The role of Viscosity Modifying Admixture (VMA) in Concrete
Viscosity Modifying admixtures or VMAs belong to the admixtures which are applied to modify various properties of fresh concrete ranging from viscosity, workableness, cohesiveness etc.
The functionality and uses of VMA for several types of concrete are given below.
Function of Viscosity Modifying Admixture (VMA) in Concrete
The prime objective of viscosity modifying admixture in a concrete mix is to modify the rheological properties of concrete- particularly the plastic viscosity of fresh concrete. If VMA is added to concrete mix, the plastic viscosity of concrete is raised and a slight surge in yield point is observed.
Yield point is another rheological property of concrete that should also be improved together with the plastic viscosity to attain perfect concrete rheology. The yield point of concrete is not impacted with VMA.
Therefore, besides, VMAs plasticizers or super plasticizers are also included to modify the yield point of concrete mix.
Advantages of Viscosity Modifying Admixtures (VMAs)
Given below, the details of various types of concretes which show different behavior with the inclusion of viscosity modifying admixture to their design mixes:
1. Self-compacting Concrete, 2. Pumped Concrete, 3. Under Water Concrete, 4. Light weight concrete, 5. Semi-dry Concrete, 6. Sprayed Concrete, 7. Porous Concrete, 8. Concrete with Poorly Graded Aggregates
1. Self-compacting Concrete: When Self-compacting concrete blends with less powder content, it remains unsafe against moisture variations and as a result segregation may take place.
Inclusion of viscosity modifying admixture to self-compacting concrete raises the segregation resistance as well as enhances the strength to moisture variations.
VMAs improve the strength of self-compacting concrete mixes.
VMAs also minimize bleeding from concrete mix.
a. Obstacle of aggregates at bends in pipe is the issue found in general that occurs for pumped concrete.
b. When Viscosity modifying admixture is included, pumped concrete turns out to be more consistent and segregation while pumping can?t occur.
c. The friction among pump-wall and concrete mix while pumping is minimized by lubricating effect resulting from VMA.
a. Use of viscosity modifying admixture reduces the rebound of aggregates from sprayed concrete by enhancing the cohesion of concrete mix.
a. Viscosity modifying admixtures resist the discharge of cement paste from porous concrete mix.
b. VMA makes the bond better among cement paste and aggregate thereby raises the strength of concrete.
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