Paving Subgrade · North Texas
Paving Subgrade Preparation in Dallas-Fort Worth & North Texas
Pavement fails from the bottom up. IRONWILL Earthworks builds paving subgrade to the geotechnical report and the client’s specification — proof rolled, moisture conditioned, stabilized with lime, cement, cement slurry, fly ash or CKD, and capped with imported flexible base.
Lime stabilization
Cement & cement slurry
Fly ash & CKD
Flex base import
Proof rolling
Built to both specs
The geotechnical report and the client’s
Five stabilizers, one call
Lime, cement, slurry, fly ash, CKD
Proof rolled first
Soft spots found before the paver arrives
Handed over paving-ready
Grade, density and moisture documented
Why it exists
Pavement fails from the bottom up
Rutting under the wheel paths. Alligator cracking that spreads a little further every summer. Potholes that come back in the same spot after every repair. Almost none of that is a problem with the asphalt or the concrete — it is the layers underneath giving way, and no amount of surface thickness fixes a subgrade that moves.
North Texas makes the problem worse from two directions at once. The metroplex sits on expansive clay that swells and shrinks with the seasons, and the pavements built on it carry loaded trucks, fire apparatus and constant traffic. IRONWILL Earthworks is a North Texas earthwork contractor. We prepare paving subgrade to the geotechnical recommendations and to whatever the client’s specification requires on top of them.
Below: what subgrade preparation covers, how the subgrade differs from the base course, which stabilizer suits which soil — lime, cement, cement slurry, fly ash or cement kiln dust — what flexible base import involves, and what gets tested before the paving crew shows up. If you have paving coming up, send us the report and the spec.
Definition
What is paving subgrade preparation?
Paving subgrade preparation is the work of turning the ground beneath a pavement into a uniform, load-bearing platform that will carry the base course and the surface above it for the life of the pavement. It covers proof rolling and undercutting unsuitable material, conditioning the soil to a specified moisture content, chemically stabilizing it with lime, cement, fly ash or cement kiln dust, importing and compacting flexible base, and testing each layer to the density and grade the specification requires.
A pavement section is a stack, and every layer in it is designed against an assumed strength for the layer below. The structural design that produced “eight inches of base and three inches of asphalt” assumed a subgrade that behaves a particular way. Subgrade preparation is the work of making the ground behave that way in reality.
It is also where uniformity matters more than raw strength. A subgrade that is consistently adequate outperforms one that is excellent in three places and soft in the fourth, because pavement distress starts at the weak spot and spreads outward from it. Finding those spots — and removing them — is most of the job.
Often confused
Subgrade, stabilized subgrade and base — what’s the difference?
You can add thickness to the asphalt. You cannot pave over a subgrade that moves.
Subgrade
The natural or prepared soil the whole pavement structure sits on. It carries every layer above it, and it is the layer the pavement design assumed a strength for. On North Texas clay it is also the layer most likely to move.
Stabilized subgrade
The same soil after chemical treatment — lime, cement, fly ash or CKD mixed into it to reduce plasticity, raise strength and cut the swell potential. Same dirt, different behavior, and a stable platform for the base above it.
Flexible base — IRONWILL
Imported crushed aggregate placed and compacted on top of the prepared subgrade. It spreads wheel loads over a wider area and lets water drain out rather than sit at the soil line. Commonly specified on Texas work to TxDOT Item 247.
The three are priced and built differently, and confusing them is expensive. Stabilization is measured by area and treatment depth and includes mix design, mellowing time and testing; flexible base is measured by the ton and includes haul. A bid that assumes untreated subgrade under a spec that calls for twelve inches of lime treatment is not a cheaper bid, it is a different job.
Scope
What paving subgrade preparation includes
Which of these a project needs is decided by the geotechnical report and the paving specification, not by preference. These are the operations, in the combination the soil and the pavement design call for.
Proof rolling and undercut
The subgrade is proof rolled and watched before anything is built on it. Areas that rut, pump or deflect are marked, undercut to competent material and replaced — because a soft spot found now costs a truckload of fill and a soft spot found later costs a lane.
Moisture conditioning
Discing, watering or aerating the subgrade full depth until it sits in the specified moisture window, then holding it there through compaction. Nothing else on this list works if the moisture is wrong.
Lime stabilization
The standard treatment for high-plasticity North Texas clay. Lime is spread at the tested rate, mixed full depth, mellowed and remixed, then compacted — reducing plasticity and producing a workable platform for the base.
