ASTM C156-20

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C156 − 17 C156 − 20
Standard Test Method for
Water Loss [from a Mortar Specimen] Through Liquid
Membrane-Forming Curing Compounds for Concrete
This standard is issued under the fixed designation C156; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers laboratory determination of the ability of liquid membrane-forming compounds for curing concrete
to reduce moisture loss from mortar specimens during the early hardening period as a measure of their applicability for curing
concrete.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. (Warning—Fresh hydraulic cementitious mixtures are caustic and may cause
chemical burns to skin and tissue upon prolonged exposure.)
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C87 Test Method for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar
C125 Terminology Relating to Concrete and Concrete Aggregates
C150 Specification for Portland Cement
C230/C230M Specification for Flow Table for Use in Tests of Hydraulic Cement
C305 Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency
C778 Specification for Standard Sand
D1475 Test Method for Density of Liquid Coatings, Inks, and Related Products
D1653 Test Methods for Water Vapor Transmission of Organic Coating Films
D2369 Test Method for Volatile Content of Coatings
E178 Practice for Dealing With Outlying Observations
This test method is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee C09.22 on
Materials Applied to New Concrete Surfaces.
Current edition approved Aug. 1, 2017Oct. 1, 2020. Published September 2017October 2020. Originally approved in 1940. Last previous edition approved in 20112017
as C156 – 11.C156 – 17. DOI: 10.1520/C0156-17.10.1520/C0156-20.
Section on Safety Precautions, Manual of Aggregate and Concrete Testing, Annual Book of ASTM Standards, Vol 04.02.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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C156 − 20
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, refer to Terminology C125.
4. Significance and Use
4.1 The moisture retaining ability of a product as determined by this test method is used to assess the suitability of materials for
contributing to an appropriate curing environment for concrete. The laboratory test method is used both in formulating and in
specifying or qualifying curing products. This test method gives the user a measure of the ability of tested curing materials to
impede the escape of water from a hydraulic cement mortar. Since it is desirable to retain water in fresh concrete to promote the
hydration process, failure of the product to minimize the escape of water may lead to loss of strength, cracking, shrinkage, or low
abrasion resistance of the hardened concrete, or a combination thereof.
4.2 Many factors affect the laboratory test results. Test results obtained may be highly variable as indicated by the precision
statement. Critical factors include the precision of the control of the temperature, humidity and air circulation in the curing cabinet,
preparation and sealing of the mortar specimens, the age and surface condition of the mortar specimen when the curing product
is applied, and the uniformity and quantity of application of the curing membrane.
5. Apparatus
5.1 Mechanical Mortar Mixer, as described in Practice C305, or a larger size mixture operating on the same principle.
5.2 Flow Table, as described in Specification C230/C230M.
5.3 Molds shall be made of metal, glass, hard rubber, or plastic, and shall be watertight and rigidly constructed to prevent distortion
during molding of the specimens or handling of the mold containing fresh mortar. They shall have a minimum surface area of
12000 mm , and a minimum depth of 19 mm. The top surface shall be round, square, or rectangular with length not more than
twice the width. The top of the mold shall have a rim to provide a firm level surface to support the wood float and to facilitate
the grooving and sealing steps of the procedure. The rim shall be parallel with the bottom surface of the mold.
NOTE 1—Take care to avoid use of an excessive amount of oil, grease, or mold release compound on molds, particularly along the top rim where sealing
compound will be applied. Use of masking tape on the top rim during application of release compound to prevent contamination has been found expedient.
5.4 Spoon—A stainless steel serving spoon having a bowl 75 to 100 mm long and 50 to 75 mm wide for transferring the mortar
from the mixing bowl to the mold.
5.5 Gloves, of rubber or plastic, to be worn while molding the specimens.
5.6 Tamper, of a nonabsorptive, nonabrasive material such as medium-hard rubber or seasoned oak rendered non-absorptive by
immersion for 15 min in paraffin at 75 to 95°C. The tamper shall be rectangular with a 25 by 50-mm cross section and it shall be
a convenient length (150 to 300 mm).
5.7 Wood Float, approximately 75 by 280 by 20 mm thick.
NOTE 2—A commercial wood float equipped with a substantial handle can be readily reduced to these dimensions. The float shall be resurfaced or replaced
when there is noticeable wear to the floating surface.
