TENNESSEE'S OWN DOT
ALREADY STUDIED THIS.
TDOT funded a two phase study that evaluated 76 local aggregate sources for alkali silica reaction. At least 65 percent of the samples tested came back reactive, TDOT documented ASR distress in eight existing Tennessee structures, and the agency recommended changing its own concrete specification as a result. ASR is not theoretical in Tennessee. It is institutionally documented by the state's own transportation agency, with a report number.
Documented at the agency level. In dispute at the residential level.
Tennessee's ASR exposure is institutionally documented in the agency record. State-DOT-grade research does the institutional heavy lifting. The regional coal-supply story sits downstream of that record as the explanation for why the protection itself is in regulatory motion.
Report RES2016-03. 76 sources. 65 percent reactive.
The Tennessee Department of Transportation, with the Federal Highway Administration, funded a two phase research program on the ASR reactivity of local aggregates, carried out by the University of Tennessee Knoxville and published in November 2021 as TDOT Report RES2016-03. In Phase I, 84 aggregate samples were acquired from 76 local sources across Tennessee, and 83 of them were tested under the ASTM C1260 accelerated mortar bar method and the ASTM C1293 concrete prism method.
The report's own conclusion is that at least 65 percent of the tested aggregates are classified as reactive, ranging from moderately reactive to very highly reactive. The finding is not narrow. Reactive aggregates were found among limestone, granite, and sand and gravel samples, the three largest categories in the study at 45 percent, 18 percent and 26 percent of the samples collected. Reactivity at the screening level is the institutional flag that downstream mix design decisions need to account for.
The study did not stop at the laboratory. A TDOT regional survey documented ASR distress in at least eight existing Tennessee transportation structures built with concretes containing reactive limestone aggregates: two bridges, four culvert structures, and two pavements. The reaction is not a screening artifact. It has been observed in structures already standing in the state.
Phase II proposed the mitigation. It recommends minimum replacement levels of class F fly ash, scaled to how reactive the aggregate is, and it recommends updating the TDOT specification to reduce ASR risk in future concrete. The agency response to the Phase I finding is mitigation at the mix design level, not aggregate substitution. The aggregates are what Tennessee has. The protection has to come from the supplementary cementitious material strategy paired with the mix.
One boundary line, stated plainly. RES2016-03 studied surface aggregates for TDOT specification concrete. It is a transportation research report and it says nothing about residential concrete. The connection PSIP draws is our own: Tennessee ready-mix producers draw on the same regional aggregate sources for residential work that they draw on for state work. The reactivity finding belongs to TDOT. The inference to a driveway or a slab belongs to us, and we mark it as ours.
Class F supply preserved. On regulatory premise.
On February 11, 2026, meeting in Hopkinsville, Kentucky, the TVA Board of Directors voted to authorize continued operation of the Kingston and Cumberland coal plants beyond their scheduled retirement dates, and directed staff to seek the permits required to do it. That walked back Records of Decision that had set Kingston's nine coal units to retire by the end of 2027 and Cumberland's two units to retire by the end of 2026 and the end of 2028. The board's stated reason, in its own resolutions, is that after a decade of flat electricity demand the TVA region is now seeing rapidly increasing demand that exceeded expectations at the time of the retirement decision. The action preserves the regional fly ash supply that has historically served Tennessee concrete. The supply preservation is real. The premise underneath it is conditional.
- ·Kingston Fossil Plant, Roane County, Tennessee: a Record of Decision had committed nine coal units, 1,171 MW, to retire by the end of 2027. The board voted to run them past that date. Board Exhibit 02/11/26J.
- ·Cumberland Fossil Plant, Stewart County, Tennessee: a Record of Decision had committed one coal unit to retire by the end of 2026 and the second by the end of 2028. The board voted to run them past those dates. Board Exhibit 02/11/26I.
- ·Gallatin Fossil Plant, Sumner County, Tennessee: not part of the February 2026 action. Gallatin has no retirement Record of Decision and no published retirement date. It remains in operation.
- ·Shawnee Fossil Plant: not part of the February 2026 action, and not a Tennessee plant. TVA places it about ten miles northwest of Paducah, Kentucky.
