1、Standard Method of Test for Potential Alkali Reactivity of Aggregates and Effectiveness of ASR Mitigation Measures (Miniature Concrete Prism Test, MCPT) AASHTO Designation: T 380-181Technical Section: 3c, Hardened Concrete Release: Group 1 (April) American Association of State Highway and Transporta
2、tion Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 380-1 AASHTO Standard Method of Test for Potential Alkali Reactivity of Aggregates and Effectiveness of ASR Mitigation Measures (Miniature Concrete Prism Test, MCPT) AASHTO Designation: T 380-181Technical Section:
3、 3c, Hardened Concrete Release: Group 1 (April) 1. SCOPE 1.1. This test method allows detection of the potential for deleterious alkalisilica reaction of aggregate in miniature concrete prisms within 56 days (8 weeks) for most of the aggregates. An additional 28 days (4 weeks) may be necessary in th
4、e case of low/slow reacting aggregates to assess their potential reactivity. To assess the effectiveness of mitigation measures of SCMs (supplementary cementitious materials, such as fly ash, slag, silica fume, and others); the test method is conducted for 56 days. 1.2. The values stated in SI units
5、 are to be regarded as standard. The values in inch-pound units are shown in parentheses and are for informational purposes only. 1.3. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its us
6、e. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 85, Portland Cement M 201, Mixing Rooms, Moist Cabinets, Moist Rooms,
7、 and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes R 70M/R 70, Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete T 19M/T 19, Bulk Density (“Unit Weight”) and Voids in Aggregate T 27, Sieve Analysis of Fine and Coarse A
8、ggregates T 303, Accelerated Detection of Potentially Deleterious Expansion of Mortar Bars Due to AlkaliSilica Reaction 2.2. ASTM Standards: C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete C157/C157M, Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar
9、and Concrete 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3c T 380-2 AASHTO C192/C192M, Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory C295/C295M, Standard Guide
10、 for Petrographic Examination of Aggregates for Concrete C490/C490M, Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete C511, Standard Specification for Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used i
11、n the Testing of Hydraulic Cements and Concretes C702/C702M, Standard Practice for Reducing Samples of Aggregate to Testing Size C778, Standard Specification for Standard Sand C1260, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) C1293, Standard Test Method fo
12、r Determination of Length Change of Concrete Due to Alkali-Silica Reaction D75/D75M, Standard Practice for Sampling Aggregates D1193, Standard Specification for Reagent Water 2.3. Federal Standard: Fed. Std. No. 29, CFR 1910.1200 OSHA Hazard Communication Standard; see also Permissible Exposure Limi
13、tsAnn otated Tables, https:/www.osha.gov/dsg/annotated-pels/ 3. SIGNIFICANCE AND USE 3.1. Alkalisilica reaction (ASR) is a chemical reaction between certain forms of reactive silica present in aggregates and alkali hydroxides present in the concrete pore solution. The alkali ions (Na+and K+) are pri
14、marily derived from portland cement, although other sources can potentially elevate their concentration in the pore solution. 3.2. This test method is intended to evaluate the potential of an aggregate (fine and coarse) to expand deleteriously due to any form of alkalisilica reactivity. A companion
15、nonreactive aggregate should be used with a reactive aggregate in question. Also, this test method is intended to assess the effectiveness of various mitigation measures. 3.3. When selecting a sample or deciding on the number of samples for test, it is important to recognize the variability in litho
16、logy of material from a given source, whether a deposit of sand, gravel, or a rock formation of any origin. For specific advice, see ASTM C295/C295M. 3.4. MCPT was developed as an alternative to the existing standard test methods such as ASTM C1260 and ASTM C1293 to evaluate aggregate reactivity. Th
17、is test method was developed with some modifications to standard test methods T 303 (ASTM C1260) and ASTM C1293. When evaluating coarse aggregate reactivity, MCPT has the advantage of not requiring the coarse aggregate to be crushed into smaller (sand-sized) particles, as typically required in ASTM
18、C1260 Also, the MCPT method yields test results in 8 weeks to characterize the aggregate reactivity, which is much shorter than the test duration required in ASTM C1293. 3.5. The total alkali content of the cement used in this test method should have a Na2Oeqcontent of 0.90 0.10 percent. 3.6. For th
