1、Standard Method of Test for Comparative Qualitative Corrosion Characterization of Uncoated Chromium-Alloyed Steel Bars Used for Concrete Reinforcement (Tombstone Test) AASHTO Designation: T 374M/T 374-171Technical Section: 4f, Metals Release: Group 2 (June 2017) American Association of State Highway
2、 and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001TS 4f T 374M/T 374-1 AASHTO Standard Method of Test for Comparative Qualitative Corrosion Characterization of Uncoated Chromium-Alloyed Steel Bars Used for Concrete Reinforcement (Tombstone Test) AASHTO Desi
3、gnation: T 374M/T 374-171Technical Section: 4f, Metals Release: Group 2 (June 2017) 1. SCOPE 1.1. This test method, the tombstone test, provides a procedure for evaluating and comparing the relative corrosion resistance of different types of steel reinforcement. This test is designed for assessing t
4、he corrosion resistance of uncoated chromium-alloyed reinforcing steel bars as compared to carbon steel bars or other selected reference bars if indicated by the purchaser. Note 1This test method was developed for use in marine substructure applications; however, it may be applied to other non-marin
5、e environments subject to deicing salts such as concrete substructure and super structure elements. Agencies should review its use related to their climatic and geographic regions in other corrosion susceptible applications. 1.2. The values stated in either SI or inch-pound units shall be regarded s
6、eparately as standard. The inch-pound units are shown in brackets. The values stated might not be exact equivalents; therefore, each system must be used independently of the other. 1.3. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to addres
7、s all of the safety concerns associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 31M/M 31, Defo
8、rmed and Plain Carbon and Low-Alloy Steel Bars for Concrete Reinforcement M 334M/M 334, Uncoated, Corrosion-Resistant, Deformed and Plain Chromium Alloyed, Billet-Steel Bars for Concrete Reinforcement and Dowels T 22 Standard Method of Test for Compressive Strength of Cylindrical Concrete Specimens
9、T 121M/T 121 Standard Method of Test for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete T 277, Electrical Indication of Concretes Ability to Resist Chloride Ion Penetration 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. D
10、uplication is a violation of applicable law.TS 4f T 374M/T 374-2 AASHTO 2.2. ASTM Standards: A1035/A1035M, Standard Specification for Deformed and Plain, Low-Carbon, Chromium, Steel Bars for Concrete Reinforcement C192/C192M, Standard Practice for Making and Curing Concrete Test Specimens in the Lab
11、oratory. C876, Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete 2.3. Other Documents: Hartt, W. H., R. G. Powers, D. K. Lysogorski, V. Liroux, and Y. P. Virmani. Corrosion Resistant Alloys for Reinforced Concrete. FHWA-HRT-07-039. Federal Highway Administration
12、, Turner-Fairbank Highway Research Center, McLean, VA, 2007. 3. SIGNIFICANCE AND USE 3.1. The purpose of this qualitative test method is to emphasize the key differences between the corrosion behaviors of uncoated corrosion-resistant chromium alloyed reinforcing steels (CRR) as compared to carbon st
13、eel, namely the enhanced resistance to chlorides. 3.2. The rating system is designed to place steels in one of four categories or levels (0, 1, 2, and 3). There is no linear relationship between levels. It is more like a tenfold or better difference between levels. If an agency runs the test, the st
14、eels will, over time, be distinguishable by groups. The 0 level will have numbers/test values around the same as the control M 31M/M 31 carbon steel black bar. There will be some variability but these bars will be lower than the bars in level 1, which have mild corrosion resistance by having some am
15、ount of chromium. There will be a spread or variability depending on what alloys and percentage of alloys are introduced into the steel but after a period of time (months or years) the level 1 bars will hover around the values for A1035CS alloy. The level 2 rating will be associated with the UNS S32
16、101 type alloy steel category, while the high chromium steels, 18 percent chromium UNS S31653 alloy steel, will be associated with level 3. 3.2.1. In laboratories performing this testing, the black bar (steels without corrosion resistant alloys) separate quickly, the low chromium types separate slow
17、er and the higher quality stainless, or quality stainless clad, bars can take an extremely long time to show a difference or separate out. The speed of the test is related to quality of concrete and whether the concrete cracks 4. SUMMARY OF METHOD 4.1. This test method cyclically immerses reinforcin
18、g steel bars embedded in a block of concrete referred to as a tombstone in a salt water bath for several months or years until corrosion develops. 4.2. The time to corrosion is used to separate types of alloy reinforcing bars into levels of corrosion resistance. 5. TEST EQUIPMENT AND MATERIALS 5.1.
