Standard Methods of Making and Storing Specimens of Concrete in the Field (Serial Designation: C 31) of the American Society for Testing Materials. Materials. 2. Materials shall be brought to room temperatures (65 to Preparation of 75° F.) before beginning tests. Cement shall be stored in a dry place; preferably in covered metal cans. The cement shall be thoroughly mixed in advance, in order that the sample may be uniform throughout the tests. It shall be sifted through a No. 16 sieve and all lumps rejected. Aggregates shall be in a roomdry condition when used in concrete tests. In general, aggregates should be separated on the No. 4, %-in. and 12-in. sieves* and recombined to the average original sieve analysis for each batch. Fine aggregate should be separated into different sizes also, in cases where unusual gradings are being studied. Tests. 3. Representative samples † of all concrete materials shall be Sampling for secured for preliminary tests prior to the proportioning and Preliminary mixing of the concrete. Cement test samples may be made up of a small quantity from each sack used in the concrete tests. Test samples of aggregates may be taken from larger lots by quartering. 4. Cement shall be subjected to test, using the methods Cement Tests. described in the Standard Specifications and Tests for Portland Cement (Serial Designation: C 9) of the American Society for 5. Fine aggregates (passing through a No. 4 sieve) shall be Fine Aggregate subjected, when required, to the following tests: (a) Sieve analysis test made in accordance with the Standard Method of Test for Sieve Analysis of Aggregates for Concrete (Serial Designation: C 41) of the American Society for Testing Materials. (b) Test for organic impurities (natural sand only) made in accordance with the Standard Method of Test for Organic Impurities in Sands for Concrete (Serial Designation: C 40) of the American Society for Testing Materials. (c) Test for quantity of silt, clay or dust made in accordance with the Tentative Method of Decantation Test for Sand and Other Fine Aggregates (Serial Designation: D 136-22 T) of the American Society for Testing Materials. (d) Test for unit weight made in accordance with the Standard Method of Test for Unit Weight of Aggregate for Con *For specifications for sieves, see Standard Method of Test for Sieve Analysis of Aggregates for Concrete (Serial Designation: C 41) of the American Society for Testing Materials, Appendix 8. † For methods of sampling large lots of deposits of aggregate, see the Standard Methods of Sampling Stone, Slag, Gravel, Sand, etc., for Use as Highway Materials (Serial Designation: D 75) of the American Society for Testing Materials, 1924 Book of A.S.T.M. Standards Tests. Coarse Aggregate Tests. Mixed Aggregate Proportioning. Size of Test Mixing Concrete. crete (Serial Designation: C 29) of the American Society for Testing Materials. (e) Strength test of 1:3 mortar by weight at 7 and 28 days in comparison with standard sand mortar. 6. Coarse aggregates (retained on a No. 4 sieve) shall be subjected when required to the following tests: (a) Sieve analysis test as specified under Section 5 (a); (b) Test for quantity of silt, clay or dust, as specified under Section 5 (c); (c) Test for unit weight as specified under Section 5 (d). 7. The unit weight of mixed fine and coarse aggregates as used in concrete tests shall be determined in accordance with the method specified in Section 5 (d). 8. The quantities of each size of aggregate to be used in each batch shall be determined on the basis of the sieve analysis and the unit weight of the mixed aggregate. The exact quantities of cement and of each size of aggregate for each batch shall be determined by weight. The quantity of water for each batch shall be accurately measured. The quantities of materials may be expressed as (a) 1 volume of cement to volumes of total aggregate mixed as used, or (b) 1 volume of cement, volumes NOTE. It is impracticable to give a general method for proportioning concrete for experimental purposes; the details will necessarily vary widely with the purpose for which the tests are made. The following procedure is suggested for specific cases: (a) Vary the cement content by 10-per-cent intervals above and below assumed quantity. (b) Vary the proportions of fine to coarse aggregate, measured separately, at intervals of 10 per cent. (c) Vary the quantity of mixing water by intervals of 10 per cent. 9. Compression tests of concrete shall be made on cylinders of a diameter equal to one-half the length. The standard shall be 6 by 12-in. cylinders where the coarse aggregate does not exceed 2 in. in size; for aggregates larger than 2 in., 8 by 16in. cylinders shall be used; 2 by 4-in. cylinders may be used for mixtures without coarse aggregate. 10. (a) Concrete shall be mixed by hand in batches of such size as to leave a small quantity of concrete after molding a single test piece. The batch shall preferably be mixed in a shallow galvanized steel pan with a 10-in. bricklayer's trowel which has been blunted by cutting off about 21⁄2 in. of the point, as follows: (b) The cement and fine aggregate shall be mixed dry until the mixture is homogeneous in color; (c) The coarse aggregate shall be added and mixed dry; (d) Sufficient water shall be added to produce concrete of the required workability; NOTE.-Concrete tests should be made on plastic mixtures. It is of the utmost importance that a uniform degree of workability be secured in tests involving comparisons of different materials and methods. (e) The whole shall be mixed thoroughly until the entire mass is homogeneous in appearance. 11. The workability or plasticity of each batch of concrete Workability. shall be measured immediately after mixing by one of the following methods: (a) Slump test made in accordance with the Tentative Method of Test for Consistency of Portland-Cement Concrete for Pavements or for Pavement Base (Serial Designation: D 138– 22 T) of the American Society for Testing Materials. (b) Flow test made by placing a metal form in the shape of a frustum of a cone 634 in. in top diameter, 10 in. in bottom diameter, 5 in. deep, on the table of the flow apparatus.