Sampling ProceduresSampling (or obtaining) concrete for theslump test should be accomplished accord-ing to ASTM C 172. In this TRAMAN, onlythe procedure of sampling from a revolvingdrum truck mixer (TM) or agitator is discussed.If you should ever need to sample from a pavingmixer, open-top truck mixer, or other type ofequipment, be sure to refer to the most recentASTM C 172.Samples taken for the test specimens mustbe representative of the entire batch. Thisis accomplished by taking the samples at twoor more regularly spaced intervals during dis-charge of the middle portion of the batch.Sample by repeatedly passing a scoop or pailthrough the entire discharge stream. Compositethese samples into one sample for testing pur-poses. Be sure that the first and last por-tions of the composite sample are taken asquickly as possible, but never exceeding 15min. If it is necessary to transport the sam-ples away from the mixer to the place wherethe slump test is to be performed, combine thesamples and remix them with a shovel to ensureuniformity.Testing ProceduresFigure 15-40.-Slump cone.to thetest loadis applied perpendicularlongitudinal axis of a standard size, premolded,and-properly cured concrete beam. From this test,the flexural strength, expressed in terms ofmodulus of rupture and given in psi, can bereadily calculated. As with the compression test,only the procedures to prepare the test beams cor-rectly will be discussed in this TRAMAN.SLUMP TESTSThe slump test is performed on newly mixedconcrete. To perform the test, you need a slumpcone and a tamping rod. The slump cone (fig.15-40) should be made of galvanized steel, 12 in.in height, with a base opening 8 in. in diameterand the top opening 4 in. in diameter. Both thetop and bottom openings are perpendicular to thevertical axis of the cone. The tamping rod is astraight, steel rod that is 5/8 in. in diameter andapproximately 24 in. in length. One end of therod is rounded to a diameter of 5/8 in. (Do notsubstitute a piece of rebar.)Perform the slump test according to ASTMC 143. Be sure to start the test within 5 minafter obtaining the final portion of the com-posite sample. In performing the test, firstdampen the slump cone and place it on a flat,moist, nonabsorbent, rigid surface. From thecomposite sample obtained and while standing onthe two foot pieces of the cone, fill the cone inthree layers, each approximately one third of thevolume of the cone. In placing each scoopful ofconcrete, rotate the scoop around the top edgeof the cone as the concrete slides from it toensure even distribution of concrete within themold.Rod each layer with 25 strokes of thetamping rod (using the rounded end), anduniformly distribute the strokes over the en-tire cross section of each layer. Rod the bottomlayer throughout its depth. Rod the second layerand the top layer each throughout its depth sothat the strokes just penetrate into the under-lying layer. In filling and rodding the toplayer, heap the concrete above the mold beforethe rodding is started. If the rodding results15-36
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