AASHTO T260-97R2009混凝土和混凝土原材料中总氯离子量的采样和试验方法

TS-3c T 260-1 AASHTO Standard Method of Test for Sampling and Testing for Chloride Ion in Concrete and Concrete Raw Materials AASHTO Designation: T 260-97 (2009) 1. SCOPE 1.1. This method covers procedures for the determination of the acid-soluble chloride ion content or the water-soluble chloride ion content of aggregates, portland cement, mortar or concrete. 1.2. The total amount of chloride is usually equal to the acid-soluble chloride. However, organic additives or minerals that contain acid-insoluble chloride may be present in concrete and concrete raw materials. These constituents may become acid soluble during long-term exposure to the alkaline environment in concrete or mortar. 1.3. The age of concrete mortar, or hydrated portland cement at the time of sampling will have an affect on the water-soluble chloride ion content. Therefore, unless early age studies are desired, it is recommended that the material be well cured and at least 28 days of age before sampling. 1.4. This standard provides for the determination of chloride ion content by two procedures: Procedure A, Determination of Acid-Soluble Chloride Ion Content and Water-Soluble Chloride Ion Content by Potentiometric Titration or Ion-Selective Electrode (Laboratory Test Method); and Procedure B, Acid-Soluble Chloride Ion by Atomic Absorption (Laboratory Test Method). 1.5. Sulfides are known to interfere with the determination of chloride content. Blast-furnace slag aggregates and cements contain sulfide sulfur in concentrations that can cause such interference, which can be eliminated by treatment as noted in the test procedures. Other materials that produce a strong odor of H2S when acid is added to them should be similarly treated. 1.6. The values stated in SI units are to be regarded as the preferred standard. PROCEDURE A—ACID-SOLUBLE CHLORIDE ION AND WATER- SOLUBLE CHLORIDE ION BY POTENTIOMETRIC TITRATION OR ION SELECTIVE ELECTRODE (LABORATORY TEST METHOD) 2. APPARATUS 2.1. Sampling equipment for Procedures A and B are listed in Sections 2.1.1 or 2.1.2. 2.1.1. Core drill. 2.1.2. Rotary impact-type drill with a depth indicator and drill or pulverizing bits of sufficient diameter to provide a representative sample of sufficient size for testing. © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. sunil.dhoundeyal Line TS-3c T 260-2 AASHTO 2.1.2.1. Sample containers capable of maintaining the sample in an uncontaminated state. 2.1.2.2. Spoons of adequate size to collect the sample from the drilled holes. 2.1.2.3. A “blow out” bulb or other suitable means of removing excess pulverized material from the hole prior to re-drilling operations. 2.1.2.4. A device capable of determining the location and depth of steel reinforcement to ±3 mm (±1/8 in.). 2.2. Equipment for Chemical Testing: 2.2.1. Chloride ion or silver/sulfide ion selective electrode and manufacturer-recommended filling solutions. Note 1—Suggested electrodes are the Orion 96-17 Combination Chloride Electrode or the Orion 94-6 Silver/Sulfide Electrode or equivalents. The Silver/Sulfide Electrode requires use of an appropriate reference electrode (Orion 90-02 or equivalent). 2.2.2. A millivoltmeter compatible with the ion electrode. Note 2—Suggested millivoltmeter is the Orion Model 701 A Digital ph/mV meter or equivalent. 2.2.3. Magnetic stirrer and Teflon stirring bars. 2.2.4. Burette with 0.1-mL graduations. 2.2.5. Balance complying with M 231, Class A. 2.2.6. Balance complying with M 231, Class G 2. 2.2.7. Hot plate, 250 to 400ºC heating surface temperature. 2.2.8. Glassware, 100 and 250-mL beakers, filter funnels, stirring rods, watch glasses, dropper, wash bottles. 2.2.9. Sieve, U.S. Standard 300 μm (No. 50). 2.2.10. Whatman No. 40 and No. 41 filter papers (or equivalent). Note 3—If equivalent filter papers are used, they should be checked to confirm they do not contain chloride, which will contaminate the sample. 3. REAGENTS 3.1. Concentrated HNO3 (sp gr 1.42). 3.2. Sodium chloride, NaCl, reagent grade (primary standard). 3.3. Standard 0.01 normality NaCl solution. Dry reagent grade NaCl in an oven at 105ºC. Cool, in a desiccator, determine the mass of approximately 0.5844 g to the nearest 0.0001 g, dissolve in © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. TS-3c T 260-3 AASHTO distilled H2O, and transfer to a 1-L volumetric flask. Make up to the mark with distilled H2O and mix. Calculate the exact normality as follows: ( ) actualNaC1 ( )0.0100 0.5844 W N = (1) where: Wactual = actual mass of NaCl, and NNaCl = normality of NaCl solution. 