1、Standard Method of Test for Water Content of Freshly Mixed Concrete Using Microwave Oven Drying AASHTO Designation: T 318-15 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3b T 318-1 AASHTO Standard Method of Test
2、 for Water Content of Freshly Mixed Concrete Using Microwave Oven Drying AASHTO Designation: T 318-15 1. SCOPE 1.1. This method covers the measurement of total water content of fresh concrete. It consists of drying a test specimen of fresh concrete using a relatively high-power microwave oven within
3、 a short period of time. The difference in mass between the fresh and dry concrete test specimen will be the water content of that test specimen. Water content per unit volume of concrete can be determined by knowing the unit weight of that concrete. Unit weight shall be determined in accordance wit
4、h T 121M/T 121 or ASTM C138/C138M. 1.2. This standard is applicable to both laboratory and field testing. 1.3. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibil
5、ity of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. WarningFresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and tissue upon prolonged exposure. 2. REFERENCE
6、D DOCUMENTS 2.1. AASHTO Standards: M 231, Weighing Devices Used in the Testing of Materials R 60, Sampling Freshly Mixed Concrete T 84, Specific Gravity and Absorption of Fine Aggregate T 85, Specific Gravity and Absorption of Coarse Aggregate T 121M/T 121, Density (Unit Weight), Yield, and Air Cont
7、ent (Gravimetric) of Concrete T 255, Total Evaporable Moisture Content of Aggregate by Drying 2.2. ASTM Standards: C138/C138M, Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete C670, Standard Practice for Preparing Precision and Bias Statements for Test
8、 Methods for Construction Materials 3. SUMMARY OF TEST METHOD 3.1. A test specimen of freshly mixed concrete is wrapped in a fiberglass cloth and dried in a microwave oven using a minimum of three drying intervals. The test specimen is broken up using a metal scraper, separating the coarse aggregate
9、 from the mortar throughout each of the drying intervals. A grinding pestle may also aid in separating the coarse aggregate from the mortar but is not required. The water content of the test specimen is calculated based on loss in mass of the test 2016 by the American Association of State Highway an
10、d Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3b T 318-2 AASHTO specimen at completion of the test. Total drying time is usually between 15 and 30 min. Drying times are reduced if a higher wattage microwave oven is used. 4. SIGNIFICANCE AND USE 4.1.
11、This test is for both laboratory and field measurements of water content in fresh concrete. The test results provide an estimate of the total water content in the fresh concrete and, with the absorption of the aggregates determined, provides an estimate of the mixing water content. 4.2. This test ca
12、n be used as a quality control tool to check the water content of as-delivered concrete and to calculate the water/cement ratio if the cement content of the tested concrete is known. 4.3. Determine the water absorption of coarse and fine aggregates representative of the aggregates used in the concre
13、te in accordance with T 84 or T 85, as applicable. 5. APPARATUS 5.1. Microwave OvenA microwave oven with a minimum power setting of at least 900 watts, a turntable, and sufficient capacity to accept the specified tray and test specimen. 5.2. Glass TrayA heat-resistant glass tray with dimensions of a
14、pproximately 230 by 230 by 50 mm (9 by 9 by 2 in.). 5.3. ScaleA scale of sufficient capacity meeting the requirements of M 231, having a capacity larger than the sample plus tare, sensitive to 0.1 g or less, and accurate to within 0.1 percent of the test load at any point within the range of use for
15、 this test method. 5.4. Metal ScraperA small metal scraper having a sharp edge and a blade approximately 25 mm (1 in.) wide. 5.5. Grinding PestleA pestle having a porcelain grinding head with a diameter of approximately 50 mm (2 in.). 5.6. ScoopMetal, hand held with a capacity of at least 1.2 L 40 o
16、z. 6. MATERIALS 6.1. Fiberglass ClothPlain weave fiberglass cloth having a mass of 0.34 kg/m2(10 oz/yd2) and a thickness of 0.35 mm (14 mil). 7. HAZARDS 7.1. Microwave radiation can be hazardous. Follow the safety precautions provided by the microwave oven manufacturer and OSHA at all times. Refer t
17、o the caution statements in T 255. 7.2. Aggregates with metallic inclusions can explode violently or melt and can be a fire hazard. 7.3. Materials and containers removed from the microwave oven may be hot, requiring the use of insulated gloves for safe handling. 2016 by the American Association of S
18、tate Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3b T 318-3 AASHTO 8. SAMPLING TEST SPECIMENS 8.1. Obtain enough concrete to determine the density and the total water content of the concrete from the same sample of freshly mixed concrete
19、as described in R 60. 8.2. Measure the density of the concrete in accordance with AASTHO T 121M/T 121. 8.3. Test at least 1500 g of concrete obtained in one scoop after the sample is thoroughly mixed. Do not attempt to add mortar to achieve a specific specimen mass. 8.4. Protect the specimen from lo
20、ss of moisture before the initial weighing. 8.5. Measure the initial mass of the test specimen within 5 min after obtaining the composite sample of fresh concrete. Start the microwave drying procedure within 15 min after obtaining the composite sample of fresh concrete. 9. PROCEDURE 9.1. Cut a piece
21、 of fiberglass cloth large enough to completely wrap at least a 1500 g test specimen of freshly mixed concrete. The piece of fiberglass cloth can be reused from a previous analysis provided it is completely dry. Note 1The minimum size fiberglass cloth that has generally been found to be adequate is
