Table 15-6.-Number of Roddings to be Used in MoldingCylinder SpecimensDiameter of Cylinder,Number ofin. (mm)Strokes/Layer6 (152)258 (200)5010 (250)75plates and squeezing out excess material to pro-vide a cap that is as thin as possible. Sulfur capsmay be applied in time to harden for at least 2 hrbefore testing. Plaster caps cannot be stored over4 hr in a moist room. Neat cement caps must beaged 6 days or more in a moist room (2 days whenType II cement is used). During capping, protectmoist, cured specimens against drying by cover-ing them with wet burlap.Beam SpecimensTests are performed on concrete beamspecimens to evaluate the flexural strength of theconcrete. The standard beam specimen is 6 in. by6 in. by 21 in. (152 mm by 152 mm by 532 mm)for concrete in which the maximum size of thecoarse aggregate is 2 in. (50 mm). When the max-imum size of the coarse aggregate exceeds 2 in.(50 mm), the smaller cross-sectional dimension isto be increased to at least three times the nominalmaximum size of the coarse aggregate. All beamspecimens prepared in the field are to be at least6 in. wide and 6 in. deep unless required other-wise by project specifications.STANDARDS FOR BEAM MOLDS.— Thebeam molds are to be smooth on all interior sur-faces and free from warpage. The molds are toproduce specimens that do not exceed the requiredcross-sectional dimensions by 1/8 in. The lengthof the specimens is not to be more than 1/16 in.shorter than the specified length, but it mayexceed that length.RODDING.— Place the concrete in the moldin the required number of layers. (See table 15-5.)Rod the bottom layer throughout, distributing thestrokes uniformly over the cross section of themold. When rodding the upper layers, allow therod to penetrate the previous layer 1/2 in.,providing the previous layer is 4 in. or less and1 in. if the previous layer is greater than 4 in. Thenumber of strokes’ per layer is one for each 2 in.2(13 cm2) of the top surface area of the specimen.After each layer is rodded, spade the concrete witha trowel along the sides of the mold to help inthe removal of surface voids. Strike off the topsurface with a straightedge, and finish it with awooden float.CURING.— YOU should cure the beamspecimens in the same manner as the cylinderspecimens with the following exceptions: (1) ex-tend the initial curing period to 48 hr ± 4 hr and(2) do not allow the surface of the beam specimento become dry between the time of removal fromcuring and the completion of testing.When transporting specimens from the fieldto the laboratory, be sure they are sufficientlycushioned to protect them from damage byjarring. Additional measures are required toprevent damage by freezing temperatures andmoisture loss. You can prevent moisture loss bycovering the specimens with plastic or surround-ing them by wet sand or wet sawdust.15-39
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