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.

Pumped Concrete

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.

Sprayed Concrete
a. Use of viscosity modifying admixture reduces the rebound of aggregates from sprayed concrete by enhancing the cohesion of concrete mix.

Porous Concrete
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.

To get more details, go through the following link theconstructor.org



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Published By
Rajib Dey
www.constructioncost.co
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Use and benefits of self compacting concrete

Self-consolidating concrete alias self-compacting concrete (SCC) is a concrete mixture that can flow into very complex forms with various reinforcing bars (rebar congestion) and leaves no voids.

It can be arranged with its own weight devoid of any mechanical vibration. SCC retains all the conventional mechanical and durability characteristics of concrete.

With extremely fluid nature of SCC, it becomes possible to arrange it in complicated conditions and in sections with congested reinforcement. It can also reduce hearing-related damages on the worksite due to vibration of concrete. In SSC, the required time is curtailed significantly for arranging bigger sections.

In some cases, the superplasticizers and viscosity modifier are provided to the mix to minimize bleeding and segregation.

A well designed SCC mix never segregates because it contains extreme deformability and outstanding stability characteristics.

Self-Compacting Concrete Properties: Self-compacting concrete has good resistance capacity against segregation as it applies mineral fillers or fines as well as special admixtures. Self-consolidating concrete is essential to flow and fill special forms under its own weight. It is flown adequately to travel over extremely reinforced areas, and should have capability to circumvent segregation of aggregate.

Self-compacting concrete contains an equivalent water cement or cement binder ratio that provides normally a slightly higher strength with regards to conventional vibrated concrete and because of non-existence of vibration, a better interface among the aggregate and hardened paste is created.

The concrete mix of SCC should be arranged at a comparatively greater velocity as compared to regular concrete. Self-compacting concrete is placed from heights longer than 5 meters exclusive of aggregate segregation. It is also useful for areas having normal and congested reinforcement, with aggregates as large as 2 inches.

Self-Compacting Concrete Uses - Self-compacting concrete is mostly utilized in bridges and even on pre-cast sections. This type of concrete is suitable for the following:

• Drilled shafts
• Columns
• Earth retaining systems
• Areas with high concentration of rebar and pipes/conduits

To know about the benefits of self consolidating concrete, go through the following link thebalance.com



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Published By
Rajib Dey
www.constructioncost.co
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Brief overview of concrete mix ratio

If cement is blended with sand, stone/aggregates and water, a paste will be developed and it can be applied to stick the building materials collectively. This paste is known as concrete.

The ration upon which the cement, sand, stones or aggregates are amalgamated, defines the strength of the concrete mix. Depending on these ratios, different types of concrete grades are accessible in the market. These concrete grades range from M10, M20, M30, M35, etc.

“M” denotes “mix”. Mix characterizes concrete with indicated ratios of cement, sand and aggregate. And the number after “M” denotes compressive strength of that concrete mix in N/mm2 after 28 days. As for instance, for M30 grade of concrete mix, its compressive strength after 28 days should have been 30 N/mm2.

Concrete mix ratio table

Given below, the standard chart table that displays different grades of concrete mix design together with their relevant ratios of cement, sand and aggregates required.

It is found that volume of sand is always retained half of that of aggregates in these standard mix designs. These proportions can be estimated and sustained with buckets or some other standard cubes which are easily utilized during the project. It is essential to keep up uniformity in each and every concrete mix produced throughout the entire project.

The site engineer/supervisor should take the responsibility to examine and implement it.

Water content ratio in concrete mix: The strength & adaptability of concrete is mainly dependent on water content. The adaptability of concrete (more fluid) will be increased with the higher quantity of water but it will decrease the concrete strength.

Contrarily, if the amount of water is low, adaptability of water will also be decreased. So, it becomes complicated to arrange such concrete in the structure. Required amount of water may differ for same volume of concrete for different grades of concrete. So, equilibrium should be maintained in the construction site throughout concrete mixing.

Video Source: Civil Engineering

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Published By
Rajib Dey
www.constructioncost.co
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How batching of concrete is done

Concrete is a multipurpose, long-lasting, eco-friendly, and inexpensive material as well as globally recognized construction material. To produce superior quality concrete, the components of concrete should be calculated properly and perfectly. Once mix design is set, the initial task should be batching materials.

Batching of concrete stands for the method of estimating and mixing necessary concrete ingredients both with weight or volume according to the mix design and implanting them into a mixture to form a consistent quality of concrete.

By perfectly computing all the material applied in the concrete formation, it becomes possible to maintain consistency of proportions in all consequent batches.

Why Batching of Concrete is Important?

Usually, following three types of batching are undertaken for concrete components:

01. Random Volumetric Batching: Batching devoid of any control on the size and shapes of applied containers leads to big errors and deviations like utilizing “ghamellas” i.e. – by tallying numbers of ghamellas. This method is totally unscientific, unrefined and should not be recommended even for a small project.

02. Volume Batching of Concrete: Volume batching of concrete is accomplished with the use of measurement boxes, locally named “farmas or gauge boxes”. Concrete components like aggregates ( Kapachi +Sand) and cement is calculated with farmas or gauge boxes and proper precaution should be maintained to ensure that the farmas or gauge boxes are filled excessively. To calculate the quantity of water, the water meter should be utilized when batching or use cans of water contain fixed volume.

03. Weigh Batching of Concrete: Weigh batching of concrete is accomplished with the use of a weigh batch or the weighing system on the batching plant. On big projects, automatic batching plants are set up to facilitate optimizing quality and uniformity.

Water is very vital material and therefore, maximum water should be used for batching. If the quantity of water is less, the functionality of concrete will be hampered whereas surplus water will minimize the strength of concrete. Water should be computed perfectly in litres.

The selection of batching method is based on the size of job, production rate and standards of batching performance.

Usually batching is performed with volume. Precision in batching is very crucial. It is better to perform weigh batching instead of volume batching. Volume batching is mostly effective where weigh batching is not possible. It is always recommended to incur additional cost for it, because in long term, it saves huge costs.

Note: The quantity of cement should also be calculated by maintaining the precision of ± 2 percent and the quantity of aggregates, admixtures and water should be calculated with a precision of ± 3 percent.

Article Source: gharpedia.com

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Published By

Rajib Dey

www.constructioncost.co

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