3.4. Standard 0.01 normality AgNO3. Determine the mass of 1.7 grams of reagent AgNO3, dissolve in distilled H2O, filter into a 1-L brown glass bottle, fill, and mix thoroughly. Standardize against 25.00 mL of the NaCl solution by the titration method given in Section 5.4. Calculate the exact normality as follows: ( )( ) 3 3 NaC1 NaC1 AgNO AgNO V N N V = (2) where: 3AgNON = normality of AgNO3 solution, VNaCl = volume (mL) of NaCl solution, NNaCl = normality of NaCl solution, and 3AgNOV = volume (mL) of AgNO3 solution. 3.5. Distilled Water. Note 4—Deionized water may be used in place of distilled water for samples where extreme precision and accuracy are not demanded. 3.6. Methyl orange indicator. 3.7. Ethanol, denatured, or methanol, technical. 3.8. Hydrogen Peroxide (30 percent). 4. METHOD OF SAMPLING 4.1. Concrete Sample: 4.1.1. Determine the depth within the concrete for which the chloride content is desired. Note 5—A convenient method of determining the location and depth of reinforcement bars is a pachometer capable of determining the location and depth of steel reinforcement to ±3 mm (0.125 in.). 4.1.2. Core Method—Drill the core to chosen depth and retrieve. 4.1.2.1. When samples are received in the laboratory in other than pulverized condition, the sample shall be crushed and ground to a powder. All sawing or crushing shall be done dry (i.e., without water). All material shall pass a 0.300-mm (No. 50) sieve. All pulverizing tools and sieves shall be washed with alcohol or distilled water and shall be dry before use with each separate sample. (See note following Section 4.1.3.7.) © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. TS-3c T 260-4 AASHTO 4.1.3. Pulverizing Method: 4.1.3.1. Set the rotary hammer depth indicator so that it will drill to 13 mm (0.5 in.) above the desired depth. 4.1.3.2. Using a drill or pulverizing bit, drill until the depth indicator seats itself on the concrete surface. 4.1.3.3. Thoroughly clean the drilled hole and surrounding area utilizing the “blow out” bulb or other suitable means. 4.1.3.4. Reset the depth indicator to permit 13 mm (0.5 in.) additional drilling. 4.1.3.5. Pulverize the concrete until the depth indicator again seats itself on the concrete. Note 6—Care must be exercised during this pulverizing operation to prevent the drill bit from abrading concrete from the sides of the hole above the sampling depth. To insure against this, some users utilize a 6-mm (0.25-in.) smaller diameter bit in this step than that used in Section 4.1.3.2. 4.1.3.6. Collect at least 10 g of the material remaining in the hole using a spoon and place in the sample container. 4.1.3.7. If the sample, as collected, does not completely pass a 0.300-mm (No. 50) sieve, additional pulverizing shall be performed in the laboratory until the entire sample is finer than 0.300-mm (No. 50). Note 7—During sample collection and pulverizing, personnel shall use caution to prevent contact of the sample with hands, or other sources of body perspiration or contamination. Further, all sampling tools (drill bits, spoons, bottles, sieves, etc.) shall be washed with alcohol or distilled water and shall be dry prior to use on each separate sample. Alcohol is normally preferred for washing because of the rapid drying, which naturally occurs. 4.2. Raw Material Sample: 4.2.1. Cement samples shall be taken and prepared as prescribed in T 127, Sampling and Amount of Testing Hydraulic Cement. 4.2.2. Coarse and fine aggregate samples shall be taken as prescribed in T 2, Sampling of Aggregates. Samples shall be reduced in accordance with T 248, Reducing Samples of Aggregates to Testing Size. © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. TS-3c T 260-5 AASHTO 4.2.3. Test samples shall contain the following minimum sizes: � cement—100 g, � sand—300 g, � coarse aggregate—3000 g. 4.2.4. Coarse aggregate samples shall be crushed to pass a 4.75-mm (No. 4) sieve and then reduced down to about 300 g. The final 300 g of coarse or fine aggregate shall be ground to a minus 0.300-mm (No. 50) sieve. 5. PROCEDURE Two distinct procedures are presented here for determination of acid-soluble chloride ion or water-soluble chloride ion content. For acid-soluble chloride ion content follow Sections 5.1 and 5.2, then continue with Section 5.4. For water-soluble chloride ion content follow Sections 5.1 and 5.3, then continue with Section 5.4. 