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123 APPENDIX C Specifications for Standard Surface Test Methods Introduction cement, concrete mix-water quickly becomes saturated with calcium hydroxide. This calcium hydroxide solution reacts Based on the experimental results conducted during this with drawing-compound residues on the strand. This is the study, four surface and chemical test methods have been rec- form of the residue on the strand when it is in concrete. Thus, ommended for inclusion in a QC program to assess strand this is the form of the residue that affects the bond, and this bond. The recommended QC methods have been written in is the form to be assessed with this test. AASHTO/ASTM standard method format and presented in 1.3 This standard does not purport to address the safety this appendix. concerns, if any, associated with its use. It is the responsibility of They are titled: the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory 1. Test Method for the Determination of the Surface Tension limitations prior to use. of Steel Strand by Contact Angle Measurement, 2. Test Method for Weight Loss on Ignition (LOI) of Steel Strand, Apparatus 3. Test Method for Change in Corrosion Potential of Steel 2.1 Contact angle meter--The contact angle of a water Strand, and droplet on a strand sample surface is measured using a contact 4. Test Method for Identification and Quantification of angle meter.1 The apparatus has a built-in syringe to dispense Residue on Steel Strand by Extraction, Gravimetric, and distilled water droplets of a small, precise size. Also, it has a Spectroscopical Analyses. fiber optic light source and a focusing lens to project the water droplet image onto a graduated screen. A photograph of the Proposed Standard Test Method apparatus is shown in Figure C-1. for Determination of the Surface Tension of Steel Strand by Contact Specimens Angle Measurement 3.1 The strand segments shall be cut to a length of 12 in., Scope a length suitable to fit on the V-shaped sample pedestal of the 1.1 The contact angle of a water droplet on a strand surface apparatus. is a measure of surface tension (wet-ability). The presence of drawing lubricants will affect this property. A relatively high Test Procedures amount of water-insoluble drawing lubricants will cause a relatively high contact angle value. The contact angle is meas- 4.1 The procedure for preparation of each strand segment ured on the projected shadow of a droplet of distilled water is described as follows: applied to the strand surface using a specialized instrument 4.1.1 Immerse the entire strand segment, or the portion to designed for this purpose. be tested, in saturated calcium hydroxide solution for 10 min. 1.2 The contact angle is measured after immersing the strand sample in a saturated calcium hydroxide [Ca(OH)2] solution to simulate the environment surrounding the strand 1 This device is commercially available as Cam Plus Micro contact angle meter when it is in concrete. Due to the chemistry of Portland manufactured by ChemInstruments, Inc., Fairfield, OH.

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124 (a) (b) Figure C-1. Contact angle meter (a) and close-up of drop projection (b). 4.1.2 Immerse in de-ionized water for 5 min. twice the angle measured from the apex of the drop, is already 4.1.3 Dry by allowing vertical strand to drip while expos- doubled on the projection screen scale. Record this contact ing to a warm air stream from a minimum 100 W heat gun angle. held at a distance of 12 in. for a period of 2 min. 4.1.4 Set strand on a clean surface and cool to room Calculation temperature. 4.2 The procedure for contact angle measurement with 5.1 Measure and record six individual contact angle the aforesaid apparatus is as follows: readings for each sample. The individual readings are used 4.2.1 Set the strand sample horizontally on the pedestal of to calculate a mean average contact angle. the test apparatus with the surface to be tested facing upward. 4.2.2 Adjust the projection lens so that silhouettes of both Report the wire surface and the syringe needle are in focus. 4.2.3 Adjust the position of the helical wire surface to 6.1 The mean average contact angle and the source of the achieve a level silhouette on the projection screen under the strand are reported. syringe needle. 4.2.4 Adjust the syringe needle so that it is directly over the Interpretation high point of the helical wire surface. 4.2.5 Form a distilled water droplet at the tip of the syringe. 