22、0.5 m by 0.5 m (20 in. by 20 in.). 9.2. Place the fiberglass cloth on the heat-resistant glass tray with the cloth uniformly overhanging the outside edges of the tray. 9.3. Determine the mass of the tray and cloth together (WS). Make this mass determination and all subsequent mass determinations to
23、the nearest 0.1 g. 9.4. Leave the tray and cloth on the scale and add at least 1500 g of the sampled concrete on the fiberglass cloth and wrap the test specimen completely with the cloth. 9.5. Determine the combined mass of the tray, cloth, and freshly mixed concrete test specimen together (WF). 9.6
24、. Place the tray with the completely wrapped test specimen on the turntable in the microwave oven. Dry the test specimen with the turntable rotating for a period of 5.0 0.5 min at the highest power setting. 9.7. At the end of the initial drying period, remove the tray and test specimen from the micr
25、owave oven and quickly unwrap the test specimen. Use the end of the scraper or grinding pestle to break up the concrete until the coarse aggregate is separated from the mortar. Use care to ensure there is no loss of any concrete material in this operation. 9.8. Rewrap the test specimen. Place the tr
26、ay with the completely wrapped test specimen on the turntable in the microwave oven and dry it with the turntable rotating for 5.0 0.5 min at the highest power setting. 9.9. Remove the tray and test specimen from the microwave oven and unwrap the test specimen. Stir the test specimen with the scrape
27、r and determine the combined mass of the tray, fiberglass cloth, and sample together. 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3b T 318-4 AASHTO 9.10. Rewrap the test specimen. Place the tray w
28、ith the completely wrapped test specimen on the turntable in the microwave oven and dry it with the turntable rotating for 2.0 0.5 min at the highest power setting. 9.11. Remove the tray containing the test specimen from the microwave oven and determine the combined mass of the tray, fiberglass clot
29、h, and specimen. If the change in mass is 1 g or more compared to what was determined in 9.9, repeat the 2-min drying period until the decrease in mass is less than 1 g. Record the combined mass of the tray, cloth, and dry test specimen (WD). 10. CALCULATIONS 10.1. Total Measured Water ContentCalcul
30、ate the total measured water content as follows: 10.1.1. For kg/m3use: MWF WDWT UWWF WS= (1) 10.1.2. For lb/yd3use: 27MWF WDWT UWWF WS= (2) where: WTM = Total measured water content, kg/m3(lb/yd3); WF = Mass of the tray + cloth + fresh test specimen, g; WD = Mass of the tray + cloth + dry test speci
31、men, g; WS = Mass of the tray + cloth, g; UW = Unit mass of the fresh concrete kg/m3(lb/ft3); and 27 = ft3/yd3, a constant (not used for SI calculation). 10.2. Estimated Absorbed Water ContentCalculate the estimated absorbed water content as follows: ( ) ( ) 100CC FFAAW AWWTV+ =(3) where: WTA = Esti
32、mated absorbed water content, kg/m3(lb/yd3); AC= Coarse aggregate absorption, percentage dry mass; WC= Dry mass of coarse aggregate in concrete batch tested, kg (lb); AF= Fine aggregate absorption, percentage dry mass; WF= Dry mass of fine aggregate in the concrete batch tested, kg (lb); and V = Bat
33、ch volume, m3(yd3). 10.3. Estimated Mixing Water ContentCalculate the estimated mixing water content as follows: MAMW WT WT= (4) MW Estimated mixing water content, kg/m3(lb/yd3). 11. REPORT 11.1. Report the following information: 2016 by the American Association of State Highway and Transportation O
34、fficials.All rights reserved. Duplication is a violation of applicable law.TS-3b T 318-5 AASHTO 11.1.1. Sample identification information; 11.1.2. Total measured water content, nearest kg/m3(lb/yd3); 11.1.3. Estimated mixing water content, nearest kg/m3(lb/yd3); and 11.1.4. Values of batch volume, m
35、3(yd3), absorption of all coarse and fine aggregates, percent, and dry masses of all coarse and fine aggregates in the batch kg (lb). 12. PRECISION AND BIAS 12.1. Single-Operator PrecisionThe single-operator standard deviation for total water content has been found to be 4.9 kg/m3(8.3 lbs/yd3). Note
36、 4 The single-operator precision was determined from 25 separate determinations of water content using a 1200 W microwave oven and the method published herein. Measurements were performed on 25 separate concrete mixtures, each prepared using the same mixture proportions. The mixtures prepared and te
37、sted used a constant cementitious material and water content of 335 kg/m3564 lb/yd3 and 141 kg/m3237 lb/yd3, respectively. The mixtures prepared used a limestone coarse aggregate with an absorption of 1.3 percent and a natural sand with an absorption of 1.8 percent. Note 5 The reproducibility of thi
38、s test method is being determined. 12.2. Multilaboratory PrecisionMultilaboratory estimates of precision have not been determined. 12.3. BiasThe bias of this method has not been determined. APPENDIX (Nonmandatory) X1. ADDITIONAL GUIDANCE TO THE USER X1.1. Users may measure water contents that are co
39、nsistently higher or lower than expected. To some extent this may be influenced by the very high temperatures developed within the aggregates, or cement that contains iron or conductive constituents, or sampling procedures that result in samples with varying amounts of coarse aggregate. In a 1500-g
40、specimen, one or two extra pieces of 19-mm 3/4-in. aggregate can have a significant effect on the measured total water content. X1.2. When errant results are observed, it is recommended that the user retain the dried test specimen, shake it over a No. 4 sieve, and determine the mass of the coarse ag
41、gregate as a percent of the original fresh concrete sample. This mass should be similar to the coarse aggregate mass percent in the concrete batch and is a good means of evaluating the sampling procedure. 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
