ACI 304R-89 Guide for Measuring, Mixing, Transporting, and Placing Concrete (Reapproved 1997).
1.2-Objective In preparing this guide, the committee followed this philosophy. 1. Progress in improvement of concrete construc- tion will be better served by the presentation of high standards rather than “common practices.” 2. In many cases, if not most, practices resulting in the production and placement of high quality con- crete can be performed as economically as those re- sulting in poor concrete. Many of the practices recommended in this document improve concrete uniformity as well as quality so that effort and in- vestment are rewarded by a smoother operation and higher production rates, both of which offset poten- tial additional cost. 3. It is assumed that anyone planning to use this guide will have a basic knowledge of the general practices involved in concrete work. If more specific information on measuring, mixing, transporting, and placing concrete is desired, the reader should refer to the list of references given at the end of this docu- ment, and particularly to References 2 and 6 and ASTM C 94, ACI 311 and 318 and EM 1110-2-2000. Committee 304 generally agrees with the information given in these references although some exceptions in emphasis and detail may be noted, To portray more clearly certain principles involved in achieving maximum uniformity, homogeneity, and quality of concrete in place, illustrations of good and poor practices are also included. Control of undersize material – Under- size material for a given aggregate fraction is defined as that material which will pass a sieve having an opening five-sixths of the nominal minimum size of each aggregate fraction. 2 In Example 1 above, that would be material passing the following sieves: No. 5 (4.0 mm), 5 / 8 in. (16.0 mm), 1¼ in. (31.5 mm) and 2½ in. (63 mm). For effective control of gradation, it is essential that handling operations do not signifi- cantly increase the undersize materials in aggregates prior to their use in concrete (Fig. 2.2,1a-d). The gra- dation of aggregate as it enters the concrete mixer should be uniform and within specification limits. Sieve analyses of coarse aggregate should be made with sufficient frequency to assure that grading re- quirements are being met. When two or more aggre- gate sizes are being used, changes in the proportions of the sizes should be made as required to improve the overall grading of the combined aggregate. When specification limits for grading cannot be met consis- tently, special handling methods should be in- stituted. Materials tend to segregate during transportation and reblending may be desirable. Re- screening the coarse aggregate, as it is charged to the bins at the batch plant, to waste or remove undersize materials will effectively eliminate undesirable fines when usual storage and handling methods are not satisfactory. Undersize materials in the smaller coarse aggregate fractions can be consistently re- duced to as low as two percent by rescreening (see Fig. 2.2.ld).ACI 304R pdf download.