7.1 A lower contact angle corresponds to better bond per- Rotate the syringe barrel to form a droplet with a diameter of formance. In our past studies, measured contact angles 7 units on the scale imprinted on the projection screen below 85 after the calcium hydroxide exposure were indica- 4.2.6 Raise the pedestal holding the strand sample until tive of, but did not guarantee, good bond potential. As was the wire surface touches the water droplet, and then lower the observed when comparisons were made with transfer length, pedestal until the water droplet is released from the syringe the contact angle measured on the strand after exposure to needle. calcium hydroxide correlated well with concrete pull-out bond 4.2.7 Adjust the sample pedestal and the projection screen stresses (that is, bond stress at first or 0.1-in. slip during con- to align the left-hand side of water droplet silhouette with the crete pull-out testing is inversely proportional to contact angle). y-axis and origin of the scale on the screen. The contact angle was lower with greater bond stress. 4.2.8 Adjust the dial of the protractor on the projection screen so that the indicator line intersects the apex of the Precision and Bias water droplet silhouette. 4.2.9 Measure the angle from the apex of the drop using the 8.1 Single-operator precision--The single-operator stan- protractor scale. Please note that the contact angle, which is dard deviation was found to be 4F. Therefore, results of two

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125 properly conducted tests by the same operator on the same Specimens source are not expected to differ from each other by more than 10F. (These numbers represent, respectively, the (1s) 3.1 Three segments per strand source shall be cut and and (d2s) limits as described in ASTM C670 [ASTM 2003].) loosely wrapped in uncoated aluminum foil for transport to 8.2 Bias--Since there is no accepted reference material minimize contamination or abrasion of the strand surfaces. suitable for determining the bias in this test method, no state- Each strand segment shall be cut to a length of 23.0 cm 0.5 ment on bias is made. cm. The operator shall handle the strand segments with pow- der-free latex gloves. Keywords Test Procedure 9.1 strand; contact angle. 4.1 The LOI of each strand segment is measured using the following procedure: Proposed Standard Test Method 4.1.1 Measure the length of the strand segment to the for Weight Loss on Ignition nearest 0.1 cm. of Steel Strand 4.1.2 Determine the nominal diameter of the strand. 4.1.3 Dry the strand segment sample for 4 h at 110C. Scope 4.1.4 Cool sample in a desiccator for at least 12 h. 1.1 The weight loss on ignition (LOI) represents the weight 4.1.5 Weigh the sample three times to 0.1 mg precision. of compounds that can be volatilized or burned off the strand Record these initial weights and calculate the average weight. surface at high temperature. This property is measured with 4.1.6 Ignite samples for 30 min at 415C. the expectation that the weight loss represents the quantity of 4.1.7 Cool samples to room temperature in a desiccator volatile residues from organic components of drawing lubri- for at least 12 h. cants and organic contaminants such as lubricating oils. 4.1.8 Weigh each sample again three times on the same 1.2 This standard does not purport to address the safety con- analytical balance. Record these final weights and calculate cerns, if any, associated with its use. It is the responsibility of the the average final weight. user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limita- Calculation tions prior to use. 5.1 The LOI reported for the strand source is the change in average weight divided by the surface area of the strand. Apparatus The surface area can be calculated by 4 nominal diameter 2.1 Balance--An analytical-grade weighing instrument shall tested length. have a maximum capacity of at least 300 g and a precision of 0.1 mg. The sample compartment shall be at least 24.5-cm Report high to accommodate a vertically set sample. 2.2 Graduated cylinder--A 25-mL glass or plastic graduated 6.1 Report the loss on ignition in milligrams per square cylinder is needed to hold the strand sample in a vertical po- centimeter (mg/cm2) of strand and the source of the strand. sition on the balance pan while weighing. The tare weight of the cylinder is subtracted from the weight reading to obtain Interpretation the net weight of the sample. 2.3 Oven and furnace--The drying oven and ignition fur- 7.1 In past studies, the mass LOI decreased as the pull-out nace instruments shall both have sufficient chamber length bond stress increased. and volume to accommodate at least three strand segments. The drying oven shall be capable of heating the samples to Precision and Bias 110C 5C, and the ignition furnace shall be capable of heating the specimens to 415C 5C. 8.1 Single-operator precision--The single-operator standard 2.4 Desiccator--A glass desiccating chamber shall use gran- deviation was found to be 0.014 mg/cm2. Therefore, results of ular calcium chloride desiccant and a ceramic disk insert on two properly conducted tests by the same operator on the same which to rest strand segments and to separate samples from source are not expected to differ from each other by more than desiccant. The chamber shall have sufficient volume to accom- 0.041 mg/cm2. (These numbers represent, respectively, the (1s) modate at least three strand segments. and (d2s) limits as described in ASTM C670 [ASTM 2003].)

