Vibrating concrete should be performed as soon as possible when pouring the concrete. This helps to ensure a more even and consistent distribution of the aggregate and cement throughout the form. Vibration helps to remove any pockets of air that may have formed when mixing and pouring the concrete, as well as helping to evenly settle the concrete into the forms.
Vibrating concrete should also be done in sections, which will further reduce the risk of air pockets forming. Once the concrete has been vibrated and settled into the forms, the forms should be screeded and leveled to ensure a smooth finished surface.
Should all concrete be vibrated?
No, not all concrete should be vibrated. While vibration is an important step in ensuring proper compaction and consolidation of the concrete, it is not a necessary part of the process in all circumstances.
For example, if only shallow pours are being made or if the concrete is being placed and consolidated using specialized methods such as rodding or bumping, then it may be possible to complete the pour without vibrating the concrete.
In other cases, such as with mass pours and in general, it is better to vibrate the concrete to ensure proper compaction. Ultimately, the decision of whether to vibrate or not should be based on the particular situation, with consideration given to the depth and type of pour being made as well as to the desired quality/strength of the finished product.
Can you vibrate concrete too much?
Yes, it is possible to vibrate concrete too much. If concrete is over-vibrated, it can result in the concrete surface being overly smooth and porous with a poor bond between any additional layers, reducing the overall strength and durability of the structure.
Over-vibration can also cause segregation of the aggregates in the mix, resulting in voids or bubbles due to trapped air, which can also weaken the structure. Additionally, excessive vibration of concrete can cause the cement paste to be stripped away from the aggregate and result in exudation of excess water and bleed water on the surface, leading to a decrease in the density of the concrete and a potential cracking of the slab.
Furthermore, over-vibration can cause an increase in the temperature of the fresh concrete, resulting in a reduced final strength and a potential reduction of the lifespan of the structure. For these reasons, it is important to ensure that the amount of vibration is carefully monitored to ensure that the concrete is properly compacted but not over-vibrated.
How do you properly vibrate concrete?
To properly vibrate concrete, you will need to use an internal vibration method such as a poker vibrator or an external vibration method such as a plate vibrator. For internal vibration, a poker vibrator is a steel rod with a pointed end which is connected to an electric motor.
It is inserted into the concrete and vibrated to remove any trapped air bubbles and consolidate the concrete. For external vibration, a vibrating plate or vibrating screed is used. It consists of a metal base plate with an electric vibrator attached.
The vibrator is attached to the bottom of the plate and vibrates the concrete by applying pressure to the surface. When properly selected and used, both types of vibrators will produce results that are acceptable for most applications.
The key to success is selecting the correct type and size of vibrator for the job, operating at the correct frequency and maintaining the correct distance from the surface.
Can you use a drill to vibrate concrete?
Yes, you can use a drill to vibrate concrete. When using a drill to vibrate concrete, it is important to use the right type of drill. Typically, the best drill choice is a rotary percussion drill with a dedicated vibrating head attachment.
Bolt-on vibrating heads are designed for heavy work such as vibrating concrete, and attach to the drill’s chuck. When vibrating concrete, the drill should be set to its maximum speed. Care must be taken to ensure that the drill is not overloaded as this may cause damage to the equipment.
When vibrating concrete, the drill bit should be placed into a hole that is slightly larger than the bit and the drill should be pointed downwards at a 45° angle. This will help ensure that the vibration is evenly distributed.
It is important to ensure that the drill is not run for more than 6 seconds at a time and is then allowed to rest for the same amount of time between applications.
Which of the following concrete does not require vibration?
Self-consolidating concrete (SCC) does not require vibration during installation. SCC is a highly flowable, non-segregating concrete that can spread into formwork and fill the form completely by its own weight.
This eliminates the need for external vibration but requires a different type of mix design that relies on special admixtures and extra fines content. The resulting concrete is highly plastic with cohesive material properties and adequate passing ability.
It spreads freely and rapidly consolidates its own structure with minimal entrapped air to produce final placements with uniform density and finish.
What happens when it rains on wet concrete?
When it rains on wet concrete, the rainwater can cause deterioration of the concrete due to hydrostatic pressure. When water is added to concrete while it is drying, the cement paste acts like a sponge and absorbs the water.
This causes it to expand, resulting in the weakened structure and eventual failure of the concrete. The water also creates air bubbles, which further weaken the surface of the concrete. The presence of water also encourages the growth of mold, mildew, and other microorganisms, which can further damage the concrete.
