EFFECT OF PARTICLE MORPHOLOGY ON THE EMULSION STABILITY AND MECHANICAL PERFORMANCE OF POLYOLEFIN MODIFIED ASPHALTS

Recent federal regulations concerning roadbed performance have motivat ed research in polymer modified asphalt binders. Earlier studies on th ese binders have shown that many of them are susceptible to gross phas e separation when the binder is stored at high temperatures under quie scent conditions. This phase separation, in turn, is affected by the i nitial morphology and storage conditions. In this effort we investigat e the effect of particle morphology on the high-temperature emulsion s tability of a low-density polyethylene-modified asphalt binder, as wel l as the concomitant effects on the mechanical behavior. We show for u nstabilized emulsions that the dominant phase separation mechanism shi fts from coalescence to creaming at a critical particle radius of 4 mu m at 110 degrees C. However, stabilized emulsions showed no evidence of gross phase separation for up to 48 hours at 110 degrees C. Dramati cally different morphologies were observed for the unstabilized and st abilized emulsions; unstabilized emulsions having teardrop shaped part icles and stabilized emulsions having both spherical particles and lon g cylindrical domains. The mechanical behavior, including the high-tem perature dynamic viscoelastic behavior and low-temperature fracture to ughness, increased with polyolefin content, but was insensitive to the particle morphology.