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126 8.2 Bias--Since there is no accepted reference material 4.4 It is recommended that the test is to be performed in a suitable for determining the bias in this test method, no state- temperature-controlled environment (e.g., an air-conditioned ment on bias is made. room), so that variation of solution temperature throughout the test is less than 3C. Keywords Interferences 9.1 strand; ignition; mass loss. 5.1. Extended exposure of reference electrodes with ceramic Proposed Standard Test Method tips of inferior quality may introduce aggressive ions such as for Change in Corrosion Potential chloride into the testing solution, and such contamination of Steel Strand might alter testing results. Immersion time of reference elec- trodes shall be minimized. Copper/copper sulfate reference Scope electrodes with porous wood plugs shall not be used. 1.1. This test method covers the estimation of change in the electrochemical corrosion potential of prestressed strands Apparatus in de-ionized water, for the purpose of indirectly estimating 6.1 Reference electrode--either a standard calomel electrode the bond performance of prestressing strand in concrete. 1.2. This standard does not purport to address the safety con- or Ag/AgCl electrode with controlled rate of leakage (about cerns, if any, associated with its use. It is the responsibility of the 3 L/h) can be used. Such electrodes are durable, reliable, and user of this standard to establish appropriate safety and health commercially available. practices and determine the applicability of regulatory limita- 6.2 Voltmeter--The division on the scale shall be such that tions prior to use. a potential difference of 0.02 V or less can be read without interpolation. Referenced Documents Test Solution 2.1 ASTM Standards: 7.1 De-ionized water shall be used. G3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing Test Specimens G15 Standard Terminology Relating to Corrosion and Corrosion Testing 8.1 Strand specimens shall be 9-in. long. 8.2 The cut-end to be immersed in solution shall be sealed with a two-component epoxy. No more than 1/2 in. of the Summary of Test Method side of the strand shall be coated. 3.1 Specimens of strands are immersed in de-ionized water 8.3 Specimens shall be tested in as-received condition, and at room temperature. Corrosion resistance of strands is char- surface contamination shall be avoided. acterized by measuring corrosion potential change from initial immersion after 6 h of immersion. Continuous potential Procedure monitoring with a potentiostat is optional. At least triplicate specimens shall be used and specimens shall be tested either 9.1 Place the strand specimen(s) in a 2-L beaker and sup- as received or after ignition. port firmly. A plexiglass plate with drilled holes shall be used to hold the specimens in place. When multiple specimens are used, the specimens shall be widely separated to avoid any Significance and Use direct contact with each other. 4.1. This test method is intended for use as a rapid quality 9.2 Introduce de-ionized water to the 2-L mark. Insert a control method to indirectly assess the bonding characteristics reference electrode into the solution without disturbing any of prestressing strand. Laboratory testing has demonstrated strand. that strands with greater changes in potential have reduced 9.3 Measure the potential of each strand specimen at the bond strength. start of testing and then after 1 h and after 6 h of the immersion. 4.2. Specimens are tested in as-received condition. It is 9.4 If the potential of strand is being monitored with a po- also possible to test specimens after ignition. tentiostat, the reference electrode shall be introduced before 4.3 Contamination of testing solution shall be avoided. monitoring starts.

