If you are bidding a TxDOT road project with soil stabilization, fly ash is likely on the table. Before you source material, you need to know what TxDOT requires: the right fly ash class, the right material certification, and the right mix design process.
The Governing Document: DMS-4615
TxDOT departmental material specification DMS-4615 is the controlling document for fly ash on TxDOT projects. It defines acceptable fly ash types, chemical requirements, and qualification procedures. Any supplier must certify their material against DMS-4615 before it can be used on a TxDOT job.
Class C vs Class F Under DMS-4615
- Class CS (equivalent to ASTM Class C) — higher calcium, self-cementing. Effective as a standalone stabilizer on most Texas soils.
- Class FS (equivalent to ASTM Class F) — lower calcium, pozzolanic only. Requires lime or another activator in most soils.
For most Texas subgrade projects, Class CS (Class C) fly ash is preferred because it reacts without an additional activator.
TxDOT Item 265: The Construction Specification
Item 265 — Fly Ash or Lime-Fly Ash Treatment (Road-Mixed) governs how fly ash is placed and mixed into subgrade soil. Key requirements:
- Fly ash must meet DMS-4615
- Mix design established per Tex-127-E before work begins
- Minimum compressive strength: 160 psi at 5-day cure at 100°F
- Mixing and compaction completed within 6 hours
- No work when air temp is below 40°F and falling
- Fly ash measured by the ton (dry weight as delivered)
Mix Design: Tex-127-E
Tex-127-E is TxDOT’s test method for lime and fly ash stabilization mix design. The engineer determines the optimum fly ash percentage and moisture content for the soil being treated. Contractors can propose a mix design, but the engineer must verify it before approval — so get your supplier’s material data sheet early.
What to Ask Your Fly Ash Supplier
- Does the material meet DMS-4615? (Get the current cert.)
- Is it Class CS or Class FS?
- What is the current chemical analysis (CaO, SiO₂, loss on ignition)?
- Can they deliver in bulk pneumatic tanker to your job site?
- What is lead time and minimum order?
Hasten Chemical: DMS-4615 Fly Ash Supply
Hasten Chemical supplies Class C and Class F fly ash meeting TxDOT DMS-4615 statewide. We provide material certifications and bulk delivery by pneumatic tanker across Texas. Contact us for pricing and availability, or learn more about our fly ash supply.
Pre-Qualification and Approved Source Lists
TxDOT maintains approved source lists for materials used on state projects. For fly ash, suppliers must be pre-qualified under DMS-4615 before their material can be specified or used on a TxDOT job. This pre-qualification process involves submitting chemical analysis data and having the material evaluated against DMS-4615 requirements.
Before committing to a fly ash supplier for a TxDOT project, confirm they appear on the current TxDOT approved source list and that their certification is current. Certifications must be updated periodically as fly ash chemistry can shift when the power plant’s coal supply changes.
Field Quality Control Requirements
Under TxDOT Item 265, the contractor is responsible for quality control during placement. Key field QC requirements include:
- Application rate verification: The engineer will check that fly ash is applied at the design rate (tons per square yard) before mixing
- Moisture control: Soil moisture must be within the range established by the Tex-127-E mix design during mixing and compaction
- Compaction testing: Density testing per Tex-114-E after compaction to verify the layer meets density requirements
- Strength verification: Field cores or lab specimens tested per Tex-127-E to verify 160 psi minimum compressive strength
- Curing protection: Treated subgrade must be protected from traffic and drying until the pavement structure is placed
Common Mistakes Contractors Make with TxDOT Fly Ash Projects
After working with Texas contractors on fly ash stabilization projects, the most common issues we see are:
- Using uncertified fly ash — Material from a supplier not on the TxDOT approved list will be rejected. Always verify certification before ordering.
- Ordering the wrong class — Specifying Class F fly ash when the project requires Class C (or vice versa). Read the spec carefully.
- No mix design before mobilization — Tex-127-E mix design must be approved before work starts. Don’t wait until you’re on the job to initiate this.
- Exceeding the 6-hour compaction window — Item 265 requires compaction within 6 hours of mixing. Plan your production accordingly.
- Late material delivery — Fly ash must be on site before mixing begins. Coordinate with your supplier on lead time and truck scheduling.
Frequently Asked Questions: TxDOT Fly Ash Specifications
What is TxDOT DMS-4615?
DMS-4615 is TxDOT’s departmental material specification for fly ash used in soil treatment. It defines Class CS (similar to ASTM Class C) and Class FS (similar to ASTM Class F) fly ash, sets chemical requirements, and governs the pre-qualification process for suppliers.
What is TxDOT Item 265?
Item 265 is TxDOT’s construction specification for fly ash or lime-fly ash (LFA) treatment of subgrade soils using the road-mixed method. It covers material requirements, mix design, application rates, mixing, compaction, and quality control.
What compressive strength does TxDOT require for fly ash-treated subgrade?
TxDOT Item 265 requires a minimum unconfined compressive strength of 160 psi, tested at 5 days curing at 100°F per Tex-127-E.
Does fly ash need to be pre-qualified before use on TxDOT projects?
Yes. The fly ash supplier must be on TxDOT’s approved source list under DMS-4615. Verify this with your supplier before ordering material for a TxDOT project.
Can Hasten Chemical provide DMS-4615 material certifications?
Yes. Hasten Chemical supplies Class C and Class F fly ash with current material certifications. Contact us for documentation and pricing on your TxDOT project.
