San Antonio sits on the Blackland Prairie, where the clay can swell up to 10% in volume from dry to saturated. That statistic is not academic; it is the reason a warehouse floor in the Medical Center area cracked six months after pour, or why a Loop 1604 connector ramp showed corner breaks before the striping was even laid. Rigid pavement design here means confronting the soil first. We run Atterberg limits and sulfate content on every subgrade sample before the first joint spacing is calculated, because a PCC slab that ignores the underlying shrink-swell cycle is a liability, not an asset. For projects near the recharge zone, combining the slab analysis with in-situ permeability testing tells us whether subgrade drainage will undermine the pavement edge over time.
A rigid pavement slab in San Antonio lives or dies by its subgrade moisture control: get the drainage right and the concrete delivers forty years; ignore the clay and you will see cracking in the first drought cycle.
Methodology and scope
Local ground factors
The Eagle Ford shale and expansive clay that underlie much of San Antonio create a double threat for rigid pavements: differential heave during wet winters and shrinkage fissures during the long, dry summers. We have measured vertical movement of over two inches across a single slab panel on untreated subgrade off Highway 281. That kind of displacement concentrates stress at the corners, where most rigid pavement failures initiate. The other risk is sulfate attack on the cement-treated base; groundwater in parts of Bexar County carries enough sulfates to degrade a standard CTB in under five years. Our lab runs ASTM D516 sulfate content on water and soil samples, then specifies Type V cement or a geotextile separation layer when concentrations exceed 0.1%. Ignoring these geochemical factors turns a 30-year design life into a 7-year maintenance headache.
Regulatory framework
ASTM C78 – Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading), ASTM D2487 – Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), AASHTO 1993 Guide for Design of Pavement Structures, ASTM C1435 – Standard Practice for Molding Roller-Compacted Concrete in Cylinder Molds
Associated technical services
Subgrade Characterization and Stabilization Design
Soil borings across the project footprint, Atterberg limits, sulfate and chloride testing, and compaction curves. We design the lime or cement stabilization dosage to bring the subgrade modulus up to spec and keep it there through San Antonio’s seasonal moisture swings.
Concrete Mix Design and Field Verification
Lab trial batches with local aggregates, flexural beam testing at 7 and 28 days, and field coring during placement to verify thickness, air content, and compressive strength. We also run joint layout reviews to minimize random cracking.
Typical parameters
Frequently asked questions
What slab thickness do you typically specify for an industrial warehouse in San Antonio?
For a warehouse with forklift traffic and rack loading, most of our designs fall between 8 and 10 inches of plain jointed concrete over a 4- to 6-inch cement-treated base. The final number depends on the subgrade k-value we measure on site, the axle loads the owner expects, and the modulus of rupture the mix can deliver at 28 days.
How do you handle the expansive clays during rigid pavement design?
We classify the soil per ASTM D2487, run swell-consolidation tests, and check the plasticity index. If the PI is above 25, we almost always specify a stabilized subgrade — usually 6 to 8 percent cement or lime by weight — and often add a moisture barrier detail at the pavement edge to keep the subgrade moisture content more uniform through the year.
Do you provide joint layout and detailing recommendations?
Yes, the joint plan is part of every rigid pavement design we deliver. We size the panels based on the slab thickness and the anticipated curling stresses, specify dowel bars at construction joints for load transfer, and detail isolation joints where the slab meets columns, pits, or existing structures.
What does a typical rigid pavement design package cost in the San Antonio area?
For a standard commercial or light industrial project, the design package — including subgrade investigation, mix design, flexural testing, and the final pavement report — typically runs between US$2,050 and US$5,660 depending on the number of borings, the complexity of the loading, and how many trial batches are needed.
Can you test an existing rigid pavement to determine why it is failing?
We do forensic pavement investigations regularly. We core the slab to check thickness and compressive strength, run a falling weight deflectometer test to map the load transfer at joints, and open test pits to see what the subgrade looks like. The report identifies whether the problem is subgrade movement, poor concrete quality, joint locking, or something else.