, aggregate size, and unit targets. Field verification of density rolls into pay factors and performance risk, so teams must plan traffic staging and documentation across seasons to avoid rework and claims.

How hot mix asphalt fits into NCDOT projects

We describe how hot-produced surfacing serves as the structural backbone for most projects and when thinner, non-structural treatments make better sense.

Dense-graded, SMA, and open-graded within HMA

Dense-graded mixtures are our all-purpose choice for base and binder courses. They deliver predictable stiffness and ride quality under traffic.

SMA provides premium rut resistance with a coarse stone skeleton and modified binder. We use it on high-load corridors where long-term results matter.

Open-graded options improve drainage and reduce spray. They are best for surface courses where stormwater control and visibility are priorities.

Where HMA sits versus maintenance treatments

Hot mix asphalt adds structural capacity. By contrast, fog seals, slurry seals, and BSTs restore surface condition but rarely add strength.

We weigh design, layer sequencing, and expected surface condition to choose the right solution. When sustainability is a goal, reclaimed asphalt and RAP can be included under defined percent and content limits.

Across families, binder choice, aggregate gradation, and weight-based batching keep production consistent. Temperature control, compaction, and joint work remain central to achieving volumetric and density acceptance results.

Dense-graded mixes: the workhorse for NC pavements

For most structural layers, dense-graded designs offer the balance of durability and constructability teams need. We rely on them across heavy corridors and low-volume roads because they are versatile and straightforward to place.

Purpose and typical uses across pavement layers

We use dense-graded mix for base, intermediate, and surface lifts. Typical uses include structural lifts, leveling courses, and patching where consistent results matter.

Materials and gradation: well-graded aggregate, binder, RAP

Well-graded aggregate, the right binder grade, and controlled RAP content produce a balanced structure. Small changes in nominal size and binder content tune workability and finishability.

Permeability and quality considerations

Target air voids and tight gradation reduce permeability and protect underlying layers from moisture. Regular sieving, asphalt content checks, and temperature monitoring help us hit density and quality targets on site.

Stone Matrix Asphalt (SMA) for high-traffic surface courses

When traffic volumes climb and wheel path shear grows, we turn to Stone Matrix Asphalt to hold the line against deformation. SMA is a gap-graded surface designed to form a stone-on-stone skeleton that resists rutting on busy corridors and interstates.

Stone-on-stone contact and rutting resistance

The coarse aggregate skeleton transfers loads through stone contact rather than relying solely on binder. That skeleton minimizes lateral movement and delivers superior rutting resistance compared with conventional surface mixes.

Modified binder, fibers, and cost-effectiveness

We use modified asphalt binder and fiber additives so higher binder content does not drain down during transport or placement. Fibers stabilize binder content, reduce construction issues, and improve long-term moisture resistance.

Friction and tire noise benefits on interstates

SMA’s coarser texture improves wet weather friction and lowers tire-pavement noise. For high-speed corridors, that combination boosts safety and rider comfort while often justifying the higher per-ton cost through better lifecycle results.

Open-graded options: OGFC, ATPB, and permeable pavement

Open-graded solutions move water through the pavement surface to improve safety and visibility during storms.

OGFC surface courses to reduce splash and spray

OGFC is a thin surface layer that drains through its thickness to the underlying impermeable lift. It cuts splash and can lower tire-road noise by up to 10 dBA on high-speed corridors.

ATPB for drainage beneath structural layers

ATPB sits under dense layers or portland cement concrete to intercept and remove water. That protection reduces moisture-driven distress and preserves long-term results.

Permeable pavements and maintenance to prevent clogging

Permeable pavements store runoff in a graded base, which can reduce conventional drainage needs in the right area. Open-graded mixes use crushed stone and controlled aggregate gradation so voids flow without excess raveling.

We stress routine vacuum sweeping and limiting sediment tracking to keep voids open. Modified binder and tight production control help resist drain-down and keep friction and performance where we expect it.

Mix design essentials under NCDOT practices

This section ties volumetric targets and material choices to the on-site practices that produce consistent pavements. We focus on simple calculations and clear field guidance so lab design becomes reliable results in the lane.

Binder selection and modifiers for NC climate

We choose an asphalt binder to balance rutting resistance in summer and low-temperature cracking in winter. Modifiers or polymer blends are used where traffic and heat demand extra shear strength.

Volumetrics, nominal maximum aggregate size, and gradation

Air voids, VMA, and VFA are set so the pavement compacts predictably and resists permeability. Minimum lift thickness must be at least three times the nominal maximum size to avoid tearing and loss of density.

Lab targets: maximum specific gravity, unit weight, and results

Calculate maximum unit weight from Gmm × 62.4 pcf (for example, 2.500 × 62.4 = 156.0 pcf). Set density targets as percent of lab unit weight, percent of maximum unit weight, or via a control strip.

Document target temperatures, compaction curves, suggested rolling patterns, and RAP adjustments up front. We keep aggregate and materials control tight so the field mixture matches lab design and minimizes on-site changes.

Air voids, density, and durability: getting the numbers right

We focus on the practical numbers that control long-term pavement results. Proper air content and field density are the most reliable predictors of durability and early distress.

