ASTM C1252 – Standard Test Methods for Uncompacted Void Content of Fine Aggregate (as Influenced by Particle Shape, Surface Texture, and Grading)
Description:
Significance and Use
5.1 Test Methods A and B provide percent void content determined under standardized conditions which depend on the particle shape and texture of a fine aggregate. An increase in void content by these procedures indicates greater angularity, less sphericity, rougher surface texture, or combinations thereof. A decrease in void content results is associated with more rounded, spherical, or smooth-surfaced fine aggregate, or a combination thereof.
5.2 Test Method C measures the uncompacted void content of the minus 4.75 mm (No. 4) portion of the as-received material. This void content depends on grading as well as particle shape and texture.
5.3 The void content determined on the standard graded sample (Test Method A) is not directly comparable with the average void content of the three individual size fractions from the same sample tested separately (Test Method B). A sample consisting of single-size particles will have a higher void content than a graded sample. Therefore, use either one method or the other as a comparative measure of shape and texture, and identify which test method has been used to obtain the reported data. Test Method C does not provide an indication of shape and texture directly if the grading from sample to sample changes.
5.3.1 The standard graded sample (Test Method A) is most useful as a quick test which indicates the particle shape properties of a graded fine aggregate. Typically, the material used to make up the standard graded sample can be obtained from the remaining size fractions after performing a single sieve analysis of the fine aggregate.
5.3.2 Obtaining and testing individual size fractions (Test Method B) are more time consuming and require a larger initial sample than using the graded sample. However, Test Method B provides additional information concerning the shape and texture characteristics of individual sizes.
5.3.3 Testing samples in the as-received grading (Test Method C) may be useful in selecting proportions of components used in a variety of mixtures. In general, high void content suggests that the material could be improved by providing additional fines in the fine aggregate or more cementitious material may be needed to fill voids between particles.
5.3.4 The dry relative denstiy (specific gravity) of the fine aggregate is used in calculating the void content. The effectiveness of these test methods of determining void content and its relationship to particle shape and texture depends on the relative density (specific gravity) of the various size fractions being equal, or nearly so. The void content is actually a function of the volume of each size fraction. If the type of rock or minerals, or its porosity, in any of the size fractions varies markedly it may be necessary to determine the specific gravity of the size fractions used in the test.
5.4 Void content information from Test Methods A, B, or C will be useful as an indicator of properties such as: the mixing water demand of hydraulic cement concrete; flowability, pumpability, or workability factors when formulating grouts or mortars; or, in bituminous concrete, the effect of the fine aggregate on stability and voids in the mineral aggregate; or the stability of the fine-aggregate portion of a base course aggregate.
Scope
1.1 These test methods cover the determination of the loose, uncompacted void content of a sample of fine aggregate. When measured on any aggregate of a known grading, void content provides an indication of that aggregate’s angularity, sphericity, and surface texture compared with other fine aggregates tested in the same grading. When void content is measured on an as-received fine-aggregate grading, it can be an indicator of the effect of the fine aggregate on the workability of a mixture in which it may be used.
1.2 Three procedures are included for the measurement of void content. Two use graded fine aggregate (standard grading or as-received grading), and the other uses several individual size fractions for void content determinations:
1.2.1 Standard Graded Sample (Test Method A)—This test method uses a standard fine aggregate grading that is obtained by combining individual sieve fractions from a typical fine aggregate sieve analysis. See the Section 9 for the grading.
1.2.2 Individual Size Fractions (Test Method B)—This test method uses each of three fine aggregate size fractions: (a) 2.36 mm (No. 8) to 1.18 mm (No. 16); (b) 1.18 mm (No. 16) to 600 μm (No. 30); and (c) 600 μm (No. 30) to 300 μm (No. 50). For this test method, each size is tested separately.
1.2.3 As-Received Grading (Test Method C)—This test method uses that portion of the fine aggregate finer than a 4.75 mm (No. 4) sieve.
1.2.4 See the section on Significance and Use for guidance on the method to be used.
1.3 The values stated in SI units shall be regarded as the standard.
ASTM C125