19、e vast majority of the aggregates that are either nonreactive or moderately to highly reactive, this test characterizes the aggregate reactivity in 8 weeks. For some specific aggregates that have a tendency to exhibit low/slow reactivity, an additional 4 weeks of testing is required. For the purpose
20、 of providing guidance on aggregate reactivity characterization, the following general guidelines are used in classifying the aggregate: 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3c T 380-3 AAS
21、HTO 3.6.1. Very highly/highly reactive aggregates are considered as those aggregates that, when present in concrete with typical alkali loading (3 to 5 lb/yd3), exhibit incipient signs of ASR distress in the field, typically at an age less than 5 years. 3.6.2. Moderate reactive aggregates are consid
22、ered as those aggregates that, when present in concrete with typical alkali loading (3 to 5 lb/yd3), exhibit incipient signs of ASR distress in the field, typically at an age between 5 and 10 years. 3.6.3. Low/slow reactive aggregates are considered as those aggregates that, when present in concrete
23、 with typical alkali loading (3 to 5 lb/yd3), exhibit incipient signs of ASR distress in the field, typically at an age beyond 10 years. 3.7. Results of tests conducted as described herein should form a part of the basis for a decision as to whether precautions should be taken against excessive expa
24、nsion due to alkalisilica reaction. This decision should be made before a particular aggregate is used in concrete construction. 3.8. The basic intent of this test method is to develop information on a particular aggregate at a specific alkali level of 5.25 kg/m3(8.85 lb/yd3). It has been found that
25、 this high alkali level is required to detect the effects of certain deleteriously reactive aggregates. 3.9. When the expansions in this test method are greater than the limit (0.040 percent) shown in Table 1, the aggregate is potentially alkali reactive. An additional 28 days (4 weeks) may be neces
26、sary in the case of low/slow reacting aggregates (percent expansion between 0.031 and 0.040 percent) to assess their potential reactivity based on rate of expansion. When the expansions are 0.030 percent, then the aggregate is considered nonreactive. Table 1Proposed Criteria fo r Characterizing the
27、Aggregate Reactivity in the MCPT Protocol Degree of Reactivity Expansion at 56 Days, % (8 Weeks) Average 2-Week Rate of Expansion from 8 to 12 WeeksaNonreactive 0.030 N/AbNonreactive 0.0310.040 0.010% per 2 weeks Low/slow reactive 0.0310.040 0.010% per 2 weeks Moderate reactive 0.0410.120 N/AbHighly
28、 reactive 0.1210.240 N/AbVery highly reactive 0.240 N/AbaExample calculation for averaged rate of expansion from 8 to 12 weeks: If the average expansions of the three prisms at 8, 10, and 12 weeks are 0.035 percent, 0.046 percent, and 0.059 percent, respectively, then the average rate of expansion b
29、etween 8 to 12 weeks is equal to (0.059 0.037)/2 = 0.012 percent per 2 weeks. bNot applicable. 3.10. The criteria to determine the effectiveness of the SCMs in mitigating ASR expansions are given in Table 2. Table 2Proposed Criteria for Characterizing Effectiveness of ASR Mitigation Measures in MCPT
30、 Method Efficiency of Mitigation Expansion at 56 Days, % (8 Weeks) Effective 0.025 aRecommend retest with MCPT using a higher dosage of mitigation. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3c
31、T 380-4 AASHTO 4. APPARATUS 4.1. The apparatus shall conform to R 70M/R 70, except as follows: 4.1.1. MoldsThe molds, the associated items for molding test specimens, and the length comparator for measuring length change shall conform to the applicable requirements of ASTM C157/C157M and ASTM C490/C
32、490M and shall have square cross sections of 50.0 0.7 mm (2.00 0.03 in.). 4.1.2. ContainersThe containers shall be of such a nature that the prisms can be totally immersed in either water or 1N NaOH solution. The containers shall be made of material that can withstand prolonged exposure to 60C (140F
33、) and must be resistant to a 1N NaOH solution. The containers must be so constructed that when used for storing specimens, the loss or gain of moisture is prevented by tight-fitting covers, by sealing, or both. The prisms in the solution must be placed and supported so that the solution has access t
34、o the entire surface of the bar; therefore, it should be ensured that the specimens do not touch the sides of the container or each other. Note 1Recommended Container The NaOH solution will corrode glass or metal containers. Polypropylene or high-density plastic have been found to be acceptable. Exp