Target air void range and field density relationships

Compacted air voids between 3% and 7% strike the balance between stability and durability. Above 8%, interconnected voids let air and moisture in and cut service life.

Below 3%, the binder lacks room to accommodate movement; at 2% or less the material can become plastic and unstable.

Establishing density targets: lab, test strip, or unit weight

We set density targets using percent of laboratory unit weight, percent of maximum unit weight from Gmm, or a control strip that proves real-world results.

Thickness affects compactability, so crews must plan rolling patterns, temperatures, and timing to hit targets. We document cores, gauge checks, and acceptance data to confirm compliance and guide corrective action.

Nominal maximum aggregate size and lift thickness

Proper pairing of nominal maximum size and layer thickness keeps compaction efficient and cuts permeability risk. We use a simple rule to plan lifts so crews meet density and durability results.

Minimum lift guidance

Minimum lift thickness should be at least three times the nominal maximum aggregate size. This helps particles align during compaction and reduce surface voids and permeability.

Equipment and maximum lifts

Static steel-wheel rollers limit practical lifts to about 3 inches. Vibratory or pneumatic rollers let us place thicker lifts, commonly 6 to 8 inches, without losing compaction control.

Open-graded considerations

Open-graded materials behave differently. For permeable layers, compaction is less critical and maximum aggregate can be up to 80% of the lift thickness. That use improves drainage but needs careful surface protection.

Construction planning and verification

We set paver speed, screed temperature, and roller timing to hold target lifts. Field checks — depth gauges and cores — verify thickness for acceptance. Coordinate ties and cross slopes with adjacent concrete to avoid rework and extra cost.

Reclaimed asphalt pavement (RAP) in NCDOT mixtures

Reclaimed material can reduce cost and embodied carbon when we set percent limits and adjust binder choices for reliable results.

Percent RAP and binder grade adjustments per FHWA guidance

We follow the FHWA and Asphalt Institute framework: at 0–15 percent RAP no binder grade change is needed.

At 16–25 percent, select a virgin binder one grade softer on both high and low temperatures (for example, PG 64-22 to PG 58-28).

Above 25 percent, use blending charts to set the virgin binder grades so low-temperature performance remains adequate.

Performance considerations for wearing courses

Reclaimed asphalt stiffens a batch, so binder adjustments offset cracking risk and preserve long-term results.

Some owners restrict RAP in surface layers to protect friction and durability. Polymer-modified binder in RAP rarely causes unique plant problems, but we still handle stockpiles carefully.

Document percent, binder rationale, and trial-blend results in the design submittal. Run validation mixes, control stockpile variability, and verify batch percentages in the plant and lab to ensure the expected results and sustainability gains.

Compaction temperatures and workability for hot mix

Keeping the mixture within its designed temperature band is one of the simplest ways to protect long-term results and meet density targets.

Binder grade sets the mixing and compaction windows. Less viscous binders need lower temperatures; more viscous binders require higher heat. Avoid changes greater than ±25°F from the target to prevent poor density and finish.

Weather and site conditions shift the workable window fast. Ambient air, base temperature, and wind force us to slow the paver or speed rolling to hold compaction quality.

Modified asphalt binder needs vendor guidance on temperature and dwell times. Follow supplier information closely and track silo, truck, and screed temperatures so results stay uniform from plant to laydown.

Reheated specimens often compact to higher lab air voids than as-produced samples. We develop project-specific correlations and run test strips to align roller patterns and target density before full production.

Document temperature and density lot-by-lot, check tarp integrity, limit haul delays, and adjust roller timing. Small changes in percent or content can restore workability and keep results on track, even during cool nights.

Surface friction and safety in North Carolina conditions

Choosing the right surface course directly shapes visibility, braking, and noise outcomes on high-speed routes. We weigh safety, maintenance burden, and budget when choosing a final course for busy corridors.

Friction course choices and where they fit

OGFC drains water through the surface to cut splash and spray. That reduction improves tire-pavement friction and driver control in heavy rain, and it can lower tire-road noise by up to 10 dBA at highway speeds.

Dense-graded textures deliver durable friction when we select angular, polish-resistant aggregate. They work well where spray control is less critical or where simpler upkeep is a priority.

Design factors that drive lasting performance

Aggregate angularity and polish resistance underpin long-term results. Mixture balance—binder content and fines—affects texture retention and guards against flushing or raveling over time.

Traffic speed and volume matter. High-speed routes often benefit from OGFC for self-cleaning pores and reduced hydroplaning risk. Lower-speed, high-wear corridors can favor dense-graded courses for durability and simpler maintenance.

We recommend routine friction and texture tests and a simple decision matrix that weighs friction, noise, maintenance, and budget to guide final surface selection.

Traffic loading, weather, and subgrade: selecting the right mix

Selecting the right surface starts with understanding how vehicles, temperature swings, and subgrade support interact. We balance stiffness and fatigue resistance so lanes resist rutting without cracking prematurely.

Load distribution, stiffness, and temperature sensitivity

We size layers around expected axle load, turning movements, and speed. Heavy turning loads need a stiffer layer or thicker section to spread the load and limit deformation.