* The fresh concrete shall be placed in the mold in two layers. Each layer shall be puddled and finished as described in Section 13. Immediately after molding, the form shall be removed by a steady upward pull; the specimen raised 1⁄2 in. and dropped 15 times in about 6 seconds by means of a suitable cam and crank. The spread of the fresh concrete due to this treatment as compared with the original bottom diameter of the cone, expressed as a percentage, is the "flow." 12. The forms shall preferably be of metal. Each form shall Forms. be provided with a machined metal base plate, and shall be oiled with a heavy mineral oil before using. Particular care shall be taken to obtain tight forms so that the mixing water will not escape during molding. NOTE. The best type of form consists of lengths of cold-drawn steel tubing, split along one element and closed by means of a circumferential band and bolt. Satisfactory forms can be made from lengths of steel water-pipe machined on the inside, from rolled metal plates, from galvanized steel, machined iron or steel castings. Paraffined cardboard molds will give good results under expert supervision. Pieces. 13. Concrete test pieces shall be molded by placing the fresh Molding Test concrete in the form in layers 3 to 4 in. in thickness. Each layer shall be puddled with 25 strokes with a 5% in. round steel bar of a length 9 in. greater than the length of the mold, pointed at the lower end. After the top layer has been puddled, the surplus concrete shall be cleaned off with a trowel, and the mold covered with a machined metal plate or a piece of plate glass at least 4 in. thick, which will be used later in capping the test piece. *For a description and illustration of one design for a flow-table, see Proceedings, Am. Soc. Test. Mats., Vol. XX, Part II, p. 242 (1920), and "Concrete," June, 1920, p. 274. Capping Curing Test Age of Test. Sequence of Preparation of Method of Application of Record of Tests. 14. Two to four hours after molding, the test pieces shall be capped with a thin layer of stiff neat cement paste in order that the cylinders may present a smooth end for loading. The cap shall be formed by means of a machined metal plate or a piece of plate glass of suitable size, at least 4 in. thick, worked down on the fresh cement paste until it rests on the top of the cylinder form. The cement for capping shall be mixed to a stiff paste before beginning to mix the concrete; in this way the tendency of the cap to shrink will be largely eliminated. The adhesion of the concrete to the metal base plate and the glass can be largely eliminated by oiling the cover plate and by inserting a sheet of paraffined tissue paper. 15. Concrete test pieces shall be removed from the forms 20 to 48 hours after molding, marked, weighed and stored in damp sand, under damp cloths or in a moist chamber until the date of test. The temperature of the curing room should not fall outside the range of 60 to 75° F. 16. Tests shall be made at the age of 7 and 28 days; ages of 3 months and 1 year are recommended, if longer-time tests are required. 17. Three to five test pieces should be made on different days in investigations in which accurate comparisons are desired. 18. Compression tests shall be made immediately upon removal of the concrete test pieces from the curing room; that is, the test pieces shall be loaded in a damp condition. The length and average diameter of the test piece shall be measured in inches and hundredths; two diameters shall be measured at right angles near the mid-length. The test piece shall be weighed immediately before testing. 19. In general, only the ultimate compressive strength of the cylinders need be observed. The metal bearing plates of the testing machine shall be placed in contact with the ends of the test piece; cushioning materials shall not be used. An adjustable bearing block shall be used to transmit the load to the test piece. The bearing block shall be placed on top of the test piece in vertical testing machines. The diameter of the bearing block shall be approximately the same as that of the test piece. The upper section of the bearing block shall be kept in motion as the head of the testing machine is brought to a bearing on the test piece. 20. The load shall be applied uniformly and without shock. The moving head of the testing machine should travel at the rate of about 0.05 in. perminute when the machine is running idle. 21. The total load indicated by the testing machine at failure of the test piece shall be recorded and the unit compressive strength calculated in pounds per square inch, the area computed from the average diameter of the cylinder being used. The type of failure and appearance of the concrete shall be noted. Concrete. 22. The weight of the concrete in pounds per cubic foot shall Weight of be determined from the weight of the specimens and their dimensions. Yield. 23. Density and yield of concrete when required shall be Density of calculated from the unit volumes of the constituent materials and the volume of the concrete. Density is here understood to be the ratio of solids in the concrete to the total volume of the mass. Yield is the volume of concrete resulting from one volume of aggregate mixed as used. 24. The report of tests shall include the following: (a) The kind and origin of concrete materials; (b) Complete data on all tests of cement and aggregates; (c) A description of methods of making and testing the concrete, where methods deviate from the proposed standards; (d) The quantities of cement, aggregates and water in each batch; (e) The method of measuring workability or plasticity with "slump" or "flow" of concrete; (f) The quantity of water expressed as a ratio to volume of cement; (g) The age at test; (h) The size of test pieces; (i) The date of molding and testing each cylinder; (j) The compressive strength in pounds per square inch of each test piece and average of tests in a set; (k) A description of failure and appearance of concrete on each test piece; (1) The unit weight, density and yield of the concrete. 10. STANDARD METHODS OF MAKING AND STORING SPECIMENS OF CONCRETE Serial Designation: C 31-21 American Society for Testing Materials Report of Tests. 1. The methods herein specified apply to molding and Scope. storing of test specimens of concrete sampled from concrete being used in construction. 2. The test specimens shall be cylindrical in form with the length twice the diameter. In general a mold whose diameter is not less than four times the diameter of the largest size aggregate shall be used. (The sizes most commonly used are 6 by 12-in. and 8 by 16-in. cylinders.) Size and Shape of Specimen. |