Additionally, the presence of water prevents the concrete from properly curing and hardening, thus decreasing its long-term durability. Overall, it is best to avoid exposing wet concrete to rain, as this can reduce the strength and lifespan of the material.
Can you pour concrete directly on dirt?
No, you should not pour concrete directly on dirt. When pouring concrete on any surface, it is essential to make sure it will provide a strong, solid base. Pouring concrete directly on dirt can cause the concrete structure to eventually settle and possibly crack, especially when exposed to extremely wet or dry conditions.
It is recommended to pave a surface with gravel or crushed stone first before pouring the concrete on top, to form a solid, stable base that will not shift or settle. This base should be at least four inches thick and compacted properly.
Any organic material such as wood, plants, and soil should be completely removed before pouring the concrete slab. This will help maintain a secure foundation, as these materials can decompose over time, compromising the stability of the structure.
If you’re planning to pour concrete directly on dirt, you should also consider the type of soil in the area in which you are working. Clay-heavy soil can cause concrete slabs to shrink and buckle because of its expansive properties when exposed to water.
If this is the case, make sure to choose the appropriate concrete mix based on the soil type that will better respond to moisture and help you avoid any long-term damage to the structure.
Can vibration break concrete?
Yes, vibration can break concrete. Vibrations are created by machines, such as jackhammers, and can cause cracking in the concrete due to its high frequency. Vibration can cause concrete to fracture, especially if there are existing weaknesses in the concrete or if under-reinforced concrete is used.
For example, when a jackhammer is used in an area where there are few or no reinforcing bars, the vibrations can cause the broken pieces of concrete to separate from each other and weaken the structure.
It is important to use the right amount of reinforcement when pouring concrete to prevent vibration damage. Additionally, vibrations can also disrupt the curing process of freshly laid concrete and cause it to crack or break.
Overall, vibration can be a serious concern when dealing with concrete and could lead to costly repairs or replacements.
What happens if concrete not vibrated?
If concrete is not vibrated after it has been placed, it can lead to a variety of issues. Concrete is a porous material and air bubbles that are trapped between the cement and the aggregate particles can reduce the overall strength of the concrete.
Additionally, when concrete is not vibrated those entrapped air bubbles can lead to a honeycomb-type pattern in the finished product which can further weaken the concrete. Finally, when vibrated, the concrete will have a better bond with the formwork and also have improved durability when exposed to environmental changes, such as freeze-thaw cycles and wetting and drying.
With out proper vibration, concrete will not be free from voids and the resulting reduction in concrete strength and durability.
What is the purpose of concrete cylinder test?
The purpose of a concrete cylinder test is to determine the compressive strength of concrete. This is done by testing concrete cylinders that are cured in a specific environment for a minimum of 28 days.
The cylinders are tested in a compression testing machine, which applies a compressive load to the cylinder until it breaks.
The results of the concrete cylinder test are used to help evaluate the overall strength of concrete structures and the quality of the made concrete mixes. This is important because concrete has very little tensile strength but high compressive strength, so this is necessary to ensure it can provide the strength needed for structural applications.
Additionally, the concrete cylinder tests are also used to confirm whether the compressive strength of the concrete is sufficient for the intended purpose of the construction project. Knowing the approximate strength of the concrete prior to construction allows engineers and contractors to accurately estimate the cost of the project and ensure the concrete mix satisfies the requirements of the building code.
What are common methods of curing the concrete?
Common methods of curing concrete are wet curing, using a membrane curing compound, using an accelerating admixture, and using a curing compound.
Wet curing involves keeping the concrete surface continuously wet for a specified period of time, usually 7 days minimum, for the concrete to properly hydrate. This can be accomplished by using a water hoses, sprinklers, plastic sheeting, and/or blankets soaked in water.
Using a membrane curing compound is another common method of curing concrete. It involves applying a thin, colored liquid membrane to the concrete surface which seals in the water needed to allow hydration and cure the concrete.
Using an accelerating admixture is a third common curing method. It involves adding an admixture to the concrete mixture prior to being poured that increases the concrete’s strength, shortens the form setting time, and accelerates the curing process.
The fourth and final common method of curing concrete is using a curing compound. This involves spraying a thin layer of liquid, usually white, to the surface of the concrete. It’s designed to slow the rate of evaporation and keep the concrete moist while curing.