5.1. Determine the mass to the nearest milligram of a 3-g powdered sample representative of the material under tests. Note 8—Some users dry the sample to constant mass in a 105ºC oven and determine the dry sample prior to analysis. This optional procedure provides a constant base for comparison of all results by eliminating moisture content as a variable. It is generally believed that drying is only necessary when very high accuracy is desired. (See Reference 1 for data in this area.) 5.2. Procedure for Acid-Soluble Chloride Ion Content: 5.2.1. Transfer the sample quantitatively to a beaker; add 10 mL of distilled H2O, swirling to bring the powder into suspension. Add 3 mL of concentrated HNO3 with continued swirling until the material is completely decomposed. Break up any lumps with a stirring rod and dilute with hot H2O to 50 mL. Stir thoroughly to ensure complete sample digestion. If the sample contains blast-furnace slag or other sulfide-bearing material, add 3 mL of hydrogen peroxide (30 percent solution). Add five drops of methyl orange indicator and stir. If yellow to yellow-orange color appears, solution is not sufficiently acidic. Add additional concentrated HNO3 dropwise with continuous stirring until a faint pink or red color persists in the solution. Cover with a watch glass, retaining the stirring rod in the beaker. Heat the acid solution or slurry to boiling on a hot plate at medium heat (250 to 400ºC) and boil for about 1 minute. Remove from the hot plate, filter through double filter paper (Whatman No. 41 over No. 40 filter paper or equivalent). 5.2.2. Wash the filter paper 10 times with hot distilled H2O, being careful not to lift the paper away from the funnel surface. Finally, lift the filter paper carefully from the funnel and wash the outside surface of the paper with hot distilled H2O; then wash the tip of the funnel. The final volume of the filtered solution should be 125 to 150 mL. Cover with a watch glass and allow to cool to room temperature in an HCl fume-free atmosphere. Note 9—Due to the presence of relatively insoluble materials in the sample, the solution generally will have a strong gray color, making the detection of indicator color difficult at times. Running of several trial samples is suggested to give the analyst practice in detecting the indicator color. Note 10—A sample prepared to 100 percent passing 0.300-mm (No. 50) sieve should generally allow determination of any expected chloride level with adequate precision and accuracy. Samples containing highly siliceous aggregates may require finer grinding to minimize bumping during the © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. TS-3c T 260-6 AASHTO procedure in Section 5.2. This may also be the case when the concrete contains modifiers such as latex or polymer. 5.3. Procedure for Water-Soluble Chloride Ion Content: 5.3.1. Transfer the sample quantitatively to a beaker, add 60–70 mL distilled H2O. Cover the beaker with a watch glass and bring to a boil on a hot plate-magnetic stirrer using a small magnet. Boil for 5 minutes, then let stand for 24 hours in an HCl fume-free atmosphere. 5.3.2. Filter the clear supernatant liquid in the beaker through double filter paper (Whatman No. 41 over No. 40 or equivalent) into a 250-mL beaker; take care to quantitatively transfer any adhering drops on the watch glass, and use a stirring rod to aid transfer. Add sufficient hot distilled H2O to cover any residue left in the original beaker, stir 1 minute on a magnetic stirrer, and filter into the 250-mL beaker with a swirling action. Wash the beaker and the stirring rod once into the filter with hot distilled H2O. Wash the filter paper once with hot distilled H2O. Lift the filter paper carefully from the funnel and wash the outside surface of the paper with hot distilled H2O. Set aside the paper and wash the interior of the funnel and its tip with hot distilled H2O. Finally, add 1–2 drops of methyl orange indicator to the 150-mL beaker; then add concentrated HNO3 dropwise with continuous stirring until a permanent pink to red color is obtained. If the sample contains blast-furnace slag or other sulfide-bearing material, add 3 mL of hydrogen peroxide (30- percent solution). Make up the volume to 125 to 150 mL with distilled H2O. 5.4. Three alternate methods are available to determine the Cl– content of the solution. All methods utilize an ion selective electrode (Cl– or Ag+) and all methods for the purpose of this analysis give results of essentially equal accuracy and precision. 