35、erience has shown that 12-qt airtight storage containers made of plastic (from IRIS USA) appear to be satisfactory for use in this test method. However, any such similar containers may be used, as long as it is ensured that the container and the lid provide an airtight environment and do not let the
36、 soak solution evaporate in the course of the test method. The concrete prisms should be placed on top of spacer bars (5- to 10-mm plastic rods) at the bottom of the container to allow the test specimens to have free access to soak solution on all surfaces. 4.1.3. Oven or Water BathA thermostaticall
37、y controlled oven or water bath capable of ma intaining a temperature of 60.0 1.7C (140.0 3F). 4.1.4. Moist Room or ClosetThe moist closet or room shall conform to M 201. 5. REAGENTS 5.1. Sodium Hydroxide (NaOH)USP or technical grade may be used provided the Na+and OHconcentrations are shown by chem
38、ical analysis to lie between 0.99N and 1.01N. 5.2. Purity of WaterUnless otherwise indicated, references to water shall be under stood to mean reagent water conforming to Type IV of ASTM D1193. 5.3. Sodium Hydroxide SolutionEach liter of solution shall cont ain 40.0 g of NaOH dissolved in 900 mL of
39、water and shall be diluted with additional distilled or deionized water to obtain 1.0 L of solution. It should include sufficient test solution to ensure complete immersion of the prisms. A soak solution volume of 4.5 L, which is equal to twice the volume of the three MCPT specimens, was found to be
40、 adequate in submerging the three test specimens in the 12-qt airtight container. Note 2Warning : Before using NaOH, review: (1) the safety precautions for using NaOH; (2) first aid for burns; and (3) the emergency response to spills, as described in the manufacturers Material Safety Data Sheet or o
41、ther reliable safety literature. NaOH can cause very severe burns and injury to unprotected skin and eyes. Suitable personal protective equipment should always be used. These should include full-face shields, rubber aprons, and gloves impervious to NaOH. Gloves should be checked periodically for pin
42、holes. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3c T 380-5 AASHTO 6. CONDITIONING 6.1. Maintain the temperature of the molding room and dry materials at not less than 20C (68F) and not more th
43、an 27.5C (81.5F). The temperature of the mixing water, and of the moist room, shall not vary from 23C (73.4F) by more than 1.7C (3F). 6.2. Maintain the relative humidity of the molding room at not less than 50 percent. The moist closet or room shall conform to ASTM C511. 6.3. Maintain the storage ov
44、en or water bath in which the specimens are stored in the containers at a temperature of 60.0 1.7C (140.0 3F). 7. MATERIALS 7.1. CementUse a cement meeting the require ments for Type I portland cement as specified in M 85. The cement must have a total alkali content of 0.9 0.1 percent Na2Oeq(Na2Oeqi
45、s calculated as percent Na2O +0.658 % K2O). Determine the total alkali content of the cement either by analysis or by obtaining a mill run certificate from the cement manufacturer. Add NaOH to the concrete mixing water so as to increase the alkali content of the mixture, expressed as Na2O equivalent
46、, to 1.25 percent by mass of cement. 7.2. Aggregates: 7.2.1. To evaluate the reactivity of a coarse aggregate, use a nonreactive fine aggregate. A nonreactive fine aggregate is defined as an aggregate that develops an expansion in the MCPT of less than 0.030 percent at 56 days. Use a fine aggregate
47、meeting T 27 with a fineness modulus of 2.6 0.3. Use the coarse aggregate gradation defined in Section 7.2.3. For the purposes of establishing the reactivity of coarse aggregate, unless a suitable local source of nonreactive fine aggregate is identified, graded Ottawa sand conforming to ASTM C778 ma
48、y be used as nonreactive sand. 7.2.2. To evaluate the reactivity of a fine aggregate, use a nonreactive coarse aggregate. A nonreactive coarse aggregate is defined as an aggregate that develops an expansion in the MCPT of less than 0.030 percent at 56 days. Use the coarse aggregate gradation defined
49、 in Section 7.2.3. 7.2.3. Sieve all coarse aggregates to which this test method is applied and grade in accordance with the requirements in Table 3. Coarse aggregate fractions larger than 12.5-mm (12-in.) sieve are not to be tested as such. When petrographic examination using ASTM C295/C295M reveals that the material making up the size fraction larger than the 12.5-mm (12-in.) sieve is of such a composition and lithology that no difference should be expected compared with the smalle
