AASHTO T 155:13(2017) Standard Method of Test for Water Retention by Liquid Membrane-Forming Curing Compounds for Concrete.
3.1. 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 moisture from a hydraulic cement mortar. Since it is desirable to retain moisture in fresh concrete to promote the hydration process. failure of the product to minimize the escape of moisture may lead to loss of strength, cracking, shrinkage, or low abrasion resistance of the hardened concrete, or a combination thereof.
3.2. 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 scaling 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.
4.1. Mechanical Mortar Mixer—as described in ASTM C305, or a larger size mixer operating on the same principle.
4.2. Molds—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 the mold containing fresh mortar. They shall have a minimum surface area of 12 000 mm2 (18.6 in.2) and a minimum depth of 19 mm (3/4 in.). 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 I 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 to be expedient.
4.3. Gloves—of rubber or plastic to be worn while molding the specimens.
4.4. Tamper—of a nonabsorptive, nonabrasive material such as medium-hard rubber or seasoned oak rendered nonabsorptive by immersion for 15 mm in paraffin at approximately 200°C. The tamper shall be rectangular with a 25-by-50-mm (l-by-2-in.) cross section and it shall be a convenient length (150 to 300mm (6 to 12 in.)).AASHTO T 155 pdf download.