AASHTO T186-20 pdf free download
AASHTO T186-20 pdf free download.Early Stiffening of Hydraulic Cement (Paste Method).
5. SIGNIFICANCE AND USE
5.1. The purpose of this test method is to determine the degree to which a cement paste develops early stiffening or establish whether a cement complies with a specification limit on early stiffening.
5.2. When used for establishing compliance with a specification limit, the specification requirement is customarily stated in terms of the minimum allowable final penetration, in percent, calculated in accordance with Section 11. When used for estimating the relative tendency of a cement to manifest early stiffening, additional infonnation of value may be obtained if the remix procedure described in Section 10 is employed. Under some conditions, a judgment may be made by comparing the behavior in the initial test and in the remix procedure to differentiate a relatively less serious and less persistent tendency to early stiffening (false set) from one that is more persistent and, consequently, more serious (flash set).
5.3. Severe false setting in a cement may cause difficulty from a placing and handling standpoint, but it is not likely to cause difficulties where concrete is mixed for a longer time than usual, as usually occurs in transit mixing, or when it is reinixed prior to placing or transporting, as occurs in concrete pumping operations. It is most likely to be noticeable when concrete is mixed for a short period of time in stationary mixers and transported to the forms in nonagitating equipment, such as on some paving jobs, and when concrete is made in an on-site batch plant.
5.4. Cements with severe false setting usually require slightly more water to produce the same consistency, which may be expected to result in slightly lower strengths and increased drying shrinkage.
5.5. Early stiffening resulting from false set is not likely to cause a cement to fail the applicable time of setting requirement.
5.6. Early stiffening resulting from flash set, depending on severity, can cause a cement to fail the applicable time of setting requirement.
10.2. Molding Test Specimens—Quickly form the cement paste into a ball with gloved hands. Press the ball, resting in the palm of one hand, into the larger end of the conical ring held in the other hand, completely filling the ring with paste. Remove the excess at the larger end by a single movement of the palm of the hand. Place the ring on its larger end on the nonabsorptive plate, H, and slice off the excess paste at the smaller end at the top of the ring by a single oblique stroke of a sharp-edged trowel held at a slight angle with the top of the ring. Smooth the top of the specimen, if necessary, with one or two light touches of the pointed end of the trowel. During the operation of cutting and smoothing, take care not to compress the paste.
10.3. Determination of initial Penetration—Set the paste confined in the ring resting on the plate, H, under the rod, B, Figure 1 of T 129, about one-third of the diameter from the edge, and bring the plunger end, C, in contact with the surface of the paste and the tightened set screw, E. Then set the movable indicator, F, to the upper zero mark of the scale, and release the rod exactly 20 s after completion of the mixing. Keep the apparatus free of all vibrations during the penetration test. Consider the paste to have proper consistency when the rod settles to a point 32 ± 4 mm below the original surface in 30 s after being released. Make trial pastes with varying percentages of water until this consistency is obtained. This consistency is the initial penetration. During the 30-s interval for the initial penetration, return the excess paste to the bowl and cover the bowl and mixing paddle with a lid.AASHTO T186-20 pdf download.
