CONSOLIDATION OF CONCRETE
Consolidation of Concrete is the process of reducing or eliminating the volume of voids, air pockets, and entrapped air from the fresh concrete mix, usually accomplished by applying mechanical energy. Concrete compaction is also known as consolidation of concrete which is used to get highest density of concrete. Historically, it was achieved by ramming or punning, but nowadays compaction is mostly carried out by vibration.
Concrete Consolidation is also related to a process of reducing the gap between aggregate and aggregate; between aggregate and reinforcement; and between aggregate and forms.
The main aim of the consolidation of concrete is to eliminate the air voids from concrete and increase the density of concrete. As we know the higher density of concrete gives high compressive strength. Proper and close contact between reinforcement and concrete is ensured by proper consolidation.
Consolidation of concrete is significantly the ultimate strength of concrete and enhances the bond with reinforcement. It also increases concrete durability and abrasion resistance decreases the permeability and helps to minimize its shrinkage-and-creep characteristics.
Concrete Consolidation Methods:-
Hand consolidation:
Hand methods of consolidation of concrete are done manually the hand which includes ramming, tamping, spading, and slicing by using suitable tools. It is normally used in unimportant works.
The hand method is good for fairly wet concrete. It should however be remembered that as soon as possible the hand compaction should be applied because the use of a vibrator may cause the segregation of the aggregates and leakage of cement slurry. Due to these reasons, the concrete mixes which can be compacted by hand should not be compacted by the use of vibrators.
Immersion Vibrator:
This is the most common used vibrator. It consists of a steel closed and round tip with an electric vibrating element inside of it. The tip is connected to an electric motor through a flexible hose. In order to have best results, the diameter of the tube shall be small enough so it can be inserted in between reinforcing bars. It is recommended to insert the vibrator into concrete at intervals of 24 inches or 8 times the diameter of the tube. When this vibrator is used, the insertion time shall vary from 30 seconds to 2 minutes. Concrete shall never be poured in layers thicker than 24 inches high.
The vibrator should be inserted vertically into the mix, and then slowly withdrawn. Vibrators work by allowing air to float up and out of the concrete, so the tip should not be withdrawn faster than the air can move upward, about 3 inches per second. If the wall is poured in multiple lifts, the vibrator tip should go deep enough to penetrate 3 to 6 inches in the previous layer. The tip of the vibrator is available in different radius, depending on how much rebar has been installed.
Vibrating tables:
Vibrating tables are in the form of a rigidly built steel platform mounted on the flexible springs and there is need of electromagnetic action or electric motors to operate it.
They can be very effective in compact stiff and harsh concrete mixes and hence they are mostly used in the preparation of precast structural products in factories like railway slippers and test specimens in laboratories.
Generally, the tables are vibrated by mechanically or by placing the springs under the supports of tables. The rate of vibration is in the range of 3000 to 7200 vibrations per minute.
Platform Vibrator
Platform vibrator is similar to table vibrator, but its size is larger than it. This type of vibrator is generally used to consolidate big prefabricated concrete elements such as electric poles, railway sleepers, prefabricated roofing elements, etc.
Factors which Influence Density:-
The density of concrete has a significant influence on many characteristics, such as workability, compressive strength, and permeability. Of all factors that influence density, the water-cement ratio is one of the most influential. Other factors influencing density are cement type, aggregates (size distribution), curing condition, and mix design method.
For example, when using coarse aggregate in a proportion higher than 40%, density will be decreased. On contrary, using a fine aggregate in a proportion higher than 40% will increase the density of concrete.
Also, using coarse aggregate with a high specific gravity in the proportion of more than 10% will increase the density of concrete; while using fine aggregate with low specific gravity in proportion of more than 10% will decrease the density of concrete.
In addition to these factors mentioned above, there are some other factors that also have an effect on density; for example temperature and porosity at the time of casting or freezing temperature and drying conditions during the hardening process, etc.
New Technology Consolidation of concrete:-
When you mix cement and water together, they create a strong bond. Over time, that bond gets stronger and creates what we call concrete. That process is called consolidation. When you take an ingredient from its natural state and apply pressure or heat, it will become denser or consolidated. If that ingredient is a liquid, like water or oil for example, then it becomes less fluid over time through consolidation.
The best way to increase density in your concrete is to use heat because it helps mix chemicals properly and allows chemical reactions in concrete to complete more effectively. By adding heat, you can improve the strength and durability of your concrete product.