1、Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete AASHTO Designation: R 70-161Release: Group 1 (April 2016) ASTM Designation: C490/C490M-111American Association of State Highway and Transportation Officials 444 North Capitol
2、Street N.W., Suite 249 Washington, D.C. 20001TS-3a R 70-1 AASHTO Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete AASHTO Designation: R 70-161Release: Group 1 (April 2016) ASTM Designation: C490/C490M-1111. SCOPE 1.1. This s
3、tandard practice covers the requirements for the apparatus and equipment used to prepare specimens for the determination of length change in hardened cement paste, mortar, and concrete; the apparatus and equipment used for the determination of these length changes; and the procedures for its use. 1.
4、2. Methods for the preparation and curing of test specimens, conditions of testing and curing, and detailed procedures for calculating and reporting test results are contained in applicable test methods. 1.3. The values stated in either SI units or inch-pound units are to be regarded separately as t
5、he standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: M 201, Mixing Rooms, Moist
6、Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes 2.2. ASTM Standard: C1005, Standard Specification for Reference Masses and Devices for Determining Mass and Volume for Use in the Physical Testing of Hydraulic Cements 3. TERMINOLOGY 3.1. length cha
7、ngean increase or decrease in the linear dimension of a test specimen, measured along the longitudinal axis, due to causes other than applied load. 4. SIGNIFICANCE AND USE 4.1. This practice is intended to provide standard requirements for apparatus common to many test methods used in connection wit
8、h cement and concrete and standardized procedures for its use. The 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3a R 70-2 AASHTO detailed requirements as to materials, mixtures, specimens, conditio
9、ning of specimens, number of specimens, ages at which measurements are to be made, interpretation of results, and precision and bias are left to be dealt with in specific test methods. 5. APPARATUS 5.1. Reference Masses and Devices for Determining Mass and VolumeShall conform to the requirements of
10、ASTM C1005. 5.2. MoldsShall have either one or two compartments and shall be constructed as shown in Figure 1 or Figure 2. Molds for test specimens used in determining the length change of cement pastes and mortars shall provide for 25-by-25-by-285-mm prisms having a 250-mm gauge length, or for 1-by
11、-1-by-111/4-in. prisms having a 10-in. gauge length. Molds for test specimens used in the length change of concretes shall provide for prisms of the desired cross section having a 250-mm or 10-in. gauge length. In some routine tests, 25-by-25-by-160-mm specimens with a gauge length of 125 mm or 1-by
12、-1-by-61/4-in. specimens with a gauge length of 5 in. are permitted, but in case of dispute, results obtained with specimens of 250-mm (10-in.) gauge length shall govern. 5.2.1. The gauge length shall be considered as the nominal length between the innermost ends of the gauge studs. The parts of the
13、 molds shall be tight fitting and firmly held together when assembled, and their surfaces shall be smooth and free of pits. The molds shall be made of steel or other hard metal not readily attacked by the cement paste, mortar, or concrete. The sides of the molds shall be sufficiently rigid to preven
14、t spreading or warping. For the molds shown in Figure 1, the tolerance on dimension “A“ is 0.7 mm. For the molds shown in Figure 2, the tolerance on dimension “A“ is 0.03 in. 5.2.2. Each end plate of the mold shall be equipped to hold properly in place, during the setting period, one of the gauge st
15、uds shown in Figure 1 or Figure 2. The gauge studs shall be of American Iron and Steel Institute (AISI)2Type 316 stainless steel or other corrosion-resistant metal of similar hardness. Gauge studs of Invar or similar metal shall be used when specimens are tested at widely different temperatures. To
16、prevent restraint of the gauge studs before demolding of the specimen, the device for holding the gauge studs in position shall be so arranged that, if necessary, it can be partially or completely released after the compaction of the paste or mortar into place in the mold. The gauge studs shall be s
17、et so that their principal axes coincide with the principal axis of the test specimen. For the molds shown in Figure 1, gauge studs shall extend into the specimen 17.5 0.5 mm and the distance between the inner ends of the gauge studs shall be 250.0 2.5 mm, and 250 mm shall be considered the gauge le