Cement and cement slurry stabilization
Cement treatment for granular and low-plasticity soils, applied dry or as a slurry. Slurry application eliminates the dust plume, meters the rate accurately and keeps work moving on windy days and beside occupied buildings.
Fly ash and CKD treatment
Self-cementing Class C fly ash and cement kiln dust as alternative stabilizers where the soil, the specification, the schedule or local material availability makes them the better answer than lime or cement.
Flexible base import and compaction
Crushed limestone base hauled in, spread, moisture conditioned and compacted in lifts to the specified density and grade — the layer the paving crew actually works off.
Methods
Stabilization methods and when each one applies
We install all of them, which means the recommendation is not shaped by what we happen to own. The soil, the specification and the schedule choose the stabilizer; the laboratory sets the rate.
Lime stabilization
The workhorse on high-plasticity clay. Lime reacts with the clay minerals to reduce plasticity, cut swell potential and raise strength. The application rate comes from laboratory testing — commonly an Eades-Grim pH series (ASTM D6276) — and road-mixed lime treatment on Texas work is typically specified to TxDOT Item 260, plant-mixed to Item 263.
Cement stabilization
Better suited to granular and low-plasticity soils, where cement builds strength directly rather than altering plasticity. It gains strength quickly, which helps the schedule and constrains the field: cement-treated material has to be mixed, shaped and compacted inside a short window. Specified to TxDOT Item 275 road-mixed, Item 276 plant-mixed.
Cement slurry application
The same cement, pre-mixed with water and applied as a slurry rather than spread dry. There is no dust plume, the application rate is metered accurately across the width, and the work keeps moving on windy days and next to occupied buildings, live traffic and finished construction where dry spreading would not be acceptable.
Fly ash treatment
Self-cementing Class C fly ash is widely available in Texas and can stabilize soils that respond poorly to lime alone. It sets fast, so the window between mixing and final compaction is shorter than anything else on this list and the day has to be planned around it. Road-mixed fly ash and lime-fly ash treatment is specified to TxDOT Item 265.
Cement kiln dust (CKD)
A by-product of Portland cement manufacture that carries free lime, CKD is used to modify and stabilize marginal soils. It suits projects where the soil responds to it, where availability favors it, or where the client’s specification names it. Like every other stabilizer here, the rate comes from a mix design rather than a rule of thumb.
Choosing between them
Plasticity index, gradation, soluble sulfate content, the treatment depth, the paving schedule and what the client’s specification permits all narrow the list before anyone picks. The mix design settles it. Habit is not a selection method, and the wrong stabilizer is worse than none.
One screening step belongs ahead of any lime decision in this region: soils carrying high soluble sulfate content can react with lime and water to form expansive minerals, heaving the pavement rather than supporting it. Sulfate testing is inexpensive — TxDOT’s colorimetric method is Tex-145-E — and where the numbers come back high the answer is a different stabilizer or a different section. That determination starts with site analysis and the geotechnical engineer.
Imported material
Aggregate import and flexible base
Above the prepared subgrade sits the base course, and on most North Texas paving that means crushed limestone flexible base hauled in from a regional pit. Its job is to spread concentrated wheel loads across a wider area of subgrade and to let water move out of the section rather than collect at the soil line.
Base is not a commodity that can be swapped freely. Gradation, plasticity and strength requirements vary by grade and by specification — Texas work usually references TxDOT Item 247 — and the material has to be placed in lifts, moisture conditioned and compacted to the specified density rather than dumped, bladed and driven on. Base placed dry never reaches density, and base that holds water fails from inside no matter how thick it is.
Aggregate import is also the answer when treatment is not. Where the soil will not respond to a stabilizer, or where the schedule cannot absorb mellowing time, undercutting and replacing with imported material is frequently the faster and more certain route to the same result.
Flexible base commonly specified to TxDOT Item 247
Crushed limestone hauled from North Texas pits
Placed in lifts, not dumped to full depth
Moisture conditioned before compaction, not after
Undercut and replace where the soil will not improve
Kept drained — trapped water is what fails a base
Verification
How a finished subgrade is verified
A subgrade is released on evidence, not appearance — and the paving crew is entitled to a documented platform, not a graded surface that looks ready.
The report and the specification
Two documents govern a paving subgrade: the geotechnical report and the client’s paving specification. They do not always agree on treatment depth, rate or required density. Where they differ we build to the stricter of the two and say so in writing before mobilizing, rather than discovering it at the density test.
Proof rolling
A loaded tandem-axle dump truck driven across the subgrade while it is observed. Areas that rut, pump or visibly deflect are marked, undercut and replaced. It is the fastest way to find the soft spots that sit between test locations, and on paving work it is standard practice rather than an extra.