19、Immersion TanksA suitable immersion tank will most likely be a fiberglass or plastic tank that is resistant to sodium chloride solution and has favorable impact resistance or can be easily repaired if a specimen strikes the tank. For example, the two fiberglass tanks shown in Figure 1 are 28 by 30 b
20、y 48 in. and hold 30 specimens each. 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS 4f T 374M/T 374-3 AASHTO Figure 1Tombstone Test Set-Up. (The 3 percent saltwater storage tank is located in the lo
21、wer left corner, with the tombstone immersion tanks adjacent to the saltwater storage tank, and the data acquisition system above the tombstone tanks at the top of the photo). 5.2. Sample BoosterThe sample booster provides a means of lifting specimens out of residual salt water during dry periods of
22、 the wet/dry exposure cycle. It must be resistant to saltwater and moisture, as well as impact resistant or easily repaired, if specimen strikes the booster material. An example of a sample booster is shown in Figures 2 and 3. 5.3. Sample SpacersA sample spacer provides a means of adding stability t
23、o specimens since the height of the specimen is much greater than the width. This item is not required for testing but should be considered to reduce the chance of damaging the specimens. The spacer must be resistant to saltwater and moisture. An example is shown in Figure 3. Figure 2Close-Up of 1-i
24、n. Plastic Square Tube That Functions as a Sample Booster 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS 4f T 374M/T 374-4 AASHTO Figure 3Picture of Sample Spacers (Upper Wooden Slots) and Sample Bo
25、osters (Lower Plastic Rails) 5.4. Saltwater Test SolutionThe saltwater test solution is a 3 percent by weight sodium chloride solution. The solution volume needed depends on the size of the immersion tank. To calculate the quantity of a saltwater solution required, the bottom 6 in. of the tombstone
26、specimens plus the height of the sample booster must be considered in conjunction with the other two dimensions of the ponding tank. 5.5. Data Acquisition System (DAS)The DAS will be used to monitor the voltage across a 1- resistor on each block. Therefore, it is important that the DAS have sufficie
27、nt channels for the number of tombstones being tested. In addition, the DAS must have high impedance terminals and, for DC voltage measurement, a maximum resolution of 1 V at 20 mV and measurement accuracy integral time 1.67 ms (0.1 percent of rdg. + 25 digits) at 20 mV, all at standard operating co
28、nditions. 5.6. Test SpecimensThe rebar tested will include, in addition to the candidate bar specimens, test specimens with types 316LN (UNS S31653), either XM-28 (UNS S24100) or type 304 (UNS S30400), and ASTM A1035/A1035M No. 5 steel bars with each bar being in an as-received condition. Each test
29、specimen, or tombstone, will have a single type of reinforcing steel embedded in a concrete block that meets the agencys specified concrete mix design, except that the concrete shall only contain cement and aggregate. The coarse aggregate fraction of concrete mix will contain 50 percent 3/8- to 1/2-
30、in. particles and 50 percent No. 4 aggregate to 3/8-in. aggregate particles sieved out of a standard AASHTO aggregate gradation. The tombstone specimens have dimensions (shown in Figure 4) that will ensure rapid corrosion test results for an embedded steel type test. After the tombstone specimens ha
31、ve been cast and cured for 28 days, the exposed ends of the bars will be cleaned to expose the base metal, and after making the electrical connections, a two part epoxy, such as a 100 percent solids high build epoxy, will be applied to the bars and top of the specimens. The bars embedded in concrete
32、, as shown in Figure.4, with the exposed bar ends connected and epoxy applied, is considered a “test specimen,” which is also known as a tombstone test specimen or simply a tombstone. The three bars of each type steel in the test specimen must come from the same lot/heat and the chemical composition
33、 of the bars should be determined or verified as specified in M 334M/M 334, Section 20.1.6 to ensure the chemical composition testing is performed. If a purchaser is interested in modifying the bar configuration, other bar configurations are possible and discussed in the report by Hartt et al. 2017
34、by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS 4f T 374M/T 374-5 AASHTO Figure 4Illustration of Tombstone Specimens with Sample Dimensions (1/16in.) 6. TEST METHOD 6.1. Description of TestsThis test meth
