What Is Plum Concrete?
In general, the term plum refers to enormous stones that are referred to as boulders or coarse aggregates in a technical sense. Plum concrete is actually a cost-eﬀective variation of the mass concrete technique.
It is one of the many various forms of concrete that are available today. When the required thickness of PCC is excessive, plum concrete is recommended over other types of concrete.
This is done primarily below the foundations, where the amount of leveling course may be excessive because of the steep slope of the stratum beneath the foundations.
It is mostly employed in the mass concreting of foundations, dams, and other large-scale concrete structures where the quantity of leveling courses required is high due to the steep slope of the stratum.
It is made by incorporating medium or big hard stones with a size of up to 300 mm into the mix.
The volume of the plums should not exceed 30 percent to 40 percent of the overall volume of the completed concrete. Plum concrete can also be referred to as Cyclopean concrete or Rubble concrete in some circles.
Specifications Of Plum concrete
The specifications of plum concrete are as given below:
- Plum shall be composed of black trap basalt with a crushing strength of at least 100 kg per square meter.
- The concrete shall have a nominal mix ratio of 1:4:8 and shall contain aggregate with a maximum size of 25mm.
- The volume of the plum in the concrete shall not exceed 50% of the overall volume of the concrete mix.
- The width of the crevices must not be less than 150 mm.
- The maximum thickness of the layer shall not exceed 900mm.
Generally, the nominal maximum size of coarse aggregate should be as large as possible within the limits specified, but in no case should be greater than one-fourth of the minimum thickness of the member, provided that the concrete can be placed without diﬃculty so that it completely surrounds all reinforcement and fills the comers of the form.
When it comes to the size of the aggregate that can be used in plum concrete, the International Standards Organization (IS code) makes varied recommendations; the code states that the size of 20 mm aggregate is adequate and best for the majority of frequent projects.
If there are no limits on the flow of concrete into the section, concrete with a thickness of 40 mm or greater can be employed. When there is reinforcement or when the cover is tiny in relation to the formwork, plum concrete with a nominal maximum size of 10 mm should be used.
In plain concrete work, plums larger than 160 mm in diameter and of any appropriate size may be used up to a maximum of 20 percent by volume of concrete if specifically approved by the engineer in charge of the project.
However, in all situations, the plums must be scattered uniformly and must not be more than 150 mm away from the surface of the water.
The step by step construction procedure with plum concrete are as follows:
Step – 1
There are massive boulders with large Stone sizes that are merely upraised by labors; they are neither too big nor too little.
Step – 2
Initially, the surface should be thoroughly leveled and cleaned by removing any soft soil that could result in a lack of bearing capacity in the future.
As soon as the clearing and grubbing are finished, water is sprinkled on the area to keep it moist until the plum concrete can be laid.
Sprinkling water is used to ensure that plum concrete is held in place exactly against the ground surface it is applied to.
Immediately after water is sprinkled, an anti-termite chemical is sprayed on the structure to ensure that the foundation is not aﬀected.
Step – 3
Concrete is distributed using a pump over the boulders in each layer of the earth, gradually penetrating into the spaces between the boulders as the stones are laid down layer by layer with minimal spacing.
Once the concrete has been poured, the stones are placed on top of the concrete and the procedure is repeated until the desired level surface has been achieved.
Step – 4
Curing should be completed within the next 7 days at the very least. Jute bags are spread over the entire area of plum concrete to hold the moisture in for an extended amount of time once it has been cured.
Boulders should be thoroughly inspected prior to distributing, and if any dirt or clay is discovered, the boulders should be cleaned properly.
Boulders should be of high quality and should not be flimsy, as the weight of the entire structure will be imposed on them during construction.
More boulders may be necessary for some situations, such as when there is a lack of concrete or when it is more cost eﬀective.
There are various applications of plum concrete, which are as follows:
1. The majority of the time, it is used to level the ground beneath the foundation in cases when the surface is uneven. Additionally, it is possible to level the ground on a steep slope with the help of this method.
2. Generally, it is used in the construction of gravity dams and bridges; however, the plum size is limited to 150 mm.
3. Water channels can be built on top of it, making it an excellent choice for surface bed building.
4. In most cases, it is used in the building of traﬃc barriers and railroad crossing bridges.
5. Construction of machine foundations, where bulk concrete is required, is a good application for this method of construction.
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