18、ngth for calculating length change. For the molds shown in Figure 2, gauge studs shall extend into the specimen 0.625 0.025 in. and the distance between the inner ends of the gauge studs shall be 10.00 0.10 in., and 10 in. shall be considered the gauge length for calculating length change. 2016 by t
19、he American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3a R 70-3 AASHTO Note: 1. All dimensions shown in millimeters unless otherwise noted. 2. Dimension “A” to be specified by purchaser. Figure 1Molds (SI Units) 201
20、6 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3a R 70-4 AASHTO Note: Dimension “A” to be specified by purchaser. Figure 2Molds (Inch-Pound Units) 2016 by the American Association of State Highway and T
21、ransportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3a R 70-5 AASHTO 5.3. Length ComparatorFor determining length change of specimens, shall be designed to accommodate the size of specimen employed and provide or permit a positive means of contact with the ga
22、uge studs and the convenient and rapid obtaining of comparator readings (see Note 1). Note 1One type of instrument that has been found satisfactory for use with small prisms is shown in Figure 3. A horizontal comparator should be used with prisms with a cross section greater than 58 cm2(9 in.2). 5.3
23、.1. The comparator for determining length changes of specimens produced in the molds shown in Figure 1 shall provide a dial micrometer or other measuring device graduated to read in 0.002-mm units or less, accurate within 0.002 mm in any 0.020-mm range, and within 0.004 mm in any 0.200-mm range, and
24、 sufficient range (at least 8.0 mm) in the measuring device to allow for small variations in the actual length of various specimens. The terminals of the comparator shall be plane, polished, and heat treated. They shall be fitted with collars held in place with set screws. The collars shall extend 1
25、.5 0.1 mm beyond the plane face of the terminal. The collars shall allow free rotation of the gauge stud tips that fit inside the collars and have an inside diameter no more than 0.5 mm larger than the average diameter of that portion of the gauge stud tips that fit into the collars. 5.3.2. The comp
26、arator for determining length changes of specimens produced in the molds shown in Figure 2 shall provide a dial micrometer or other measuring device graduated to read in 0.0001-in. units, accurate within 0.0001 in. in any 0.0010-in. range, and within 0.0002 in. in any 0.0100-in. range, and sufficien
27、t range (at least 0.3 in.) in the measuring device to allow for small variations in the actual length of various specimens. The terminals of the comparator shall be plane, polished, and heat treated. They shall be fitted with collars held in place with set screws. The collars shall extend 0.062 0.00
28、3 in. beyond the plane face of the terminal. The collars shall allow free rotation of the gauge stud tips that fit inside the collars and have an inside diameter no more than 0.02 in. greater than the average diameter of that portion of the gauge stud tips that fit into the collars. 5.3.3. The desig
29、n shall provide a means for checking the measuring device against a reference bar at regular intervals. 5.4. Reference BarShall have an overall length of 295 3.0 mm or 170 3.0 mm 1158 18in. or 658 18in., whichever is appropriate for the specimen in use. The bar shall be of a steel alloy having a coe
30、fficient of thermal expansion not greater than two-millionths per degree Celsius. Each end of the reference bar shall be fitted with heat treated, hardened, and polished tips machined to the same shape as the contact end of the gauge studs used in test specimens. That portion of the bar that extends
31、 into the comparators collar shall have a diameter of 6 0.25 mm 0.250 0.010 in., and the length of that portion shall extend beyond the depth of the collar. Except for the tips, which are attached after heat treatment, no part of the reference bar shall be heat treated (see Note 2). The central 100
32、mm 4 in. of the length of the reference bar shall be covered by a rubber tube with a wall at least 3 mm 18in. thick to minimize the effect of temperature change during handling. The reference bar shall be provided near one end with a positioning mark. Note 2Alloys such as Invar lose their low coeffi
33、cient of thermal expansion properties when heat treated. 5.5. Check and document the bar mold dimension, gauge stud projection into the mold interior, length comparator, and length measuring device for conformance to the design and dimensional requirements of this specification at least every 21/2ye
34、ars. 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3a R 70-6 AASHTO Figure 3Type of Suitable Apparatus for Measurement of Length Changes 6. PROCEDURE 6.1. Preparation of MoldsPrior to the molding of
