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Short answer
ASTM C1260 is the standard test method for the potential alkali reactivity of aggregates, run on mortar bars. It is an accelerated test: it lets a laboratory detect, within 16 days, whether an aggregate has the potential for deleterious alkali-silica reaction (ASR). It screens the aggregate alone, and ASTM points readers to Guide C1778 for interpreting the results.
Definition and scope
The full title is ASTM C1260, “Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method)”. The ASTM store page for the C1260-23 edition (checked 2026-10-29) lists it as active, last updated 22 November 2023, and states that SI units are the standard.
The scope statement says the method permits detection, within 16 days, of the potential for deleterious alkali-silica reaction of aggregate in mortar bars. The significance section adds that the method is based on the NBRI Accelerated Test Method and that it is especially useful for aggregates that react slowly or produce expansion late in the reaction.
How it is used in practice
C1260 works on the aggregate by itself. Specimens are exposed to a sodium hydroxide (NaOH) solution, and because of that exposure the standard notes that the alkali content of the cement is not a significant factor in affecting expansions. The result therefore speaks to the aggregate, not to a particular cement.
The standard does not interpret its own output. Section 4.3 sends the reader to ASTM Guide C1778 for interpreting the test results. C1778, “Standard Guide for Reducing the Risk of Deleterious Alkali-Aggregate Reaction in Concrete” (ASTM store page, checked 2026-10-29), gives guidance on addressing the potential for deleterious alkali-aggregate reaction in concrete construction. It covers identifying aggregates susceptible to ASR or to alkali-carbonate reaction (ACR) through standardized testing procedures, and selecting mitigation for ASR aggregates.
For a laboratory, the practical implication is that the number coming off a C1260 run is an input to a decision framework, not a verdict by itself. Whoever writes the test report or the acceptance requirement should cite which guide or specification governs interpretation. Where a lab runs this test under its own quality system, the method belongs in a controlled procedure; see how to write a lab SOP for structuring one.
What C1260 can and cannot tell you
The significance section of the standard sets clear limits. The checklist below restates them.
- It tests aggregate, not mixtures. The method does not evaluate combinations of aggregates with cementitious materials.
- It is not a service-conditions simulation. The test conditions are not representative of those encountered by concrete in service.
- Cement alkali content is not the driver. Because of the NaOH exposure, cement alkali is not a significant factor in the expansions measured.
- It is fast by design. Detection takes up to 16 days, and the method suits slowly reacting aggregates or those that expand late.
- Interpretation sits elsewhere. Guide C1778 governs how results are read.
Related concepts: C1260 compared with C1293
The closest companion standard is ASTM C1293, “Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction” (ASTM store page, checked 2026-10-29; active version listed as C1293-23AE01). The table compares only attributes stated on the two ASTM pages.
| Attribute | ASTM C1260 | ASTM C1293 |
|---|---|---|
| Specimen | Mortar bars | Concrete prisms |
| What is measured | Potential for deleterious ASR of aggregate in mortar bars | Length change of concrete prisms |
| What it can evaluate | Aggregate alone; does not evaluate aggregate combined with cementitious materials | An aggregate alone, or combined with pozzolan or slag |
| Speed | Detection within 16 days (accelerated) | The store page gives no duration |
| Alkali loading | Specimens exposed to NaOH solution; cement alkali not a significant factor | Concrete alkali content of 5.25 kg/m³ Na2O equivalent, reduced proportionally with pozzolan or slag |
The difference to take from the table: if the question is whether an aggregate on its own is potentially reactive, C1260 is the accelerated screen. If the question involves an aggregate combined with a pozzolan or slag, C1293 is the one of the two that is written to address combinations.
Where it matters for labs and clinics
C1260 is a materials-testing method for construction-materials laboratories. It is not a clinical or biomedical test, and it has no role in patient care. Its relevance to a laboratory manager is as follows.
- Choosing the test to match the question. Aggregate alone: C1260. Aggregate with pozzolan or slag: C1293. Reading the results and picking mitigation: C1778.
- Writing the right claim into the report. A C1260 result describes the potential reactivity of the aggregate under accelerated test conditions. It does not describe how concrete performs in service.
- Keeping the edition in the record. The edition described on this page is C1260-23, so a report should name the edition used.
Other concrete test standards explained on CASRAI include ASTM C31 on making and curing test specimens, ASTM C42 on drilled cores and sawed beams, ASTM C78 on flexural strength and ASTM C1107 on nonshrink grout.
Common misunderstandings
“A pass means the concrete will never have ASR.”
The standard says its test conditions are not representative of those encountered by concrete in service, and it leaves interpretation to Guide C1778. A C1260 result is a screening input, not a guarantee about a structure.
“C1260 tests my cement and fly ash blend.”
It does not. The method does not evaluate combinations of aggregates with cementitious materials, and cement alkali content is not a significant factor in its expansions.
“Sixteen days is the length of the whole evaluation.”
Sixteen days is the detection window stated in the scope. Reading the result and deciding on mitigation fall under the guidance in C1778.
FAQ
What is ASTM C1260 used for?
It is used to detect, within 16 days, the potential for deleterious alkali-silica reaction of an aggregate in mortar bars.
How long does ASTM C1260 take?
The scope says detection is possible within 16 days, which is why it is called an accelerated method.
Does C1260 depend on the cement used?
No. Because specimens are exposed to a NaOH solution, cement alkali content is not a significant factor in the expansions.
Where do I find how to interpret C1260 results?
ASTM C1260 refers to Guide C1778 for the interpretation of results.
Sources
- ASTM International, C1260-23, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method): store.astm.org/c1260-23.html, checked 2026-10-29.
- ASTM International, C1778, Standard Guide for Reducing the Risk of Deleterious Alkali-Aggregate Reaction in Concrete: store.astm.org/c1778-20.html, checked 2026-10-29.
- ASTM International, C1293, Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction: store.astm.org/c1293-20a.html, checked 2026-10-29.