35、od is a low maintenance test procedure that allows for the penetration of chlorides from the surface of the concrete to the reinforcing steel through multiple sides of a test sample. 7. EXPERIMENTAL PROCEDURE 7.1. Tombstone Concrete Mix DesignThe concrete used for the tombstone specimens will meet t
36、he requirements of the reference mix design below or a mix design set by the specifying agency. 7.1.1. Reference Concrete Mix Design: 7.1.1.1. 635 lb Type I/II cement; 7.1.1.2. 900 lb 3/8- to 1/2-in. coarse fraction of AASHTO No. 7 or No. 8 limestone aggregate; 7.1.1.3. 900 lb No. 4 to 3/8-in. coars
37、e fraction of AASHTO No. 7 or No. 8 limestone aggregate; 7.1.1.4. 1200 lb fine aggregateOttawa graded sand; 7.1.1.5. 300 lb water; and 7.1.1.6. 6 percent air. 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable
38、 law.TS 4f T 374M/T 374-6 AASHTO 7.1.1.7. Permeability range greater than 4000 coulombs 7.1.2. Agency Mix DesignAn agency should select a representative mix for their geographic and climatic region. The water cement ratio for the agency should be chosen to represent the highest anticipated acceptabl
39、e w/c for a project to yield realistic results. The better the quality of the concrete mix, the longer the projected time until corrosion is initiated. Therefore, it is recommended to not incorporate fly ash, granulated iron blast-furnace slag, silica fume, or metakaolin into the mix design. 7.1.2.1
40、. Example Typical DOT Mix Design Based on Absolute Volume Method of ACI: 7.1.2.1.1. 635 lb Type I/II cement; some variability in cement content is permissible as long as the water-to-cement ratio is within the range of 0.45 to 0.50). 7.1.2.1.2. 900 lb 3/8- to -in. coarse aggregate indicative to regi
41、on or district (Specific Gravity x.xxx). 7.1.2.1.3. 900 lb No.4 to 3/8-in. coarse aggregate indicative to region or district (Specific Gravity x.xxx). 7.1.2.1.4. 1200 250 lb Natural sand indicative to region or district (Specific Gravity x.xxx). 7.1.2.1.5. 286 to 318 lb water (watercement ratio rang
42、e of 0.45 to 0.50). 7.1.2.1.6. 5 to 8 percent air. 7.2. Tombstone MoldsAn illustration of a tombstone mold is shown in Figure 5. These molds have two regions. The upper mold region does not receive concrete and is used to align and secure the bars prior to casting. The lower mold region is where the
43、 concrete is placed to embed the steel bars. Figure 5Illustration of Forms Used to Cast Tombstone Specimens 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS 4f T 374M/T 374-7 AASHTO 7.3. Casting Tombs
44、tonePlace a single type of reinforcing steel in the tombstone molds, adjust the bar heights to ensure that the concrete cover will be consistent, and cover all bolt hardware and exposed form edges with tape, as shown in Figure 6. 7.3.1. Mix and cast concrete specimens following T 121M/T 121, ASTM C1
45、92/C192M, and specifying agency protocol. The concrete can be placed in a single lift and consolidated by vibrating the entire form. In addition to casting tombstone specimens, 4-in cylinder specimens should also be cast for 28-day compressive strength (T 22) and permeability (T 277) testing to conf
46、irm the concrete quality. After casting, specimens should be allowed to cure properly before performing any additional work on the specimens. Figure 6Photograph of Tombstone Molds That Are Ready for Concrete Casting Phase 7.4. Connections and WiringAfter the specimens have properly cured (28 days),
47、remove specimens from the curing room and clean the exposed bar ends to remove any rust and ensure quality electrical contact between the rebar and the wire. To make connection between embedded rebar, stranded copper wire (size range: No. 10 to No. 16) will be used. The connectors can be soldered or
48、 solderless. Solderless connectors are used if the connections will be unplugged and plugged frequently. Examples of solderless connectors used to couple the blocks to the data acquisition system and to connect the wire to each rebar are shown in Figure 7. A rivet will be used to join the solderless
49、 connector and the rebar. A hole, slightly larger than the rivet, is drilled into the end of each piece of rebar and the rivet is used to secure the solderless connector to the rebar. The size of the rivet is not as important as the fit between the rivet and the ring style solderless connector. A 3/16-in. rivet, which is shown in Figure 8, has been used successfully. A 1- resistor is placed in series between the electrically connected anode bars and cathode bar, as shown in Figure 9. 2017 by the American Association of State High
