Explain the AASHTO Classification System  

1.  Identify the percent passing the No.10, No. 40, and No. 200 sieves. Identify the LL and PI of the fraction passing the No. 40 sieve.  

2.  Use AASHTO Classification Table. Move from left to right using process of elimination until the first group consistent with the laboratory data is identified. 

3.  Special Notes: 

a) For groups A-4, A-5, A-6 and A-7: Calculate the group index (GI) using the equation shown below the classification table.  If GI is negative, it is reported as zero.   

b) For group A-7, the Plastic Limit (PL = PI - LL) is the differentiating factor between A-7-5 and A-7-6.  This is expressed in terms of Plasticity Index (PI = LL - LL), which you already use for classification.