35、 specimens, the outside joints of the mold and the contact lines of the molds and base plate shall be sealed to prevent loss of mixing water from a freshly molded specimen. Thinly cover the interior surfaces of the mold with mineral oil. After this operation, set the gauge studs, taking care to keep
36、 them clean and free of oil, grease, and foreign matter. 6.2. Use of Reference BarFor each reference reading taken, place the reference bar into the comparator with the positioning mark in the same orientation. With the bar in the comparator, rotate it slowly through at least one complete revolution
37、 while the gauge reading is being taken. Record the minimum (shortest) gauge reading (see Note 3). Monitor and record the room temperature in which the comparator is used. Use the reference bar when the temperature difference is more than 1.0C of the previous use of the comparator apparatus, and at
38、least at the beginning and end of the specimen readings made within a half day. Note 3The reference bar is used in the comparator to correct for changes occurring to the comparator apparatus and gauge that affect length readings. The reference bar is always placed in the same orientation in the comp
39、arator apparatus to minimize changes in reading due to differences in contact surfaces. Frequent use of the reference bar can result in significant wear of the tips, which affects the indicated length of the bar. Appropriate steps should be taken to monitor reference bar condition and replace as nee
40、ded. 6.3. Obtaining Comparator ReadingsRotate specimens slowly in the measuring instrument while the comparator reading is being taken. Record the minimum reading of the dial if the rotation causes a change in the dial reading. Place specimens in the instrument with the same end up each time a compa
41、rator reading is taken. 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3a R 70-7 AASHTO 6.3.1. Obtaining Comparator Readings of Specimens Stored MoistClean the hole in the base of the comparator into
42、 which the gauge stud on the lower end of the bar fits before and after every reading. Read and record the comparator indication of the length of the reference bar and temperature of the room in which the comparator is being used (see Note 4). Take one bar out of immersion, blot only around the pins
43、, put the bar in the comparator, and read and record the indication (see Note 5). Return the bar to immersion. Take out the second bar and treat it in a like manner. Return the second bar to immersion and record the reading. Continue the procedure until all bars have been read, returned to immersion
44、, and the readings recorded. After reading the last bar, read and record the reference-bar indication and temperature of the room in which the comparator was used. Compare the two reference bar readings. If the difference in the reference bar readings is greater than 0.010 mm 0.0004 in., then use th
45、e average of the beginning and ending values for the Lx and Li factors in the formula in the calculations section. Otherwise use the beginning reading only. Note 4The equation given in the section on calculation of length change contemplates that a comparator reading for the reference bar will be re
46、corded each time the reference bar is used and a difference calculated for each test specimen reading. Alternatively, the dial gauge setting can be reset, if necessary, to its original setting with the reference bar in place each time the reference bar is read. Doing so simplifies the calculation of
47、 length change by canceling the comparator reading of the reference bar from the values of Lxand Li. If this procedure is used, care should be taken to ensure that the dial set screw is tightened adequately each time the dial is reset. Note 5The purpose of the minimal blotting of the pins and no blo
48、tting of the bars is to avoid drying and shrinkage of the bars. It has been observed that if the pins are blotted, the bar placed in the comparator and the dial read, and the bar then wiped gently with a dry cloth, the bar will shrink measurably. Therefore, drying should be minimized. 7. CALCULATION
49、 OF LENGTH CHANGE 7.1. Calculate the length change at any age as follows: ()100xiLLLG= (1) where: L = change in length at x age, percent; Lx= comparator reading of specimen at x age minus comparator reading of reference bar at x age, in inches when using Figure 2 apparatus, in millimeters when using Figure 1 apparatus; Li= initial comparator reading of specimen minus comparator reading of reference bar at that same time, in inches when using Figure 2 apparatus, in millimeters when using Figure 1 apparatus; and G =