Seasonal swings and rainfall drive binder selection. Cooler nights or coastal humidity push us to use binders and additives that keep the mixture workable and resistant to low-temperature cracking.

Subgrade quality changes layer choices. Weak support calls for thicker base and a durable surface family. In firm areas, a thinner structural section can still meet performance goals.

Control air and voids to keep moisture out and extend service life. We run iterative design checks, involve geotechnical inputs early, and monitor early-life performance so our design choices deliver the expected results.

Quality management: labs, certifications, and QMS in NC

Accurate testing and disciplined documentation are the backbone of consistent construction results. Certification is not the only route to valid data, but it raises confidence by showing equipment calibration, technician competence, and documented systems meet audited requirements.

Why certification matters for test accuracy and compliance

We rely on certified labs to reduce re-testing and disputes by aligning procedures and traceability with contract needs. That clarity shortens acceptance cycles and protects project schedules.

Synchronizing plant and field testing keeps the production properties aligned with design intent. We document chain-of-custody, timestamps, and method references so results stay defensible.

Routine internal audits, round-robin checks, and retained materials let us validate weight and unit conversions across crews and labs. When results fall outside limits, we follow a clear escalation path that minimizes downtime and restores compliance quickly.

Finally, we recommend early owner collaboration to confirm testing requirements and acceptance plans. That shared information makes quality systems practical and keeps materials and design feedback loops active for continuous improvement.

Materials and additives: fibers, mineral fillers, and specialty binders

We focus on practical additives that stabilize binder and protect the pavement skeleton under real-world hauling and paving.

Minimizing drain‑down and enhancing durability

Fibers and mineral fillers absorb excess binder and hold it in the stone matrix. That control reduces drain‑down during long haul and placement, so the surface keeps the intended binder content and texture.

Specialty binders and modifiers increase rut resistance, improve fatigue life, and lower the risk of low‑temperature cracking. We select them based on traffic severity, climate, and subgrade support.

Selection, dosing, and field checks

Pick additives that boost adhesion and moisture resistance without hurting workability. Introduce fibers in the pugmill or in the binder stream per supplier guidance to ensure uniform dispersion.

Document the intended amount and where it is added in the design. Run a pilot lane to verify dispersion, dosing, and acceptance tests before full production.

Compatibility and practical tips

Confirm aggregate chemistry and surface area so the additive and mineral skeleton act together to meet stiffness goals. Adjust binder grade or modifier type to tune cracking versus rutting for local conditions.

In the field, confirm delivery with simple checks: weigh additive loads, inspect stockpiles, and run short production samples to verify content and performance.

From design to construction: best practices for paving and compaction

We bridge design intent and field action by locking in roller types, temperature windows, and acceptance methods before full production. A short control strip proves roller passes, paver speed, and head of material that reliably meet unit and weight targets under the day’s conditions.

Rolling patterns and control strips

Build a control strip at project start. Use it to set breakdown, intermediate, and finish passes and to record mat temperature ranges that give the best results.

Acceptance, joints, and troubleshooting

Translate lab percent and unit targets into clear field checks: gauge readings, cores, and lot reports for pay decisions. For joints, ensure proper tack, overlap, and immediate rolling to avoid cold seams and permeability.

If percent compaction falls short, adjust roller speed, add passes, change amplitude or frequency, or raise mix temperature slightly. Keep daily logs and run short team huddles to refine patterns as conditions shift. That discipline reduces rework and delivers the construction results owners expect.

Where to find more NCDOT/CAPA resources and training

We point readers to a compact set of resources that deliver practical information for field crews and spec writers. Use these to link lab targets to better paving results.

Workshops, webinars, and manuals

Check CAPA annual meetings and archived workshop presentations for sessions on mix design, paving best practices, and QMS updates that align with current acceptance criteria.

Attend hands-on topics like Best Practices Paving & Compaction and Tack Coat Problems & Solutions to convert classroom information into predictable field results.

Keeping teams current

Use Roadway Profile Testing materials to tie smoothness specs to equipment setup. Join annual summits and webinars to follow changes in materials, performance approaches, and asphalt innovations.

Find QMS Manual updates for roles, testing frequencies, and acceptance pathways that apply across our area projects and pavements work.

Share lessons learned, pair classroom sessions with ride-alongs, and use post-project results to refine SOPs and future training plans.

Asphalt mix types ncdot guide: our practical takeaways for today

We close with a short action plan that turns design intent into repeatable field results.

Confirm the selected mix family, binder grade, and aggregate structure to match climate and load. Verify percent targets and unit weight before production starts.

Keep compaction tight: aim for air voids between 3% and 7%, use test strips, and lock in rolling patterns. Respect lift thickness rules so size and thickness support proper density and durable pavement surfaces.

Use SMA for heavy rutting risk, OGFC where spray matters, and dense-graded for daily work. Manage RAP with FHWA-informed binder adjustments, control temperature from plant to paver, and document QC/QA with certified labs.

Finally, confirm materials, execute compaction, record results, and review performance to improve future projects.