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A-1 These proposed changes to AASHTO M 295, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, are the suggestions of the NCHRP Project 18-13 research team. These changes have not been approved by NCHRP or any AASHTO committee nor formally accepted for the AASHTO specifications. In this summary, the proposed deletions are indicated by strikethrough text and proposed insertions indicated by under- lined text. A T T A C H M E N T A Summary of Proposed Changes to AASHTO M 295-11, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
A-2 Specification Change Commentary Section 2.1 Add references for the new coal fly ash iodine number and direct adsorption isotherm tests. Both are new test methods added to the specification. Section 2.2 Add references for ASTM C1567. ASTM C1567 added to replace ASTM C441. Section 4.3 Note 3. Note 3 - Class F fly ash is typically produced from burning anthracite or bituminous coal, but may also be produced from subbituminous coal and from lignite. Class C fly ash is typically produced from burning lignite or subbituminous coal, and may also be produced by anthracite or bituminous coal. Class C fly ashes contain total calcium contents, expressed as calcium oxide (CaO), higher than 10 percent. Class C fly ashes typically have total calcium contents, expressed as calcium oxide (CaO), that are higher than Class F fly ashes. This change is proposed to provide clarity to specifiers. It is confusing to have a numerical, quantitaive limit for CaO content in a note when CaO is not specified in Table 1. Also, this change is proposed to keep AASHTO M 295 consistent with ASTM C618. ASTM has recently approved the same change. Section 5.1 5.1 The purchaser shall specify any supplementary optional chemical and physical requirements. This change is proposed for clarity. The reference to supplementary optional chemical and physical requirements is redundant given the only supplementary optional requirements are chemical and physical supplementary optional requirements. Table 1 â Chemical Requirements Modify Table 1 as shown below. Classify the ash using the sum of the oxides reported to the nearest whole number to reflect the precision of the actual chemical determination. Add a maximum sum of the oxides value to Class C ash to eliminate Class Fashes also qualifying as Class C ashes. Report CaO, MgO, Na2O, K2O, and equivalent alkali to provide specifiers more information about the coal fly ash and also to provide information necessary to apply AASHTO PP 65, Standard Practice for Determining the Reactivity of Concrete Aggregates and Selecting Appropriate Measures for Preventing Deleterious Expansion in New Concrete Construction. Coal Fly Ash and Raw or Calcined Natural Pozzolan Class N F C Silicon dioxide (SiO2) plus aluminum oxide (A12O3) plus iron oxide (Fe2O3), percent 70.0 min 70.0 min 50.0 min, less than 70 Sulfur trioxide (SO3), max percent 4.0 5.0 5.0 Moisture content, max percent 3.0 3.0 3.0 Loss on ignition, max percent 5.0 5.0 5.0 Calcium oxide (CaO), percent no limit â report only no limit â report only no limit â report only Magnesium oxide (MgO), percent no limit â report only no limit â report only no limit â report only Sodium oxide (Na2O), percent no limit â report only no limit â report only no limit â report only Potassium oxide (K2O), percent no limit â report only no limit â report only no limit â report only Equivalent alkali (Na2Oe)a, percent no limit â report only no limit â report only no limit â report only a Na2Oe = Na2O + (0.658 x K2O) Table 1. Chemical requirements.
A-3 Table 2 - Supplementary Optional Chemical Requirements Modify Table 2 as shown below. Delete available alkali limits due to limitations and poor precision of the test. Replace this requirement with reporting total alkalis in Table 1 to be consistent with AASHTO PP 65. Add determination and reporting of the coal fly ash iodine number (AASHTO T XXX) and, if necessary, determine and report the Air-Entraining Admixture Adsorption by Coal Fly Ash (AASHTO T YYY). These two tests provide an approach to quantifying the adsorption of air-entraining admixtures by coal fly ash. Specification Change Commentary Section 6.2 6.2 Other oxides commonly reported for fly ash include CaO, MgO, Na2O and K2O. Redundant with changes to Table 1. Table 2. Supplementary optional chemical requirements. Coal Fly Ash and Raw or Calcined Natural Pozzolan Class N F C Available alkalies, or equivalent, as Na2O, max percenta 1.5 1.5 1.5 Coal fly ash iodine number (AASHTO T XXX)a not applicable report coal fly ash iodine number a Applicable only when specifically required by the purchaser for mineral admixture to be used in concrete containing reactive aggregate and cement to meet a limitation on content of alkalies a If the reported value for the coal fly ash iodine number (AASHTO T XXX) is greater than 0.10 mg iodine/gram coal fly ash, then perform AASHTO T YYY (Determination of Air-Entraining Admixture Adsorption by Coal Fly Ash) using a single air-entraining agent specified by the ash purchaser, and report both the coal fly ash iodine number and the information specified in the reporting section of AASHTO T YYY.
