two vegetal aggregate types are studied for their performance regarding immersion and outdoor weathering. the most widely researched bio-aggregate to date is hemp shiv; which is used in this study as well as chopped rapeseed straw which is an alternative bio-aggregate widely available in the uk. in this study the binder used is vicat prompt natural cement as well as a viscosity modifying agent (vma) admixture. it was found that the hemp aggregate produced the most durable concrete when compared to rapeseed, and the addition of a vma resulted in a much more durable material for both aggregate types. organic and inorganic leaching was also investigated, and it was found that the binder and soluble organics were leaching from all of the concrete types.