Effect of viscosity modifying admixtures on the workability and mechanical resistances of self compacting mortars

Concrete is one of the most widely manufactured materials in the world and.today's concrete has to fulfil a wide range of requirements in both the fresh and hardened state. in most cases the properties of fresh concrete also affect the quality of the hardened concrete and ultimately its durability. this means that concrete has to be correctly proportioned and must remain homogeneous during placing and after compaction in order to avoid effects such as bleeding and segregation.self-compacting concrete is a concrete that is able to flow and consolidate under its own weight,completely fill the formwork even in the presence of dense reinforcement,whilst maintaining homogeneity and without the need for any additional compaction.one of the latest innovations is the development of improved viscosity modifying admixtures (vma) also referred to as stabilisers,viscosity enhancing admixtures (vea) and water retaining admixtures. water retaining admixtures are a type of vma already defined in en 934-2.the key function of a vma is to modify the rheological properties of the cement paste. a suitable quantity of welan gum,a kind of natural water soluble polysaccharide,is very effective in stabilizingthe rheology of self-consolidating concrete.the objective of this article is to focus on the effect of the viscosity modifying admixtures on the workability and mechanical resistances of self compacting mortars. for this purpose two types of vma have been used,a colloidal agent(medacol bse) and a bentonite. the experimental results have shown that mortars prepared with bentonite have given a better workability than the ones prepared with the medacol bse. on the contrary,mechanical resistances values are higher with the medacol bse.