5.8 Brush, medium-soft bristle 50-mm paint brush to brush the surface of the specimens prior to sealing.
5.9 Curing Cabinet, maintained at a temperature of 37.8 6 1.1°C and a relative humidity of 32 6 2 %. The curing cabinet shall
be of a design that allows movement of conditioned air such that the solvent from the curing compound will be readily evaporated
and eliminated from the system. Air flow over the specimens shall be adjusted to provide an evaporation rate of 2.0 to 3.4 g/h as
measured by the procedure of Annex A1. The evaporation rate shall initially be measured for each position in the cabinet in which
a specimen will be placed, and shall be verified annually and whenever any changes are made to the cabinet. The range of
evaporation rates for all specimen positions in the test cabinet shall be reported.
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5.10 Balance, having the capacity to determine the mass of a filled specimen mold to the nearest 0.1 g or less.
5.11 Applicator—For spray application, any apparatus that can be used to apply the curing compound uniformly and with
minimum overspray is acceptable. For brush or roller application, use the equipment recommended by the curing compound
manufacturer.
6. Materials
6.1 Portland Cement, conforming to the requirements for Type I of Specification C150.
6.2 Graded Standard Sand, conforming to the requirements of Specification C778.
6.3 Sealing Compound, that will not be affected by the curing material and which effectively seals against moisture loss between
the boundary of the specimen and the edge of the mold.
NOTE 3—Tissue embedding wax, readily available from scientific supply houses, is a convenient and reliable sealant.
7. Conditioning
7.1 The temperature of the room and of all materials when used in this test shall be 23 6 2°C unless otherwise specified, and the
room humidity shall be 50 6 10 %.
8. Number of Specimens
8.1 A set of three or more test specimens shall be made in order to constitute a test of a given curing material.
NOTE 4—When more than one set of specimens is to be prepared, each set should be handled as a group throughout the preparation to make the elapsed
time between molding and application of the curing product as uniform as possible. This may require mixing the mortar for each set separately.
8.2 For determining the quantity of curing compound to be applied (MA) calculate the total top surface area of the specimen,
including the seal and the rim of the mold in square millimetres using appropriate geometric formulae.
NOTE 5—The area (A) used in calculating the mass loss per unit area (L) is calculated in 14.215.2 from the surface dimensions measured inside the seal
of the specimen.
9. Proportioning and Mixing Mortar
9.1 Proportioning—Determine the sand content of the mortar by adding dry sand to a cement paste having a water-cement ratio
of 0.40 by weight, to produce a flow of 35 6 5 in 10 drops of the flow table, following the procedure described in Test Method
C87. Discard the mix used to determine the proportion of sand to cement.
NOTE 6—The sand:cement ratio required varies with the source of the cement. A ratio of 2.5:1 is suggested as a starting point. Flow may be determined
on a 3 to 4 kg batch of mortar which is conveniently mixed in the mixer described in Practice C305. The mixture used to establish the sand:cement ratio
is discarded because it is thought that the age and mixing history of the mortar affect the final moisture loss results and must be controlled.
9.2 Mixing—Combine the components of the mortar in a mortar-mixing machine to produce a homogeneous mortar not more than
6 min from the time the water and the cement are combined.
NOTE 7—A generally effective sequence is to add the cement to all of the water in the mixing bowl and allow it to stand for 30 s. Then, mix at low speed
for 30 s and, without stopping the mixer, add the sand within 30 s and continue mixing for 1 min. Stop the mixer for 1 min. During the first 15 s, scrape
down the sides of the bowl. Finish by mixing for an additional 1 min, and promptly begin molding the specimens.
10. Preparing Specimens
10.1 Thoroughly clean the molds before each use. Use of a mold release is acceptable. Avoid its application to the top rim of the
mold to prevent interference with sealing of the edge.
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10.2 Half fill the mold and spread the mortar with the back of the spoon to create a layer of approximately uniform thickness. Tamp
over the entire surface with one stroke of the 25 by 50 mm face of the tamper per 1000 mm of surface area rounded to the nearest
integer. Place a second layer of mortar, sufficient in amount to slightly overfill the mold and tamp in a similar manner. Using the
25-mm wide by 150 to 300-mm long edge of the tamper, fill the indentations made by the tamping and level the surface by pressing
down firmly with a series of contacts across the entire surface. Strike off the specimen level with the top of the mold using a wood
float with one pass only, in the direction of the long axis of the specimen for rectangular molds, using a sawing motion of the float.
Keep the 75-mm face of the float firmly in contact with the mortar and edges of the mold so that the float creates a uniformly dense
surface free of voids and cracks.
10.3 Wipe the outside surfaces of the molds clean, and place the specimens in the curing cabinet maintained at the conditions
specified in 4.95.9. The specimens shall be level and not subject to vibration. The spacing between the individual specimens and
between the specimens and
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