Which vibratory generally is used for compaction of concrete?
Immersion or Needle Vibrators are most commonly used vibrator for concrete. It consists of a steel tube (with one end closed and rounded) having an eccentric vibrating element inside it. This steel tube called poker is connected to an electric motor or a diesel engine through a flexible tube.
What happens to concrete if excessive vibration is given?
For most of concrete mixes, over-vibration creates the problem of segregation in which the denser aggregates settle to the bottom while the lighter cement paste tends to move upwards. If concrete is placed in a single lift for road works, the resistance to abrasion is poor for the laitance surface of the carriageway.
What is compaction by vibration?
Vibratory surface compaction is a method used on the surface of a reclamation area to increase the density, shear strength, and stiffness of the fill. This compaction method is undertaken at the surface of the site using vibratory rollers, plates and/or tampers.
Why is it important to vibrate compact concrete?
Why is it Important? Vibrating concrete is critical because by removing air pockets & packing the aggregate particles together, it increases the density and strength of the concrete. Tightly packed particles will result in a stronger, more durable concrete structure.
Which is the best method for curing flat surfaces *?
Which is the best method for curing flat surfaces? Explanation: Curing is the process of maintaining moisture in freshly laid concrete to strengthen it. For flat surfaces like floors and slabs, ponding or stagnating water is the best method.
How long should you vibrate concrete?
Therefore, workers should vibrate between 5 and 15 seconds to ensure the second phase of consolidation or de-aeration is achieved. Doing so will reduce the amount and size of surface voids including bug holes and in general, improve the overall quality and appearance of the concrete.
Which of the concrete does not require vibration?
Self-compacting concrete (SCC) is a special type of concrete which can be placed and consolidated under its own weight without any vibration effort due to its excellent deformability, and which at the same time is cohesive enough to be handled without segregation or bleeding.
What is compaction MCQs?
This set of Soil Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Compaction Introduction”. Explanation: Compaction is a process by which the soil particles are artificially rearranged into a closer state. This arrangement reduces the voids ratio and hence there is decrease in the porosity.
Do you need to vibrate concrete?
Is Vibrating Concrete Necessary? Vibrating your concrete is almost always recommended since your vibrated concrete will be stronger. But depending on the project, you may have no choice but to vibrate your concrete, as it may be a building code requirement.
What happens if you don’t vibrate concrete?
What are the effects of poor vibration techniques? Poor vibrations will result in voids at the surface of the concrete – normally called honeycombing. This is caused because the entrapped air was not removed, the concrete did not settle, and the voids were not filled with the paste from the concrete mixture.
What is pumpable concrete?
Pumpable concrete is the concrete which can easily pass through a pipeline without causing segregation and bleeding is called pumped concrete. They are mostly used in concrete pumps for high rise building. The pump should be made in such a way that the friction at the inner wall should less.
How does vibration affect the compaction of concrete?
In case of vibration, compacting gets effected by reduction in internal friction between various particles of concrete due to oscillation of particles which results in a dense and compact mass of concrete. Produced in the interior of the concrete using Internal vibrator, or
When to extend the compaction of fresh concrete?
Compaction should therefore be prolonged until this is accomplished, i.e. until air bubbles no longer appear on the surface. The effect of vibration on the properties of fresh concrete needs to be understood to ensure that the type and amount of vibration applied to the concrete are appropriate.
What causes defects in the compaction of concrete?
Defects due to poor compaction of concrete under vibrations: Highly entangled air vessels: Under vibration, a lot of entrapped air is released into the concrete which reduces the strength. Sand streaks: When heavy bleeding washes the mortar, a hard mixture left behind impairs its ability to work. It is also caused by insufficient fine aggregate.
Is it harmful to re vibration of concrete?
Re-vibration of concrete is not harmful unless the concrete is well established that it does not become plastic again by vibration. Even though there are hand compaction techniques available, they are comparatively less effective when used for insignificant tasks.