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127 Report Apparatus 10.1 Record the test procedure used, specimen size, temper- 2.1 Balance--An analytical-grade weighing instrument ature, and potentials. shall have a maximum capacity of at least 300 g and a precision 10.2 Calculate changes in potential from the initial meas- of 0.1 mg. The weighing instrument shall have a maximum urement to the potential measurement after 1 h and 6 h of capacity of at least 50 g and a precision of 0.1 mg. exposure. 2.2 Glassware--The test procedure requires the use of 10.3 Report following information: the following glassware: a glass cylinder (Pyrex No. 2962), 10.3.1 Strand identification, a 1000-mL glass separatory funnel (Pyrex No. 6402), a 400-mL 10.3.2 Type of reference electrode, and glass beaker, and a 50-mL glass beaker. 10.3.3 Change in potential at 1 h and at 6 h. 2.3 FTIR--Use an FTIR spectroscope capable of analyzing 10.3.4 When a potentiostat is used to monitor potential the chemical make-up of the organic residue. Spectroscopic change, a plot of potential change versus time shall be reported. grade potassium bromide (KBr) plates will be required for FTIR analysis. 2.4 Reagents--Reagent grade hydrochloric acid (HCl), de- Precision and Bias ionized water, and HPLC grade chloroform are required for 11.1 Single-operator precision--The single-operator stan- this procedure. dard deviation was found to be 0.047 V. Therefore, results of two properly conducted tests by the same operator on the same Specimens source are not expected to differ from each other by more than 0.133 V. (These numbers represent, respectively, the (1s) 3.1 Each strand sample shall be cut to a minimum length and (d2s) limits as described in ASTM C670 [ASTM 2003].) of 35.5 cm (14 in.). A preferable strand segment length is in 11.2 Bias--Since there is no accepted reference material the range of 40.6 cm (16 in.) to 45.7 cm (18 in.) long. The suitable for determining the bias in this test method, no state- upper boundary of the test portion area shall be marked by ment on bias is made. cutting a small notch at a length of 30.5 cm (12 in.) from the bottom of the strand segment. Keywords Test Procedure 12.1 Corrosion potential, strand, reference electrode. 4.1 The organic drawing-compound residues on the strand segment sample are extracted, quantified, and identified using Proposed Standard Test the following procedure: Method for Identification 4.1.1 Perform all steps involving hydrochloric acid and and Quantification of Residue chloroform under a fume hood. Place a straight strand seg- on Steel Strand by Extraction, ment with a minimum length of 35.5 cm (14 in.) in a clean Gravimetric, and Spectroscopical Pyrex No. 2962 glass cylinder, which is about 31.8 cm (12.5 in.) Analyses deep by 3.6 cm (1.4 in.) inside diameter. While wearing powder-free latex gloves, handle the strand segment only Scope above the test portion length of 30.5 cm (12 in.). 1.1 The test methods for identification and quantification 4.1.2 Fill glass cylinder containing strand sample to a of organic drawing-compound residues on strand surfaces 12-in.-deep mark with 10% hydrochloric acid solution (about are based on solvent extraction procedures, together with gravi- 280 mL) pre-heated to 120F. Two-liter quantities of acid metric and Fourier transform infrared spectroscopy (FTIR) solution can be prepared in advance by adding 472 mL of analyses. Essentially, the amount of material extracted from ACS-grade concentrated hydrochloric acid (37.2% hydrochlo- a defined length of strand is determined by weighing the ric acid assay, 1.19 specific gravity) to 1528 mL of de-ionized extraction residue on an analytical balance. The material(s) water to achieve a 10% hydrochloric acid solution. in the extraction residue are then identified by FTIR spectro- 4.1.3 Allow 12-in.test portion of strand segment to set in scopical analysis. 10% hydrochloric acid solution for 10 min, with frequent 1.2. This standard does not purport to address the safety con- agitation of solution by stirring with strand segment. Carefully cerns, if any, associated with its use. It is the responsibility of the transfer acidic solution to a clean 1000-mL glass separatory user of this standard to establish appropriate safety and health funnel (Pyrex No. 6402). Rinse strand and cylinder with practices and determine the applicability of regulatory limita- 20 mL of 10% hydrochloric acid solution, and transfer acidic tions prior to use. solution to separatory funnel.

