TENNESSEE,
TDOT REPORT RES2016-03.
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.
Documented at the agency level.
Report RES2016-03. 76 sources. 65 percent of samples tested 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/C1293M 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.
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.
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.
Kingston and Cumberland. A vote to run past retirement.
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. Records of Decision had set retirement dates for Kingston's nine coal units and Cumberland's two. 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.
- ·Kingston Fossil Plant, Roane County, Tennessee: a Record of Decision had set a retirement date for nine coal units, 1,171 MW. The board voted to run them past it. Board Exhibit 02/11/26J.
- ·Cumberland Fossil Plant, Stewart County, Tennessee: a Record of Decision had set retirement dates for its two coal units. The board voted to run them past those dates. Board Exhibit 02/11/26I.
The answer to what is in the regional mix is not a constant, so a mix specified some years ago and reordered by habit is not guaranteed to be the same concrete today.
Class C vs Class F: the chemistry distinction.
Fly ash is supplied as Class F or Class C. They differ in chemistry, they differ in alkali silica reaction mitigation behaviour, and they are not interchangeable at the same replacement percentage. 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. Under the current edition, both classes have the sum of those three oxides at 50 percent or higher. Calcium oxide separates them: 18 percent or less for Class F, more than 18 percent for Class C.
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. Class F is the ash most of the alkali silica reaction mitigation literature is anchored to.
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. It is a legitimate material with a different long term durability profile, and it is not the material the ASR literature is anchored to. Mix designs developed around Class F performance assumptions do not translate one-for-one to Class C ash.
The ASTM C618 class designation, the source plant, and the percentage replacement matter as separate variables. A batch ticket may not name the class. PSIP does not rank the two classes or say which one to use.
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.
None of it says what went into a given Tennessee driveway or slab. That is a fact somebody either wrote down or did not. The contractor builds it. The building department enforces the code. PSIP keeps the record.
The report is about the aggregate. The record is about the pour.
On a concrete pour, a PSIP record holds the specified mix design, the cement type, and the supplementary cementitious material by type, or that none is specified, as the contractor states them at setup, before placement. On a pool shell, it holds the batch tickets for each shoot day, the delivery method, wet shotcrete or dry gunite, and the nozzle operator by name, as the builder states it. Every batch ticket is photographed, and the photograph records what the ticket shows. Tickets vary, and many do not list everything in the load, so the contractor adds what he knows in the notes, as his own statement. PSIP records the work and certifies that it was recorded. The contractor is responsible for local building codes, permits and licensing. PSIP certification is not an inspection, a code approval or a warranty. No material supplier can pay for a say in PSIP, and PSIP does not recommend products.