Density and moisture testing
Field density and moisture measured against the laboratory moisture-density relationship — on Texas work commonly Tex-114-E for subgrade soils and Tex-113-E for base materials, with in-place density by Tex-115-E or a nuclear gauge to ASTM D6938. Both density and moisture have to be in range for a lift to pass.
Plasticity and sulfate testing
Plasticity index tells you whether lime is the right stabilizer and roughly how much work the soil needs; soluble sulfate content tells you whether lime is safe to use at all. Neither is expensive, and both are far cheaper than treating a subgrade twice.
How it works
Our paving subgrade process
Each step depends on the one before it being right, and the stabilizer chosen in step four decides how much of the day step five has to happen in. This is the order we work in and where the schedule time actually goes.
01
Review the report and the specification
Treatment type, depth and rate, required density, base thickness and material grade all come out of these two documents. Conflicts between them get resolved before mobilization rather than in the field.
02
Strip, shape and proof roll
Topsoil, organics and unsuitable fill come off, the subgrade is brought to rough grade, and it is proof rolled and watched. Soft areas are undercut and replaced before anything is built on top of them.
03
Moisture condition the subgrade
Disced, watered or aerated full depth until the soil sits inside the specified moisture window. On expansive clay the target is frequently above optimum, so the swell is taken out before the pavement goes down.
04
Spread, mix and mellow
The stabilizer goes down at the tested rate — lime, cement, cement slurry, fly ash or CKD — and is mixed full depth. Lime mellows and is remixed; cement, slurry and fly ash are worked and compacted inside their much shorter windows.
05
Compact, test and trim to grade
Compaction with the right roller for the material, then density and moisture testing against the specification. Failing areas are reworked and retested, and the treated subgrade is trimmed to line and grade.
06
Place base and hand over
Flexible base hauled in, spread in lifts, moisture conditioned and compacted to the specified density and grade — then handed to the paving contractor with the test results that go with it.
Why it matters
What a properly prepared subgrade prevents
Pavement distress is legible. Rutting in the wheel paths points at a subgrade or base that is deforming under load. Alligator cracking points at a section that has lost support from below. Potholes that reappear in the same place after every patch point at water reaching a layer that cannot tolerate it. None of those are surface problems, and none of them are fixed at the surface.
The economics are lopsided. Subgrade preparation is a modest fraction of a paving budget; a parking lot or roadway that reaches half its design life and needs full-depth reconstruction is not. Owners rarely see the subgrade — they see the pavement five years later, which is the same thing measured differently.
There is a schedule argument as well. A subgrade that passes on the first round of testing releases the base, and the base releases the paving, on the dates everyone planned around.
Pavement that reaches its design life, not half of it
Rutting and alligator cracking designed out at the subgrade
Uniform support under truck and fire-lane loading
No soft spots discovered by the paving crew
Density, moisture and grade documented for the owner
A base that drains instead of holding water
Have paving coming up?
Send the geotechnical report, the paving specification and the area to be paved. We will tell you which stabilizer the soil calls for, what the treatment and base actually cost, and how many days mellowing and testing add to the schedule.
Who we work for
Paving projects we support
From a retail parking lot to a municipal roadway, the questions are the same: what does the soil do, what does the specification require, and what has to be true before the paver arrives.
Parking lots and drive aisles
Commercial, retail and multifamily paving where the drive aisles take the loading and the stalls take the scrutiny.
Fire lanes and truck courts
Heavy-duty sections carrying fire apparatus and loaded trailers, where the pavement design assumes a subgrade that will not deform under a concentrated axle.
Public streets and municipal roadways
City and county paving built and documented to the owner’s specification and testing regime, often alongside construction management.
Industrial yards and laydown areas
Large paved and stabilized areas carrying containers, equipment and constant heavy traffic, where uniformity across the footprint is the whole specification.
Site access and haul roads
Stabilized running surfaces built early so the rest of the site work has somewhere to drive, and rebuilt into permanent pavement later.
Reconstruction and rehabilitation
Removing failed pavement, treating or replacing the subgrade that caused the failure, and rebuilding the section instead of resurfacing the symptom.
The IRONWILL difference
How we approach paving subgrade
Built to both specs
The geotechnical report and the client’s specification, with conflicts raised before we mobilize.
Every stabilizer in one scope
Lime, cement, cement slurry, fly ash and CKD — so the recommendation follows the soil.
Slurry when dust is not an option
Accurate rates and no plume, next to occupied buildings, traffic and finished work.