5.4.1. Method 1: Potentiometric Titration—Fill the Cl– or the Ag+ electrode with the solution(s) recommended by the manufacturer, plug it into the millivoltmeter (preferably the type with a digital rather than a dial readout), and determine the approximate equivalence point by immersing the electrode in a beaker of distilled H2O. Note the approximate millivoltmeter reading (which may be unsteady in H2O). Take the cooled sample beaker from Section 5.3 and carefully add 4.00 mL of 0.0100 normality NaCl, swirling constantly. Remove the beaker of distilled H2O from the electrode, wipe the electrode with absorbent paper, and immerse the electrode in the sample solution. Place the entire beaker-electrode assembly on a magnetic stirrer and begin gentle stirring. Using a calibrated buret, add gradually and record the amount of standard 0.01 normality AgNO3 solution necessary to bring the millivoltmeter reading to –40 mV of the equivalence point determined in distilled H2O. Then add standard 0.01 normality AgNO3 solution in 0.10 mL increments recording the millivoltmeter reading after each addition. As the equivalence point is approached, the equal additions of AgNO3 solution will cause larger and larger changes in the millivoltmeter reading. Past the equivalence point, the changes per unit volume will again decrease. Continue the titration until the millivoltmeter reading is at least 40 mV past the approximate equivalence point. The endpoint of the titration usually is near the approximate equivalence point in distilled water and may be determined by (1) plotting the volume of AgNO3 solution added versus the millivoltmeter readings. The endpoint will correspond to the point of inflection of the resultant smooth curve, or (2) calculating the differences in millivoltmeter readings between successive AgNO3 additions and calculating the total volume of AgNO3 that corresponds with each difference (i.e., the midpoints between successive additions). © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. TS-3c T 260-7 AASHTO Raw Data Differences Titrant Volume Millivolt Reading Titrant Midpoints Millivolt Difference 4.2 mL 130.0 4.25 mL 5.0 4.3 mL 135.0 4.35 mL 7.0 4.4 mL 142.0 4.45 mL 10.0 4.5 mL 152.0 etc. etc. The endpoint will be near the midpoint, which produced the largest change in millivoltmeter reading. It may be determined by plotting midpoints versus differences and defining the AgNO3 volume, which corresponds to the maximum difference on a smooth, symmetrical curve drawn through the points. However, it can usually be estimated accurately without plotting the curve by choosing the midpoint, which corresponds to the maximum difference and adjusting for asymmetry, if any. In other words, if the differences on each side of the largest difference are not symmetrical, adjust the endpoint mathematically in the direction of the largest differences. Detailed examples of this adjustment are contained in Reference 1. 5.4.1.1. Calculations: Determine the endpoint of the titration as described in Section 5.4.1 by either plotting a curve or estimating from the numerical data. Calculate the percent Cl– ion from the equation: ( )( )1 1 2 23 5453Cl percent . V N V N W − −= (3) where: V1 = endpoint in mL of AgNO3; N1 = normality of AgNO3; W = mass of original concrete sample in grams; V2 = volume of NaCl solution added, in mL; and N2 = normality of NaCl solution. 5.4.2. Method II: Gran Plot Method—This method is compatible with either a Cl– or Ag+ ion selective electrode. Attach the electrode of choice to a compatible digital millivoltmeter after filling the required solutions as per the electrode manufacturer’s instructions. Clean the electrode with distilled H2O and pat dry with absorbent paper. Determine the mass of the solution and beaker from Section 5.3 without the watch glass and record the mass. Using a calibrated buret, titrate the sample to 225 ± 5 mV (Cl– electrode) or 310 ± 5 mV (Ag+ electrode) with standard 0.01 normality AgNO3 solution. Record the volume added and the millivoltmeter reading. Continue to titrate in 0.50-mL increments recording the volume added and the millivoltmeter reading for each increment. Add and record the data for at least five increments. Empty, clean, dry, and determine the mass of the beaker. Subtract beaker mass from beaker + solution mass determined above to define solution mass. Example shown in Figure 1. Additional information on the Gran Method is given in Reference 2. © 2010 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. TS-3c T 260-8 AASHTO Figure 1—Use of Gran Method to Determine Endpoint in the Potentiometric Titration of an Acid Extract of Concrete 5.4.2.1. Gran Method Calculations: Calculate corrected values for each of the volumes recorded in Section 5.4.2 by the equation: record correct 100 V V W = (4) W = original solution mass in g, and Vrecord = volumes recorded in mL. If any of the V correct values are greater than 10, see Section 5.4.2.2. If less than 10, plot these corrected values versus the corresponding millivolt readings on Orion Gran Plot Paper (10 percent volume corrected type with each major vertical scale division equal to five millivolts) or equivalent. Draw the best straight line through the points and read the endpoint at the intersection of the line with the horizontal axis of the graph. Calculate the actual endpoint by the e