A-4 Specification Commentary Table 3 - Physical Requirements Modify Table 3 as shown below. Increase the 7- and 28-day limit for the strength activity index (SAI) to 85 to protect inert (non-pozzolanic) materials from passing the test. Allow for qualification for SAI at 28 and 56 days to allow Class F ashes with low early strength gain to qualify. Editorial changes to Note B to eliminate references to accelerated tests, âexpectedâ contribution to strength, and a redundant reference to testing with portland cement. By definition, the SAI test is performed with portland cement. Coal Fly Ash and Raw or Calcined Natural Pozzolan Class N F C Fineness: Amount retained when wet-sieved on 45 µm (No. 325) sieve, max percenta 34 34 34 Strength activity index:b With portland cement, at 7, 28, or 56 days, min percent of control 75 75 85e d 75 85 e d With portland cement, at 28 or 56 c days, min percent of control 75 75 e 75e Water requirement, max percent of control 115 105 105 Soundness: d c Autoclave expansion or contraction, max percent 0.8 0.8 0.8 Uniformity requirements: The density and fineness of individual samples shall not vary from the average established by the 10 preceding tests, or by all preceding tests if the number is less than 10, by more than: Density, max variation from average, percent 5 5 5 Percent retained on 45 µm (No. 325) sieve, max variation, percentage points from average 5 5 5 a Care should be taken to avoid the retaining of agglomerations of extremely fine material. b The strength activity index with portland cement is not to be considered a measure of the compressive strength of concrete containing the coal fly ash and raw or calcined natural pozzolan. The strength activity index with portland cement is determined by an accelerated test, and is intended to evaluate the contribution to be expected from the coal fly ash and raw or calcined natural pozzolan to the longer strength development of concrete. The mass of coal fly ash and raw or calcined natural pozzolan specified for the test to determine the strength activity index with portland cement is not considered to be the proportion recommended for the concrete to be used in the work. The optimum amount of coal fly ash and raw or calcined natural pozzolan for any specific project is determined by the required properties of the concrete and other constituents of the concrete and should be established by testing. Strength activity index with portland cement is a measure of reactivity with a given cement and is subject to variation depending on the source of both the coal fly ash and raw or calcined natural pozzolan and the cement. c Only applicable when testing at 56 days is specified. d c If the coal fly ash and raw or calcined natural pozzolan will constitute more than 20 percent by mass of the cementitious material in the project mix design, the test specimens for autoclave expansion shall contain that anticipated percentage. Excessive autoclave expansion is highly significant in cases where water to coal fly ash and raw or calcined natural pozzolan and cement ratios are low, for example, in block or shotcrete mixes. e d Meeting the 7-day, 28-day, or 56-day (if specified) strength activity index will indicate specification compliance. Table 3. Physical requirements.
A-5 Specification Commentary Table 4 - Supplementary Optional Physical Requirements Modify Table 4 as shown below. Modifications involve elimination of ASTM C441 and insertion of ASTM C1567 for determining effectiveness in controlling alkali-silica reaction. The acceptance limits of 0.10 max percent are consistent with AASHTO PP 65. Note B eliminated as it referred specifically to ASTM C441. Reletter remaining notes accordingly. Coal Fly Ash and Raw or Calcined Natural Pozzolan Class N F C Increase of drying shrinkage of mortar bars at 28 days, max difference in percent over controla 0.03 0.03 0.03 Uniformity requirements: In addition, when air-entrained concrete is specified, the quantity of air- entraining agent required to produce an air content of 18.0 vol percent of mortar shall not vary from the average established by the 10 preceding tests or by all preceding tests if less than 10, by more than, percent 20 20 20 Effectiveness in controlling alkali-silica reaction (as per ASTM C1567): Expansion of test mixture as percentage of low-alkali cement control, at 14 days, max percent 100 0.10 100 0.10 100 0.10 Effectiveness in contributing to sulfate resistance: b Procedure A: Expansion of test mixture: For moderate sulfate exposure after 6 months of exposure, max percent 0.10 0.10 0.10 For high sulfate exposure after 6 months of exposure, max percent 0.05 0.05 0.05 Procedure B: Expansion of test mixture as a percentage of sulfate resistance cement control after at least 6 months of exposure, max percent 100 100 100 a Determination of compliance or noncompliance with the requirement relating to increase in drying shrinkage will be made only at the request of the owner. b Coal fly ash and raw or calcined natural pozzolans meeting this requirement are considered as effective in controlling alkali aggregate reactions as the use of the low-alkali control cement used in the evaluation. However, the coal fly ash and raw or calcined natural pozzolan shall be considered effective only when the coal fly ash and raw or calcined natural pozzolan are used at percentages by mass of the total cementitious material equal to or exceeding that used in the tests and when the alkali content of the cement to be used with the coal fly ash and raw or calcined natural pozzolan does not exceed that used in the tests by more than 0.05 percent. See Appendix X1, ASTM C 311. b Fly ash or natural pozzolan shall be considered effective only when the fly ash or natural pozzolan is used at percentages, by mass, of the total cementitious material within 2 percent of those that are successful in the test mixtures or between 2 percentages that are successful, and when the C3A content of the project cement is less than or equal to that which was used in the test mixtures. See Appendix X2 of ASTM C311. Note: These optional requirements apply only when specifically requested. Table 4. Supplementary optional physical requirements.
