AASHTO T90-00 pdf free download
AASHTO T90-00 pdf free download.Determining the Plastic Limit and Plasticity Index of Soils.
4.2. If both the liquid and plastic limits are required. take a test sample with a mass of about 8 g from the thoroughly wet and mixed portion of the soil prepared in accordance with T 89. Take the sample at any stage of the mixing process at which the mass becomes plastic enough to be easily shaped into a ball without sticking to the fingers excessively when squeezed. If the sample is taken before completion of the liquid limit test, set it aside and allow to season in air until the liquid limit test has been completed. If the sample taken during the liquid limit test is too dry to permit rolling to a 3-mm thread, add more water and remix.
5.2.1. Hand Rolling Method—Roll the mass between the palm or lingers and the ground-glass plate (or a piece of paper laying on a smooth horizontal surface) with just sufficient pressure to roll the mass into a thread of unifbrm diameter throughout its length. The thread shall be further deformed on each stroke so that its diameter reaches 3 mm, taking no more than 2 minutes. The amount of hand or finger pressure required will vary greatly, according to the soil. Fragile soils of low plasticity are best rolled under the outer edge of the palm or at the base of the thumb.
5.2.2. Alternate Proce’dure, Plastic Limit Device’ Method—Place the soil mass on the bottom plate. Place the top plate in contact with the soil mass. Simultaneously apply a slight downward force and back and forth motion to the top plate so the plate comes in contact with the side rails within 2 minutes. During this rolling process. do not allow the soil thread to contact the side rails.
Note 3 In most cases, more than one soil mass (thread) can be rolled simultaneously in the plastic limit rolling device.
5.3. When the diameter of the thread becomes 3 mm, break the thread into six or eight pieces. Squeeze the pieces together between the thumbs and fingers of both hands into a uniform mass roughly ellipsoidal in shape and then reroll. Continue this alternate rolling to a thread 3 mm in diameter, gathering together, kneading, and rerolling, until the thread crumbles under the pressure required for rolling and the soil can no longer be rolled into a thread. The crumbling may occur when the thread has a diameter greater than 3 mm. This shall be considered a satisfactory end point, provided the solid has been previously rolled into a thread 3 mm in diameter. The crumbling will manifest itself differently with various types of soil. Some soils fall apart in numerous small aggregations of particles; others may form an outside tubular layer that starts splitting at both ends. The splitting progresses toward the middle, and finally the thread falls apart in many small platy particles. Heavy clay soils require much pressure to deform the thread, particularly as they approach the plastic limit, and finally, the thread breaks into a series of barrel-shaped segments each about 6 to 9 mm in length. At no time shall the operator attempt to produce failure at exactly 3-mm diameter by allowing the thread to reach 3 mm. then reducing the rate of rolling or the hand pressure, or both, and continuing the rolling without further deformation until the thread falls apart. It is permissible. however, to reduce the total amount of deformation for feebly plastic soils by making the initial diameter of the ellipsoidal-shaped mass nearer to the required 3-mm final diameter.AASHTO T90-00 pdf download.