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128 4.1.4 Fill glass cylinder containing strand sample to a for analysis by FTIR spectroscopy. The FTIR spectrum is in- 12-in.-deep mark with HPLC-grade chloroform (approxi- terpreted to identify the residue. mately 280 mL). Allow 12-in. test portion of strand segment to set in chloroform for 10 min, with frequent agitation of Calculation solvent by stirring with strand segment. 4.1.5 Wearing powder-free latex gloves and handling the 5.1 The extraction residue weight shall be determined by strand segment only above 12-in. test portion, very slowly lift weighing on an analytical balance once to the nearest 0.l mg. the strand sample from the solvent while scrubbing the strand This weight shall be divided by the surface area of the strand at solvent surface using a rubber policeman (a spatula-shaped, sample's test portion, in square centimeters (cm2). The surface latex-rubber tip on the end of a glass rod). The elapsed time area of the strand shall be calculated in cm2 as follows: 30.5 for the scrubbing process of the entire 12-in. test portion should 4/3 D where D = nominal diameter of the strand. After be about 3 min. Briefly immerse the 12-in. test portion into weighing, the residue is identified by FTIR spectroscopical solvent and agitate to remove as much solvent-soluble mate- analysis, and the FTIR spectrum interpretation is reported. rial as possible. Remove strand sample from solvent. 4.1.6 Carefully transfer solvent to the glass separatory fun- Report nel that contains the acidic solution. Rinse strand sample over glass cylinder with about 20 mL of chloroform, swirl solvent 6.1 The weight of the residue shall be reported in units of in glass cylinder, and pour rinse solvent into same separatory mg/cm2 of strand surface. Our past studies have found that a funnel. Stopper the separatory funnel, and shake it for 5 min. relationship exists between the extracted organic residue and Vent funnel occasionally to release vapor pressure. After the average bond stress over the transfer length. As bond stress shaking, allow separatory funnel with liquid contents to rest increased, extraction residue decreased. The relationship is in an upright position so that chloroform settles to bottom of especially evident in the total extraction residue (combined funnel. The acidified aqueous solution becomes the top liquid from water and acid/chloroform wash solutions) plotted for layer. both of these procedures. 4.1.7 Place the beaker below the separatory funnel and open The report shall also include the infrared spectrum of the stopcock of separatory funnel slowly and carefully to drain residue, and the interpretation of the spectrum by the spec- chloroform only into the beaker. Place beaker on a hot plate troscopist. set at less than 70C to evaporate chloroform in a controlled manner. The evaporation process can be aided by directing Precision and Bias the air flow of a fan over the top of the beaker. 4.1.8 The 400-mL beaker with dried residue is rinsed with 7.1 Single-operator precision--The single-operator stan- about 10 mL of chloroform, and the chloroform with solvent- dard deviation was found to be 0.013 mg/cm2. Therefore, re- soluble residue is transferred to a clean, pre-weighed 50-mL sults of two properly conducted tests by the same operator on beaker. The chloroform rinse procedure is repeated twice the same source are not expected to differ from each other by (a triple rinse procedure). The chloroform with solvent- more than 0.037 mg/cm2. (These numbers represent, respec- soluble residue in the 50-mL beaker is evaporated at less than tively, the (1s) and (d2s) limits as described in ASTM C670 70C. The beaker is reweighed to determine the net weight [ASTM 2003].) gain due to solvent-soluble, dried residue. Bias--Since there is no accepted reference material suit- 4.1.9 The dried residue, if any, is transferred with chloro- able for determining the bias in this test method, no state- form to a spectroscopical-grade potassium bromide salt plate ment on bias is made.