Microsoft Word 7- part d doh test Methods doc

6. MOLDING SPECIMENS 
6.1 Location of Molding – Specimens shall be made promptly after sampling of the concrete.
Molds should be made on a level, rigid, horizontal surface, free from vibration and other 
disturbances, at a place as near as practicable to the location where they are to be stored 
during the first 24 hours. If it is not practical to mold the specimens where they are to be 
stored, move them to the place of storage immediately after being struck off. Take care not 
to jar, strike, tilt, or scar the surface of the specimens when moving them.
6.2 Placing the Concrete – Place the concrete in the molds using a scoop, blunted trowel, or 
shovel. Select concrete from the mixing pan to ensure that it is representative of the batch.
It may be necessary to remix the concrete in the mixing pan to prevent segregation during 
molding of the specimens. Move the scoop or trowel around the top edge of the mold as the 
concrete is discharged in order to ensure a symmetrical distribution of the concrete and to 
minimize segregation of coarse aggregate within the mold. Further distribute the concrete 
by use of a tamping rod prior to consolidation. The operator shall attempt to add an amount 
of concrete for the final layer that will exactly fill the mold after compaction. Do not add 
non-representative concrete to an under-filled mold. 
6.2.1 For standard cylinders (6" x 12" (15 cm x 30.5 cm)), 3 layers of approximately equal 
volume should be used to fill the mold. 
6.2.2 For standard beams (6" x 6" x 21" (15 cm x 15 cm x 53 cm)), 2 layers of 
approximately equal volume should be used to fill the mold. 
6.2.3 For all other specimen sizes, consult AASHTO T23, Table 1 for the appropriate 
number of layers to be used during specimen molding. 
6.3 Consolidation -- Preparation of satisfactory specimens requires different methods of 
consolidation. The methods of consolidation are rodding, internal vibration, and external 
vibration. The method selected should be based on the slump, unless the method is stated in 
the specifications under which the work is being performed.
6.3.1 Slump greater than 3" (76mm) – Rod the concrete 
6.3.2 Slump between 1" and 3" (25mm to 75mm) – Rod or vibrate the concrete. 
6.3.3 Slump less than 1" (25mm) – Vibrate the concrete. 

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D-30 
6.4 Rodding – Place the concrete in the mold following proper procedures. For cylinders, rod 
each layer with the rounded end of the rod using the number of strokes specified (for 6” 
diameter molds, rod each layer 25 times). The number of roddings per layer required for 
beams is one for each 2 in
2
(1290mm
2
) top surface area of the specimen. Rod the bottom 
layer throughout its depth. Distribute the strokes uniformly over the cross section of the 
mold. For each upper layer allow the rod to penetrate about ½” (13mm) into the underlying 
layer when the depth of the layer is less than 4” (102mm), and about 1” (25mm) when the 
depth is 4” (102mm) or more. If voids are left by the tamping rod, tap the sides of the mold 
lightly to close the voids. After each layer is rodded, spade the concrete along the sides and 
the ends of beam molds with a trowel or other suitable tool. 
6.5 Finishing – After consolidation, strike off the surface of the concrete and float or trowel it as 
required. Perform all finishing with the minimum manipulation necessary to produce a flat, 
even surface that is level with the rim of the mold, and that has no depressions or projections 
larger than 1/8 in. (3.2mm). 
6.5.1 Cylinders – After consolidation, finish the top surfaces by striking them off with 
the tamping rod where the consistency of the concrete permits, or with a wood 
float or trowel. 
6.5.2 Beams – Beams shall be finished with a wood or magnesium float.