Handed over paving-ready
Grade, density, moisture and test results delivered with the subgrade.
Service area
Paving subgrade across Dallas-Fort Worth and North Texas
We prepare paving subgrade on commercial, industrial, multifamily and municipal projects throughout North Texas — the same expansive clay, the same specifications, the same short weather windows. Crews, water trucks, reclaimers and compaction equipment are based in Dallas.
If your site is in or around the metroplex, ask — it is usually in range.
Allen
Lucas
Melissa
Richardson
Lewisville
The Colony
Prosper
Celina
Little Elm
Rockwall
Mesquite
Grapevine
Flower Mound
Weatherford
Kaufman
Waxahachie
Wylie
Sherman
Collin County
Send with your inquiry
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Site address and area to be paved
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Geotechnical report and paving specification
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Required stabilizer, depth and rate
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Base thickness and material grade
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Target date for paving
FAQ
Paving subgrade preparation FAQ
What is paving subgrade preparation?
Paving subgrade preparation is the work of turning the ground beneath a pavement into a uniform, load-bearing platform that will carry the base course and the surface above it. It includes proof rolling and undercutting unsuitable material, moisture conditioning, chemical stabilization with lime, cement, fly ash or cement kiln dust, importing and compacting flexible base, and testing each layer to the specified density and grade.
What is the difference between subgrade, stabilized subgrade and base?
The subgrade is the soil the whole pavement structure sits on. Stabilized subgrade is that same soil after a chemical treatment has been mixed into it to reduce plasticity and raise strength. Flexible base is imported crushed aggregate placed on top of the prepared subgrade to spread wheel loads and drain the section. All three are separate layers with separate specifications and separate pay items.
Why does pavement fail when the subgrade is wrong?
Because every layer of a pavement is designed against an assumed strength for the layer below it. If the subgrade deforms under load or swells with moisture, the base loses support, the surface flexes further than it was designed to and cracking begins. That is what rutting in the wheel paths and alligator cracking are telling you, and neither can be repaired at the surface.
When is lime used instead of cement to stabilize subgrade?
Lime is used on high-plasticity clay, where it reacts with the clay minerals to reduce plasticity, cut swell potential and produce a workable platform. Cement suits granular and low-plasticity soils, where it builds strength directly. On Texas projects road-mixed lime treatment is commonly specified to TxDOT Item 260 and cement treatment to Item 275.
What is cement slurry stabilization and why use it?
Cement slurry stabilization uses the same cement, pre-mixed with water and applied as a slurry instead of spread dry. The advantages are practical: there is no dust plume, the application rate is metered accurately across the treatment width, and work continues on windy days and next to occupied buildings, live traffic and finished construction where dry spreading would not be acceptable.
What is fly ash stabilization and when does it apply?
Self-cementing Class C fly ash can stabilize soils that respond poorly to lime alone and is widely available in Texas. Its distinguishing characteristic in the field is speed: it sets quickly, so the window between mixing and final compaction is shorter than for lime or cement and the day has to be planned around it. Road-mixed fly ash and lime-fly ash treatment is specified to TxDOT Item 265.
What is cement kiln dust (CKD) and is it a real stabilizer?
CKD is a by-product of Portland cement manufacture that carries free lime, and it is used to modify and stabilize marginal soils. It is a legitimate option where the soil responds to it, where material availability or economics favor it, or where the client’s specification names it. As with lime, cement and fly ash, the application rate comes from a laboratory mix design rather than a rule of thumb.
How is the stabilizer application rate determined?
By laboratory mix design against the actual soil. For lime the usual method is an Eades-Grim pH series (ASTM D6276), which identifies the lowest percentage that holds the soil-lime mixture at the pH the stabilizing reaction needs. Cement, fly ash and CKD rates are established by strength and plasticity testing at trial percentages. Soluble sulfate content is checked before any lime decision, because high-sulfate soils can heave when lime is added.
What is flexible base and how is it specified?
Flexible base is imported crushed aggregate — in North Texas usually crushed limestone — placed and compacted over the prepared subgrade to spread wheel loads and drain the section. Gradation, plasticity and strength requirements vary by grade, and Texas work commonly references TxDOT Item 247. Thickness comes from the pavement design, not from a standard detail.
What is proof rolling on a paving job?
Proof rolling is driving a loaded tandem-axle dump truck across the prepared subgrade while it is observed. Areas that rut, pump or visibly deflect are marked, undercut and replaced. It finds the soft spots that sit between density test locations, and it is standard practice on paving work rather than an optional extra.