Class C & Class F Fly Ash in Texas

What Is Class C Fly Ash?

Class C fly ash is produced from burning sub-bituminous or lignite coal. It contains higher calcium oxide (CaO) content — typically 20% or more — which gives it self-cementing properties. These properties make Class C fly ash highly effective for soil stabilization, road base treatment, and as a supplementary cementitious material (SCM) in concrete mixes.

In Texas, Class C fly ash is specified under TxDOT DMS-4610 and is used extensively for fly ash soil treatment (Item 260) and fly ash treated base (Item 265). Its high calcium content means it reacts with clay soils more aggressively than Class F, producing faster strength gain with lower application rates.

What Is Class F Fly Ash?

Class F fly ash is produced from burning bituminous or anthracite coal. It contains low calcium content — typically less than 10% CaO — and requires an activating agent such as lime or Portland cement to develop its pozzolanic properties. Class F fly ash is widely used in ready-mix concrete for improved workability and long-term durability, and it is the preferred fly ash type for oilfield well cementing applications.

TxDOT DMS-4615 governs the use of Class F fly ash in concrete applications on Texas highway projects. Class F fly ash also meets ASTM C618 requirements for use as a pozzolan in concrete.

TxDOT Specifications for Fly Ash in Texas

All fly ash supplied by Hasten Chemical meets the following TxDOT and ASTM standards:

• DMS-4610 — Fly Ash and Other Pozzolans for Soil Treatment
• DMS-4615 — Fly Ash for Use in Concrete
• Item 260 — Lime, Fly Ash, or Cement Treatment (subgrade)
• Item 265 — Fly Ash Treated Base
• ASTM C618 — Standard Specification for Coal Fly Ash and Natural Pozzolan

Applications for Class C and Class F Fly Ash

Concrete Mix Design (SCM Replacement)

Fly ash replaces 15–35% of Portland cement in concrete mixes, reducing material cost while improving workability, reducing heat of hydration, and increasing long-term compressive strength. Hasten Chemical supplies fly ash to ready-mix plants, precast operations, and batch plants across Houston and Texas.

Soil Stabilization and Subgrade Treatment

Class C fly ash is one of the most cost-effective stabilization agents for Texas expansive clay soils. Applied at 6–12% by dry weight of soil, fly ash increases bearing capacity, reduces plasticity index (PI), and prevents moisture-driven heave. It is commonly used for TxDOT highway subgrade treatment and commercial site preparation.

Fly Ash Treated Base (Road Base)

Fly ash treated base (Item 265) uses Class C fly ash to stabilize existing base material in place, providing a durable, bound layer that resists rutting and moisture infiltration. This is a cost-effective alternative to full base replacement on Texas roads and highways.

Class F Fly Ash for Oilfield Cementing

Class F fly ash is widely used in oilfield well cementing slurries across Texas and the Permian Basin. Its low calcium content and controlled particle size make it suitable for extending cement slurries, reducing cost per well, and meeting API well cementing specifications.

Bulk Fly Ash Delivery Across Texas

Hasten Chemical delivers Class C and Class F fly ash in pneumatic bulk tanker loads to project sites throughout Texas — including Houston, Dallas/Fort Worth, San Antonio, Austin, Midland, and the Permian Basin. We work with contractors, engineers, DOT projects, and private developers.

Contact Hasten Chemical today for pricing, material certifications, and delivery scheduling. Call or submit a quote request and our team will respond within one business day.