For road construction in Austin, the applicable standard is AASHTO T-99 (Standard Proctor) and AASHTO T-180 (Modified Proctor) for compaction control, alongside ASTM D4318 for Atterberg limits on the local clay. Austin sits on a thick layer of Taylor clay, which has a high plasticity index, so the compaction curve shifts depending on whether you treat it with lime or cement. Before we set the mix design, we always run a subgrade soil evaluation to classify the material and measure the pH and sulfate content. That step avoids the risk of a sulfate-induced heave that would break the road base within two years.
On Austin clay, a 2% lime pretreatment followed by 4% cement can reduce the plasticity index from 45 to under 15.