Preservation is real. The premise is in motion.
The February 2026 vote preserves the regional fly ash supply in the near term. It does not solve the structural picture. TVA's own stated reason was demand, and demand forecasts move. The board reversed a retirement decision once on a changed forecast, which establishes that these dates are revisable in both directions. A shift in the demand outlook, or in the federal emissions rule cycle running alongside it, could move the Tennessee supply trajectory back toward contraction at any point in the coming years.
A Tennessee ready-mix producer planning mix design strategy for the next five years operates with this regulatory dependency in plain view. A Tennessee residential contractor operates with the same dependency one step downstream. The protection that exists today exists conditionally. The mix design assumptions built around that protection inherit the same condition.
Class C vs Class F: the chemistry distinction.
The fly ash produced by TVA Tennessee coal differs in chemistry from the Class F fly ash that dominated the 2018 Texas narrative. The distinction is real. The collapsible appendix below carries the technical detail.
Expand the technical appendix · Class C vs Class F fly ash chemistry
ASTM C618 is the formal classification standard. It defines two coal fly ash classes by chemistry: Class F (low-calcium, sourced typically from bituminous and anthracite coals) and Class C (higher-calcium, sourced typically from sub-bituminous and lignite coals). The classification is set by the sum of silicon dioxide, aluminum oxide, and iron oxide content in the ash, along with the calcium oxide content. Class F ash has the sum of those three oxides at 70 percent or higher with relatively low calcium. Class C ash has the sum at 50 percent or higher with elevated calcium content.
The behavioral difference matters at the mix-design level. Class F ash is pozzolanic. It reacts with the calcium hydroxide produced by cement hydration to form additional calcium silicate hydrate, the binding phase responsible for concrete strength and durability. The reaction is slower than direct cement hydration. The benefit accrues over months, not days. Long-term durability gains, including the reduction of alkali-silica reaction expansion, are the documented Class F contribution.
Class C ash behaves differently. The elevated calcium content gives Class C ash some of the cementitious character of Portland cement itself. It can react with water directly, contributing to early strength and accelerated set time. The pozzolanic contribution exists but is paired with the cementitious contribution, and the long-term durability profile, including ASR mitigation benefit, is generally lower than for Class F at the same replacement percentage. Mix designs developed around Class F performance assumptions do not translate one-for-one to Class C ash.
TVA Tennessee coal historically produces ash that trends toward Class C chemistry, with elevated calcium content relative to the Texas-sourced Class F ash that defined the 2018 narrative. A Tennessee residential pour that historically used TVA-sourced ash was operating on a Class C-leaning chemistry, not the Class F chemistry that the broader ASR-mitigation literature anchors to. This affects how the regional supply picture translates into actual ASR protection at the slab level.
For a Tennessee ready-mix producer or residential contractor, the implication is that the supplementary cementitious material strategy needs to be specified to the actual ash chemistry being delivered, not to a generic "fly ash" line item. The ASTM C618 class designation, the source plant, and the percentage replacement matter as separate variables. The Phase II TDOT mitigation alternatives are responsive to this distinction. The closeout documentation on a PSIP-certified pour captures the ash source and class at the time of delivery, so the long-term performance record is tied to the chemistry that was actually in the slab.
Documented picture. Documented pour.
TDOT evaluated 76 aggregate sources, found at least 65 percent of the samples tested reactive, documented ASR distress in eight structures already standing, and recommended changing its own specification. TVA then voted to keep two coal plants running past dates it had committed to. The institutional picture is what it is, and it is in the public record with a report number and a board exhibit number.
The protocol layer is where that picture translates into a documented pour. PSIP-certified contractors specify the supplementary cementitious material strategy in writing before the mix is ordered. The ash source and class are recorded at delivery. The climate-day conditions and curing protocol are captured on the slab. Tennessee residential concrete decisions sit at the contractor of record. The protocol exists to make those decisions documentable.
The protocol turns institutional research into a documented record on the slab.
PSIP-certified contractors document the specific ash source, the climate-day conditions, and the SCM tier used. The closeout packet is signed at completion. The protocol is structurally independent of every material supplier.