1、 Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete AASHTO Designation: R 70M/R 70-181Technical Section: 3a, Hydraulic Cement and Lime Release: Group 1 (April) ASTM Designation: C490/C490M-171American Association of State High
2、way and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001TS-3a R 70M/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 70M/R 70-181Technical Section:
3、3a, Hydraulic Cement and Lime Release: Group 1 (April) ASTM Designation: C490/C490M-1711. SCOPE 1.1. This 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 an
4、d equipment used for the determination of these length changes; and the procedures for its use. 1.2. 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
5、. 1.3. The values stated in either SI units or inch-pound units are to be regarded separately as the 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 nonconfor
6、mance with the standard. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: M 201, Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes 2.2. ASTM Standards: C219, Terminology Relating to Hydraulic Cement C1005, Standard Specification fo
7、r Reference Masses and Devices for Determining Mass and Volume for Use in the Physical Testing of Hydraulic Cements 3. TERMINOLOGY 3.1. For definitions of terms used in this test method, refer to ASTM C219. 2018 by the American Association of State Highway and Transportation Officials. All rights re
8、served. Duplication is a violation of applicable law.TS-3a R 70M/R 70-2 AASHTO 4. SIGNIFICANCE AND USE 4.1. This practice is intended to provide standard requirements for apparatus common to many test methods used in connection with cement and concrete and standardized procedures for its use. The de
9、tailed requirements as to materials, mixtures, specimens, conditioning 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 fo
10、r Determining Mass and VolumeShall conform to the requirements of 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 2
11、5-by-25-by-285-mm prisms having a 250-mm gauge length, or for 1-by-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,
12、25-by-25-by-160-mm specimens with a gauge length of 125 mm or 1-by-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 leng
13、th between the innermost ends of the gauge studs. The parts of the 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 conc
14、rete. The sides of the molds shall be sufficiently rigid to prevent 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 pro
15、perly in place, during the setting period, one of the gauge studs shown in Figure 1 or Figure 2. The gauge studs shall be of American Iron and Steel Institute (AISI)3Type 316 stainless steel or other corrosion-resistant metal of similar hardness. Gauge studs of Invar or similar metal shall be used w
16、hen specimens are tested at widely different temperatures. To 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 past
17、e or mortar into place in the mold. The gauge studs shall be set 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 shal
18、l be 250.0 2.5 mm, and 250 mm shall be considered the gauge length 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 consid
19、ered the gauge length for calculating length change. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3a R 70M/R 70-3 AASHTO Note: 1. All dimensions shown in millimeters unless otherwise noted. 2. Dim
20、ension A to be specified by purchaser. Figure 1Molds (SI Units) 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3a R 70M/R 70-4 AASHTO Note: Dimension A to be specified by purchaser. Figure 2Molds (I
21、nch-Pound Units) 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3a R 70M/R 70-5 AASHTO 5.3. Length ComparatorFor determining length change of specimens, the length comparator shall be designed to ac
22、commodate the size of specimen employed and provide or permit a positive means of contact with the gauge 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 h
23、orizontal comparator should be used with prisms with a cross section greater than 58 cm2(9 in.2). 5.3.1. 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
24、 less, accurate within 0.002 mm in any 0.020-mm range, and within 0.004 mm in any 0.200-mm range, and 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
25、 treated. They shall be fitted with collars held in place with set screws. The collars shall extend 1.5 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 t
26、he average diameter of that portion of the gauge stud tips that fit into the collars. 5.3.2. The comparator 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 wi
27、thin 0.0001 in. in any 0.0010-in. range, and within 0.0002 in. in any 0.0100-in. range, and sufficient 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.
28、 They shall be fitted with collars held in place with set screws. The collars shall extend 0.062 0.003 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 th
29、e average diameter of that portion of the gauge stud tips that fit into the collars. 5.3.3. The design 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 18
30、in., whichever is appropriate for the specimen in use. The bar shall be of a steel alloy having a coefficient 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 sha
31、pe as the contact end of the gauge studs used in test specimens. That portion of the bar that extends 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 af
32、ter heat treatment, no part of the reference bar shall be heat treated (see Note 2). The central 100 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 sha
33、ll be provided near one end with a positioning mark. Note 2Alloys such as Invar lose their low coefficient 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 f
34、or conformance to the design and dimensional requirements of this specification at least every 21/2years. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3a R 70M/R 70-6 AASHTO Figure 3Type of Suitab
35、le Apparatus for Measurement of Length Changes 6. PROCEDURE 6.1. Preparation of MoldsPrior to the molding of 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 in
36、terior surfaces of the mold with mineral oil. After this operation, set the gauge studs, taking care to keep 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
37、 same orientation. With the bar in the comparator, rotate it slowly through at least one complete revolution 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 ba
38、r when the temperature difference is more than 1.0C of the previous use of the comparator apparatus, and at 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 a
39、nd gauge that affect length readings. The reference bar is always placed in the same orientation in the comparator 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 indicate
40、d length of the bar. Appropriate steps should be taken to monitor reference bar condition and replace as needed. 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 c
41、auses a change in the dial reading. Place specimens in the instrument with the same end up each time a comparator reading is taken. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-3a R 70M/R 70-7 AAS
42、HTO 6.3.1. Obtaining Comparator Readings of Specimens Stored MoistClean the hole in the base of the comparator into 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 th
43、e room in which the comparator is being used (see Note 4). Take one bar out of immersion, blot only around the pins, 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 b
44、ar to immersion and record the reading. Continue the procedure until all bars have been read, returned to immersion, 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 refer
45、ence bar readings. If the difference in the reference bar readings is greater than 0.010 mm 0.0004 in., then use the 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
46、the section on calculation of length cha nge contemplates that a comparator reading for the reference bar will be recorded 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
47、 setting with the reference bar in place each time the reference bar is read. Doing so simplifies the calculation of 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 i
48、s tightened adequately each time the dial is reset. Note 5The purpose of the minimal blotting of the pins and no blottin g 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
49、 wiped gently with a dry cloth, the bar will shrink measurably. Therefore, drying should be minimized. 7. CALCULATION 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 ba
